Silicon is an attractive high-capacity anode material for Li-ion batteries, but to design better-performing Si anodes, it is necessary to develop a comprehensive understanding of both the fundamental nature of the Li-Si reaction and the effects of silicon&’s ~300% volume change. Here, in situ transmission electron microscopy (TEM) is used to observe the reaction of crystalline Si nanoparticles in real time. The experiments reveal that the lithiation reaction slows dramatically as the reaction front progresses into particles of all sizes. Analysis of the reaction front trajectories suggests that the lithiation kinetics are not diffusion-controlled in the conventional sense, but that instead the reaction slows because large hydrostatic stresses in the vicinity of the reaction front diminish the driving force for the reaction. In addition, it was observed that in many cases, larger particles that fractured during lithiation were lithiated fully in a shorter time than smaller particles that did not fracture. This is attributed to stress relaxation that occurs during fracture, which results in faster reaction rates. Overall, our experimental results suggest that mechanical stress has a central role in governing the reaction kinetics in this unique large-volume change reaction. These findings inform our understanding of the rate performance of real Si anodes, and the observed dependence of reaction rate on size and fracture characteristics is important for designing optimized electrode architectures.

Performance of current Li-ion battery with liquid electrolytes is strongly dependent on the unique physical properties of the solid-electrolytes interphase (SEI) formed on the anode surface at the first-time charging. It has been known that the desolvation and solvation processes of the Li ion at the interface between the SEI and liquid electrolytes with solute molecules are crucial to determine the throughput rate or power of the Li-ion battery. Large-scale, first-principles molecular dynamics (FPMD) simulation of the desolvation/solvation processes with the accurate density-functional theory (DFT) is therefore highly desirable to analyze theoretically and then to improve the Li-ion battery.
We have recently developed the linear-scaling, divide-and-conquer-type real-space grid DFT code (DC-RGDFT) [1], which has remarkable features of high parallelizability in addition to the high physical accuracy in ionic forces and universality in target materials and external conditions. In the present paper we apply the DC-RGDFT code to perform a series of large-scale FPMD simulation runs of a system that models the SEI-electrolytes interface; it is surrounded by a soft external potential to realize a weakly pressurized setting (< 1GPa). The overall shape of the system is cube with the side length of about 35Ang; the left half is composed of the dilithium ethylene dicarbonate (Li2EDC) relating to the SEI, while the right half, the ethylene carbonate (EC) relating to the liquid electrolytes. The total number of atoms is about 3,000 in either charge neutral or negatively charged state mimicking the realistic situation in the battery. In the case of the Li-ion transport from the Li2EDC to the EC side, for instance, additional Li ions are inserted at the left end after the equilibration at 550K. Concentration of the Li ions occurs in the Li2EDC in the close proximity of the EC through a sequential, billiard like, transport of the Li ions. It is followed by solvation of the Li ion by the EC molecules. We will also investigate possible effects of charging state of the target system on the transport and (de)solvation processes of the Li ions.
Reference
[1] N. Ohba S. Ogata, T. Kouno, et al., Comp. Phys. Commu. 183 (2012) 1664-1673.

A judicious choice of the liquid electrolytes used in lithium-ion batteries and an understanding of the solid-electrolyte interphase (SEI) is required to achieve a good balance between high-energy storage, high rate capability, and lifetime. We perform accurate ab initio molecular-dynamics simulations of ethylene (EC)-, propylene (PC)- and dimethyl (DMC)- carbonate and their mixtures with LiPF6 at experimental concentrations to build solvation models that explain available Neutron and NMR results. Our results corroborate why EC is a preferred choice for battery applications over PC [1, 2] and how mixtures with DMC help improve Li-ion diffusion [3]. We study the role of functionalization of graphite-anode edges on the reducibility of the electrolyte and the ease of Li-ion intercalation at the initial formation stages of the SEI [4]. We find that oxygen terminated edges readily bind to Li and act as strong reductive sites, while hydrogen edges allow faster Li diffusion. Orientational ordering of the solvent molecules precedes reduction at the interphase. We further identify reductive components forming the SEI with different solvents and compare with known experiments and gas-phase calculations. To understand Li diffusion in graphite, we benchmark Li-graphite interactions using quantum monte carlo calculations and validate existing van der Waals density functional schemes against our benchmark calculations. We infer that while van der Waals is important in determining the binding energy of Li, i.e. its voltage, Li diffusion is not affected by the exclusion of van der Waals interactions. Our studies also reveal interesting electronic transitions with possible ramifications for Li intercalation in graphite [5].
[1] Kang Xu, Energies 3, 135 (2010)
[2] P. Ganesh et al, Journal of Physical Chemistry B 115, 3085 (2011)
[3] P. Ganesh et al, (in preparation for JPCC in 2012)
[4] P. Ganesh et al, accepted for publication in JPCC (2012)
[5] P. Ganesh et al, (in preparation for Phys. Rev. Lett. in 2012)
SUPPORT:
This material is based upon work supported as part of the Fluid Interface Reactions, Structures and Transport (FIRST) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number ERKCC61. Computations were performed using resources at NERSC and NCCS.

Silicon is a promising anode material for next-generation lithium-ion batteries with a theoretical energy density of 4200 mAh/g. One of the challenges facing the use of silicon as a commercial anode material is the 400% volume expansion upon lithiation. Si nanowires (NWs) haven been shown to better accommodate this volume expansion over the bulk phase. However, due to increased surface area these nanostructures suffer from a greater irreversible capacity loss upon initial cycling due to formation of a solid electrolyte interphase (SEI) layer resulting from breakdown of the organic electrolyte, limiting rate capability of the anode. Numerous studies have shown that application of thin ALD coatings to electrode materials can improve cycle life, but this mechanism is poorly understood. We report the electrochemical performance of thin ALD Al2O3 coatings serving as artificial SEI layers on nanostructured as well as planar silicon anodes and discuss morphological changes during lithiation of these heterostructures, using conventional electrochemical techniques as well as in-situ TEM electrochemical experiments.
Lithiation of the artificial ALD SEI layer proceeds faster than does the bulk silicon, as evidenced by the relative motions of the volume expansion fronts in the two materials. ALD coated electrodes show increased lithiation rate capability, while the rate-limiting step of the heterostructured anode is bulk diffusion in the silicon. The delithiation process results in a volume contraction of the silicon core but not the ALD Al2O3 shell, suggesting that the lithiation of Al2O3 is irreversible. This study contributes to the fundamental understanding of the lithiation behavior of ALD coatings on electrode materials, and provides insights to further the development of solid heterostructured electrodes for next-generation lithium-ion batteries.
Acknowledgement:
This material is based upon work supported as part of Nanostructures for Electrical Energy Storage, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DESC0001160. In addition, this work was performed, in part, at the Sandia-Los Alamos Center for Integrated Nanotechnologies (CINT), a U.S. Department of Energy, Office of Basic Energy Sciences user facility.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. Department of Energy&’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

Silicon has drawn increasing interest as an anode material for lithium ion-batteries due to its high theoretical gravimetric and volumetric energy density (4008 mA h/g and 9339 A h/L, respectively). Silicon undergoes lithiation via an alloying reaction, with the kinetics and reversibility being dependent on mechanical and structural factors such as the rate of charging, material phase, surface orientation and micro/nano-morphology of the material. Furthermore, the silicon lithation and delithation reactions take place at potentials beyond the window of stability of current commercial electrolytes, leading to electrochemical decomposition of the electrolyte solvent and ions. Some of the resulting electrochemical decomposition products of these reactions form a mixed organic/inorganic surface layer known as the solid-electrolyte interphase (SEI). Many of the same mechanical and structural factors that effect lithium-silicon alloying also effect the SEI formation and evolution. Consequently, many questions remain unresolved in determining silicon SEI composition, stability, electronic insulation, ion conductivity and how SEI contributes to overall silicon lithation kinetics. Past research has focused around mixed electrodes (e.g., PVDF carbon binder and nanowires) and employed ex situ FTIR(1) and X-ray photoelectron(2) spectroscopies to characterize the SEI. Here we develop in situ and anoxic spectroscopic techniques (for XPS(3) and vibrational spectroscopies) in conjunction with electrochemical measurements to accurately determine the composition and formation mechanisms of SEI on silicon surfaces. Surface chemistries (such as the effect of native silicon oxide) and electrochemical preparation (e.g., comparing variable potential, and potentiostatic methods) are shown to influence SEI formation and stability.
References:
(1) Nguyen, C. C.; Song, S.-W. Elelctrochim. Acta 2010, 55, 3026-3033.
(2) Chan, C. K.; Ruffo, R.; Hong, S. S.; Cui, Y. J. Power Sources 2009, 189, 1132-1140.
(3) Schroder, K. W.; Celio, H.; Webb, L. J.; Stevenson, K. J. J. Phys. Chem. C 2012, 116, 19737-19747.

Battery electrodes are hierarchically complex structures formed by different components and their distribution determines the final properties. These structures must enable fast ion and electron transport. As a consequence, they are usually composite films of a redox active material with carbon and a polymer binder, cast onto a metal foil current collector. Ion transport is ensured by the presence of pores that provide points of contact between the electrolyte and the active material throughout the depth of the electrode. Because these hierarchies are assembled at scales much larger than a few nanometers, tools that can probe multiple levels of complexity are required to fully determine the parameters that control performance.
Direct visualization of phase distribution within an active particle or an electrode, which could be used to validate models, is challenging. Since reactions at an electrode involve redox phase transformations, which are largely controlled by interfaces, the state of charge can easily be correlated to composition. Spectroscopic and diffraction tools are widely available that can produce this chemical information, but very specific setups are needed to move beyond averages over a relatively large volume. In addition, data should be produced in 3D so that the study of buried interfaces is possible. The field is mature for the implementation of tools that can access chemical speciation at spatial resolutions below 1 um, yet with the ability of producing fields of view that can span up to several hundreds of micron. Because thermodynamic pathways can be controlled by the presence of electrical potential, the harvesting of a sample from a cycled battery, while providing a useful preliminary insight, can lead to misleading results due to the relaxation of components into a different state that is more stable under open circuit conditions. Therefore, measurements performed during device operation (in operando) are preferred.
In this presentation, recent advances will be discussed in the development of imaging tools to follow oxidation state changes in a battery active electrode material. Data from tools with different chemical and spatial sensitivities will be discussed, with an emphasis on spectromicroscopy using synchrotron radiation.

Understanding the rate limiting steps in an electrochemical cycle is fundamental to increasing both the energy density and power density of Li-ion batteries. By spatially mapping the reduction and oxidation sites within active materials using transmission X-ray microscopy (TXM), we are able to visualize reaction fronts. With the long mean-free path of X-rays, hard X-ray TXM has already proven to be a powerful in situ tool in visualizing morphological changes occurring during battery operation (see for example [1,2]).
Alternatives to commercial LiCoO₂ cathodes are higher capacity, lower cost, and more thermally stable compounds with the general formula LiNi_yMn_yCo_1-2yO₂ (0 < y le; 0.5). However, the lower Co loading reduces electronic conductivity and increases structural instability, which greatly affect performance. By constructing a LiNi_0.4Mn_0.4Co_0.2O₂ cathode with 5 wt.% single-walled carbon nanotubes [3] and surface coating [4], high capacities can be maintained even at high rates and cut-off voltages up to 4.5 V. Despite this success, the mechanism of capacity fading at high voltage and the effects of surface coating are not fully understood. Utilizing the chemical speciation capabilities of TXM, we can compare the electrochemical reactions occurring in situ on both coated and uncoated cathodes. We will present our latest results using TXM to chemically map Ni, Mn, and Co in these electrodes with down to 30 nm resolution, throughout the electrochemical cycle.
1. S.-C. Chao, et al., Journal of The Electrochemical Society, 158 (2011), A1335-A1339.
2. J. Nelson, et al., Journal of the American Chemical Society, 134 (2012), 6337-6343.
3. C. Ban, et al., Advanced Energy Materials, 1 (2011) 58-62.
4. L. A. Riley, et al., Journal of Power Sources, 196 (2011) 3317-3324.

Bond valence parameters exploit crystal chemical information from reference structures. Translating the BV approach into an energy-scaled Morse-type interaction potential we can exploit this structural information to analyze low-energy pathways in inorganic ion and mixed conductors Both static analyses of energy landscapes for mobile ions in local structure models and molecular dynamics simulations enable us to fast-screen candidate solid electrolytes and mixed conductors from structure databases. To demonstrate the versatility of the BV-based force-field it is applied in exploring strategies to enhance the power performance of safe low cost battery cathode materials. The method allows us to explore effects of homogeneous doping, tailoring the concentration of disorder, and "heterogeneous doping" via interface engineering of cathode:electrolyte nanocomposites (e.g. Li_xFePO₄:Li₄P₂O₇).[1,2] Combining the BV analysis with in situ diffraction studies of structural variation (during synthesis or cycling) now permits us to fine-tune synthesis conditions and identify bottlenecks for charge transport and transfer across interfaces.
Among the promising solid electrolytes for use in Li-air or Li redox or solid state batteries, garnet-related Li_7-x-3yAl_yLa₃Zr_2-xM_xO₁₂ (“LLZ”, M = Nb, Ta)[3] and Li thiophosphates will be discussed. In situ neutron diffraction of the synthesis process allows to optimise the synthesis conditions. Simulations with our force field reproduce static and dynamic characteristics of this material, the different effects of tri- and pentavalent dopants on the ionic conductivity and reveal the temperature of the Li distribution over tetrahedral and octahedral sites in cubic LLZ.
For various thiophosphate solid electrolytes our studies show the importance of disorder in the immobile anion sublattice. This includes argyrodites[4] as well as Li₁₀GeP₂S₁₂ (LGPS)[5], the fastest known Li+ ion conductor. Dynamic Li distribution, structural stability and transport mechanism in LGPS or structural analogues (e.g.Li₁₀SiP₂S₁₂) are clarified by MD simulations, revealing a coupling of Li⁺ diffusion to PS₄^3- rotational mobility. Key features of LGPS: (i) high vacancy concentration in equidistant chains of Li sites with nearly equivalent energy, (ii) the cross-linking of 1D channels for fast ion conduction to a 3D network by paths with moderate activation energies, (iii) compositional and rotational disorder of in the immobile sublattice containing polyatomic anions of slightly different size, can serve as a guideline for a systematic design of fast ion conductors.
References
[1] S. Adams, Applied Energy 90, 323 (2012).
[2] S. Adams, R. Prasada Rao, Phys. Stat. Sol. A 208, 1746 (2011).
[3] S. Adams, R. Prasada Rao, J. Mater. Chem. 22, 1426 (2012).
[4] R. P. Rao, N. Sharma, V.K. Peterson, S. Adams, Solid State Ionics
DOI 10.1016/j.ssi.2012.09.014.
[5] S. Adams, R. Prasada Rao, J. Mater. Chem. 22, 7687 (2012).

We have developed novel hierarchical hybrid multiscale simulation technique for modeling coupled ion and electron transport in nanostructured energy storage materials. The model uses multiphysics approach, in which instead of formal consecutive upscaling we introduce novel types of collective long-range interactions along with short-range effects of the finer scale models. The fine scale model take advantage of high accuracy embedded cluster quantum mechanical simulations of elementary charge transport as well as the state-of-the-art molecular dynamics free energy simulations of coupled ion and electron diffusion. The collective long-range electrostatic and excluded volume interactions are introduced on the mesoscale (10-300 nm) via classical Density Functional theory coupled with Poisson-Nernst-Planck formalism for dynamic effects. The mesoscopic free energy, which includes contribution from short-range activation dynamics of ions and electrons, derived in the atomistic models, is then used in a larger scale (microns) phase field model to simulate charge transport in a network of nano-sized grains. As a demonstration of the application of the model for elucidating the basic principles of charge transport in nanostructured energy materials, the fundamental physics of Li+ and electron transport in nanostructured TiO2 will be discussed.

In the search for new battery chemistries, sodium has been recently revisited due to its abundance and chemical similarity to lithium. High temperature systems such as the Na-S cell and the ZEBRA cell are well known examples for commercialized sodium based batteries, however the electrochemistry of sodium based batteries at room temperature is, compared to lithium, a largely unexplored field of research.
Metal/air batteries are among the most attractive but also most challenging battery systems with energy densities significantly exceeding current lithium-ion technology.
In 2011 Peled et al. reported on a Na/O2-cell with a polymer electrolyte and a molten sodium cathode operating at 100 °C that could be cycled several times.[1] And recently Sun et al. published a work on room temperature sodium-air batteries with a carbonate based non-aqueous electrolytes that is quite analogue to most of the studied Li/O2 cells.[2] However both Na/O2-concepts suffer, analog to the lithium system, from high over-potentials for cell charge and potential electrolyte decomposition.
In this work we discuss the charge/discharge characteristics of a rechargeable sodium/oxygen cell at room temperature with sodium superoxide (NaO2) as discharge product.[3] During discharge, the NaO2 particles grow to cubic crystals of several micrometers in size. The cell reaction corresponds to a theoretical energy density of 1108 Wh.kg(NaO2). A comparison with an analog lithium/oxygen cell shows a superior performance, with a more than 10 times higher discharge capacity at more than 6 times higher current densities and most importantly, at much lower overpotentials (Ucharge-Udischarge < 200 mV).
Next to the electrochemical measurements, we followed the cell reaction using x-ray powder diffraction, Raman spectroscopy, electron microscopy and DEMS. As a result, we can provide first fundamental insights and explanations on the large discrepancy in the electrochemical performance between lithium and sodium based oxygen batteries. Also, we studied the evolution of additional interfaces between discharge products, the carbon electrode and the electrolyte in order to identify possible degradation mechanisms during cell cycling.
ACKNOWLEDGMENT: The research was supported by the BASF scientific network of electrochemistry and batteries.
[1] Peled, E., Golodnitsky, D., Mazor, H., Goor, M., Avshalomov S.; J. Power Sources 196, 6835-6840 (2011).
[2] Sun, Q., Yang, Y., Fu, Z.-W.; Electrochem. Comm. 16, 22-25 (2012).
[3] Hartmann, P., Bender, C., Vracar, M., Garsuch, A, Dürr, A. K., Janek, J., Adelhelm, P.; Nature Materials (manuscript accepted) doi: 10.1038/nmat3486.

The influence of HF concentration, from 1 wt% to 15 wt% on the electropolishing rates of p-type silicon in hydrofluoric acid has been studied over a wide resistivity range from 0.001 Omega; cm to 10 Omega; cm. The technique used was analysis of current voltage (IV) curves and the results have been used to propose a possible mechanism for the electropolishing process
If it is assumed that the in the electropolishing plateau of the IV curve all the current (or at least constant fraction that is independent of HF concentration) is consumed by oxide formation then the anodic oxide removal must be directly proportional to the current density flowing. Therefore the dependence of the oxide removal rate on HF concentration can be determined by constructing a series of IV curves. This revealed that although the anodic oxide removal rate increases with HF concentration, the relation between the two parameters is not linear. Instead a cubic relation is found that has the same form as previously reported for thermal oxide removal rates. Unfortunately, such empirical fits are not very satisfactory and provide no useful mechanistic insights.
However, a deeper inspection of the data reveals that the loss of linearity between oxide dissolution rates and HF concentration can be explained if the rate determining step is the mass transport of the products of oxide dissolution away from the silicon&’s surface. Furthermore, the dissolution products contain both fluoride and protons; since HF is a weak acid its pH does not scale directly with its concentration. Silicon dissolution rates are shown to give an excellent fit to second or third order rate equations, that is first order in HF and either first or second order in proton. Based on these rate equations possible mechanisms for the rate determining step in the dissolution of anodic silicon oxide in HF are proposed, something not possible from the empirical relationships previously reported.

Alternative energy sources such as wind and solar energy are being utilized to deal with rising CO₂ levels and the increasing difficulty to obtain cheap fossil fuels. Due to the intermittency of the energy supply from these sources, energy storage will be necessary to match energy demand. One option is to store the energy in chemical bonds by converting CO₂ and water to fuels and oxygen, creating a carbon neutral cycle. This can be done at room temperature electrochemically by using voltage to drive the uphill energetics. Heterogeneous catalysts studied for the CO₂ reduction reaction in aqueous environments consist mainly of metals, which produce varied product distributions but all require large overpotentials.¹ Some attempts to improve catalysts have been made using chemical modification of metal surfaces.^2-4 This study is looking to find more active heterogeneous catalysts by modifying the activity of metal surfaces by adding bifunctionality. The first system explored is platinum metal - a poor CO₂ reduction catalyst - modified by polyaniline (PANi) to change the energetics of the reaction with CO₂. CO₂ electrolysis experiments were run for 1 hour potentiostatically using a custom electrolysis cell. Gas Chromatography (GC) and Nuclear Magnetic Resonance (NMR) were used to detect gas and liquid products, respectively. The PANi was electrodeposited on the Pt foil substrates using cyclic voltametery. These PANi-Pt catalysts as well as the bare Pt foils were tested at a variety of potentials that spanned current densities from 0.5 to 15 mA/cm². The Pt foils performed similar to literature reports, with H₂ as the dominant product with formate (<0.4%) as a minor product.1 However, CO, methane, and methanol were also detected in small amounts (<0.2%), which have been seen in one report.⁵ The PANi-Pt catalysts show a small but noticeable increase in efficiency for formate (up to 1.5%) and CO (up to 0.8%) and a decrease in methanol production compared to the pure Pt metal catalyst. Degradation of PANi to carbon products was ruled out using a ¹³C-labeled CO₂ experiment and ¹H NMR analysis of the formate. The current hypothesis is that the amine groups in the leucoemeraldine form of the PANi interact with the CO₂ intermediates at the surface of the Pt catalyst to lower the barrier for the rate-limiting step for the 2e- products, CO and HCOO^-. Ongoing work is aimed at exploring the mechanism and applying it to other metal-polymer systems and alloys.
REFERENCES
1. Hori et al. Electrochimica Acta, 39, 1833-1839, 1994.
2. K. Ogura et al. J. Electrochem. Soc., 145, 3801-3809,1998.
3. B. Aurian-Blajeni et al. J. Electroanal. Chem., 149, 291-293, 1983.
4. R. Aydin et al. J. Electroanal. Chem., 535, 107-112, 2002.
5. G.M. Brisard et al. Electrochem. Comm., 3, 603-607, 2001.

Electrochemical double layer capacitors (EDLC) show outstanding promise for high power density energy storage devices. As capacitance scales with surface area, electrodes made of nanostructured materials (with high surface area/volume ratios) have been widely investigated. Carbon nanotube (CNT) electrodes have tremendous potential for EDLC electrodes due to their high surface area, exceptional electrical conductivity and the ability to incorporate functional groups on CNT surfaces to modify their electrochemical properties.It has been established that the double layer capacitance of graphitic material is an order of magnitude higher along the edge plane orientation compared to the basal plane. Defect introduction aims to exploit this behaviour. In this work we show enhanced capacitance in multi walled CNTs (MWCNTs) on silicon substrate by probing their electrochemical behaviour using Cyclic Voltammetry and Electrochemical Impedance Spectroscopy.The average length and diameters of the CNTs are 30 microns and 50 nm respectively. We report a specific double layer capacitance ~5mF/cm^2 at a scan rate of 800mV/s in aqueous electrolyte system . We then recorded, with great repeatability, an improvement of 200-300% in the specific capacitance by extrinsically introducing defects on the CNTs through irradiation with Argon (Ar) ions. Electrolyte wetting and the sparse density of the CNTs (~ 10^9 tubes/ cm^2) can further be enhanced to increase the double layer capacitance and will be discussed. We also investigate the issues related to the dispersion of double layer capacitance with voltage scan rates which is inconsistent with present ideas on macroporous electrodes. Our study has significant implications in simultaneously increasing the power and energy density of EDLCs using the features of nanoscale materials.

Graphene is considered an ideal candidate in developing nano-structured materials in electrochemical applications due to its high surface area, chemical stability and excellent electrical properties. In this work, fabrication of low temperature micro Solid Oxide Fuel Cells (µSOFCs) with graphene-based nano-structured electrodes was presented. The main goal of this study was to develop a nano-structured electrode material to overcome sluggish reaction kinetics at the cathode by applying graphene and study its kinetic mechanism interface with the electrolyte. To enhance ORR activity, platinum and silver nanoparticles supported on graphene nanosheets were prepared as the cathode. Throughout this work, chemical fabrication procedures were implemented for the production of graphene and graphene sheets which were coated on silicon wafers by electrospinning. To minimize ohmic losses from the electrolyte at low temperatures (~400°C), < 100 nm ultra-thin layer yttrria-stabilized-zirconia (YSZ) electrolytes were fabricated by Atomic Layer Deposition. Porous platinum was sputtered onto the ultra-thin YSZ electrolyte layer as the anode material. Polarization curves and ac impedance spectra were measured to evaluate the performance and the losses of SOFC cells.

Silicon is one of the most promising candidates for energy storage due to its high capacity and wide abundance. However, large volume change of Si upon insertion and extraction of lithium is the major challenge limiting the implementation of Si-based anodes. Various Si morphologies such as thin film, particle, nanowires, and nanotubes have been investigated to deal with the volume change issue. Here, we have successfully fabricated the silicon nanowires (SiNWs) and silicon nanotubes (Si NTs) by Low Pressure Chemical Vapor Deposition system (LPCVD) as an anode. The diameters and lengths of SiNWs and Si NTs can be tailored by controlling growth time. The scanning electron microscopy (SEM) and the transmission electron microscopy (TEM) have been used to investigate the morphology of the Si nanostructures. To determine the morphology and composition of the Si nanostructures, the x-ray diffraction (XRD) and Raman spectroscopy have been used. The electrochemical performances of the SiNWs and Si NTs have been evaluated using electrochemical potential spectroscopy (EPS) and galvanostatic cycling.

In this work, ruthenium-based C106 and organic D131 sensitizers have been judicially chosen for demonstrating co-sensitization in dye sensitized solar cells owing to their complimentary absorption properties and different molecular sizes. By the process of co-sensitization, a higher light-harvesting efficiency as well as better dye coverage to passivate the surface of TiO2 have been achieved. The co-sensitized devices C106 + D131 exhibited enhanced performance of eta; = 11.1 %, which is a marked improvement over baseline devices sensitized with either D131 (eta; = 5.6%) or C106 (eta; = 9.5 %). The improved performance of the co-sensitized cell is attributed to the combined enhancement in the short circuit current, open circuit voltage, and the fill-factor of the solar cells. Improvement in Jsc is due to the complementary absorption spectra and favorable energy level alignments of both the dyes; whereas improvement in Voc is because of the better surface coverage by both the dyes which helps in reducing the recombination and increasing the electron life time. The origins of these enhancements have been systematically studied through dye desorption, absorption spectroscopy, and intensity modulated photovoltage spectroscopy investigations.

Major issues with the reduced operating temperature to intermediate temperature range (600-800°C) are the increase in the cathodic polarization resistance and the low electrochemical activity, and it demands to development of cathode materials for intermediate temperature solid oxide fuel cell (IT-SOFCs). Complex perovskite oxides with A1-xA&’xB1-yB&’yO3-δ structure as a kind of mixed ionic and electronic conductor (MIEC) have acquired extensively attention as a potential cathode to overcome cathodic polarization at the lower temperature.
Ce doped SrMnO3 oxides are considered the possible cathode materials for IT-SOFCs. The formation of oxygen vacancies and the change of valence state of B-site cations caused by non-stoichiometry are occurred due to addition of Ce cations, simultaneously, which can increase the cathode performance for oxygen reduction reaction (ORR). These are significant factors to enhance ORR, and thus the investigation of these factors is important when selecting suitable cathode materials for IT-SOFCs.
We investigated the effect of Ce content on structural change and electrochemical property in Sr1-xCexMn0.8Cu0.2O3-δ (0le;xle;0.5, SCMCu) system. Manganese and copper are selected to B-site elements, and Ce cations are doped into A&’-site to form the oxygen vacancy and to control the valency of ions in B and B&’-site. The SCMCu powder was synthesized by EDTA citrate complexing process (ECCP). The crystal structure according to Ce content was measured by X-ray diffraction (XRD) and the lattice parameters were calculated by Rietveld refinement method. The electrical conductivity was measured by 4-probe DC method as a function of temperature. Polarization resistance related to oxygen reduction reaction was also investigated to symmetric cell by impedance analysis.

We have studied the electrochemical reduction of CO₂ to produce short chain hydrocarbons and alcohols using two types of supported Cu₂O electrocatalysts. The first group of catalysts was prepared using Cu₂O nanoparticles prepared by chemical reduction of aqueous CuCl₂ mixed with polyethylene glycol surfactant followed by addition of NaOH and L-ascorbic acid (sodium). The Cu₂O nanoparticles were then added to a Nafion/ethanol solution, coated onto porous Toray carbon paper, and allowed to dry. The second group was prepared by electrochemically depositing a Cu₂O layer from a CuSO₄/lactic acid bath onto similarly prepared Nafion-coated Toray carbon. The CO₂ reduction experiments were performed at fixed cathode potential of -1.5 V(NHE) in aqueous KHCO₃ electrolyte saturated with continuously flowing CO₂ using a two-compartment cell with Nafion membrane separator and three-electrode configuration. Both gas-phase and solution-phase products were analyzed quantitatively using gas chromatography, and identification of solution-phase products was confirmed using NMR spectroscopy.
The highest hydrocarbon and alcohol production rates were obtained using the supported Cu₂O nanoparticle catalysts. For the highest Cu₂O nanoparticle loadings studied (ca. 30 mg/cm²), the formation rate of ethylene (the major hydrocarbon product) was 15 mu;mole/cm²/hr, corresponding to a Faradaic efficiency around 25%. The major alcohol product is ethanol, with a Faradaic efficiency around 6%. Smaller amounts of 1-propanol are also observed (FE = 2%). Methane is observed in still lesser amounts (FE = 0.5%), and methanol could not be resolved. The other measured products include CO (FE = 6%) and H₂ (FE = 60%).
By comparison, electrodes prepared using the electrochemically deposited Cu₂O showed a 2-fold decrease in alcohol formation rates (FE = 2-3%). This was accompanied by a somewhat larger 3-fold decrease in ethylene formation (FE = 8%), and a much more pronounced 6-fold decrease in CO formation (FE = 1%). Control experiments confirm that both uncoated and Nafion-coated Toray carbon electrodes produce H₂ almost exclusively, with no other products observed except minimally detectable amounts of methane (FE = 0.2%).
The overall results are discussed in terms of a model in which the Cu₂O particles cover a significant fraction of the carbon support area, decreasing the H₂ formation rate of the electrode support. Hydrocarbon and alcohol selectivities are attributed to differences in the dispersion of surface metal clusters on freshly reduced Cu₂O nanoparticles vs. electrodeposited Cu₂O surfaces, where the surface reduction behavior of both materials is influenced by the method of preparation.

Nanocrystal perovskite catalysts with high phase purity are of great interest as replacements for precious metals and oxides used in the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Herein, we demonstrated precise control over the synthesis of essentially single phase perovskite nanocrystals with small crystallite size (14 nm). The calcination of rapidly dried nanoparticle dispersions gave rise to the unusually high phase purity of the catalysts. OER mass activities for LaNiO₃ supported on nitrogen doped carbon were almost 3x that of 6 nm IrO₂, a noble metal oxide benchmark catalyst. Moreover, strong OER/ORR bifunctional character for the catalysts is shown by a low total overpotential, 1.02 V, between ORR and OER, on par or better than observed for noble metal catalysts such as Ir (0.92 V) and Pt (1.16 V). This scheme for forming phase pure, highly active nanocrystal catalysts, by calcining rapidly dried nanoparticle dispersions, may be utilized for a wide variety of perovskite catalysts.

Silver has been an attractive material for various applications due to its unique combination of desirable properties. As it possesses the highest electronic conductivity among metals, considerable solubility of oxygen in silver allows its significant conductivity of oxygen. Moreover, its catalytic activity for reduction of oxygen makes it a highly promising candidate for electrode applications in solid-state electrochemical devices such as solid oxide fuel cells (SOFCs), solid oxide electrolysis cells (SOECs) and solid-state oxygen sensors. Since extended surface area is crucial for enhanced kinetics of the surface processes (e.g. adsorption/desorption and reduction), three-dimensional morphologies involving a percolated pore structure and integration with the underlying substrates are desired. However, relatively low melting temperature of Ag (962^oC) limits its use at elevated temperatures (>500^oC) as it leads to densification in a short period of time. There were many attempts to stabilize the porous microstructure of Ag based composites. Incorporation of oxide particles into Ag matrix was the most common technique. Optimization of the particle size ratios and compositions allowed stabilizing Ag based porous composites at 800^oC in air for over 5000 hours. Although its electronic conductivity was not severely affected, the loss of the contact area with the underlying substrate resulted in a significant decrease in the electrochemical performance. Moreover, disconnected oxide particles did not contribute to the electrode processes, even though they are catalytically active or demonstrate intrinsic ionic/electronic conductivity. Considering the interrupted contiguity of the oxide particles and the loss of the contact area at the Ag matrix-substrate interface, continuous layers of various oxides (e.g. yttria-stabilized zirconia and lanthanum-strontium manganite) were formed on the surface of the porous Ag by infiltrating their polymeric precursors, in this study. Detailed analysis of the microstructures after exposing to elevated temperatures revealed that the nano-size oxide grains covered the complete surface area of the Ag grains and the stability of the porous composites was maintained at temperatures as high as 900^oC in air. Further characterization of the stability and electrochemical properties of the Ag based composite electrodes was performed on their symmetrical cells using impedance spectroscopy and voltammetric measurements. The results of the measurements at 900^oC for over 1000 hours demonstrated that the surface coverage by the nanostructured oxide layers gave rise to the electrode reactions by extending the contact area between the Ag matrix and the substrate as well as forming a percolating network of the oxide particles. Relationships between the developed microstructures and their electrochemical performance will be discussed for a better understanding of the stabilization of porous Ag for high temperature applications.

Polyaniline (pani) is an attractive conducting polymer given its wide range of applications such as: battery, supercapacitors, corrosion control, electrochromic and electroluminescent devices, pani can be easily synthesized, chemically an electrochemically in both aqueous and non-aqueous solutions, however few papers report the influence of monomer concentration on growth of pani films, it is important to realize a study kinetics growth associated with the concentration of monomer in the electrolytic medium used.
In this work we present a systematic electrochemical study of the grown of aniline on stainless steel 304 substrate using different concentration of monomer (10-1M, 10-2M, 10-3M of aniline) in 1M H2SO4. Polyaniline films were electrodeposited by using cyclic voltammetry (CV) the deposition of pani was carried out varying the potential limit anodic (Elim) 0.9 V and 1.0 V vs SCE while the lower potential limited was -0.2V vs SCE, Chronoamperometry (CA) upon varying the applied potential (Eap) 0.9V and 1.0 V vs SCE, Chronopotenciometry (CP) techniques was used varying the current applied between 10-6 and 10-2 A. The cyclic voltammograms show peaks anodic/cathodic associated at the different stages of growth and its correlation with oxidation states de pani, the analysis of potential and peak currents shows small differences in the concentrations tested. Moreover the electrochemical responses of grown of Pani films show a strongly influence due to hydrolysis reaction at potential more positive and this is manifested in the films pani morphology obtained. The pseudocapacitance response was evaluated by cyclic voltammetry (CV) and constant current charge/discharge tests.

Li-ion batteries are of great interest, however they would find increasing application if their energy density could be increased. The graphite/LiCoO2 and related anode/cathode systems are dominate. The graphite anode is, however, not ideal (nor is the cathode). Among other issues, graphite has a low capacity (372 mAh g-1), and is fragile. SnO2 is an interesting alternative given its high theoretical capacity of 780 mAh g-1. When the characteristic size of the primary SnO2 particles are reduced to the nanoscale, the electrochemical properties may improve due to an increase in the surface-to-volume ratio and shortening of the lithium diffusion distances. However, application of SnO2 nanoparticles has been limited by poor conductivity, instability, a large volume expansion upon lithiation, and a non-uniform solid electrolyte interface (SEI). Previous efforts have focused on coating a carbon layer on the SnO2 to address these issues. The incompact structure of carbon layer after thermal treatment does not provide a stable protection, resulting in a serious decay of stability and capacity after multiple charge-discharge cycles.
Here we put forward a novel multi-layered inverse opal concept as an anode electrode. First, a Ni inverse opal was fabricated by electrodepositing Ni through a polystyrene (PS) opal. After removal of the PS opal, dense SnO2 NPs in a size of ca. 5 to 8 nm were in-situ grown onto Ni inverse opal using a water-bath approach combining with a thermal treatment under N2. Following this, a SiO2 flake-like layer which can minimize material stress to achieve good reversibility and stability was coated on SnO2 NPs through a hydrothermal route. The results show that the SiO2 flakes-coated Ni/SnO2 inverse opal possesses a stable capacity of ca. 604 mAh g-1 after 40 cycles. The SiO2 coated anode exhibits a weaker SEI formation at the first cycle as well as a very small recurrence during following cycles relative to the one without coating. This can be ascribed to the effective protection of SnO2 NPs by the SiO2. The SiO2 layer may serve to decrease the surface energy of SnO2 NPs, and then reduce the formation of SEI, as well as limit pulverization due to volume changes during cycling. Our investigations provide a new strategy for fabricating electrodes of Li-ion batteries which can effectively overcome the disadvantages of conventional materials to achieve a remarkably improved performance.

Phosphorus and nitrogen doped carbon (PNDC) materials with varying nitrogen content were synthesized by microwave technique using tannin (renewable carbon resource), melamine and hexamine. Nitrogen content of the materials was varied by changing the concentrations of the melamine and hexamine with respect to tannin. Results from the XPS analysis, indicates the presence of nitrogen and phosphorous in the carbon lattice. Capacitance measurements were performed both in alkaline (6.0M KOH) and acidic (1.0M H2SO4) electrolyte solutions. Supercapacitors with the electrodes made out of high nitrogen containing PNDC material indicated higher interfacial capacitance when compared to the low nitrogen doped and undoped carbons. Microwave assisted synthesis of non-metal doped carbon using cheap and renewable sources reduces the cost of material and tedious synthetic procedures in the application of energy storage devices. Details of the synthetic process, analysis and capacitance measurements will be presented.

Fuel cells have been utilized for a wide variety of applications such as powering vehicles, portable devices and buildings. Traditional low-temperature fuel cells use a proton-exchange membrane and expensive Pt catalysts which drive up the fuel cell cost. Hence there has been renewed interest in alkaline-based fuel cells which allow for the use of non-precious catalysts due to the more facile oxygen kinetics and reduced corrosivity in an alkaline environment. However, current non-precious catalysts are not as active as Pt and hence there is room to develop better oxygen reduction catalysts. Manganese oxide (MnOx) electrocatalysts are potential candidates for oxygen reduction catalysis in an alkaline fuel cell due to their high activity, low toxicity and low cost.1 Previously, we have synthesized thin films of nanostrucutred MnOx via electrodeposition, and the activity for the oxygen reduction reaction and the oxygen evolution reaction is comparable to that of the best known precious metal catalysts such as Pt, Ir and Ru.2 However, the MnOx films are deposited onto a glassy carbon (GC) disk and in this particular form, the catalyst is not suitable for use in a fuel cell. Hence the goal is to translate this active catalyst to a fuel cell environment.
The high temperature calcination involved in the synthesis procedure necessitates a support that is heat-resistant. We have found that traditional high-surface area carbon supports for fuel cells degrade rapidly in the calcination environment required to produce active MnOx catalysts. We thus turned our attention to GC particles which we found are appropriate for this application due to their high temperature resistance, high corrosion resistance which is needed due to the harsh alkaline testing environment, and high conductivity to enhance electron transport to and away from the catalyst surface. MnOx was deposited onto GC particles via an impregnation technique followed by calcination, which resulted in a nanostructured surface dominated by Mn2O3 as determined from SEM and XPS analysis. Electrochemical testing in a rotating disk electrode setup revealed that the ORR activity is similar to the MnOx thin films. The active MnOx-GC particles were then utilized as a non-precious cathode catalyst in an actual membrane electrode assembly for use in fuel cells.
References
1. J.O.M. Bockris, Int. J. Hydrogen Energ. 1999, 24, 15
2. Y. Gorlin, T.F. Jaramillo, J. Am. Chem. Soc. 2010, 132, 13612

Tin (Sn)-based materials have been of interest for a use as alternative anode materials in rechargeable lithium batteries because of larger theoretical capacity (990 mAh/g) than graphite (372 mAh/g). Large volume change during alloying/dealloying with lithium however is the major drawback responsible for a rapid capacity fade. Continued electrolyte decomposition in the absence of solid-electrolyte interphase (SEI) layer has been noticed to be another cause for a poor cycling ability. Control of electrode-electrolyte interfacial reaction and the formation of a stable SEI layer can suppress electrolyte decomposition and mechanical/electrochemical particle disintegration, and improve cycling ability. We report here the impacts of surface modification of Sn-based film model electrodes, prepared by pulsed laser deposition, and various electrolyte additives on the SEI stability and cycling ability, utilizing X-ray photoelectron and infrared spectroscopy for surface chemistry studies.
Acknowledgements : This work was supported by the Converging Research Center Program (2012K001255) through the MEST of Korea.

We present a study on electrochemical CO2 reduction using a polypyrrole (PPy) covered platinum working electrode modified with pyridine.
In comparison to previous work an organic semiconductor is used to support the pyridine catalyst for CO2 reduction [1, 2]. Organic semiconductors like polypyrrole provide several favorable properties, such as high availability, tuneable bandgaps and ease of processing. Polypyrrole has a high conductivity and is further advantageous in electrochemistry due to the ability to form very smooth films from electropolymerisation. Further it has been reported that pyridine is convenient for CO2 reduction, due to improved charge transport [3]. The CO2 reduction using a pyridine modified polypyrrole electrode is proposed to proceed via a Metal/Organic Semiconductor/Electrolyte pathway. Cyclic voltammetry (CV) measurements are performed after purging the electrochemical setup with N2 and CO2, respectively. Comparison of the CV- curves for CO2 reduction at the pristine PPy electrode and the same electrode after modification with pyridine, shows that the reduction is catalyzed by a protonated form of pyridine. The suggested cationic form of pyridine results from adding aqueous solution of sulfuric acid, which is as a strong acid suitable for protonation. Further it is observed that the current density for the reduction peak increases with increased amount of sulfuric acid added. Following our preliminary results we suggest a protonation of pyridine and dependency of the CO2 reduction on the degree of protonation.
[1] E. Portenkirchner, K. Oppelt, C. Ulbricht, D. A. M. Egbe, H. Neugebauer, G. Knör, N. S. Sariciftci, J. Organomet. Chem., 716, 19-25 (2012).
[2] S. Cosnier, A. Deronzier, J. C. Moutet, J. Electroanal. Chem., 207, 315-321 (1986).
[3] E. Barton Cole, P. Lakkaraju, D. Rampulla, A. J. Morris, E. Abelev, A. B. Bocarsly, J. Am. Chem. Soc., 132, 11539-11551(2010).

As smaller, lighter, and longer-lasting energy storage devices become more desirable for mobile electronic devices and electric vehicles, improving the energy density and cycle life of Li-ion batteries becomes more important. Silicon is considered one of the most promising anode materials for Li-ion batteries because of its exceptional specific capacity of 4200 mAh g-1, which is about ten times that of commercial graphite anodes. However, conventional Si anodes typically suffer from rapid capacity decay due to mechanical fracture caused by large volume changes (300%) during repeated electrochemical lithium insertion and extraction. Preventing fracture during the first lithiation, where most fracture has been observed to occur, is important for reducing irreversible capacity loss. Various theoretical models have been developed to study mechanical fracture of amorphous Si during electrochemical Li insertion by considering Li diffusion-induced stress. These models have revealed that high stresses are possible and have also suggested a critical size below which Si nanostructures will avoid fracture. However, Li diffusion-induced stress does not explain the observed dominant fracture of crystalline Si during the first lithiation. Furthermore, recent studies have revealed anomalous volume expansion behavior of crystalline Si nanostructures during lithiation that contradict the commonly held belief that volume expansion of Si occurs via isotropic Li reaction and diffusion. In this talk, the mechanical behavior of crystalline Si nanostructures during electrochemical lithiation will be discussed in relation to volume expansion, stresses, and fracture. First, anisotropic volume expansion and anomalous fracture behavior of crystalline Si nanopillars of various axial orientations will be shown. Second, we will show that there is find facets of reaction front between crystalline Si core and Li-Si alloy shell. Then, new stress models and numerical analysis will explain how anisotropic expansion contributes to fracture of Si nanostructures during lithiation. Finally, the critical size below which Si nanostructures do not fracture will be discussed and compared to amorphous Si nanostructures, and design rules for nanostructured Si Li-ion battery anodes will be suggested.

One of the key obstacles to widespread commercialization of solid oxide fuel cell (SOFC) systems is their weakness to contaminants in the fuel stream. Hydrogen sulfide has been observed to reduce the performance of state-of-the-art commercial SOFC anode/electrolyte composites by forming sulfide phases or sulfur on the surface and deactivating the catalyst. A novel anode/electrolyte composite, consisting of Ni as the anode and BaZr0.1Ce0.7Y0.1Yb0.1O3±δ (BZCYYb) as the electrolyte, has been developed and shows promising tolerance to hydrogen sulfide. However, the mechanism of tolerance is not well understood, although the surface of the anode and the interface between Ni and BZCYYb are believed to be the key area of interest. The purpose of this study is to investigate how the BZCYYb electrolyte modifies the anode and prevents the formation of surface sulfide or sulfur from deactivating the Ni catalyst and degrading the performance. The hypothesis is that the high temperature synthesis process volatilized BZCYYb, which then deposits onto the Ni surface and is the phase responsible for the sulfur tolerance. X-ray photoelectron spectroscopy was employed to study the presence of BZCYYb on the surface and only Ba and Ce were detected in appreciable concentrations on the Ni surface. Quantitative analysis revealed that the stoichiometry also varied from the original BZCYYb. X-ray absorption near-edge spectroscopy was applied to study the oxidation state and electronic structure of the Ba-containing phase on the Ni surface. The roles of the constituent elements of the Ni/BZCYYb electrode towards sulfur tolerance were determined and will be presented as a comprehensive picture.

Platinum is widely used in solid state oxygen sensors and solid oxide cells (SOCs) as electrodes due to its high catalytic activity for oxygen reduction reaction and its chemical stability at relatively high operation temperatures (700-1000°C). The electrode reactions in such applications are limited to the Pt/electrolyte interface. The restricted length of triple phase boundaries (TPBs) limit the performance of the electrode which results in the loss of sensitivity in oxygen sensors and lowers performance in SOCs. Another issue with the Pt electrodes is the microstructural stability at operational temperatures. Although Pt is a chemically stable electrode material, high operational temperatures results in significant grain growth corresponding to losses in effective surface area which causes degradation of the electrode performance.
Infiltration of porous Pt electrodes by a precursor of the electrolyte material, yttria stabilized zirconia (YSZ) was proposed as a method to increase the length of the triple phase boundaries and stabilize Pt microstructure. Symmetrical cells were prepared by depositing Pt paste on both sides of a dense YSZ electrolyte followed by partial sintering to obtain porous Pt layers which were infiltrated by a polymeric precursor of YSZ.
Impedance spectroscopy measurements were carried out in air in order to evaluate the performance of the electrodes. Polarization resistance of the symmetrical cells with non-infiltrated Pt electrodes was ~0.1 Ohm.cm² per electrode at 800 °C which increased to ~0.35 Ohm.cm² per electrode after 30 hours of operation at this temperature. On the other hand, YSZ infiltrated Pt electrodes showed significantly reduced polarization resistance of ~0.045 Ohm.cm² per electrode at 800 °C which remained stable after >100 hours of operation at this temperature. Performance and the stability of the electrodes were also evaluated in fuel cell regime. Cells with non-infiltrated Pt electrodes showed a total electrode resistance of 2.8 Ohm.cm² at 800°C while YSZ cells with YSZ infiltrated Pt electrodes had total electrode polarization resistance of 0.3 Ohm.cm² at 800°C. Possible mechanisms governing stabilization of the porous Pt microstructure and significant enhancement of the electrode performance in oxidizing and reducing conditions will be discussed.

Lithium-Sulfur batteries have 5 times the theoretical capacity of lithium-ion batteries, but have relatively poor cyclability [1], primarily due to dissolution of the sulfur cathode into the polymer electrolyte as the neutral octasulfur (insoluble) is reduced to shorter and shorter polysulfide di-anions (soluble) and eventually lithium sulfide (insoluble) [2]. We currently lack a fundamental understanding of the dissolution processes and the relative population of the sulfur species in the polymer [3]. With the assumption that the various sulfur species exist in thermodynamic equilibrium in the polymer, then their relative populations are driven by corresponding relative Gibbs free energies, which we expect to have a varying entropic components. This necessitates a means of accurately calculating the system entropy. Here we utilize the efficient Two-Phase Thermodynamics method [4], within the context of ab-initio molecular dynamics simulations, to access the relative stability of sulfur species in tetraglyme. We find that the entropy plays a prominent role in stabilizing the Li2S8 species relative to the shorter-chain polysulfides. We also provide simulated characterization of the dissolved sulfur species by calculating the X-ray absorption spectra at the Lithium and Sulfur K-edges using constrained density functional theory within the eXcited electron and Core Hole (XCH) [5] approach.
This work was supported by the Laboratory Directed Research and Development Program of Lawrence Berkeley National Laboratory under U.S. Department of Energy Contract No. DE-AC02-05CH11231.
References
1. Scrosati, B. and Garche, J., Lithium batteries: Status, prospects and future. Journal of Power Sources, 2010. 195(9): p. 2419-2430.
2. Diao, Y., Xie, K., Xiong, S., and Hong, X., Analysis of Polysulfide Dissolved in Electrolyte in Discharge-Charge Process of Li-S Battery. Journal of the Electrochemical Society, 2012. 159(4): p. A421-A425.
3. Barchasz, C., Molton, F., Duboc, C., Leprecirc;tre, J.-C., Patoux, S., and Alloin, F., Lithium/Sulfur Cell Discharge Mechanism: An Original Approach for Intermediate Species Identification. Analytical Chemistry, 2012. 84(9): p. 3973-3980.
4. Lin, S.T., Blanco, M., and Goddard, W.A., The two-phase model for calculating thermodynamic properties of liquids from molecular dynamics: Validation for the phase diagram of Lennard-Jones fluids. Journal of Chemical Physics, 2003. 119(22): p. 11792-11805.
5. Prendergast, D. and Galli, G., X-Ray Absorption Spectra of Water from First Principles Calculations. Physical Review Letters, 2006. 96(21): p. 215502.

Currently, ionic liquids (ILs) are being widely investigated as electrolytes within electric double-layer capacitors (EDLC) due to their inherent ionic conductivity, wide electrochemical windows, non-volatility, and high temperature stability. Sputter deposition of metal directly into an IL—a task made feasible by their negligible vapor pressure—can achieve a potentially cleaner (i.e., “ligand-free”) “dry” synthesis of a nanoparticle-in-IL dispersion compared to conventional wet chemistry means. In a conceptual framework, the high intrinsic viscosities of ILs have the advantage of retarding growth rates for nanoparticle growth, permitting better resolved investigations into size-dependent behaviors and mechanisms for particle evolution and ripening. Indeed, apparent growth rates for nanoparticles have been shown to fall sharply upon storage at low temperatures, a result of decreased Brownian motion in the more viscous IL phase. In the current investigation, cyclic voltammetry and electrochemical impedance spectroscopy (EIS) measurements were used to study dispersions of gold nanoparticle (AuNPs) in the IL 1-ethyl-3-methylimidazolium ethyl sulfate ([emim][EtSO4]) prepared by sputter deposition. Our EIS results reveal that a colloidal AuNPs in [emim][EtSO4] dispersion is well characterized by a modified Randles equivalent circuit. Immediately following Au deposition, when the IL contains a substantial fraction of sub-nanometer-sized particles, the double-layer capacitance increases ~180% whilst charge transfer resistance (Rct) decreases ~70 % with respect to an Au-free IL control. An exponential rise in resistance (i.e., a decrease in capacitance) accompanies nanoparticle growth until a critical size is achieved—typically within 10 h at room temperature—beyond which, capacitance and resistance are asymptotic to certain limits. For longer post-sputtering aging times (t > 10 h), the final capacitance is typically ~60 % higher than the control for a Rct close to that of the control. Overall, our results reveal an anomalous capacitive rise and low internal resistance for nanoparticle-in-IL dispersions, suggesting intriguing potential as electrolytes for advanced EDLCs, fuel cells, sensors.

The La2NiO4 ternary phase has been considered as a potential cathode material for intermediate temperature solid oxide fuel cell applications. In recent works it is reported that the performance of nickelate type cathode can be improved by SrO doping. However, there is no detailed literature information on phase equilibria of the La2O3-SrO-NiO ternary oxide system. In order to build chemically stable fuel cells, not only the thermodynamic stability of the electrolyte and electrodes themselves, but also the reactivity between component materials should be well established. The work aimed to investigate ternary phase equilibria of the cathode itself and also compatibility/reactivity between the cathode and LSGM electrolyte. The experimental work has been designed based on the calculated phase diagrams. In the La-Sr-Ni-O system, extended solid solutions (L,Sr)2NiO4 was found. Also chemical potential diagram of the system simulation fabricating and operation conditions was calculated.

It is widely accepted that clustering of ions in polyelectrolyte membranes (PEM) affects the conductivity. Investigation of the relationship between clustering and conductivity is challenging due to lack of experimental tools for assessing the geometry of the clusters. Indeed most of our knowledge about ion clustering is based on SAXS experiments that cannot uniquely identify the cluster geometry . SAXS results may be explained by various, sometimes contradictory models. In our experiments we use electron microscopy (EM) to directly visualize the clusters [1] in the model system of poly(styrenesulfonate-methylbutylene) block copolymer (PSS-PMB) with polystyrene randomly sulfonated to 40 % level. We perform annealing experiments at 98% relative humidity and show that annealing in water vapor irreversibly reduces the conductivity of the sample [2]. EM investigation reveals that the drop in conductivity is accompanied by the development of ionic clusters within the PSS phase. We found that after the clusters have developed, conductivity depends linearly on temperature. Saturation of a sample with water during annealing also changes the arrangement of the PSS and PMB phases from lamellae in dry sample to a cylinder-like honeycomb phase. This transformation, however, is fully reversible, and annealing in THF restores the lamellar morphology maintaining clusters inside the PSS phase. The change we observe in PSS and PMB phase arrangement may be described by the standard Gaussian model for block copolymer melts because water and THF preferentially solvate and swell PSS and PMB phases respectively. To explain the stability of the clusters after their formation, we suggest that there is some bound water that remains in the ionic clusters even after drying of the sample.
References
[1] Yakovlev, S.; Wang, X.; Ercius, P.; Balsara, N. P.; Downing, K. H. Journal of the American Chemical Society 2011, 133, 20700.
[2] Wang, X.; Yakovlev, S.; Beers, K. M.; Park, M. J.; Mullin, S. A.; Downing, K. H.; Balsara, N. P. Macromolecules 2010, 43, 5306.

Despite the promising synergetic properties of MnO2 - a low cost, high specific energy material - with graphitic carbon - an electrochemically stable, high specific power material - the MnO2-graphitic carbon pseudocapacitor has yet to achieve its full potential in terms of specific energy or specific power. To improve these devices it is critical to understand all of the mechanisms that limit the performance: charge transfer at the electrolyte-MnO2 interface, Li+ ion diffusion, MnO2 electronic transport, and charge transfer at the MnO2-graphitic carbon interface. To this end, we have fabricated MnO2-graphitic carbon systems using individual single-walled carbon nanotube (SWNT) and multi-walled carbon nanotube ( MWNT) support electrodes, as well as platinum electrodes with precisely controlled geometries. The SWNT and MWNT electrodes are engineered such that only a 1mu;m subsection of the sidewall is exposed to a MnO2 plating solution, and uniform electrochemical deposition of MnO2, 100nm-900nm, is achieved by applying a pulsed potential. The capacitance is characterized using cyclic voltammetry. We find that, even in the limit of sub-picogram quantities of MnO2 on a single SWNT, the specific capacitance agrees with bulk MnO2-CNT pseudocapacitors in literature. In addition, we fit the cyclic voltammograms to a RC circuit model to find the time constant of charging and discharging. The time constants range from .1 s - 1 s, depending on the scan rate, but are independent of the size and chemistry of the conductive support. In fact, there is no deviation in the time constant even in the limit of a 10^9 MnO2:C ratio and a 1000 A/m^2 current density at the MnO2-SWNT interface. In conclusion, by scaling down the MnO2-graphitic carbon system to the smallest of its constituents we were able to rigorously exclude the MnO2-graphitic carbon interface as a power limiting mechanism in theses pseudocapacitors. This research is supported by the NEES Energy Frontier Research Center of the U.S. DOE Office of Basic Energy Sciences (#DESC0001160).

Palladium is an important hydrogen separation material for fuel cells, and offers high volumetric power density in metal hydride batteries and pseudocapacitors. Performance in these applications is often limited by the stability of the surface hydride, which results in slow transport of hydrogen between the surface, gas phase and bulk solid phase [1]. Theoretical and experimental reports [2,3] suggest that adlayers of another metal can destabilize the surface hydride, which may facilitate hydrogen transport, especially at low temperatures. We have used electrochemical atomic layer deposition to grow such layers on palladium electrodes, and an electroless version to prepare bulk powders, achieving a high degree of compositional precision and synthetic flexibility. We present examples of enhanced hydrogen transport through electrode surfaces, and powder surfaces in the presence of hydrogen gas. A multiscale model combining gas flow, surface kinetics, and solid-state hydrogen diffusion allows design of hydrogen storage and separation media optimized for a material with enhanced kinetics.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
1. TL Ward and T Dao, J. Membrane Sci. 153 211 (1999)
2. PN Bartlett and J Marwan, Phys. Chem. Chem. Phys. 6 2895 (2004)
3. J. Greeley and M. Mavrikakis, J. Phys. Chem. B 109 3460 (2005)

Solid oxide fuel cells (SOFCs) represent the most efficient way to generate electricity from a variety of fuels such as hydrogen, methane and natural gases. To increase the output voltage of the SOFC system, multiple cells are connected in electrical series using interconnects. In a stack, an interconnect electrically connects unit cells and separates fuel from oxidant in the adjoining cells. The key requirements of the interconnect are high electronic conductivity and chemical stability in both oxidizing and reducing atmospheres, negligible gas permeability, and chemical/thermal compatibility with other SOFC components. In this paper, we present recent developments of transition metal oxides for SOFC interconnects with specific attention to materials synthesis and thin layer coating. A dual-layer interconnect for flat-tubular SOFCs is first discussed that consists of an n-type conducting (Sr,La)TiO3 layer on the anode side and a p-type conducing (La,Sr)MnO3 layer on the cathode side. Then, protective spinel coatings on metallic interconnects are presented, which are capable of mitigating oxide scale growth and inhibiting Cr evaporation. The synthesis of (Sr,La)TiO3 perovskites and doped Mn-Co spinels and their properties (e.g., structures, electrical conductivities and thermal expansion coefficients) are discussed in detail, followed by a description of coating processes.

Three-components Li(Ni-Mn-Co)O2 high-voltage cathode materials have been extensively studied for high-energy density lithium-ion batteries because of their excellent performance with respect to specific capacity and rate capability. As conventional electrolyte is subjected to severe oxidative decomposition when a lithium cell is charged to over 4.3 V vs. Li/Li+, the control of cathode-electrolyte interfacial reaction is an important prerequisite for charge-discharge cycling stability. Carbonate-based and sulfone-based additives can be used for cycling performance improvement of high voltage lithium ion battery. The reason is that additives preferably oxidized on cathode compared to solvents, forming a protective film or an SEI on the cathode, which prevents electrolytes and cathode materials from oxidative decomposition. Studies of interfacial reaction behavior and the SEI stability at high-voltage are yet to be explored in-depth. In this presentation, we report the synthesis of Li(Ni0.5Mn0.3Co0.2)O2 cathode material using hydroxide precursor and its electrochemical and interfacial reaction behavior at high voltage operation upto 4.6 V vs. Li/Li+ in the presence of electrolyte additives.
Acknowledgments: This research was financially supported by the Ministry of Education, Science Technology (MEST) and National Research Foundation of Korea (NRF) through the Human Resource Training Project for Regional Innovation (No. 2012026203) & KIAT (No. A0022-00725).

Current commercial proton exchange membrane (PEM), Nafion, has disadvantages of low operation temperature (<80°C), environmental incompatibility, high production cost, and especially unsatisfactory proton conductivity (around 0.9 S/cm). In order to improve the performance of Nafion, many inorganic powdery materials, for example silica, were used to construct Nafion-based composite PEMs. However, most Nafion-based PEMs lack protogenic groups or have insufficient ionic pathways, which restrict the performance and further improvement of these membranes.
In this work, we incorporated sulfated zirconia (S-ZrO2) nanofibers into Nafion matrix to prepare a novel type of solid superacid nanofiber-Nafion hybrid PEMs. Sol-gel electrospinning method was used to prepare the nanofibers with polyvinylpyrrolidone (PVP)/zirconium propoxide (Zr(OPr)4)/isopropanel as the pre-spinning solution. After sulfonation and calcination processes, the superacidic S-ZrO2 nanofibers mats were obtained. Different fibers with various diameters ranging from 81 nm to 369 nm and different fiber volume fractions from 8% to 20% were acquired. With simple casting method, the superacid nanofiber-Nafion hybrid PEMs were prepared.
It was found that with the decrease of fiber diameters and the increase of fiber volume fractions, the proton conductivities of hybrid PEMs were highly improved, indicating that the incorporated superacidic nanofibers play a key role in the proton transport mechanism. Transmission Electron Microscopy proved that with the assistance of superacidic nanofiber mats, large amount of clusters of sulfonic acid groups in recast Nafion aggregate onto the interfaces between S-ZrO2 fibers and the ionomer matrix, forming continuous pathways for facile proton transport, which in turn lead to a much higher proton conductivity of 0.31 S/cm at 100°C and 80% relative humidity, compared with Nafion. In addition, the application of superacidic nanofibers as the filler material also effectively avoids the agglomeration of inorganic particulate components, which may cause localized stress and poor mechanical properties. The S-ZrO2 nanofiber-Nafion hybrid membranes are easy to fabricate, highly controllable, and can be used in practical fuel cell systems.

In a polymer electrolyte membrane fuel cell (PEMFC), one of the most important factors affecting the performance is the contact resistance at the interface of the gas diffusion layer (GDL) and bipolar plate (BP). General contact resistance theory cannot be applied to this interface because the GDL, which is highly porous (>80%), cannot be considered a normal solid. Theoretical and numerical approaches are therefore necessary to understand the mechanism and to predict the magnitude of contact resistance in a PEMFC. In this work, a contact resistance model is developed to determine the contact area between the GDL and BP by considering the contraction of the GDL. Furthermore, the influence of surface roughness on the contact resistance is investigated using BP samples polished at different grades. As the average surface roughness was increased, the contact resistance values decreased, which was in good agreement with the results from the contact resistance model.

The efficient electrochemical reduction of CO2 to fuels could be a viable means to store electricity generated by renewable technologies such as solar cells or wind turbines. Almost all metals have the ability to electrochemically reduce carbon dioxide at low temperatures, however, most do so with low current efficiencies for carbon based fuels or at high overpotentials [1]. Gold has previously been shown to produce carbon monoxide with faradaic efficiencies around 90%, as well as formate with ~1% faradaic efficiency [2]. CO2 reduction, as with many electrochemical reactions, is often dependent upon the electrode surface structure and preparation. Thus, this presentation will focus on enhancement of the activity and product selectivity of CO2 reduction on gold by changing the topology of a polycrystalline gold surface.
In this study, the surfaces of gold foils were subjected to different surface pretreatments and then tested for the electrochemical reduction of carbon dioxide. Testing was performed in a 3-electrode, 2-compartment compression cell separated by an anion exchange membrane. Gas product analysis was achieved by a gas chromatograph, liquid products by NMR.
CO2 reduction activities were measured with a continuous flow of CO2 in saturated 0.1M potassium bicarbonate solution at room temperature. An anion exchange membrane was used to prevent liquid products from being oxidized at the counter electrode which consisted of a platinum foil. A Ag/AgCl reference electrode was used during experimentation. Potentials were adjusted post experimentation to the reversible hydrogen electrode (RHE). Potentials were also adjusted 100% for solution resistance.
Hydrogen and carbon monoxide were the main products formed from the electrochemical reduction of CO2 on gold. This paper will describe our efforts to modify the surface of gold and how such modifications translate to differences in activity and selectivity for CO2 reduction.
REFERENCES
[1] M. Azuma, K. Hashimoto, M. Hiramoto, M. Watanabe and T. Sakata, Journal of The Electrochemical Society 137 (1990) 1772.
[2] Y. Hori, H. Wakebe, T. Tsukamoto and O. Koga, Electrochimica Acta 39 (1994) 1833.

One of the most pivotal issues is the large overpotential associated with the slow reaction rate of the oxygen reduction reaction (ORR) at the cathode. Considerable efforts have been devoted previously to understand the kinetics and mechanisms of the ORR in order to search for inexpensive and catalytically active electrocatalysts such as bi- and multimetallic alloys. Furthermore, in recent times, studies have been conducted on the correlation between the electronic structure and catalytic activity of metallic alloys for the ORR. The adsorption energy of oxygen is proportional to the oxygen-metal bond strength and the relative position of the d-band center to the Fermi level. Another tremendous challenge is the stability of electrochemical reactions such as metal dissolution and surface oxide formation, which occur intensively in acid mediums at high potentials. Recently, Noslash;rskov et al., Chorkendorff et al., and Yoo et al. reported stable cathode catalysts by alloying Pt with early transition metals such as Hf, La, Sc or Y. However, despite the significant technological interest in finding active and stable catalysts for the ORR, direct experimental investigations into the contributions of the activities involving stability have rarely been performed in the electrochemical reduction of oxygen.
In this paper, we report the realistic parameters elucidating stability and activity of Pt3M (M = Y, Zr, Ti, Ni, and Co) alloy nanocatalysts prepared by a high-pressure sputtering method. In particular, we have focused on the electronic structure modification of the Pt3M alloy nanocatalysts in order to analyze the more active and stable electrocatalytic cathode materials. The results suggest that this concept has distinct merit, since significant changes in the catalytic behaviour and stability of Pt were observed when Pt-based alloy nanocatalysts were made of early transition metals.

The growth in the lithium battery industry over the past decade has been driven predominantly by the demand for consumer electronic devices such as cellular telephones and laptop computers. A lithium ion-type has been widely used in different types of the batteries developed so far due to its excellent properties such as high voltage, high energy density, and durable cycle charge characteristics. Lithium manganese oxides (Li-Mn-O) may be an alternative material to LiCoO2 because of their properties similar to those of LiCoO2. There are several kinds of lithium manganese oxides such as LiMn2O4, Li4Mn5O12, Li2Mn4O9, LiMnO2, and Li1+xMn2-xO4. Electromotive force of about 3 to 4 V can be exhibited when lithium manganese oxides are used as cathode active materials in a lithium ion battery.
Herein, we prepared mesoporous Li2MnO3-Li4Mn5O12 electrode for lithium-ion batteries by means of modified inverse micelle method. The structural characterization of Li2MnO3-Li4Mn5O12 electrode was carried out using field-emission scanning electron microscopy and field-emission transmission electron microscopy. The surface area and porosity of the electrodes were analyzed by a nitrogen sorption measurement. To evaluate the performance of the electrodes for lithium-ion batteries charge-discharge characteristics of the cathode materials were measured using a lithium coin cell.

Noble metallic nanoparticles (NPs) have received extensive interests due to their particular electrochemical, photochemical, biochemical, sensor, and catalytic properties. The shape-controlled metal NPs have been synthesized with 0-dimentional (cube, octahedron, truncated cube, and tetrahedron, etc.), 1-dimentional (nanowire, nanorod, and nanotube, etc.), 2-dimentional (nanoplate and nanosheet, etc.), and 3-dimentional structures (nanostar, nanoflower, and nanodendrite, etc.). In recent, it has been reported that shape-controlled NPs exhibits much improved thermal, chemical, magnetic, electronic, and catalytic properties as compared to bulk structure. In particular, the shape-controlled Pt-based nanoparticles for electrochemical power sources such as fuel cells have shown much enhanced electrocatalytic activity and stability. To improve the electrocatalytic properties of Pt-based nanostructure catalysts, there have been many efforts to manipulate the structure and shape of NPs during the synthetic process. For shape-controlled metallic NPs, the various synthetic methods are polyol method in aqueous or organic solution, chemical, thermal and photochemical reduction methods. Among them, the polyol and thermal decomposition (reduction) process have many advantages for the preparation of structure- or shape-controlled noble metallic nanoparticles with homogeneous size and shape. Herein, we synthesized shape-controlled Pt-based nanoparticles by the polyol and thermal decomposition (reduction) process. The electrochemical properties of as-prepared Pt-based nanostructures for anodic and cathodic reaction were evaluated using a typical electrochemical cell.

Platinum as an anode electrocatalyst for direct methanol fuel cells has shown an excellent catalytic activity in acid electrolytes. In particular, the catalytic properties of Pt nanoparticles strongly depend on their shape, size and crystallinity. Herein, we report hexapod Pt nanoparticles (Hexa-Pt) synthesized by means of polyol process in the presence of poly(vinyl pyrrolidone) and NO3- and Fe3+/Fe2+ ions. The NO3- and Fe3+/Fe2+ ions as additive ions could expose {111} facets of Hexa-Pt NPs by means of a different potential reaction and reducing rate. The Hexa-Pt with controlled surface structure of {111} facets favorable for catalytic reaction could result in an excellent catalytic activity and stability for methanol electrooxidaion in comparision with the commercial Pt/C.

The carbon supported Ru85Se15 nonoparticles were synthesized by microwave assisted polyol method at the optimized pH. The catalyst coated membrane method with ultrasonic-spray technique without hot press step was employed to prepare membrane electrode assemblies (MEAs), which were composed of Nafion 212 membrane, carbon blacks (XC-72R) or multi-wall carbon nanotubes (MWCNTs) supported Ru85Se15 as a cathode catalyst and carbon supported platinum as an anode catalyst. The single cell tests and the accelerated degradation tests of MEAs were carried out in both H2/air and H2/O2 fuel cells at 65 degree centigrade under ambient pressure. The degradation behaviors of MEAs were extensively analyzed. It was found that Nafion contents affected the cell performance and durability more significantly than Ru loads. Very severe losses of 80% and 82% were found for the 20% and 43% Nafion contents, respectively, while relatively moderate losses of 57% and 64% for the 0.14 and 0.61 mg Ru cm-2, respectively. Based on the systematic analyses of cathode catalyst layers and membranes in MEAs before and after the accelerated degradation tests, the dissolution and migration of Se/Ru and the corrosion of carbon support from the catalyst, together with the shrinkage and release of sulfonic acid from the membrane were identified and correlated to the decayed cell performances.

Polymers with stable pendant radical groups have emerged as a unique class of electroactive materials that are emerging as potentially deployable materials for energy storage, transport and conversion. These polymers facilitate remarkably rapid, efficient and reversible multi-step charge transfer processes. However, there is currently not an advanced understanding of the mechanism(s) involved in electron or ion transfer for these polymeric materials, this hinders rational design efforts to improve the electroactive properties of radical containing polymers. This presentation will summarize our recent results via a correlation of our empirical electrochemical results to theoretical modeling. Specifically, we have investigated the mechanism for a nitroxide-radical based cathode with respect to the electron- and ion- transfer within a p-type radical polymer, poly(4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl) (PTMA), cathode matrix with varying pendant group chain length. The work also offers further insight into the mechanism of charge-transfer across polymer cathode-electrolyte interface. Through a series of dynamic and static in-situ spectroelectrochemical photoluminescent and Raman experiments we have found how segmental motion within the polymer chain affects both mass-transfer and charge transfer for a series of Li-ion based electrolyte systems with varying anion charge density. A summary of our results will be presented.

The design of efficient and cost-effective catalysts for the oxygen evolution reaction (OER) is crucial for the development of electrochemical conversion technologies. However, little is known about the atomic and electronic structure and thermodynamic properties of realistic catalytic interfaces, which impedes the development of catalysts with high activity and low cost. In this work, we apply first-principles density functional theory computations in combination with kinetic modeling to investigate the environment-dependent chemical and physical properties of perovskite oxide heterostrucutre catalysts, particularly LaMnxM1-xO3. We develop a methodology to identify constraints on the interface structure phase space, and use this approach to relate the atomic characteristics of catalytic interfaces to the realistic interface reconstructions caused by different environments during fabrication, measurement, and eventual device operation. Our work could lead to rapid and accurate prediction of surface/interface structures and properties under different environmental conditions, and contribute to the design of new high-activity OER catalysts.

The influence of the pore structure and pore size distribution of the cathode catalytic layer by the addition of multi-walled carbon nanotubes (MWCNTs) on the oxygen reduction reaction (ORR) of polymer electrolyte membrane fuel cells (PEMFC) was investigated. The catalyst layers were fabricated based on various weight ratios of Pt/C to MWCNTs. The structure of the catalyst layer was studied by using scanning electron microscopy (SEM) and mercury porosimetry (MP). The performance of the ORR for PEMFC was evaluated by the I-V characteristics, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). The macro pore (secondary pore, approximately 1 µm) volume in a catalyst layer was increased as a function of weight ratio of MWCNTs. In contrast, the micro pore (primary pore, below 100 nm) volume was decreased. From the results, it was obtained that the performance of the ORR (increase in capacitance and decrease in proton transport and charge transport resistance) for single cell was increased and the pore size distribution was optimized, as the Pt/C to MWCNTs weight ratio of 90 wt% to 10 wt%.

Much interest exists in advancing the power, capacity, recharging speed, and durability of the Li-ion battery relating to the recent electric power conservation and environmental problems. Among the key processes, the transport process of the Li ions in graphite is related directly to the recharging speed and power of the battery.
Previously we have investigated the dependencies of the thermal diffusivity of a single Li ion in defect-free graphite on the external stress [1] and on the vertical alternating electric field [2] by the hybrid quantum-classical simulation method [3]. In the method, the real-space grid implemented Kohn-Sham density-functional theory (RGDFT) is applied to a small (i.e., QM) region around the Li-ion, while the classical empirical inter-atomic potential is applied to the rest (i.e., CL) region of the total system. The RGDFT code has remarkable features of high parallelizability in addition to the high physical accuracy in ionic forces and universality in target materials and external conditions. In the present research we investigate the diffusion of several Li-ions in graphite with a vacancy defect to understand the effects of the Li-Li and Li-vacancy interactions on the Li diffusivity. Much larger and plural number of the QM regions around the defect and Li ions need to be treated in the present setting as compared to the previous simulations [1,2]. To meet this need, we have recently advanced the RGDFT code to the linear-scaling, divide-and-conquer-type one (DC-RGDFT) [4]. Either the RGDFT or DC-RGDFT is applied adaptively to the QM regions during a simulation run considering the overall computation speed and physical accuracy. We will show that the Li ions are trapped by the vacancy and that the Li diffusivity is affected sensitively by the expansion stress caused by the Li-ions trapped at the vacancy.
References
[1] N. Ohba, et al., Comput. Modeling Eng. Sci. 75 (2011) 247.
[2] N. Ohba, S. Ogata, et al., J. Phys. Soc. Jpn. 81 (2012) 023601.
[3] S. Ogata, Phys. Rev. B 72 (2005) 045348.
[4] N. Ohba S. Ogata, T. Kouno, et al., Comp. Phys. Commu. 183 (2012) 1664.

Lithium ion batteries are the most common rechargeable storage devices for portable electronics, and will play an important role in large-scale applications, such as electric vehicles and grid-scale storage. In order to design safe, high-energy electrodes with long-cycle life, we need a better understanding how electrode materials function by real-time tracking of lithium transport and electrochemistry in a working electrode, ideally at the level of single particles. However, this type of characterization requires high sensitivity to all constituents including lithium and the capability of capturing chemical and physical changes of electrodes at relevant spatial and temporal resolution. Although high-resolution transmission electron microscopy (TEM) imaging and energy-loss spectroscopy (EELS) are powerful tools for probing Li with sub-nm spatial resolution, they have not been well developed for studies of batteries largely due to the issues related to acute radiation damage. In addition, most of the available in situ techniques, such as those based on hard x-ray scattering, are suited for studying bulk electrodes and have inadequate spatial resolution for exploring nanoscale morphological and structural changes and determining where and how new phases nucleate and propagate. TEM, on the other hand, is capable of exceptional spatial resolution, but, until recently, has been unsuitable for these studies due to space limitations, low electron transparency and an incompatibility of the liquid electrolyte with the high vacuum environment.
Recently we developed a novel in situ TEM-EELS approach to track electrochemical reactions in real time and used to track intra and inter-particle lithium transport and conversion reaction in FeF2 electrodes by nano-scale imaging, diffraction and spectroscopy [1]. The in situ measurements enable us, for the first time, to reveal the real time formation of sub-nm to ~2 nm Fe particles intermixed with LiF within the domain of the FeF2 precursor. The formation of an interconnected iron network provides a pathway for electron transport, while the interface between the iron and LiF phases is believed to facilitate Li transport [1, 2]. The structural and chemical changes occurring during Li conversion were monitored with in situ EELS, coupled with TEM images and diffraction patterns acquired from a same area. These results were combined with first principles calculations and Monte Carlo simulations to gain insight on reaction pathways and the factors limiting the kinetics of the conversion process.
References
[1] F. Wang, H-C. Yu, M-H. Chen, L. wu, N. Pereira, K. Thornton, A.V.d. Ven, Y. Zhu, G. Amatucci, J. Graetz, Nat. Comm. (in press); [2] F. Wang, et al, J. Am. Chem. Soc., 133 (2011) 18828.
This work was supported by the Northeastern Center for Chemical Energy Storage, an Energy Frontier Research Center funded by the U.S. DOE, BES under award No. DE-SC0001294.

Newly developed conversion materials such as iron fluorides exposed to Li ions enable access to the multiple valence states of the cathode cation in high capacity Li-ion batteries, which result in crystalline LiF and metallic Fe nanoclusters during discharge. Even with the use of various experimental techniques, the detailed atomistic mechanisms and reaction pathways of this very complex conversion are not well understood. To address this problem at the atomistic level, we have developed a dynamically adaptive variable charge potential for MD simulations that allows for the charges on all species to respond to the local atomistic environment. This potential accurately describes the charges on the ions in FeF2, FeF3, and LiF in comparison to ab-initio calculations and results in crystal structures, elastic constants, and surface energies consistent with experiment and ab-initio calculations, as well as the structure, cohesive energy, and surface energy of α-Fe (BCC iron). With this potential, the cations in FeF2 in the presence of the Li ions and implicit electrons change from the +2 state to the metallic state during the conversion reaction, forming metallic clusters of α-Fe and crystalline LiF, consistent with XRD and EXAFS studies, with nanocluster sizes and shapes consistent with post-reaction TEM analysis. The conversion occurs via the initial formation of amorphous phases that enable Li insertion and continued reaction prior to the formation of the crystalline reaction products that significantly inhibit further Li transport and conversion. In addition to showing, for the first time, the conversion mechanisms of FeF2 + Li+ to LiF + α-Fe, the simulations also show the role of the exposed surface orientation and different transport paths on the extent of conversion.

Modeling of charge/discharge behavior of Li-ion cells, in particular, the electrochemical insertion and de-insertion of Li⁺ is challenging because of the complexity of the ion transport and phase transformations corresponding to intercalation/deintercalation. Mesoscopically, this requires analytical solutions of diffusion that incorporate moving phase boundaries due to phase transitions. Here, we present a computational scheme, using which one can predict the charge/discharge behavior of Li-ion cells. The computational scheme uses analytical diffusion solutions for each electrode, which include moving phase boundaries. The migration and diffusion of Li⁺ ions within the electrolyte are modeled using the Nernst-Planck equation. Butler-Volmer kinetics is used to calculate the charge transfer overpotentials at the two electrode/electrolyte interfaces. A comparison of the simulation results with experimental data is presented. The computational scheme is more direct, intuitive and can be adopted to simulate the behavior of Li-ion batteries.

Cation substitution of LiFePO₄ has been shown to enhance its electrochemical performance. However, the reason why has not been determined. We have shown that by controlled reactions it is possible to incorporate up to 10 mol. % of vanadium into LiFePO₄ structure at either the iron or the Li site. We investigated the structural changes accompanying the chemical and electrochemical lithiation and delithiation, and the kinetics of these processes by in-situ and ex-situ x-ray diffraction (XRD) and absorption (XAS), and electrochemical methods. Thermal stability of the partially delithiated phases was studied by in-situ XRD upon heating up to 800 °C. The GITT measurements show that vanadium substitution at the Fe site results in faster kinetics compared to the unsubstituted LiFePO₄, while placing V at the Li site results in much slower kinetics. XRD shows vacancy formation at the Li site or at the Fe site, when V is substituted at each of these sites, respectively. Most importantly, vanadium substitution (a) reduces the lattice mismatch between the lithiated and the delithiated olivine phases; (b) increases the solid solution regions and (c) reduces the temperature at which complete solid solution, Li_xFePO₄for 0le;xle;1, is found. Thus, substitution makes Li_xFePO₄act as a single-phase system, resulting in its much enhanced rate capability. This research is supported as part of the Northeastern Center for Chemical Energy Storage, an Energy Frontier Research Center funded by the U.S. Department of Energy Office of Basic Energy Sciences under Award Number DE-SC0001294.

We present data and a corroborating model that there are three modes of mesoscale mechanical failure for battery electrodes. There is mounting evidence that ``electrochemical shock"---the electrochemical cycling-induced fracture of materials---is an active degradation mechanism in lithium-ion batteries.
We have undertaken a systematic effort to classify and model the electrochemical shock mechanisms applicable to each of the major classes of lithium storage compounds. Micromechanical fracture mechanics models for specific electrochemical shock mechanisms are developed and validated using acoustic emission measurements. Microstructure design rules to enable electrochemical shock resistant electrode materials have emerged from these results. At least three distinct electrochemical shock mechanisms have been identified. First, concentration-gradients develop in proportion to the applied C-rate and can cause diffusion-induced stresses analogous to thermal stresses. Second, materials with limited solid-solubility ranges can develop two-phase coherency stresses. The effects of such stresses are surprisingly large even in high symmetry compounds such as cubic spinels. Third, materials with anisotropic electrochemical expansion experience grain boundary compatibility stresses when used as polycrystals.
An important distinction between each of these electrochemical shock mechanisms is cycling rate (C-rate) sensitivity. Two-phase coherency stresses and intergranular compatibility stresses develop independent of the applied C-rate and can cause fracture even during slow cycling. In contrast, concentration-gradient stresses develop in proportion to C-rate and only contribute to fracture during fast cycling.
Our modeling and experiments together show that electrochemical shock in most active materials, at the particles sizes typically used, is dominated by C-rate-independent behavior. In spinel compounds such as LiMn₂O₄, and LiNi_0.5Mn_1.5O₄, and in olivines such as LiFePO₄ (except at the nanoscale), two-phase coherency stresses dominate. In layered materials such as LiCoO₂ and its derivatives, anisotropy effects dominate.
The combined modeling and experimental approach also reveals several strategies to engineer electrochemical shock resistant materials. First, C-rate-independent mechanisms depend sensitively on the crystallite and particle sizes; if these sizes are kept below critical sizes, electrochemical shock can be avoided. Second, chemical modifications which reduce anisotropy, shrink miscibility gaps, and reduce misfit strains all improve electrochemical shock resistance.

High-rate Li-ion batteries increasingly involve electrode materials, such as iron phosphate and graphite, which undergo phase separation into Li-rich and Li-poor phases upon intercalation of lithium. Complex dynamical phenomena arise because phase separation occurs in nanoparticles, limited by surface reactions, and far from equilibrium. The key to understanding these effects is a new phase-field theory of ion intercalation kinetics, which unifies the Cahn-Hilliard or Allen-Cahn equation with Butler-Volmer or Marcus kinetics for charge transfer. For individual nanoparticles, the theory predicts surface-nucleated intercalation waves at low current, which relax to striped morphologies driven by elastic coherency strain. Above a critical current (and/or temperature) typical of battery operation, phase separation is suppressed, which helps to explain the revolutionary performance of LiFePO4 in nanoparticle form. In porous electrodes, the theory predicts nucleation-limited mosaic instabilities at low current, giving way to diffusion-limited intercalation at high current. It can easily be applied to materials with three or more metastable phases, as illustrated by the staging dynamics of graphite anodes. The porous electrode theory based on nonequilibrium thermodynamics is very general and can also be applied to non-electrochemical adsorption phenomena with hysteresis, such as water sorption in concrete.

Observing the distribution of Li in a Li-ion battery electrode is difficult. Li is a light element and has few spectroscopic signatures. Also, one characteristic Li spectroscopic feature, its K-shell absorption edge, overlaps with the M edge of many transition metals. In LiFePO₄, however, Fe changes valence from +2 to +3 when the cathode transforms from LiFePO₄ to FePO₄. This valence state change can be used to map the microstructural distribution of Li. Here, we will show that a parallel, energy-filtered electron beam can map the Li distribution in LiFePO₄. This type of measurement mitigates the beam damage that occurs using a focused electron probe such as in STEM-EELS. Further advantages of this approach are simultaneous determination of the particle-by-particle microstructure and chemistry at high spatial resolution (~1 nm). We will show that we can make electron transparent cross sections that span the entire width of battery electrodes (35 µm), image the morphology of LiFePO₄ particles as they were during cycling, and map out the Li distribution at a specific battery state of charge for a given charging rate. Forensic analysis on the deconstructed battery cathodes shows that the transformation rate within each LiFePO₄ particle is fast relative to the total charging time. Therefore, the transformation process is completely nucleation limited and follows a mosaic pathway. Increasing the charge/discharge rate in LiFePO₄ requires that the energetic barrier to nucleating the new phase be reduced. We develop a simple phenomenological model that is consistent with the observed data.

Despite the widespread use of phase-separating insertion compounds in battery technologies, the physics of ion intercalation in these systems is just beginning to be understood. The most basic open questions involve the nucleation of phase separation in nanoparticles, which is difficult to observe experimentally and beyond the reach of ab initio molecular calculations. Surfaces are thought to play an important role in nanoparticles because of their large ratio of surface area to volume. Binary fluids at a solid surfaces have been studied in great detail by Cahn and others, but a theory for surfaces in binary solids, which have coherency strain, has not been developed.
The role of surfaces in binary intercalation compounds is investigated with a phase-field model that
includes electrochemistry and coherency strain. In contrast to binary fluids which form arbitrary
contact angles at surfaces, complete wetting by one solid phase is favored at binary solid surfaces, which promotes nucleation and growth. By balancing surface tension and elastic energy, the nucleation barrier for a nanoparticle is found to decrease with its surface-to-volume ratio and vanishes below a critical size, where particles exist in the homogeneous equilibrium state favored by their surface. As a result porous electrodes tend to fill in order of increasing particle size at low current. These phenomena are illustrated by simulating intercalation n in realistic nanoparticle geometries for LixFePO4 battery electrodes. Experiments in literature report the overpotential to initiate lithiation in LiFePO4 nanoparticles varies from 2mV to 37mV. Here we resolve this apparent discrepancy by showing that surface energy leads to a critical overpotential is size-dependent. The theory is able to predict the size-dependent nucleation barrier (critical overpotential) from experiments. Examples in literature from metallic alloy systems will also be presented.

Electrochemical equilibrium and the transfer of mass and charge through interfaces at atomic scale are of a fundamental importance for the microscopic understanding of elementary physicochemical processes. Approaching atomic dimensions, phase instabilities and instrumentation limits restrict the resolution. An uncertainty is additionally introduced by the fact that the well defined macroscopic quantities are averaged and even single crystalline substrates show local structural defects leading to microscopic inhomogeneities of the material properties. Therefore, the atomically resolved measurements of electrochemical processes require: i) a high precision in detecting mass and charge flow, ii) a stabilisation of thermodynamically meta-stable clusters of few atoms and iii) a knowledge of the local atomic structure and topography.
Here we demonstrate the ability to study electrochemical processes at vacuum/solid electrolyte surfaces at the atomic scale with an ultimate lateral, mass and charge resolution based on the atomic switch concept[1, 2]. We found that increasing the electronic partial conductivity of RbAg4I5 by small amount Fe doping we were able to use the STM technique on superionic conducting solids, which allowed for recording of an atomically resolved image of solid electrolyte at room temperature for the first time[1]. The crystallographic structure and the superionic properties of RbAg4I5 were preserved, i. e. the transference number of the ions is tion > 0.99, but an electronic conductivity in the order of was sufficient for quantum mechanical tunnelling. We show results on electrochemical process of phase formation, where the new phase consists of a few to some tens of atoms (as far it can be physically defined as a phase). The very initial stage is limited by the critical nucleus formation. The results are interpreted in the terms of atomistic theory of nucleation.
We further discuss the possibility of extending our method to other solid and liquid based ionic conductors which are used in sensors, fuel cells, and photo-/electro-catalysts.
References:
1. I. Valov, I. Sapezanskaia, A. Nayak, T. Tsuruoka, T. Bredow, T. Hasegawa, G. Staikov, M. Aono, and R. Waser. Atomically controlled electrochemical nucleation at superionic solid electrolyte surfaces. Nature Materials, 11, 530-535 (2012).
2. K. Terabe, T. Hasegawa, T. Nakayama, and M. Aono. Quantized conductance atomic switch. Nature, 433, 47-50 (2005).

Nanostructured materials exhibit dramatically enhanced energy storage properties as compared to their bulk counterparts due to the increased contribution of the surface in determining the energy storage kinetics and ion storage sites. Nanosheets are novel 2D materials with thicknesses of only a few atomic layers, rendering these materials essentially all surface. Currently, the most intensely studied 2D material is graphene, but recent efforts have found routes for synthesizing nanosheets of transition metal oxides including anatase TiO₂. Here, we describe the fundamental energy storage behavior of anatase nanosheets for lithium and sodium-ions, and compare the nanosheet morphology to anatase nanoparticles. In these studies we measured the electrochemical properties of thin films of the nanosheets directly in order to remove the influence of variables such as electrode additives and thickness in determining the energy storage properties.
The results show that the 2D nanosheet morphology has a profound influence on the potentials and the reaction kinetics associated with energy storage in anatase. Due to the large exposed surface of the nanosheets, the rate limiting step for ion storage is a surface-limited process and solid-state ion diffusion is no longer rate-limiting, even at the peak voltage. As compared to nanoparticles, the peak voltage for lithium insertion in the nanosheets occurs 0.4 V lower. The peak voltage separation is also affected by the change in morphology. At a cyclic voltammetry sweep rate of 1 mV s^-1, the peak voltage separation is decreased from 0.36 in the nanoparticles to 0.13 V for the nanosheets indicating the highly reversible nature of the redox reaction. In addition, at a sweep rate of 100 mV s^-1 the nanosheets retain approximately 70% of the capacity at 1 mV s^-1vs. 20% for the nanoparticles. Nanosheets possess several features that are advantageous for energy storage. The fact that the thickness is limited to a few atomic layers leads to high rate energy storage as all storage sites are located very close to or on the surface. Moreover, the openness of the structure enables charge storage to occur with larger ions such as sodium. The results of this fundamental study demonstrate that the nanosheet architecture allows for the tuning of energy storage properties beyond what is observed with other nanostructured morphologies.

Electrochemical oxidation/reduction reactions on solid electrolytes (like yttria-stabilized zirconia, YSZ) are among the most efficient methods to convert electricity into chemical fuels and vice versa. While the traditional ‘‘macroscopic&’&’ studies have generated insight, the reaction pathways remain speculative. The main open questions are what are the intermediate reaction steps, which adsorbed species are involved in the different steps, including the slowest (rate-limiting) step, and where do the different reactions occur, i.e., on the metal electrode or the solid-oxide electrolyte surface? Answering these questions provides the basic knowledge needed to develop more efficient electro-catalysts. We use spatially resolved photoelectron spectroscopy performed in operando to identify the reaction intermediates of the hydrogen electro-oxidation reaction on YSZ electrolytes with Pt electrodes. We find that hydroxyl on the zirconia electrolyte is a reaction intermediate in the hydrogen oxidation reaction and that it participates in the rate-determining step. The limiting step does not involve the transfer of charge. These results allow us to propose the detailed reaction pathway, which provides direct insight into how to accelerate the kinetics.

In this work, we present a modeling study
of triple phase boundary regions of
solid oxide fuel cells (SOFCs)
based on a density functional theory
approach. In particular, we consider the
following solid oxide electrolytes,
yttrium-doped barium zirconate (BZY) and
yttrium-doped barium cerate (BCY), and
the following metallic catalysts, palladium,
nickel, and copper. Thus, we use
density functional theory calculations
to construct the energy landscape for
a hydrogen species crossing triple phase
boundaries based on the materials above.
This study focuses, in particular, on the
role played by the metal-oxide interface
in controlling the proton transfer
from the catalyst to the electrolyte
component of triple phase boundaries.
Our results are discussed in light of the
hydrogen spilling process occurring at
triple phase boundaries based on nickel
and yttria-stabilized zirconia.

A fundamental understanding of H₂ and CO oxidation and the reverse reactions is crucial towards designing more efficient electrocatalysts. While in recent years we have seen the successful use of CeO₂-based materials in a wide range of solid oxide electrochemical devices, a microscopic picture of the electrochemical processes at the solid-gas interface still missing.
In this contribution, we will present our recent studies on the above-mentioned electrochemical reactions using synchrotron-based ambient pressure X-ray photoelectron spectroscopy and current-voltage measurements. We fabricated high purity doped ceria model electrode and exposed the cell to H₂-H₂O and CO-CO₂ environments at ~ 550 C. Using electrical polarization to drive the cell to non-equilibrium steady states, we were able to observe the evolution of surface adsorbates, oxygen ions, and electrons (at the first nm of the surface), as well as the surface dipole that influences the charge transfer process across the gas/solid interface. Based on our experimental findings, we relate thermodynamic driving forces with kinetic phenomena, enabling a quantitative picture of the surface dynamics and reaction pathways.

TBD

Hydrogen electro-oxidation kinetics at the Pt | CsH2PO4 interface have been evaluated. Thin films of nanocrystalline platinum 7.5 - 375 nm thick and 1 - 19 mm in diameter were sputtered atop polycrystalline discs of the proton-conducting electrolyte, CsH2PO4, by shadow-masking. The resulting Pt | CsH2PO4 | Pt symmetric cells were studied under uniform H2-H2O-Ar atmospheres at temperatures of 225 - 250 C using AC impedance spectroscopy. For thick platinum films (> 50 nm), electro-oxidation of hydrogen was found to be limited by diffusion of hydrogen through the film, whereas for thinner films, diffusion limitations are relaxed and interfacial effects become increasingly dominant. Extrapolation to vanishing film thickness implies an ultimate interfacial resistivity of 2.2 Omega;cm^2, likely reflecting a process at the Pt | H2(g) interface. Films 7.5 nm in thickness displayed a total electro-oxidation resistivity of 3.1 Omega;cm^2, approaching that of Pt-based composite anodes for solid acid fuel cells (1 - 2 Omega;cm^2). In contrast, the Pt utilization (electro-oxidation resistivity x Pt loading)^-1, 19 S mg^-1, significantly exceeds that of composite electrodes, indicating that the thin film approach is a promising route for achieving high performance in combination with low platinum loadings.

It is beginning to be realized that the space charge of electronic and ionic carriers at heterointerfaces can drastically modify the conducting properties of materials [1]. It may even affect the activity of electrochemical reactions that take place at interfaces. Theoretical understanding of the behavior of space charge at interfaces under various conditions is desired for taking advantage of this degree of freedom in materials design.
In a previous study, we examined the space charge at the metal/acceptor-doped zirconia interface by combining defect energetics calculated from first principles with a continuum Poisson-Boltzmann model [2]. We found that oxidizing atmosphere and high valence band offset result in negative space charge formation (oxygen vacancy depletion and interstitial accumulation), while reducing atmosphere and low valence band offset result in the opposite behavior. It was pointed out that this phenomenon can be understood in a similar manner to band alignment at metal/semiconductor Schottky junctions.
An issue that was not addressed in the abovementioned work is the validity of the continuum approximation: the calculated space charge width was of the order of few nanometers, which is not much larger than the lattice spacing of zirconia. Thus, to go beyond the continuum approximation, we employ a parallel-sheets model in this work. That is, we consider all ions fixed to planes of zero thickness corresponding to crystal layers parallel to the interface. Within each plane, a homogeneous distribution of ions is assumed (i.e., we don&’t consider discrete lattice sites). We solve for the electrostatic potential and defect concentration profiles under this constraint [3].
First, we performed calculations under the Mott-Schottky approximation (acceptor dopant profile is assumed to be flat) for {100} and {111} interface orientations of cubic zirconia. We found that the results resemble closely those obtained in the continuum model, even for the polar {111} orientation. This is surprising because the continuum model assumes a homogeneous system. We also examined the effect of acceptor dopant segregation on the space charge profiles. We found that the dopant segregation near the interface leads to a decrease in the depletion of vacancies in oxidizing atmosphere, and that it leads to an increase in the accumulation of vacancies in reducing atmosphere.
[1] J. Maier, Nature Mater. 4, 805 (2005).
[2] S. Kasamatsu et al., Solid State Ionics 183, 20 (2011).
[3] S. Kasamatsu et al., Solid State Ionics 226, 62 (2012).

Ionic conduction in micro-/nanoscaled thin films differs significantly compared to the properties found in the bulk phase. This can be attributed to the transport properties in interfaces and surfaces due to their modified structure and local composition. Several studies have been performed to determine the influence of interfaces to the transport properties, but boundaries transport between ionic materials is still less understood. So far, theoretical models are mainly based on the formation of space charge regions close to the interfaces. Recently, structural parameters like interfacial strain, misfit dislocations and less dense packed interface regions, get in the focus of interest. Moreover, space chare models are limited to (intrinsic) ionic conductors with only a small concentration of mobile defects.
This is a study on the thickness dependence of the strain states in multilayers, consisting of alternating layers of an extrinsic O2- ion conductor YSZ and of an insulating rare earth metal oxide (Y2O3, Gd2O3 Sc2O3 and Er2O3). Multilayers with narrow columnar crystallites and (semi-)coherent phase boundaries were grown by pulsed laser deposition (PLD). Depending on the mutual lattice mismatch between YSZ and the rare earth metal oxide we are able to adjust the strain originated from the phase boundaries in the multilayer.
A detailed strain analysis is performed by XRD. Distinct reflections are measured in and perpendicular to the interface planes. Because of the columnar texture of the multilayers, the interfacial strain within a layer decays by shear with increasing distance from an interface. The strained fractions are measured as a function of the layer thickness. The extent of the strained interface regions in the YSZ layers is estimated (~ 10 nm). The results are compared to former published experimental studies on O2- ion conductivity and diffusion in YSZ and backups the findings that tensile strain enhances and compressive strain decreases the interfacial transport compared to the bulk.

Solid oxide fuel cells (SOFCs) are regarded as an alternative source for cleaner and more efficient energy production. One of the grand SOFC design challenges is ensuring microstructural stability of the constituent phases at operating temperatures. Recent experimental findings suggest that SOFC anodes, consisting of Ni and yttria-stabilized zirconia (YSZ), undergo a series of morphological evolutions that tend to degrade cell performance. In particular, Ni phase coarsening, an interface driven phenomenon, leads to a total reduction in the density of triple phase boundary (TPB) lines. Furthermore, the re-distribution of Ni, electron-conducting phase, within the anode during coarsening can have a profound effect on the contiguity of Ni phase and the resulting electron transport paths in the anode.
In this study, we present a meso-scale phase-field model capable of capturing the coarsening behavior of Ni in multi-phase SOFC anodes in response to microstructural thermodynamic driving forces. The model accounts for the polycrystalline nature of the Ni phase along with the Ni interaction with the YSZ skeleton. In order to identify combinations of morphological parameters that lead to enhanced Ni phase stability, a systematic study of the effects of the Ni phase characteristic length scales on the coarsening rate was conducted. Several microstructural features, such as Ni particle size distribution, three-phase boundary lines and contiguity degree were monitored as SOFC anode systems evolved over time. Simulation results provide future avenues that can be utilized to design the next generation of stable SOFC microstructures. This work is supported by the Energy Frontier Research Center on Science Based Nano-Structure Design and Synthesis of Heterogeneous Functional Materials for Energy Systems funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (award DE-SC0001061).

Cation segregation on perovskite oxide surfaces affects cathode activity in solid oxide fuel cells (SOFCs). A unified theory that explains the physical origins of this phenomenon is needed for designing cathode materials with optimal surface chemistry. We quantitatively assessed the elastic and electrostatic interactions of the dopant with the surrounding lattice as key driving forces for the segregation on model perovskite compounds, LnMnO3 (Ln=La, Sm). Our approach combines surface chemical analysis with x-ray photoelectron and auger electron spectroscopy on model dense thin films, density functional theory (DFT) calculations and analytical models. To systematically induce elastic energy differences in the system, the radius of the selected dopant cations (Ca, Sr, Ba) is varied with respect to the host cation. Electrostatic energy differences are induced by controlling the oxygen chemical potential in experiments and the distribution of charged oxygen- and cation-vacancies in our models. Our results demonstrated that the largest size mismatch between the host and dopant cation, associated with the largest elastic energy in the system, showed the strongest tendency to surface segregation and secondary phase formation. Cation rearrangements near the surface were also strongly affected by the electrostatic interactions, distribution of charged defects near the surface. The additive effects from the elastic and electrostatic energies evaluated by analytical models are in agreement with the DFT-calculated segregation energy, confirming that both factors are important drivers of the cation enrichment on the perovskite surfaces. A model based on a database generated by our DFT calculations is constructed to quantitatively predict the enrichment behavior of dopants on the surface. Lastly, the diffusion kinetics of larger cation is found to be slower, thus can kinetically trap the segregation despite the larger elastic driving force to segregation. Our results can provide fundamental insights into tailoring the cathode surface compositions for high-performance SOFCs.

Ba0.5Sr0.5Co0.75Fe0.25O3-d (BSCF) shows the best oxygen exchange kinetics among mixed conducting perovskites (despite other drawbacks) and is a candidate for permeation membranes and solid oxide fuel cell (SOFC) cathodes [1]. As it is well established now, the two key factors, which control the oxygen reduction, are the high oxygen vacancy (Vo) concentration at the cathode surface and the high vacancy mobility.
In this talk, we discuss calculated from first principles the atomic and electronic structure of oxygen vacancies, their formation and migration energies in the bulk and in the surface layer, the defect-induced electronic density redistribution, and dependence of defect properties on the chemical composition of the BSCF (Fe/Co ratio) [2-4]. Additionally, the adsorption energies of an oxygen molecule and an O atom were obtained. Our calculations confirm that the O-vacancy formation and, in particular, migration energies in BSCF are considerably smaller than in similar LSM and LSCF perovskites [5,6] which explains its good performance. The gradual increase of these energies with an increase of the iron content is explained by analysis of the relevant density of the states.
We predict that in both (La,Sr)(Co,Fe)O3 (LSCF) and BSCF perovskites the dissociation of surface peroxide or superoxide ion occurs with assistance of VO, their encounter being the rate-determining step. The estimated reaction rate for this mechanism is significantly higher than in other perovskites, in good agreement with the experimental observations.
This work was partly supported by the GIF research project # 1-1025-5-10/2009 and National Science Foundation.
[1]. L.Wang et al, J.Electrochem. Soc., 157, B1802 (2010).
[2]. Yu.Mastrikov et al, Energy Env. Sci., 3, 1544 (2010).
[3]. R. Merkle, E.A. Kotomin et al, Sol. St. Ionics, 188, 1 (2011)
[4] R.Merkle et al, J Electrochem. Soc. 159, B 219 (2012).
[5]. E.A.Kotomin et al, Phys Chem Chem Phys 10, 4644 (2008).
[6]. Yu.Mastrikov et al, J.Phys.Chem. C 114, 3017 (2010).

Oxygen-ion conducting perovskiteoxides, with the general chemical formula of ABO₃, are candidates for electrodes in solid oxide electrochemical cells operating at elevated temperatures. One of the key properties is the catalytic activity of the oxygen-evolution reaction (OER) and the oxygen-reduction reaction (ORR). It has been shown that the bulk composition and electronic structure of the electrocatalysts have a significant impact on its electrochemical activity.^1,2 However, the surface electronic structure is not well known. Understanding the evolution of surface electronic structure under dynamic, non-equilibrium condition is the first step towards tailoring the electrochemical properties of perovskite catalysts.
In this work, we used surface-sensitive in operando X-ray techniques³ to investigate the electrochemical activity and the changes in the electronic structure of model thin film electrodes with the overall composition of (La,AE)TMO_3-δ (AE = alkaline earth, TM = transition metal). By combining X-Ray absorption and valence band photoelectron spectroscopy, the unoccupied and occupied states of the oxygen and transition metal bands were probed as a function of bias, revealing a complete picture of the dynamic band structure and its behavior during operation. As different chemical compositions of electrodes were investigated, the impact of the chemistry and the apparent surface segregation on electrochemical activity could also be elucidated and paired with the knowledge of the band structure. We will present a new model of the surface chemistry and the OER and ORR reaction pathways.
1. F. S. Baumann, J. Fleig, G. Cristiani, B. Stuhlhofer, H.U. Habermeier, J. Maier, J Electrochem. Soc. 152 (2007) B931-B941.
2. J. Suntivich, H. A. Gasteiger, N.Yabuuchi, H. Nakanishi, J. B. Goodenough, Y. Shao Horn, Science 334 (2011) 1383-1385.
3. D. F. Ogletree, H. Bluhm, E. D. Hebenstreit, M. Salmeron, Nucl. Ins. Phys. Res. Section A 601 (2009) 151-160.

LaxSr(1-x)MnO3 (LSMO) is widely used as a cathode material for solid oxide fuel cells. However, due to its inherent complexity, especially when used in real-world fuel cell devices, the electronic and chemical properties at the surface are still a subject of intense investigation. To gain more insight into the fundamental properties of these materials, it is helpful to study thin-film reference systems (e.g., deposited by pulsed-laser deposition on a SrTiO3 substrate) and their surfaces. Current research efforts, among others, focus on the migration of Sr and other cations to the surface (and possibly to buried interfaces as well). Measuring such migration processes is difficult because of the high operating temperatures of solid oxide fuel cells, suggesting that ex-situ measurements may not capture reversible migrations. Recent results using in-situ Scanning Tunneling Spectroscopy (STS) show a pressure- and temperature-dependent transition in the bandgap of these materials, in which the change from semiconducting to metallic behavior occurs at 200 °C or below in vacuum. This transition is largely reversible, but requires additional annealing in pO2 to completely return to starting conditions.
To determine the cause of this transition, we have measured a series of X-ray Photoelectron Spectroscopy (XPS) spectra using different excitation sources (Mg Kα and Al Kα) and angles (normal and 45°) to derive a non-destructive depth variation in the surface chemical and electronic structure. For this purpose, an LSMO thin film (x = 0.7) was annealed to 550 °C in 1 x 10-5 mbar pO2 to return the surface to an initial state equivalent to the STS measurements. XPS spectra were then measured at every 50 °C up to 300 °C in ultra-high vacuum, including a room temperature (23 °C) measurement both before and after the series. Additionally, valence band measurements using a monochromated Al Kα X-ray source are used to shed light on the bandgap changes as a function of temperature. As a result, we will present a full picture of the surface chemistry and electronic states relevant to the bandgap transition, including insights into the extent of surface segregation of Sr and other cations. Such in-situ results may help in the fundamental understanding of the surface conditions of thin-film model SOFC cathodes, especially when these methods will be expanded to higher temperatures to more closely mimic operating conditions.

Solid solutions with perovskite-type structure are used as cathodes in solid oxide fuel
cells at elevated temperature. During operation of the SOFC the electrodes may undergo severe chemical and microstructural changes which cause de-activation or activation - depending on the electrical load.
During the last years we constructed electrochemical cells for high temperature studies of electrodes with ESCA, ToF-SIMS and HRSEM. Model-type cells were prepared by pulsed laser deposition and microlithography, offering well defined three phase boundaries. In this lecture the results for different electrode systems (metal/YSZ, LSM/YSZ) will be summarized and first attempts towards the equivalent study of battery electrodes will also be presented.

The oxygen evolution (OER) and reduction reactions (ORR) are ubiquitous in many energy conversions. Of particular interest are reactions that take place over the solid/gas interface, for example, in elevated-temperature solid oxide fuel cells and electrolyzers operating at 500-800°C. Although OER and ORR generally dominate the overpotential in these electrochemical cells, an in-depth understanding of what controls reaction rate and material stability has not been achieved yet.
Combining in-situ and ex-situ spectroscopy and microscopy, we seek to better understand factors that control these chemical reactions at the surface of perovskites (with the general ABO_3-δ). We use an alkaline earth-doped lanthanum ferrite series as a model system, with Ba, Sr, and Ca as A-site dopants. Dense, thin film electrodes were grown by pulsed-laser deposition. The surface cation and oxygen concentrations were probed in-situ using ambient pressure x-ray photoelectron spectroscopy, and ex-situ using scanning Auger microscopy on quenched samples. Large deviation from bulk to surface concentrations was observed, the extent of which depends strongly on the dopant and cation nonstoichiometry. These spectroscopy and microscopy results were combined with current-voltage measurement to assess the active phase for the oxygen evolution reaction.

Developing novel cathode materials that has high oxygen reduction reaction (ORR) activity at intermediate temperature (<700 o C) is one key issue to achieve high performance Solid Oxide Fuel Cells (SOFC). The (La,Sr)CoO3-δ (LSC113) and (La,Sr)2CoO4+δ (LSCnot;214) heterostrucutre was reported to show orders of magnitude improvement in oxygen reduction kinetics at around 500 o C. While the interfaces are believed to be responsible for such high ORR activity, the underlying mechanism has not been clarified to date. The understanding of the role of the interface holds promise for directed research capable of attaining highly active cathodes for solid oxide fuel cells, as well as for other catalytic oxide systems.
In this study, we use a novel combination of in-situ scanning tunneling microscopy/spectroscopy and focused ion beam milling to probe the local electronic structure of LSC113/214 model multilayer super lattice at high temperature and oxygen environment. This information is directly and quantitatively tied to oxygen reduction activity near the interface. Our results show that while the LSC113 in the ML structure behaves similar to its single-phase counterpart at high temperatures (200-300 oC), the LSC214 is electronically activated through an interface coupling with LSC113. This is evidenced from the electronic structure of LSC214 that differs significantly from its single phase counterpart by exhibiting a large density of states near the Fermi level similar to that on LSC113. Such electronic activation, concurrent with the anisotropic oxygen incorporation kinetics on the LSC214, is expected to facilitate charge transfer to oxygen near the LSC113/214 interface, explaining the vastly accelerated ORR kinetics.
Our results put forward a new understanding of oxide hetero-interfaces at high temperatures and points towards electronically coupled oxide structures as novel cathodes. We further test the validity of this model on the LSC113/La2NiO4 hetero-system. La2NiO4 is another oxide with highly anisotropic oxygen interstitial incorporation kinetics, but limited by charge transfer in ORR, thus carries similar characteristics as LSC214. Importantly it is considered to be promising cathode material, and further activating its ORR kinetics promises an enabling route for high performance cathodes for intermediate temperature SOFC.

Lanthanum strontium manganite (LSM) has been studied extensively and developed as a cathode material for solid oxide fuel cells (SOFCs) owing to its high thermal and chemical stability, and high electro-catalytic activity for oxygen reduction at high temperatures. In the intermediate-temperature range (operated between 600 °C and 800°C, IT-SOFCs), LSM does not provide satisfactory performance due to the poor kinetics of the electrode reactions.
To improve the electrode performance for oxygen reduction reaction at lower temperature, we studied the copper-doped lanthanum strontium manganite system for cathode application. Compounds with the general formula La_0.8Sr_0.2Mn_1-xCu_xO_3-δ, 0le;xle;0.3) were prepared by EDTA combined citrate process and the effects of Cu ion at B-site were investigated about the change of structural and chemical state of B-site elements. In all compositions the single perovskite phase with rhombohedral structure was obtained at calcination temperature of 750°C. The compositions after the sintering process showed a decrease in the unit cell parameters with increasing Cu contents.
The maximum electrical conductivity at elevated temperatures was obtained at a composition of x=0.2 (over 200 S/cm at 750 °C), whereas the sample with x=0.3 showed the minimum value (100 S/cm at 750 °C). The cathode area specific resistance by impedance analysis decreased with increasing Cu contents. The enhanced performance with the addition of Cu can be explained by the additional Mn⁴⁺ promoting the formation of surface oxygen vacancies when Mn⁴⁺ is converted to Mn³⁺ at high temperature.
We analyzed the Mn L_2,3 and O K edge spectra by near edge x-ray absorption fine structure (NEXAFS) to investigate the detailed electronic structure. A shift of the Mn L_2,3 main peaks to higher energies with addition of Cu was observed, which indicates that Cu doping have an effect on the increase Mn⁴⁺ ions for LSM system. In the O K edge spectra, a pre-edge region (528 - 532 eV) corresponding to covalent mixing of the O 2p and Mn 3d unoccupied states decreased with increasing Cu contents. It can be explained by the presence of oxygen vacancies, which can affect electrode performance for oxygen reduction reaction. We concluded that copper doping at the B-site of LSM affected the formation of oxygen vacancies and the increase of Mn³⁺/Mn⁴⁺ couples, which can enhance the oxygen reduction reaction.

Due to high ionic conductivity and favorable oxygen electrocatalysis, doped Bi₂O₃ systems are promising candidates as solid oxide fuel cell cathode materials. Recently, several researchers reported reasonably low cathode polarization resistance of 0.3 - 0.4 Omega;cm² at 600 C by adding electronically conducting materials such as (La,Sr)MnO₃ (LSM) or Ag to doped Bi₂O₃ compositions [1,2]. Despite extensive research efforts toward maximizing cathode performance, however, the inherent catalytic activity and electrochemical reaction pathways of these promising materials remain largely unknown. This may be due, in part, to the morphological complexity of the electrode and of the electrode-electrolyte interface in typical composite structures.
Here, we prepare a symmetrical structure with identically sized Y_0.5Bi_1.5O₃/LSM composite electrodes on both sides of a YSZ electrolyte substrate. AC impedance spectroscopy (ACIS) measurements of electrochemical cells with varied cathode compositions reveal the important role of bismuth oxide phase for oxygen electrocatalysis. This, in combination with the fabrication of simplified, well-defined metal current collectors onto dense and smooth surfaces of Y_0.5Bi_1.5O₃ pellets via physical vapor deposition and micro-fabrication methods, enables identification of the reaction pathways and facilitates measurement of the site-specific electro-catalytic activity. The observations give guidance for optimizing SOFC cathode structures with doped Bi₂O₃ compositions.
[1] K. T. Lee, et al., J. Power Sources, 220, 324 (2012).
[2] C. Xia, et al., Appl. Phys. Lett., 82, 901 (2003).

In order to develop new catalysts for solar energy conversion to useful fuels and for energy consumptions in fuel cells we need to obtain a fundamental understanding of the molecular processes occurring at the solid-electrolyte interface. We have undertaken to develop in-situ spectroscopic methods to probe the interface during real electrocatalytic conditions in order to derive intermediates on the surface and the chemical state of the operating catalyst. I will present how various spectroscopic techniques can be used to address the hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and the corresponding oxygen reduction reaction (ORR) using a combination of hard and soft x-ray spectroscopies and ambient pressure x-ray photoelectron spectroscopy.

Water is a polar molecule with a strong response to electric fields, which gives rise to its high dielectric constant. It is expect therefore that near electrified interfaces the average orientation of the molecules will follow the direction of the electric field. Determining the degree of molecular orientation as a function of field is critical to understand electrochemical reactions in aqueous electrolytes.
We explored the orientation of the water molecules by measuring the oxygen XAS at the K-edge, which is sensitive to the degree of hydrogen bonding of the molecules. The XAS of liquid water presents a pre-edge peak around 535 eV, which is associated with dangling hydrogen bonds [2]. In the bulk of liquid water about 25% of the molecules have unsaturated (or dangling) H-bonds. Two more peaks are present in the XAS spectrum, at 537.6 eV and at 540.4 eV that are indicative of the disorder in oxygen sublattice [3]. We measured the dependence of the intensity of the pre-edge peak as a function of the strength and sign of the electric field in the Helmholtz layer on a graphene electrode in aqueous 0.1 mM NaCl solution. The graphene is mounted over a thin SiN membrane (~100 nm) transparent to the x-rays. Interfacial sensitivity is achieved by detecting the total electron yield (TEY) current collected in the same electrode. To separate the small TEY signal from the large Faradaic current we modulated the incoming x-ray beam with a mechanical chopper driven by a piezo-electric ceramic. The results show that at positive voltages the pre-edge peak is minimized, while at negative voltage the pre-peak increases. We interpret the result as indicative of an increased average orientation of the water dipole towards the surface under negative potential, and the opposite effect under positive potential.
References:
[1] P. Jiang, J.L. Chen , F. Borondics, P.A. Glans, M.W. West, C.L. Chang, M. Salmeron, J. Guo, “In situ soft X-ray absorption spectroscopy investigation of electrochemical corrosion of copper in aqueous NaHCO3 solution”, Electrochemistry Communications 12, pp. 820-822, 2010.
[2] L.A . Naslund, J. Luning, Y. Ufuktepe, H. Ogasawara, Ph. Wernet, U. Bergmann, L. G. M. Pettersson, and A. Nilsson, “X-ray Absorption Spectroscopy Measurements of Liquid Water”, J. Phys. Chem. B, vol. 109, 13835-13839, 2005.
[3] W. Chen, M. Sharma, R. Resta, G. Galli, and R. Car, “Role of dipolar Correlations in the infrared spectra of water and ice“,Phys. Rev. B 77, pp. 245114, 2008.

Photocatalytic water splitting using semiconductor materials, such as titanium dioxide (TiO2), provides a way to store solar energy in the form of chemical bonds, producing oxygen alongside a reduced fuel such as hydrogen [1]. The required solar-to-fuel efficiencies for economically viable devices have proven to be unattainable [2]. Understanding the surface chemistry involved in water splitting relies on a reliable atomistic description of the structure of the oxide-water interface. Fundamental insight into transition metal oxide photocatalyst surfaces could facilitate the design of more efficient systems.
In this study, periodic hybrid-exchange density functional theory calculations are used to predict the structure of water on the rutile TiO2(110) surface (with coverage less than or equal to 1 ML). A detailed model describing the water-water and water-surface interactions is developed by exploring thoroughly the adsorption energetics. The possible adsorption mode - molecular, dissociative or mixed - and the binding energy are studied as a function of coverage and arrangement, thus separation, of adsorbed species. These dependencies (coverage and arrangement) have a significant influence on the nature of the interactions involved in the TiO2-H2O system [3]. The importance of both direct intermolecular and surface-mediated interactions between surface species is emphasised.
[1] N. S. Lewis and D. G. Nocera, Proc. Natl. Acad. Sci. U.S.A, 2006, 103, 1572-15735.
[2] M. Li, M. K. H. Leung, D. Y. C. Leung and K. Sumathy, Renewable and Sustainable Energy Reviews, 2007, 11, 401-425.
[3] M. Patel, G. Mallia, L. Liborio, and N. M. Harrison, Phys. Rev. B, 2012, 86, 045302.

Oxides offer a low-cost, earth abundant alternative to noble metals for catalysis of the oxygen reduction and evolution reactions (ORR and OER) in fuel cells and electrolyzers.[1,2,3] The interaction of catalysts with water as a reactant, intermediate, or product plays a key role in both of these reactions.[4] Ambient pressure X-ray photoelectron spectroscopy (APXPS) provides a unique way to obtain qualitative and quantitative understanding of the surface species that form under different relative humidities.[5,6] We have investigated the evolution of surface species on LaCoO₃ epitaxial thin films at various pressures (p(H2O) 10^-6 Torr to 0.5 Torr) and temperatures (T = 25 ^#9675;C to 300 ^#9675;C), accessing a range of relative humidities. Deconvolution of the O 1s spectra, coupled with monitoring of the C 1s spectra, provides new insight into the wetting of perovskite oxides through the formation of hydroxyls and carbonates, as well as surface hydration. Features in the valence band can be attributed to the interaction of adsorbates with the oxide surface. We also observe a shift in binding energy of the water vapor peak relative to the Fermi level of the sample, directly related to a change in the work function[7] due to surface dipole effects induced by polar adsorbate bonds.[8] We will discuss the strength of interaction with different oxygen containing surface species and the role of these intermediates in ORR/OER catalysis.
References
[1] D. B. Meadowcroft. Nature 1970, 226, 847-848.
[2] J. Suntivich, H. A. Gasteiger, N. Yabuuchi, H. Nakanishi, J. B. Goodenough, Y. Shao-Horn. Nature Chem. 3, 546 (2011).
[3] J. Suntivich, H. A. Gasteiger, J. B. Goodenough, Y. Shao-Horn. Science, 334, 1383 (2011).
[4] J. B. Goodenough, B. L. Cushing. Handbook of Fuel Cells - Fundamentals, Technology and Applications. Vol. 2, 520-533 (eds W. Vielstich, h. A. Gasteiger, H. Yokokawa). Wiley, 2003.
[5] H. Bluhm. Journal of Electron Spectroscopy and Related Phenomena 2010, 177, 71-84.
[6] S. Yamamoto, T. Kendelewicz, J. T. Newberg, G. Ketteler, D. E. Starr, E. R. Mysak, K. J. Andersson, H. Ogasawara, H. Bluhm, M. Salmeron, G. E. Brown Jr., A. Nilsson. Journal of Physical Chemistry C 2010, 114, 2256-2266.
[7] H. Bluhm, M. Havecker, A. Knop-Gericke, E. Kleimenov, R. Schlogl. Journal of Physical Chemistry B 2004, 108, 14340-14347.
[8] K. Wandelt. Surface Science Reports 1982, 2, 1-121.

To expand our knowledge of electrochemical systems at the atomic level, we seek to understand several physical phenomena associated with the electric double layer with molecular dynamics simulations. Simulations provide a detailed picture of how real physical quantities, such as charge mobility and capacitance, can be translated from atomic data. This capability is useful for discerning the specific effect of introducing different solvents, ions, and substrates to the system. In our simulations, we begin with a salt-water electrolyte system near a structureless wall, and we gradually add more complexities. With water as solvent, the structure of the molecule yields a complex staggered packing arrangement in the electric double layer that is not be predicted by Poisson-Boltzmann theory. Interestingly for certain surface potentials, charge inversion is observed in the double layer, and we will discuss how other complex molecular solvents modify those observations. We will also show how different ions and substrate lattices perturb the packing arrangement, which in turn greatly affects the solvent polarization (i.e. the dielectric medium) and the electric field and electric potential behaviors. These cases are all studied under varied surface charge loading conditions, which reveal trends associated with charging and discharging. Moreover, in understanding all these effects in conjunction, we discern the capacitance dependence as a function of the basic components of the system.
Funding for this effort was provided by the Laboratory Directed Research and Development (LDRD) program at Sandia National Laboratories, a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy&’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

Over the last decade, electrochemical double-layer capacitors (EDLCs, often called supercapacitors) have emerged as attractive devices for electrical energy storage because of their high power density (800 - 1200 W kg-1) and extremely long cycle life (> 106). Balancing an optimized energy density with maintaining a very high power handling ability and a very long lifetime requires a detailed and fundamental understanding of the mechanisms of electrochemical energy storage. This includes factors that limit capacitance, rate handling, and chemical/mechanical stability which are beyond the scope of classical electrochemical measurements. It was found recently, that significant macroscopic expansion and contraction were measured in EDLCs during the charge and discharge caused by ion insertion into pores in the electrode material. Based on this finding, we employ in situ atomic force microscopy (AFM) to investigate the electrochemical expansion of thin film EDLC electrodes. AFM measurements provide unmatched resolution in z-direction of roughly 10&’s to 100&’s of picometers in static AFM mode and lateral resolution of typically around 20-30 nm. This allows for measurements with high spatial resolution and offer the possibility of studying the electrochemical expansion of EDLC electrodes on the order of individual structural elements, such as grains or particles. The investigation and understanding of sample expansion and contraction with regard to device performance and failure is especially important as we move to more complex device designs (e.g. 3-D) and high voltage ionic liquids. It also allows exploring the rate dependence of the strain response, hence decoupling it from electrochemical processes. With the unique combination of electrochemical information (e.g., capacitance, rate handling) and the expansion behavior (including spatial variations thereof), it is possible to provide a much more fundamental insight into structure-function relationships compared to conventional EDLC electrode testing, which can lead to improved understanding of charge/discharge processes and improved EDLC design strategies.
Here, we investigate Carbide Derived Carbon (CDC) supercapacitor electrodes by in situ AFM methods. The CDC films are placed in an in situ AFM electrochemical cell and cycled during AFM topographical measurements using a room temperature ionic liquid. The kinetic volume changes that occur as a result of cycling at different rates allow us to differentiate between processes at the solid-liquid interface and ion insertion processes. Additionally, ion size effects on macroscopic performance will be presented to reveal the origin of pore size dependent electrochemical performance.

Solid oxide fuel cells (SOFC) are one of integral components of current and future electrochemical conversion energy technologies. The energy conversion in these systems is underpinned by ion and vacancy diffusion, electronic transport and solid-gas reactions at surfaces and triple phase junctions. One of the critical elements of SOFCs is the kinetics of the oxygen reduction reaction (ORR). However, the exact mechanisms of OER/ORR remain elusive, largely due to the lack of experimental techniques capable of probing ORR on the nanoscale. In fact, by understanding the elementary mechanisms of ORR can we bridge the gap between experiments and advanced computational models, paving the way for rational design and optimization of SOFCs.
The application of a new scanning probe microscopy technique called electrochemical strain microscopy (ESM) can now relate local surface displacement to electrochemical activity at a resolution below 10 nm and provide unique insight ORR in ionic materials such as Yttria-Stabilized Zirconia (YSZ) and doped Cerium Dioxide (doped-Ceria).
In this talk we present a continuum modeling framework used to study ESM on the nanoscale [1] and we show how it applies to YSZ and doped-Ceria. In particular, we discuss the physical-chemical approach and the relative coupling of three processes that directly affect the strain response:
1. Self-consistent electro-migration, described by Poisson Nernst-Planck Equations
2. Elastic response of the ionic material
3. Electrokinetics of ORR
The framework effectively decouples electrochemical response and strain and it constitutes a first step towards quantitative ESM probing. In addition, it elucidates the local the coupling strain/transport properties and strain/double layer charging. Extensions of the approach will also be discussed to include non-linear detection of harmonics and quantum corrections.
FC acknowledges support funding from the Hong Kong University of Science and Technology. The research of AK, SVK and SJ was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.
Reference:
[1] A. Kumar, F. Ciucci, A.N. Morozovska, S.V. Kalinin & S. Jesse. Nature Chemistry 3, 707-713 (2011)

Chalcogenide materials represent an important class of materials, which are crucial for practical applications as optical fibers or waveguides, active materials in memory storage, solid electrolytes for solid state batteries, chemical sensors for ecotoxic ions in aqueous media. As a result, the preparation, characterization, and use of bulk chalcogenide materials have been investigated in details. In contrast, the study and investigation of nanochalcogenides such as nanoporous chalcogenide glasses have received only little attention. Obtaining in a controlled way such materials, which exhibit a large surface area from ~10 to 500 m2/g made up of highly polarizable atoms, is a very interesting challenge as it may lead to breakthroughs in various fields in which applications rely on the surface properties of host materials [1,2]. Ionic Liquids (ILs) represent promising potential candidates as structuring agents in view to optimize and customize the internal pore morphology and surface chemistry of the final chalcogenide framework[3,4].
In the present work, a computational approach has been set up in order to obtain structural insights into ionic liquids (ILs) confined in between amorphous nanochalcogenide surfaces (nanopore). By ab-initio Car-Parrinello Molecular Dynamics (CPMD) simulations, representative models of a-GeS2 surfaces have been obtained and compared with an amorphous GeS2 bulk model. After the insertion and equilibration, by classical MD simulations, of different amount of ILs molecules in-between two a-GeS2 surfaces, the structural and dynamical features of the internal ILs layer have been analyzed.
The present work represents, for our knowledge, the first computational study of ILs-Nanochalcogenide hybrid systems and opens the door to the complete understanding and optimization of the real application potentialities of these hybrid systems as promising catalysts or components in Li/Na-ions batteries, etc.
References
[1] S. Bag, P. N. Trikalitis, P. J. Chupas, G. S. Armatas, M. G. Kanatzidis, Science, 2007, 317, 490.
[2] G. S. Armatas, M. G. Kanatzidis, Nature Mater., 2009, 8, 217.
[3] S. Murugesan, P. Kearns, K. J. Stevenson, Langmuir, 2012, 28, 5513.
[4] Q. Zhang, I. Chung, J. I. Jang. J. B. Ketterson, M. G. Kanatzidis, J. Am. Chem. Soc., 2009, 131, 9896.

Graphene is the best electrode material to characterize the electrolytic double layer mechanisms because it is an approximately ideally hydrophobic interface and is not complicated by the specific adsorption of water or anions characteristic of metals. Characterization of graphene&’s capacitance in > 10 different aqueous electrolyte compositions results in several mechanistic behaviors contrary to Gouy-Chapman-ish theory, which is well-known for failing to quantitatively describe interfacial capacitance in the relevant conditions of high electrolyte concentration or high potential bias. The experimental interfacial capacitance of graphene in aqueous electrolytes is instead mechanistically and quantitatively consistent with the solvation of electrons within the aqueous interface. The thermodynamics of electron solvation mechanisms in the aqueous bulk phase are well-established experimentally and density functional theory (DFT) simulations can now accurately replicate experimental behavior. The remarkable affinity of solvated electrons for the aqueous-hydrophobic interface has been characterized through DFT. The thermodynamics of electron solvation at the aqueous interface has been adapted here to interfacial capacitances and accurately corresponds with the values and behaviors determined experimentally on graphene. The solvation of interfacial electrons causes a dielectric relaxation through a water dissociation step, which is a process slow enough to affect capacitance values when EDLCs are (dis)charged faster than 10 - 0.1 Hz. The aqueous solvent structure making/breaking properties of ions cause either dielectric enhancement or decrement at power densities relevant to aqueous EDLCs through the local ordering of water dipoles.

Based on first-principles density-functional theory, we conduct a theoretical study on the structural, electronic and electrochemical properties of cyclopentene-transition metal (CpTM, with TM = Fe, Co, Cr, V, Ni) complexes adsorbed on pristine and B-doped SWCNTs and graphenes, which may serve as new catalysts as well as next-generation electrochemical sensors. Significant increases of the binding energies are predicted on the B-doped SWCNTs and graphenes, surpassing even the adsorption of the isolated metals atoms (increased by about 2eV). Relevant to the well-studied electrochemical donor-acceptor ferrocene, new CpFe/SWCNT or graphene-based electrochemical sensors may benefit from the strong stabilization on pristine or doped nanocarbons as well as the enhanced sensing abilities attainable by doping. Therefore, the redox potentials of these complexes in acetonitrile (MeCN) are calculated to evaluate potential applications in electrochemical sensing. In addition, the electronic structures of CpTM (M= Fe, Co, Cr, V, Ni) ligands on SWCNTs and graphenes are reported to shed light on the mechanisms of enhanced binding between CpTM ligands and nanocarbon supports. Moreover, the reaction between CpTM/SWCNTs and oxygen exhibits a dissociative adsorption, which we have studied using ab-initio molecular dynamics (AIMD).

Alternative clean energy sources have risen as a key area which could overcome the increasingly dire environmental problems and counteract the limited supply of energy from fossil fuel conversions. Solar energy is a particular field of study which has promise to be completely sustainable and is essentially a limitless source of power. Among many materials, p-type Cu2O has attracted attention for solar and photo-electrochemical cell (PEC) applications due to its direct band gap at around 2 eV and its high absorption coefficient, combined with material abundance, non-toxicity and low cost of fabrication. The main limiting factor in the use of Cu2O as a photocathode for water reduction is its poor stability in aqueous solutions, because the redox potentials for the reduction and oxidation of monovalent copper oxide lie within the bandgap. Electrodeposition of Cu2O thin films has been attracting attention because its many advantages such as cost-effectiveness, rapid deposition rate, and ease of controlling their microstructure and crystallinity by adjusting electrodeposition parameters. There have been many studies of PEC applications using nanostructured Cu2O in formations such as nanowires and nanotubes arrays for high efficiency, as well as passivation with TiO2 and ZnO for increased stability. However, there has been no systematic study on the effect of crystal orientation of Cu2O on the properties of PEC. In this study, the polarity of Cu2O films was controlled by electrochemical conditions. Cu2O grains in the film became smaller when deposited at more negative potentials, which is attributed to the fact that frequencies of nucleation of Cu2O crystallites during the deposition tends to be higher when the applied potentials become more negative. The polar terminated Cu2O films show higher photocurrent than non-polar ones due to charge separation. Carrier concentrations and band structures have been correlated to PEC performance.

Silicon (Si) is the most promising candidate for the anode materials in lithium ion batteries due to its high theoretical specific capacity. However, volume expansion up to as much as 400% during the reaction with Li caused particle pulverization and fracture, resulting in rapid capacity fading. In this work, we propose a facile method to synthesis a novel Si membrane structure with good mechanical strength and three-dimensional configuration that is capable of accommodating large volume changes associated with lithiation in batteries applications. In specific, the cycliability and rate capability are promoted based on the merits of this membrane nanoarchitecture; pre-defined interior spaces within the capped hexagonal nanowalls as well as the exterior spaces between them can effectively accommodate the reversible volume change. In addition, the underline layer does not only interconnect the current collectors but also clamp the end of every hexagonal nanowall so that it ensures robust electrical and mechanical connection. We achieved a high initial discharge capacity of 3684 mAh g-1 with first coulombic efficiency of above 86%. Over 81% capacity was preserved after 100 cycles, and superior capability is demonstrated.

The sluggish oxygen reduction reaction (ORR) has been one of the most important problems in fuel cell. Many researchers have studied Pt-based alloy (Pt-M, M = Co, Ni, Fe) catalysts since the alloyed transition metal could make the d-band center of Pt lowered by the electronic and strain effects, which resulted a decreased binding energy between Pt and O species on the catalyst surfaces. However, the development of non-precious catalysts has been required since the price of Pt is too much high in the fuel cell applications. In addition, the hydrogen production by water splitting has been important for the fuel cell operation. However, the oxygen evolution reaction (OER) is the key factor in water splitting involving the hydrogen evolution reaction (HER) because the multiple electron transfer is demanded as same as in the ORR. In these regards, non-precious Co-based catalysts such as CoxOy (cobalt oxide) and Co-Pi (cobalt-phosphate complex) have been recently developed for the ORR and OER catalysts, respectively. Additionally, MnxOy (Manganese oxide) was studied as the bi-functional catalyst for both the ORR and OER.
Herein, we propose Co-Ac (A = P, B, N, S) nanoparticles for the ORR and OER catalysts. Synthesized catalysts were applied to the ORR and OER in alkaline medium. The electrochemical and physical properties of the catalysts were evaluated, and the fundamental reasons for the high activities were studied by investigating the electronic structures of the nanoparticles. The crystalline structure of Co could be changed by incorporation of P, B, N, and S. The incorporated P, B, N, and S interacted with the electronic structure of Co atom, and the active sites of the developed Co-based catalysts were increased compared to the common Co nanoparticles. Finally, the relation between the catalytic activities and structures was elucidated.

In state of the art Solid Oxide Fuel Cells (SOFC) a Ce0.8Gd0.2O2-δ (CGO) barrier layer between the La0.58Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode and the Zr0.85Y0.15O1.925 (YSZ) electrolyte prevents diffusion of Sr from the cathode to the electrolyte, and thus the fast formation of a blocking SrZrO3 layer on the electrolyte. For stationary applications of a SOFC system lifetimes up to 10 years are required. To date there is no long term data on the formation of the SrZrO3 layer and on the thereby provoked slow degradation in this kind of cells. The formation rate is controlled by grain boundary diffusion of Sr in CGO, because generally the grain boundary diffusion is much faster than the bulk diffusion. There is only spare literature data available for a temperature of 1200 °C. Thus, detailed data on Sr grain boundary diffusion in CGO is required, especially for lower temperatures relevant for future SOFC operation.
In this experimental study CGO is deposited onto YSZ single-crystals as well as on polycrystalline YSZ substrates by magnetron sputtering and electron beam evaporation. Different crystalline orientations and texturings of the CGO layer are prepared by using different deposition techniques or changing the deposition parameters. As a Sr source the CGO surface is covered with Sr(NO3)2 by application of a aqueous solution and subsequent desiccation. After annealing in air at different temperatures and times the Sr diffusion profiles are determined by ToF-SIMS analysis. First results for grain boundary diffusion coefficient Dgb and for the activation energy Ea,gb of Sr in CGO grain boundaries are presented.
From the diffusion data the amount of SrO transported through the CGO layer is estimated. With a suitable model for the contribution of a blocking SrZrO3 film to the total resistance of the YSZ and CGO electrolyte layer a prediction of the critical SrZrO3 covering of the CGO/YSZ interface will be made. Aim is the estimation of best- and worst-case scenarios for the lifetime of a SOFC system with CGO barrier layer regarding to Sr diffusion.
CGO: Ce0.8Gd0.2O2-δ; LSCF: La0.58Sr0.4Co0.2Fe0.8O3-δ; YSZ: Zr0.85Y0.15O1.925; ToF-SIMS: Time of Flight Secondary Ion Mass Spectroscopy

The research on Li-ion-batteries (LIBs) focuses on the prediction of lifetime. Many efforts have been made on the investigation of the dominating degradation phenomena in LIBs. These include: mathematical modeling[1] and material-research[2], both supported by practical studies of the calendaric and cyclic aging in real and laboratory test conditions[3].
We report a detailed literature review of numerous experimental datasets on cyclic and calendaric aging of different LIBs. It reveals a linear correlation between the capacity-based state-of-health (SOH-Q) and the impedance-based state-of-health (SOH-R) over storage or cycling time which has already been communicated for particular degradation studies[4]. The influence of external parameters such as cell chemistry, rate dependent capacity, aging procedure, temperature and particle-dimensions of the active materials has been analyzed to identify a correlation between the fade of capacity and rise of impedance. From these findings it was possible to postulate a degradation-model for state of the art LIBs. The temporal change of SOH-R and SOH-Q is characterized by a square root dependency. This effect can be attributed to an irreversible reaction of the electrolyte leading to the growth of a surface layer on the electrodes. The limiting process is the diffusion of the organic solvent through the surface layer to the electrode interface[1]. The thickness of the passivation layer is directly related to SOH-R whereas the volume of the formed layer is proportional to the loss of active material and therefore correlates with SOH-Q. It is derived that the identified correlation is in accordance with the developed model. Own aging experiments on high-voltage LiMn0.5Ni1.5O4-cathodes show the same square-root-dependency of SOH-Q with cycling-time and a linear correlation with SOH-R. This shows that degradation of next-generation high-voltage cathodes can be described by the same model.
[1] Sankarasubramanian, S.; Krishnamurthy, B., Electrochim. Acta 2012, 70 (0), 248-254.
[2] Dubarry, M.; Liaw, B. Y.; J. Pow. Sourc. 2011, 196 (7), 3420-3425.
[3] Belt, J.; Bloom, I.; J. Pow. Sourc. 2011, 196 (23), 10213-10221.
[4] Braatz, P. O.; Lim, K. C.; Electrochmical Society Proceedings 1998, 97-18, 479-487.

Solid electrolyte interphase (SEI) is an in-situ formed electronic insulating but ionic conducting thin coating on lithium ion battery (LIB) electrodes. It is widely accepted that the physical and chemical properties of the SEI film have significant impacts on the electrochemical performances of Li-ion batteries. Especially, the mechanical properties of SEI largely defines the cycling performance and the safety of LIBs. Many techniques including optical spectroscopy, electron microscopy, X-ray diffractometry and thermo-analysis, have been used for analyzing the composition and microstructure of SEI films. Great efforts have been paid to modify the mechanical properties of SEI films by adding additives in electrolyte and/or modifying electrode surfaces, aiming at the formation of elastic and flexible SEI films to accommodate large volume variation during charging/discharging cycles. This is especially important for high capacity alloy or conversion reaction type anode materials in order to achieve excellent cycling performance and high Coulombic efficiency. However, the mechanical properties of SEI films have been rarely investigated.
In this work, we investigate the SEI film on MnO and graphite anodes using AFM imaging and force spectroscopy. Inhomogeneity of SEI film in both morphology and mechanical properties is quantitatively identified for the first time. Single-layered and double-layered SEI films with similar Young&’s modulus distribution coexist on the surface of discharged electrodes. This result provides new insights about previously widely accepted double-layer SEI model. The effects of additives, LiBOB and VC, on the structure and properties of the SEI on MnO anode was also investigated.
The methodology established in this study is generally applicable to the investigation of SEI in lithium ion battery systems. Combining both mechanical indentation and spatial mapping capabilities at the nanometer scale, AFM imaging and spectroscopy techniques are uniquely suited to evaluate the effect of different solvents, salts and additives in the electrolyte on the properties of the SEI film on various electrode materials, as well as the mechanical properties of active electrode materials and binders during electrochemical charging and discharging. This methodology paves an important initial step for rational design of SEI films with desired mechanical properties.
Reference:
Jie Zhang, Rui Wang, Xiaocheng Yang, Wei Lu, Xiaodong Wu, Xiaoping Wang, Hong Li and Liwei Chen “Direct Observation of Inhomogeneous Solid Electrolyte Interphase on MnO Anode with Atomic Force Microscopy and Spectroscopy” Nano Lett., 12, 2153-2157 (2012)

Silicon(Si) particles as an anode material offer an order of higher capacity than that of graphite, which is commercially used in Li-ion batteries. However, it has a limitation in practical usage because of its poor cycling performance. The primary problem of Si anode is due to the dramatic volume expansion and contraction during the Li alloying-dealloying processes, resulting in rapid anode degradation. Several studies have reported that employing polymeric binders plays an important role on anode stability. Polyvinylidene fluoride(PVdF) has been widely used as a polymeric binder, but the role as a binder was not as effective as initially expected. Stiff polymers such as carboxymethyl cellulose (CMC) exhibited improved binding performance. In practice, carboxymethylcellulose (CMC), which is highly brittle and stiff polymer, is widely used for Si anode research. As a binder, the CMC is expected to form hydrogen bonds between carboxyl groups and surface oxide. In this study, we synthesized a new polymer, alginate-catechol (Alg-C) for effective binding performance. Alginate is a polymer that contains more carboxyl groups than that of CMC. Furthermore, catechol is a well-known adhesive chemical moiety found in the adhesive proteins of marine mussels.(1-3) Catechol-conjugated polymers have shown excellent wet-resistant adhesion.(4, 5) Thus, we hypothesized that the catechol-conjugated polymer might show better adhesion, which can be characterized by force mode operation of atomic force microscopy (AFM). Single-molecule adhesion force of a variety of polymeric binders used in Li-ion batteries will be presented.

1. H. Lee, S. M. Dellatore, W. M. Miller, P. B. Messersmith, Science 318, 426 (2007).
2. H. Lee, Nature 465, 298 (2010).
3. S. Hong et al., Adv Funct Mater., in press (2012).
4. I. You, S. M. Kang, Y. Byun, H. Lee, Bioconjugate Chemistry 22, 1264 (2011).
5. J. H. Ryu et al., Biomacromolecules 12, 2653 (2011).

Computational modeling of electrochemical interfaces offers the possibility to develop an enhanced scientific understanding of the complex processes taking place at electrode/electrolyte systems, as well as a capability to design engineered energy storage devices. Molecular simulation in particular can illuminate key aspects of the interfacial dynamics, such as ion packing, effects of nano-patterned surfaces, and the effects of different solvents. An important requirement for these calculations is the ability to accurately account for complex electric fields imposed by external biases and their interactions with ions and polar molecules. This work describes a methodology to model the electric potential in atomistic simulations of electrochemical interfaces.
Underlying the computational approach is an atomistic-to-continuum framework in which atomic quantities are coarse-grained to create a continuous field. When combined with molecular dynamics calculations, atomic charges are restricted to a finite element mesh, creating a charge density field. A coarse approximation to the true electric potential can be efficiently solved for on this mesh using the Poisson equation. This method can be thought of as a generalization of the Particle-Particle/Particle-Mesh (PPPM) method to a general basis, while possessing two key advantages over the PPPM formulation. First, the use of a finite element basis enables complex geometries to be modeled. Second, it has the ability to prescribe boundary conditions representative of operating conditions. This talk will describe appropriate boundary conditions for conducting and insulating surfaces that can be used to simulate solid/fluid interactions. The boundary conditions have specific forms to correctly capture the long-range behavior on the finite element mesh, while also adding in appropriate charge densities to obtain the correct short-range physics. Free boundary conditions will also be presented to account for the presence of a far-field bulk solution without the expense of representing it directly in the simulation. The final aspect of this talk will focus on error analysis and efficient coarse-graining of molecular electrical properties. Several representative calculations will be provided to evaluate the method&’s performance in canonical configurations.
Funding for this effort was provided by the Laboratory Directed Research and Development (LDRD) program at Sandia National Laboratories, a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy&’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

A self-terminating rapid electrodeposition process for controlled growth of Pt monolayer films from a K2PtCl4-NaCl electrolyte has been identified and developed that is tantamount to wet atomic layer deposition (ALD). Despite the deposition overpotential being in excess of -1 V, Pt deposition is quenched at potentials just negative of proton reduction by an alteration of the double layer structure induced by a saturated surface coverage of underpotential deposited hydrogen, (Hupd). The surface is reactivated for Pt deposition by stepping the potential to more positive values where Hupd is oxidized and fresh sites for adsorption of PtCl42- become available. Periodic pulsing of the potential enables sequential deposition of two dimensional (2-D) Pt layers to fabricate films of desired thickness relevant to a range of advanced technologies.

Solar fuel generation by direct photoelectrolysis of water provides a possible solution for the energy storage and transportation needs of a sustainable energy economy. Sufficient photoelectrochemical water splitting is directly related to challenging materials science. Beyond photovoltaic performance, chemical stability in contact to an electrolyte, alignment of the band edge potentials, and sufficient voltage are essential for photoelectrodes. Tandem absorber structures overcome the undesirable efficiency trade-off between too high (less absorption) and too low (insufficient voltage) band gaps. Epitaxial InGaP/GaAs photoelectrodes enabled world record solar to hydrogen conversion efficiencies of up to 12.4%, but are still susceptible to destructive photocorrosion. In contrast, lattice matched III-V integration on Si enabled the growth dilute nitride GaPN structures, which showed both unbiased water splitting and significantly improved stability. So far, demonstrated photoelectrochemical energy conversion efficiencies have not exceeded values as low as 1%, most probably due to limited optoelectronic performance of the heteroepitaxial dilute nitride GaPN structures. Material quality and defect density are affected by both the polar on non-polar transition at the crucial GaP/Si interface and the difficulties of dilute nitrogen incorporation. Recent progress in Si substrate preparation in metal-organic vapor phase epitaxy ambient, in GaP nucleation procedures, and in the in situ control of anti-phase disorder promise better epitaxial templates for dilute nitride GaPN integration on Si substrates. Higher nitrogen precursor purity, reduced impurity incorporation, and in situ observation during dilute nitride growth represent pathways to improved material quality, eventually enabling more efficient hydrogen generation with GaPN/Si heterostructures.

Fullerene-like hosts have promising potential as proton conducting materials and yet it has been the subject of only a few fundamental investigations so far. Proton transfer between two fullerene molecules, H+(C60)2, with and without the presence of water was explored using a Density Functional Theory (DFT) approach.
The energy barrier for the proton transfer between fragments of C60 molecules was investigated by previous authors. For instance, K. Tasaki (J. Electrochem Soc. 2006, 153, A941) used the PM3 semiempirical method for a preliminary study of proton transfer between two fullerenes. However the absence of quantitatively reliable high level calculations has hindered rigorous discussion of the proton conductivity of fullerenes.
In our analysis, we adopt the high symmetry, H+(C60)2 molecular structure. The lowest energy configuration has the proton attached to a carbon atom of one of the C60 molecule at the top position. This ground state was characterized by all positive frequencies. Two states with the proton attached to a carbon atom of one fullerene and the adjacent atom of the other C60 regarded as a reactant and product of the proton transfer reaction. The transition state (TS) structure has a proton displaced exactly in the midpoint between the two C60 molecules. This TS structure possesses C2v symmetry. The gas-phase reference barrier is computed using a hierarchy of model chemistries using various density functionals and basis set combinations. For comparison, the microsolvation effect and bulk dielectric effect on the activation energy is evaluated using explicit spectator H2O molecules and a Poisson-Boltzman continuum solvation model.

The development of aqueous electrolytes beyond 5 M KOH can improve both energy and power densities of an electrolytic double layer capacitor (EDLC) by a factor of 3 over the conventional electrolyte for graphene-based aerogels. The optimization of aqueous electrolytes involves a systematic, experimental evaluation of electrolyte properties and effects beyond just conductivity and solution resistances. Understanding the mechanisms of electrolyte or carbon breakdown at the voltage stability limits leads to an increase in the voltage window to 2 V and failure prevention when cycling in the practical conditions of incomplete discharge. The ability to affect capacitance through the distance between the electrolyte ion and electrode surface by managing the ion&’s radius or primary hydration shell strength will be discussed. The electrolyte ions also have aqueous solvent structure making and breaking properties. The results indicate that the high power densities of fast electrode architectures can have a greater dependence on an effective dielectric decrement or enhancement caused by the ion&’s solvent structure than the dependence on electrolyte conductivity.

Efficient catalysis of the oxygen reduction reaction (ORR) is of utmost importance for widespread commercialization of polymer electrolyte membrane fuel cells (PEM FCs). 3M&’s nanostructured thin film (NSTF) type ORR catalyst layers have attracted considerable attention over the past decade. These layers exhibit an improved Pt mass activity and specific power, yielding an overall reduction in catalyst material costs. Despite these improvements, current catalyst layers are still not able to meet the demanding requirements of automotive applications. The research presented in this talk focuses on novel ordered porous NSTF type catalyst layers. These ordered porous NSTFs are fabricated using a modular sacrificial template. Templates of spherical colloids are assembled into close-packed lattices and the spaces between these spherical templates filled with another material (e.g., platinum). Selective removal of the template creates a porous material containing an ordered array of spherical pores. This method provides control over pore size, catalyst layer thickness, and NSTF composition. Tuning these parameters will enable important insight into further optimization of the catalyst layers, as well as provide a framework for an in-depth evaluation of processes governing ORR electrocatalysis in porous catalyst layers relevant to PEM FCs. Ordered porous NSTFs of platinum or gold supported Pt nanoparticles with varying thickness have been reproducibly fabricated over relatively large areas. This talk will discuss the characterization of these materials, including the surface area enhancement and ORR activity of these catalyst layers.

Lithium-ion batteries have been widely used for portable electronic devices and shown great potential in clean energy (e.g. hybrid vehicles) for it superior energy density and prolonged lifetime. However, with the accumulation of charge-discharge cycles, its performance may gradually deviate from the theoretical prediction, which is related to surface reactions occurring on the anodes and cathodes. The formation of surface films (solid electrolyte interface / SEI) on electrodes in contact with the non-aqueous electrolytes in lithium-ion batteries, thus, is of significant influence on battery performance. In order for an in-depth understanding of the formation mechanism of the films, we investigate SEI formation on Au film using in-situ ATR-IR technique. In present study, we not only find the pronounced traditional component of SEI, but also probe some other soluble products that could never been found with DMC washing. These in-situ spectrum results shed light on some unknown procedures related to the formation of the films, which might be detrimental on battery performance in one way or another.

Lithium-air(O2) battery is attracting a great deal of attention because it can archive significantly higher energy density than that for conventional lithium ion batteries. However, Li-O2 batteries using conventional liquid electrolytes suffer from irreversible side-reactions caused by the reduction product of oxygen, superoxide anion radical. Even with organic electrolytes stable to superoxide anion radical, such as acetonitrile, their volatility and cathodic stability still remain problems for battery operation in open-air. To address these issues, we used a solvate ionic liquid, glyme-Li salt complexes, as electrolyte. Glyme molecules having the chemical structure CH3-O-(CH2-CH2-O)n-CH3 can coordinate with Li+ to form a 1:1 complex of [Li(glyme)1]+ when n = 3 or 4 and lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) is used for the salt. These equimolar glyme-Li salt complexes are liquid under ambient conditions and show similar properties to those of conventional room-temperature ionic liquids, such as high thermal stability and low volatility. Furthermore, oxidative stability of glyme is increased by the complexation so that it could be stable up to E = 4.6 V vs. Li/Li+. Ordinary ionic liquids-Li salt binary system having low volatility and low reactivity with superoxide anion radical have been used as electrolytes of Li-O2 battery. However, Li+ transport property in the binary system is insufficient due to the limited solubility of Li salt and the increased viscosity with the addition of Li salt. In this regard, glyme-Li salt complexes appear to have better Li+ transport properties than the binary systems of ordinary ionic liquids.
In this study, we adopted glyme-Li salt complex as electrolytes of Li-O2 battery and examined its properties. Cyclic voltammetry was performed to examine the reversibility and oxidative stability of the system using glyme-Li salt complex. The results showed that the glyme-Li salt complex was stable toward superoxide anion radical so that reversible redox reaction was possible in this system. After confirming reversibility of the system, we practically assembled Li-O2 cells and confirmed 1000mAh/g-carbon of capacity of the cell using the glyme-Li salt complex electrolyte. Moreover, we observed reversible charge-discharge curves even after repeated cycles.

We report on the recent development of, and results obtained with, an ab initio method for the direct simulation of ionic conduction and diffusion in solid state materials [1]. The colour-diffusion algorithm, a nonequilibrium molecular dynamics method originally developed for the simulation of transport phenomena in fluids [2], is applied to the ab initio molecular dynamics (AIMD) simulation of solid state lithium ion conductors to determine the lithium diffusion coefficient and diffusion mechanisms.
The method enables the direct simulation of ionic diffusion, which in the solid state is governed by ion site jumps occurring on a time scale that is computationally intractable by AIMD: they are rare events in this context. In the presented method, rare events are accelerated by the application of an artificial external field, designed such that ionic diffusion is provoked as a response to the field. The system response to the external field is accurately described in the framework of linear response theory; the method is exact.
Determination of ionic diffusion in solids is important not only for hydrogen storage materials, where bulk diffusion of ions is central to the hydrogen absorption/desorption reaction mechanisms [3,4], but also in other component materials of hydrogen fuel cell systems or batteries, such as ion-exchange membranes, solid electrolytes or electrodes. The method was tested on the well-studied superionic conductor and hydrogen storage material LiBH₄ at 535K. The calculated lithium ionic conductivity closely matched published measurements, and the diffusion mechanism was elucidated directly, while a minimum of new adjustable parameters are introduced by this method. Results on battery cathode materials LiFePO₄ and LiMn₂O₄ shall also be presented.
References:
[1] P. C. Aeberhard, S. R. Williams, D. J. Evans, K. Refson, and W. I. F. David, Physical Review Letters 108, 095901 (2012).
[2] D. J. Evans, W. G. Hoover, B. H. Failor, B. Moran, and A. J. C. Ladd, Physical Review A 28, 1016 (1983).
[3] W. I. F. David, M. O. Jones, D. H. Gregory, C. M. Jewell, S. R. Johnson, A. Walton, and P. P. Edwards, Journal of the American Chemical Society 129, 1594- 601 (2007).
[4] H. Gunaydin, K. N. Houk, and V. Ozolins, Proceedings of the National Academy of Sciences of the United States of America 105, 3673-7 (2008).

Gaining insight to the phase distribution as well as morphological evolution on the mesoscale of a battery material during operation or at intermediate stages is the key to understanding the mechanism of transport and phase transformations. This paper will focus on in- and ex situ XANES microscopy of materials for electrodes in Li-ion batteries, where application in high demand fields such as transportation and grid storage require ever increasing energy density. A new chemical imaging technique, X-ray absorption near edge structure (XANES) microscopy, combines the high resolution and large field of view (FOV) of full-field transmission X-ray microscopy (TXM) with the chemical speciation capabilities of XANES to produce 2D and 3D chemical speciation maps. Using the TXM on beam line 6-2 at the Stanford Synchrotron Radiation Lightsource (SSRL) this method illustrates the phase distribution and the advance of the reaction at intermediate stages and in situ with resolutions down to 30nm and a FOV of ge; 30x30 microns. As an example for the importance of obtaining correlated information on morphology and chemical phase we will present our single particle studies on LiFePO4 where this information was obtained simultaneously. The experiments were performed at the Fe K-edge to map the distribution of LiFePO4 and FePO4 and revealed the interplay between morphological properties such as cracks and defects and the chemical phase distribution. Further experiments using scanning beam techniques were performed at beam line P06 at PETRA III at DESY, Hamburg.

Today&’s demand for portable energy supplies remains unbroken and the growing wish for green mobility fuels the use of lithium-ion batteries. However, many difficulties remain upon intense use of these batteries, in particular at low-temperatures, where lithium is likely to deposit on the carbon anode in preference to lithium intercalation. Reaction kinetics play a major role in the suppression and control of lithium-plating on graphite anodes being mainly determined by the characteristics of the electrode/electrolyte interface.
In this work we provide a further step towards a better understanding of the electrochemical reactions taking place at the electrode/electrolyte interface of graphite anodes in lithium-ion batteries. Comprehensive kinetic studies of the charge-transfer process were conducted in a three electrode arrangement, investigating graphite anodes prepared in-house as well as commercially available graphite anodes.
The competing processes of lithium intercalation and lithium deposition on graphite electrodes were looked at in detail, using electrochemical impedance spectroscopy, forced overcharge and polarization experiments. We further paid attention to the reverse processes of lithium deintercalation and lithium stripping. Exchange current densities, as a measure of the speed of a reaction, were obtained using Tafel-Plots. Strong differences were observed, pointing out that lithium intercalation is considerably slower than lithium deposition, not only at low temperatures.
The kinetic parameter was further applied to an extended Butler-Volmer equation to calculate the contribution of intercalation and plating current to the total amount of current in the cells.
Different temperatures between -10°C and 40°C were systematically studied in order to get an in-depth understanding of the temperature dependence of the interfacial reactions. Activation energies calculated using Arrhenius&’ Law, revealed relevant differences in the temperature characteristics of the processes. This allowed us obtain limiting factors for cell operation. The electrochemical investigations are supported by high-resolution SEM images of lithium-deposition and -stripping as well as XRD-studies of the graphite electrodes.
Furthermore we present ways to improve the interfacial properties by electrochemically and physically applying thin coatings of lithium-intercalating metals (such as tin) as well as non-intercalating metals (such as copper). Their role in the reaction kinetics is evaluated, mainly influencing the overall current density distribution at the interface.
Our work clearly shows that the reaction kinetics at the electrode/electrolyte interface play a key role in the mechanisms of lithium intercalation and deposition. As most experiments were performed in symmetrical lithium metal cells too, our results do not only apply to commercial LIBs, but they can also be adopted for next-generation lithium-based batteries using lithium-metal electrodes.

Conductive Nb-doped TiO2 nanofibers (Nb0.1Ti0.9O2) were fabricated by electrospinning of a mixture of Ti(IV)isopropoxide and poly(vinyl pyrrolidone) PVP in acidic alcoholic solution. Subsequently, Pt nanoparticles were deposited on the surface of the nanofibers through chemical reduction by either ethylene glycol (EG) or sodium borohydride (NaBH4). The structural and electrochemical characteristics of the prepared Pt/Nb0.1Ti0.9O2 catalysts were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), and cyclic voltammetry. The mean particle size of Pt nanoparticles reduced by ethylene glycol was 5 nm while the reduction with sodium borohydride method produced larger Pt nanoparticles of an average size of 7.6 nm. This difference is attributed to the stabilization of Pt nanoparticles by the attachment of glycolic anions to the surface, which arrests the growth of the nanoparticles. The samples prepared by the ethylene glycol (EG) method also showed a higher electrochemical specific surface area (ECSA) of about 5.45 m2/gPt. Both catalysts retain about 60% of their electrochemically active surface area after 1000 voltammetric cycles in the range of 0.03 to 1.4 V vs. RHE that confirms a strong metal support interaction between the support and Pt nanoparticles. These results are relevant for the development of new catalyst layers for PEM Fuel Cells.

We systematically improve the photoelectrochemical water splitting activity and chemical stability of zinc oxide nanowire photoanodes by combined surface and bulk passivation. Surface-passivated zinc oxide/titanium dioxide core/shell nanowire arrays supply a photocurrent density of 0.5 mA/cm2 at the thermodynamic oxygen evolving potential, an improvement of 20 percent compared to unpassivated zinc oxide wires. The core/shell nanowire also exhibits excellent chemical stability. We further increase the photocurrent density to 0.7 mA/cm2 - the highest reported value for doped or undoped zinc oxide photoanodes - by annealing the zinc oxide wire arrays in addition to surface passivation. Photoexcitations at energies above the zinc oxide band gap are converted with efficiency greater than 80 percent. Photoluminescence measurements of the best-performing nanowire arrays are consistent with improved water splitting activity from removal of deep trap states.

Hausmannite Mn3O4 octahedral nanoparticles with a {101} faceted surface have been prepared via an oxygen-mediated growth synthesis with a resulting average diagonal width of less than 20 nm. The electrochemical properties of this Mn3O4 as cathode materials for pseudocapacitor applications were characterized in both a three-electrode half-cell and two-electrode asymmetric button cells. A maximum mass specific capacitance of 260 F/g was obtained from half-cell cyclic voltammetric analyses. These structured Mn3O4 cathodic materials exhibited superb cycle ability during 10,000-cycle galvanostatic charge/discharge analyses with a capacitive retention of 85% ; and likewise exhibited stable coulombic efficiency of over 98%. The charge-storage mechanism of Mn3O4 was further studied via in-situ X-ray absorption near edge spectroscopy and X-ray diffraction. The resulting data showed that: (1) the major change of electronic state (redox reactions) occurred at potentials between 0.6 V and 0.9 V (vs. Ag/AgCl); and (2) {101} facets showed a much stable electrode/electrolyte interface via electrochemical cycling. DFT calculations further corroborated this mechanism by confirming the enhanced redox activity afforded by abundantly exposed {101} facets of Mn3O4 octahedra that subsequently facilitates the adsorption and intercalation of Na cations.

Solid oxide fuel cells (SOFCs) have attracted attention for their high energy-conversion efficiency, their fuel flexibility, and their use of non-precious metal catalysts due to their high operating temperature (800-1000 oC). However, that high operating temperature hinders practical applications and poses challenges in material selection and thermal stability.Therefore, efforts have been made to reduce the operating temperature to the low temperature regime (300-500 oC). However, lowering the operating temperature adversely affects the oxygen reduction reaction (ORR) at the cathode. Because ORR is known as the rate-determining step for SOFC reactions, diminishing the effectiveness of that step reduces the exchange current density and, in turn, the fuel cell performance.Therefore, in this temperature regime, Pt may be a suitable catalyst because it is considered to be the best catalyst for the ORR enhancement.
To deposit Pt catalysts, typically a porous Pt layer is fabricated by DC magnetron sputtering in order to provide a sufficiently large TPB density. However, there are two issues with using the DC-sputtering method to fabricate Pt electrodes. The first is that a relatively large amount of the electrode material is required to achieve a porous electrode structure that provides a large enough TPB density. The second issue has to do with the constraints imposed by the anisotropic deposition scheme of the physical vapor deposition (PVD) technique. Since DC-sputtering has vertical directionality, it is hard to coat the side-walls of 3-D structures when the aspect ratio becomes large.
In order to address both of the above issues (materials cost and physical constraints), this study looked at the technique of atomic layer deposition (ALD). ALD is a thin film fabrication technique which can deposit conformal films on high aspect ratio substrates. We successfully demonstrate the utilization of ALD of Pt as a thin (10 nm) fuel cell cathode. By controlling the number of ALD cycles, we systematically varied the geometry of ALD Pt electrodes, and the cell performances with those electrodes were characterized by current-voltage measurements in the temperature range of 350-450 oC. The fuel cell performance of the cells with a 10 nm ALD Pt electrode was comparable to that obtained with the typical DC-sputtered 80 nm porous Pt electrode. We further determined that there is an optimal ALD Pt electrode thickness, which is approximately 10 nm (180 cycles), due to the compromise between the need to achieve TPB density and to maintain the connectivity which was elucidated by TEM observations.

The electrochemical reduction of CO2 grants us an interesting pathway towards sustainability by allowing for the conversion of CO2 into green fuels and chemicals, provided that the energy is supplied from renewable energy sources. One key barrier to the utilization of this technology is the lack of effective catalysts for this reaction which has major challenges in its efficiency and selectivity. In an effort to deepen our understanding of the surface chemistry and gain insight into the factors important to designing better catalysts, our group has characterized the activity and selectivity of the reaction on several transition metal surfaces utilizing a custom made electrochemical cell [1]. The focus of this work is placed on the results on Ag and Zn surfaces. The potential dependence of activity and selectivity were observed, where the primary CO2 reduction product was CO for both of these metal surfaces. The high sensitivity of our cell for liquid phase products allowed for the observations of new, previously unreported products on both surfaces. Insights into the kinetics and mechanisms are obtained from the potential dependence of the activity, and comparison is drawn between the activity on both metals. Key surface characteristics such as the carbon monoxide binding energy are found to be useful for the explanation of the observations, as suggested in the theoretical work by Peterson et al. [2].
[1] K. P. Kuhl et al. Ener. Env. Sci., 2012, 5, 7050-7059.
[2] A. A. Peterson et al. J. Phys. Chem. Lett., 2012, 3, 251-258.

Three kinds of oxidant are synthesized, Ferric benzenesulfonate (Fe(OBs)3), Ferric 4-methylbenzenesulfonate (Fe(OMBs)3) and Ferric 4-ethylbenzenesulfonate (Fe(OEBs)3). Then, 3,4- ethylenedioxythiophene (EDOT) is polymerized with these oxidants to obtain PEDOT-OBs, PEDOT-OMBs, and PEDOT-OEBs, respectively. The surface conductivity of PEDOT-OBs shows the highest value among the fabricated materials because PEDOT-OBs shows the better defined crystalline structure and the doping concentration of PEDOT-OBs is much higher than that of PEDOT-OMBs and PEDOT-OEBs. Capacitance, equivalent series resistance (ESR) and leakage current of PEDOT-OBs show the enhanced value compared to PEDOT-OMBs and PEDOT-OEBs because of the high electrical conductivity and low degree of un-doped oxidant of PEDOT-OBs. The thermal degradation temperature of all of the polymerized materials are observed in the range of 300~330 celsius, indicating that all of the polymerized materials show excellent thermal stability when applied to aluminum solid electrolyte capacitors.

Proton exchange membrane (PEM) fuel cells are being developed as alternative energy sources for both residential and automotive application. In order for this technology to become fully commercial, a further reduction of cost and improvements in performance and durability of PEM fuel cells membrane electrode assemblies (MEAs) are still required.
Significant cost reduction can be achieved with by reducing the Pt loading within the cathode catalyst layer in catalyst coated membranes (CCMs) to 0.2 mg/cm2 or less. In order to maintain the high currents and efficiency in fuel cells with low catalyst loading, it is necessary to increase both the catalytic activity and the utilization of the electrochemically active surface area of the catalyst layer. Therefore it is particularly important to obtain deeper understanding how to design the 3-phase boundary in order to promote the effective usage of Pt and to maximize the transport of active reactants to the electroactive sites.
Recently, a combination of a focused ion beam (FIB) and scanning electron microscopy (SEM) as well as scanning transmission x-ray microscopy (STXM) has been used for characterization of two-dimensional (2D) and the three-dimensional (3D) microstructure of a PEM fuel cell catalyst layer. The insights provided using this approach are critical for a move towards rational catalyst layer design.

Platinum-based materials have been generally used as catalysts for fuel cell due to high activity and stability. However, the commercialization of fuel cell cannot be pictured without replacing Pt, because the cost of fuel cell depends on platinum greatly. Therefore, the development of low cost catalyst is needed. Some researchers developed highly active and relatively inexpensive anode catalyst such as PdPt/C and PtRu20/C, but they still used Pt in their catalysts [1,2]. Recently, Li et al. reported highly active and durable Ir-V/C catalyst. According to their results, the power density of Ir-V/C was higher than that of commercial Pt/C catalyst at the equal level of Pt loading [3]. This result was remarkable achievement, however they did not show any intrinsic activity toward hydrogen oxidation of their catalyst.
In this study, we investigated a synergistic effect of Pd-Ru bimetallic catalyst in anode electrode to develop more realistic catalyst for replacing the commercial catalyst. The Pd and Ru were chosen due to the analogous properties with platinum in exchange current density and CO tolerance, besides lower price. The intrinsic activity of PdRu9/C was measured by half-cell test, which was finally confirmed by single-cell test. PdRu9/C showed the highest activity comparable to that of commercial PtRu1.5/C catalyst. According to the results of XRD measurement and DFT calculation, the synergistic effect mainly caused to lower hydrogen binding energy due to hexagonal-structured Pd-Ru bimetallic alloy.
[1] S. J. Yoo, H.-Y. Park, T.-Y. Jeon, I.-S. Park, Y.-H. Cho, Y.-E. Sung, Angew. Chem. 47, 9307-9310 (2008)
[2] J.X. Wang, S. R. Brankovic , Y. Zhu, and R.R. Adzic, J. Electrochem. Soc., 150, A1108-A1117 (2003)
[3] B. Li, J. Qiao, D. Yang, R. Lin, H. Lv, H. Wang and J. Ma, Int. J. Hydrogen Energy, 35, 5528-5538 (2010)

Magnesium (Mg) is being investigated as an alternative to lithium (Li) in rechargeable batteries, because Mg can contribute two electrons to current flow instead of one for Li. Currently Mg batteries are designed with Mg metal serving as the anode [1]. Such a design might not be safe enough in consumer applications, especially considering that a Mg fire cannot be extinguished with traditional means. Using Mg in minimal quantities incorporated into a host like graphite would be a safer approach.
Mg which is lower in the periodic table than Li might be more difficult to intercalate into graphite. The objective of the research is to investigate by first principle calculations whether inserting noble gas atoms like helium (He), neon (Ne) or argon (Ar) into graphite would increase interlayer spacing enough to facilitate the intercalation of Li+ and Mg++ ions. In practice, noble gas atoms can be inserted into graphite by preprocessing it in a noble gas environment at high temperature and gas pressure.
Atomic models consist of two layers of graphene with noble gas atoms and ions sandwiched in between. In addition to Li+ and Mg++, hydrogen (H+) ion is also included in the study as a test case, since it is the smallest atom. Optimal spacings between the layers with and without the noble gas atoms are calculated by the ab initio method and Pople type basis sets augmented with polarization functions.
For the case of H+ ion, calculated distance between the graphene layers without any noble gas atoms is 3.6 A which is about 7% greater than the actual interlayer spacing of 3.35 A for graphite. Distance between the graphene layers increases to 4.4 A with He atoms, 4.9 A with Ne atoms, and 6.7 A with Ar atoms in between the graphenes.
For Li+ and Mg++, calculated interlayer spacings without any noble gas atoms are 4.3 A and 4.1 A, respectively. The doubly charged Mg++ pulls the graphene layers even more than Li+. Both Li+ and Mg++ can fit into the interlayer spacing created by He which is the smallest of the 3 noble gases. Ne provides even greater room, but at the expense of straining the graphite lattice more than He.
[1] "Moving beyond lithium with low cost, high energy, rechargeable magnesium batteries," white paper by Pellion Technologies, MA, September 2011

The demand for stationary energy storage has rapidly changed the worldwide landscape of energy system research [1, 2], which has brought vanadium redox flow battery (VRB) technology into the spotlight in recent years [3, 4, 5, 6]. However, one technical obstacle haunting VRB technology is the substantial capacity decay that occurs during cycling, which is critically important to the long-term operation of VRBs [7. 8. 9, 10]. In this paper, phenomena, mechanism, and remediation of capacity decay during the long term charge-discharge cycling of VRB were presented as following:
1. The relationship between the electrochemical performance of vanadium redox flow batteries (VRB) and electrolyte compositions has been investigated, and the reasons for capacity decay over long term charge-discharge cycling have been analyzed and are discussed in detail.
2. In situ investigation of vanadium ions transfer during operation of flow battery. It is shown that the electric field accelerated the positive-to-negative and reduced the negative-to-positive transport of vanadium ions in the charging process and affected the vanadium ion transport in the opposite way during discharge.
3. Methods for remediating the lost capacity were proposed on the base of above finding: Long-term operation of VRBs was achieved without the substantial loss of energy resulting from periodic remixing of electrolytes.
Acknowledgements
The authors would like to acknowledge financial support from the U.S. Department of Energy&’s (DOE&’s) Office of Electricity Delivery and Energy Reliability (OE) (under Contract No. 57558). We also are grateful for beneficial discussions with Dr. Imre Gyuk of the DOE-OE Grid Storage Program. Pacific Northwest National Laboratory is a multi-program national laboratory operated by Battelle for DOE under Contract DE-AC05-76RL01830.
References
[1] B. Dunn, H. Kamath, J.-M. Tarascon, Science 334 (2011) 928-935.
[2] Z. Yang, J. Zhang, M.C.W. Kintner-Meyer, X. Lu, D. Choi, J.P. Lemmon, J. Liu, Chemical Reviews. 111 (2011) 3577-3613.
[3] M. Skyllas-Kazacos, M.H. Chakrabarti, S.A. Hajimolana, F.S. Mjalli, M. Saleem, Journal of The Electrochemical Society. 158 (2011) R55-R79.
[4] A. Weber, M. Mench, J. Meyers, P. Ross, J. Gostick, Q. Liu, Journal of Applied Electrochemistry. 41 (2011) 1137-1164.
[5] M. Skyllas-Kazacos, M. Rychick, R. Robins, in: US Patent 4,786,567, 1988.
[6] L. Li, S. Kim, W. Wang, M. Vijayakumar, Z. Nie, B. Chen, J. Zhang, G. Xia, J. Hu, G. Graff, J. Liu, Z. Yang, Advanced Energy Materials. 1 (2011) 394-400.
[7] Q. Luo, H. Zhang, J. Chen, D. You, C. Sun, Y. Zhang, Journal of Membrane Science. 325 (2008) 553-558.
[8] X. Li, H. Zhang, Z. Mai, H. Zhang, I. Vankelecom, Energy & Environmental Science. 4 (2011).
[9] Q. Luo, L. Li, Z. Nie, W. Wang, X. Wei, B. Li, B. Chen, Z. Yang, Journal of Power Sources 218 (2012) 15-20.
[10] W. Wang, Q. Luo, B. Li, X. Wei, L. Li, Z. Yang, Advanced Functional Materials, DOI: 10.1002/adfm.201200694

Li-excess electrode materials, Li2MnO3-stabilized LiMO2 (M = Transition Metal), were prepared using the method of mechanochemical process followed by the heat treatment to yield the layered-layered integrated structure nanocomposites. X-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy studies confirmed the structural integration of 0.5Li2MnO3-0.5LiMO2 electrode materials. We further carried out first principles calculations to obtain activation energy barriers of Li+ de-/intercalation, and it suggested that utilizing both Li2MnO3 and LiMO2 components can enhance the Li+ diffusion for the layered-layered integrated structure. We observed the activation barrier for lithium de-/intercalation in 0.5Li2MnO3-0.5LiCoO2 has the lowest value of 74.1 meV from our calculation results. It also has the highest values in the c-axis and the volume of the unit cell, which we believe that results in the lowest activation energy barrier for Li migration. More details will be discussed at the meeting.

Platinum has a superior electrocatalytic activity toward methanol oxidation reaction
(MOR) and, therefore, Pt is the most preferred catalyst used in direct methanol fuel cells (DMFCs). In the present time, the most widely studied subject in DMFC research is to reduce the size and to optimize the distribution of Pt nanoparticles for minimizing the use of the precious Pt catalyst and concurrent increasing the electroactivity surface area for methanol oxidation. In addition, metal oxides can be used as the Pt support to enhance the electrocatalytic efficiency of the Pt catalyst. In this works, we used plasma-enhanced atomic layer chemical vapor deposition (PEALD) to deposit Pt nanoparticles on the TiO2 substrate, and studied the electrocatalytic activity of Pt nanoparticles toward MOR as a function of the particle size.
Pt nanoparticles were deposited on the TiO2 substrate by PEALD at 200oC using
MeCpPtMe3 as the Pt precursor. The size of Pt nanoparticles can be well controlled by varying the number of the ALD reaction cycle. Scanning electron microscope and transmission electron microscopy showed that well-dispersed Pt nanoparticles were deposited on the TiO2 surface and the particle size of Pt nanoparticles was in the range between 2 nm and 10 nm depending on the ALD cycle number. Cyclic voltammetry (CV) and CO stripping analysis were performed to study the electrocatalytic activity of the Pt/TiO2 electrode toward MOR in acidic media. The electrocatalytic activity and the CO tolerance of the electrode are a function of the Pt ALD cycle number. We found that the electrode with a Pt ALD cycle number of 20, which produces Pt nanoparticles of ~3 nm in size, had the best electrochemical performance. When the ALD cycle number was larger than 50, Pt nanoparticles coalesced, and the electrode exhibited an electrochemical performance for MOR similar to a Pt thin film. The excellent electrocatalytic activity of the Pt nanoparticle is ascribed to the synergistic effect of the nanometer sized Pt nanoparticles and the electronic interaction between the TiO 2 support and the Pt nanoparticles. A schematic model describing the synergistic effect in terms of the electronic effect and the bi-functional mechanism will be presented at the meeting.

In both academia and industry, tremendous effort has been devoted to improving the power conversion efficiency of dye-sensitized solar cells (DSCs) to exploit their high efficiency, and low production costs. The efficiency of a DSC is determined by the short circuit current density (JSC), the open circuit voltage (VOC), and the fill factor (FF). These key parameters are strongly governed by the characteristics of the TiO2/dye/electrolyte interface, at which many electrochemical reactions occur. Modifications of the interfacial properties can alter the conduction band edge and shield the trap states of TiO2, thereby influencing VOC, JSC, and the recombination reaction of the photoinduced electrons with any oxidized species. In addition, interfacial recombination pathways act as a loss mechanism in competition with the transport processes. The photoinjected electrons in the TiO2 have two possible recombination pathways: Direct recombination with cations of the dye, or with the HTM. In this talk, I will present some modifications of heterogeneous interface using coadsorbents, organic dyes and electrolytes, influencing the energy gap (VOC) between the potential of the redox couple and the Fermi level, and discuss charge transportation phenomena in DSCs studied using nanosecond transient absorption spectrophotometer (TAS) and electrochemical impedance spectrophotometer (EIS).
References
1. T. Park et al. Adv. Energy Mater. 2012, ASAP (DOI: 10.1002/aenm.201200437).
2. T. Park et al. Chem. Commun. 2012, ASAP (DOI:10.1039/C2CC33629D).
3. T. Park et al. Adv. Energy Mater. 2012, 2(2), 219-224.
4. T. Park et al. J. Mater. Chem. 2012, 22 (17), 8641 - 8648.
5. T. Park et al. ACS Appl. Mater. Interfaces, 2012, 4 (6), 3141-3147.
6. T. Park et al. RSC Adv. 2012, 2(8), 3467-3472.

Solar energy provides an abundant potential source of renewable clean energy provided there exists an efficient method of energy storage. Photoelectrochemical water splitting can be used to store solar energy in the form of hydrogen. However, the efficiency of the overall water splitting reaction is severely limited by the high overpotential costs required for the oxygen evolution half reaction. Furthermore, there exists a need for a non-precious metal catalyst to drive the oxygen evolution reaction (OER) at low overpotentials to make the process more economical.
As an alternative to the best known precious metal OER catalysts like RuO2 and IrO2, previous work has focused on manganese oxide and cobalt oxide catalysts. We have identified amorphous CoTiOx as a novel, active, non-precious metal catalyst for OER. Using a simple and scalable sol gel synthesis, thin films (50 nm - 200 nm) of CoTiOx can be deposited on a number of different substrates. This work begins by characterizing the structure and morphology of this material and studying the effect of varying the heat treatment temperature and elemental ratio of Co:Ti on catalytic activity and material stability. Furthermore, we characterize the effect of preparation route on the oxidation state of cobalt using ex situ L-edge x-ray absorption spectroscopy (XAS). We also investigate the effect of catalytic testing on cobalt oxidation state of the surface layer.
We also probe the photospectral properties of this material. The wide band gap of CoTiOx allows most photons from the visible portion of the solar spectrum to pass through such that thin, conformal films of this material can also be used as a protective layer for absorber materials that are prone to degradation. CoTiOx has been successfully deposited as a co-catalyst and protective layer on tantalum-based photoabsorbers and is shown to significantly improve photocurrent and material stability.

Electrowetting is a phenomenon in which a droplet wetting increases when an electric field is applied across the droplet/substrate interface. Applications include electrowetting displays, electrowetting lenses, vibration energy harvesting, and lab on a chip diagnostics. In electrowetting systems, the hydrophobic dielectric layer is subjected to highly intensive electrical tensions which causes dielectric failure. At the failure spots, the electrochemical reactions can quickly damage the electrode.
However, careful selection of the electrolyte and electrode materials to create passivating systems can reduce the damage for anodically polarized systems. However, if the voltage reverses, then the passivation effect is lost. This work will examine the case in which pairs of electrode/electrolyte interface with opposite polarity are used in series to create systems that are stable under reversed voltages. The effects of cycle frequency, electrolyte, voltage levels, and initial anodization state are examined and the effects applied to a novel electrowetting mechanism that enables continuous electrowetting actuation over long distances with a single electrode pair.

A lithium solid battery has features such as flexibility in the shape of a cell design, leak proof of electrolyte, high safety. During last two decades, a lithium-based glass have been studied extensively as electrolytes for solid-state secondary batteries but poses the challenge of how close its electrical performance can be made to that of a liquid electrolyte cell. For practical use, solid electrolyte must have high ionic conductivity as well as chemical, thermal and electrochemical stability. Recent progresses have focused on glass electrolytes due to advantages over crystalline solid. Therefore, various efforts have so far been made to improve the ionic conductivity of the solids especially in consideration of its practical application,
In this study, major effort has been focused on the improvement of the ion conductivity of nanosized LiAlTi(PO4)3 oxide electrolyte prepared by mechanical milling (MM) method. In LiTi2 (PO4)3, Ti4+ ions are partially substituted by Al3+ ions by heat-treatment of Li2O-Al2O3-TiO2-P2O5 glasses. Heat treatment to the glass ceramics were made to study its structure, morphology and the lithium ionic conductivity of the solid electrolyte. It is suggested that the processing temperature affects the ionic conductivity, easy fabrication and low cost make this glass-ceramics promising to be used as inorganic solid electrolyte for all-solid-state Li rechargeable batteries.

Over the last decades, there has been considerable interest in the synthesis of semiconductor photocatalysts for potential environmental applications which include air purification and water disinfection. Among them, due to their chemical and physical properties, V2O5 and TiO2 nanostrucutres have been extensively studied as photocatalysts (1; 2). There are many reports showing that the photocatalytic activity can be increased effectively by combining different semiconductor nanomaterials with different band energies (3). In this sense, the main objective of this work is study the synthesis of one-dimensional (1D) TiO2/V2O5 heterosctructures for photocatalytic applications. In a typical procedure, an appropriated amount of solution containing peroxytitanate and V2O5 nanowires was prepared. Then, this mixed solution was placed in a 100 mL hydrothermal cell and subjected at different temperatures during 6 hours. The method employed for the synthesis of V2O5 nanowires and peroxytitanate were described in greater detail by Avansi et al (4) and Ribeiro et al (5), respectively. The precipitates were separated by centrifugation, washed with pure alcohol for several times and then dried at 50 °C for 24 h. The as-prepared samples were characterized with X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) techniques. For the samples obtained through hydrothermal treatment at 2000C, XRD patterns revealed only the presence of V2O5 nanowires in orthorhombic phase and TiO2 nanoparticles in anatase phase. The TEM images confirms that V2O5 nanowires are coated with TiO2 nanoparticles with around 15 nm. High resolution TEM images reveals some points of coalescence in the interface region between TiO2 and V2O5 nanostructures. Additionally, chemical analysis performed by X-ray Energy-Dispersive Spectroscopy (XEDS) confirms only the presence of titanium (Ti), vanadium (V) and oxygen (O) without impurities. The as-synthesized samples exhibited an enhancement of the photocatalytic activity for degradation of Methilene Blue (MB) solution, under visible-light irradiation (lambda;>420 nm).
References:
1. Sun, Q. O. e Y. M. Xu. Journal of Physical Chemistry C, 114, 44, 18911-18918 (2010).
2. Li, B. X., Y. Xu, G. X. Rong, M. Jing e Y. Xie. Nanotechnology, 17, 10, 2560-2566 (2006).
3. Zou, C. W., Y. F. Rao, et al. Langmuir, 26, 14, 11615-11620 (2010).
4. Avansi, W., C. Ribeiro, E. R. Leite e V. R. Mastelaro. Crystal Growth & Design, 9, 8, 3626-3631. (2009).
5. C. Ribeiro, C. M. Barrado, E. R. Camargo, E. Longo, E. R. Leite, Chemistry-a European Journal 2009, 15, 2217

Electrical properties of mixed ionic and electronic conducting oxides, PrxCe0.95-xGd0.05O2-δ (0.15 le; x le; 0.40) have been investigated as cathode materials for low temperature solid oxide fuel cells. Four compositions of PrxCe0.95-xGd0.05O2-δ (PCGO) have been prepared by varying the Pr content. Phase formation, thermal expansion, ionic conductivity, electronic conductivity, ionic transference number and electrochemical performance have been studied. XRD results indicate that PrxCe0.95-xGd0.05O2-δ samples crystallize in the fluorite structure, and the lattice volume decreases with increasing Pr content, x. The coefficient of thermal expansion increases with increasing x, and at x = 0.2 shows an optimum value of 12 x 10-6 K-1 matching with coefficient of thermal expansion of GDC electrolyte. Area specific resistance and ionic transference number decrease while cathodic over potential and electronic conductivity increase with increasing x. Gd3+ contributes to ionic conduction by creating oxygen vacancies and Pr4+ contributes electronic conduction by decreasing the band gap of CeO2. NiO-GDC//GDC//PCGO-GDC single cell with x = 0.2 shows a power density of 258.7 mW cm-2 at 550 C and the x=0.4 composition shows power density of 435 mW cm-2 at 700 C. The results signify that the PCGO sample with x=0.2 could be a promising material for low temperature cathode applications.

Design and synthesis of energy efficient and stable electrochemical interfaces (materials and double layer components) with tailor properties for accelerating and directing chemical transformations is the key to developing new alternative energy systems - fuel cells, electrolizers and batteries. In aqueous electrolytes, depending on the nature of the reacting species, the supporting electrolyte, and the electrodes, two types of interactions have traditionally been considered: (i) direct - covalent bond formation between adsorbates and electrodes, involving chemisorption, electron transfer, and release of the ion hydration shell; and (ii) relatively weak non-covalent metal-ion forces that may affect the concentration of ions in the vicinity of the electrode but do not involve direct metal-adsorbate bonding. The range of physical phenomena associated with these two classes of bonds is unusually broad, and are of paramount importance to understand activity of both substrate-electrolyte two phase interfaces and substrate-Nafion-electrolyte three phase interfaces. Furthermore, in the past, researcher working in the field of fuel cells (converting hydrogen and oxygen into water) and electrolyzers (splitting water back to H2 and O2) ) seldom focused on understanding the electrochemical compliments of these reactions in battery systems, e.g., the lithium-air system.
In this lecture, we address the importance of both covalent and non-covalent interactions in controlling catalytic activity at the two-phase and three-phase interfaces. Although the field is still in its infancy, a great deal has already been learned and trends are beginning to emerge that give new insight into the relationship between the nature of bonding interactions and catalytic activity/stability of electrochemical interfaces. In addition, to bridge the gap between the “water battery” (fuel cell harr; electrolyzer) and the Li-air battery systems we demonstrate that this would require fundamentally new knowledge in several critical areas. We conclude that understanding the complexity (simplicity) of electrochemical interfaces would open new avenues for design and deployment of alternative energy systems.

The oxygen evolution reaction plays a critical role in energy conversion devices which generate fuel from electricity or sunlight. However, sluggish reaction kinetics limit the net current that can flow through such devices, resulting in the need for precious metal catalysts such as IrO₂. Nickel-based oxides/hydroxides are promising catalysts for oxygen evolution in alkaline electrolytes. Specifically, the nickel-iron system exhibits electrocatalytic activities for oxygen evolution which are notably higher than those of their end-members, but neither the composition of maximum activity nor the source of enhanced activity is well-established.
In our work, we aim to understand the mechanism by which the presence of iron influences the electrocatalytic activity of Ni-Fe. Ni-Fe films of known composition are electrochemically deposited atop gold working electrodes, and confocal Raman microscopy is employed to characterize the Ni-Fe catalysts, in-situ, as the oxygen evolution reaction is being driven, to gain insight into the relationship between the catalyst chemistry/structure and catalyst activity. By examining the complete compositional range, we find that a maximum in activity occurs at 30-50% bulk Fe content. At this optimum catalyst composition, the specific current density for oxygen evolution, in alkaline electrolytes, is increased by two orders of magnitude compared to Ni alone and almost four orders compared to Fe. We report in-situ Raman signatures for the Ni-Fe system across the full composition range. Raman spectra reveal that, under oxygen evolution conditions, NiOOH and γ-Fe₂O₃/FeOOH phases are observed. In particular, the composition of highest activity contains NiOOH as one of its components.

Platinum is known to be among the best catalysts for oxygen reduction (ORR), though in recent years researchers have discovered that it binds oxygen too strongly for optimum activity [1]. Improvements have come by modifying the Pt-O adsorption strength via alloying platinum with other transition metals such as Pt₃Y [2] and Pt₃Ni [3].
It has been shown that single monolayers of platinum supported on various substrates can exhibit properties drastically different from platinum in its bulk form. In particular, one monolayer of platinum on ruthenium has been shown to have a much weaker Pt-O bond [4]. By adding additional layers of platinum and increasing the number of undercoordinated sites by nanostructuring, we can increase the ORR activity through strengthening the O-Pt/Ru bond. We are bounded by a single monolayer of platinum that binds oxygen too weakly and bulk platinum that binds it too strongly.
In an effort to develop improved ORR catalysts, we have synthesized core-shell nanoparticles with several Pt-shell thicknesses.Using a combination of STEM-EDS and Z-contrast (ADF-STEM) imaging, we confirm that the nanoparticles have the intended Ru-core, Pt-shell structure. Rotating disk electrochemistry was used to test catalytic activity and understand how Pt-shell thickness affects Pt-O bond strength. Optimally prepared samples exhibit increased ORR activity by a factor of two compared to state of the art TKK platinum catalysts, 0.58 mA/cm²_Pt at 0.9V vs. RHE. This improvement is attributed to a weaker Pt-O bond, as evidenced by an anodic shift of ~35mV in the Pt-OH peak in the base cyclic voltammogram.
This paper will ultimately describe how the combination of theory and experiment can expedite the development of new ORR catalysts.
References:
[1]Noslash;rskov, J. K. et al. Origin of the Overpotential for Oxygen Reduction at a Fuel-Cell Cathode. The Journal of Physical Chemistry B108, 17886-17892 (2004).
[2]Greeley, J. et al. Alloys of platinum and early transition metals as oxygen reduction electrocatalysts. Nature chemistry1, 552-6 (2009).
[3]Stamenkovic, V. R. et al. Improved oxygen reduction activity on Pt3Ni(111) via increased surface site availability. Science (New York, N.Y.)315, 493-7 (2007).
[4] Zhang, J., Vukmirovic, M. B., Xu, Y., Mavrikakis, M. & Adzic, R. R. Controlling the catalytic activity of platinum-monolayer electrocatalysts for oxygen reduction with different substrates. Angewandte Chemie (International ed. in English) 44, 2132-5 (2005).

One of the main goals of catalyst development currently is to modify near-surface platinum group metals (PGMs), namely platinum, iridium and gold, through size-, strain- and ligand-effects with the support, in order to increase robustness and efficiency while decreasing the cost. We present here our research on tailoring the near-surface electronic structure of the overlayer/support catalytic systems under low-loading limits of PGM overlayers on a wide variety of catalysts for electrochemistry.
Surface-limited redox replacement (SLRR) is used for layer-by-layer PGM growth, while the evolution of electronic and atomic structure is measured using X-ray Photoelectron Spectroscopy (XPS) and X-ray absorption spectroscopy. Synchrotron-based XPS, using a tunable energy photon source, allowed us to profile the transitions in the electronic structure from the surface down to the adlayer/support interface and beyond. By varying the source photon energy, we altered the photoelectron kinetic energy, which in effect allowed us to analyze the electronic structure of the layered system at several penetration depths. In addition to depth profile studies of these layered metal architectures, the effects thermally activated near-surface alloying on the PMG electronic structure is also presented here. Undulations of near-surface electronic structure brought on by the low-dimensionality of the PMG adlayer as well as the adlayer-support interactions are observed and can explain the resulting surface electrochemistry in these systems.
By analyzing the XPS peak area ratios of the Pt4f and Au4f photoemissions, a relative quantification of the PMG deposit can be achieved. An increase in the ratio of the PMG 4f peaks area to the Au 4f peaks area can be seen as the number of SLRR iterations increases, showing a continuing growth of the adlayer through the SLRR process. Lowering the photon energy increases the area ratio of the PMG adlayer emission to the Au substrate emission, confirming that the overlayers are remaining unmixed with and on top of the substrate at room temperature. When temperatures are raised to the range of 300K-500K, the Au photoemission becomes large at low photon energies, thus the gold diffuses to segregate to the surface. Additionally, a significant negative shift of ~1.5eV in the binding energy is measured for the Pt adlayer photoemission between 3 and 6 iterations of the SLRR process at room temperature. This shows that Pt is not fully reduced and exhibits cationic intermediaries at low iteration numbers of the SLRR process, and only becomes fully metallic Pt above a sufficient thickness of overlayer at higher iteration amounts. The 4f7/2 photoemissions for Ir however, remain around a binding energy of around 62eV up to 8 iterations of the SLRR process which is indicative of a cationic state.

Electrochemical degradation of the durability of Pt based nanocatalyst materials exposed to acidic media is one of the key issues hindering the development of efficient fuel cells. In this study, we used first principles calculations to analyze the atomistic mechanism of the electrochemical degradation. Model systems for Pt-M alloy nanoparticles of different sizes were conceptualized for calculating their electrochemical dissolution potential, which essentially indicates the nanoparticle&’s resistance to dissolution. We adopted a step by step mechanism for dissolution of atoms on the outermost shell of the nanoparticle by accounting for various possible pathways which lead to complete dissolution. Based strictly on thermodynamic considerations, our findings point towards a strong size dependent behavior of the Pt alloy nanoparticles, whose properties become similar to bulk for size more than 3 nm. Remarkably, we find that that for all cases, the dissolution proceeds by exposing more (111) facets at the expense of other atomic sites. Our results indicate that the competition between two major thermodynamic factors, the cohesive energy and the surface energy, decides the dissolution pathway. Based on our findings, we propose some desired characteristics which can serve towards rational design of model Pt nanocatalysts. Our findings may be of importance in understanding of the electrochemical stability in other applications as well, for instance the photo-catalysts for fuel generations via water splitting.

Although the oxygen reduction reaction (ORR) is important in variety of electrochemical processes and technologies including corrosion (and corrosion inhibition), sensors, and metal-air batteries, the application of the ORR in fuel cells is of particular interest. The slow kinetics of Oxygen reduction reaction (ORR) of modern energy technologies like in metal air batteries, PEM fuel cells had opened the scientific research door for the development of novel catalysts for the commercialization of such energy technologies1. Platinum and platinum alloys are the most efficient catalysts for speeding up such chemical reactions1,2. But high cost factor of platinum based catalysts leads the researcher to turn their head towards the novel less expensive materials to ameliorate the large scale industrial as well as general applications of such energy technologies. Ceria based complex metal oxides were extensively studied as electrolyte in solid oxide fuel cells3, 4. This current paper is concentrated upon these catalysts for their activity in acidic and alkaline media applicable to the key ORR reaction in metal air battery and PEM fuel cells.
The synthesis of ceria based doped complex metal oxides, such as CeO2 and Gd0.1Ce0.9O3-δ were performed using modified Pechini method. Their structural identification was performed by XRD, BET-SSA, pore size distribution, and SEM morphology. Besides these, their electrochemical catalytic activity for oxygen reduction reaction in acidic and alkaline media was studied in rotating disc electrode. Preliminary study demonstrates that ceria based complexes impregnated on carbon aerogel based support have the similar performances in comparison with platinum based catalysts for the ORR.
References:
1. Gewirth, A. A.; Thorum, M. S., “Electroreduction of Dioxygen for Fuel-Cell Applications: Materials and Challenges”. Inorg. Chem. 2010, 49, 3557-3566.
2. Gasteiger, H. A.; Kocha, S. S.; Sompalli, B.; Wagner, F. T., “Activity Benchmarks and Requirements for Pt, Pt-Alloy, and Non-Pt Oxygen Reduction Catalysts for PEMFCs”. Appl. Catal., B 2005, 56, 9-35.
3. Allan J. Jacobson, “Materials for Solid Oxide Fuel Cells”. Chemistry of Materials, 2010 22 (3), 660-674.
4. Dr Scott L. Swartz, Matthew M. Seabaugh, Christopher T. Holt, William J. Dawson, “Fuel processing catalysts based on nanoscale ceria”. Fuel Cells Bulletin, 2001, 4(30), 7-10.

Carbon onions, or onion-like carbon (OLC), are small nanoparticles, diameter ~5 nm, consisting of concentric layers of graphitic carbon. This material has shown promise in the field of electrical energy storage, particularly for supercapacitor electrodes, because of OLC&’s high conductivity (5 S/cm) and moderate surface area (500 m2/g). Quinones are compounds that are comprised of aromatic rings with oxygen containing groups. These molecules have been increasingly studied as electrochemically active compounds, as some are able to undergo highly reversible redox processes in aqueous medium. In this study, different quinones, (phenanthrenequinone (PQ), naphtoquinone (NQ), and pyrenedione (PY)) were adsorbed on the surface of OLC to create a pseudocapacitive layer. The high surface area and high conductivity of OLC make it an ideal material to support electrochemically active compounds. The quinones were absorbed on the surface as a thin monolayer, allowing for very fast charge/discharge rates and high current densities. The resulting capacitance of the OLC/quinone composite, ~140 F/g, was six times that of the bare OLC material at 1.3 A/g. Additionally, the quinones were shown to be stable for 10,000 cycles, with only a 2% loss in capacitance. The electrochemical study was correlated with thermogravimetric analysis (TGA) and DFT calculations to obtain the energies of absorption. The observed trend showed an increase in the energy of absorption with the size of the molecule. Interestingly, the energy stored by the three quinones increased with the size of the molecule.

The development of a cost effective process for the electrochemical reduction of CO₂ could enable a shift to a sustainable energy economy. Coupled to a renewable energy source such as wind or solar, such a process could generate carbon neutral fuels or commodity chemicals that are conventionally produced from petroleum. The key to developing such a process is a catalyst capable of performing the conversion at a low overpotential and high selectivity to the desired product. Unfortunately, known catalysts do not meet these requirements. More understanding of the factors that affect catalytic activity are needed to design improved catalysts.
To learn more about the catalytic factors important for CO₂ electroreduction, we have used experiments and theoretical computations to study the activity of a group of transition metals: Au, Ag, Zn, Cu, Pt, Fe, and Ni. The experimental measurements were made using a custom electrolysis setup that allows for highly sensitive product detection a potential range where currents from 0.5-10 mA/cm² were generated. Computations were carried out using the DACAPO plane wave implementation of density functional theory and the RPBE exchange-correlation functional.
Our experimental and theoretical data fits well with the trend expected from literature reports suggesting that the major products of CO₂ electroreduction are determined by CO binding energy to the metal surface. Due to the sensitivity of our experimental setup, we were able to identify a number of minor products that have not been reported before. The distribution of minor products showed a number of correlations to the calculated binding energies of key intermediates. By combining theory and experiment, we expect that a deeper understanding of CO₂ electroreduction on transition metals can lead to the development of improved catalysts for this important reaction.

Oxygen electrocatalysis is central to the efficiencies of direct solar and electrolytic water-splitting devices, fuel cells, and metal-air batteries. Oxides have shown high activity for the oxygen reduction and oxygen evolution reactions (ORR/OER).[1-4] However, the lack of fundamental understanding of the oxide surfaces limits mechanistic understanding at the molecular level. Probing a fundamental catalyst “design principle” that links surface structure and chemistry to the catalytic activity can guide the search for highly active catalysts that are cost effective and abundant in nature. Although activity descriptors such as eg occupancy and O p-band center, have been shown recently to correlate with ORR/OER activity,[2,3,5] such descriptors have not been measured directly from experiments. In study, we will present methods to correlate the measured occupied and unoccupied electron density of states of valence and conduction bands to ORR/OER activities, discuss how in situ methods such as ambient pressure X-ray photoelectron spectroscopy measurements[6,7] can reveal the changes of oxide surfaces as a function of temperature, potential and oxygen/water partial pressure, which provide insights into reaction mechanisms and active sites that govern the activity of oxygen electrocatalysis.
References
1. J. Suntivich, H. A. Gasteiger, N. Yabuuchi, Y. Shao-Horn. J. Electrochem. Soc. 157, B1263 (2010).
2. J. Suntivich, H. A. Gasteiger, N. Yabuuchi, H. Nakanishi, J. B. Goodenough, Y. Shao-Horn. Nature Chem. 3, 546 (2011).
3. J. Suntivich, H. A. Gasteiger, J. B. Goodenough, Y. Shao-Horn. Science, 334, 1383 (2011).
4. M. J. Kevin, C. E. Carlton, K. A. Stoerzinger, M. Risch, J. Suntivich, Y.L. Lee, A. Grimaud and Y. Shao-Horn, JPCL, 3, 3264 (2012).
5. Y.-L. Lee, J. Kleis, J. Rossmeisl, Y. Shao-Horn, D. Morgan. Energy & Environ. Sci. 4, 3966 (2011).
6. E. Mutoro, E.J. Crumlin, H. Pöpke, B. Luerssem, M. Amati, M.K. Abyaneh, M.D. Biegalski, H.M. Christen, L. Gregoratti, J. Janek and Y. Shao-Horn, JPCL, 3, 40 (2012).
7. E.J. Crumlin, E. Mutoro , Z. Liu , M. E. Grass , M. D. Biegalski , Y.L. Lee , D. Morgan , H. M. Christen , H. Bluhm and Y. Shao-Horn, EES, 5, 6081, (2012).

Oxides have shown high activity for the oxygen reduction and oxygen evolution reactions (ORR, OER), however a lack of fundamental understanding of the physical-chemical properties of these oxides has limited mechanistic understanding and optimal catalyst design. Although analytical and theoretical frameworks for the electronic structure of perovskites, such as e_g occupancy and O p-band center, have been shown to be good descriptors of ORR and OER activity^1,2, such frameworks have yet to be connected to experimental measurements of electron density of states (DOS). Electronic structure measurements of oxides have largely been accomplished through photoelectron spectroscopy, which probes total DOS and thus requires theoretical aid to resolve the transition metal 3d-DOS and anion 2p-DOS. Furthermore, photoemission only probes the occupied DOS, and few inverse photoemission measurements have been performed to provide complete information of both the valence and conduction bands of these oxides. We present a comprehensive investigation of the perovskite family, AA&’BO3, using a combination of soft x-ray absorption spectroscopy (XAS) and x-ray emission spectroscopy (XES). Through the combination of O K edge and M L edge spectra, we obtain detailed information regarding the transition metal and anion character of the occupied valence band DOS, as well as the unoccupied conduction band DOS. We experimentally verify trends in the electronic structure for differing chemistries, as well as their relation to catalytic activity.
1. J. Suntivich, H. A. Gasteiger, N. Yabuuchi, H. Nakanishi, J. B. Goodenough, Y. Shao-Horn. Nature Chem. 3, 546 (2011).
2. Y.-L. Lee, J. Kleis, J. Rossmeisl, Y. Shao-Horn, D. Morgan. Energy & Environ. Sci. 4, 3966 (2011).

A primary challenge limiting future grid-scale implementation of many renewable energy sources, is their inherent intermittency. This problem is notably acute for solar energy, prompting interest in energy storage technologies that are viable at very large scale. As an alternative to batteries, synthesis of fuels from sunlight is one promising option, and requires optimized photoelectrochemical devices and materials. In a prior report, [1] silicon photoanodes protected by atomic layer deposited (ALD) ultrathin TiO2 tunnel oxides and coated with a known oxidation catalyst (Ir) were demonstrated to achieve highly efficient water oxidation and to avoid Fermi level pinning that is typical of many electrolyte/semiconductor interfaces . With an optimized tunnel oxide, single-junction silicon devices can achieve a photovoltage exceeding 600 mV under one sun. In this presentation, we will report on the effect that varying the surface catalyst metal layer has on the water oxidation efficiency of these protected silicon photoanodes. In solid-state capacitance-voltage (C-V) measurements on metal-oxide-semiconductor capacitors composed of the same materials as in the nanocomposite photoanodes, varying the workfunction of the gate metal produces near-ideal shifts of the flat band voltage as well as C-V curves that suggest a low density of charge-trapping defects in the tunnel oxide structure. In addition, we will present a study of other water oxidation catalysts, including Ru and Pt, comparing their ability to mediate hole transport from the silicon substrate to redox couples in aqueous solution, and their overpotentials for water oxidation with results obtained for Ir. Oxidation of the catalyst layer and its effects on photoelectrochemical cell performance will also be discussed.

The assembly of semiconductor nanoparticles into mesoporous electrodes has enabled rapid advancements in solar cells and water splitting, although the ability to probe charge transport and correlate it with specific structural features has remained a challenge. In the present work, we develop an approach to understand charge transport in a porous nanocrystalline electrode assembled from hematite nanoparticles, which is a material that has attracted significant interest in water splitting. In our approach, we couple a new transmission electron microscopy (TEM) technique with conducting atomic force microscopy (C-AFM). The TEM technique maps the spatial distribution and relative orientation of nanocrystals within a large number of nanoparticle aggregates. Meanwhile, C-AFM provides information about the size, shape, and charge transport characteristics of distinct regions within each aggregate. By correlating TEM and C-AFM analyses, we deduce how nanocrystalline structure influences transport in individual nanostructures. The approach suggests that presence/absence of high angle grain boundaries governs long-range charge transport. To relate this observation to the photoelectrochemical properties of the electrodes, we have developed a model that describes how grain boundaries impact photo-induced charge transfer at the semiconductor/electrolyte interface. The new model describes three effects of the grain boundaries: (1) thermionic emission across potential barriers at grain boundaries decreases charge transport through the nanostructure; (2) the potential drop at the grain boundaries subtracts from the band bending at the semiconductor/electrolyte interface, thereby decreasing charge separation; (3) the decreased interfacial band bending fills traps at the hematie/electrolyte interface, thereby promoting recombination. The predictions of the model are in quantitative agreement with the experimental photocurrents. Our combined approach for assessing structure and charge transport at the nanoscale and its relationship to photocurrent provides greatly improved insight into the challenges associated with the use of polycrystalline, nanostructured semiconductors.

Recently, transition metal doped-TiO2 has gained attention as an earth-abundant, affordable catalyst for the oxygen evolution reaction (OER). To accurately deduce the influence of doping on the catalytic activity of the film, it is important to decouple doping&’s effects of activity versus conductivity of the TiO2. In this work, we study the effect of TiO2 thickness on the overpotential for OER. Thin films of TiO2 on glassy carbon electrodes were synthesized using atomic layer deposition (ALD), a vapor phase deposition method that is capable of creating conformal thin films with fine control over the film thickness. We show that the activity of the films for OER is strongly dependent on the thickness of the TiO2, with films thicker than around 6-10 nm showing a sudden decrease in activity. Electrochemical experiments using a reversible redox couple and a first principles metal-insulator-metal charge transport model of TiO2 thin films further confirm that changes in thickness of the TiO2 on a nanometer scale can have a dramatic impact on the charge transport. In any electrochemical reaction, the charge transport to the catalyst-electrolyte interface must support the electrochemistry at the interface. In the ALD-grown TiO2, very thin films are needed or else the effects of low electrical conductivity in the TiO2 severely limit the reaction, revealing how charge transport limitations can mask the intrinsic activity of a material. Hence, when comparing the activity of semiconducting catalytic materials, it is important to also consider the effects of charge transport.

III-V semiconductors have been studied as both anodes and cathodes for a variety of electrochemical reactions, most notably the hydrogen evolution and oxygen evolution reactions involved in solar-to-hydrogen electrolysis. In this work, the electrochemical behavior of InN thin films was investigated in two processes: as a cathode for the electrically driven reduction of H+ ions to H2 gas, and as an anode for the light driven oxidation of Ce3+ to Ce4+ ions. Single-crystal hexagonal n-type InN thin films were grown by RF plasma-assisted molecular beam epitaxy on GaN/sapphire templates. The structural and elemental qualities of these films were analyzed with high-resolution x-ray diffraction and x-ray photoemission spectroscopy. The cathodic behavior of InN was analyzed in an environment of aqueous H2SO4. Cyclic voltammetry and impedance measurements were used to construct the energetics of the semiconductor-electrolyte interface, with nonidealities such as the surface electron accumulation layer and material polarity taken into account. Stability testing confirmed the robustness of InN in extreme pH solutions. The anodic behavior of InN was analyzed in an environment of aqueous cerium sulfate. Cyclic voltammetry and impedance measurements under LED illumination at various wavelengths were used to analyze the photoelectrochemical properties of these films under various amounts of potential bias, including the light absorption, charge transport, and interfacial kinetics of the semiconductor-electrolyte junction. These studies pave the way for potential future work in incorporating InN semiconductors within both photocatalytic and dye-sensitized systems for solar energy conversion applications.

Tandem photoelectrochemical devices utilize two or more semiconductors to efficiently convert broadband illumination into electrons and holes for chemical reactions. Transport of reactants and light trapping can be improved in these devices by structuring the materials. However, when coupling materials with disparate electronic and optical properties, the optimal structure for each material is potentially very different. Here we outline a strategy to independently structure metal oxide layers on silicon scaffolds by electrodeposition with colloidal templates. This method can be used to reduce path lengths for minority carrier diffusion in a metal oxide photoanode and to improve light trapping in the device. Using colloidal templating and electrodeposition, we explore this strategy for hierarchical structuring of WO₃ photoanodes on Si microwire arrays. We describe photoelectrochemical and spectroscopic measurements on these superstructured photoanodes and consider their implications on future device design.

The hydrogen generation from the water splitting reaction driven by the visible light provides a direct method for converting the solar energy to clean, storable and transportable fuel energy. One key issue for realizing this method is to find the low-cost, high-efficiency and stable semiconductor as the photoelectrode. Although there are plenty of study on tuning the electronic structure and optical properties of photoelectrode semiconductors to improve their light absorption and thus the efficiency, it is currently short of a universal way to predict the stability of the photoelectrode in the aqueous solution. Actually the photo-generated electrons (holes) can not only reduce (oxidize) water to drive the hydrogen (oxygen) evolution, they can also reduce (oxidize) the photoelectrode itself and cause the photocorrosion. In this work, we demonstrate that the reduction and oxidation potentials of any compound semiconductors can be calculated ab initio and compared with the water redox potentials, based on which their thermodynamic stability against photocorrosion in aqueous solution can be predicted directly and quantitatively.
According to the calculated potentials for more than 30 popular photocatalytic semiconductors, including metal oxides (Cu2O, Fe2O3, TiO2, WO3, BiVO4, etc), non-oxides and doped metal oxides (TaON, GaN, GaP, GaAs, Cu2ZnSnS4, Si, etc), we identified two trends in their stability: (i) only the oxide semiconductors are thermodynamically stable against oxidization, and all the non-oxides or even oxynitrides are susceptible to the oxidation by the photo-generated holes, (ii) many non-oxides are stable against the reduction by the photo-generated electrons, while some oxides are not. This can guide the future design of the stable photoelectrode semiconductor, and highlight the importance of the protection from the photoreduction and photooxidation for different classes of photoelectrodes.

Rational design of membrane electrode assemblies (MEAs) or catalyst coated membranes (CCMs) for polymer electrolyte membrane fuel cells (PEM-FC) requires an evaluation of the actual local component distributions in the porous electrodes, both for virgin and post-operational samples. Such postmortem structural analysis can provide insights into control and optimization of the fabrication process, as well as material modifications and degradations pathways happening either during fabrication or during operation. As a compliment to existing microscopy and microanalysis techniques (TEM, SEM, EDX, XPS) we are using scanning transmission X-ray microscopy (STXM) which uses the intrinsic near edge soft X-ray absorption fine structure (NEXAFS) signal to quantitatively map chemical components at better than 30 nm spatial resolution [1,2]. In particular, STXM is used to map the ionomer, carbon support and catalyst components [3-6], as well as porosity, in 2D and 3D [7]. Comparisons of results from PEM-FC produced using different materials, and different fabrication methods, before and after degradation tests [3] have all proven useful. A detailed description of our methodology, along with examples of studies of local component distributions in postmortem fuel cell samples as well as virgin MEAs, CCMs and raw components will be presented.
1. D. Bessarabov and A.P. Hitchcock, Membrane Technology 6 (2009) 6.
2. A.P. Hitchcock, Chapter 22 in Volume II of Handbook on Nanoscopy, eds. Gustaaf Van Tendeloo, Dirk Van Dyck and Stephen J. Pennycook (Wiley, 2012) 745-791.
3. V. Berejnov, Z. Martin, M. West, S. Kundu, D. Bessarabov, J. Stumper, D. Susac and A.P. Hitchcock, Phys. Chem. Chem. Phys. 14 (2012) 4835.
4. V. Berejnov, D. Susac, J. Stumper and A.P. Hitchcock, ECS Transactions 41 (2011) 395.
5. D. Susac, V. Berejnov, A.P. Hitchcock and J. Stumper, STXM Study of the Ionomer Distribution in PEM Fuel Cell Catalyst Layers ECS Transactions 41 (2011) 629.
6. D. Susac, V. Berejnov, A.P. Hitchcock and J. Stumper, STXM Characterization of PEM Fuel Cell Catalyst Layers, ECS Transactions 42 (2012) in press
7. V. Berejnov, D. Susac, J. Stumper and A.P. Hitchcock, 3D Chemical Mapping of PEM Fuel Cell Cathodes by Scanning Transmission Soft X-ray Spectrotomography, ECS Transactions, 42 (2012) in press

Proton-conducting sulfonated aromatic polymers are well-known electrolyte membranes for proton exchange membrane fuel cells. The recent development of micro fuel cells relies on the accomplishment of suitable thin proton-conducting polymer membranes. The conformal deposition directly on supporting electrodes is another asset for reducing the cost of this technology.
We have achieved the one-pot electrodeposition of Sulfonated Poly-Phenyl-Oxide (SPPO). The electrolytic solution used for electrodeposition contains sulfonated phenol in sulfuric acid as supporting electrolyte. The deposition of micron-thick polymer films is achieved in around one hour. The structure and properties of the films were investigated by X-Ray diffraction, scanning electron microscopy and EDX, FTIR, NMR and impedance spectroscopies. The degree of sulfonation is about 0.5 and the proton conductivity at 25°C is about 3 mS/cm. These values can be improved by using stronger sulfonation conditions for the precursor phenol.
Altogether, this work opens perspectives for conformal deposition of proton-conducting polymers.
Reference
H. Hou, F. Vacandio, M.-L. Di Vona, P. Knauth, Sulfonated polyphenyl ether by electropolymerization. Electrochimica Acta, 81, 58-63 (2012).

Polymer electrolyte fuel cells have the potential to provide cleaner and more efficient energy. Often, current polymer electrolyte membranes for these fuel cells are limited in terms of their operating conditions, especially with regard to humidity and temperature. By using different polymers than have been traditionally used, more versatile operating conditions and better efficiencies may be achieved. Because many different properties are needed for an effective polymer electrolyte membrane, multiple polymers often need to be used. Also, these multi-polymer systems often lead to phase separation and self-assembly that can greatly impact material properties. Aromatic polyimides are known to be very stable, both thermally and mechanically. Poly (ethylene glycol) (PEG) has been known to provide proton conduction properties under certain conditions. In the current work, aromatic polyimide and PEG composite membranes have been synthesized for fuel cell polymer electrolyte membrane applications. The goal is to exploit the drastically different properties of the polymers and understand how the structure of this hybrid material relates to the conductivity. The polyamic acid precursors to these polymers were synthesized by a random, one pot poly-condensation method that has been shown to work for many polyamic acids. The PEG (Mn 1500) was used in pre-polymerized form and incorporated in the polyamic acids through chemical bonding to achieve structural self-assembly. These polymer systems were converted to polyimide-PEG systems through thermal imidization. This thermal processing can achieve a variety of material properties easily if varied. Composition and morphology of these hybrid systems was varied to create a family of materials. The polyamic acid precursors and polyimides were characterized using Fourier transform infrared spectroscopy. Thermal properties of the films were analyzed using thermal gravimetric analysis. Small angle x-ray scattering was used to determine the polymer structure on a length scale between 0.5 and 80 nanometers, because it has been shown that features on this length scale can often lend themselves to governing material properties. Understanding exactly how these structures are correlated with material properties is important for these polymer systems. Since acids are often needed to provide any significant conduction properties for polymers, phosphoric acid was incorporated into the films by soaking. The films were then analyzed for protonic conductivity properties using impedance in conjunction with cyclic voltammetry. Effects of temperature and humidity were studied with regards to conductivity. These composite systems were analyzed in order to determine composition-structure-property relationships for fuel cell membrane applications. Composite or hybrid systems are often studied for structure, or properties, but rarely is the relationship between structure and properties well understood.

Ultra-thin Nafion films of thickness less than 100 nm are model systems for studying the properties of this interesting class of ionomers in the active component of functional electrochemical devices such as polymer electrolyte fuel cells, polymer electrolyte water electrolyzers, sensors, and artificial photosynthesis system. Many factors influence the structure and properties of these films including preparation method, post-preparation thermal treatment (annealing), parent solution, and substrate characteristics. Our group has successfully prepared self-assembled Nafion films of thickness ranging 4nm to 300 nm on thermally grown SiO2 on Si-wafer. The films exhibit thickness-dependent protonic conductivity, free surface wettability, and water uptake. GISAXS measurements also reveal some of these differences. Most recently, we have focused on the influence of thermal annealing and substrate. This talk will discuss our findings on the ultra-thin Nafion films.

Solid proton conductor membranes have many high technological applications, including hydrogen generation by water electrolysis, hydrogen and direct methanol fuel cells, electrochemical chlorine production and redox flow batteries (“open batteries”).
The membrane is one of the key components of open batteries. It physically separates the positive and the negative solutions and prevent cross-mixing of the half-cell electrolytes. The future application of this type of technology depends greatly on the enhancement of the polymer electrolyte membrane stability and durability.Most importantly, it must operate in an aggressive environment under harmful experimental conditions, and it must present a reduced permeability. In general, anion exchange membranes show lower permeability than cation exchange membranes. Unfortunately, most of commercial anion exchange membranes do not have sufficient chemical stability and present high water transport.
The most promising group of ion exchange membranes, alternative to Nafion, is that of Aromatic Polymers (AP). We have in recent years concentrated on improvement of existing AP, introducing Van der Waals bonds (organic-inorganic hybrids) or covalent bonds (“cross-links”).The formation of cross-links is a well-established technique to improve the performances of polymers, used in a variety of applications. A direct cross-linking reaction performed in situ during the casting procedure is an interesting and promising methodology to obtain stable and long-life membranes.For example thermally treated membranes can resist in water also at 145 °C without significant swelling, having a higher Young modulus than untreated ones, with remarkable conductivity. These improved functional properties are of great interest in electrochemical applications and are related to the formation of covalent cross-links between macromolecular chains occurring by an electrophilic aromatic substitution. The presence of cross-linking can be of fundamental importance for anion exchange membrane that suffer of insufficient stability. In this contribution anionic membranes based on cross-linked PEEK and PPSU will be presented and their characterization by means of FTIR, NMR and UV/Vis spectroscopy and conductivity will be illustrated.