Graphite is the most commonly used anode material for commercial lithium ion batteries and has been very well studied. The excellent properties of graphite are due primarily to the robust solid electrolyte interphase (SEI). Consequently, numerous studies have been conducted to study these properties utilizing various techniques. Many of these techniques such as EDS, XRD, and TGA, are unable to resolve subtle changes in these thin SEI films due to their large information depths. [1,2] Due to these problems analyses using high spatial resolution have been applied using XPS and TOF-SIMS to observe the chemical and concentration gradients of these complex SEI films on the nanometer scale and as a function of their cycle life. This research analyzed commercially available electrodes composed of a graphite anode, nickel manganese oxide cathode, and PC:EC:DEC 1:1:3 with LiPF6 electrolyte at three stages of cycling. Cell 1 experienced only formation process to form a protective solid electrolyte interface film on the surface of graphite electrode. Cell 2 stored 14 days at 10 % of state of charge (SOC) at 25°C and then 700 cycles with 50-100% of SOC at 45°C and Cell 3 had 495 cycles with 0-50% of SOC at 45°C and had additional 1317 cycles with 50-100% of SOC at 45°C. Once cycled, these cells were opened in an argon glovebox and the anode material was prepared without cleaning to avoid removal of the SEI or dissolution of ionic species. Samples were mounted using carbon tape and transferred to the analysis chamber with < 1 minute of exposure to air. XPS depth profiling was performed using a Thermo K-Alpha (Al Kα peak) with an 1000keV Ar+ ion beam. TOF-SIMS depth profiling was performed using an Ion- ToF-SIMS5-300 configured with a 25keV Bi+ primary liquid metal ion gun. The sputter rates for TOF-SIMS and XPS were calibrated vs. a 100 nm layer of SiO2 grown on a Si wafer. SEI thickness was measured by FIB/SEM as well as the C+ profile and graphitic carbon in TOF-SIMS and XPS respectively and was found to be ~150 nm thick and grow by 50nm after cycling. The ionic concentration of Mn+ was observed to be inhomogeneously distributed within the SEI which may be used to estimate the Mn+ dissolution and migration behavior in anode materials. Acknowledgement: This work was partially supported by the American Honda Motor Co., Inc. References [1] E. Peled, D. Golodnitsky et al, “Composition, depth profiles and lateral distribution of materials in the SEI built on HOPG-TOF SIMS and XPS studies,” Journal of Power Sources, vol. 97-98, pp. 52-57, Jul. 2001. [2] H. Ota, Y. Sakata, A. Inoue, and S. Yamaguchi, “Analysis of Vinylene Carbonate Derived SEI Layers on Graphite Anode,” J. Electrochem. Soc., vol. 151, no. 10, p. A1659-A1669, Oct. 2004. [3] J. Benson, N. Nitta, J. T. Lee, A. Magasinski, I. Kovalenko, T. Fuller, and G. Yushin, “Comparative Study of the SEI on Graphite in Full Li-ion Battery Cells Using XPS, SIMS, and Electron Microscopy,” submitted 2012.

Layered Transition Metal Dichalcogenides (LTMDs) can be exfoliated to atomically thin 2D nanosheets. The monolayered 2D nanoshseets have dramatically interesting properties. MoS2 can be exfoliated chemically via lithium intercalation and the properties are significantly different from the bulk material as well as mechanically exfoliated MoS2 [1]. We have investigated the influence of the chemical exfoliation parameters on the electro-catalytic performance for various LTMDs. Specifically, we have measured the hydrogen evolution reaction (HER) properties of LTMDs. We have found that chemical exfoliation leads to a dramatic enhancement of the HER catalytic properties and we have observed that this improvement is correlated to modifications of the atomic and electrronic structure of LTMDs due to the chemical exfoliation. Density functional theory calculations confirm that the highly strained structure induced by the atomic displacement during the lithium intercalation has a great influence on the ability of these LTMDs to evolve hydrogen at low overpotential. [1] Eda, G. et al. Nano Lett. 11, 5111-5116 (2011).

Zinc is an attractive material for energy storage since it is both inexpensive and energy dense (both gravimetrically and volumetrically). Zinc based energy storage has already been proven to exhibit high cyclability in rechargeable zinc-flow batteries and has exhibited high energy densities in primary zinc-air batteries. The zinc electrode, however, is typically the limiting electrode in rechargeable applications since detrimental morphologies such as dendrites can form during deposition leading to reduced cyclability. This research focuses on understanding the dynamics of the zinc deposition and dissolution processes in both aqueous alkaline electrolytes and ionic liquid based electrolytes. The goal of this research is to link the early nucleation and growth behavior to the formation of detrimental morphologies. This research couples three in-situ analysis techniques: electrochemical optical microscopy (EC OM), electrochemical atomic force microscopy (EC AFM) and electrochemical ultra-small-angle x-ray scattering (EC USAXS). These in-situ analysis techniques are complimentary in terms of length and time scales accessible and allow for the analysis of zinc deposition and dissolution from the sub-nanometer to micron regime. From the AFM analysis, feature shapes, aspect ratios, and size distributions were quantified and these results were used to build the model that analyzed the USAXS scattering data. Subsequent ex-situ SEM characterization was conducted to verify the morphologies observed by the in-situ techniques during deposition. This talk also compares and contrasts the deposition behavior of zinc within an aqueous alkaline electrolyte and within an ionic liquid electrolyte. Portions of this work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

We previously demonstrated a battery fabricated from polypyrrole (pPy) doped with redox active dopants.[1] This battery was shown to deliver higher energy density than that of commercial electric double-layer capacitors at high power demands. This battery consisted of pPy doped with ABTS (pPy[ABTS]) and pPy doped with indigo carmine (pPy[IC]) forming the cathode and anode respectively, with a cell emf of 0.5 V. Other candidates for cathode and anode dopants are being considered to increase the cell emf. Viologens or 4, 4&’-bipyridine derivatives are versatile compounds with three different oxidation states (i.e., V0, V+. and V2+).[2] They are known for their negative redox potentials and rapid rates of electron transfer, and thus are good candidates for increasing the cell emf of the original battery when used in the anode. Typical examples include benzyl and methyl viologens, which have reversible redox chemistries centered at -0.5 and -0.9 V (vs.SCE).[2] Different approaches have been used to incorporate viologens into a polymer matrix,[3, 4] although previous reports did not utilize the redox capacity of viologens for energy storage. We report on the stability and performance of films of conducting polymers (CP) containing viologen molecules, bound either by electrostatic or covalent means. To incorporate electrostatically a viologen molecule as an anionic dopant to a polycationic pPy, it structure must be modified to possess sulfonate groups (i.e. a disulfonated viologen[5] or a tetra-sulfonated viologen). This structural modification ensures that viologen is anionic during electropolymerization of the CP and hence incorporated into the polycationic matrix. Alternatively, viologens can be attached directly to the pyrrole monomer via covalent linkage to an N-substituted pyrrole.[3] This viologen substituted pyrrole monomer was then electropolymerized to obtain a polymer film to be used as the anode. All polymer films exhibited the distinct redox activity of the viologen dopant, however the covalent composite exhibited the best charge-discharge behavior as determined by galvanostatic testing with a maximum capacity of 55mAh/g. References 1. H.K. Song et al, Adv.Mater., 18 (2006) 1764-1768. 2. C.L. Bird et al, Chem.Soc.Rev.10 (1981) 49-82. 3. M.S. Wrighton et al, J.Phys.Chem., 92 (1988) 5221-5229. 4. G. Bidan et al, J.Chem.Soc.Chem.Commun., (1984) 1185-1186. 5. Y. Kawanishi et al, J.Phys.Chem., 90 (1986) 2469-2475

A metal/air battery is one of the promising candidates for a next generation of secondary battery which is possible to show higher energy density than current lithium ion batteries. Especially, the air battery using a metal hydride negative electrode and an alkaline aqueous solution, i.e., metal hydride/air battery, is expected to show such a high energy density and maintain safety even though the capacity increases, because the negative electrode uses no less noble metal such as lithium, sodium, or magnesium. This paper presents our recent results of metal hydride/air secondary batteries using an alkaline aqueous solution with a metal hydride negative electrode and a nickel-based air electrode. The negative electrode consisted of MH powders supported by a nickel form, and the air electrode was a mixture of nickel powders, bismuth-iridium composite oxide as catalyst, and PTFE binder. The cell comprising a single negative electrode, a single positive electrode, and a separator with an alkaline solution was examined at constant current at ambient atmosphere, and the polarization behaviors and cycling performance were discussed. The results indicated some excellent properties for charge-discharge cycles such as high energy density more than 400 Wh/L and stable voltages for 300 cycles or more. The capacity of the examined cells depended only on the negative electrode capacity, suggesting that the metal hydride/air battery has no limitation on the positive electrode capacity, because no plugging by discharge product occurs. This was quite different from the other air batteries using less noble metals and a particular feature of metal hydride/air batteries. This paper will also present the results of the cells comprising double positive electrodes and a single negative electrode between them.

Vanadium redox flow batteries (VRFBs) have emerged as a novel energy storage technology with great promise for grid-scale energy applications due to their high energy efficiency (70-85%) and long cycle life (12,000+ cycles). The power density of these systems is limited by the performance of the electrodes used in each half cell. Among currently studied electrode materials, carbon felt is of particular interest because of its high surface area and relatively low cost. The carbon felts are functionalized with thermal and acid treatments to increase their performance in VRFBs. To date, the performance of functionalized carbon felt electrodes has been studied only in symmetric configurations, where identical electrodes are used in positive and negative half cells. In this study, the performance of a VRFB in asymmetric electrode configurations is measured with raw and functionalized electrodes. A base case of functionalized electrodes in both half-cells was chosen for comparison since this combination is observed to provide the best performance. When the positive electrode in the base case is replaced with a raw felt, the efficiency is found to be comparable to that of the base case. However, when the negative electrode in the base case is replaced with a raw felt, a significantly lower efficiency is observed, suggesting that the negative electrode is limiting the performance. To determine the reason for this drawback, cyclic voltammetry is used to measure the reaction kinetics at raw and functionalized electrodes. At a specific electrode, the reaction rate constants are found to be roughly the same for the negative and positive half-cell redox reactions. However, the potential required for the reduction reaction at the negative electrode is observed to cause hydrogen evolution, which reduces the performance of the cell. The reaction kinetics data suggests that the lower negative electrode performance is not due to a slower reaction rate, but rather because of the presence of hydrogen evolution.

Vanadium redox flow batteries (VRFBs) are an emerging technology for grid-scale energy storage applications because the energy and power densities are decoupled, which enables scalable energy storage with the potential for high energy efficiency (70-85%) and long cycle life (12000+ cycles). However, currently the long-term performance of these batteries is severely limited due to the crossover of vanadium ions through the membrane. Species crossover leads to the depletion of vanadium ions in one half-cell, which reduces the system&’s overall capacity (available charge) with each cycle, and presents a major obstacle to widespread implementation of VRFBs. Most of the efforts to reduce crossover, both experimental and computational, are focused on tailoring the structure and properties of the membrane to reduce the vanadium crossover across the membrane. In this work, a transient, two-dimensional, VRFB performance model is developed that accounts for convection, diffusion, and migration across the membrane. By incorporating all these three transport modes, this model allows for more accurate predictions of the capacity loss experienced during long-term performance. Using the model, different case studies are conducted and the relative contributions of each transport mechanism are determined. The results of long-term performance studies show that convective transport in particular contributes significantly to the capacity loss during VRFB operation. To reduce the impact of convective transport on the species crossover, different electrolyte management strategies are explored.

Flow batteries are a potentially important technology for grid-scale electrical energy storage in the face of rising electricity production from intermittent renewables like wind and solar. Many chemistries and configurations could be used in the operation of a flow battery, and this presentation will focus on some that we find particularly promising. We have developed novel alloy oxide electrocatalysts that have permitted the development of a hydrogen-chlorine flow battery with power densities exceeding 1 W/cm2 with a precious metal loading of about 0.1 mg/cm2. The cell exhibits virtually no activation loss, allowing for very high efficiency operation. The effects of varying operating parameters and cell design will be discussed, along with substantive comparisons to a quantitative model of this device. Alternate chemistries, including the use of small organic molecules in a flow battery setup, will be discussed, highlighting some promising preliminary results from our lab. The advantages of using such compounds will be shown.

Electrochemical supercapacitors have high energy density with an excellent reversibility, and operate at greater specific power than most rechargeable batteries. Therefore, research has been focused on improving the novel materials, and methods to enhance the operation of supercapacitors. Activated carbon metal oxides (manganese oxide ‘MnO2&’ and ruthenium oxide ‘RuO2&’) take advantage over conducting polymers for their stability. Mixing conducting polymers and metal oxides has recently been investigated to understand the behavior and stability of the hybrid supercapacitor. This research project focuses on supercapacitor electrodes coated with MnO2 and graphene (G)-MnO2 synthesized materials. The G-MnO2 and MnO2 nanomaterials were synthesized using sol-gel technique. The MnO2 and G-MnO2 materials were characterized using electrochemistry, Scanning Electron Microscopy (SEM), Raman spectroscopy, X-ray-diffraction, and Transmission Electron Microscopy (TEM) techniques. The synthesized G-MnO2 and MnO2 powder were mixed with nafion and coated on graphite electrodes. The cyclic voltammogram, charging-discharging, stability and life cycle of the various MnO2 and MnO2 materials were studied in supercapacitor configurations. This study provides a fundamental understanding for high performance synthesized MnO2 as well as G-MnO2 material. The high specific capacitance and stable charging -discharging cycles have been observed in G-MnO2 containing equal ratio of graphene to MnO2. This study provides a fundamental understanding of supercapacitor applications for high performance synthesized MnO2 and G-MnO2 nanoparticles. Based on our experimental data shown in this work, we believe that G-MnO2 material could be exploited for commercial purposes.

Supercapacitors offer high energy density electrochemical charge storage without the necessity of Faradaic charge transfer processes. In contrast to batteries, they can be cycled hundreds of thousands of times with minimal performance losses.1 One of the major factors limiting the longevity of batteries is caused by the significant strains induced during intercalation processes.2 Supercapacitors store charge in the electrochemical double-layer and therefore should undergo little to no mechanical fatigue. However, numerous electrochemical dilatometric studies3-5 have indicated that the carbonaceous electrodes employed in supercapacitors can exhibit strain on the order 1 to 10 %. Such strain processes can lead to diminished lifetime. These strains are believed to be attributed to meso and micropore swelling during charge/discharge cycles. Other studies have identified intercalation processes as possible explanations for the larger than expected volume expansion. Electrochemical dilatometry is a useful tool to observe large changes in material volume during cycling. However, these measurements are performed on relatively large working electrode areas, precluding any microscopic volume changes (i.e. changes to volume on individual grains or pores). Such information would be valuable in diagnosing potential failure or cell lifetime issues. Scanning probe microscopy (SPM) is capable of measuring surface deformations as small as 10s of picometers, thus offering a promising avenue to study minute volume changes in supercapacitor materials. Additionally, the lateral resolution of modern AFM instruments is sufficient to resolve individual grains and defects. Therefore we are capable of measuring very small volume expansion on single particles or defects. Here, we investigate Carbide Derived Carbon (CDC)6 supercapacitor electrodes by in situ SPM methods. The CDC films are placed in an in situ AFM electrochemical cell and cycled during AFM topographical measurements. The volume change that occurs as a result of cycling is evident in the topographical image, allowing us to investigate the kinetics of double layer formation. This allows us to study the role of ion intercalation as it pertains to the observed volume changes and separate it from that of double-layer formation. Additionally, ion size effects on pore/particle swelling can also be investigated by these methods. This talk will highlight our recent findings. Research at ORNL was supported by the Fluid Interface Reactions, Structures and Transport (FIRST) Center, ORNL, an Energy Frontier Research Center funded by DOE, Office of Science, Office of Basic Energy Sciences (ERKCC61). Work was conducted at the Center for Nanophase Material 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.

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, electrolyzers and batteries. In aqueous electrolytes, depending on the nature of the reacting species, the supporting electrolyte, and the metal 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 metal-electrolyte two phase interfaces. 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 of electrochemical 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.

Core-shell catalysts have attracted significant attention for various chemical reactions due to their higher utilization of costly noble metals, activity improvement caused by electronic and structural effects from the core materials.Recent studies have demonstrated that the ORR activity of Pt monolayer can be further tuned by an interlayer. For instance, with a Pd9Au alloy sublayer between Pt monolayer and Pd nanoparticle, the ORR activity can be enhanced by 70%. The role of the sublayers in the activity enhancement is unclear. We report here the ORR activity improvement on Pt monolayer supported on conventional Pd nanoparticles by introducing an Au submonolayer (~60% coverage) between the Pd core and Pt shell. The activity of Pt/Au/Pd/C is ~2 and 7 times higher than that of Pt/Pd/C and Pt/C, respectively. By controlling the shape (cubic and octahedral) of the Pd cores, we are able to distinguish the role of Au on the activity improvement at different facets. Our results demonstrate that the Au interlayer can enhance the Pt monolayer activity toward oxygen reduction on both (100) and (111) surfaces, with the enhancement on (100) much more pronounced. The density functional theory (DFT) calculations were conducted to explain this observation and will be discussed in the meeting.

One of the main barriers to the commercialization of fuel cells is the catalysts which generally consist of Pt-based precious metals. Since Pt is costly and scarce, it poses the question of how to lower the Pt loading and increase its efficiency. Most previous studies focused on Pt alloyed with some 3d-transition metals, such as Fe, Co, Ni, etc. However, the activity and stability are not good enough for fuel cell applications. Recently, ordered intermetallic nanoparticles have attracted some attention, since the ordered intermetallic phase provides definite composition and structure. They can provide predictable control over structural, geometric, and electronic effects, which are not afforded by alloys. However, previous reports on ordered intermetallics were focused on anode catalysts. In addition, the synthesis procedures tend to be complex. Moreover, the particles are unsupported and it is not easy to clean the particle surface. We present data on carbon supported ordered intermetallic nanoparticles that can be easily formed using a simple impregnation-reduction method followed by high temperature treatment. We will discuss two main subjects in this talk: (1) Structurally ordered intermetallic Pt3Co@Pt/C Core-Shell nanoparticles as oxygen reduction reaction (ORR) catalysts, and (2) Dealloying study of Cu3Pt/C ordered intermetallic nanoparticles for ORR catalysis. For Pt-Co nanoparticles, ordered Pt3Co intermetallic cores with a 2-3 atomic-layer thick platinum-rich shell were found according to electron energy loss spectroscopic (EELS) mapping. These nanoparticles showed over 200% increase in mass activity and over 300% increase in specific activity when compared to disordered Pt3Co alloy nanoparticles for the ORR. Stability tests showed a minimal loss of activity after 5,000 potential cycles and according to EELS mapping the ordered core-shell structure was maintained virtually intact. Two dealloying methods (electrochemical and chemical) were implemented to control the atomic-level morphology and enhancing the performance for the ORR. It was found that the electrochemical dealloying method resulted in formation of a thin Pt skin of ca. 1 nm with an ordered Cu3Pt core structure, while the chemical leaching gave rise to a spongy structure, with no ordered structure being preserved. Both dealloying methods yielded enhanced specific and mass activity toward the ORR and higher stability relative to Pt/C. The chemically dealloyed nanoparticles exhibited better mass activity than electrochemically dealloyed particles after 50 potential cycles, although with a slight lower specific activity. In both cases, there wea an enhancing in activity even after 5000 potential cycles. These findings are important to build next-generation fuel cell catalytsts.

Pt-M (M is an element less noble than Pt) alloy catalysts are a useful pathway to reduce the amount of Pt needed to adequately catalyze the slow oxygen reduction reaction (ORR) at the cathode of proton exchange membrane (PEM) fuel cells. The Pt-M alloy catalysts have the potential to lower the Pt cost per vehicle from the current level of several thousands of dollars (calculated from a Pt-metal catalyst with a mass activity of 0.1 A/mgPt at 900 mV vs. reversible hydrogen electrode) to levels acceptable for mass production of PEM fuel cell vehicles. Interactions between Pt and M in the form of geometric and/or ligand effects are believed to be responsible for the enhanced activity of Pt-M alloy vs pure Pt catalysts. To finely tune the geometric and ligand effects for the maximum activity, Pt-M alloy catalysts have been engineered into small particles (a few nanometers) with complex chemistry and microstructure. In this presentation, we will first review examples of various types of Pt-M alloy catalysts that have been studied in our labs. We determined the Pt shell thickness and the distribution of Pt and M within the Pt-M alloy nanoparticles by using atomic-scale compositional mapping based on electron energy loss spectroscopy (EELS) in an aberration-corrected scanning transmission electron microscopy (STEM). We also determined the interior structure of the Pt-M alloy nanoparticles and their dispersion on the catalyst support by using 3-dimensional tomography in the STEM mode. We will then discuss and comment on the links between the fundamental findings and their practical relevance to the performance enhancements and Pt-loading reduction in fuel cell vehicles.

Recent progress on alkaline anion-exchange membranes that conduct the negatively charged OH- has opened up the way to further develop direct alkaline fuel cells. Electrocatalysis of redox reactions is facilitated in alkaline electrolytes because, unlike in acidic media, there is a minimum poisoning thanks to weak bonding of the chemisorbed intermediates on the catalyst surface [1]. Alkaline fuel cells are economically more advantageous because of the abundant and cheap non-precious metal catalysts. Ethanol is an attractive fuel for direct ethanol fuel cells due to its high energy density (8.30 kWh kg-1) and its ease in handling and production from the biomass. The state of the art electrocatalysts for ethanol oxidation in both alkaline and acidic media still lack the capability to cleave the C-C bond at low temperature, and produce CO2 as a final product [2]. Ammonia is considered a major toxic pollutant of domestic, industrial and agricultural waters and its removal is very essential for ecological reasons. Additionally, anhydrous liquid NH3 is a compact H2 carrier as well as a distribution and storage medium. It can be directly used as a fuel in direct ammonia fuel cells as the theoretical specific charge of complete ammonia oxidation to N2 is 4.75Ah/g that is 95 % of the charge of methanol oxidation to CO2. The requirements of recent electrochemical studies to oxidize ammonia consist on finding high-performance electrocatalysts with low overpotential and low production of NOx and COx. While platinum group metals (PGM) and its bi-metallic alloys (e.g. PtIr, PtRu, PtPd, PtSnO2) exhibit the highest degradation strength and stability towards this process [3,4], their application at industrial scale is limited due to economical constraints, and therefore, there is an urgent need to utilize non-PGM catalysts. The aim of our current projects is to investigate the electrooxidation of ethanol and ammonia on NixPd1-x nanoparticles in alkaline media. To achieve this goal our strategy is (i) to synthesize predominately Ni-based bimetallic nanoparticles of uniform size and well-defined composition and structure (ii) use SEM/TEM, XRD, and XPS for their morphological and surface characterization and (iii) use electrochemical methods to evaluate the catalytic performance of the products with real-time monitoring of the electrooxidation reactions by in situ PM-IRRAS. The wealth of information from these experimental techniques is coupled with surface-decomposition DFT calculations for deeper understanding of the reaction network and prediction of the best electrocatalysts. [1] Beden, B.; Leger, J. M.; Lamy, C. In Brockris, J. O., Conway, B. E. and White, R. E., Eds.; Modern Aspects of Electrochemistry; Plenum Press: New York, 1992; Vol. 22, pp 97. [2] Yu, E. H.; Krewer, U.; Scott, K. Energies 2010, 3, 1499-1528. [3] Vitse, F.; Cooper, M.; Botte, G. J. Power Sources 2004, 142, 18-26. [4] Endo, K.; Katayama, Y.; Miura, T. Electrochim. Acta 2005, 50, 2181.

The characterization of oxide catalysts is often limited by heterogeneity of exposed surfaces and the composite nature of electrodes within fuel cells [1]. Epitaxial thin films can provide well-defined surfaces of known orientation, the nature of which can be tuned through interaction with the substrate, via strain and variation of the electronic structure [2]. We have fabricated (001) epitaxial films of LaMnO3 on Nb-doped SrTiO3 and investigated the relationship between film thickness and catalytic activity for the oxygen reduction reaction (ORR) in an alkaline environment. The activity decreases with film thickness; electrochemical measurements using the facile redox couple [3] [Fe(CN)6]3-/4- suggest that this trend is related to the ability to inject charge, arising from changes in the electronic structure of the film. Below a critical thickness around 10 nm, we observe distinct changes in film capacitance and interaction of the LaMnO3 with water. References: [1] J. Suntivich, H. A. Gasteiger, N. Yabuuchi, and Y. Shao-Horn, J. Electrochem. Soc. 157, B1263 (2010). [2] J. Fujioka, M. Nakamura, M. Kawasaki, and Y. Tokura, J. Appl. Phys. 111, 016107 (2012). [3] P. Chen, M. A. Fryling, and R. L. McCreery, Anal. Chem. 67, 3115 (1995).

Compared to the well-known proton exchange membrane fuel cells (PEMFC), alkaline fuel cells (AFCs) offer high degree of versatility both in terms of fuels and electro-catalysts. In addition to hydrogen, economically viable small organic molecules such as methanol and ethanol can be potentially used as fuels as their oxidation has been indicated to be enhanced in alkaline media. Also, instead of traditional platinum-based catalysts, less expensive metals such as silver could be used. However, AFCs have been plagued by carbonation wherein there is buildup of solid carbonate in the porous matrix saturated with base. This leads to loss of ionic conductivity and eventual device failure. Use of alkaline anion exchange membrane (AAEM) as the ion conducting medium can potentially counter carbonation due to the absence of mobile cations in the membrane. AAEMs are, thus, critical to the realization of high performing alkaline fuel cells. However, fundamental studies on this new class of functional polymer materials are yet to be carried out. In our study, we have extensively characterized a prototypical quaternary ammonium based AAEM material. In a systematic approach, categorical studies focusing on various fundamental aspects of a practical AAEM have been carried out: (i) Physical transport - Movement of molecules through the membrane was investigated by rotating disc electrode (RDE) voltammetry using neutral probe molecules. (ii) Charge transport - Charge conduction pathways through the network of cationic ion-exchange sites were probed electrochemically using negatively charged redox probe molecules. (iii) In-situ determination of carbonate formation - Electrochemical quartz crystal microbalance studies were conducted to test for carbonate uptake in the membrane. A complimentary study focusing on the swelling of the membrane in water and in presence of fuels such as methanol using acoustic impedance spectroscopy was also undertaken. (iv) Fuel cell testing - Preliminary device testing was also carried out with membrane electrode assemblies constructed using the AAEM material. This study represents an essential step in our understanding of a class of functional polymer materials that is poised to become one of the critical components driving future energy technologies, specifically alkaline fuel cells.

Anion exchange membranes (AEMs) open an exciting door for the development of non-Pt group metal (PGM) catalysts in fuel and electrolysis cells. Operation in alkaline media enables overcoming the “stability criterion” problem of the acid analog, which restricts its use to PGM catalysts. AEMs allow the use of inexpensive transition metal (TM) catalysts for both hydrogen evolution/oxidation reactions (HER/HOR) and oxygen evolution/reduction reactions (OER/ORR). Activity of TM electrodes relative to PGM is a function of several factors including inner/outer sphere charge transfer, changes in coverage of spectator ions and changes to the nature of the transition state. At a certain performance barrier, the cost per kWh or kgH2 will undoubtedly out-compete PGM electrocatalysts. The low cost and abundance of TM catalysts should pave the way for the commercialization of clean portable power devices. Water electrolyzers can produce H2(g) for ~$5/kg, slightly more than the comparable metric of $/gal gasoline, largely due to expensive PGM catalysts required. The development of Ni-alloy electrocatalysts will significantly decrease this cost. Although the OER is the primary source of overpotential in PEM electrolyzers, this may not be the case for AEMWEs. Pletcher et al. (PCCP 2010) have observed excellent OER activity from electrodeposited Ni-Fe catalysts. RDE results in our lab have shown that high surface area Ni-Fe-Mo catalysts can outperform even standard IrO2 nanoparticle catalysts, with in-house samples achieving ~200A/g @eta;=370mV compared to ~30A/g for IrO2 at the same over-potential. Studies are currently underway to test and optimize the OER activity of novel Raney Ni-alloys and Ni-alloy nanoparticles at the AEM interface. On the hydrogen side, Ni and previously studied Ni-alloys require a large Δeta; vs. standard Pt catalysts to achieve similar current density. However, recent RDE results have significantly decreased the gap between Ni-alloy and Pt HER performance. Ni-Mo electrodes have long exhibited the best non-PGM HER activity. The electrocatalytic properties of Ni-Mo alloys have been explained by Brewer-Engel theory in terms of optimized Hads bond strength versus other TM alloys. However, recent RDE results show greatly increased performance from Ni-Cr alloys and layered Ni/TM-oxide/C catalysts. Although the cause of increased performance is still under investigation, the answer may lie in synergistic “spillover” effects resulting from the highly reversible redox properties of some TM-oxides in alkaline media. Lyons et al. (JEAC 2010) have recently investigated the OER on TMs and their passivating surface oxides and developed a model of hydrous oxy-hydroxide films which increase the electrochemical surface area and OER activity of TM electrodes. It seems plausible that these oxy-hydroxide films could facilitate the “spillover” or surface effusion of OHads & Hads at relevant OER & HER potentials, increasing reaction kinetics and cell performance.

The design of clean, efficient and environmentally friendly routes has become a central issue of chemical research both in industry and academia. One of the approaches being used in green chemistry practices is to use water as a solvent and reaction medium where possible. Much of this work deals with liquid water at temperatures exceeding the normal boiling point which is denoted as sub-critical water. Electrochemical reaction, usually operated at atmospheric condition in water, is generally slow, although it has advantages over chemical reaction such as suppression of side reaction by tuning operating conditions. Since sub-critical water (7 MPa and 250 oC) has remarkable properties such as high ion product and low dielectric constant, it could be a suitable reaction media. We have been studying electrolysis of organic compounds in sub-critical water as a waste treatment and molecular degradation technologies. Electrolysis in sub-critical water could degrade harmful and thermally stable organic compounds into innocuous compounds such as hydrogen and water. In this research, we focused on the investigation of the electrochemical reactions of alcohols in sub-critical water to evaluate possibility for selective production of hydrogen and added-value chemicals. Electrochemical reactions were carried out in sub-critical water using both specially designed 500 mL batch and continuous-flow type hydrothermal electrolysis reactors made of SS 316. For comparison, thermal degradation experiments of alcohols were also conducted without any direct current loading at identical conditions. Here we employed glycerol and 1-butanol as model compounds of alcohols. As a result of 1-butanol experiments, butanal and butyric acid were produced via partial oxidation at 250 oC and 1-3 A of direct current while no oxidation products were observed at the hydrothermal degradation run. As a gaseous product, hydrogen was generated according to electrochemical reaction. In the case of glycerol experiments, the main gaseous product was hydrogen, whereas glycolaldehyde, lactic acid, and formic acid were the main liquid products at 280 oC. Results indicated that greater than 92% of the glycerol could be decomposed under optimum conditions by hydrothermal electrolysis technique. This presented research will help to degrade stable organic materials in an environmentally friendly way and without need for secondary treatment processes. It will also address the need for novel more efficient techniques for degradation of stable organic compounds in aqueous conditions and it will advance the use of water as a reaction medium in an efficient way without any organic solvent.

Methanol-dehydrogenation properties on platinum surfaces with different electronic structures were studied for direct methanol fuel cell (DMFC). Most of previous researches for methanol oxidation have focused on the poisoning of carbon monoxide with Pt that can be relaxed by oxygen-containing species (bifunctional mechanism). However, the initial stage of methanol dissociation is also important for high efficiency fuel cells, and is governed by the electronic structure of Pt. In this research, the electronic structures of metal surfaces were systematically modified by co-sputtering of FePO₄ or CePO₄ with Pt, and were confirmed by x-ray photoelectron spectroscopy. Rate constants for methanol dehydrogenation of Pt surfaces were obtained by measuring CO coverage as a function of time. This study tries to establish a relationship between activity for methanol dehydrogenation and the surface electronic structure of Pt, and thereby provide an insight for designing a new catalyst for DMFC. [1] Y. Park, S. Nam, Y. Oh, H. Choi, J. Park, and B. Park, J. Phys. Chem. C115, 7092 (2011). [2] M. A. Rigsby, W.-P. Zhou, A. Lewera, H. T. Duong, P. S. Bagus, W. Jaegermann, R. Hunger, and A. Wieckowski, J. Phys. Chem. C112, 15595 (2008). Corresponding Author: Byungwoo Park: [email protected]

In the present work, several Pt-based anode catalysts supported on carbon XC-72R were prepared by using a novel method, and these materials were characterized and tested by XRD, XRF, SEM and TEM. XRD analysis and TEM images indicated that all of anode catalysts consist of uniform nanosized particles with sharp distribution and that the Pt lattice parameter becomes shorter with the addition of Ru and Ni and bigger with the addition of Sn and Rh. Cyclic voltammetry (CV) measurements and single direct ethanol fuel cell (DEFC) tests jointly showed that Sn, Ru, Ni, Ir and Rh can enhance ethanol electro-oxidation activity of Pt in the following order: PtSn/C > PtSnIr/C > PtSnRh/C > PtSnNi/C > PtRuNi/C. It was found that the DEFCs performances were improved with these modified Pt-Metals/C catalysts as anode catalysts. This distinct DEFC performance behavior is attributed to the so-called bi-tri-functional mechanism and to the electronic interaction between Pt and additives. He is very obvious like the current increase with the temperature according to but, in the same way, it is possible to observe a progressive decay of this in the time for effect of the formation of superficial poisons. The better catalyst for the process of electro-oxidation of the ethanol is the PtSnIr/V for which in the range is recorded catalytic worst of upgrades them of interest, between 0,25 V to 0,6.

The methanol oxidation reaction (MOR) is a key step in the operation processes of a direct methanol fuel cell (DMFC). Despite intensive research over the past decades numerous problems concerning the electrocatalyst for the MOR still remain. Among those are the high costs caused by the requirement of platinum, the relatively slow electrode kinetics at the anode and the poisoning of the catalyst due to intermediately formed carbon monoxide.^[1] A modern approach to reduce these problems is the use of nanoscaled Pt-bimetallic alloys as electrocatalysts.^[2] These materials feature a high surface to volume ratio which minimizes the overall amount of platinum required for the heterogeneous catalysis whilst showing improved electrocatalytic activity and better resistance to CO poisoning compared to pure platinum. Suitable Pt alloy nanoparticles described in the literature include CoPt, FePt, TiPt and NiPt.^[3] However, so far there are hardly any thorough studies on how a change of the particle size on the one hand or the composition on the other hand effects the catalytic activity of such Pt alloy nanoparticles since those two properties often change concomitantly. We present a simple and straightforward approach to investigate the electrocatalytic activity of NiPt nanoparticles for the MOR using Cyclic Voltammetry. The NiPt nanoparticles used for this study are highly crystalline and have a narrow size distribution as can be shown by TEM and XRD measurements. They are synthesized following a wet chemical synthesis developed in our group.^[4] The particles are then grown to the desired size by continuous injection of one of the metal precursors Ni(ac)₂ or Pt(acac)₂. This method yields ligand stabilized nanoparticles in colloidal solution which possess a tunable size whilst having a constant composition and vice versa. To our knowledge this has not been reported before. The as described synthesized nanoparticles of either different size or composition are further investigated in regard to their electrocatalytic activity for the MOR in an effort to discern true size and composition dependencies respectively. [1] A. S. Aricograve;, S. Srinivasan, V. Antonucci, Fuel Cells2001, 1, 133-161. [2] Z. Peng, H. Yang, Nano Today2009, 4, 143-164. [3] V. R. Stamenkovic, B. S. Mun, M. Arenz, K. J. J. Mayrhofer, C. A. Lucas, G. Wang, P. N. Ross, N. M. Markovic, Nat. Mater.2007, 6, 241-247. [4] K. Ahrenstorf, O. Albrecht, H. Heller, A. Kornowski, D. Gccedil;rlitz, H. Weller, Small2007, 3, 271-274.

Potentiostatic deposition of highly porous platinum in the form of thin films and nanowires with a large proportion of preferentially-oriented {100} surface sites was recently outlined [1]. A systematic study of the electrodeposition parameters, e.g. electrodeposition potential and charge, temperature and Pt salt concentration has been undertaken [2]. Under optimal deposition conditions, rough Pt surfaces containing up to ca. 50% of (100) surface sites were obtained. Such Pt films combine a high surface area and a large fraction of highly active (100) Pt sites. This type of catalyst surfaces has already demonstrated interesting properties for ammonia [2] and formic acid oxidation [3]. In the following communication, we go one step further by showing how the deposition potential can be used to further modify the balance between (100) terraces and (100) step sites (keeping the total amount of (100) surface sites high and constant) and how this can further enhance the electrocatalytic activity towards ammonia oxidation [4]. In the case of formic acid oxidation, the (100) surface orientation is well known to be the most active Pt crystallographic plane. However, it is also rapidly poisoned by oxygenated surface intermediates, resulting in poor long term stability [3]. In this regard, significant improvement will be demonstrated by surface functionalization of the preferentially oriented Pt(100) films with gold atoms deposited by pulsed potential electrodeposition. The effect of the Au surface coverage on the HCOOH electro-oxidation current will be assessed. [1] S. Garbarino, A. Ponrouch, E. Bertin and D. Guay, Mat. Res. Soc. Symp. 1311 (2011) 7. [2] A Ponrouch, S. Garbarino, E. Bertin, C. Andrei, G A. Botton and D. Guay, Adv. Funct. Mater., doi 10.1002/adfm.201200381. [3] J. Solla-Gulloacute;n, F.J. Vidal-Iglesias, A. Loacute;pez-Cudero, E. Garnier, J.M. Feliu, A. Aldaz, Phys Chem Chem Phys, 10 (2008) 3689. [4] E. Bertin, C. Roy, S. Garbarino, D. Guay, J. Solla-Gulloacute;n, F.J. Vidal-Iglesias, J.M. Feliu, Electrochem. Commum., doi 10.1016/j.elecom.2012.06.011.

Platinum remains one of the most studied catalysts, mainly because of its high electrocatalytic activity for several oxidation and reduction reactions.[1, 2] Due to its cost and its scarcity, it is of primordial importance to increase the surface to mass ratio of Pt-based catalysts, using nanoparticles or 1D nanostructures, and/or to mix it with others elements (Co, Ru, etc.) to increase both their activity and poisoning tolerance.[3, 4] Recently, another strategy has emerged to tune the electrocatalytic activity of platinum-based catalysts that relies on the synthesis of platinum surfaces with a specific crystallographic surface orientation.[5],[6] As most electrochemical reactions are surface structure sensitive, this method has shown promising results for several reactions, such as ammonia and methanol oxidation.[5, 7] In the case of formic acid oxidation, Pt (100) surfaces also display enhanced activity compared to other surface crystallographic orientations. However, they are rapidly poisoned by CO surface intermediates and display the same activity as polycrystalline Pt after 1800s. To overcome this issue, several methods have been employed, using surface decoration by gold or bismuth atoms.[8, 9] In this study, we will focus on the decoration by spontaneous adsorption of bismuth on electrodeposited Pt films with a preferential (100) orientation (ca. 30 % of (100) surface sites). The initial electrocatalytic activity will be assessed and compared with a polycrystalline platinum electrode based on cyclic voltammetry (CV) and chronoamperometric (CA) analyses. After Bi decoration, both CV and CA curves reveal a marked improvement in the long term activity for HCOOH oxidation. However, as Bi decoration also reduces the electrochemically active surface area of Pt, a careful balance needs to be established between the Bi coverage and the HCOOH oxidation rate in order to increase both the initial electrocatalytic activity and the poisoning tolerance. References [1] V. Rosca, M. Duca, M.T. DeGroot, M.T.M. Koper, Chem Rev, 109 (2009) 2209-2244. [2] C.M. Sánchez-Sánchez, J. Souza-Garcia, E. Herrero, A. Aldaz, J. Electroanal. Chem, 668 (2012) 51-59. [3] S. Garbarino, A. Ponrouch, S. Pronovost, D. Guay, Electrochem Commun, 11 (2009) 1449-1452. [4] F. Maillard, M. Martin, F. Gloaguen, J.M. Léger, Electrochim. Acta, 47 (2002) 3431-3440. [5] J. Solla-Gulloacute;n, F.J. Vidal-Iglesias, J.M. Feliu, Annu Rep Prog Chem Sect C, 107 (2011) 263. [6] A. Ponrouch, S. Garbarino, E. Bertin, C. Maunders, G.A. Botton, D. Guay, Adv. Funct. Mater., (2012) 10.1002/adfm.201200381. [7] E. Bertin, C. Roy, S. Garbarino, D. Guay, J. Solla-Gulloacute;n, F.J. Vidal-Iglesias, J.M. Feliu, Electrochem Commun, (2012) 10.1016/j.elecom.2012.06.011. [8] A. Sáez, E. Expoacute;sito, J. Solla-Gulloacute;n, V. Montiel, A. Aldaz, Electrochim. Acta, 63 (2012) 105-111. [9] M.D. Obradovicacute;, J.R. Rogan, B.M. Babicacute;, A.V. Tripkovicacute;, A.R.S. Gautam, V.R. Radmilovicacute;, S.L. Gojkovicacute;, J. Power Sources, 197 (2012) 72-79.

Nanomaterials have a number of advantages in catalysis when compared to their bulk counterparts. As metal particle size reaches the nano scale, the surface area to volume ratio greatly increases along with the percentage of atoms occupying catalytically active corner and edge sites. In the last fifty years, much of nanomaterials research has focused on the size and shape control of transition metal nanoparticles. Because different shapes can better catalyze different reactions, nanomaterial shape control has become a vital step in the search for alternative energy. Nanoparticles have the potential to catalyze reactions necessary for solar cells, water splitting, fuel cells, and the production of hydrocarbons. In this study, shape-controlled palladium nano-octahedrons and nano-cubes of various sizes were synthesized, via both single-step and seed-mediated growth methods. The as-prepared palladium nanoparticles were then used as seeds in a rhodium overgrowth procedure, yielding particles with palladium cores and dendritic rhodium shells. Rhodium is an extremely catalytically active metal, but it is difficult to manipulate into shape-controlled structures. To resolve this problem, palladium seed particles are used as structure-directing templates. The palladium seeds have a controlled shape, and the rhodium that grows over the palladium acquires an identical shape. Electrocatalysis is commonly utilized to test the catalytic activity of transition metal nanoparticles. In this study, rhodium-coated palladium particles were used as catalysts for both carbon monoxide oxidation and formic acid electrooxidation, a reaction that is being studied as a promising way to power fuel cells. The data for these reactions was recorded using cyclic voltammetry and the resulting graphs were analyzed to obtain information about the catalytic efficiency and surface structure of the particles being tested.

Designing highly active catalysts for electro-oxidation of small organic molecules can help to reduce the anodic overpotential for more efficient utilization of hydrocarbon fuels. The challenge in developing more active electrocatalysts for electro-oxidation reactions is to satisfy the stringent bifunctional requirement, which demands both adsorption and water oxidation sites. In this contribution, we explore the possibility of using Pt-Si alloys to fulfill this bifunctional requirement. Silicon, a highly oxophillic element, is alloyed into Pt as a site for water oxidation, while Pt serves as a CO adsorption site. We will discuss the enhanced activity of Pt-Si alloys for small organic molecule oxidation, which can be attributed to the improved CO electro-oxidation kinetics on Pt-Si.

Electrocatalysts that are capable of catalyzing oxidation of organic compounds have enormous appeal because of their potential applications in fuel cells aswell as organic syntheses. In the last decade, a number of fuel cells based on oxidative electrocatalytic systems have been designed and demonstrated to work using methanol, methane, ethanol, hydrazine, formic acid, and L-ascorbic acid as fuels. However, these fuels cells operate using expensive noble metal and bimetallic nanoparticles such as PtRu and PtSn supported on carbon were used as the electrocatalysts. Besides the cost, the stability of the noble metal nanoparticles electrocatalysts is also an issue, considering the nanoparticles aggregation and their high affinity by carbon monoxide. Thus, stable noble metal free catalysts are highly desired for liquid fuel cells. Herein, an efficient nanocomposite electrocatalyst composed of mesoporous silica (SBA-15) with polyaniline (PANI) nanostructures within its channel pores (PANI/SBA-15) is synthesized and characterized [1]. The resulting PANI/SBA-15 is capable of chelating Co(II) ions, presumably via its nitrogen atoms on PANI/diamine groups. Both the metal-free (SBA-15/PANI) and the Co(II)-doped SBA-15/PANI nanocomposite materials showed high electrocatalytic activity for oxidation of L-ascorbic acid, with very low overpotential and high current density. The activity of PANI/SBA-15 toward oxidation of L-ascorbic acid is comparable to that obtained from a conventional Pt/C electrocatalyst.

In recent years, platinum-based single crystal nanoalloys as nanoscale catalysts, such as Pt-M (M = Ni, Co, Fe..etc.), have exhibited improved catalytic performance due to the increase in the surface-to-volume ratio and reduced Pt-content. Pt-M monodisperse nanocubes and/or nanoctahedra have been reported to show enhanced activity when used as electrocatalysts. In order to further establish a correlation between the exposed nanocrystal facets (shapes) and the corresponding activities, the pursuit of shape-controlled nanocatalyst synthesis is essential. Although PtPb nanoalloys have been prepared using solution-based methods, few studies have highlighted their catalytic activity as a function of the particle shape. This work focuses on a modified polyol synthesis technique and an adjustment of the Pb-metal precursor, which serves as a “buffer” in the nucleation stage of the shape-controlled nanoalloy development. Using our developed synthetic strategy, shape-controlled intermetallic hcp PtPb nanoalloys can be prepared in a one-pot synthesis without additional post-treatment. The as-prepared PtPb nanocrystals demonstrate an improved anode electrocatalytic performance.

Improvement of electrocatalytic performance of anode catalysts is an important task in direct methanol fuel cell development. Trace metal as an impurity of catalysts could modify the density of electronic structure on their surfaces and accordingly alter their electrocatalytic behavior. In this work, shape-controlled Pt nanoparticles with different hetero-elements on surfaces as trace impurities were prepared using a high-temperature solution synthesis approach, and their electrocatalytic performance towards methanol oxidation was investigated. The investigation indicates that Pt nanoparticles synthesized using Cr(CO)6 exhibit enhanced electrocatalytic activity and stability with decreasing amount of Cr-residue on the surface of particles compared with Pt nanoparticles prepared with other carbonyl compounds. In addition, the electro-cycling plays an important role on dealloying the surface metal residue. Results show that dealloying the trace-amount of Mo on the Pt nanocatalyst surfaces may also favor an enhancement of methanol oxidation activity. This study suggests that variation of trace-amount hetero-metal residue on the surface of Pt nanocatalysts may be an effective way to alter electrocatalytic activity towards methanol oxidation reaction.

In this work, we describe the ‘one-pot&’ synthesis and characterization of ordered, large-pore (>30 nm) mesoporous carbon/silica composites (OMCS) with well-dispersed intermetallic PtPb nanoparticles on pore wall surfaces as anode catalyst for direct formic acid fuel cells (DFAFCs). We believe this work sets itself apart from previous efforts in the following ways: 1.) Tedious multiple processing steps are replaced by a simple one-pot approach. 2.) The block copolymer used in this work is synthesized by atom transfer radical polymerization (ATRP), a polymerization technique that makes block copolymer synthesis, and preparation of large-pore mesoporous materials from it, accessible to the non-expert. 3.) The one-pot synthesis provides access to both, an ordered, large pore (pore diameter > 30nm) mesoporous carbon/silica support as well as intermetallic PtPb nanoparticles well-dispersed on the surface of the pore walls. 4.) The intermetallic PtPb nanoparticles are significantly smaller than the pore diameters of the support enabling formation of the desired triple phase boundary (TPB) through efficient mass transport of ionomer (Nafion) and fuel through the pores. 5.) The quality of the resulting anode catalysts is tested under realistic direct formic acid fuel cell (single cell) conditions rather than merely by half-cell electrochemical characterization. 6.) Despite larger nanoparticle size, the resulting anode catalysts outperform commercial Pt/C and Pd/C catalysts.

Several promising new applications of bipolar electrochemistry have emerged over the past ten years. Crooks and co-workers have shown how electrochemical techniques for concentrating, separating and detecting analytes in microfluidic channels can be implemented using bipolar electrodes (BPEs). The Bjoerefors group has demonstrated the ability to generate and manipulate chemical concentration gradients of organic adsorbates using bipolar electrochemistry. Recently, our research group introduced the concept of bipolar electrodeposition (BP- ED) and demonstrated the use of this approach to generate solid-state material libraries along the length of a BPE. When an external electric field is applied across an electrically isolated conductor immersed in an electrolyte solution, a position-dependent interfacial potential difference is generated along the length of the conductor. This potential gradient can be used to induce variations of chemical composition within thin films electrodeposited onto the bipolar electrode (BPE). Thin films formed by BP-ED represent continuous one-dimensional solid-state material libraries and can be screened using conventional surface analysis techniques. In this paper, we will discuss two examples that highlight the advantages of BP-ED for the generation of chemical composition gradients relevant to electrocatalysis. First, Pd-Au chemical composition gradients were generated using BP-ED, and the composition dependent oxidation of formate was studied using confocal Raman microscopy. Second, CoOx phases were electrodeposited and screened for water oxidation efficiency using scanning electrochemical microscopy.

The stabilities and catalytic activities of clean and O-substituted surfaces of the tantalum nitride (Ta3N5), which is one of the promising materials for polymer electrolyte fuel cells (PEFCs) cathode catalyst, have been theoretically examined and the reaction mechanism of oxygen reduction reaction (ORR) has been clarified. Density functional theory calculations are performed with SIESTA code. Exchange correlation energy is calculated with generalized gradient approximation (GGA) using RPBE functional. First, we examined the stability of (100), (010) and (001) surfaces to clear which surface is the most stable. We first construct the slab model including three unit cells with 20 Å vacuum space and compare their surface energy. Calculated surface energies of (100), (010), (001) surfaces are 0.067 eV Å-1, 0.072 eV Å-1, and 0.081 eV Å-1, respectively. Since surface with the lowest surface energy is the most stable, (100) surface is considered to be the most stable surface. Therefore we studied surface reactivity on Ta3N5 (100) surface afterward. Then, we examine the density of states (DOS) on both clean and O-substituted surfaces. The property of band structure on clean surface is semiconductor whereas the property on O-substituted surface is n-type semiconductor. By introducing substituted O atoms in the surface, Ta d orbital came to locate just below the Fermi energy level. Therefore it is expected that Ta d orbital has excess electron which can attack π* orbital of oxygen molecules. Thus, we found that O-substituted surface has higher surface reactivity. Next, we examined the reaction mechanism of ORR by calculating the adsorption energy and activation energy of the reaction. We calculated the oxygen adsorption which is the first elementary step of ORR. We examined how adsorption sites and strength change according to the surface structures and the electronic states on Ta3N5 (100). We took surface Ta atoms as active sites and oxygen molecule adsorbs on them. We revealed that surface substituted O atoms prevent oxygen molecule&’s horizontally adsorption nearby. We also revealed that surface structure is distorted by introducing substituted O atoms which affect the adsorption energy of bridge type molecular adsorption, because adsorption energy of bridge style strongly depends on the length between two active sites. Furthermore, we found that dissociative adsorption of oxygen molecule may not occur on Ta3N5 (100). In conclusion, we studied surface stability of Ta3N5 surfaces and surface reactivity of clean and O-substituted Ta3N5 (100) surfaces. Then, we revealed the first elementary reaction step of ORR by examining how substituted oxygen atoms affect the oxygen adsorption reaction both energetically and structurally. The consecutive reaction step will be discussed in my presentation.

The polymer electrolyte fuel cell (PEFC) is a promising power source for automobile application. However the PEFC has a major issue that the activity and durability of the electrode materials needs further improvement, which prevents large commercialization of fuel cell vehicles (FCVs) due to the high cost of precious metals used as electrocatalyst. In order to realize the commercialization of FCVs, it is essential to clarify the degradation mechanism of the electrocatalyst, especially the cathode catalyst. Schlögl et al. investigated the degradation of electrocatalyst with an electrochemical cell system. They observed the morphology of the electrocatalyst before and after the electrochemical treatment [1]. In this study, we investigated the degradation mechanism of Nafion-coated Pt/C catalyst under humidified air by in situ TEM. The catalyst sample was prepared with Pt/C electrocatalyst (TEC10E50E, Tanaka Kikinzoku Kogyo K. K.) and Nafion® PFSA Polymer Dispersion (D2020, DuPont) as the ionomer. The ionomer to carbon ratio was 0.9 by dry weight. In situ TEM observation was conducted using a Hitachi H-9500 high-resolution 300 kV analytical TEM equipped with an AMT CCD camera system. The catalyst sample was mounted on a specimen-heating holder with a gas-injection nozzle. The temperature of the sample was maintained at 300°C and the total pressure was controlled to 0.2 Pa during the observation. To control the gas environment near the sample, we set up an air supply unit that introduced humidified air into the specimen chamber through the gas-injection nozzle. The morphological changes of the catalyst sample were dynamically observed under humidified air condition. The observation revealed that the carbon support was gradually oxidized to shrink without any changes of higher-order structure of the support, leading slowly to the coalescence and growth of Pt particles. In contrast to the previous results without Nafion coating [2], the active movement of Pt particles was not confirmed. Even though the catalyst sample was observed at high magnification, the Pt particles stayed at their original position on the support. In addition, an amorphous substance was found at the surface of Pt particles, which was supposed to consist of Nafion ionomer layer. Therefore, it appears that Nafion provides a protection against the carbon corrosion and the movement of Pt particles, and retards the degradation of Pt/C electrocatalyst. Acknowledgments: This work was partly supported by Grant-in-Aid for Scientific Research (C) 23510136 from the Japan Society for the Promotion of Science (JSPS). References: [1] Katrin Schlögl, Karl J.J. Mayrhofer, Marianne Hanzlik, and Matthias Arenz, J. Electroanal. Chem., 662, 355 (2011). [2] T. Yaguchi, T. Kanemura, T. Shimizu, D. Imamura, A. Watabe, and T. Kamino, J. Electron Microsc., in press (2012).

The oxidation of H2O, CH3OH and CO was investigated at Pt electrodes in the protic ionic liquid diethylmethylammonium trifluoromethanesulfonate as a function of temperature using cyclic and linear sweep voltammetry. Oxidation of trace H2O in the ionic liquid results in coverage of the Pt surface with adsorbed oxide species and increasing the temperature significantly reduces the potential at which this reaction occurs. CH3OH and CO oxidation kinetics also increased significantly with increasing temperature and oxidation of each species coincided with coverage of the Pt surface by the oxide. These observations indicate that CH3OH oxidation proceeds in this liquid via a surface reaction between adsorbed CO and Pt oxides, in a similar manner to that observed in conventional aqueous electrolytes. While the overpotential for CH3OH oxidation in the ionic liquid was drastically higher than that observed in aqueous electrolytes, it decreased with increasing water content of the ionic liquid. The results described here have implications for the development of protic ionic liquid-based fuel cells and these implications are discussed

Pt based alloy nanoparticles supported on a carbon carrier are expected to be used for electrocatalysts in polymer electrolyte membrane fuel cells. However, their internal microstructures often change depending on fabrication conditions and operating conditions because of the thermodynamic instability of nanoparticles. In particular, the catalytic activity and durability of an alloy catalyst are considerably affected by its surface structure and the compositional variation. Hence, there is great interest in controlling a radial distribution of each alloying component within a nanoparticle, which improves the activity and durability of the nanoparticle catalysts and enables us to decrease the Pt amount of loading. The phase-field method has recently attracted attention as a possible numerical simulation technique for investigating nano-scale phenomena. An objective of this study is to construct a phase-field model that describes the phase decomposition and phase transformations inside the Pt based alloy nanoparticles to understand influences of particle size, alloy composition, and heat-treatment temperature on the microstructure formation. This model is based on formulation of thermodynamic energy functions. Specifically, we determined bulk chemical free energies mainly based on the previously reported thermodynamic assessments of Pt based binary systems, using CALPHAD (CALculation of PHAse Diagrams) method. The radial distribution of each atomic component in the nanoparticles was numerically calculated in the polar coordinate system. Fe-Pt, Co-Pt, Ni-Pt, Cu-Pt and Ir-Pt binary alloy nanoparticles with their diameters of less than 10 nm were investigated. The radial distribution of the long-range order parameter was also evaluated for the binary alloys showing the order-disorder phase transition. The calculation results clearly showed that surface segregation was sensitive to alloy components. For example, the CuPt particle with a diameter of 2 nm had a Cu-rich surface at 973 K because the surface energy of pure Cu was lower than that of pure Pt and because the chemical interaction between Pt and Cu was weak. On the other hand, there was no remarkable surface segregation in Fe-Pt system. The absolute surface energy difference between Fe and Pt was almost identical to that between Cu and Pt. Nevertheless, the strong chemical interaction between Fe and Pt, which drove to the L1₀ or L1₂ ordering, prevented segregation in the Fe-Pt system at 973 K.

Polymer electrolyte fuel cells (PEFCs) are promising power sources for vehicles, co-generation systems, and mobile devices. However, the durability of their electrocatalysts is one of the most important technological issues. Especially, Pt electrocatalysts supported on carbon materials suffer from carbon corrosion on the cathode side under the start-up and shut-down condition. To solve this problem, we have developed cabon-free Pt electrocatalysts using SnO2 as the electrocatalyst support material. The use of SnO2 as an alternative support improves durability under the start/stop voltage cycling, as SnO2 is thermochemically stable under such operational conditions. We have reported that the durability test with voltage cycles between 0.9 and 1.3 V revealed that the Pt electrocatalyst supported on SnO2 maintained electrochemical surface area (ECSA) even after 60,000 voltage cycling. However, SnO2-supported electrocatalyst has a tendency to show lower power performance, comparing to conventional carbon materials, and one of the reasons is the contact resistance between SnO2 particles. Therefore, the aim of this study is to develop new preparation procedures to lower contact resistance between the particles of SnO2 and to obtain higher performance SnO2-supported PEFC electrocatalysts. Conventionally, we prepare SnO2 powder by the co-precipitation method and Pt nano-particles are then impregnated on SnO2 by the colloidal method, and coating electrocatalyst layers on the nafion membrane using the spray printing method. However, in this study, two new methods are introduced. The first method is done by coating the tin and other metal compounds on gas diffusion layer (GDL) and by dissolving the other metal (dealloying). The second method is the direct coating of SnO2 by sputtering on GDL in order to reduce the contact resistance. We started with dealloying process in powder to optimize the systhesis condition. Crystal structure by X-ray diffusion (XRD), microstructure by field emission scanning electron microscopy (FE-SEM), and specific surface area by the BET method were analyzed. As the result, SnO2 powder with a larger specific surface area than the conventional one was obtained. Cyclic voltammetric (CV) measurement was applied to evaluate electrochemical characteristics of the new catalysts, which were them compared with the conventional one. The power performance by the single cell is also examined. Regarding to the second method, coating SnO2 by sputtering, similar analysis is performed and the results are compared with SnO2 made by other methods, such as wet-chemical method, for further investigating new preparation methods.

PEM fuel cell technology is one of the most promising future alternative energy sources because it has relatively low operating temperature, high power density, quick response, pollution-free operation. However, its relatively low power output compared to that of its price has prevented it from many practical applications. Nanoparticles have been widely known to possess catalytic capabilities. Marvrikakis et al have predicted that gold nanoparticles that are platelet shaped and have direct contact to the substrate to be the “perfect” catalysts. In our experiment, thiol-functionalized and spherical gold nanoparticles (around 2nm in diameter) were synthesized through two-phase method developed by Brust et al. When a solution containing these particles was spread at the air/water interface, X-ray reflectivity and EXAFS spectroscopy indicated the formation of platelet shaped particles. Langmuir-Blodgett (LB) was then used to deposit monolayer of these platelet shaped gold nanoparticles onto the surface of Nafion® membrane. Up to 80% enhancement for output power of single cell and 33% enhancement for three stacks cell were found after applying the modified Nafion® membrane on PEMFC. Effects of gold nanoparticels are studied by varying the surface pressure (to deposit gold nanoparticles onto membrane) and gases at cathode side.

There is a growing need for grid-scale storage of electrical energy from intermittent renewable sources such as wind and solar. Flow batteries have generated Interest due to their potential to decouple energy and power and thereby store very large amounts of energy cost effectively. We will report on our explorations of small organic molecules in electrochemical cells with the objective of developing novel flow batteries.

O binding energy has been shown to be an effective descriptor for oxygen reduction reaction (ORR) activity. Trends in oxygen binding energy were calculated with density functional theory to determine the ORR activity of two types of Pd based nanoparticles: random alloy (Pd/X) and alloy-core@shell (X/Y@Pd). In the Pd/X random alloy system, a quadratic O binding trend was calculated as a function of Pd composition. A model was derived in which O binding to each component metal varies linearly due to the presence of the other; multiplying by a linear change in composition yields the quadratic trend found in our explicit calculations. The alloy-core@shell structure was observed to have a linear O binding trend as a function of alloy-core composition. An advantage of the X/Y@Pd structure as compared to the Pd/X random alloy nanoparticles is the improved stability of the noble Pd shell, allowing for a wider variety of non-noble alloying metals. Our simple models of O binding to these particles provide guidelines for designing non-Pt ORR catalysts.

Photoelectrochemical (PEC) water splitting is a beneficial way to produce hydrogen as a clean fuel using solar energy and many materials have been investigated as photoelectrodes. p-type semiconductor materials act as photocathode and hydrogen evolution through the reduction reaction of water takes place on the electrode. Among them, chalcopyrite materials have attracted many attentions due to its high absorption coefficient of more than 105 cm-1 and p-type conductivity. CuGaSe2 film with a band gap of 1.7 eV was reported and the possibility of water splitting was shown. However, due to the shallow valence band edge position, it was not possible to generate hydrogen at the surface of the electrode without a large external bias voltage. In order to solve this problem, the Cu-deficient copper gallium selenide, namely CuGa3Se5 and CuGa5Se8, which have deeper valence band maximum and larger band gap, were investigated. In these reports, the films were prepared by vacuum co-evaporation method. Using this method, polycrystalline thin films with good quality can be prepared. However, high vacuum system is required so that this method has difficulty for large scale manufacturing. In this study, we focused on utilization of particles of Cu-Ga selenides (CGSe) to fabricate photoelectrodes. Since PEC water splitting takes place at solid-liquid interface, the form of interface is flexible. If the particles with good quality contact to conductive substrate properly, high performance photoelectrode expect to be obtained more easily. The micron sized particles of CGSe were prepared by solid state reaction method and these properties were investigated. The precursor materials, Cu2Se and Ga2Se3, were mixed in inert ambient and were sealed into quartz ampules after the drying in vacuum. The mixtures were calcined to obtain CGSe particles. In the preparation process, the ratio of precursors was decided to control the ratio of Cu/Ga to 1 or 3. The prepared particles were characterized by XRD to confirm these structures and by UV-vis diffuse reflectance spectra to reveal absorption edge. SEM observations were also performed.The photoelectrodes used these particles were prepared by particle transfer (PT) method. A thin metal layer (contact layer) was deposited on particle layer by sputtering method followed by deposition of thick metal layer (current collecting layer). Then these layers which taking hold a CGSe particles were transferred to another glass plate by fixing epoxy resin. Three-electrode system was used in PEC measurements. Pt wire and Ag/AgCl electrodes were used as counter and reference electrodes, respectively. 0.1 M Na2SO4 aqueous solution (pH adjusted to 9 by NaOH addition) was used as an electrolyte. A 300 W Xe lamp equipped with a cut off filter (L42) was employed as a light source. The CGSe electrodes prepared by PT method worked as photocathode stably for over 10 h. In order to get high performance, surface modifications have been investigated.

Ethanol is a promising fuel for low-temperature direct fuel cell reactions due to its low toxicity, ease of storage and transportation, high energy density, and availability from biomass, compared to hydrogen and methanol. However, the lack of effective electrocatalysts for ethanol oxidation reaction (EOR) is a major hindrance for the commercialization of direct ethanol fuel cell technology. The problems include: the sluggish kinetics, incompleteness of EOR, and high cost of Pt-based catalysts. Here we present two Pt-free Ir-M (M: Sn, Ru) binary systems as potential alternative electrocatalysts for EOR in acid solution. A series of carbon-supported Ir-M alloyed fine nanoparticles (3~4 nm) were prepared through Polyol method with different compositions. Several characterization techniques were used to characterize the Ir-M/C catalysts, including aberration-corrected scanning-transmission electron microscopy (STEM) equipped with electron energy loss spectroscopy (EELS), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS), whereas Ir-M alloyed structures were determined. The Ir-Sn/C and Ir-Ru/C catalysts showed superior mass current densities in cyclic voltammetry (CV) and chronoamperometry (CA) measurements compared to that of commercial Pt/C (ETEK). In particular, the Ir-Sn/C catalyst showed exceptional electro-activity for EOR at very low potential in CV measurements. Density functional theory calculations demonstrate that the superior electro-activity of Ir-Sn and Ir-Ru is directly related to the high degree of alloy formation. Our study highlights the potential of Ir-based metal alloys as alternative electrocatalyst for direct ethanol oxidation reaction applications.

Highly active catalysts for energy storage and conversion are pivotal in the pursuit of sustainable energy. However, a better understanding of catalysis at a fundamental level is required for rational design of more efficient catalysts. It is therefore paramount to identify structure-function relations at the atomic scale and to obtain practical activity descriptors with predictive power. Suntivich et al. have proposed that the occupancy of the transition metal eg orbital can serve as design criterion for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) of Perovskite catalysts [1-2]. First steps towards a correlation between structure and oxygen evolution activity of these materials are presented herein. X-ray absorption spectroscopy (XAS) is ideally suited to simultaneously study the averaged local structure of materials and the metal oxidation state as a function of voltage. Perovskite electrodes were prepared by drop-casting an ink suspension of the catalyst on glassy carbon electrodes [3]. In ongoing synchrotron experiments, we have studied the OER at the electrochemically active surface potentiostatically for selected voltages and after cyclic voltammetry. Preliminary ex-situ measurements showed that the local structure in the vicinity of the cobalt ions differs significantly before and after catalytic activity. These structural modifications and conceivable chemical changes are currently investigated by in-situ combinations of electrochemical methods and XAS. [1] Suntivich, May, Gasteiger, Goodenough, Shao-Horn (2011) Science 334, 1383. [2] Suntivich, Gasteiger, Yabuuchi, Nakanishi, Goodenough, Shao-Horn (2011) Nat. Chem. 3, 546. [3] Suntivich, Gasteiger, Yabuuchi, Shao-Horn (2010) J. Electrochem. Soc. 157, B1263.

Among non-Platinum Group Metal (non-PGM) based catalysts for energy technologies, binary alloys are considered to be promising materials since properties of an alloy might be additive or synergistic. Synergism is an ability of a material to perform better as a catalyst in comparison with initial components due to the over-additive increase of catalytic properties. Electrodeposited cobalt alloys are a good example of catalytically active alloys. Thin films of binary Co-Fe, Co-W, and Co-Ag alloys were electrochemically deposited from citrate (Co-Fe, Co-W) and citrate-pyrophosphate (Co-Ag) electrolytes using direct (Co-Fe) and pulse (Co-Ag, Co-W) currents. Preliminary testing of additive Co-Fe alloy with ~ 20 wt% of Co and 80 wt% of Fe demonstrated that utilization of thin films of this composition allows for ~ 15 % voltage decrease voltage in the aqueous electrolyzer due to the lowered overpotentials of hydrogen and oxygen evolution. Both corrosion resistance and coercivity of Co-Fe deposit improve with the increase of Co content. Thin films of synergistic Co-Ag and Co-W alloys contained 5-8 at% of Ag and 5-50 wt% of W, respectively. Introducing this amount of Ag and W into Co deposit allows for significant increase of catalytic activity of Co-Ag and Co-W alloy in comparison with Co metal. Catalytic activity of Co-W and Co-Ag was estimated in the reaction of electrolytic hydrogen evolution. The negative logarithm of exchange current density -lgj0(H2) (A/cm2) for Co-Ag was determined to be 2.8 and for Co-W with 25-35 wt% of W 4.2, while for Pt metal it was 3.0. Corrosion resistance and catalytic activity of Co-W alloy depends nonlinearly on its composition. Electrochemically deposited thin films of Co-Fe and Co-Ag were tested in the gaseous oxidation reaction of CO to CO2 conversion. The preliminary data suggests that utilizing Co-Fe alloy films with ~ 70 wt% of Co and 30 wt% of Fe as catalysts allows for some decrease of temperature of the reaction triggering in comparison with traditional PGM catalytic materials. For Co-Ag alloy with as little as 8 at% of Ag, the CO to CO2 conversion reaction starts at temperature close to that typical for platinum metal. This justifies the approach to an alloy catalytic activity prediction based on the value of exchange current density for electrolytic hydrogen evolution reaction. Results obtained suggest the possibility of developing efficient non-PGM catalytic materials based on electrochemically deposited cobalt alloys.

Transition metal dichalcogenides with layered structure, especially MoS2, have attracted much physical-chemical interest due to their 2D structure analogous to graphene. This 2D material has been investigated and used as a catalyst for hydrodesulfurization reactions, anodes for lithium batteries and semiconductors as well as electrocatalyst for hydrogen evolution reactions (HER). Taking advantage of good microwave absorption of graphene, we merged the microwave synthesis approach with an extension of the nonhydrolitc sol-gel method to induce a higly selective crystallization of MoS2 layers over graphene sheets. Thus, we describe a simple, versatile and highly selective synthesis method (figure 1) to prepare MoS2 layers over reduced graphene oxide (RGO). The HRTEM analysis suggests that this hybrid material is formed by several layers (from 1 to 6 layers) of MoS2. The complementary energy dispersive X-rays (EDX) analysis indicates the formation of a compound with stoichiometry compatible to MoS2. The SAED pattern was indexed as the hexagonal MoS2 phase, which confirms the formation of this sulfide over graphene sheets. The electrochemical characterization was made for three MoS2/GO ratios. The exchange current density (Jo) and Tafel slope (b) was evaluated to demonstrate the activity of this hybrid material for hydrogen evolution reactions (HER). The exchange current density value for the hybrid material with medium (J0 = 120 mu;A/cm2) and high (J0 = 117 mu;A/cm2) MoS2 concentrations shows a value similar to the exchange current density measured for Pt (J0 = 117 mu;A/cm2).

As one of the most promising fuel cells, direct formic acid fuel cell (DFAFC) has been intensively studied because formic acid has high energy density and easy to store and can handle more safely than hydrogen. Platinum is the most active electrocatayst toward almost all the reactions which are related to fuel cells. However, the development of direct formic acid fuel cells has been slowed down by the low activity because of Pt high price and the dominance of the indirect reaction pathway and strong CO poisoning effects. Size and shape of the metal particles have been controlled to obtain as high as possible catalytic activity. In addition, alloying metals has been attractive due to its synergetic effect and usually had much higher activity than pure metals. Here, we report the facile synthesis of Platinum Palladium alloy with good size and shape controls in aqueous phase. The PtPd octahedral alloy nano particles around 7nm are characterized by TEM, HRTEM, EDX and XRD and show much higher activity for formic acid oxidation compared to other electrocatalysts. Furthermore, to achieve even higher catalytic activity, besides alloying metals, core-shell structure has been investigated. Taking the advantage of successful PtPd alloy synthesis, the activity can be further improved by manipulating the Au@PtPd core-shell octahedral structure. The surface electronic structure changes on the Au@PtPd core-shell octahedral nano particles(~20nm) definitely have a great impact on the interactions between formic acid and PtPd alloy shell, which result in higher catalytic activity toward the electro-oxidation of formic acid. The composition of PtPd alloy can be changed (3:1, 1:1 and 1:3) and still maintain octahedral structure with high catalytic activity for all cases.

Proton exchange membrane fuel cell (PEMFC) has attracted large amount of interests those years due to its high energy conversion efficiency, low pollution and high power density. However, the main limitation of PEMFC is the sluggish kinetics at the cathode reaction oxygen reduction reaction. In order to find a more effective cathode catalyst than commonly used Pt catalyst, alloying with another transition metal would help to build up a more favorable kinetic for the oxygen reduction reaction. Here we demonstrate a new method to fabricate uniform Pt-alloy nanorods with trimetallic structures. And these trimetallic nanorods exhibit relatively both higher activity and stability than state-of-art commercial Pt catalyst for oxygen reduction reaction.

Facet-controlled catalytic nanoparticles have received a great attention due to excellent selectivity and reactivity, and various methodologies are being developed to prepare facet-controlled nanoparticles. The manipulation of surface energy of a given facet by using surface-binding molecules has been the major synthetic strategy. The great popularization of this methodology in providing facet-controlled nanocrystals, however, has engendered a very simplistic view for nanocrystal growth, in which the nondescript precursors are decomposed to give a nanocrystal seed and the facets of a growing nanocrystal are determined by the degree of interactions between facets and surface binding moieties. In this mechanism, the effect of the surface-binding moiety is marginal on the exact process of precursor attachment/decomposition on the growing nanocrystal, because action of the surface-binding moiety commences only after each precursor attachment step to the nanocrystal surface. Therefore, in order to significantly affect the precursor attachment/decomposition step by the surface-binding process, it is required to use a precursor pre-coordinated by the surface-binding moiety; this ensures the lasting effect of surface-binding moiety throughout the entire crystal growth process. This strategy indeed leads to a completely new set of nanostructures from common precursors, and herein, we report its application in the preparation of novel Pt nanostructures.

Porous ceramics play a significant role in industry for a variety of applications related with environmental protection and energy production. Those include filters and catalyst supports for environmental purification systems, thermal insulators for energy saving and solid oxide fuel cell (SOFC) supports for energy production. In these applications, shape forming is one of the most important factors. Advanced shape forming technologies can facilitate porous ceramic components with complicated or large shapes, such as near-net shapes formed by gel casting or extrusion, and machined by cutting and polishing. In addition, porosity is another key factor, especially, where interconnected pores are required to provide high flux with low pressure drop in filter and catalyst supports. The porosity of porous materials manufactured in a natural way is on the level of approximately 40 vol.%. Thus, ultra highly porous components (porosity above 80%) with good permeability and desired shapes are essentially important in these industrial applications. Recently, we have developed an solid oxide electrolysis cell (SOEC). It was achieved drastic improvement of selective NOx decomposition in the presence of excess O2 at a low temperature range. However, it is necessary to make a large-scale reactor for step toward the practical use of SOEC. The purpose of this paper is to provide an ultra highly porous solid oxide solid oxide electrolysis cell with nano-structured electrode. New type of SOEC with ultra high porosity and unidirectionally oriented micrometer-sized cylindrical pores was prepared using a novel gelation-freezing (GF) method, which has advantages of high porosity (>70%), pore orientation control and near-net shape forming. The porous SOEC could be cut to varied sizes and shapes. Chipping was not observed during either wet or dry cutting processes. From the SEM observation of the porous SOECs with layered structure, there were also no delamination observed at the interfaces of each layers.

Micro-supercapacitors are getting continuously increasing attention in recent time because of their very high application potential in various MEMS energy storage applications, including portable electronics. Here we have introduced carbon nanotube (CNT) based micro-supercapacitor, which can be easily integrated to Microelectromechanical system (MEMS) - based energy devices, with very high specific areal capacitance of 2.78 mF cm-2 in organic electrolyte and 3.2 mFcm-2 in aqueous electrolyte. This device provides a very high volumetric energy density of 3.67 x 10-2 Wh.cm-3 in organic electrolyte. CNT thin films were used as active material for charge storage, and different thickness of CNT thin films were experimented for performance comparison. The areal capacitance was enhanced almost linearly with increasing thickness of the sample, with a very little change in volumetric capacitance. A 155% increment in areal capacitance, resulted in change in volumetric capacitance only by 5.6%. This indicates very good efficiency of the device, which is caused by easy electrolyte access to the active material, even for the case of thicker CNT films (~ 3 um). This phenomenon leads to successful fabrication of a MEMS-supercapacitor of variable capacitance, which capacitance is easily controllable by varying thickness of active material, exploiting the linear relationship of thickness and capacitance. At the same time fixed device, which is of highest priority in a MEMS device, promotes relative scaling of related electronics much simpler. Simple one step photolithography based easy and simple fabrication technique ensures very high reproducibility and promotes mass scale fabrication

Proton exchange membrane (PEM) fuel cells based on formic acid/methanol have attracted growing attention due to the high energy density and the convenient storage, transport of the small organic molecules. Pt-based nanoparticle (NP) catalysts are catalytically active towards the formic acid/methanol oxidation reaction (MOR/FAOR), but are prone to be severely poisoned by CO or other intermediate species during the catalytic process. Here we report a chemical synthesis of monodisperse trimetallic FePtM (M= Au, Ag, Cu) NPs with controlled composition and structure which exhibit exciting enhancements in both activity and durability for MOR/FAOR compared to traditional Pt and bimetallic Pt-based catalysts. Meanwhile, the design of trimetallic NP is further extended to Pd-based NPs which show reliable activity and durability towards FAOR.

Employing p-type Si nanowires as photocathodes, aromatic ketones can be readily reduced to its radical and further react with CO2, producing alpha-hydroxy acids. The reaction is powered by solar light and does not need precious metal as a catalyst, which makes it close resemblance to natural photosynthesis. Following advantages of p type Si nanowires (SiNWs) make them suitable to be utilized as the light-harvesting cathodes: 1. they are reasonably easy to fabricate; 2 they have relatively low price; 3 they have been shown high efficiency to convert solar energy into electronic forms; 4 they are quite stable at reductive conditions. First of all, the Si NWs is used to carry the formation of benzilic acid through CO2 fixation from benzophenone. The light is been absorbed by Si NWs, and photoelectrons-hole pairs are generated. The photogenerated electron transfers from Si NWs surface to the benzophenone in the solution, producing benzophenone radical which will quickly capture surrounding CO2 molecule. The radical-CO2 species will further accept one photogenerated electron from the Si NWs, forming the product anion. The sacrificial Al anode will accept the holes and form Al3+. After the protonation process, the corresponding alpha-hydroxy acids are converted from the reaction with high Faradic efficiency, yield and selectivity (as high as 94 %, 98 % and 100 % respectively). The fact that solar light are utilized as an important energy source makes our work distinguishable from other electrochemical reports. The reaction route is different from existing methods which seek to directly photo-reduce CO2 by p type semiconductors as well. Our approach tries to solve the critical challenge when direct reducing CO2 to fuels under light illumination: the involved multielectron transfer processes are usually suffering low Faradic efficiencies and low selectivities with significant byproducts. Futher more, two of the carboxylation products from acromate ketones (1-(4-isobutylphenyl)ethanone and 2-acetyl-6-methoxynaphthalene) serve as precursors to the anti-inflammatory drugs (NSAID) ibuprofen and naproxen are also made by this method with high yield (64 % and 97 % respectively). This reaction strategy has the potential to broaden the scope of artificial photosynthesis.

In this work, we will first report our efforts to produce PEDOT/carbon nanotube composites with highly crystalline structures for low overpotential and high efficient oxygen reduction. We would also share with you our recent efforts to fabricate vertically aligned carbon nanotubes directly grown on metallic substrates to further reduce ORR overpotential and increase fuel cell outputs. We first used ss-DNA dispersed single walled carbon nanotubes (SWNTs) to modify the working electrode (graphitic carbon, GC), and then a thin layer of PEDOT was deposited either by vapor phase polymerization (VPP) or electrochemical polymerization to obtain PEDOT/carbon nanotube composites on the GC electrode surface. We found that all the PEDOT/carbon nanotube composites shows dramatically higher ORR efficiency compared to PEDOT alone, demonstrated by the large positive shift (reduced overpotential) of the oxygen reduction potential and largely increased reduction current (Figure 1). The positive potential shift depends on the quality of the PEDOT in the composites. When PEDOT was deposited by vapor phase polymerization, which was known to produce PEDOT with better crystallinity compared to electrochemical polymerization approach, larger positive shift was observed. The synergistic enhanced effect of CNT and PEDOT in ORR was also demonstrated in the fast response to O2, which is related to the mass transport properties of O2 in the PEDOT-SWNT composite films. The PEDOT composite not only exhibited higher catalytic current toward reduction of O2, the response to O2 is also much faster compared to the control PEDOT and ss-DNA-SWNT only. Using rotating ring disk electrode (RRDE) to study the ORR route for the ORR, a four electron pathway was found for both PEDOT and DEDOT-SWNTs, a two electron pathway was found for SWNT alone. In the second part of the work, we directly grow vertically aligned carbon nanotube on metal substrates which is used as working electrodes for PEDOT deposition and ORR. We found that the ORR efficiency was further dramatically improved due to the largely reduced contract resistance between CNTs and CNT with the electrodes. Very importantly, the O2 catalytic activity has been monitored for 9 days, and did not found any sign of decrease of the catalytic activity. The excellent stability, demonstrated the ability for practically applications.

We have shown that titanium dioxide (TiO2) can reduce carbon dioxide (CO2) to methane and other hydrocarbons in the presence of UV light and a copper co-catalyst. Langmuir Blodgett thin films of TiO2 nanostructures, including nanoparticles, nanowires, and nanotubes, are used to study the photoreduction of CO2. The thin films are coated with a uniform, well-distributed array of electroplated copper nanoparticles. When illuminated with high energy light in an atmosphere of CO2 and water vapor, the films form primarily methane, as well as other products. Nanoscale interactions between copper and TiO2 were investigated to optimize copper nanoparticle dispersion. In addition, we demonstrate how device performance is dependent on the type of TiO2 nanostructure used. The TiO2 structure that gave the highest yield of methane was enhanced by introducing WO3 or quantum dots to broaden light absorption and improve methane yield.

Nowadays chemists are requested to envisage materials more and more complex in nature and structure, bearing some polyfunctionnality. When it turns to chemistry of materials, there is a crucial need for a “rational design” of functional architectures obtained through integrative chemistry[1]. We have synthesized three-dimensional carbonaceous electrodes with interconnected hierarchical porosity modified with Glucose Oxidase and Os 10 polymer.[2] The glucose electrooxidation current is 13-fold bigger on the porous electrode than on glassy carbon for the same enzyme loading. Therefore they have been proposed for devices needing high current output, such as biofuel cells. More recently, we have recently [3] shown that carbonaceous micro/macrocellular foams can be used for efficient and stable non-specific enzyme entrapment. In this context, Bilirubin Oxidase adsorbed into the porous electrode is able to reduce O2 to water and electrons are transfer directly from the electrode to the enzyme without the need of a redox mediator. The reduction current is stable for several days under continuous operation and therefore we consider the carbonaceous foams are very promising candidates for the construction of 3-dimensional biofuel cell cathodes. Mediator free, the electrode preparation and further enzyme adsorption are extremely simple, low cost and versatile. Most important, the excellent mechanical strength and the synthetic route allow us to design at will the size and external shape of the electrodes, which is of vital importance if we wish to incorporate electrodes into devices. [1] N. Brun, S. Ungureanu, H. Deleuze and R. Backov. Chem. Soc. Rev., 2011, 40, 771 [2] V.Flexer, N. Brun, R. Backov and N. Mano. Energy & Environmental Science, 2010, 3, 1302. (Cover) [3] V. Flexer, N. Brun, O. Courgean, R. Backov and N. Mano.Energy sect; Environmental Science, 2011, 4, 2097. (Cover)

This work centers on developing advanced free-standing nanoarchitectured layers including the current collector, the catalyst Pt, the nanostructured metal oxides (NMOs) catalysts promoter (SnO2, CeO2, TiO2, MnO2 and ZnO) and the multiwalled carbon nanotubes (MWNTs) as the catalyst support for direct ethanol fuel cells (DEFCs). For the first time NMOs-doped Pt catalysts were synthesized directly onto MWNTs by using the combination of chemical vapor deposition (CVD) and crossed beam laser deposition (CBLD) techniques. The formation of NMO-doped Pt materials were studied as a function of the CBLD deposition conditions background atmosphere, i.e. vacuum vs. helium (He) gas which allowed us to obtain various morphologies of the deposits: i.e., from discrete nanoparticles with controlled size to formation of a continuous smooth layered or highly porous layered film. In this talk, we will report the structure-electrocatalytic properties relationship associated with these nanostructures. These insights were obtained using a myriad of physico-chemical characterization techniques such as SEM, TEM and HR-TEM, XPS, MicroRaman, and XRD combined with electrochemical studies for ethanol electrooxidation, an electrochemical reaction that is central to DEFC technology.

Metallic glasses are multi-component metallic alloys that can be formed in fully amorphous, near-net shapes with nano-scale precision. They exist in a wide range of chemical compositions and have desirable chemistry for electro-catalysis. We have recently shown that the surface of metallic glasses can be electrochemically tuned to different morphologies with large active surface area. Motivated by these characteristics, we have explored the use of metallic glasses for electro-catalysis in direct alcohol fuel cells. We demonstrate that the activity and durability of metallic-glass nanostructures are superior compared to benchmark catalysts. The activity is further enhanced by de-alloying mediated surface engineering. New strategies to develop large surface area hierarchical nanostructures by accelerated de-alloying will be discussed.

The development of a cost effective process for the electrochemical reduction of CO2 could enable a shift to a sustainable energy economy and chemical industry. Coupled to a renewable energy source such as wind or solar, such a process could generate carbon neutral fuels or industrial chemicals that are conventionally derived from petroleum. A key technological challenge necessary to enable such a process is the development of catalysts that are active and selective for this reaction, i.e. catalysts that can reduce CO2 at low overpotentials, generate desirable products at high current densities over long periods of time, and do so selectively without the formation of unwanted byproducts. In this paper, we report new insights into the electrochemical reduction of CO2 on a number of metallic surfaces, enabled by the development of an experimental methodology with unprecedented sensitivity for the identification and quantification of CO2 electroreduction products. This involves a custom electrochemical cell designed to maximize product concentrations coupled to gas chromatography and nuclear magnetic resonance for the identification and quantification of gas and liquid products, respectively. We will start by addressing CO2 reduction chemistry on copper, where across a range of potentials we observed a total of 16 different CO2 reduction products, five of which are reported for the first time. This provides the most complete view of the reaction chemistry on copper reported to date. Taking into account the chemical identities of the wide range of C1-C3 products generated and the potential-dependence of their turnover frequencies, mechanistic information is deduced. We discuss a scheme for the formation of multicarbon products involving enol-like surface intermediates as a possible pathway, accounting for the observed selectivity for eleven distinct C2+ oxygenated products including aldehydes, ketones, alcohols, and carboxylic acids. We then expanded our studies to several other transition metal surfaces, including Ni, Pt, Au, Zn, Ag, and Fe among others. Utilizing the same experimental methodologies described above, we identified a number of new products never-before reported on these metals, and have uncovered design principles based on the electronic and geometric properties of these surfaces that influence reaction activity and selectivity. These results will be presented within a coherent framework that will provide insight for developing improved catalysts for the electrochemical conversion of CO2 to fuels and chemicals.

Atomically precise, ligand-stabilized Au₂₅ nanoclusters are exciting catalyst candidates for reactions like CO₂ reduction because they have an inherent negative charge (q = -1), their surface structure is precisely known from single-crystal x-ray diffraction studies, and they bridge the size-gap between molecules and nanoparticles. One problem facing traditional electrocatalysts is the large overpotential typically required to convert CO₂ into useful products like CO, CH₄, CH₃OH, etc. Remarkably, we found the Au₂₅ nanocatalysts can promote the reduction of CO₂ into CO within 90 mV of the formal electrochemical potential (thermodynamic limit). This represents a ~300 mV improvement over larger Au nanoparticles and bulk Au. Peak CO₂ conversion occurred at -1 V vs. the reversible hydrogen electrode with ~100% efficiency and rates 7-700 times higher than larger Au catalysts and 10-100 times higher than current state-of-the-art processes. Optical spectroscopy, non-aqueous electrochemistry and density functional theory (DFT) computational modeling were used to study the Au₂₅-CO₂ interaction. Specifically, we found CO₂ adsorption was based on an electrostatic interaction with the Au₂₅ surface. Our studies indicate the low-voltage conversion of CO₂ was promoted by unique reaction centers at the Au₂₅ nanocatalyst surface. The work described in this presentation has been published in the Journal of the American Chemical Society; electronic DOI: 10.1021/ja303259q.

Catalytic reduction of CO2 has been the target of many researchers since it is a direct source of global warming [1]. In electrochemical catalysis, copper is a well-known catalyst. However, a relatively high overpotential is observed for CO2 reduction [2]. In the present work we are report copper nanoparticles on graphene oxide as a catalyst system for reducing CO2. We have analyzed the catalytic activity of our hybrid system by cyclic voltammetry (CV) measured from 0.0 to -1.7 vs. normal hydrogen electrode (NHE) in acetonitrile with 0.1mol/L of tetra-n-butylammonium hexafluorophosphate at a scan rate of 50 mV/s. In addition we compare these results with Cu films, Cu nanoparticles supported by polymer (PAAm), rGO and glassy carbon. Was observed considerable reduction of the overpotential and good stability of CuNPs on rGO for CO2 reduction. Our results suggest that the Cu nanoparticles deposited on rGO are electrochemically more stable. [1] Barbara Fisher, R. E. (1980). Electrocatalytic reduction of carbon dioxide by using macrocycles of nickel and cobalt. Journal of the American Chemical Society, 102, 7361-7363. [2] Gattrell, M., Gupta, N., & Co, a. (2006). A review of the aqueous electrochemical reduction of CO2 to hydrocarbons at copper. Journal of Electroanalytical Chemistry, 594(1), 1-19. doi:10.1016/j.jelechem.2006.05.013

Ni foam, a low-cost and high surface area metal, has been used as a electrode in basic solutions. However, it is not suitable for the electrocatalytic reaction in an acidic solution such as the hydrogen evolution reaction (HER). Here, we report that the graphene sheets grown on Ni foams provide robust protection and efficiently increase its stability in acid. With the deposition of MoS2 nanoparticles it, the graphene-protected Ni foam is able to perform highly efficient HER reaction in 0.5M H2SO4 solutions. The MoS2 nanoparticles grown on exhibit high performance in electrochemical HER and the high H2 evolution rate reaches 1702.7 mlg-1h-1 at 200 mV overpotential. The average current density is around 42.07 mA/cm2 in this condition. The high H2 evolution rate is attributed to the unique 3D MoS2/graphene/Ni foam structure and the defected Mo6+ oxidation state in MoS2 materials.

For energy conversion the oxygen reduction and oxygen evolution reactions are of extreme interest. For both reactions a huge over potential is needed to obtain a reasonable current, and in both cases this is mainly due to sluggish catalysis. I study the reasons for the over potential on the basis of density functional simulations and determine activity descriptors, which are easy to calculate and therefore suited for computational screening for more active catalyst materials. Furthermore, descriptors for stability are fund. At last I show examples on design of new catalysts which was suggested by the simulations and later in rotating disk experiments showed an increased activity [1,2,3]. References 1 J.Greeley et al. Nature Chem 1. 552 (2009) 2 J.K. Noslash;rskov et al. Nature Chem 1. 37 (2009) 3 I.C. Man et al Chem.Cat.Chem 3. 1159 (2011)

The oxygen evolution reaction (OER) is kinetically slow and hence represents a significant efficiency loss in both electricity-driven and photo-driven water electrolysis. Understanding the relationships between catalyst architecture, composition, and activity are critical for the development of better catalysts. We report the solution-synthesis of ultra-thin-film metal-oxide electrocatalysts onto quartz-crystal microbalance electrodes where the mass is measured and monitored in-situ during electrocatalysis. The thin film architecture allows measurements of the intrinsic catalyst activity in the absence of confounding effects due to mass and electronic transport through typical thick high-surface area films. We quantitatively compare the intrinsic OER activity of ~2 nm-thick films of NiO_x, CoO_x, Ni_yCo_1-yO_x, Fe:NiO_x, IrO_x, MnO_x, and FeO_x catalysts in basic media, study the films&’ electrochemical redox behavior, and follow changes in the active catalyst structure during oxygen evolution using electrochemical and ex-situ surface analytical techniques. Fe:NiOx was found to be the most active OER catalyst in basic media, with the 2-nm-thick film passing ~20 mA cm^-2 at an overpotential of ~350 mV with a Tafel slope of < 30 mV/dec. Remarkably, the intrinsic OER activity measured for the Fe:NiO_x was roughly an order of magnitude higher than IrO_x control films, which is typically considered to be one of the best OER catalysts. The high activity is partially attributed to the in-situ formation of layered Fe:NiOOH with nearly every Ni atom electrochemically active. In contrast to previous reports that showed synergy between Co and Ni oxides for OER catalysis, Ni_yCo_1-yO_x showed decreasing activity relative to the pure NiO_x films with increasing Co content, which is partially due to the suppressed in-situ formation of the active layered NiOOH. These thin-film Ni-based catalysts are practically useful because the solution deposition techniques can be used to deposit the catalysts onto semiconductor photoelectrodes for sunlight-driven water splitting or to incorporate them into designer three-dimensional high-surface area electrodes for optimized dark OER performance.

The oxygen evolution reaction (OER) is a source of significant efficiency loss in electrochemical and photoelectrochemical water splitting, owing to its sluggish kinetics. In order to mitigate this problem in the pursuit of clean, low-cost hydrogen fuel generation, it is essential to develop highly efficient catalysts with an understanding of the surface structure-function relationship. Herein, we report that Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), a highly active perovskite oxide catalyst for the OER in alkaline electrolyte [1], undergoes a morphological change at its surface when electrochemically cycled through oxygen-evolving potentials. High-resolution transmission electron microscopy (HRTEM) showed that the surface of BSCF forms an amorphous layer, the thickness of which increases with longer cycling time. Energy-dispersive x-ray spectroscopy of the amorphous layer reveals reduced Ba2+ and Sr2+ concentrations, likely a result of the amorphization process. In addition, HRTEM revealed that several other perovskite oxides were found to remain crystalline at the surface under identical electrochemical conditions. We will discuss how an understanding of the interplay between electrochemical stability and surface structure doing the oxygen-evolving condition can lead to the design of high activity catalysts. [1] J. Suntivich, K.J. May, H.A. Gasteiger, J.B. Goodenough, Y. Shao-Horn, Science 334, 1383 (2011).

Water dissociation and formation have been investigated intensively for the realization of next generation energy storage and conversion systems. To overcome the current limits of energy systems, harnessing the tunable physical and chemical properties of novel complex perovskite oxides is a promising route. However, the electrochemical reaction mechanisms on complex oxide surfaces and interfaces are poorly understood, particularly with regard to time-dependent phenomena occurring in aqueous solutions and applied electric fields. To elucidate the electrocatalytic properties of oxide surfaces and interfaces, it is necessary to employ in-situ experimental tools to detect and analyze the complex time-dependent phenomena. We performed in-situ synchrotron studies, combining structural, spectroscopic, and electrochemical characterization on epitaxial SrRuO3 thin films grown on Nb-doped SrTiO3 (001) substrates, under electrocatalytic conditions. We found that SrRuO3 exhibited high oxygen evolution reaction activity, but the surface is not structurally stable under high electric field. The c-axis (out-of-plane) lattice parameter of SrRuO3 was observed to change reversibly with varying electric field at potentials smaller than 1.25 V vs. RHE, but the SrRuO3 irreversibly changed at potentials greater than 1.55 V vs. RHE. The structural instability correlated with changes of our in-situ spectroscopic measurements that showed a change in Ru valence connected to the loss of perovskite structure. With this methodology, we can determine the stability of active sites on complex oxide surfaces during water dissociation and formation. The results will provide much needed insight into the creation of new stable and active electrocatalysts designed on the atomic level.

The design of efficient and cost effective catalysts is fundamental for many electrochemical energy conversion and storage reactions such as Oxygen Evolution Reaction (OER) or Oxygen Reduction Reaction (ORR). However, only the understanding of materials structure - properties relationship could provide an accurate descriptor to design effective catalysts and achieve high activity. Perovskite-related oxides AMO3-d are the perfect playground for chemists to tailor the metal-oxygen bond and to shape oxides with the required physical properties as their electronic structure can be easily tuned either by A site doping or by the modification of transition metals. As shown by Suntivich et al., whilst the ORR activity of Perovskite can be perfectly predicted by the filling of transition metal eg orbital electrons [1], the transition metal-oxygen bond covalency appears as another key parameter for OER activity completing the eg filling descriptor [2,3]. In addition to these electronic considerations, everything remains to discover in the understanding of the active site at an atomic level. Once again, chemist can take advantage of the incredible flexibility of Perovskite oxides to design oxygen reactive sites with different coordination numbers. Starting from Ba0.5Sr0.5Co0.8Fe0.2O3-d (BSCF) which shows the highest OER activity [2], we will discuss in this contribution how the oxygen coordination affects the Perovskite activity. For this purpose, hexagonal Perovskites such as 2H, 5H or 6H which consist of alternative plans of corner and face shared octahedral were selected and tested. [1] - J. Suntivich, H.A. Gasteiger, N. Yabuuchi, H. Nakanishi, J.B. Goodenough and Y. Shao-Horn, Nature Chemistry, 2011, 3, 546 [2] - J. Suntivich, K.J. May, H.A. Gasteiger, J.B. Goodenough and Y. Shao-Horn, Science, 2011, 334, 1383 [3] - J. Suntivich et al. To be published

Bi-functional oxygen electrodes are an enabling component for rechargeable metal-air batteries and regenerative fuel cells, both of which are regarded as the next-generation energy devices with zero emission. Nonetheless, at the present, no single metal oxide component can catalyze both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with high performance which leads to large overpotential between ORR and OER. This work strives to address this limitation by studying the bi-functional electrocatalytic activity of the composite of a good ORR catalyst compound (e.g. palladium oxide, PdO) and a good OER catalyst compound (e.g. ruthenium oxide, RuO2) in alkaline solution (0.1M KOH) utilizing a thin-film rotating disk electrode technique. The studied compositions include PdO, RuO2, PdO/RuO2 (25wt.%/75wt.%), PdO/RuO2 (50wt.%/50wt.%) and PdO/RuO2 (75wt.%/25wt.%). The lowest overpotential of ~0.495 V is obtained for PdO/RuO2 (50wt.%/50wt.%) showing ORR onset at ~-0.045V and OER onset at ~0.45V (all potentials versus Ag|AgCl (3M NaCl) reference electrode). The Koutecky-Levich plots of ORR suggest two-electron mechanism for RuO2 and four-electron mechanism for PdO containing compositions. The fact that the ORR is limited by the oxygen in the solution and its diffusion to the electrocatalyst surface is evidenced by the formation of current plateau at ~-0.6V. The OER, in contrast, does not show any formation of current plateau up to ~1.8V due to its dependence on water which is abundantly available in the solution.

Soft liquid-liquid interfaces can be polarized either using an external power supply or chemically by a judicious choice of the distribution of supporting electrolytes. Different electrochemical reactions can be studied at soft interfaces such as ion transfer reactions such as proton transfer or electron transfer reactions. We have recently shown that it was possible to functionalize soft interfaces with molecular electroacatalysts and also by nano particles catalysts. This presentation will describe oxygen reduction at liquid-liquid interfaces catalyzed by self assembled molecular rafts. We shall then present hydrogen evolution at liquid-liquid interfaces catalyzed by molybdenum based nano catalysts. Finally, we shall discuss reactivity at the water- supercritical CO2 interface.

Carbon nanotube reinforced mesoporous or microporous graphitized carbon-based materials have many applications in sustainable energy storage and energy conversion devices, such as supercapacitors, PEMFCs, DMFCs, and batteries. It is well known that high level of graphitization improves chemical stability, durability, and electric conductivity. The transition metals such as iron, nickel and cobalt impregnated into carbon-based materials are known to decrease the graphitization temperature. Defective graphite phases observed after nitrogen doping display higher activity and stability. Furthermore, high electrical conductivity, high transport capability, and high mesoporosity of carbon nanotubes enhance accessibility of electrolyte for higher rates of charging-discharging cycles and stability of supercapacitor electrodes. However, the correlation between the carbon sintering temperature, morphology, and crystal structure is not very well understood. In our study, carbon nanotubes growth within 3D-nanostructure of iron and nitrogen impregnated graphitized mesoporous carbon aerogels have been investigated. The morphology, structure, and chemical composition of the synthesized architectures as a function of heat treatment conditions, sintering temperature, and iron content were investigated. The chemical stability and catalytic activity of these materials was studied in fuel cell and super capacitor electrode materials. Iron nanoparticles were impregnated into the 3D-carbon aerogel nanomatrix by wet incipient method under ultrasonic conditions using stoichiometric amounts of iron nitrate solution. After drying at 50^oC in air the samples with 10 wt.% and 20 wt.% of iron in carbon aerogel were obtained. These samples as well as the untreated carbon aerogel samples (0 wt.% Fe) were heat treated at 900^oC, 1200^oC and 1400^oC in argon for 1 hour. The TEM analysis confirmed formation of the targeted compositions of iron and nitrogen doped carbon aerogels with uniformly distributed iron nanoparticles surrounded by graphite layers. The XRD and temperature programed reduction (TPR) analysis demonstrated that the level of graphitization was sensitive to the sintering temperature and the concentration of iron phase. The BET and pore size distribution studies revealed that the mesoporous nature of 3D-modified carbon aerogels remained intact after high temperature heat treatment. Carbon nanotubes growth in Ar/H2/acetylene within the iron impregnated 3D nanostructures of carbon aerogels will be discussed in terms of parameters optimization for carbon nanotube growth. The comparative study of the iron and nitrogen doped carbon aerogels before and after the nanotube growth will be presented as well as their catalytic activity and chemical stability as electrode materials for fuel cell and supercapacitors.

Electrochemical Atomic Layer Deposition (E-ALD) is a two-step process that exploits the fact that some materials electrodeposit as a monolayer onto a dissimilar substrate at a less negative potential than they would deposit onto themselves. In the second step, yet another dissimilar material is deposited, or a more noble element displaces the first. The process can be repeated with varying reagents, allowing deposition of nanoscale structures, including superlattices of compound semiconductors, and multilayer noble metal films for catalysis and sensing. The films can be grown to arbitrary thicknesses, albeit one layer at a time. This is typically done in an electrochemical flow cell, so milliliter quantities of deposition and rinse electrolytes are needed for each step. When scaled up for substrates with high surface areas, large electrical current sources may be required. We have developed versions of this method in which a surface hydride is formed by electroless (chemical) deposition, effectively creating a metal hydride electrode. The hydride is then displaced by reduction of a more noble metal salt in a surface-limited reaction. If the more noble element also forms a surface hydride, this process can be repeated. Since the hydride is formed chemically, by exposure to H2 gas or a hydride-containing reducing agent, the electrochemical instrumentation need not scale with the substrate size, and electrical contact to the substrate is not required. The displacing element can be potentiometrically titrated, allowing controlled growth in a batch reactor, so the waste stream does not scale with sample size, as it would with a flow cell. Furthermore, some transition metal salts typically used as reagents in E-ALD, that may require waste remediation, are replaced by benign gaseous reagents in this technique. While we are primarily studying catalytic noble metal films and sensors, we believe that this can be a widely applicable approach to the large-scale preparation of crystalline materials that have precisely defined nanoscale structure, and the enhanced mechanical, electrical, thermal, optical, or other properties that are predicted to result from this. 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.

Recently, paper has been suggested as a low cost, flexible, lightweight and biocompatible alternative for low cost diagnostics, sensing and electronics. Microelectrodes are common in biomedical applications like biopotential recording and stimulation, electrochemical sensing and as electrodes for supercapacitors and battery. However, fabrication of high surface area electrode on paper has not been demonstrated yet. In this paper we present an efficient approach for making high surface area electrode using low temperature electrodeposition of nickel nanoparticles through pores on paper. This method allows alignment of nanoparticle on substrate without any template and lithography. First patterned stencil is fabricated on a tape using laser cutter and attached to paper. Second, 200nm gold is sputtered on paper and stencil is removed leaving behind the desired electrode pattern. This creates an electrode on one side of the paper. At next step these electrodes are covered using plastic tape or photoresist and nickel nano particle is deposited using constant current electrodeposition through pores on paper. Removing the cover results in a two sided electrode with high surface area due to nanoparticle deposition on one side. Impedance measurement of the new electrode respect to Ag/AgCl as a reference in buffer solution showed impedance reduction of greater than 4 percent compared to bare gold electrode on paper. Utilizing papers with high porosity and adjusting the parameters of electrodeposition, one can expect over 50% improvement in electrode impedance.

Hydrogen fuels for Fuel Cell Vehicle (FCV) should be highly purified because Polymer Electrolyte Fuel Cells (PEFC) are sensitive against impurities. Especially, CO, sulfuric compound and NH3 can be included in practical hydrogen fuel gases depending on hydrogen production methods and can decrease fuel cell performances seriously. The International Organization for Standardization (ISO) proposed an international standard of technical specification which specifies the kinds of impurities and their acceptable concentrations. In this specification, concentrations of CO, sulfuric compound, and NH3 are considered to be less than 0.2 ppm, 0.004 ppm, and 0.1 ppm, respectively. Therefore, sensors which can detect impurities in hydrogen fuels in an inexpensive way are strongly required. In this study, we use a PEFC with a low amount of catalyst down to 0.075 mgPt/cm2, as a unique hydrogen pump type sensor cell which exhibits increased overvoltage by impurity poisoning. We investigated the impurity response by changing the amount of Pt, humidity, temperature, impurity concentration, and current density. Moreover, Electrochemical Impedance Spectroscopy (EIS) was applied to separate different resistances. Hydrogen-pump-type sensor cell was prepared in accordance with a common Membrane Electrode Assembly (MEA) preparation procedure of PEFC. All cell tests were conducted at galvanostatic condition and the performance of the sensors are evaluated by measuring cell voltage. It is obvious that these impurities were detectable by using this sensor as cell voltage increases by impurities such as CO in hydrogen fuels. Optimized operational temperature and humidity conditions have been revealed.

To suppress the concentration of carbon dioxide (CO2) in atmosphere, it is quite important to reduce and recycle the CO2 worldwide. One of the most expecting methods is a direct conversion of CO2 with light and water, so-called artificial photosynthesis. We found that gallium nitride (GaN) is a good candidate for CO2 photoreduction due to its low electron affinity and large band-gap. Combined with copper (Cu) cathode electrode, CO2 reduction by light illumination was realized without external bias and sacrificial materials. It has been also reported that the hetero structure with aluminum doped GaN, such as AlGaN/GaN, improves its capability for CO2 reduction. One of the characteristic features of this system is to have a capability for designing the cathode and anode independently. This means that a series of reaction products can be produced from CO2 reduction by applying an appropriate cathode electrode. In this study, we report that selective CO2 conversions to formic acid (HCOOH) and carbon monoxide (CO) are realized with AlGaN/GaN hetero structure photoelectrode and respective metal cathode electrodes. We applied indium (In) for HCOOH and gold (Au) for CO. Although there have been a lot of researches of selective production of CO and HCOOH using metal-complex system, it is the first report in inorganic system to convert the CO2 to HCOOH and CO selectively with high efficiency. We used H-type cell which contains two chambers separated by cation exchange membrane. AlGaN/GaN and In were immersed in 1 M NaOH and 0.5 M KHCO3 electrolyte, respectively, for HCOOH production. In the case of CO, AlGaN/GaN was immersed in 5 M NaOH and Au in 3 M KCl electrolyte. In both cases, cathode and anode electrodes were electrically connected via an ammeter. A 300-W Xe arc lamp with a UV spectroscopic mirror (250 ~ 400 nm) was used as a light source. The illuminated area was about 4cm2. For estimating the conversion efficiency of CO2 reduction from solar light, we introduced a quasi-solar light by adjusting the UV intensity the same as that of AM1.5. With UV illumination, the absolute value of photocurrent was 0.8 mA and Faradaic efficiency of HCOOH production was ~61% in AlGaN/GaN-In system. Estimated energy conversion efficiency of HCOOH production from solar light was 0.15%. For evaluation of CO production in AlGaN/GaN-Au system, we applied the concentrated UV light whose intensity was 10 times larger than that of AM1.5. The photocurrent was 7.5 mA and Faradaic efficiency of CO production was 71% in which estimated energy conversion efficiency from concentrated solar light was 0.20%. In each case, the efficiency is close to that of natural photosynthesis in plants. The selective CO2 conversion presented here will make it possible to expand its application to practical use.

The photoelectrochemical production of liquid fuels from carbon dioxide is appealing both in terms of climate change issues and new sustainable energy resources. To this end, we have proposed the electrosynthesis of alcohols containing one or more carbons from carbon dioxide . The large activation energy associated with this multielectron, proton coupled reduction makes the conversions of interest problematic. However, we have found that pyridinium and its derivatives catalyze the reduction of carbon dioxide to methanol at a variety of electrode interfaces including illuminated p-GaP photocathodes. In the presence of pyridinium, the observed reduction involves a mediated charge transfer process, which is initiated by the one electron reduction of pyridinium. Reaction of this neutral pyridinyl radical with dissolved carbon dioxide is hypothesized to lead to the formation of a carbamate radical intermediate. Further reduction produces formate then formaldehyde and finally methanol. The processes outlined here can be modified to introduce the formation of carbon-carbon bonds by introduction of other aromatic amines or by variation of the electrode material. The appropriate mating of substituted aromatic amine with semiconductor surface is found to produce high energy products such as isopropanol and butanol. The product distribution obtained is found to be sensitive to the specific electrode surface employed. Additionally, long-term electrode stability is found to be an issue. Thus, new photocathode materials that provide for the stable formation of specific products via the aromatic amine mediated reduction pathway are desirable. To this end, we are investigating a set of delafossite oxides as p-type photocathodes. This class of materials has been selected due to their anticipated stability under reducing conditions, along with their amenability to bandgap engineering. This allows the semiconductor band edges to be positioned with respect to the redox potentials of interest. In addition to controlling interfacial energetics within the electrochemical cell, one must also consider the rate constants for the reduction of the pyridyl catalyst. These parameters are only accessible experimentally. Therefore, we have undertaken a broad spectrum study of delafossite oxide structures as photocathodes for the catalytic reduction of carbon dioxide. We find that structures containing copper, iron, or chromium appear to provide improved charge transfer dynamics. The specific current-voltage response of key cathode materials will be presented in this talk along with a generalized energetics/kinetics scheme that correlates material composition, structure, and electrochemical parameters. Through this work a more detailed mechanistic understanding of pyridine as an electrocatalyst is developing. Our latest mechanistic understanding is provided.

Reducing carbon dioxide (CO2) in atmosphere is a grand challenge in this century. Among numerous approaches, the photo-catalytic conversion of the CO2 draws an attention for many scientists since it can recycle a waste combustion product into hydrocarbon fuel. Ever since the photo-catalytic reduction of CO2 on TiO2 discovered in a few decades ago, numerous researchers have been extensively studied to understand and improve the photo-catalytic reaction on the TiO2 surface. It is commonly believed that the photo-catalytic reduction of CO2 into the hydrocarbon fuel takes two different reaction routes: formic acid route and CO desorption route. Using accurate first principal approaches, we have shown that both reaction pathways have significant amount of energy barrier on the TiO2 surface. Following-up studies, however, show that the reaction barriers for CO2 reduction can be significantly reduced on small TiO2 nano-cluster. Using accurate first principal approaches, we have identified that the origin of the barrier reduction comes from a lower coordinated Ti atom. In conclusion, the energetics of the photo-catalytic reduction of CO2 on TiO2 are understood by employing first principal approaches.

Photoelectrochemical (PEC) water splitting has been regarded as the promising scheme to produce hydrogen utilizing solar energy. One of the advantageous point of this method is applicability of powder semiconductor materials by coating method like spraying and squeegee methods because of the driving force of PEC water splitting coming from the band bending formed at the solid-liquid interfaces. Even if the surface is a rough particle layer, the electrolyte solution automatically forms the proper solid-liquid interface for whole semiconductor surfaces, where photoexcited carriers are separated by built in potential. Oxynitride materials are promising candidates of semiconductor electrodes in PEC water splitting. LaTiO2N have a proper electronic structure for water splitting. LaTiO2N absorbs visible light up to 600 nm (Eg = 2.1 eV), so that they can utilize more solar energy than oxide photocatalysts, which typically have absorption in the UV region. Photoelectrodes based on the material have been studied extensively by various methods and they were highlighted in this study. In the present study, we report a novel fabrication method of photoelectrodes for PEC water splitting using semiconductor powders. This method, which we have named the particle transfer (PT) method, is shown to be applicable to a variety of semiconductor powders. LaTiO2N was demonstrated to exceed those prepared by the reported method of photoelectrode fabrication from powder materials. LaTiO2N electrodes were fabricated by the PT method. First, photocatalyst particles are deposited on a primary substrate, followed by deposition of thin metal layers to form a proper contact to LaTiO2N particles. Thin metal layers were formed on the contact layer for sufficient electric conductivity. Finally, the primary substrate and excess particles are removed. In this study, Ta and Ti were employed as the contact layer material and conductor layer material and sputtering method was used to form the contact layers and the conductor layers. Excessive particles were removed by ultrasonic cleaning underwater. The electrodes fabricated by PT-method were characterized by scanning electron microscopy (SEM) to declare the obtained structure. PEC properties were measured by a 3-electrode system. The specimen, an Ag/AgCl, and a Pt wire were connected to a potentiostat as the working, reference and counter electrodes, respectively. All PEC measurements were performed under Ar atmosphere. Through this study, we confirmed the potential of the PT method to prepare high-performance photoelectrodes easily and simply.

Abstract: CdS modified TiO₂ nanotube arrays were fabricated using an anodic oxidation-sequential chemical bath deposition process. By means of FESEM, EDS, XRD and XPS, it could be confirmed that the use of a ultrasonication-assisted deposition approach improved the distribution of CdS QDs on the tube walls. The radius of the formed hexagonal CdS QDs was about 3nm. The as-prepared CdS modified TiO₂ nanotube arrays exhibited enhanced photoelectrochemical properties and hydrogen production activity, which depended on the extended light absorption and more on the improved interfacial properties of TiO₂ nanotube arrays, caused by the deposition of CdS QDs. By analyzing of the interfacial properties, the flatband potential, the depletion layer and the capacitance and impedance of the CdS/TiO₂ photoelectrode, it can be concluded that, compared to pure TiO₂ nanotube arrays, the CdS QDs modified arrays exhibited a more negative flat band potential and a lower energy barrier for theinterfacial electron transfer. The calculated depletion layer width (d_SC) of TiO₂ nanotube arrays sensitized by CdS QDs was larger, which under a sufficiently high applied potential, could facilitate the formation of a completed depletion layer; the space charge capacitance (depletion layer capacitance) and the double layer capacitance increased with the CdS QDs modification, and the impedance and charge transfer resistance were reduced. Thus, an increase of the photoelectrochemical reaction rate on the CdS-TiO₂ photoelectrode resulted in higher energy conversion efficiency.

Energy storage system from sunlight is extremely important technology to establish renewable energy cycle. Photoelectrochemical (PEC) water splitting is most expecting technique for the energy storage due to the theoretical usable sunlight energy being over 50%. Most of the experimental energy conversion efficiency is, however, up to a few %. In this report, we propose a new concept for electrochemical hydrogen generation from water. The system consists with a concentrated photovoltaic cell (CPV) and a polymer electrolyte electrochemical cell (PEEC). In comparison, conventional poly-crystalline silicon solar cells (c-Si SC) and PEEC system was also used. The CPV and PEEC were directly connected electrically without any conversion. The CPV was GaInP/InGaAs/Ge 3-tundem cell with 1.0 x 1.0 cm² square. The PEEC was Pt-loaded carbon paper electrode with proton conducting polymer membrane as an electrolyte with 4.0 cm² electrode area. Pure water was used as a splitting source. The illumination for the CPV was performed using concentrated light of AM1.5G solar simulators instead of the concentrated sunlight. The cooling equipment for CPV was not used, thus, the cell temperature rose with increasing the light intensity. The turn-on voltage of PEEC was 1.46 V. The operating voltages were 1.56 V at 100 mA, and 1.71 V at 500 mA. The open-circuit voltage (Vop) of c-Si SC is around 0.6 V, thus, series connection of c-Si SC is required in order to operate the PEEC. For our case, the Voc of 3-series connection c-Si SC was 1.52 V under 291 mW/cm² illumination (2.91 SUN), and that of 4-series connection c-Si SC was 2.23 V under 0.49 SUN. This shows that at least 3-series connection of c-Si SC is needed to operate the PEEC. The PEEC operation by 4-series connection c-Si SC (total area 81.1 cm²) was 1.71 V and 198.4 mA under 0.49 SUN. The electrical conversion efficiency (Eff-e) and estimated hydrogen energy conversion efficiency (Eff-h: using the voltage of 1.23 V as the energy storage as hydrogen) were 8.5% and 6.1% respectively. The characteristics of the CPV were short-circuit current (Isc) 25.3 mA, open-circuit voltage (Vop) 2.64 V, and maximum operation power (Pmax) 58.6 mW (Imax = 25.3 mA, Vmax = 2.32 V) under 2.91 SUN. The Voc shows that series connection is not necessary to operate the PEEC by this CPV. The operation of the PEEC with direct connected to the CPV was 25.5 mA and 1.51 V under 2.91 SUN. The operation of 100.5 mA and 1.61 V was observed under 10.12 SUN. The Eff-e and Eff-h under 10.12 SUN were 16.0% and 12.2%, respectively. This is much higher than that with c-Si SC case. The time dependence of the operation was stable, and 20 ml hydrogen and 10 ml oxygen were obtained after 27.5 min operation under 10.12 SUN. The electron conversion efficiency from the current to hydrogen was estimated to be 0.97.

Continuous electrochemical flow reactors for efficient conversion of electrical energy into chemicals and vice versa, i.e. fuel cells and electrolyzers, become increasingly important for our energy sustainability and environmental concerns. The search for improved electrocatalyst materials, which constitute the core of electrochemical energy conversion devices, has been typically dominated by the optimization of kinetic activity of catalysts and efficiency of whole cells. However, also the stability of the materials is highly important for a potential commercialization, if not even more important, and should at least always be considered in parallel. In this presentation I will demonstrate how such investigations are done on a fundamental level, and what can be learned from these studies for large scale applications. The focus will be on the methodological developments from our group like identical location electron microscopy (IL-EM) and the scanning flow cell (SFC) coupled to an ICP-MS [1-3], as well as typical carbon supported noble metal catalysts as used in low-temperature fuel cell electrochemical reactors. [1] K. J. J. Mayrhofer et al., Journal of Power Sources 2008, 185, 734. [2] J.C. Meier et al., ACS Catalysis 2012, 2, 832. [3] S. O. Klemm et al., Electrochemistry Communications 2011, 13, 1533.

Extended platinum surfaces have recently been pursued for their use as oxygen reduction reaction catalysts. The initial results from these studies show promising performance metrics capable of surpassing the DOE benchmarks for fuel cell development. In this study, we utilize an anodized aluminum oxide template approach in conjunction with gas phase deposition of platinum to produce a controlled layer of platinum nanoparticles and to study the effect of platinum layer morphology. Atomic Layer Deposition is used to grow layers of platinum of varied continuity and particle size, a unique capability of this precise technique. Following platinum deposition, a thin carbon film is created via chemical vapor deposition to support the platinum nanoparticles and to improve electrical continuity. These extended platinum surfaces are then recovered via etching of the template and tested for electrochemical performance versus the film morphology and carbon support composition. Specifically, we analyze the performance of samples of varied platinum weight percent and with doped versus undoped (boron and nitrogen) carbon supports.

We present a study of size selected Pt-Nanoclusters (NCs) - supported either on glassy carbon tips or on TEM gold grids covered by an amorphous carbon film - probing their electrocatalytic properties. The well-defined Pt-NCs have been prepared by an ultra-high vacuum (UHV) laser vaporization source and were deposited with low kinetic energy. Samples thus prepared can be employed as working electrodes in a standard electrochemical three electrode setup, where the Pt-NCs can be subjected to different electrochemical treatments, such as ORR activity measuremetns or accelerated degradation tests. While the ORR studies allow a precise study of the so-called particle size effect, enable the TEM measurements a characterization of the Nanoclusters before and after the treatment concerning particle size and distribution on the support. Depending on the electrochemical treatment protocol, e.g. potential window and cyclic profiles (linear sweep or potential steps), different degradation mechanisms are revealed. Interestingly, all treatments cause a more or less pronounced migration of particles, so that the initial random distribution of the Nanoclusters on the support is abrogated and an agglomeration process is initiated, as was also observed previously after potential cycling in presence of CO. Further we found that a severe amount of particles is lost during accelerated degradation tests by simple detachment from the support, while only rare indications could be found for a massive dissolution of the particles.

Electrocatalysis in Polymer Electrolyte Fuel Cells (PEFCs) is a lively field in PEFC research, due to the fact that especially the cathodic oxygen reduction reaction is one of the reasons for efficiency limitations. In addition, the cathode itself is one of the components with major challenges for lifetime, due to corrosion instabilities of both, the catalyst support and the active phase consisting of typically Pt nanoparticles. One of the approaches to overcome catalyst lifetime limitations is the transition from supported Pt nanoparticles to unsupported extended Pt-surfaces (i.e., Pt-black type catalyst layers). During the last decade, this approach is mainly driven by 3M with their nanostructured thin-film (NSTF) catalysts, currently representing one of the most feasible catalyst (layer) systems availabe for PEFCs [1, 2]. In this contribution, we will demonstrate the advantages and drawbacks of extended Pt-black type surfaces by using our own approach for preparation of model and PEFC electrodes, respectively, utilizing Pt particle and layer growth by Magnetron sputtering [3]. Strategically, we combine model studies using rotating-disk electrode measurements of layered and nanoparticle Pt catalyst and electrochemical PEFC electrode characterization in order to understand both, kinetic and stability properties of the different systems, including elucidating the effect of low Pt loading limits for both anode and cathode. In addition, we demonstrate the effect of Pt surface area on the kinetic surface and mass specific activities, respectively, commonly known as particle size effect. References [1] M.K. Debe, ECS Transactions 45(2) (2012) 47-68 [2] A. Rabis, P. Rodriguez, T.J. Schmidt, ACS Catal., 2012, 2 (5), pp 864-890 [3] B. Schwanitz, A. Rabis, M. Horisberger, G.G. Scherer, T.J. Schmidt, Chimia 66 (2012) 110-119.

Development of advanced electrocatalysts for PEMFCs and electrolyzers requires improvement in both catalytic activity and stability. Extensive effort has been placed on making small platinum (Pt) nanoparticles by taking advantage of the large surface/volume ratio to reach high mass activity. Commercial catalysts with Pt nanoparticles of 2 to 3 nm in size, however, have been found to be unstable under PEMFC operation conditions, where migration and dissolution/re-deposition of Pt surface atoms result in substantial losses of electrochemically active surface area and catalytic activity. Therefore, understanding the particle size effect on stability becomes important for the development of advanced electrocatalysts with both high activity and high stability. Here we report a systematic investigation of particle size effect on the stability of Pt electrocatalysts for the oxygen reduction reaction (ORR). Instead of using commercial catalysts with broad particle size and shape distributions, we developed an organic solution approach to synthesize monodisperse and uniform Pt nanoparticles of various particle sizes (2 - 10 nm). The obtained Pt nanoparticles were supported on high-surface-area carbon, and the employed organic surfactants were removed by simple low-temperature thermal treatment. Electrochemical studies by rotating disk electrode revealed that, not only the catalytic activity, but also the catalyst stability is dependent on the particle size. Moreover, a volcano-type dependence of catalytic performance on particle size was established, with an intermediate particle size of 5 nm reaching the fine balance between activity and stability and showing the highest mass activity after extensive potential cycling.

Hydrogen-powered fuel cells provide the sole automotive powertrain option that offers the combined potential of petroleum-free, local-emissions-free and green-house-gas-emission-free driving with range and fast recharge commensurate with current customer expectations. Over the last decade, commercially viable performance and durability of automotive polymer-electrolyte fuel cells have been demonstrated, and automakers are now focused on cost reduction. The cathode, currently containing tens of grams of platinum per vehicle, is the most significant technical challenge impacting cost. Reasonable development targets, corresponding with cost equivalence with the precious metal in a catalytic convertor, can be set at no more than 10 gm Pt/vehicle and preferably less than 5 gm Pt/vehicle. At high loadings, in the neighborhood of 0.4 mg Pt/cm2 (corresponding to 40 gm Pt/vehicle assuming 100 kW, 1 W/cm2), the polarization curve is controlled by relatively well understood voltage loss terms. However, as the loading decreases to 0.05 mg Pt/cm2 (5 gm Pt/vehicle), kinetics deviate from standard formulations and new transport-limited regimes are encountered. Moreover, small amounts of anion contaminants become more critical and mitigation approaches must be developed. In this talk, we will establish the unique challenges associated with these low-Pt-loaded cathodes, ones not apparent in the studies of higher-loaded systems.

In this paper we present a physical multiscale modeling study combining Mean Field simulations with Monte Carlo and Molecular Dynamics-generated PFSA ionomer structural databases to understand the electrochemical double layer formation in PEMFC electrodes [1]. Based on previously reported results [2], the impact of the catalyst physicochemical properties on the ionomer interfacial structure is discussed and the consequent impact of the iinterfacial ionomer on the effective ORR kinetics and catalyst stability (dissolution) is in particular evaluated based on Mean Field elementary kinetic simulations. Advances and limitations of this model are discussed. The relevance of deeply understanding these processes on determining the overall PEMFC performance and the Pt catalyst loading reduction is highlighted. References [1] A.A. Franco, PEMFC degradation modeling and analysis, book chapter in: Polymer electrolyte membrane and direct methanol fuel cell technology (PEMFCs and DMFCs) - Volume 1: Fundamentals and performance, edited by C. Hartnig and C. Roth (publisher: Woodhead, Cambridge, UK) (2012). [2] D.D. Borges, S. Mossa, K. Malek, G. Gebel, A.A. Franco, ECS Trans., submitted (2012).

Transition metal (TM) macrocyclic complexes have been studied extensively as electrocatalysts for oxygen reduction reactions (ORR), particularly for fuel cell application in alkaline solutions. Despite much progress, reaction mechanisms of ORR on these catalysts at a molecular level have not been well understood yet. Employing density function theory (DFT) calculations, we have studied the adsorption process of O2, H2O, OH, and H2O2 molecules on TM porphyrins, TM tetraphenylporphyrins, TM phthalocyanines, TM fluorinated phthalocyanines, and TM chlorinated phthalocyanines (here, TM=Fe or Co). In this way, we achieved a fundamental understanding about the proceeding of ORR catalyzed by the Fe- and Co- macrocyclic molecules. By relating our theoretical results with published experimental observations, we concluded for ORR on the Fe- and Co- macrocyclic molecules that (1) O2 adsorption process is the limiting step affecting the kinetics of ORR, (2) OH adsorption process determines the durability of the molecular catalysts, and (3) H2O2 adsorption process distinguishes the four-electron and two-electron routes of ORR. Moreover, our study provides new guiding principles on how to tailor the chemistry to attain better TM macrocyclic molecule catalysts for solid electrolyte alkaline fuel cells. Specifically, we found that (1) the type of the central transition metal is the most determinant factor in influencing the adsorption energies of O2, OH, and H2O2 (chemical species involved in ORR) molecules on these macrocyclic complexes; (2) the peripheral ligands are capable of modulating the binding strength between the adsorbed O2, OH, and H2O2 and the TM macrocyclic complexes; and (3) a N-TM-N cluster structure (like N-Fe-N) with a proper distance between the two ending N atoms and a strong electronic interaction among the three atoms is required to break the O-O bond and thus promote the efficient four electron pathway of the ORR on the TM macrocyclic complexes.

Over the past decade, carbon nanotubes (CNT) have retained high attention due to their potential interest for the elaboration of fuel cells electrodes. They are studied as both, conducting support for platinum (Pt) based electrocatalysts and more recently, as electrocatalyst itself when doped with nitrogen. Within this frame, we developed an approach involving controlled handling of CNT and Platinum Organically Grafted Electrocatalysts (Pt-OGE&’s) in liquids, which allows the formation of model porous electrodes having a controlled Pt loading ranging from less than 0,1 to few hundreds µg of Pt per square centimeter. The coverage density of CNT surface by Pt-OGE&’s can be controlled using specific surface areas of both nanomaterials. For Pt-OGE&’s, it is determined through compression isotherm recorded in a Langmuir-Blodgett trough. Different kind of Pt-OGE&’s are involved: those with a Low Molecular Weight Organic corona (Pt-LMWO) [1] and a low specific surface area and those with a high molecular weight organic corona (Pt-HMWO) and a high specific surface area [2]. Because Pt-OGE&’s have a low or non-measurable Platinum Electroactive Surface Area we have studied the O2 reduction reaction (ORR) of such electrodes by Cyclic Voltammetry and exploited available equations to calculate the electrode area related to this reaction [3] (called ADiffO2). The determination of ADiffO2 is presented here as well as an alternative method to RDE and RRDE devices utilization [4] for the determination of the ORR selectivity which is necessary to calculate ADiffO2. This new method can be implemented directly on electrode with various shape and porous electrodes (active layer and gas diffusion layer). The paper reports the remarkable consistency observed in the trends for the specific value of ADiffO2 expressed in m2.g-1Pt as a function of platinum coverage density at the carbon nanotube surface and platinum loading (µgPt.cm-2): this for Pt-LMWO or Pt-HMWO set at different coverage densities on the CNT surface [5]. These new approaches can be used for various porous structures based on noble or non-noble metal electrocatalysts. Indeed, we recently used them on active layers based on combination of Pt-OGE&’s and carbon blacks which can be compared to CNT&’s based structures, as well as on porous electrode structures based on Nitrogen doped CNT synthesized by aerosol-assisted Catalytic CVD. 1. B. Baret, P-H Aubert, M. Mayne- L&’Hermite, M. Pinault, C. Reynaud, A. Etcheberry, H. Perez Electrochim. Acta 54 (2009) 5421-5430 2. G. Carrot, F. Gal, C. Cremona, J. Vinas, H. Perez Langmuir 25 (2009), 471 3. G. March, F. Volatron, F. Lachaud, X. Cheng, B. Baret, M. Pinault, A. Etcheberry, H. Perez Electrochim. Acta 56 (2011) 5151-5157 4. X. Cheng, L.Challier, A. Etcheberry, V. Noel, H. Perez, Int. J. Electrochem.Sci. online July 2012 5. X. Cheng, F. Volatron, X. Cheng, A. Borta, G. Carrot, E. Pardieu, M. Mayne, M. Pinault, A. Etcheberry, H. Perez, Electrochim. Acta submitted

Carbon black is commonly used as the state-of-the-art electrocatalyst support material in polymer electrolyte fuel cells (PEFCs). High power density can be obtained because of its high electrical conductivity, large surface area, and porous structure,. However, during the fuel cell start-stop cycles, the potential of the cathode can reach up to 1.44V, resulting in severe carbon corrosion. Tin oxide (SnO2) has been studied as an alternative support material because of its thermochemical stability. We have demonstrated that no significant degradation is observed within 60,000 cycles both in half-cell tests and in membrane-electrode-assembly (MEAs) tests, indicating that Pt/SnO2 electrocatalyst can exhibit considerable durability, which corresponds to a lifetime of fuel cell vehicles (FCVs) beyond 15 years. However, relatively low electrical conductivity in such semiconducting oxides, due to e.g. by grain-boundary resistivity, often causes poor cell performance. Preparation procedures of Pt/SnO2 electrocatalysts should be therefore optimized. In this study, SnO2 support materials were synthesized via the ammonia co-precipitation method or the microwave heating method. The former method used ammonia, which was added into SnCl2 solution. The latter used urea, and ammonia was generated by the decomposition of urea during the microwave heating. Specific surface area of SnO2 was characterized by the BET method. Although an increase in dropping speed of ammonia could decrease agglomeration in the ammonia co-precipitation method, specific surface area was still low. In contrast, the use of the microwave heating method led to 5 times higher specific surface area, beyond 100 m2/g. Impregnation of Pt particles was made using a colloidal method to prepare Pt/SnO2 electrocatalysts. Microstructure was observed by FE-SEM. Electrochemical surface area (ECSA) and oxygen reduction reaction (ORR) activities were measured by cyclic voltammetry (CV) and rotating disk electrodes (RDE), respectively. We prepared the cells of 5cm2 electrode area and measured their I-V characteristics and impedance spectra. We have verified using MEAs that the use of SnO2 as a catalyst support enables to retain a large part of the initial cell voltage even after the voltage cycling, indicating that the use of carbon-free electrocatalysts can be a solution to prevent carbon corrosion of PEFC electrocatalysts.

One of key issues in the development of renewable energy production and storage technologies is the discovery of efficient and cost-effective catalysts for use in electrochemical energy conversion processes such as oxygen reduction reaction (ORR) in fuel cells and metal-air batteries. In fuel cells and metal-air batteries, catalytic materials work under extreme chemical conditions, such as high electric potential ( 1 V/SHE) and high hydrogen ion concentration ( 1 pH), in the cathode. For such severe chemical conditions, the use of elements other than precious metals as cathodic catalysts is somewhat alchemical in terms of long-term durability. Doped carbon nanomaterials are attractive in principle for catalytic applications because their unique molecular structure facilitates the four-electron ORR. In addition, there are even more appeals because of their extreme flexibility, the large surface area, excellent mechanical and electrical properties, and highly stability in the extreme environment. A fundamental understanding of carbon-based catalyst design principle that links material structures to the catalytic activity can accelerate the search for highly active and abundant metal-free catalysts to replace platinum. In this talk, we present a first-principles study of ORR on nitrogen-doped graphene in acidic environment. We demonstrate that the ORR activity primarily correlates to charge and spin densities of the graphene. The nitrogen doping and defects introduce high positive spin and/or charge densities that facilitate the ORR on graphene surface. The identified active sites are closely related to doping cluster size and dopant-defect interactions. For four-electron transfer, the effective reversible potential ranges from 1.07~1.15 V/SHE, depending on the defects and cluster size. The catalytic properties of graphene could be optimized by introducing small N clusters in combination with material defects. The catalytic mechanism of (B,N) co-doped carbon nanomaterials is also discussed.

Alternative energy and environmental protection have become urgent correlated issues needed to be resolved, proton exchange membrane fuel cell (PEMFC) as a clean and efficient energy-conversion technology has attracted more and more attention. Electrocatalyst is a crucial component of PEMFC, catalyzing fuel oxidation and oxygen reduction at the anode and cathode, respectively. Currently, the state-of-the-art electrocatalyst for PEMFC is composed of semi-spherical 2-5 nm platinum particles supported on carbon (Pt/C). However, the semi-spherical Pt/C electrocatalyst is prone to degradation, preventing PEMFC from widespread commercialization. With activity maintenance or increment as a prerequisite, the durability improvement of electrocatalysts remains a challenge. Herein, a supporting-templating bi-functional reaction micro-environment is designed and created by localization of carbon into liposomal bi-layer, leading to facile synthesis of carbon-supported foam-like platinum nanostructures composed of convoluted 2-nm thick dendritic nanosheets. Compared with commercial Pt/C electrocatalysts, the shaped platinum foam on carbon exhibits significantly improved electrocatalytic activity and durability. The activity enhancement can be attributed to the highly active {1,1,0} crystalline planes of the dendritic nanosheets. Platinum nanomaterial enclosed preferentially by {1,1,0} crystalline planes is reported for the first time. The remarkable durability of the supported platinum foam is mainly due to the formation of metastable holey sheets evolved from the constituent dendritic nanosheets of the supported platinum foam. The bi-functional reaction environment approach opens up opportunities to directly grow other shaped (non-spherical) metal and alloy nanostructures on various supports and the resultant platinum foam on carbon has potential applications as catalysts and electrocatalysts [1-3]. This work is supported by National Key Basic Research Program of China (973 project, No. 2012CB215500), National High-Tech Research & Development Program of China (863 project, No. 2011AA11A273), National Natural Science Foundation of China (No. 21003114, No. 21103163), and “100 Talents” Program of Chinese Academy of Sciences (CAS). References: [1] Y. J. Song, R. M. Dorin, R. M. Garcia, Y. B. Jiang, H. R. Wang, P. Li, Y. Qiu, F. van Swol, J. E. Miller, J. A. Shelnutt, J. Am. Chem. Soc. 2008, 130, 12602. [2] Y. J. Song, M. A. Hickner, S. R. Challa, R. M. Dorin, R. M. Garcia, H. R. Wang, Y. B. Jiang, P. Li, Y. Qiu, F. van Swol, C. J. Medforth, J. E. Miller, T. Nwoga, K. Kawahara, W. Li, J. A. Shelnutt, Nano Lett. 2009, 9, 1534. [3] R. M. Garcia, Y. J. Song, R. M. Dorin, H. R. Wang, A. M. Moreno, Y. B. Jiang, Y. M. Tian, Y. Qiu, C. J. Medforth, E. N. Coker, F. van Swol, J. E. Miller, J. A. Shelnutt, Phys. Chem. Chem. Phys. 2011, 13, 4846.

Proton-exchange membrane fuel cells (PEMFCs) are expected to provide a complementary power supply to fossil fuels in the near future. The current reliance of fuel cells on platinum catalysts is undesirable. However, even the best-performing nonnoble metal catalysts are not as efficient. To drive commercial viability of fuel cells forward in the short term, increased utilization of Pt catalysts is paramount. We have demonstrated improved power and energy densities in a single PEMFC using a designed cathode with a Pt loading of 0.1 mgcm_2 on a mesoporous conductive entangled carbon nanotube (CNT)-based architecture. This electrode allows for rapid transfer of both fuel and waste to and from the electrode, respectively. Pt particles are bound tightly, directly to CNT sidewalls by a microwave-reduction technique, which provided increased charge transport at this interface. The Pt entangled CNT cathode, in combination with an E-TEK 0.2 mgcm-2 anode, has a maximum power and energy density of 940 mWcm-2 and 2700 mAcm-2, respectively, and a power and energy density of 4.01 WmgPt-1 and 6.35 AmgPt-1 at 0.65 V. These power densities correspond to a specific mass activity of 0.81 g Pt per kW for the combined mass of both anode and cathode electrodes, approaching the current US Department of Energy efficiency target. In this talk, I will further describe our nanomaterials research centered upon electrochemical energy storage and conversion devices.

We explore combinatorially sputter deposited Ti-Al-Ta and Ti-Al-Nb nitride thin films as replacements for carbon catalyst supports used in proton exchange membrane (PEM) fuel cells. Conductive probe atomic force microscopy (cp-AFM) was used as a high throughput tool to screen electrical conductivity as a function of composition. This work is motivated by observations that carbon particles traditionally used as catalyst supports in fuel cells are oxidized to CO₂ at high potentials (~1.5 V), which exist at the cathode during startup and shutdown and under fuel starvation conditions. More durable supports are thus desired. Pourbaix diagrams reveal oxides of Ti, Ta, Nb, and W (TiO₂, Ta₂O₅, Nb₂O₅, WO₃) are thermodynamically stable at the high potentials and low pH experienced in PEM fuel cells, yet these oxides do not meet the requirement that catalyst supports must be as electrically conductive as the fuel cell electrolyte is ionically conductive (sim;0.1 S/cm). Knowing that nitrides, such as TiN, exhibit high electrical conductivity and that the oxidation of nitrides is thermodynamically favored, we hypothesize that surface oxidation of nitrides could wed the durability and electrical conductivity necessary for high performing catalyst supports. Two-dimensional electron energy loss spectroscopic imaging on a 5th order aberation corrected electron microscope revealed oxidation is limited to the surface of the prepared nitride films. Using cp-AFM, we observed conductivity varied significantly with nitride film composition. In Ti-Al-Ta films, a larger fraction of Ti compared to Al and Ta exhibited the highest conductivity. Surprisingly, for films with Nb instead of Ta, compositions with equal fractions of Ti, Al, and Nb exhibited the highest conductivity. An advantage of oxide and nitride catalyst supports over nanostructured carbon materials is their ability to enhance the activity of supported catalyst particles. This work allows recommendations to be made regarding material selection for high performing catalyst supports.

The design of high surface area conducting metal oxide electrodes containing evenly dispersed and narrow sized metal nanoparticles is a crucial issue in chemical and biological electrocatalysis. Transparent conductive oxides (TCO), such as ITO are promising support materials when compared to carbon, as they are more stable against corrosion and exhibit stronger metal-support interactions. Many attempts have been made to incorporate high amounts of metal nanoparticles into mesoporous supports. However until now common techniques, based mostly on the impregnation of metal precursors or preformed nanoparticles, do not provide a sufficient control over the immobilized metal particle sizes, size distribution and dispersion within the materials, crucial parameters for the catalysts activity. Herein a facile templating strategy for the one-pot synthesis of such electrodes named Evaporation Induced Hydrophobic Nanoreactor Templating (EIHNT) is presented. This approach is exemplified with the synthesis of mesostructured tin-rich ITO thin films which are remarkably homogenously loaded with one gold nanoparticle per pore. In Line with SAXS, DLS, UV-Vis, TEM, SEM and XPS characterizations, material templating and formation will be discussed. Moreover, the applicability of the as-prepared nanocomposites thin films for electrocatalytic applications is demonstrated by i) the specific and patterned immobilization of high loadings of electroactive molecules through thiol-gold interactions as well as ii) electrocatalytic CO oxidation with high activity. Finally, the extension to other metal-TCO mesostructured electrodes will be discussed.

A photoelectrochemical cell (PEC) has attracted considerable interest for water splitting to produce hydrogen. Silicon is a useful semiconductor material for a photocathode in PEC applications owing to its small band gap (~1.12 eV) which is capable of absorbing a large portion of solar spectrum. Given a superior antireflection characteristic of Si nanostructures, there have been recent efforts for utilizing silicon nanowires and nanopores to improve a conversion efficiency in a PEC system, but the overall amount of photocurrent in the PECs employing silicon nanostructures are still lower than expected because the increased surface area also causes to increase a surface recombination loss. We focus on the usefulness of tapered Si nanoholes (SiNHs) for a photocathode application. Tapered SiNHs are found to behave as an effective medium for better matching in optical impedances between silicon and air; moreover, the increase in a depth of SiNHs emulates the number of dielectric multilayers which are impedance-matched for antireflective coating (ARC). This feature allows for adopting the nanohole depth of only 200 nm that can act as a triple-layered ARC for effectively suppressing both of light reflection (<4%) and surface recombination in comparison with other nanostructures. Compared to a planar Si, the junction area increased in tapered SiNHs significantly reduces the kinetic overpotential required for photoelectrochemical hydrogen-production. Tapered SiNHs which are specifically tailored for optical density gradient were fabricated using a metal-assisted electroless etching method. We also suggest the optimal design of tapered SiNHs which can achieve the maximum photocurrent enhancement for hydrogen production.

A general methodology introduced by our group to compute the charge injection time for a large number of dyes will be reviewed and some recent applications presented. They include the prediction of the best anchoring group to be used in dye sensitized solar cells and the study of the effect of different semiconducting surfaces. The problem of predicting the very slow charge recombination rates (to the electrolyte or to the oxidized dye) is addressed. The discussion of these results will focus on the realistic possibility that first principle calculations can guide the design of new materials for dye sentitized solar cell. A new class of dyes is proposed on the basis of these models. 1) Ambrosio F, Martsinovich N, Troisi A, What is the best anchoring group in a dye for dye sensitized solar cells, J. Phys. Chem. Lett. 3, 1531-1531, 2012 2) Ambrosio F, Martsinovich N, Troisi A, Effect of the Anchoring Group on Electron Injection: Theoretical Study of Phosphonated Dyes for Dye-Sensitized Solar Cells, J. Phys. Chem. C 116, 2622, 2012 3) Martsinovich N, Troisi A, Theoretical Studies of Dye-Sensitised Solar Cells: From Electronic Structure to Elementary Processes, Energy Environ. Sci. 4, 4473, 2011 4) Martsinovich N, Troisi A, High-throughput Computational Screening of Chromophores for Dye-Sensitized Solar Cells, J. Phys. Chem. C 115, 11781, 2011 5) Martsinovich N, Jones DR, Troisi A, Electronic structure of TiO2 surfaces and effect of molecular adsorbates using different DFT implementations, J. Phys. Chem. C 114, 22659, 2011

Static and dynamic charging of molecular films at interfaces is important in many diverse fields of science and technology. In this report recent results from our lab will be presented on the (static) positive and negative charging of layers of amorphous solid water (ASW). We found very stable charging at the water-vacuum interface below surface temperature of 110K, behaving as nano-capacitor and accumulating well defined amounts of charges. These charges develop electrical fields of more than 10**6 V/cm, near the discharge threshold. We have investigated the role of such fields on the UV photons and low energy electron-induced chemistry of trapped molecules within the ice film, as a new mode of photo-catalysis and a model for, e.g. interstellar photo-activity. Transient charging at the nsec timescale of nano-scale silicon sharp edges within porous silicon matrix were studied for their effect on photo-reactivity. It was found that such laser induced, transient charging lead to photo-desorption of atoms (Xe) and molecules (CO) that are enhanced up to 3 orders of magnitude compared to the adjacent flat surfaces. Possible tip-enhanced desorption mechanism and its potential application in photo-catalysis and photo-voltaics will be discussed.

A Quantum Dot Sensitized Solar Sell (QDSSC) , which in principle adopts the design of Dye Sensitized Solar Sell (DSSC) , is one of the most promising cost-efficient candidates for the development of next generation solar cells. Compared to DSSC, Quantum Dots (QDs) as a photo sensitizer allow for rapid charge separation, tunable band gaps, and multiple excitons from a single photon. Unfortunately, the most efficient I-/I3- redox couple used in DSSC is not suitable for QDSSC, because the most QDs such as CdS, and CdSe suffer from photodegradation when used in conjunction with the I-/I3- solution. The optimal redox couples for QDSSC are sulfide/polysulfide (S2-/Sn2-), but the surface activity and conductivity of the classic Pt counter electrode (CE) are reported to diminish due to chemisorption of S atoms, then seriously increase the charge transfer resistance (Rct) at the interface of electrode/CE. This is one of the main reasons why the efficiencies of QDSSC still remain very low to date. Here, we introduce the multicomponent chalcogenide semiconductor, copper-zinc-tin-sulfur-selenium (CZTSSe) which can be exploited as an effective CE material to replace Pt in QDSSC. Cu2ZnSn(SxSe1-x)4 nanoparticles (NPs) with controlled S/Se ratios (X=0, 0.15, 0.5, 0.75, 1) were synthesized via a "hot injection" method using Oleylamine for both solvent and surfactant. The NPs were drop-cast onto a fluorine-doped tin oxide (FTO) glass followed by sintering, then the NPs-coated-FTO substrate served as CE was assembled together with a QDs-sensitized-TiO2-photoanode (FTO/TiO2/CdS/CdSe/ZnS). The polysulfide (S2-/Sn2-) electrolyte was then injected between two electrodes so as to form a “sandwich-like” QDSSC. A QDSSC employing Cu2ZnSn(S0.5Se0.5)4 as CE shows the highest efficiency out of all group based on Cu2ZnSn(SxSe1-x)4 CEs, also demonstrates a higher fill factor (FF) and efficiency (eta;) than that using Pt CE.The electrochemical impedance spectroscopy (EIS) measurement was performed on dummy cells with a “sandwich-like” structure between two counter electrodes, i.e., CE/electrolyte/CE. The Rct of CZTSSe CE was found to lower than that of Pt CE, implying a better electrocatalytic activity of Cu2ZnSn(S0.5Se0.5)4 CE in polysulfide reduction, which explains a higher efficiency in QDSSC employing a Cu2ZnSn(S0.5Se0.5)4 CE than that using Pt CE.

The importance of TiO2 nanoparticles in environmental remediation is well-known and one of those processes involve the electron and hole transference when semiconductor is illuminated as TiO2 nanoparticle. One way to investigate this process is by electrochemical techniques. However, the majority of the research in this area was done investigating thin films, which are different in structure and in some properties than freestanding nanoparticles.Then, the use of TiO2 nanoparticles in solid carbon paste electrodes instead of thin-film electrodes may be a good alternative to study the behavior of such semiconductor nanoparticles in photoactivated processes through electrochemical studies.In our research, such electrodes were prepared by mixing different amounts of a synthesized TiO2 nanopowder, doped and undoped with N, in a carbon paste electrode. The electrodes containing TiO2 exhibited lower currents than the carbon paste electrode under UVC illumination on electrochemical characterization.This is expected, as the incident light should induce a charge separation.When a semiconductor-electrolyte interface is illuminated with energy greater than its band-gap energy, electron-hole pairs are generated at the electrode surface.The simultaneous application of a positive potential to the flat-band potential produces a shift of the conduction and valence bands, leading to a more effective separation of the photogenerated carriers within the space charge layer.This separation of carriers increases the photocurrent and promotes the oxidative degradation process.The gradient potential efficiently forces the electrons through the counter-electrode allowing the photogenerated holes to react with H2O/OH- giving rise to OH radicals, or to react directly with the organic compounds present in the solution.The carbon paste electrode with 60% TiO2 was used for photoelectrocatalysis experiments initially with Rhod-B. The better condition for degradation was potential applied was 2.0 V vs SCE under UVC illumination.A significant difference was observed in the performance of the N:TiO2/carbon paste electrode, where the decomposition profiles indicated higher catalytic performance under UVA illumination.The pesticide diuron photoelectrocatalysis experiments were done with carbon paste electrode with and without TiO2 nanoparticles (60%).The goal of these experiments was to determinate lower applied potential that allow the diuron degradation without efficiency system loss.The better condition for carbon paste electrode with TiO2 nanoparticles was 0.5 V vs SCE applied potential with UV-C illumination for diuron degradation.Another experiments with others light wavelength, applied potential and N:TiO2 nanoparticles electrodes is in progress, but is expected with N:TiO2 the applied potential should be lower as light wavelength energy illumination. These results will support future research regarding the influence of different materials in photodegradation processes.

Single particle spectroelectrochemistry was used to investigate the electrochemical environment at an ITO substrate and to characterise Ag nanoparticles. Two kinds of Ag nanoparticle were used, commercially obtained Ag particles in the range 20 to 80 nm and 5 nm particles that we prepared. Luminescent Ag nanoparticles were made by chemical reduction of Ag ions stabalized by PAMAM-OH dendrimer macromolecules. The particles were then extracted with mercaptothiol molecules terminated with carboxylic acid for surface attachment and spectroelectrochemistry studies. The extracted particles are fully characterized by TEM and found to have size 5.26 ± 0.3 nm. The monodisperse nanoparticles serve as fluorescent redox probes for studying the linker molecule dependence of electron transfer at conductor and semi-conductor surfaces with the single molecule fluorescence imaging method. In single particle fluorescent silver nanoparticle spectroelectrochemical measurements it is found that the fluorescence of single silver nanoparticles decreases as the electrochemical potential at the silver nanoparticles is increased because of the oxidation of silver. There is little difference in the averaged oxidation half potential of the silver particles encapsulated with different linker molecules. To test the oxidation potential dependence on particle size, we measured the luminescence for individual particles of size 20, 40, 60, 80 nm and their response to applied potential. We observed that the larger particles cease luminescence at lower potential than the smaller particles and this may be due to the larger conductivity of the larger particles. There is greater distribution of oxidation potentials for larger particles. Action spectra recorded for silver nanoparticles encapsulated in different linker molecules on TiO2 substrates show that silver nanoparticles can sensitize the TiO2 to provide visible light response, and that the photocurrent at rest potential is negative when the wavelength corresponds to the resonance of the surface plasmon. There is no influence from the linker molecule chain length on the size of the photocurrent response.

Core-shell catalysts, in which Pt monolayer (ML) is deposited on different metal core nanoparticles (NPs), are one of the key techniques to improve the mass activity of Pt and to reduce the Pt usage in PEFCs. We started a NEDO project on low-Pt catalyst in 2008 to reduce the Pt usage to 1/10 of the 2007 level (i.e. 0.1 g kW-1), especially focusing on the core/shell structure. Here we overview our research results on the development of core/shell catalysts at Doshisha University. We have used the so-called Cu-UPD method [1] to form Pt ML on Au/C (5 and 20 nm, BASF, 50 wt%) and Pd/C (3.4, 4.8 and 11.5 nm) cores, and confirmed that Pt(ML)/Au/C and Pt(ML)/Pd/C catalysts had ca. 5-fold and 6-fold higher mass activity, respectively, at 0.9 V than that of a commercially available Pt/C catalyst (TKK, TEC10E50E) [2]. The Cu-UPD method is an excellent technique for Pt ML formation, but is not suitable for commercial mass production of the core/shell catalysts. We developed a very simple method (hereafter called the soaking method) to obtain Pt ML on Au core NPs, in which the Au/C core particles and Pt(II) complex (e.g. K2PtCl4) in water for 24 h under Ar atmosphere [3]. Pt(ML)/Au(5nm)/C prepared by the soaking method showed inferior durability in the MEA tests at 80oC. Postmortem analysis of the Pt(ML)/Au(5nm)/C by 3-D TEM tomography revealed that the catalyst NPs, especially those on the carbon support surface, strongly agglomerated to be big particles (several tens of nm). Weak interactions between Au core NPs and carbon support is the reason for the agglomeration, and hence an enhancement of the adhesive force is important to improve the durability in MEAs at 80oC. To enhance the adhesiveness of Au core NPs, Au NPs were synthesized using dodecanetiol (DDT) as a stabilizer [4], The Au particle size after the heat-treatment was kept to be small (2.8 nm) though it slightly increased. This clearly indicated that the carbon residue of DDT enhanced the adhesiveness of Au NPs and suppressed particle agglomeration at 300oC. Unfortunately the durability of Pt(ML)/Au(3nm)/C prepared by this method is short of our expectations at present. However, the particle growth was negligible and the Pt/Au ratio hardly changed after the durability test (5,000 cycles). These facts suggested that the primary reason for the degradation is that Pt dissolution into the Au core to make a solid-solution. In the next stage, we design the structure of the Au core to suppress of Pt dissolution into the Au core, and develop highly durable Pt(ML)/Au/C catalysts. References [1] J. Zhang et al, J. Phys. Chem. B, 109, 22701 (2005). [2] M. Inaba et al., ECS Trans, 33 (1), 231 (2010). [3] H. Tsuji et al., The 218th ECS Meeting, Abstract #858, (2010).; H. Daimon et al., The 220th ECS Meeting, Abstract #1052, Boston (2011). [4] M. J. Hostetler et al., Langmuir, 14, 17 (1998).; J. Luo et al., Langmuir, 22, 2892 (2006).

In order to practical use for polymer electrolyte fuel cells (PEFCs), degradation should decrease, and its mechanism should be understood for the prediction of the lifetime. Decrease of the electrochemical surface area (ECSA) is one of important degradation causes. The ECSA decrease corresponds to particle growth. It is considered to follow the Ostwald ripening, but quantitative understanding of the degradation should not be enough. In this study, the ECSA decrease and particle growth were experimentally determined, and quantitative particle growth model was proposed based on Gibbs-Thomson equation to understand the degradation of Pt/C electrocatalyst during potential cycling. The particle growth was assumed the cycling of the anodic process with Pt metal oxidation and anodic dissolution, and the cathodic process with reduction of the oxide and the cation to metal. The simplified anodic process was simultaneity reactions of Pt = Pt²⁺ + 2e^- and Pt + H₂O = PtO + 2H⁺ + 2e^-, and the anodic dissolution was terminated by the full coverage of the metal surface with the oxide. The simplified cathodic process was simultaneity reactions of Pt²⁺ + 2e^- = Pt and PtO + 2H⁺ + 2e^- = Pt + H₂O, and the cathodic dissolution was terminated by the complete of the dissolved cation and the surface oxide reduction. In this simple model, smaller particle had faster dissolution rate and slower deposition rate than larger particle based on the Gibbs-Thomson equation. The particle growth was determined for 50 wt. % Pt of the Pt/C made by TKK with rectangular potential cycling up to 10,000 cycles in sulfuric acid. The ECSA and the particle size distribution were determined by hydrogen desorption charge of cyclic voltammogram and TEM analysis, respectively. The ECSA decrease rate of the initial several hundred cycles was faster than later cycles. The particle diameter distribution could fit to log-normal distribution during all period of potential cycling. The potential cycling function of the ECSA, the peak particle size, and the standard deviation of the particle distribution could be expressed with adequate value combination of the surface tension of Pt in the electrolyte and the rate constants of the dissolution, oxidation, deposition, and reduction of Pt/C. Therefore, the particle growth was quantitatively conformed to follow the Ostwald ripening, and the particle growth should predict by this model. In order to decrease the particle decrease, the decrease of the ration of the anodic dissolution rate divided by the surface oxidation rate, the standard deviation function of the particle distribution, and the surface tension should be effective.

One of the main limitations of polymer electrolyte membrane fuel cells is the slow oxygen reduction reaction (ORR) in the potential region close to the reversible potential. In general, the PEMFC electrochemical processes need of Pt-based electrocatalysts to occur at significant rates. Several methods to improve the electrocatalytic activity of Pt-based catalysts are actively investigated by either tailoring the particle size or alloying Pt with transition metals. The aim of this work is to evaluate the influence of different thermal treatments on the performance and stability of in-house synthesised PtCo alloy catalysts supported on Ketjenblack carbon. The choice of cobalt was derived from recent works in our group where we observed that the PtCo alloy catalyst provided the best compromise between performance and resistance to sintering in high temperature PEMFCs. The synthesis methods were optimised to obtain a suitable dispersion of the metal particles on the support for high metal concentration catalysts (50 wt. %) with a mean particle size of about 3 nm. Two specific temperatures were selected for the thermal reduction (600 °C and 800 °C) since it was preliminarily observed that different structural properties for the catalysts are correspondingly achieved. The electrocatalysts were characterized by different electrochemical and physico-chemical techniques to try to understand as the different thermal treatments influence the electrochemical behaviour. The electrocatalyst were also investigated in a single PEMFC, using Nafion 115 as electrolyte, under various operating conditions i.e. high temperature (HT) and low relative humidity (R.H.). Furthermore, an accelerated degradation test was adopted to analyzed the performance and the resistance to corrosion of PtCo/C electrocatalysts. In conclusion, both catalysts showed good performance at 80 °C, 100% R.H. , 3 bar abs. O2. Interesting, the different characteristics of the two catalysts were exacerbated by operation under low relative humidity (33% R.H.). In the presence of low relative humidity, the low temperature treated catalyst (600 °C) was performing better at low temperature but only at high current densities; at high temperature, the high temperature treated catalyst (800 °C) was performing better both at low and high current densities achieving a mass activity of 0.32 A/mg at 0.9 V, 110 °C, 33% R.H., 3 bar abs. O2. Acknowledgements The authors acknowledge the financial support of the EU through the QuasiDry Project 256821. “The research leading to these results has received funding from the European Community&’s Seventh Framework Programme (FP7/2010-2013) under the call ENERGY-2010-10.2-1: Future Emerging Technologies for Energy Applications (FET).”

One of the main drawbacks hindering a widespread commercialization of polymer electrolyte fuel cells (PEFCs) is the slow kinetics of the oxygen reduction reaction (ORR) at the cathode and the cathode&’s corrosion stability. In the last years, important progresses have been made towards the development of advanced catalytic materials based on Pt-alloy nanoparticles supported on high-surface area carbons.[1] However, despite of the good performance as cathode catalyst, Pt-supported on carbon suffers from corrosion instability, being fuel cell lifetime determining. Indeed, during PEFC start/stop cycles, the cathode can reach potentials as high as 1.5 V, which cause severe oxidation of the carbon support. Carbon corrosion results in a decrease of the support surface area and detachment of the Pt-nanoparticles, followed by rapid failure of the whole fuel cell. Therefore, a growing interest is raising towards alternative, more stable support materials to carbon, such as metal oxides in their highest oxidation state . Thermochemically calculated pH-potential diagrams have shown that only few oxides are stable under typical PEFC cathode operating conditions.[2] Among the stable oxides, we have selected antimony and other doped tin oxides since they can achieve high electronic conductivity and are relatively low-cost materials. Doped-tin oxide nano-powders have been synthesized by a modified sol gel method. Single phase doped-tin oxide nano-powders, with a specific surface area up to 60-70 m2g-1, were achieved as revealed by X-ray diffraction, nitrogen-BET surface and scanning electron microscope analysis. The powder processing significantly influenced the dopant distribution between the bulk and the surface of the oxide particles; X-ray phothoelectron spectroscopy was used to investigate the conditions leading to dopant surface segregation, allowing correlating the surface chemistry of oxide semiconductors with their interfacial electrochemical properties in liquid electrolyte. For the electrochemical characterization, thin films were prepared by spin-coating a cathode ink made by the oxide nano-powders and an organic binder on glassy carbon disks. Cyclic voltammetry measurements were carried out to evaluate the oxide electrochemical stability in acid media and towards applied potential up to 1.6 V. On the porous oxide thin films, Pt nanoparticles were deposited by magnetron sputtering and cyclic voltammetry and rotating disc electrode (RDE) measurements were performed on the Pt/oxides system to evaluate their electrochemical stability and activity towards ORR. Acknowledgements This work was supported by the Competence Center Energy and Mobility (CCEM), Switzerland and by Umicore AG & Co. KG within the project DuraCat. References [1] A. Rabis, P. Rodriguez, T.J. Schmidt, ACS Catal., 2012, 2 (5), pp 864-890. [2] K. Sasaki, F. Takasaki, Z. Noda, S. Hayashi, Y. Shiratori, K. Ito, ECS Trans., 33 (2010) 473-482.

Electron occupancy at the surface of materials is known to be crucial on determining their catalytic properties. It has been shown that, in the particular case of transition metal oxides with perovskite structure AMO3, the electronic orbital filling largely determines their activity for oxygen reduction reaction. In all experiments reported so far, orbital filling has been modified by changing the electron number by appropriate atomic substitutions in the perovskite matrix. Here, we will report on a different approach to modify the electron filling in the outermost 3d orbitals of the transition metals in AMnO3 perovskite. We use epitaxial strain to modulate the crystal field and thus the energy splitting of eg orbitals. By combining the strain-dependence eg splitting and the inherent symmetry breaking at the surface, the overall 3dz2 and 3dx2-y2 occupancy can be fine tuned. Epitaxial AMnO3 thin films have been gown on distinct single crystalline substrates by pulsed laser ablation, thus exposing the films to distinct epitaxial strain. X-ray linear dichroism has been used to map the orbital occupancy. Results clearly show that orbital occupancy at fixed electron concentration can be easily modified. While it is expected that surface chemical reactivity will be subsequently modified, our approach illustrate a potential novel approach for active control of surface electronic occupancy.

Discovering the fundamental principles that govern electrochemical reactivity is the key to the design of new materials for a range of scientific applications, particularly in energy-related technologies. Such information can only be obtained from model systems with well-defined elemental reaction sites using state-of-the-art instrumental probes. Improvements in the fundamental understanding of electrochemical interfaces have begun to revolutionize the development of materials that can solve the challenging problems of clean energy production, conversion and storage. These advances have enabled an unprecedented level of detail in the understanding of the atomic-level structural and electronic characteristics of metal-electrolyte interfaces to be attained. In turn this has formed the basis for predictive ability in tailor-making a new generation of electrocatalytic materials that are urgently needed to address the delivery of reliable, affordable, and environmentally-friendly energy. Deposition processes and structure formation at the electrochemical interface enables a number of modern technologies, ranging from the formation of nanosized electronic components to the tailoring of surface reactivity in catalytically active materials. The deposition of a foreign metal on a metallic substrate, in particular underpotential deposition (UPD) of a single monolayer, has been widely studied in this respect as it represents a methodology for structure formation that is both versatile and reversible, in contrast to structure formation in the ultra-high vacuum (UHV) environment. With emergent interest in materials such as core shell nanoparticles in which the surface atomic layer of the nanoparticle is a different metallic element to that which forms the core, there is a renewed interest in understanding the physical properties of the two-dimensional metal layer and its interaction with adsorbing species. In model electrochemical systems, surface x-ray scattering (SXS) is a unique probe of both the atomic structure of the electrode surface and the ordering in the electrolyte adjacent to the electrode surface and can also give insight into the electron transfer at the interface. Such measurements have been used to probe a wide range of electrochemical phenomena, for example, metal deposition, the adsorption and ordering of spectator species and the adsorption and reaction of reactive species. Recent results will be presented illustrating how phenomena such as surface alloying, thin film growth and surface restructuring can be linked to electrochemical reactivity and stability.

Sluggish oxygen reduction reaction (ORR) at the cathode limits the overall performance of proton exchange membrane fuel cells (PEMFC). It has been experimentally found that alloying Pt with other transition metals (for example, Ni, Co, and Fe) led to the formation of a special surface composition profile (in which precious Pt enriches the outermost layer and the transition metals enrich the subsurface layer of the catalyst surface) and had even enhanced activity for the ORR. Using first-principles density functional theory calculations, we have investigated how the subsurface transition metal Ni would affect the energetics and mechanisms of ORR on the outermost Pt mono-surface layer of the Pt-Ni (111) and (100) surfaces. For the Pt-Ni (111) surfaces, our DFT results revealed that due to the influence of the subsurface Ni, ORR would adopt hydrogen peroxide dissociation mechanism with activation energies about 0.15 eV for their rate-determining O2 protonation reaction. In contrast, ORR would follow peroxyl dissociation mechanism on the pure Pt (111) surface with activation energy of 0.79 eV for its rate-determining O protonation reaction. Thus, our theoretical study explained from a reaction kinetics point of view that the subsurface Ni could lead to multi-fold enhancement in catalytic activity for ORR on the Pt mono-surface layer of Pt-Ni (111) surfaces. Moreover, our DFT results suggested that the ORR would follow the same oxygen dissociation mechanism (whose rate-determining step is O protonation reaction) on the Pt (100) and the Pt-Ni (100) surfaces. We found that the activation energy for the rate-determining O protonation reaction was 0.43 eV on the pure Pt (100) surface and 0.44 eV on the Pt-Ni (100) surface. In summary, our first-principles transitions state calculations predicted that the activation energy of the rate-limiting step (O protonation reaction) for ORR on the Pt (100) was lower than that on the Pt (111) surface and hence the Pt (100) extended surface was more active for ORR than the Pt (111). In contrast, the activation energy of the rate-limiting step (O2 protonation reaction) for ORR on the Pt-Ni (111) was lower than that of O protonation step on the Pt-Ni (111) surface and consequently the Pt-Ni (111) extended surface was more active for ORR than the Pt-Ni (100) surface.

Improvements to the oxygen reduction reaction (ORR) on Pt-based catalysts require a fundamental understanding of the factors that control their functionality.[1] By studying the oxygen reduction on model mass-selected Pt and PtxY alloy nanoparticles, we develop a comprehensive understanding of the relationship between their activity, stability and microstructure. Pt3Y was originally identified through a density functional theory (DFT) based screening study, as being a potentially active and stable catalyst for the ORR. Subsequent measurements showed that Pt3Y exhibited the highest activity ever reported for a bulk polycrystalline electrode.[2] The nanoparticulate catalysts are formed in the gas phase using the gas aggregation technique and deposited under ultra-high vacuum, directly onto planar glassy carbon supports. The particles are characterised with an extensive range of ex-situ characterisation techniques, including X-ray photoelectron spectroscopy, temperature programmed desorption (TPD) of CO, ion scattering spectroscopy, scanning electron microscopy and transmission electron microscopy. Their activity is tested using rotating ring disk electrode measurements in 0.1 M HClO4. By conducting our experiments under such well-defined conditions, we provide a measure of the intrinsic ORR activity of nanoparticulate Pt and PtxY. For pure Pt, we find that that the specific activity for the ORR increases with particle size; there is a maximum in mass activity for 3nm particles.[3] Using CO-TPD, we were able to quantify the proportion of terraces on the nanoparticles. It turns out that the ORR activity scales with the proportion of terraces; this confirms the theoretical notion that the active sites for the ORR are located on the terraces.[4] We also confirm that the high activity of PtxY upon extended surfaces is reproduced in the more technologically relevant nanoparticulate form, with a maximum surface specific activity at 0.9 V RHE, of 8.5 mA/cm2 Pt, corresponding to a mass activity of 2.8 A/mg Pt. Combining the ex-situ characterisation of the particles with DFT calculations, we elucidate the origin of the high activity of these catalysts. We also test the stability of the PtxY and Pt nanoparticles under extensive cycling. References: [1] I. E. L. Stephens, A. S. Bondarenko, U. Groslash;nbjerg, J. Rossmeisl, I. Chorkendorff, Energy Environ. Sci. 2012, 5, 6744-6762. [2] J. Greeley, I. E. L. Stephens, A. S. Bondarenko, T. P. Johansson, H. A. Hansen, T. F. Jaramillo, J. Rossmeisl, I. Chorkendorff, J. K. Noslash;rskov, Nature Chemistry 2009, 1, 552-556. [3] F. J. Perez-Alonso, D. McCarthy, A. Nierhoff, P. Hernandez-Fernandez, C. Strebel, I. E. L. Stephens, J. H. Nielsen, I. Chorkendorff, Angewandte Chemie International Edition 2012, 51, 4641-4643. [4] G. A. Tritsaris, J. Greeley, J. Rossmeisl, J. K. Noslash;rskov, Catal. Lett. 2011, 141, 909-913.

Developing proton exchange membrane fuel cells (PEMFCs) for automotive and stationary applications requires long-term sustainment of oxygen reduction reaction (ORR) activity of Pt-based catalysts. In this contribution, we seek to develop a design principle for Pt-based electrocatalyst to against electrochemical dissolution, a common degradation mechanism, in ways of alloying the electrocatalyst with other transition metal chemistries. By studying a series of Pt-alloy nanoparticles (Pt-M, where M = Co, Cu, Sn, Sc, etc.) with similar size distributions, we systematically analyze how the particle morphologies and their intrinsic activity evolve under long-term cycling condition. We demonstrate that the stabilities of surface areas, ORR activities, morphologies and chemical compositions depend significantly on the choice of M. Ongoing research is to identify a fundamental principle of how transition metal chemistry and the interaction between Pt and M elements can influence the degradation processes of Pt-alloy nanoparticle electrocatalyst, the result of which will be discussed in this presentation.

Recently, the rise of monolayer Pt catalysts provides a promising approach for the sustainable use of PEMFCs (1). Herein, the key role of core materials in controlling the activity of monolayer Pt catalysts is to induce the strain effect, tensile or compressive, in which the resulting d-band center shifts as a major factor determine the catalysts&’ activity (2). Monolayer Pt catalysts with uniquely catalytic properties toward ORR can be created by tuning the structure of core materials (3). Several investigations have been carried out to resolve the role of core structure in the catalytic activity of monolayer Pt catalysts toward ORR; a definitive determination, however, still remains elusive. One of the difficulties in clarifying the core effects is that core materials have some intrinsic properties such as shape, size, and composition. Moreover, fundamental understanding of the interactive model between core materials and monolayer Pt shells lacks. Thus, these complexities decide that tailoring the structure and activity of monolayer Pt catalysts toward ORR is still devoid of direction and purpose, although some efficient catalysts have been developed. By changing the properties (size and roughness) of Pd core, we clarified the core effects on monolayer Pt structure, namely, small size and high roughness engender a compressed Pt-Pt bond distance. Comparing the above core effects, a 2 nm size increase only leads to 0.01 Å change in Pt-Pt bond distance; on the contrary, a 0.2 roughness increase can engender 0.06 Å change in Pt-Pt bond distance. Thus, the influence of roughness effect on Pt-Pt bond distances is much larger than that of the size effect. We proposed a “filling model” to well explain the core effects. It involves three hypotheses. One is some Pt atoms preferentially deposit on low-coordination Pd sites such as Pd kinks and steps, another is these Pt atoms on low-coordination Pd sites (kinks and steps) possess possible shift to different directions, and the other is the following Pt atoms completely fill in the formatively compressed terrace space. And, the three mentioned hypotheses were demonstrated, respectively. A volcano-type correlation between Pt-Pt bond distance and the resulting specific activity is obtained. At the volcano peak, the specific activity toward ORR has near seven-fold increase compared to commercial Pt nano-particles (TKK), and the corresponding optimal Pt-Pt bond distance is about 2.69 Å. It means that monolayer Pt catalysts with the only optimized Pt-Pt bond distance can bring a probable 20-fold improvement in mass activity toward ORR. This work is supported by NEDO in Japan. Reference 1) J.L Zhang, et al., Angew. Chem. Int. Ed., 44 (2005) 2132-2135. 2) R. R. Adzic, et al., Top. Catal., 46 (2007) 249-262. 3) M Shao, et al., J. Am. Chem. Soc., 132 (2010) 9253-9255.

The Li-air battery can far exceed the specific energy of lithium-ion batteries, but prototypes suffer from poor discharge-charge efficiency, low current density, and capacity fading.(1,2) While the stability of the electrolyte has become the focus of current Li-air battery research, the efficiency of the key electrochemical processes, the O₂ reduction reaction by lithium (Li-ORR) and the O₂ evolution reaction (OER), is also potentially of concern. Direct evidence regarding the details of the Li-ORR/OER has been scarce. Hummelshoslash;j et al. have suggested that the growth and decomposition of the bulk Li₂O₂ phase have overpotentials (eta;) of 0.4 and 0.6 V respectively.(3) Discharge of experimental cells with carbon cathodes without added catalysts occurs at eta;=0.4~0.5 eV.(4,5) Lu et al. have shown reduced eta; for ORR and OER by adding metal catalysts.(6) The necessity for electrocatalysts, however, has been disputed by McCloskey et al.(7) To shed light on the role of the metal catalysts, we have carried out density functional theory (DFT) calculations coupled with electrochemical modeling techniques to directly interrogate the reaction on Au, Ag, Pt, Pd, Ir, and Ru, via different reaction mechanisms.(8,9) The intrinsic activity of the Li-ORR is limited by the initial reduction step and directly related to the reactivity of the metal surfaces. On Au(111) and Ag(111) the reaction begins with the lithiation of molecular O₂ to form Li superoxide. On the (111) or (0001) surfaces of the more reactive Pt, Pd, Ir, and Ru, O₂ dissociation is facile at room temperature and the initial reduction occurs between Li and O instead. Step edges are more active than the close-packed surfaces in catalyzing the initial reduction step. Overall, the Pt and Pd step edges impose the smallest overpotential, at eta;~0.22 V with respect to bulk Li₂O₂. The DFT-based results form a volcano trend when plotted against the oxygen adsorption energies, in qualitative agreement with the recent report by Lu et al.(10) References (1) Girishkumar, G.; McCloskey, B.; Luntz, A. C. et al. J. Phys. Chem. Lett. 2010, 1, 2193. (2) Christensen, J.; Albertus, P.; Sanchez-Carrera, R. S. et al. J. Electrochem. Soc. 2012, 159, R1. (3) Hummelshoslash;j, J. S.; Blomqvist, J.; Datta, S. et al. J. Chem. Phys. 2010, 132, 071101. (4) Abraham, K. M.; Jiang, Z. J. Electrochem. Soc. 1996, 143, 1. (5) Débart, A.; Bao, J.; Armstrong, G. et al. J. Power Sources 2007, 174, 1177. (6) Lu, Y.-C.; Xu, Z.; Gasteiger, H. A. et al. J. Am. Chem. Soc. 2010, 132, 12170. (7) McCloskey, B. D.; Scheffler, R.; Speidel, A. et al. J. Am. Chem. Soc. 2011, 133, 18038. (8) Xu, Y.; Shelton, W. A. J. Chem. Phys. 2010, 133, 024703. (9) Dathar, G. K. P.; Shelton, W. A.; Xu, Y. J. Phys. Chem. Lett. 2012, 3, 891. (10) Lu, Y.-C.; Gasteiger, H. A.; Shao-Horn, Y. J. Am. Chem. Soc. 2011, 133, 19048.