Symposium EE9 : Hydrogen and Fuel Cell Technologies for Transportation---Materials, Systems and Infrastructure

This presentation will provide an overview of the U.S. Department of Energy’s (DOE) hydrogen and fuel cell activities within the Office of Energy Efficiency and Renewable Energy (EERE), focusing on key targets, progress towards meeting those targets and materials-related issues that need to be addressed. The most recent, state-of-the-art data on metrics such as cost, durability and performance of fuel cell and hydrogen technologies will be presented. Key technical accomplishments to date include a 50% reduction in the modeled high volume cost of fuel cells since 2006 and an 80% cost reduction for electrolyzers since 2002. The status of various hydrogen production, delivery and storage technologies will also be presented along with a summary of materials-related challenges for hydrogen infrastructure technologies such as compression, dispensing, seals, pipeline materials/embrittlement, and storage materials. In addition, the status of crosscutting activities such as safety, codes and standards, technology validation, systems analysis, and market transformation will be summarized. Specific examples and areas requiring more research will be discussed.
Finally, future plans including EERE’s lab consortium approach such as HyMARC (Hydrogen Storage Materials Advanced Research Consortium) and FC-PAD (Fuel Cell Performance and Durability) Consortium, will be summarized, along with upcoming Technology to Market activities within EERE’s Fuel Cell Technologies Office.

In June 2014, Japanese Ministry of Ecomomy, Trade and Industry (METI) compiled the “Strategic Road Map for Hydrogen and Fuel Cells” toward the realization of a “hydrogen society.” This road map states how Japan would be able to make use of hydrogen, what are goals to be achieved in each step of manufacturing, transportation and storage of hydrogen, and what kind of collaborative efforts could be possible among industry, academia and government for achieving these goals. It has clear time frames, taking into account the significance of an initiative for disseminating hydrogen energy. The fuel cell vehicle (FCV) is expected to play an increasingly important role as a clean energy vehicle. The first commercial Fuel Cell Vehicle was delivered to the Japanese market in December 2014 and 81 Hydrogen Refueling Stations are going to be available by the end of March 2016. Accoding to the road map, Government of Japan aims to full-fledged dissemination of FCVs around 2025. The New Energy and Industrial Technology Development Organization (NEDO) has been conducting comprehensive technology development and demonstrative research programs on hydrogen energy including PEFC, as one of the most promising technologies for future clean transportation under the direction of METI. NEDO is now implementing R&D projects for advanced fuel cells that could achieve high performance, high durability and low cost at the same time to meet the road map target. The project aims to establish the fundamental technology such as analysis technology of morphology, electrochemical reaction and mass transfer of MEA materials to determine a new material design guideline, evaluation technology for long time fuel cell durability and so on. In addition, NEDO started a new program for developing manufacturing technology to improve productivity of PEFC. Several themes such as direct coating of catalytic layer on an electrolyte membrane, low cost separater, mass production of low platinum catalyst are now being conducted under this program.

The need for energy storage is growing with the ever-increasing addition of wind and solar renewable energy to the traditional electrical grid. Lux Research estimates the energy storage market to exceed $100 Billion by 2017 and a recent study projected the value of energy storage for just wind and solar integration worldwide to exceed $30 Billion by 2023. Hydrogen from electrolysis is a promising technology for renewable energy capture as it has the capability to store massive amounts of energy in a relatively small volume. Additionally, electrolysis can also provide ancillary services to the grid such as frequency regulation, load shifting, and demand response resulting in multiple value streams. The hydrogen produced can alternatively be injected into the natural gas pipeline (thus making that energy carrier more green), in the production of high value chemicals such as ammonia, in upgrading of methanization-produced biogas, or used as a carbon-free transportation fuel.

The potential ability to act as energy “currency” between the electrical grid, the gas grid and the transportation grid makes hydrogen a unique solution in the energy storage space. In Germany, hydrogen and electrolysis is looked upon as a key part of the energy storage solution under “Energiewende,” their national sustainable energy transition plan. Some estimates indicate that in order to meet the target of 80% green house gas reduction by 2050, as much as 80 GW of electrolysis will be needed to compensate for the high penetration of variable renewable energy. Other countries such as the U.K., Denmark, the U.S. and China will add to this market potential with their own green house gas reduction plans.

In response to these market triggers, Proton OnSite, the commercial leader in PEM-based water electrolysis, has developed a megawatt-class electrolyzer to address these emerging applications. Proton is leveraging its established history in supplying products to the industrial markets for hydrogen. Proton has been active in early demonstration projects for hydrogen energy storage as well as a market leader in supplying equipment for refueling stations for hydrogen powered fuel cell vehicles. This presentation will provide an overview of Proton OnSite’s activities in these areas and a perspective on the role of hydrogen in the whole future energy infrastructure.

Toyota Motor Corporation released “MIRAI” hydrogen fuel cell vehicle (FCV) on November 18th, 2014 in Japan. We will introduce our view of next-generation vehicles and their energy source hydrogen with its characteristics and advantages. We will review performance and specifications of the MIRAI. The key technology of the new Toyota FC Stack are 3D fine mesh flow channels for a world-leading power output density of 3.1 kW/L and internal water circulation system without a humidifier. High pressure hydrogen tanks have been developed in-house. We will mention in-situ observation technology, especially on water freezing.

FC-Cubic TRA (established on April 2, 2010) is promoting the research on common subjects of fuel cell development. Currently 7 industrial members, 1 national institute and 5 universities are the member.
Stationary fuel cell (Ene-farm) initiate commercialization at 2009 and FCV(Fuel Cell Vehicle) has been introduced into the commercial market at 2014. As a “Strategic Energy Plan” of Japan, realization of future hydrogen society based on the expansion of fuel cell technology, i.e. application of stationary, automotive use and other fields, are strongly expected. In order to realize this, drastic cost reduction and improvement of durability of fuel cell systems are necessary. But still fuel cell technology is not matured and the fundamental technical issues are not solved and still some of the issues are not clarified. Aiming to break down this situation and spread the knowledge to the industrial field, we promoted a research and development from FY2000 to FY2014 under NEDO(New Energy and industrial Technology Development Organization) funding based on collaboration between government, industry and academia members, that were totally 11 research groups participated. In this R&D activity, we focused on “Electrolyte materials”, “Electrode-Reaction” and “Mass Transfer in Catalyst layer”. Along with the development of experimental tools, both technique of experiment and computational sciences are fully combined and utilized. In the research field of “Electrolyte materials”, understanding phenomena and finding the primary factor of low proton-conductivity of electrolyte membrane at low humidity were the main challenge. In the research field of “Electrode-Reaction”, one approach is the numerical simulation and vibrational spectroscopy analysis for the interface of catalyst and surrounding materials using the model catalyst material, and the other approach is development and utilization of in-situ XAFS (X-ray Absorption Fine Structure) technology, for an analysis of surface atomic structure and electronic structure of catalyst during operation. In “Research field of “Mass Transfer in Catalyst layer”, clarifying the correlation between proton conduction, oxygen permeation, water transfer and phase change and cell performance under various environmental/operating conditions were the main target. To clarify the mechanism of oxygen transfer in the porous media used in fuel cell, that is the biggest impact on cell performance, was analyzed by achieving 3D-structure reconstruction with developing a quantitative MPL(Micro Porous Layer) and 3D structure of catalyst layer.
Based on the result and experience obtained through this project, FC-Cubic has just started new NEDO project “Highly-Coupled Analysis of Phenomena in MEA(Membrane Electrode Assembly) and its Constituents and Evaluation of Cell Performance” to contribute technology development for significant progress of durability and reliability and innovative low cost which the industry is expecting.

New materials discoveries can lead to advances that will help address the cost, performance and infrastructure issues hindering large-scale commercialization of fuel cell and hydrogen technologies. These new materials must be integrated into cell architectures, components and systems. At the far end of the R&D spectrum is manufacturing. Implementing new materials, structures, and assemblies in high-volume manufacturing processes is critical to the commercial success of these technologies. For polymer electrolyte fuel cell and electrolysis materials, high-volume manufacturing will often take the form of roll-to-roll (R2R) processing. These processes can be run sequentially to enable multiple coatings, lamination, curing and drying, and converting on a single high-throughput manufacturing line (or “web-line”). Maintaining high film and coating quality on such lines is demanding. Techniques must gather data very rapidly and be able to operate in the web-line environment. Moreover, for fuel cell and electrolysis materials, not only is wide-area uniformity of concern, but we know that discrete defects – such as a pinhole in a membrane – can have a large effect on cell performance and durability, and therefore must be detected and excluded from cells used in a stack. With the support of the DOE Fuel Cell Technologies Office, the National Renewable Energy Laboratory (NREL) and its collaborators and industry partners have embarked on an exploration of two critical questions related to implementing in-line quality control techniques for R2R production of fuel cell and electrolysis materials: what kinds of defects need to be detected, and what types of techniques will accomplish this detection on a web-line. The team is studying what type, size and extent of defects, in different layers of the cell, have strong effects on performance or lifetime. Established cell models are used to predict the performance effects of different defects as a function of operating conditions and cell design parameters. Cells are then fabricated with known, characterized defects, and tested using unique hardware and systems enabling spatially resolved performance and location of failure. The team also develops and validates novel real-time in-line techniques for inspecting these materials based on optical and infrared imaging. First principles modeling assists in the design and optimization of techniques, and testbeds at multiple scales are used to understand the applicability of different techniques to different materials and constructions. Ultimately, techniques can be validated on an industrial-scale web-line at relevant manufacturing speeds and conditions. This presentation will address the need for and status of in-line quality control for these materials and review the technical accomplishments of the NREL project in understanding thresholds for defect detection and developing relevant in-line inspection techniques.

Graphene is considered as one of the most interesting materials due to its unique two-dimensional structure and properties. However, the commercialization and large scale production of graphene still face great challenges at the moment. Thermal reduction of graphene oxide can be an effective method to fabricate graphene in large scale, but the necessity of inert gas protection and high reaction temperature leads to high cost of production thus limited production capacity of graphene. In this paper, for the first time we report a facile, safe and scalable method to achieve simultaneous thermal reduction and nitrogen doping of graphene oxide (GO) in normal ambient air at much lower reaction temperature, while upholding a high quality end product. The reduction and nitrogen doping of GO are evidenced by ultravioletvisible absorption spectroscopy, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The N-doped rGO fabricated via this method has a high C/O ratio of 15 and a nitrogen content of 11.87 at.%. The N-doped rGO is also investigated by applying it as the electrocatalyst for the oxygen reduction reaction. As a result, the catalytic activity has presented itself to be much higher than the undoped rGO.

There is a prominent interest for controlled and well-ordered synthesis of high surface area nanomaterials for superior catalysis and efficient energy production. In this work, we harnessed the advantage of self-assembling peptide amphiphile nanofibers forming 3-D network of high-aspect-ratio fibrous nanostructures as sacrificial organic template. This 3-D nanonetwork was used to deposit TiO₂ via atomic layer deposition (ALD) in a highly-controlled manner. As-synthesized peptide nanofiber-TiO₂ nanonetwork was further decorated with highly mono-disperse ALD-coated Pt nanoparticles. These high surface area TiO₂ nanofibers ornamented with Pt nanoparticles were tested for hydrolytic dehydrogenation of ammonia borane at room temperature. The nanocatalyst demonstrated high turnover frequencies (TOF) at very low Pt loading.

One barrier to the widespread usage of hydrogen as a transportation fuel is its safe,efficient and inexpensive on-board storage, which is a combination of currently lacking in conventional hydrogen storage technologies including cyrogenic and high-pressure vessels. However, chemical hydrides offer high volumetric capacity and energy density. An effecive hydrolysis reaction occurs only when chemical hydrides are in contact with costly precious metal catalysts. In this study, we have demonstrated inexpensive, catalyst free hydrogen generation from chemical hydrides for fuel cells by using fluorinated poly(arylene ether sulfone) (6FBPSH) proton exchange membranes (PEM). Ion exchange capacities (IEC) of 6FBPSH membranes were tailored at the various percent degrees of disulfonation (25, 35 and 45 molar %). Since proton conductivity is a function of IEC, conductivities of 6FBPSH series with 25, 35 and 45 molar % disulfonation were 26, 55 and 130 mS cm^-1, respectively. Similarly, water uptake was scaled with the IEC values and increased with increasing the degree of disulfonation. A two-compartment reactor where an acid solution was separated from NaBH₄ solution via a PEM was used to evaluate hydrogen generation capacity. The state of art membrane Nafion^TM (N212) was used for comparison purposes. Hydrogen generation rate was simply controlled by tailoring the proton conductivities of the membranes. Therefore, hydrogen generation rates of 6FBPSH 25, 35 and 45 were measured as 110, 144 and 200 mL min^-1, respectively. Influence of the type of acids and their concentrations on the rate have also been investigated. Once phosphoric, hydrochloric and sulfuric acid solutions were utilized, the hydrogen generation performance were observed as 90, 133 and 144 mL min^-1, respectively. The maximum rate with 18 M H₂SO₄ for the membranes with the area of 8.4 cm² was observed as 400 mL min^-1, which was one of the highest rates reported in the literature. The influence of temperature on the rates was also investigated. It was demonstrated that the hydrogen generation performance of N212 was deteriorated at temperatures higher than 80 °C due to considerable loss in its proton conductivity. However, the hydrogen generation rate of 6FBPSH continued to increase for the temperatures greater than 80 °C. Additionally, the rate remains almost constant at about 200 mL min^-1 for 30 hour. Then it decreased about 4% along 40 more hours. Once the membrane was washed to remove the by-product salt, the hydrogen generation performance was easily recovered. We have also developed a novel system involving a flow cell in order to avoid washing step. With our continuous hydrogen generation system, an 8 W fuel cell has been powered for about 300 h without the need for the washing step. Depending on the disulfonation level, these membranes can be tailored for the specific hydrogen generation processes such as micro fuel cells and on-board hydrogen generation.

The quantitative calculation regarding the phase formation and the effect of atmospheric carbon dioxide on surface segregation of LSCF-6428 is calculated using La-Sr-Co-Fe-O-C database with respect to the compound energy formalism model by applying CALPHAD approach. The results were compared with the available experimental data for a wide range of carbon dioxide levels and different temperatures. Based on the quantitative calculation, the most efficient atmospheric condition and temperature in equilibrium for this cathode were proposed.

In this work, we investigate catalytic activity of Pd/C catalyst (i) synthesized by modified polyol method and (ii) used as catalyst for anode electrode of direct formic acid fuel cell (DFAFC). In turn, we measured optimal amount of loading for Pd/C catalyst required to gain excellent DFAFC performance. Based on the results, performances of the DFAFC are examined to prove that the new catalyst plays a critical role in improving DFAFC performance, while chemical and electrochemical characteristic of Pd is measured. Distribution of Pd particle in the Pd/C catalyst is evaluated by TEM and electrochemical activities including formic acid oxidation reaction and active surface area are measured by cyclic voltammogram (CV). With that, the Pd/C catalyst synthesized by modified polyol demonstrates superior catalytic activity and DFAFC performance with small loading amount of Pd/C. As optimal values, in case of loading amount of Pd/C, it is 1.5 mgcm^-2, on the other hand, in case of maximum power density of DFAFC employing the 1.5 mgcm^-2 Pd/C catalyst, it is 122mWcm^-2.

Clathrate hydrates have attracted much attention for problems as varied as energy storage and global warming [1]. We studied the stability of hydrogen molecules and the diffusion process in clathrate hydrates by first-principles calculations including van der Waals interactions.
The calculation was done using SIESTA [2]. We studied the structure H (St-H) clathrate hydrate consisting of three 5¹² cavities, two 4³5⁶6³ cavities, and one 5¹²6⁸ cavities. Hereafter, we call those cavities as S(mall), M(edium), and L(arge) cavities.
We find adsorption energies of 0.24 eV, 0.23 eV and 0.17 eV for S, M and L cavities, respectively, relative to H₂ in vacuum. This is consistent with previous works. In S and M cavities, a H₂ molecule sits at the center, while in an L cavity, the molecule sits close to a wall. This means that for the smaller cavities, S and M, the contribution of vdW forces comes from all directions, while for the larger cavity, L, they come from only one side. We find that the L cavity accommodates eight H₂ molecules with a positive adsorption energy, while S and M cavities accepts only one molecule.
For H₂ diffusion, we performed nudged elastic band (NEB) calculations [3]. For St-H, six routes are available. We found that the activation energy depends only on the polygon of O atoms through which H₂ molecule penetrates. We obtained a transition state energy E_TS = 0.36 eV for a hexagonal face and E_TS = 0.83 eV for a pentagonal face, relative to the S cavity.
We also investigated the adsorption energy and diffusion barrier for the structure I. Almost the same results as for St-H are obtained. The S cavity is the most stable site for H₂. Barriers are ~0.36 eV for a hexagonal face and 0.83eV for a pentagonal face. We conjecture that we would obtain very similar results also for the structure II.
To take the entropy effects into consideration, we performed blue moon (BM) calculations at a temperature of 250K [4]. For a hexagonal face, the entropic effects increase the free energy barrier by 0.1 eV. The energy difference between the L and M cavities decreases from 0.07 eV to 0.02 eV because of the larger volume in the L cavity. For a pentagonal face, near the transition state, in which a H₂ molecule is close to the center of a pentagon, the polygon broke during the MD calculation. This prevented to find a complete BM trajectory and to obtain the relative energy between the L and S cavities. However, we conjecture that the pentagon might recover during a longer simulation time.

[1] E. D. Sloan and C. A. Koh, Clathrate Hydrates (CRC, Boca Raton, 2008)
[2] J. M. Soler et al., J. Phys. Cond. Mat. 14, 2745
[3] Q. Li et al., Phys. Rev. B 84, 153103
[4] M. Sprik et al., J. Chem. Phys. 109, 07337

Mobile platforms powered by hydrogen in a future Hydrogen Economy will require technology enabling the storage of hydrogen with high gravimetric and volumetric densities.[1, 2] Metal borohydrides (M(BH₄)_n; (M=metal, n=oxidation state of metal) are coveted as a hydrogen storage material with high storage capacity.[3] We investigate whether the addition of an amino ligand could serve to increase hydrogen loading, while stabilizing the metal borohydride to give a more controlled release of H₂. In this work, transition metal amino borohydrides (Cr, Fe, and V) are synthesized and the characteristics of their decomposition and hydrogen release are analyzed.
Structural analysis confirmed that the synthesized complexes contained amino and borohydride ligands. Thermogravimetric analysis (TGA) coupled with evolved gas mass spectrometry (MS) analysis showed Cr and Fe complexes ligated with protic amino ligands to release the highest amounts of H₂ upon decomposition. Complexes containing V or methylated amino ligands showed release of diborane (B₂H₆) upon decomposition, an undesirable decomposition product for hydrogen storage applications. Cr(BH₄)₂ with a diethyltriamine (DETA) ligand showed a weight loss of 7.5% at 100 °C, with minimal signal for B₂H₆ release. A calculated activation energy of 281 kJ/mol was obtained for dehydrogentation of the Cr(BH₄)₂(DETA) complex. The metal complexes that released hydrogen, rather than B₂H₆, produced a boron nitride type structure similar to decomposed ammonia borane materials.[4] In hopes to identify regenerable hydrogen storage materials, studies assessing the feasibility of re-hydrogenation of the decomposed metal complexes are ongoing.

[1] W. Grochala and P. P. Edwards, "Thermal decomposition of the non-interstitial hydrides for the storage and production of hydrogen," Chemical Reviews, vol. 104, pp. 1283-1315, Mar 2004.
[2] S.-i. Orimo, Y. Nakamori, J. R. Eliseo, A. Zuettel, and C. M. Jensen, "Complex hydrides for hydrogen storage," Chemical Reviews, vol. 107, pp. 4111-4132, Oct 2007.
[3] H.-W. Li, Y. Yan, S.-i. Orimo, A. Züttel, and C. M. Jensen, "Recent Progress in Metal Borohydrides for Hydrogen Storage," Energies, vol. 4, p. 185, 2011.
[4] O. T. Summerscales and J. C. Gordon, "Regeneration of ammonia borane from spent fuel materials," Dalton Transactions, vol. 42, pp. 10075-10084, 2013.

Photocatalytic/electrocatalytic splitting of water is attracting enormous research attention for efficient and eco-friendly generation of hydrogen. Unfortunately, relatively large thermodynamic overpotential for hydrogen evolution reaction (HER) reduces the overall energy conversion efficiency. In this regard, various catalysts, such as Pt and noble analogues, have been studied to improve energy conversion efficiency and minimize the energy barrier. However, the most catalysts are based on expensive and rare earth materials which are unsuitable for conventional energy conversion devices. Therefore, Cost effective HER catalyst without using precious metallic elements is a crucial demand for environment-benign energy production. Molybdenum sulfide is one of the promising candidates for solve such demand, particularly in acidic condition, but its catalytic performance is limited by the poor electrical conductivity and only catalytic edge sites. We present synthesis and HER catalysis of hybrid catalysts composed of amorphous molybdenum sulfide (MoS_x) layer directly bound at vertical N doped carbon nanotube (NCNT) forest surface. Owing to the high wettability of N-doped graphitic surface and electrostatic attraction between thiomolybdate precursor anion and N-doped sites, ∼2 nm scale thick amorphous MoS_x layers are specifically deposited at NCNT surface under low-temperature wet chemical process. Unlike widely used functionalization, which severely degrade the electrical properties of inherent carbon materials, electron-rich N doping provides additional electrons to carbon materials to improve high electro conductivity. Moreover, while pristine graphitic carbon surface has a low surface energy and chemical inertness, the N-doped graphitic plane with electronegative, readily protonated N shows greatly improved surface energy and favorable reaction affinity for MoS_x precursor molecules without any intermediate adhesive layer. The synergistic effect from the dense catalytic sites at amorphous MoS_x surface and fluent charge transport along NCNT forest attains the excellent HER catalysis with low onset overpotential and small potential of 110 mV for 10 mA/cm² current density, which is the highest HER activity of molybdenum sulfide-based catalyst ever reported thus far.

Polymer electrolyte membrane fuel cells (PEMFC) are appealing for transportation, stationary and portable applications due to their high conversion efficiency (up to 60%) and their zero pollutant and greenhouse gas emissions. Electrocatalytic oxygen reduction, the reaction at fuel cell cathodes, has been the focus of attention because of cathode catalyst layer uses expensive and rare noble metals such as platinum, and the oxygen reduction reaction (ORR) which typically occurs with overpotentials more higher than hydrogen oxidation reaction (HOR) on the anode side of fuel cells. Since Jasinski’s discovery that cobalt phthalocyanine, metal-N4 macrocycles as a class of non-precious cathode catalysts, exhibits catalytic activity for the ORR has received considerable attention.. In recent years, iron (cobalt)-nitrogen doped carbon (Fe(Co)-N-Cabon) nanomaterials have been proposed as promising non-precious metal catalysts for ORR because of their superior electrocatalytic activity, low cost, long durability and high tolerance to methanol.
As continuation of our previous studies, herein, we report the facile synthesis of Fe-N-OMC catalysts. Catalysts were prepared by nanocasting method, 1,10-phenanthroline as the nitrogen-rich ligand to form the Fe-1,10-phenanthroline complex precursor, sulfuric acid as the catalysts and rod-type SBA-15 as template. It was then pyrolyzed through a solid-state reaction, to form a carbon supported ORR catalyst. The Fe-N-OMC catalyst was found to display the best ORR activity with a highest onset potential of 1.003 V vs. RHE and current density of 6.771 mA/cm², which was 29 mV and 0.888 mA/cm² even higher than that of the commercial 20 wt% Pt/C and highest half-wave potential of 0.851 V vs. RHE. Furthermore, durability and methanol tolerance tests showed that the catalyst had a better electrochemical stability than commercial Pt/C catalyst.

Currently, there is a huge interest to improve the properties of the electrolyte in PEM fuel cells for operating temperatures above 100 °C. Many works have been done to enhance the conditions of hydration, thermal stability and conductivity of the Nafion proton-exchange membranes. Recently, there has been growing interest in developing proton-exchange membranes non-fluorinated, using non-fluorinated polymers such as polyesters, aromatic polibenzimidazoles (PBI), polyimides, poly (aryl ether Sulfones) and policetonas, functionalized with acid groups.
The PBI membranes are the most interesting material due to they could operate in a range of temperatures of 150-200 °C and mechanical properties. Membranes based-on PBI increasing its proton conductivity when is doped with a strong acid (H3PO4).
The PBI was synthesized by polymerization using polyphosphoric acid (PPA) obtained from 3,4 –diaminobenzoic acid.The membranes were obtained by polymer dissolution in methanesulfonic acid, doped with H3PO4 and modified with yttria-stabilized zirconia, which acts as an inorganic filler.
The as-prepared membranes synthesized were structurally characterized by X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The proton conductivity were evaluated using electrochemical impedance spectroscopy with a four-probe system.

Proton exchange membrane fuel cells (PEMFCs) is currently considered as a potential next-generation alternative energy technology because of the high energy density and high abundance of hydrogen in nature. One of the most important parts in PEMFCs is membrane-electrode assembly (MEA) which provides the electrochemical reactions at electrode, the permeation of fuel and/or oxidant gas and the drainage of water product. In MEA, Nafion dispersion is the most widely used as the ionomer binder for catalyst inks. The structure of electrode in MEA could be significantly determined by formation characteristics of ionomer binder. Upon the structure of the electrodes formed by agglomerates of catalyst and ionomer binder with different size, it has reported that MEA performance and durability is highly affected. The former could be achieved by reducing overvoltages, and the latter by reducing electrode cracking. The structure of electrodes in MEA significantly determines the performance and durability of PEMFCs. Electrode structure of MEA, including the Pt-ionomer interface, could be determined when electrodes are solidified from catalyst inks during a drying step. Thus, the properties of the solvent system in catalyst inks play an important role in determining the electrode structure in MEA. A fundamental understanding of the phenomenological outcome from the relationship between morphology and property for perfluorosulfonic acid (PFSA) membranes is crucial in obtaining high power and durable MEA. In this study ion and liquid water behavior in PFSA membranes formed from different dispersing solvents were investigated with thickness and equivalent weight which cause various morphology. In addition, water sorption and water hydration number diffusivity were measured with water activity by the solid state NMR, and the morphology of the PFSA membranes were investigated by small-angle X-ray scattering and wide-angle scattering. Finally, MEAs with different electrodes prepared by different ionomer binder solutions were investigated in terms of current-voltage polarization, cyclic voltammetry and overvoltage.

ACKNOWLEDGMENTS

This work was supported by the New and Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning(KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20153010031920)

Hydrogen fuel cells have been significant paid attention for an alternative energy source substituting fossil fuel which emit toxic pollutants. Hydrogen as an alternative fuel has promising features such as zero pollutant emission, inexhaustible resource, and highly efficient. However, hydrogen fuel has a limitation due to highly flammable nature when it is exposed to air. Therefore, to utilize hydrogen energy safely, hydrogen sensor with high selectivity and stability is highly required. Hydrogen gas sensors have been composed by metal oxides or noble metals because of their high sensing performance and their quick response. However, most metal oxides based gas sensors required proper operating temperature around 200~400 degree Celsius and noble metals possess low sensitivity owing to high free electrons. In recent years, hybrid structure of palladium with single layer graphene are studied to overcome the low sensitivity but it has the decay of gas sensor characteristic due to low structural stability under volume expansion. Here, we study to synthesize high stable palladium nanostructure on single layer graphene with an interconnecting atom using wet chemical method. The hydrogen gas sensor performance of fabricated hybrid structure were evaluated under internal and external stress. The fabricated hydrogen sensor shows good response with exceptional stability in detecting 1% of hydrogen gas at room temperature. Presumably, the stability of fabricated hydrogen gas sensor is correlated to the novel hybrid structure with interconnecting atom.

The FeSe₂/C catalysts were prepared with various selenium to iron ratios (Se/Fe), namely, Se/Fe=2.0, 2.5, 3.0, 3.5 and 4.0, through facile microwave route by using ferrous oxalate (FeC₂O₄) and selenium dioxide (SeO₂) as precursors. Accordingly, effects of Se/Fe ratio on the crystal structure, crystallite size, microstructure, surface composition and electrocatalytic activity for oxygen reduction reaction (ORR) of FeSe₂/C in an alkaline medium were systematically investigated. The results revealed that all the FeSe₂/C catalysts obtained with the Se/Fe ratios of 2.0~4.0 exhibited almost pure orthogonal FeSe₂ structure with the mean crystallite sizes of 32.9~36.2 nm. The electrocatalytic activities in potassium hydroxide solutions were higher than those in perchloric acid solutions, and two peak potentials or two plateaus responded to ORR were observed from cyclic voltammograms and polarization curves, respectively. The Se/Fe ratios slightly influenced the degree of graphitization in carbon support and the amount of active sites for ORR.

Doped graphene with various heteroatoms, such as sulfur (S), nitrogen (N), boron (B), and phosphorous (P), has attracted intense attention due to its reportedly high catalytic activity, high long-term durability and tolerance to poisoning as a metal-free ORR electrocatalyst. However, its electrochemical activity is strongly affected by N atom content, the limited N content of 2-5% in N-doped graphene still revealed lower catalytic activity compared to Pt-based catalysts. To utilize the outstanding properties of graphene and improve the catalytic efficiency towards ORR, the efficient nanostructure design of graphene-based composites with high content of C-N functional groups is of great interest.
Herein, we report the facile synthesis of graphene decorated with N-doped carbon nanowires as an efficient ORR electrocatalyst. The proposed method here involves the formation of polypyrrole (PPy) nanowires decorated on reduced graphene oxide (rGO-PPy) by in situ polymerization of pyrrole monomer in the presence of rGO. Subsequently, the synthesized rGO-PPy is annealed at 800 ^oC in an argon atmosphere to afford the N-doped carbon nanowires decorated on rGO (rGO-CN) by the carbonization of PPy nanowires. The prepared rGO-CN exhibits the high nitrogen content and a unique nanostructure afforded by the integration of carbon nanowires and graphene sheets, which facilitate the efficient adsorption of oxygen molecules for improved electron transfer efficiency and increased electrocatalytic activity for ORR.
The electrocatalytic activity of rGO-CN was preliminarily evaluated by cyclic voltammetry with a three-electrode system, which shows better adsorption and the reduction of oxygen molecules on the surface of rGO-CN, compared rGO and rGO-PPy. In the rotating disk electrode (RDE) measurements, the higher onset potential and three times higher in the diffusion limited current, compared to the other two electrodes, were observed for the rGO-CN electrode, due to the higher electron accepting capability of the N-doped sites of rGO-CN. The number of electrons transferred per oxygen molecule (n) of rGO-CN in the ORR process was determined to be 3.08, suggesting that the rGO-CN electron follows a combination of two- and four-electron transfer process. These results suggest that the superior ORR activity with more efficient electron transfer have been demonstrated by the greater amount of N-doped active sites in the rGO-CN electrode.

Current proton exchange membranes require water and strong acid for proton transport, which limits their durability and effectiveness at high temperature. In this project we are developing a membrane that transports protons via a dry proton hopping mechanism. For this membrane a variety block-copolymers containing fluorinated blocks and imidazole as the proton transporting group were synthesized. Several combinations of hydrophilic and hydrophobic blocks have been synthesized and characterized and their data will be presented. Initial membranes have been prepared, and mechanical strength, thermal stability, porosity, and possibly proton transport data will be presented as well.

Lithium cobalt oxide (LiCoO₂) has been found to be an efficient catalyst for the oxygen evolution reaction (OER); however, the underlying catalytic mechanism, let alone its surface structure, remains poorly understood. We investigated the surface structure and electronic states of layered and spinel-like LiCoO₂ using hybrid functional calculations. We found that surface Li atoms can be rather easily removed under aqueous conditions, leaving an oxygen-terminated surface. As a result, subsurface Co³⁺ ions are oxidized to Co⁴⁺, leading to destabilization of the surface. Our calculations predict the Li-deficient LiCoO₂ surface is stabilized via hydrogenation, while the H-terminated layered surface appears to be more stable compared to the spinel-like counterpart. Knowing the surface properties, we examined the OER pathway and energetics on the H-terminated layered LiCoO₂ (111) surface using density functional theory (DFT) calculations and ab-initio molecular dynamics (AIMD) simulations. According to our study, when an excess hole is supplied, a subsurface Co³⁺ ion is oxidized to Co⁴⁺, leading to deprotonation of the surface. In an aqueous solution, the H-terminated LiCoO₂ (111) surface is found to be restored by abstracting a hydrogen atom from water, which in turn results in the reduction of subsurface Co⁴⁺. As such, the OER tends to proceed by forming hydrogen peroxide, followed by its decomposition to dioxygen. In this talk, we will discuss in depth the OER mechanisms and activities of LiCoO₂ in aqueous solution based on our recent findings.

Due to the necessity of Pt metal for the anode catalyst, it is highly desirable to develop effective strategies for improving the activity and durability of Pt-based catalysts for methanol electrooxidation. The unique 3D-network structured carbon-coated TiO₂ nanowires are synthesized by in-situ carbonized res orcinol–formaldehyde polymer and are used as highly efficient Pt-based catalyst support. The 3D-network structure has high porosity, good flexibility, large surface area and efficient transport channel, and has been confirmed by a number of physical characterizations. The carbon network derived from resorcinol–formaldehyde polymer carbonization plays a critical role in facilitating the final morphology. Strikingly, compared with the commercial Pt/C, the obtained catalyst exhibits far better electrochemical activity and durability for methanol electrooxidation. Under the condition of the same electrochemical activity, the Pt loading of our catalyst can be reduced by 33.3 %. More importantly, the obtained Pt-based catalyst in the single direct methanol fuel cell also exhibits higher polarization current and power density than Pt/C. The enhanced performance could be attributed to the design of special 3D-network structure, the numerous anchoring sites for Pt deposition, as well as the synergetic effect among carbon, titania and Pt.

Favorable dissociative adsorption of H₂ on electrocatalysts is a key requirement of the anode in a proton exchange membrane fuel cell (PEMFC). To enhance the electrocatalytic activity of the anode, we prepared bimetallic Pt-Ir electrocatalysts loaded on carbon supports (Pt-Ir/C) to improve the HOR of the PEMFC anode. We investigated the characteristics of the hydrogen oxidation reaction (HOR) on bimetallic nanoparticles of Pt–Ir over a carbon support. The findings of the study indicate that the bimetallic Pt-Ir nanoparticles, which are distributed well on the carbon support, enhance the electro-catalytic activity of the anode facilitating H₂ dissociation to form H⁺ atoms, owing to strong H₂ dissociation and ready formation of H⁺ atoms. In addition, we investigated the adsorption configuration and electronic properties of the optimized structure using density functional theory calculations, to gain insight into the mechanisms and characteristics of H₂ dissociation on Pt (111), Ir (111), and Pt–Ir (111). From the DFT calculations, the energy profiles of H₂ dissociative adsorption suggest that the HOR is thermodynamically favored on bimetallic Pt-Ir, confirming the beneficial role of the bimetallic Pt-Ir phase for the surface reaction. In addition, the H⁺ chemisorption affinity is enhanced on the Pt-Ir surface, which is attributed to the improved adsorptive binding energy with a narrow HOMO-LUMO band-gap. The reaction profile of H₂ dissociative adsorption on the catalysts indicated enhanced HOR on Pt–Ir (111) compared to pure Pt (111), which was attributed to more favorable H₂ dissociation in the former, owing to a reduced electronic band-gap. The integrated experimental and theoretical study suggests that Pt–Ir/C is a potential candidate for preserving the high performance of an anodic electrocatalyst in PEMFCs. The experimental findings as well as the DFT calculations provide insights into the fundamental and systematic characteristics of H₂ dissociative adsorption on Pt-Ir and possibly, other bimetallic electro-catalysts such as Pt and Ir-based alloys. This methodology is useful to develop the outstanding electro-catalysts for PEMFC anode.

Nowadays, hydrogen seems to be the best potential energy carrier for the future, which will solve the triple threats of climate change, urban air pollution and petroleum dependence. However, the storage stage is one of the key issues to be solved before the advent of a hydrogen based economy [1]. Among the current ways of storing hydrogen, the storage of hydrogen in metal hydrides is perhaps the most interesting and challenging [2]. If we want to turn towards renewable energy in a green world, the storage solutions must also be respectful of the environment. But it is not really true with polymer composite tank for high pressure gas or insulated vessel in cryogenic storage, due to major issues concerning their recycling. Then we have chosen a metal hydride alloy without any rare element, but with intrinsic storage capabilities boosted by a particular thermochemical treatment. As desorption of 80% of the hydrogen content takes 80 min for the raw metal hydride, it takes only 9 min for a full desorption step (100%) after this specific treatment.
First, we will present the modifications induced by the thermochemical treatment on the raw intermetallic powder by means of the PCT (pressure-composition-temperature) diagrams. Then, we will study the influence of the different parameters of the treatment on the properties of the resulting metal hydride. And we will analyse and discuss the effects of the treatment on microstructure in the bulk and on segregation of species on the surface of the metal hydride powder. The optimal combination of parameters for the thermochemical treatment will be explained. Finally, the characteristics of this TiFe base alloy after treatment will be compared to the wide used LaNi₅ base alloy hydrides.
In order to address mass-market development of hydrogen energy in transportation in the near future (2020), which is one of the objectives of the Europe Union, cost-effective and environmental-friendly solutions for hydrogen storage must be rapidly proposed. Besides the development of new hydride alloy compositions, the increase of performances of well-known metal hydride is an interesting alternative way. Although TiFe base alloy do not fulfil the DOE criterion for gravimetric hydrogen density, they can release hydrogen at temperature as low as -8 °C at a pressure of 1 bar [3]. By increasing their desorption kinetics, they become serious low-cost solutions for niche market like forklifts.

[1] K. Hirose, Faraday Discuss., 2011, 151, 11-18, DOI: 10.1039/C1FD00099C
[2] A. Zuttel, Hydrogen storage methods, Naturwissenschaften 91 (2004) 157– 172.
[3] A. Andreasen, Ris National Laboratory Report 2004, Ris-R-1484(EN)

Molybdenum disulfide (MoS₂) is a promising catalyst for hydrogen evolution reaction (HER) because of its unique nature to supply active sites in the reaction. However, the low density of active sites and their poor electrical conductivity have limited the performance of MoS₂ in HER. In this work, we synthesized MoS₂ nanosheets on three-dimensional (3D) conductive MoO₂ via a two-step chemical vapor deposition (CVD) reaction. The 3D MoO₂ structure can create structural disorders in MoS₂ nanosheets (referred to as 3D MoS₂/MoO₂), which are responsible for providing the superior HER activity by exposing tremendous active sites of terminal disulfur of (in MoS₂) as well as the backbone conductive oxide layer (of MoO₂) to facilitate an interfacial charge transport for the proton reduction. In addition, the MoS₂ nanosheets could protect the inner MoO₂ core from the acidic electrolyte in the HER. The high activity of the as-synthesized 3D MoS₂/MoO₂ hybrid material in HER is attributed to the small onset overpotential of 142 mV, a largest cathodic current density of 85 mA cm^-2, a low Tafel slope of 35.6 mV dec^-1, and robust electrochemical durability.

Alkaline anion exchange membrane fuel cell (AEMFC) is expected as a promising candidate for getting rid of the dependence of nobel metals, it will shows advantage on polymer electrolyte and cheap electrocatalyst options. However, the AEMFC needs high anion conductive membrane material which should be stable under fuel cell operating condition. Comparing with proton exchange membrane, anion conductive material is facing more challenges, i.e., low anion conductive rate, less stable in fuel cell conditions. The possibility of composite anion exchange membranes were investigated in this work. Based on the in-house composite anion exchange membrane, membrane electrode assemblies were prepared. Measurements of a single cell, as well as a stack, were implemented to evaluate the performance and the application possibility of AEMFC.

New membranes for alkaline fuel cells and other ion transport applications continue to generate a lot of interest in the electrochemical community. Over the last 10 years there has been great progress in determining the key attributes of anion exchange membranes that lead to high fuel cell performance and moderate lifetime devices. A current limitation of the field is the lack of readily available membranes and ionomer solutions. Scalable, inexpensive materials are needed to promote more studies of electrode fabrication, device operation, and optimization, particularly in the area of longevity.

Our group has demonstrated a number of new polymer structures based on commercially-available polymers and inexpensive modification reagents. We have focused on poly(phenylene oxide) as a backbone platform and employed ammonium cations that have relatively good stability in light of their low cost and reasonable performance. In previous work, we employed alkyl chains to cause phase separation in random copolymers. This phase separation increased the conductivity and decreased the water uptake of the materials. We have since continued to investigate crosslinking and interpenetrating networks as further methods to optimize the properties of anion exchange membranes. Many of these polymers have shown reasonable performance in anion exchange membrane devices, but more work is required to extend the lifetimes of the cells beyond 1000 hours.

This talk will highlight our recent work on new polymer structures and demonstrate how stability and conductivity can be increased by nanostructuring quaternary ammonium-based materials.

Polymer electrolyte materials are being developed and studied for an increasing diversity of clean energy technologies, such as low temperature fuel cells, redox flow batteries, biological fuel cells, and reverse electrodialysis cells.

This invited presentation will highlight the versatility of the radiation-grafting methodology in that it allows the production of anion-exchange polymer electrolytes containing numerous different morphologies and chemistries. Once initial (small-scale) experiments have been conducted and synthesis protocols have been developed, this methodology has the advantage that reasonably large (for lab-scale) quantities of materials can be synthesized (e.g. 10 – 100 gram scale and/or several square meter sized batches of membrane) with excellent repeatability; this also allows for a large number of tests and experiments to be conducted on the same batch of material.

This synthesis platform therefore facilitates fundamental materials research that compares ion-exchange materials where a single variable has varied: e.g. anion-exchange polymer electrolyte materials with the same ion-exchange capacities and polymer backbones but where the chemistries of the cationic head-groups is varied.

Data on a new radiation-grafted anion-exchange membrane will be presented that exhibits a higher alkali stability (at 80°C) relative to the benchmark benzyltrimethylammonium type. This development is relevant for technologies such as alkaline polymer electrolyte fuel cells or alkaline membrane water electrolyzers. Strategies for moving this radiation-grafted anion-exchange membrane technology forward toward even more alkali stable types will also be discussed.

Radiation-grafted anion-exchange membrane types that are not stable to alkali will also be presented. These types are more relevant to energy technologies such as reverse electrtodialysis.

Alkaline membrane fuel cells (AMFCs) remain an area of great research interest due to their ability to enable non-precious oxygen reduction. However, anion exchange membranes (AEMs) have exhibited limitations in a number of areas including: their ability to remain stable under operating conditions, ability to reject carbon dioxide, ability to maintain high temperature operating conditions, and their ability to be incorporated into high performance membrane electrode assemblies. Perfluorinated membranes have been the standard for polymer electrolyte fuel cells and offer advantages in overcoming specific aspects limiting the performance of current generation AMFCs. This presentation will report on properties and performances obtained using perfluorinated anion exchange membranes in AMFCs.

While water electrolysis is achievable under alkaline or acidic conditions, electrolysis under acidic conditions requires a platinum group metal catalyst such as iridium oxide whereas alkaline electrolysis can be conducted using nickel or silver as the catalyst. Thus the development of an alkaline electrolysis system would result in a significant reduction in the capital cost due to the less expensive catalyst. However, liquid electrolyte systems present additional challenges such as hazardous materials handling requirements due to the corrosive electrolyte, balanced pressure operating requirements due to the low bubble point of the porous separator and associated hazards with pressurized oxygen, and efficiency losses due to ionic resistance across the relatively large electrode gap. An anion exchange membrane (AEM) approach provides a solution to these challenges while retaining the advantages of the alkaline chemistry.

A key barrier to the success of AEM systems has been the need for an AEM with the necessary conductivity, water swelling, and chemical stability under operating conditions. Conductivity is generally dependent on water swelling and the latter can be controlled by varying the ion content of the polymer or by crosslinking to restrict free volume within the membrane. Chemical stability relates to both the polymer backbone and the fixed cationic groups attached to the backbone. The fixed ion in most, if not all, commercially-available AEMs is the benzyl trimethylammonium (BTMA) cation. At the high pH and elevated temperatures found in electrolysis cells, BTMA groups can undergo attack by hydroxide ions leading to a decrease in membrane conductivity. This presentation will describe the synthesis, characterization, and testing results for a series of AEMs prepared at Sandia. Several backbone and cation structures have been prepared and evaluated, particularly for alkaline stability.

High-throughput computational screening could be used to identify promising new materials for hydrogen separation membranes or fuel cell electrolytes. However the use of ab-initio methods such as density functional theory (DFT) to screen proton mobility in tens of thousands of candidate materials could be prohibitively expensive. To address this problem, we have developed a potential energy model for rapidly screening tens of thousands of candidate materials to identify the materials (or classes of materials) that are most likely to exhibit high proton mobility. We will present initial results of our model on a variety of materials including well-known proton-conducting oxides. The discussion will focus mainly on diffusion pathways in the bulk and the performance of the model relative to DFT.

Sulfonated poly(ether ether ketone) [sPEEK] has been one of the most desirable hydrocarbon membranes due to low price and superb thermal/mechanical properties as opposed to PFSA such as Nafion. However, sPEEK at 60% degree of sulfonation (DS) has a proton conductivity of 0.07 S/cm at 80 °C/100% RH, equivalent to only 70% of that of Nafion (0.1 S/cm). Another problem is its brittleness which results in higher interfacial resistance between electrode and membrane. Through our earlier work, we tried sulfonated POSS (POSS-SA) as an external proton source into nanochannels of sPEEK and its nanocomposite membranes had a proton conductivity of 0.096 S/cm at 80 ^oC/100% RH without water swelling. Nevertheless we require the better membranes with the higher cell performance for them to be really applicable to PEMFC.
To promote the conduction of protons via Grotthuss mechanism, we adopted nanocomposite membrane with proton donor and acceptor. Proton donors and acceptors based on POSS were nanocomposited with sPEEK. Maximum proton conductivity of nanocomsposite membrane was 0.125 S/cm at 80 °C/100% RH and cell performance was 1.6 A/cm², which was almost 60% higher than Nafion. Its superb cell performance was due to very high conductivity of the membrane and significant decrease of contact resistance between membrane and electrodes. We will present the effect of proton donor-acceptor on the conductivity and cell performance and explain why.

Hydrogen is a clean chemical fuel capable of storing energy obtained from renewables and, therefore, can relax the associated intermittency problem of these sources. In order to become an economically viable solution, the production cost of hydrogen needs to reach levels competitive with fossil fuels prices. Today, clean hydrogen is produced by implementing water electrolyzers, but their high cost has proved to be a major obstacle for their large scale deployment. State-of-the-art electrolyzers commonly incorporate proton exchange membranes (PEM) to separate the product gases while conducting the charged species between the reaction sites. Despite their critical role in the electrolysis process, membranes tend to account for a significant share of the electrolyzers’ cost. In addition to the added cost, the low ionic conductivity of membranes limits the device efficiency, and their acidic nature prevents the incorporation of earth-abundant electrocatalysts. Alternatively, electrolysis processes under liquid electrolytes can have lower ionic resistances, and take place over a broad range of pH conditions. On the other hand, operating under liquid electrolytes without a separation mechanisms can lead to large amounts of gas crossover.
Here, we report the successful demonstration of a versatile membrane-less elctrolyzer with the ability of working under liquid electrolytes across the pH scale [1]. The device runs with highly conductive electrolytes and separates the gas streams by means of fluidic forces acting on the generated gas bubbles. The first prototype is a microfluidic device which can support current densities of more than 300 mA/cm² at 2.6 V and produce hydrogen gas streams with less than 0.4% of oxygen crossover. Devices that incorporate noble metal and earth-abundant catalysts have been demonstrated and their gas crossover, device performance, stability, and the behavior of gas bubbles under different flow rates are probed. Moreover, the extension of the working principle to a larger 3D printed prototype will be discussed. The scaled-up prototype has an active catalytic surface two orders of magnitude larger than the microfluidic device and outperforms it in terms of efficiency and throughput. Lastly, the potential of this device to produce high pressure hydrogen gas in a scheme where several unit cells are stacked together will be presented.

[1] S. M. H. Hashemi, M. A. Modestino and D. Psaltis, Energ Environ Sci, 2015, 8, 2003-2009.

The cost and durability of Polymer Electrolyte Membrane Fuel Cells (PEMFCs) are the two major barriers to the commercialization of these systems for stationary and transportation power applications. While there has been significant progress in improving PEM Fuel Cell durability with lower cost materials, further improvements are needed to meet the commercialization targets. Past improvements have largely been made possible because of the fundamental understanding of the underlying degradation mechanisms. By investigating component and cell degradation modes; defining the fundamental degradation mechanisms of components and component interactions new materials can be designed to improve durability.

One of the primary degradation modes involves the various forms of carbon used in PEMFC components. Corrosion of the carbon electrocatalyst support is one of the major contributors to degradation which leads to changes in the catalyst layer structure and reduces its activity. The cost of the noble metal used in the catalyst makes this a crucial area that requires improvement in durability. Surface properties of the carbon also changes in both the catalyst support and the gas diffusion layers (GDLs) which changes water transport and effect gas mass transport to the catalyst sites.

Carbon corrosion is induced by air/hydrogen (or hydrogen/air) fronts during shut-down/start-up which cause high potentials leading to carbon support corrosion. The degree of the effect is dependent on many factors including the types of carbon utilized as the catalyst support, water content, and the anode catalyst layer. Electrode structure degradation has been shown to occur in microscopically localized regions, with support corrosion leading to detachment and agglomeration of catalyst particles, while weakening of the carbon structure allows collapse of electrode pores and can severely limits gas transport.

Catalyst support carbon corrosion also exists at normal fuel cell operating conditions and is exacerbated by the voltage cycling inherent in transportation drive cycles. A peak in CO₂ evolution occurs when the cell potential increases from high power operation to low power near open circuit. This correlates to where CO₂ evolution is observed during cyclic voltammograms which occurs. The evolution of this CO₂ peak suggests that at oxygen is adsorbed onto the carbon and/or CO is formed on the Pt surface, with the CO being oxidized at the Pt surface.

Many material and operating variable affect the amount of carbon corrosion, including the types of carbon, Pt loading and operating conditions such as Relative Humidity and temperature. High surface area carbons show the greatest amount of corrosion with the least amount of carbon corrosion with graphitized carbons.

Acknowledgments
Funding for this work is from DOE EERE FCTO, Technology Development Manager Nancy Garland

Nanostructured Pt catalyst has broad applications including fuel cells, hydrogen production. Imaging its structure evolution under (simulated) working conditions is very helpful for understanding catalyst fading mechanisms and provides fundamental insights for new catalyst design and development. In this presentation, we will discuss our new findings about the role of O₂, H₂O and electron beam in Pt/CNT nanostructure evolution using Environmental TEM.

The nature of active sites in electrocatalysis is an often topic in the literature. However, despite decades of persistent studies aimed to revealing the real active sites at electrochemical interfaces, scientific community is still lacking insight at atomic level. Properties such as surface crystallographic orientation, morphology, composition and defects are yet to be assigned to the structure-function correlations that determine electrocatalytic behavior in conjunction with applied electrolyte. Such knowledge is of paramount importance in design of advanced highly functional nanoscale materials. Here a detailed insight into the extended well-defined surfaces will be used to reveal the real active sites for several electrochemical reactions. Well-defined surfaces were characterized in ultra-high vacuum using AES, LEED and UPS, followed by controlled transfer into electrochemical, in-situ FTIR and STM cell. These findings have been used to perform targeted synthesis of nanomaterials with superior electrocatalytic properties.

Carbon supported metallic catalysts are widely studied for fuel cell and many other chemical processes. In fuel cells, the dispersion and stability of the catalysts on the carbon support is critical in improving the activity and durability of the catalysts, but in most systems the structures of the catalysts/supports are very complicated. In this presentation we will discuss a fundamental study of the binding and nucleation processes on model carbon surfaces, reveal the nature of the binding and nucleation sites and detailed interfacial structures using electrochemical, high resolution transmission electron microscopy and theoretical calculation. We will also discuss recent studies of the catalyst stability using in-situ transmission electron microscopy techniques.

Due to being highly efficient and environmentally friendly, fuel cells are one of the most promising energy conversion devices to power the energy demands of the future. However, commercialization of fuel cells is hindered by the sluggish kinetics of the oxygen reduction reaction and high cost materials. Therefore methods to improve the catalyst activity and reducing the noble metal usage have been and continue to be a popular area of research. Accomplishments that have been achieved through tailoring the activity by alloying and core-shell at the nanoscale level will be discussed. Also, since electrocatalytic reactions are strongly dependent on the surface structure of metal catalysts, the atom-level design of the surface structure plays a significant role in a high catalytic activity and the utilization of electrocatalysts. I will suggest the design of highly durable and active electrocatalyst through nanoscale engineering. Further, nanoscale architecture such as three-dimensional ordered electrode structure, 1-dimensional support-less electrocatalyst and multiscale architecture for fuel cell application will be discussed in the symposium.

In this work, we demonstrate a novel approach to nanostructure the cathode of polymer-exchange membrane fuel cells (PEMFC) free of carbon support. The electrode consists of an array of vertical platinum nanotubes onto Nafion[GD21] ® membrane. We investigate two different fabrication processes, both using a porous alumina template (AAO) as a sacrificial mold.

The first method involves e-beam evaporation of platinum on the top of the AAO template [1]. During the deposition, the alumina mold is tilted; thereby platinum penetrates in the pores and is deposited onto the wall. Following this step, a Nafion® membrane is hot pressed on the samples and the porous alumina is wet etched. Finally, we obtain platinum nanotubes stuck onto the Nafion® membrane. This method is very suitable to study the effects of geometric parameters (diameter, spacing between nanotubes, length of nanotubes, and thickness of the walls) on the MEA performance. Moreover, we are able to deposit other metals such as nickel, copper, iron-cobalt which allows us to perform galvanic displacement with chloroplatinic acid resulting in different Pt based nanotubes.

The second method is based on an electrochemical process. The pores of the AAO template are filled with copper by pulsed electrodeposition. A galvanic displacement with chloroplatinic acid is then performed. This process yields porous nanotubes of copper-platinum with a weight composition of 80% of Pt and 20% of Cu; the size of crystallites is about 5 nm. The sample configuration (copper nanowires are electrically connected to the silicon substrate), allows to follow in real time the alloy formation by measuring the OCP and to well define the different mechanisms occurring during the galvanic replacement.

All electrodes are tested in fuel cell operation and results are compared with those obtained with a Tanaka commercial Pt/C dispersion. The platinum loading of electrodes nanotubes varies from 80µg_Pt/cm²_geo to 160µg_Pt/cm²_geo. Active area is ranging between 8cm²_Pt/cm²_geo and 20cm²_Pt/cm²_geo. Since these new structures are self-supported, there is no problem of corrosion of carbon support. Moreover, nanotubes arrays exhibit high specific activity (250µA/cm²_Pt at 0,9V vs 120µA/cm²_Pt for Tanaka Pt/C dispersion). The later proposed method represents a promising method for scale-up production of PEMFC, due to the very low cost of fabrication compared to metal evaporation processes.

[1] S. Galbiati, A. Morin, N. Pauc, Volume 165, April 2015, Pages 149-157, ISSN 0926-3373

Toray has developed highly-reliable hydrocarbon-based (HC) membrane for PEFC in NEDO FY2013-2014 Next Generation Project. Newly-developed HC membrane using newly-developed organic peroxide decomposition catalysts showed higher cell performance under high temperature and low humidity condition, and more than 5.2 times higher chemical durability, in comparison with the reinforced PFSA membrane NafionHP as a reference membrane. Consequently, newly-developed HC membrane accomplished the FY2014 target of NEDO Project on both cell performance and chemical/mechanical durability.
Acknowledgement: This work was partially supported by the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

One of the keys to optimizing polymer-electrolyte-fuel-cell performance is understanding it’s transport phenomena. This is especially critical in the polymer electrolyte in both the bulk and in particular the catalyst layers, where it exists as thin, nanometer-thick film covering the catalyst agglomerates. In these structures, it is known to perhaps inhibit performance, especially as the total platinum content is reduced. Interactions of the membrane with the local environment and as a thin film within the CL result in highly complex material behavior that is highly dependent on the environmental conditions, ionomer thickness, and the material interactions, e.g., carbon, platinum, etc. Thus, characterization of the role of ionomer in fuel-cell catalyst layers requires understanding the transport properties and water-uptake behavior throughout a wide thickness range.

In this talk, the role of the ionomer and its underlying structure/function relationships will be elucidated. Ex-situ testing of the catalyst-layer ionomer demonstrates reduced water content for both Nafion and the short-side-chain, lower equivalent weight 3M ionomer. These studies are complemented by thin-film structural and swelling measurements using x-ray scattering and ellipsometry, respectively, which likewise show reduced water content and phase separation as the film thickness decreases. This decrease is caused by an increase in the packing of the polymer chains resulting in increases in mechanical modulus. In addition, advanced grazing incidence x-ray scattering (GISAXS) is used to understand film morphology on various substrates.

Acknowledgement
The authors thank Steve Hamrock and Mike Yandrasits from 3M for helpful discussion and ionomer samples.. This work made use of facilities at the Advanced Light Source (ALS), supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy. This work was funded by the Assistant Secretary for Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U. S. Department of Energy under contract number DE-AC02—05CH11231.

Ionomer thin films form the proton-conducting pathways within the catalyst layers (CL) of polymer electrolyte membrane fuel cells (PEMFCs) and the web-like ionomer network provides support for the porous CL structure. The recast ionomer is assumed to be relatively uniform in thickness, structure, and chemistry across the entire CL thickness, forming very thin films around the various materials constituents; however, there are numerous factors that can significantly influence the homogeneity, dispersion, aggregation of the ionomer that will in turn have a significant impact on catalyst utilization within the CL, as well as overall CL durability during electrochemical aging. These factors include (1) the loading, dispersion, composition, and size/shape of Pt-based electrocatalysts, (2) the type of carbon support material used, including the extent of graphitization (or lack thereof) and the presence of surface oxide functional groups, (3) the CL pore size and structure, and (4) the ink preparation method employed (e.g., solvent use, drying procedure, etc.). Recently, studies have been conducted at Oak Ridge National Laboratory to identify the optimum conditions for examining ionomer thin films in “real” CLs using electron microscopy and spectroscopy techniques. The current work will expand on this microscopy research to apply specific microscopy methods, including high-resolution imaging and energy dispersive X-ray spectroscopy (EDS) coupled with 3D electron tomography, towards identifying the nature of ionomer film dispersions and/or ionomer aggregation within CLs prepared using Pt or Pt-alloy catalysts at different catalyst loadings or with unique geometries, carbon supports having varying degrees of graphitization, and ionomer distributions in CLs derived from inks prepared via different processing routes. In addition, changes to these ionomer films within the different CLs during accelerated stress testing (AST) will be analyzed as a function of these CL variables.

Electrochemical water splitting normally requires a voltage between 1.6 and 2.5 V, due to the thermodynamic requirement (1.23 V at 25 °C), ohmic resistance and overpotentials on the anode and cathode. Here, we demonstrate a new but simple concept that successfully splits water into oxygen and hydrogen at a voltage as small as 0.8 V, at room temperature (25 °C), and with earth-abundance catalysts.

The goal of this work is to study the properties of magnetically aligned CNT/PC nanocomposites towards the development of hydrogen gas separation membranes. A fraction (0.1 weight %) of synthesized carbon nanotubes (CNT) have been dispersed homogeneously throughout polycarbonate (PC) matrix by ultrasonication. The alignment of CNTs in PC matrix has been accomplished by applying an external magnetic field of 1200 Gauss. These nanocomposites have been studied by gas permeation using H2, N2 and Co2 electrical and dielectric constant measurements. Experimental results of gas permeability measurements exhibit here that H2 is more selective than N2 and Co2 in magnetically aligned nanocomposite membranes which can be used as good hydrogen separating media. I-V characteristics show the electron hopping like behavior and dielectric constant shows the enhancement in permittivity of these nanocomposites. Overall experimental results exhibit here that alignment of CNTs in polymer matrix shows the dramatic improvement in mass and charge transport properties. These magnetically aligned CNTs/polymer nanocomposites may be used as proton and anion exchange membranes for hydrogen and fuel cell applications.
Keywords: CNT/PC nanocomposites; Magnetic field alignment; Gas Permeability; Dielectric constant; Mass and Charge Transport

The search of cheap, earth-abundant and efficient hydrogen evolution reaction (HER) catalysts is significant for developing sustainable hydrogen economy. Here we introduce a simple and cost-effective strategy for one-step synthesis of 3D porous NiSe₂/Ni hybrid architectures as promising HER catalysts from commercially available Ni foams via thermal selenization. Due to the improved electrical conductivity and contact of catalytic NiSe₂ with Ni foam, the constructed hybrid structures exhibit superior catalytic performance to NiSe₂ films, featured by a small overpotential (~ 143 mV) to afford 10 mA/cm², small Tafel slope (49.0 mV/dec), large exchange current density (15.7 μA/cm²) and good stability in acid, which benefits from the good contact and electrical conductivity of NiSe₂ catalysts on Ni foam and the increase of mesoporous structures during NiSe₂ growth. The performances of pyrite NiSe₂ are greatly improved, which is superior to most of well-studied MoS₂ or WS₂-based catalysts, and the exchange current density is much larger than CoSe₂ or MoS₂-based catalysts. This achievement provides an alternative strategy to achieve cheap and efficient catalysts from commercially available materials for large-scale water splitting.

There are intense efforts worldwide to find renewable and green energy sources as alternatives to fossil fuels with rising concerns about energy shortages. Efficient catalysts for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) are of paramount importance for electrochemical energy applications in fuel cells, batteries, and electrochemical water splitting.^1–2 However, the high cost of Pt catalysts commonly used for such applications restricts widespread applications. The considerable challenge is to develop robust electrocatalysts composed exclusively of low-cost, earth-abundant elements that exhibit activity comparable to that of the noble metals. Herein, we report, a cost effective, cobalt selenide based catalyst which exhibits significant catalytic activities towards ORR, OER and HER.
Electrocatalysts were prepared by electrodeposition³ on GC electrodes. This catalyst was found to be highly active for OER & HER in alkaline and ORR in acidic media. The catalysts were characterized using TEM, SEM, EDX, XRD and XPS for morphology, elemental chemical compositions, phases and electronic states. The detail results will be presented in the meeting.

References:
1. O. Khaselev, J. A. Turner, Science 1998, 280, 425
2. J. Suntivich , H. A. Gasteiger, N. Yabuuchi, H. Nakanishi, J. B. Goodenough, Y. Shao-Horn, Nat. Chem. 2011 , 3 , 546 .
3. Z. Zhang, S. Pang, H. Xu, Z. Yang, X. Zhang, Z. Liu, X. Wang, X. Zhou, S. Dong, X. Chen, L. Gud and G. Cui, RSC Advances, 2013, 3, 16528.

The optical, catalytic and photocatalytic properties of nanomaterials strongly depend on their shape and size. Therefore, a lot of studies have been carried out to control the size and shape of nanomaterials. Herein, we use hexagonal lyotropic liquid crystals that are composed of surfactant, brine, oil, and co-surfactant as soft templates to synthesize several metal, polymer and composite nanostructures of controlled size and shape. Interestingly, the volume ratio of oil to water can be adjusted, thus allowing us to control the diameter of the oil tube of the hexagonal mesophases. These soft templates are stable and easy to remove by using ethanol or 2-propanol.

On the other hand, radiolysis is a powerful method to synthesize metal nanoparticles (NPs) of controlled size and shape, and in particular bimetallic NPs of controlled structure (core/shell or alloys) and composition in solution or in heterogeneous media. The hydrated electrons and the reducing radicals produced during the radiolysis of the solvent induce homogeneous reduction in the water phase. Compared to chemical reducing processes that follow a diffusion front, radiolysis presents the advantage of inducing a homogeneous nucleation and growth in the bulk.

Soft surfactant-stabilized hexagonal templates were used to synthesize different nanostructures by radiolysis such as bimetallic porous nanoballs (AuPd, AuPt, and PtNi and PdPt) of controlled composition, conducting polymer nanostructures (Poly Diphenyl Butadiene, PDPB, and Poly 3-hexylthiophene), and nanocomposites (Pd-PDPB).

The electrocatalytic oxidation of ethanol has been selected as a test reaction in alkaline medium where Pd is known to be among the best electrode materials. We found that the Pd-based nanostructures and Pd/conducting polymer^2,3 hybrid composites both exhibit a superior electrocatalytic activity for ethanol oxidation with high stability, which is suitable for direct fuel cells applications.

Recent results on Pt-based nanostructures (AuPt and PtNi nanoballs) for application in glucose oxidation and Oxygen Reduction Reaction (ORR) will be also presented.

For decreasing the high loads of precious metals on PEMFC catalysts, the graphitic-C₃N₄ quantum dots (g-C₃N₄ QDs) modified CNT composite material is structured by π-π stacking for supporting PtRu catalyst, in which the g-C₃N₄ QDs play a bridged unit between CNT and metal nano-particles (NPs). Comparing the conventional acid-functionalized CNTs, the g-C₃N₄ QDs modified CNT (CNT-QDs) has lessen structural damage leading a higher stability. While, the forward peak current densities of prepared PtRu/CNT-QDs catalysts is about 1.22 A mg_Pt⁻¹ with a factor of 2.3 higher than that of PtRu/CNT. This means there was an 56.5% reduction of precious metal in the PEMFC catalysts.
The highlights of our work are enumerated as follows:
(1) The graphitic-C₃N₄ quantum dots modified carbon nanotubes (CNT-QDs)) support material has been prepared through a direct π-π stacking method. The abundant Lewis acid and base sites (terminal and bridging NH− groups and lone pairs of N in triazine/heptazine rings, respectively) of g-C₃N₄ QDs are potential anchoring sites for Pt and adsorption sites for CO.
(2) The PtRu/CNT-QDs catalyst has excellent activity due to more uniform dispersion and smaller size of PtRu nanoparticles (PtRu NPs), and higher stability ascribed to the stronger metal–support interaction (SMSI) between PtRu NPs and composite support. Even after 1000 accelerated potential cycling tests (APCTs), PtRu nanoparticles supported on g-C₃N₄ nanosheets show the better distribution and stability comparing with the sharply agglomerated and dissolved PtRu NPs on the surface of CNT.
(3) The results of electrochemical measurements indicate that the PtRu/CNT-QDs catalyst has the highest current densities with a factor of 2.3 and 1.6 times higher than PtRu/CNT and PtRu/acid-functionalized CNTs. The excellent electro-catalytic ability and the unusually high poison tolerance is attributed to three critical reasons: a) the inherently excellent mechanical resistance and stability of g-C₃N₄ in acidic and oxidative environments, b) the undamaged structure of CNT, c) the increased of Pt(0) composition in PtRu/CNT-QDs catalyst and d) the strong metal-support interaction between metal nanoparticles and composite support. Full tests of these supported catalysts in single fuel cells are in process. Considering the importance of the preformance of the catalysts in fuel cell environments, CNT-QDs material is a promising catalyst support not only for direct methanol fuel cells and proton exchange membrane fuel cells, but also for higher temperature fuel cells where the problem of catalyst growth is more serious.

Fuel cells have been regarded as one of the most promising candidate for next-generation power sources owing to their high efficiencies, fast start-up and low emission and are well suited for transportation and portable electronics. Large-scale commercialization of fuel cells must meet three major criteria: cost, performance and durability. Impressive progress in the research and development of Pt-based catalysts has been made in terms of performance increases and cost reduction. Three dimensional (3D) graphene aerogel (GA) has received enormous interest in catalysis and energy storage applications due to their rich macroporosity and multidimensional electron transport path ways. It is of great importance and necessity to develop a convenient and effective strategy for the synthesis of high stable Pt-based catalysts
Herein, we report a novel 3D Pt/C/GA hybrid catalyst via a facile and green hydrothermal process. The optical image reveals that the as-synthesized Pt/C/GA is a self-supported porous three-dimensional cylinder around 1.3 cm in diameter and 0.8 cm in height. SEM images reveal that Pt/C/GA possesses a well-defined and interconnected, porous 3D graphene framework. The partial overlapping or coalescing of graphene sheets results in the formation of crosslinking network with continuous macropores in the micrometer size range, which would effectively facilitate mass transfer of reactant and products. It is noteworthy that a significant proportion of the Pt/C catalyst is “encapsulated” within the graphene layers, indicating efficient assembly between the Pt/C catalyst and the graphene sheets. TEM images reveal that the Pt NPs with a uniform size of about 2 nm are homogenously distributed on the carbon black, and nearly no bare Pt NPs are observed on the surface of graphene sheets. Electrochemical measurements reveal that The electrochemically active surface area (ECSA) of Pt/C/GA is 70.4 m² g^-1, which is a little lower than that of Pt/C catalyst (76.3 m²g^-1), and electrocatalytic activity towards methanol electrooxidation is evaluated in a solution of 0.5 mol L^-1 H₂SO₄ containing 0.5 mol L^-1 CH₃OH at 25 ^oC. Pt/C/GA catalyst exhibits an initial mass activity of 405.3 mA mg^-1 Pt at 0.86 V (vs. RHE) for methanol electrooxidation, which is very close to that of Pt/C (424.6 mAmg^-1 Pt), suggesting electrocatalytic performance is not much affected by the hydrothermal process. Pt/C/GA hybrid catalyst exhibits a significantly enhanced stability towards methanol electrooxidation compared with the standard Pt/C catalyst: Pt/C catalyst lost nearly 40% of its initial activity after 1000 cyclic voltammetry cycles, by contrast, only 16% for Pt/C/GA. It confirms that the 3D graphene encapsulation structure is important in enhancing the durability and that this unique structure can be extensively applicable to commercial catalytic products.

Porous carbon materials are known for their applicability in important areas such as electrochemistry (e.g. fuel cell catalysts, where a lot of interest aroused due to possible coupling of advantageous structural properties and unique chemistry. The preparation of high content doped and conductive graphitic carbons can be achieved e.g. by employing ionic liquids (ILs) as precursors. We and others have shown that mesoporous carbon with structurally integrated nitrogen acts as an inexpensive and highly active metal-free catalyst in the oxygen reduction reaction (ORR).^[1-3] A key-drawback was still the necessity of using silica templates and their hazardous removal to obtain porous high surface area materials. Our recent research focuses first on the porosity development in alternative fashion and second on the employment of naturally abundant carbon precursors, both for the perspective of large scale synthesis.^{[4, 5]} Materials with very high surface areas and total pore volumes are accessible using alternative templates and molten salt syntheses and even completely new carbon morphologies are obtained throughout a carbonization from the wet state.^{[6, 7]} The performance as non-noble electrocatalysts for the oxygen reduction reaction and the role of porosity will be discussed

[1] W. Yang, T.-P. Fellinger, M. Antonietti, J. Am. Chem. Soc. 2011, 133, 206.
[2] R. Liu, D. Wu, X. Feng, K. Muellen, Angew. Chem. Int. Ed. 2010, 49, 2565.
[3] T.-P. Fellinger, F. Hasché, P. Strasser, M. Antonietti, J. Am. Chem. Soc. 2012, 134, 4072-4075.
[4] N. Fechler, T.-P. Fellinger, M. Antonietti, Adv. Mater. 2013, 25, 75-79.
[5] K. Elumeeva, N. Fechler, T.-P. Fellinger, M. Antonietti, Mater. Hor. 2014, 1, 588-594.
[6] Y. Chang, M. Antonietti, T.-P. Fellinger, Angew. Chem. 2015, 54, 5507-5512.
[7] J. Zhu, K. Sakaushi, G. Clavel, M. Shalom, M. Antonietti, T.-P. Fellinger, J. Am. Chem. Soc. 2015, 137, 5480-5485.

Along with the recent intensive research efforts in reducing or replacing Pt-based electrode in fuel cells, we have previously demonstrated that vertically aligned nitrogen-doped carbon nanotubes (VA-NCNTs) produced by pyrolysis of iron (II) phthalocyanine could actively catalyze ORR via a four-electron process free from the crossover and CO poisoning effects with a 3-time higher electrocatalytic activity and better long-term durability than that of commercially available Pt/C electrocatalysts in both alkalin and acidic media. Similar ORR electrocatalytic activity was also observed for nitrogen-doped graphene (N-graphene). On the basis of these experimental observations and quantum mechanics calculations, we have attributed the observed ORR catalytic activities of the VA-NCNTs and N-graphene to the electron-accepting ability of the chemically-bonded nitrogen atoms, which create a net positive charge (via intramolecular charge-transfer) on adjacent carbon atoms in the nanocarbon structures to readily attract electrons from the anode for facilitating the O₂ adsorption and ORR on the cathode. These findings prompted us to develop carbon-based metal-free ORR catalysts by positively charging carbon atoms in the nitrogen-free carbon nanotubes and graphene plane through intermolecular charge-transfer with functionalized/adsorbed moieties. We have also demonstrated that nitrogen-doped 3D graphene foam (N-GF) could be used as a metal-free electrocatalyst for the reduction of triiodide to replace the Pt cathode in dye-sensitized solar cells (DSSCs). Recently, carbon nanomaterials have been further found to act as not only single functional but also bifunctional metal-free catalysts for ORR, OER, and HER - reactions crucial to fuel cells, metal-air batteries, and photoelectrochemical water splitting for fuel generation.
In this talk, we will summarize some of our work on the metal-free catalysts based on carbon nanomaterials for various energy-related reactions, along with an overview on the recent developments and perspsectives in this exciting field.

Carbon nanomaterials, such as carbon nanotubes (CNTs) and graphene, are appealing for metal-free catalysts to replace expensive Pt in fuel cells and metal-air batteries because of their potentially low cost, unique molecular structures with a large surface area and catalytic activities, excellent mechanical, thermal and electrical properties, and high stability in both acidic and alkaline environments. Heteroatom-doping with p-block elements in the periodic table can effectively modify the electronic structures of carbon nanomaterials to facilitate two critical chemical reactions: oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) that determine the efficiencies of energy conversion and storage. Although The development of design principles or descriptors that correlate doped structures to the catalytic activity of carbon-based catalysts will accelerate the search for metal-free highly active catalysts based on earth-abundant, cost-effective materials to replace noble metals, including platinum. In this study, we have, for the first time, identified a material property that serves as the activity descriptor for predicating bifunctional ORR/OER activities, and established a volcano relationship between the descriptor and the intrinsic bifunctional activity of heteroatom-doped carbon-based catalysts. Such descriptor enables us to design new metal-free catalysts with enhanced ORR/OER activities, even better than those reported for platinum-based metal catalysts. As supported by a large number of reports for ORR activity of p-block element doped carbon nanomaterials, this descriptor can also be used as a powerful guidance to develop various new earth-abundant, cost-effective catalyst materials.

The investigation of cheap alternative materials for energy storage and conversion is one of the main tasks for the continuously growing energy needs of our society. Although fuel cells are a highly promising approach for the efficient transformation of chemical into electric energy, their widely spread utilization is still hindered. One of the central challenges are the high costs of the platinum@carbon (Pt/C) catalyst for the oxygen reduction reaction (ORR) on the fuel cell cathode.¹ We and others were showing that mesoporous nitrogen doped carbons (NDCs), e.g. from pyrolysis of ionic liquids, can serve as alternative ORR-catalysts.^2,3 NDCs can perform as good as Pt/C under alkaline conditions and even outperform Pt/C referring to stability and lifetime.³ However, mechanistic discussions are still ongoing and rather expensive methods for porogenesis are widely employed.
Among the various methods to obtain highly porous NDCs the ionothermal approach (the so called “salt templating”) is - due to its facility, scalability and the ability to achieve high surface area - an explicitly interesting alternative.⁴ Herein we adopt the original procedure to the employment of an inexpensive, biomass-derived precursor and the use of less corrosive inorganic salt i.e. ordinary NaCl. This way micro- and mesoporous NDCs with high specific surface area of 2900 m² g^-1 and large porosity (<5 cm³ g^-1) are obtained. In the presentation we will present a new pore tuning tool allowing a continuous and highly precise variation of the mesopore size and additional macropore formation. Surprisingly, ORR measurements under alkaline conditions reveal a strong influence of the pore structure on the half wave potential (E_1/2) and indicate a predominance of porosity effects if compared to nitrogen content or specific surface area. The optimization of the pore structure leads to a catalyst with a high selectivity towards the four electron process and an outstanding E_1/2 for non-metal catalysts of ~ 880 mV (vs. RHE).

References
(1) Debe, M. K. Nature 2012, 486, 43.
(2) Yang, W.; Fellinger, T.-P.; Antonietti, M. Journal of the American Chemical Society 2011, 133, 206.
(3) Liu, R.; Wu, D.; Feng, X.; Müllen, K. Angewandte Chemie 2010, 122, 2619.
(4) Fechler, N.; Fellinger, T.-P.; Antonietti, M. Advanced Materials 2013, 25, 75.

In this this presentation, we will provide a summary of the accomplishments in the development of non-precious metal catalysts (NPMCs) for oxygen reduction reaction (ORR), the performance limiting electrode reaction in polymer electrolyte fuel cells (PEFCs). While the analysis will primarily concentrate on research performed at Los Alamos National Laboratory (LANL), references will be also made to the state of the art of NPMC development as reported by other researchers in the field. We will summarize the challenges facing NPMC research that, in spite of an impressive progress achieved in the past decade in the advancing the catalyst activity, demonstrated in aqueous electrolytes and fuel cells as well, is yet to produce materials capable of competing with the incumbent Pt-based ORR catalysts, especially in terms of performance durability or cost. While performance durability is universally viewed as the greatest challenge, at least for the currently prevailing carbon-based catalysts (especially at high cathode potentials, up to approximately 1.5 V, reached during the fuel cell startup and shutdown), the specific ORR activity of NPMCs continues to be insufficient in spite of the very high loadings used. Low ORR activity results in very thick electrodes, limiting performance at high power. It also leads to the prohibitively high cost of stack components, which, according to recent projections, outweighs savings associated with the low cost of the cathode catalyst.

We will outline a pathway for further development of non-precious metal catalysts relying heavily on the understanding of the ORR mechanism. That understanding is imperative for a rational design of catalysts with higher activity and acceptable durability under relevant cathode operating conditions.One way of achieving controlled functionality of NPMCs for ORR attempted at LANL has been through an experimental investigation of graphene- and graphene-oxide-based model systems, combined with advanced theory, modeling and simulation. Successful incorporation of nitrogen heteroatoms into the graphitic structures of the starting precursors has been obtained via an ammonia treatment at varied temperatures (500°C-900°C). Efficient oxygen reduction with low H₂O₂ yield has been achieved from model systems with low concentrations of Fe and Mn (less than 0.5%). Finally, density functional theory (DFT) and ab initio molecular dynamics were used to characterize the structural properties and activity of ORR centers in NPMCs. This part of research has focused on the active-site molecular configuration, surface accessibility, sensitivity to N and Fe chemical potentials, response to an aqueous environment, and adsorption of ORR intermediates. Particular attention has been paid to the clustering tendencies of different N-coordinated Fe structures in order to illuminate the configuration of the Fe-N centers thought to occur at graphene edges.

Electrochemical processes, such as oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) are important steps for many energy conversion and storage technologies, including fuel cells, metal-air batteries, and water splitting. Although Pt and Pt-based alloys, up to now, are known as the most efficient catalysts for ORR and HER, the high costs and scarce reserves of Pt significantly hinder its large-scale applications. Substantial efforts have been dedicated to searching for alternative ORR catalysts with low cost, high activity, and long-term durability. Recent experimental observations and theoretical calculations both revealed that heteroatoms (e.g., nitrogen or/and phosphorus, boron)-doped carbon materials could serve as efficient metal-free electrocatalysts for ORR as the result of their unique electronic properties, which are derived from the heteroatom-induced charge transfer and delocalization. Moreover, incorporation of earth-abundant metal (e.g. Fe, Co) into N-doped carbons can dramatically improve the catalytic performance, in particular under the acidic conditions. In order to achieve a high catalytic performance, it is essential to fabricate carbon-based materials with rationally nanostructural design that would offer a desirable combination of high internal active surface area and straightforward transport path during electrochemical process.
Herein, we will present our recent efforts on the design and synthesis of porous carbon nanostructures as metal-free and non-precious metal electrocatalysts for ORR and HER, particularly including mesoporous N-doped and Fe (Co)/N-doped carbons prepared by the hard-templating synthesis, graphene integrated templated doped carbons, and porous polymer-derived 2D doped carbons. We will highlight the great potential for significantly improving the electrocatalytic performance by designing rational porous structures with micropores to mesopores. Moreover, we also try to understand the correlation between the doping properties/porous structure and their electrocatalytic performances.

In various electrochemical cells, oxygen has been regarded as a cost effective, sustainable, nature-friendly, and scalable electron acceptor. However, sluggish oxygen reduction reaction (ORR) usually requires precious metal catalysts such as Pt or Pt alloys, which prevents the large-scale deployment of electrochemical cells due to their high prices.
Therefore, there have been many trials to reduce Pt loading such as using its alloys or completely replacing Pt with transition metals and/or nitrogen-doped carbon. Nevertheless, most of Pt-free catalysts have excellent performance in only cyclic voltammetry or rotational disk electrode (electrochemical characterization) testing rather than actual testing in electrochemical cells, or/and only “initial” performances are comparable to commercial Pt/C (poor long term stability). Moreover, the previously reported non-Pt based catalysts involve complicated and time-consuming processes, and most of them, if not all, are powdery like commercial Pt/C catalysts, requiring not only an additional supporting layer such as carbon cloth but also catalyst loading processes. The extra materials and production processes negate the cost benefit of eliminating Pt.
Here we present 3D sponge-like structures made of N-Fe-C coordinated self-assembled carbon nanotubes, serving as both precious metal free electrocatalysts and self-standing cathodes (i.e. without extra catalyst loading/gas diffusion layers). The self-assembled nanotubes during their growth process made it possible to have a facile low-cost scalable manufacturing unlike the previously reported precious metal free catalysts. The catalyst/cathode was also tested in a microbial fuel cell (MFC), which is a promising renewable energy technology for the production of electrical energy during wastewater treatment. The long term study over 3 months revealed that the sponge cathode has stable and high power outputs, comparable to those of a MFC loaded with a commerical Pt/C based cathode. Furthermore, we uncovered that the dependency of pore volume and mass (proportional to surface area) of our 3D electrode on power production for optimal MFC operation, which provides a guidance to synthesize porous 3D electrodes. To our best knowledge, this is the first demonstration of a self-standing catalyst/cathode with a performance of an actual fuel cell (rather than only catalyst characterization) comparable to those of commercial Pt-based catalysts.

Development of non-precious metal catalysts (NPMCs) has become a well-known strategy to replace the platinum-based catalysts for the oxygen reduction reactions at the cathode of fuel cells, metal–air batteries and air-breathing cathodes in industrial electrocatalytic processes. There are two crucial factors governing the performance of carbon based catalysts. One is the intrinsic nature of the active sites which are determined by the selection of the doping elements. Another important factor is the large specific area and porous structure feature which can introduce more active sites and promote the electrons and oxygen species transportation. Among numerous carbon-based electrode materials, hollow carbonaceous spheres have attracted attention due to the high surface-to-volume ratios and more accessible active sites on the shell. Here, hierarchical porous carbon-nanoshells with about 40 nm cavities are synthesized by using CdS@mSiO₂ core-shell structured materials as hard templates and 4, 4’-bipyridine, FeCl₃ as nitrogen, carbon and iron sources. This method demonstrate outstanding stability and electrocatalytic activity for ORR.

High costs are today a major obstacle to the market introduction of fuel cells in particular for automotive applications. A number of studies have shown that the high costs are largely due to the high material expenditure in particular of platinum group metals for catalyst. Part of the expenditure is rationalised by the positive effect of high catalyst loading on the stack life time as a limited lifetime of the stack would be a cost burden for itself.

A major source of performance degradation is the corrosion of materials like the carbon support, the carbon in the micro porous layer or the electrolyte membrane and ionomer components. Carbon is thermodynamically unstable at least for the cathode operating potentials but features a high kinetic stability under a wide range of conditions. As a consequence carbon corrosion occurs only at special operating conditions and often transiently. This fact renders the investigation of carbon corrosion processes difficult. A good approach is the use of mass spectrometry as investigation tool as it allows for the detection of CO₂ as indicator molecule with a good sensitivity and a quick time response if CO₂ free feed-gases are employed.

In this contribution results for the catalyst support corrosion using different online mass spectrometry tools will be reported for three different polymer electrolyte fuel cell (PEMFC) environments, i.e. low temperature PEMFC, high temperature PEMFC and anion exchange membrane fuel cells. On the catalyst level tests were performed in a flow through cell for differential electrochemical mass spectrometry formerly used to study alcohol oxidation reaction. In addition a gas phase DEMS cells was used to study carbon corrosion under HT-PEMFC conditions. In addition tests were performed with an online MS set-up connected to the exhaust of a LT-PEMFC single cell to study carbon corrosion occurring during standard accelerated stress tests for automotive LT-PEMFC. The latter test method allowed for a quantitative determination of the carbon release per stress test cycle as well as for discerning carbon support and GDL corrosion. The latter was achieved by comparing measurement of MEAs with regular supported catalyst with measurements at MEAs with platinum black electrode and a regular carbonaceous GDL and measurements at MEA with platinum black electrode and a metallic GDL. Here it could be shown the carbon loss due to GDL corrosion is small compared to the support corrosion but still measurable.

As a further result it was found that the exposure of catalysts or fuel cell electrodes to high potentials did not only caused CO₂ release at that high potentials directly but also caused some changes to the platinum support interface which caused CO₂ release upon the reduction of platinum oxide scales.

In the contribution the results for the different PEMFC environments will be compared and discussed.

With the recent development of high-performing Pt-based electrocatalysts, fuel cells for automotive applications are becoming increasingly viable, and understanding the multiple mechanisms contributing to catalyst degradation is a priority to enable further catalyst optimization. In this respect, the 3D structure of the catalyst, support, and ionomer within actual catalyst layers of membrane electrode assemblies (MEAs) must be fully resolved, complete with compositional profiles (4D), and correlated with the structural evolution of the material components during fuel cell use.
Scanning transmission electron microscopy (STEM)-based tomography methods represent an effective way to interrogate the MEA architecture despite several inherent microscopy challenges, most of which are coupled to the long data acquisition times involved and can include beam damage, contamination, insufficient angle collection ranges/increments for the data reconstruction, and the quality of the algorithm in producing an accurate tomogram from the tilt series. In addition, varying image contrast levels produced by the different material constituents within the electrode can complicate their specific segmentation for a precise analysis of pore sizes, ionomer distributions, carbon corrosion, catalyst dealloying/leaching, and catalyst nanoparticle coalescence within the catalyst layer, all of which are important factors contributing to fuel cell degradation.
In this work, the steps taken toward producing 4D datasets of the nm-scale structure within actual PEM fuel cell catalyst layers will be highlighted. This will include results of 3D STEM-tomography of Pt nanoparticles on carbon supports, which addresses the problems of missing wedge artifacts and low contrast of the carbon support from the background. A tilt-series reconstruction of electron energy loss spectroscopy (EELS) and/or energy dispersive X-ray spectroscopy (EDS) elemental maps from the cathode catalyst layer will be presented, that provide information regarding porosity and ionomer distributions within catalyst layers. Future work is aimed at quantifying changes in structure of cathode catalyst layers over the operating lifetime.

Research supported by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy (DOE) and as part of a user project through Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences, which is a U.S. DOE Office of Science user facility.

Devices for clean energy conversion such as fuel cells are an attractive alternative to mankind’s dependence on fossil fuels. However, for the fuel cell technology to become commercially viable a key challenge is to be resolved, that is efficient catalysts to speed up the chemical reactions driving cells’ operation have to be developed beforehand. Indeed, thanks to the sustained effort of numerous research groups, a number of excellent catalysts for fuel cells, including metallic nanocatalysts for the sluggish Oxygen Reduction Reaction (ORR) taking place at the cathode of virtually all fuel cells, were developed lately, as testified by traditional laboratory studies. Unfortunately, many of these catalysts are found not to perform so well inside operating fuel cells. The reality check underlines the fact that transferring excellent catalytic properties into real devices without losing the former is not a trivial task. We will show that the task can be facilitated by in operando high-energy XRD coupled to atomic pair distribution functions (PDFs) analysis. In particular, we will show results from recent in operando high-energy (110 keV) XRD and atomic PDFs studies on a series of binary and ternary metal nanocatalysts from the NM-TM family, where NM=Pt and Pd, and TM=Ni, Co, Cu and V, as tested for ORR activity and stability at the cathode of a fully functional Proton Exchange Membrane Fuel Cell (PEMFC) cycled between 0.6 and 1.2 V for at least 12 hours. The results will be discussed in terms of competing scenarios for the concurrent evolution of the chemical composition, 3D atomic structure, activity and stability of metallic nanocatalysts during PEMFCs operation. Answers as to how indeed these fundamental characteristics of metallic nanocatalysts are related to each other will be given thus demonstrating the ability of in operando high-energy XRD to provide a valuable feedback to the ongoing effort to develop efficient catalysts for fuel cells.

The water gas shift (WGS) reaction CO+H₂ to CO₂ + H₂ is the basis of heterogeneous catalysis in hydrogen production for fuel cells and transportation fuels [1]. Ceria supported gold and related nanoparticle catalysts are potentially viable catalysts for low temperature WGS heterogeneous catalysis [2]. The current understanding of reaction pathways of WGS on gold and related WGS catalysts is based on postulations from static ex-situ studies and indirect chemical studies making it hard to establish the nature of the catalyst or the fundamental reaction pathways in dynamic WGS catalysis. Using real time in-situ environmental (scanning) transmission electron microscopy (E(S)TEM) with single atom resolution [3-6] we present the direct evidence for atomic dynamics on an essentially unsintered ceria substrate. We have studied the dynamics on the surface of ceria in practical WGS catalysts under water gas shift reaction conditions and environments (carbon monoxide + water), as well as in the component gases of the reactant and product mixtures (CO, CO/N₂ and hydrogen). During the reaction lower surface energy configurations for metal catalysts are observed with the loss of low coordinated surface adatom sites. We suggest that these atomic scale mechanisms may be important in transportation fuel applications which involve similar combinations of materials.

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Nanoporous metals exhibit unique properties - including high specific area, bi-continuous conductivity and catalytic properties - which lead to great potential in alternative energy applications. However, conventional aqueous solution-based dealloying method used to form nanoporous metals are limited to noble element such as Au, Pt and Pd. A novel metallic-melt dealloying method was recently invented to fabricate low-cost, less-noble nanoporous materials, such as stainless steel and silicon. Both materials have great potential applications in energy conversion/storage materials, such as fuel cells and batteries. Nevertheless, morphology and composition changes during de-alloying process remain unclear; the correlation between the processing parameters, three-dimensional (3D) structure and chemical evolution is unknown, limiting practical applications. In particular, nanoporous stainless steel applied in the gas diffusion layer in proton exchange membrane fuel cells or the electrode substrate of Li-air batteries, requires precisely designed 3D morphology for effective materials transportation within the porous structure.
Here, we quantitatively analyzed critical 3D morphological parameters and compositional variation of nanoporous stainless steel, and correlate them to key processing conditions, using synchrotron-based advanced x-ray microscopy. First, full-field x-ray nano-tomography was carried out to image the 3D structure of the nanoporous material as function of the dealloying processing parameters. Quantitative x-ray fluorescence mapping utilizing micro-scanning probe at the newly commissioned synchrotron, NSLS-II, provides a map of elemental distribution where residual Ni was discovered and spatially correlates with the Fe and Cr distribution in the steel sample. The present result shows that the 3D morphology of nanoporous stainless steel can be tailored, by selecting nickel concentration, dealloying time and temperature to yield the ideal structure. Furthermore, we discovered a pore size gradient resulted from the dealloying process, which with capillary pressure gradient, can facilitate water removal and oxygen diffusion in the application of gas diffusion layer. A thorough investigation on the processing-process correlation in these nanoporous sample will be presented. Our study opens opportunities to design better structure for energy applications based on this novel class of nanoporous materials.

Accurate measurements of the thermal properties of hydrogen-storage materials are critical for the design of efficient hydrogen storage systems. Low thermal conductivity materials require additives such as graphite and/or macroscopic heat-transfer enhancing structures such as fins in the storage vessel for thermal management during charging and discharging of the hydrogen. Furthermore, the thermal conductivity of these materials depends on both temperature and the hydrogen gas pressure. For hydrogen sorption materials, the required temperatures and pressures may be as low as 77 K and as high as 150 bar, respectively. Therefore, it is imperative to design proper heat exchangers for a given material to maximize performance, which requires comprehensive knowledge of the thermal conductivity under the expected operating conditions. We report on a new apparatus for the characterization of the thermal conductivity and diffusivity of hydrogen storage materials over a temperature range of 77 – 350 K, and at hydrogen pressures up to 150 bar. The measurement technique is based on the transient plane source approach and its variants. This transient methodology allows for rapid determination of the thermal properties at a given pressure and temperature. The pressure can then be continuously varied to investigate its effect on the thermal properties. Likewise, the temperature can be continuously varied and these measurements repeated to produce a complete thermal properties profile as well as investigate pressure and temperature cycling effects. The system is capable of measuring materials with different form factors, including solids, densified pucks, and loose powders and can accommodate small sample volumes. We will report on studies on various materials that illustrate the unique performance parameters of this novel apparatus.

The development of lightweight materials for compact onboard storage of hydrogen remains one of the key challenges for large-scale deployment of fuel-cell vehicles. Complex metal hydrides have long been of interest as potential candidates, and recent investigations showing that nanoconfinement can improve hydrogen uptake have renewed interest in the long-term viability of these materials. Typically, enhancements associated with nanoconfinement of complex hydrides have been attributed to shortened diffusion pathways or surface-driven changes in phase stability. By contrast, the role of solid-solid interfaces within these materials remains almost entirely unexplored, despite notable similarities with batteries and other energy storage systems where interfaces can control kinetics and reaction pathways. By combining experimental and multiscale theoretical approaches, we show that nanoconfinement of the high-capacity Li₃N/[LiNH₂ + 2LiH] system fundamentally alters both the hydrogenation and dehydrogenation reaction pathways as a direct consequence of solid-solid nanointerfaces within the material. This dramatically improves the kinetics and lowers the thermodynamic requirements to achieve full reversibility, culminating in the highest-capacity reversible nanoconfined hydrogen storage material reported to date. This establishes the importance of nanointerfaces in solid-state hydrogen storage reactions and introduces a new paradigm for controlling performance of complex hydrides for hydrogen storage by engineering the internal microstructure.

Although hydrogen provides multiple advantages as an energy carrier, efficient storage remains problematic, especially for mobile applications. The major hydrogen storage technologies considered to date have significant drawbacks, including insufficient volumetric capacity (compressed gas), desorption temperatures that are too high (bulk metal hydrides) or too low (physisorbed hydrogen), and low gravimetric capacity (interstitial hydrides). Solid-state hydrogen storage in complex metal hydrides has attracted a lot of attention in recent years, as these materials are able to store a relatively large amount of hydrogen (in some cases >10 wt% H). However, slow reaction rates, presumably due to kinetic barriers arising from the creation and destruction of multiple solid phases and rearrangement of kinetically stable bonds, have prevented their use in practical systems. One approach to enhancing reaction kinetics and improving reversibility is to minimize the number of phases that form during hydrogen release and absorption. Here we describe the results of calculations and experiments on novel mixed-metal borohydride (Mg_(x)M’_(1-x)(BH₄)₂) and ternary boride (Mg_(x)M’_(1-x)B₂) phases (where M’ = Mn and Co). Our results indicate that incorporation of the transition metal M’ decreases the desorption temperature of the mixed-metal borohydrides. In addition, the bulk ternary borides Mg_(x)M’_(1-x)B₂ display faster kinetics of hydrogen absorption compared to the corresponding monometallic MgB₂ or transition metal borides. These mixed-metal borohydride/boride systems have the potential to have a single hydrogenated and dehydrogenated phase, eliminating the phase segregation and promoting reaction kinetics. The observed improvements in hydrogen desorption/absorption will be discussed and explained using the results from FTIR, XRD, RGA and Sieverts techniques, as well as the results of Density Functional Theory (DFT) calculations.

Understanding the kinetis and the thermodynamics of adsorption/desorption is essential for the hydrogen storage research field. The management of large amounts of heat released during the formation of a metal hydride is critical for all practical applications. Therefore quantifing and validating the hydriding enthalpies in situ during a sorption measurement becomes a necessity. Using coupled calorimetric and volumetric techniques is the most direct method to experimentally obtain the heat od adsorption/desorption.
The gas sorption manometric Sievert’s technique has proven to have many advantages for the evaluation of the ad- or ab- sorbed amount of gas by porous materials in a wide range of temperature and pressure. In addition, there is a total freedom in the size and shape of the sample holder, which allows coupling of techniques and in-situ measurements of various chemical and physical parameters. Coupling calorimetry and manometry allows a full characterization of the H₂ adsorption on solids. In addition to the adsorption isotherms and the derived isosteric heat, the differential heat of adsorption as a function of the adsorbed amounts can be obtained directly.
Several examples, including sorption on metals will be presented to illustrate the methodology.

Porous materials are an important class of materials, which can be efficiently used for catalysis, gas storage or membrane applications.[1,2] Methodologies reported to date for synthesis of porous metals are based on template synthesis.[1] This method suffers from high temperature sintering processes and also oxidation possibilities of electropositive metals at high temperature cannot be ruled out. Recently, development of template-less general synthetic approach for the synthesis of porous metals has been attracting attention.[3] In this context, synthesis of metal (Ag, Au, Pd, Pt and Cu) nanosponges by template-less method in gram scale by the reaction of metal salt and ammonia borane in water has been developed. The effect of the ratio and concentration of metal salt and reducing agent, temperature, solvent, counter anion and reducing agent on the final nanostructures has been studied. Based on these studies we proposed a mechanism for nanosponge formation. Here the evolved hydrogen gas in the reaction acts as a dynamic template for nanosponge formation. The materials were characterized thoroughly using SEM, TEM, EDS, PXRD, XPS, BET, solid state UV-vis and FT-IR spectroscopic techniques.
The hydrogen storage properties of these metal nanosponges have been evaluated using Pressure-Composition isotherm study. In this presentation, the details of synthesis, characterization and hydrogen storage properties of the metal nanosponges will be presented.
[1] Jintao Zhanga, Chang Ming Li. Chem. Soc. Rev., 2012, 41, pp 7016–7031.
[2] Debra R. Rolison. Science 2003, 299, pp 1698-1701.
[3] Katla Sai Krishna, C. S. Suchand Sandeep, Reji Philip, Muthusamy Eswaramoorthy. ACS Nano, 2010, 4, pp 2681-2688.