In contrast to conventional PEMFC type of gas-fed fuel cells the researchers from Daihatsu Motor Co. have introduced the idea of anion-exchange membrane fuel cell with liquid fuels.^[1-3] Switching from acidic proton exchange to alkaline, anion-exchange membranes has many benefits including: fast kinetic towards fuel oxidation and oxygen reduction reaction (ORR), and possible use of less costly non-platinum group metal (non-PRM) catalysts as anode and cathode material for both sides of the membrane electrode assembly (MEA). The liquid fuel of choice was hydrazine hydrate, which has no carbon atoms and thus will not contribute to increased CO₂ levels. The theoretical electromotive force of such direct hydrazine fuel cell is 1.56V and hydrazine hydrate as a fuel can be oxidized by number of cheap catalysts.^[4] The use of alkaline media allows switching to completely non-PGM materials set not only from anode side (oxidation of hydrazine hydrate), but also from cathode (oxygen reduction reaction). The high activity of cathode catalysts was confirmed in both RDE and MEA tests (Figure 1). As synthesized materials were extensively studied by XPS, SEM, TEM, BET and other methods in order to elucidate the structure-to-properties correlations. This paper describes a new class of templated, self-supported Non-PGM catalysts deroved by sacrificial support method (SSM) and their activity in free alkaline electrolyte (KOH) and in anion-exchange MEA. It will address the issues of alkaline ionomer integration with membrane and he catalyst material, the sensitivity of these ORR catalysts to fuel (hydrazine) crossover, and their successful integration with Non-PGM Ni-Zn based anode catalyst in a functional automotive fuel cell stack to power an electric service vehicle demonstrated by Daihatsu Corp.^[5]
1. Sakamoto, T., Deevanhxay, P., Asazawa, K., Tsushima, S., Hirai, S., Tanaka, H. J. Power Sources, 2014, 252, 35-42.
2. Sakamoto, T., Asazawa, K., Sanabria-Chinchilla, J., Martinez, U., Halevi, B., Atanassov, P., Strasser, P., Tanaka, H. J. Power Sources, 2014, 247, 605-611.
3. Sakamoto, T., Asazawa, K., Martinez, U., Halevi, Suziki, T., Arai, S., Matsumura, D., Nishihata, Y., B., Atanassov, P., Tanaka, H. J. of Power Sources, 2013, 234, 252-259.605-611.
4. Serov, A., Kwak, C., Appl. Cat. B: Environmental, 2010, 98, 1-9.
5. Serov, A., Padilla, M., Roy, A.J., Atanassov, P., Sakamoto, T., Asazawa, K., and Tanaka, H., AngewandteChemie Intern. Ed., 2014, 53, 10336 -10339

Platinum is the main materials component of polymer electrolyte fuel cells. The amount of Pt required to achieve stringent performance targets of these cells is still too high. High Pt loadings are needed in particular on the cathode side, where the oxygen reduction reaction (ORR) incurs a major portion of irreversible voltage losses. Recent theoretical and experimental studies show consistently that effectiveness factors of Pt utilization in the present generation of fuel cell catalyst layers are extremely low, in the range of 3%. Efforts in catalyst and electrode design, which aim to reduce the Pt loading, clash with stability requirements; a drastically reduced Pt loading is often accompanied by markedly enhanced degradation rates. The presentation will provide a systematic account of factors that determine ORR activity and stability of Pt in fuel cell catalyst layers. Insights deduced from catalyst layer modeling will be used to rationalize different reaction conditions in the two main catalyst layer designs, viz. typical gas diffusion electrodes and flooded nanoporous electrodes. These reaction conditions have a critical impact on oxide formation at Pt, surface charging state, ORR kinetics and Pt dissolution rate. The fundamental function in this context is the dependence of the total charge at the metal surface, as “seen” by ions in solution, on metal phase potential. Recent efforts in theory and modeling that aim at systematically uncovering this relation will be presented.

Growing global interest in electric vehicles (EV) in recent years has driven the need for smaller and lighter rechargeable batteries. A rechargeable Zn-air battery is considered as one of the potential candidates for next generation secondary batteries due to its high theoretical energy density. However, at the current state of technology, its further application and commercialization have been limited due to insufficient kinetics for the air electrode reactions, which are oxygen reduction and oxygen evolution (ORR/OER) upon discharging and charging, respectively. Platinum-based materials are known to be the most active bifunctional catalysts in both acidic and alkaline conditions. However, large scale commercial application of Pt has been precluded by its high cost and scarcity. Therefore, increasing efforts have been devoted to developing an efficient, durable and non-precious metal-based bifunctional catalyst to replace Pt-based materials. In this regard, various materials such as transition metal oxides may be applicable as alternative, low cost bifunctional catalysts.
Recently, Mn and Co mixed oxides and spinels have been widely investigated as promising bifunctional catalysts in alkaline media due to their low cost, high abundance, low toxicity, multiple valence states and high catalytic activity. In this study, we report on the synthesis of nanocrystalline Mn-Co oxide/PEDOT catalysts using facile and rapid sequential anodic electrodeposition on glassy carbon electrodes. Free standing Mn-Co oxide rods (10 µm long) are first synthesized and then coated by electro-polymerization of a conducting polymer (PDEOT). The Mn-Co oxide/PEDOT electrodes consist of MnO₂, with partial substitution of Co²⁺ and Co³⁺ ions for Mn⁴⁺ ions. The amorphous PEDOT coating is added to compensate for the poor conductivity of Mn-Co oxide. Structural characterization of as-deposited and cycled electrodes is conducted using XPS, SEM and TEM. The electrocatalytic properties of Mn-Co oxide/PEDOT is studied using rotating disk electrode (RDE) techniques in 1 M KOH electrolytes and Koutecky-Levich modeling. Mn-Co oxide/PEDOT electrode has comparable bifunctional activity towards ORR/OER relative to Pt/C, as a result of abundant defects and high surface area.

Non-aqueous lithium oxygen (Li-O₂) batteries are very attractive energy stores due to their exceptionally high theoretical energy densities. However, one of the major drawbacks of Li-O₂ batteries are the high charging overvoltages (up to 1.5 V) arising from the low electric conductivity of the insoluble discharge product lithium peroxide (Li₂O₂). Redox mediators have been recently proposed as soluble catalysts enabling a significant reduction of the charging overpotentials [1,2]. Here, we show that TEMPO (2,2,6,6-tetramethylpiperidinyloxyl), homogeneously dissolved in the electrolyte, can act as a mobile redox mediator (RM) during the charging process which enables the oxidation of Li₂O₂ particles even without a direct electric contact to the positive electrode [3]. The incorporation of only 10 mM TEMPO provides a distinct reduction of the charging potentials by 500 mV. In addition TEMPO enables a significant enhancement of the cycling stability leading to a doubling of the cycle numbers compared to a regular Li-O₂ cell.
We present systematic results on the electrochemical performance and the catalytic mechanism of dissolved TEMPO in Li-O₂ cells. This includes a detailed investigation on the relevant chemical and physical properties of TEMPO such as the electrochemical stability of TEMPO (using cyclic voltammetry), the diffusion coefficient of TEMPO in diglyme (by chronoamperometry) and the TEMPO dependent oxygen solubility in diglyme (based on a monitoring of the oxygen pressure). Moreover we studied the discharge reactions in a Li-O₂ battery with TEMPO by means of XRD, Raman spectroscopy, ¹H-NMR spectroscopy and SEM. The catalytic influence of TEMPO on the charging reaction was systematically investigated by varying current density and cathode material. Since the charging plateau merely corresponds to the electrochemical oxidation of the mediator at the cathode surface, a parallel monitoring of the cell pressure and differential electrochemical mass spectrometry (DEMS) were applied to proof the subsequent oxidation of Li₂O₂ to O₂. Herein, the predominant formation of O₂ was confirmed for the charging plateau in the presence of TEMPO. In addition, we present a systematic study on the charging mechanism of Li-O₂ cells with redox mediators combining electrochemical methods with a parallel pressure monitoring. As an important result, we show that the redox mediator can form a parasitic shuttle mechanism between both electrodes, which is of crucial importance for the performance of homogeneously catalyzed Li-O₂ cell. In conclusion, we demonstrate that TEMPO is a stable and effective redox mediator for Li-O₂ cells.
[1] Chen et al., Nat. Chem. 2013, 5, 489
[2] Lim et al., Angew. Chem. Int. Ed.2014, 53, 4007
[3] Bergner et al., J. Am. Chem. Soc. 2014, 136, 15054

The oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are key chemical transformations ubiquitous in a number of renewable energy technologies including fuel cells, unitized regenerative fuel cells (URFCs), and water electrolyzers. Critical to these technologies is the development of catalysts that can effectively drive these reactions in a stable manner while minimizing or eliminating precious metals. This paper will focus on several aspects of materials and device development for these technologies. First, manganese oxide based materials will be discussed as bi-functional, non-precious metal catalysts for the ORR and the OER in alkaline media. We will then describe their integration into fuel cell and URFC devices that employ alkaline anion exchange membranes (AEMs). These are technologies that could potentially couple to renewable, intermittent electricity such as wind and solar to provide grid-scale storage. Finally, we will discuss our catalyst development efforts for the ORR in an acidic environment, namely our approach to tailor Pt-based core-shell nanoparticles with greater mass activity and stability than commercial standard Pt/C nanomaterials.

Improving oxygen electrochemistry is a ‘holy grail&’ problem with major impacts across many technologies. Here we present discovery of a catalyst system offering reversible oxygen electrochemistry. The catalyst delivers chemically and electrochemically reversible two-electron ORR and OER. We will present electrochemical and other experimental evidence supporting this claim.

The High Throughput Experimentation (HTE) project of the Joint Center for Artificial Photosynthesis performs accelerated discovery of new earth-abundant photoabsorbers and electrocatalysts. We will describe several new screening instruments for high throughput (photo-)electrochemical measurements and summarize the discovery pipelines. This approach will be illustrated using the high throughput discovery, follow-on verification, and device implementation of a new quaternary metal oxide catalyst. Discovering improved electrocatalysts for the oxygen evolution reaction (OER) is of great importance for efficient solar fuels generation, regenerative fuel cells, and recharging metal air batteries. We report a new Ce-rich family of active catalysts composed of earth abundant elements, which was discovered using high-throughput methods to produce 5456 discrete compositions in the (Ni-Fe-Co-Ce)Ox composition space. The activity and stability of this new OER catalyst was verified by re-synthesis and extensive electrochemical testing of samples in a standard format in 1.0 M NaOH. Characterization of selected compositions by XRD, XPS, SEM, TEM, EDS, XRF mapping, and EXAFS both as-synthesized and after electrochemical testing, reveal the importance of nanostructure to the observed electrochemical performance. The discovery of additional electrocatalysts by expansion of the composition space investigated and of new composition spaces tested for OER activity and stability under acidic conditions will be reported.

Non-noble metal electrocatalysts (NNMEs) with a high performance are urgently needed to rival Pt-based electrocatalysts for fuel cells and metal-air batteries. Exploration of unique synthetic approaches is the key to the creation of highly efficient NNMEs yet remains rare. Herein, we report an unprecedented synthetic route that combines ionic self-assembly (ISA) of iron (III) porphyrin (FeP) with traditional pyrolysis, leading to flower-like electrocatalysts. Remarkably, the original morphology of nanoflowers of self-assembled FeP was nearly retained after carbonization, enabling highly desired manipulation over the size, shape and surface area closely related to the performance of NNMEs. The obtained flower-like electrocatalysts exhibited a high oxygen reduction reaction (ORR) activity, excellent durability and methanol tolerance in both alkaline and acidic solution. This approach opens up a new avenue to produce high performance NNMEs with controllable structural features that are difficult or impossible to be achieved prior to this study.

Oxygen electrodes are playing a key role in electrochemical energy conversion devices such as fuel cells and water electrolyzers. In both acidic and alkaline environment, both the oxygen reduction and oxygen evolution reaction (ORR and OER), respectively, are limiting the overall energy/voltage efficiency due to its sluggish kinetics. [1, 2]
Whereas in acidic environment, mainly precious metals are used to catalyze the ORR (e.g., Pt or its alloys) or the OER (e.g., IrO₂ ), the variety of possible catalysts in alkaline electrolyte is significantly increased and also many metal oxide based systems can be employed. Generally the oxygen reduction or evolution mechanisms are only partly understood independent of the electrolyte environment and material used.
In this contribution, some new light will be shed on the electrocatalysis of oxide based systems used in acidic and alkaline environment for the ORR and OER. Similarities and differences as compared to noble metal based systems will be provided supplemented with theoretical considerations.
References
[1] A. Rabis, P. Rodriguez, T.J. Schmidt, ACS Catal., 2012, 2 (5), 864-890
[2] E. Fabbri, A. Habereder, K. Waltar, R. Kötz, T.J. Schmidt, Cat. Sci. Tech., 2014, 4, 3800-3821

Electrochemical water splitting driven by a renewable energy source such as wind or solar, is a promising method to produce hydrogen. Already an important chemical commodity in industry, hydrogen may also potentially be used as a carbon-free fuel. However, the efficiency of electrochemical water splitting is severely limited by the high overpotential costs required for the oxygen evolution half reaction (OER). In order to develop active nonprecious metal-based electrocatalysts for the OER, a better understanding of the activity of transition metal catalysts is needed. Previous studies have shown that depositing transition metal catalysts on metal supports leads to formation of different oxide phases and significantly higher activities.^{1, 2}
In this work we investigate the interaction between manganese oxide (MnO_x) and noble metals to determine the effect on oxidation state and catalytic activity. Beginning with a study on the interaction of MnO_x with gold (Au), we characterize the catalyst using SEM and ex situ L-edge x-ray absorption spectroscopy (XAS) to determine the morphology and oxidation state.³ As a surface sensitive technique, ex situ XAS provides information on the oxidation state of the surface atoms of the MnO_x nanoparticles both alone and in the presence of Au. Electrochemical characterization of this system shows that adding Au to MnO_x greatly increases the activity for the OER and results in an order of magnitude higher turnover frequency compared to MnO_x without Au. Finally, in situ XAS studies provide insight into the oxidation state of the MnO_x both with and without Au under OER operating conditions. Expanding this study to characterize the interaction of MnO_x with other noble metals provides insight to trends with respect to the effect on OER activity.
REFERENCES:
1. Yeo, B.S. & Bell, A.T. Enhanced Activity of Gold-Supported Cobalt Oxide for the Electrochemical Evolution of Oxygen. J Am Chem Soc133, 5587-5593 (2011).
2. Yeo, B.S. & Bell, A.T. In Situ Raman Study of Nickel Oxide and Gold-Supported Nickel Oxide Catalysts for the Electrochemical Evolution of Oxygen. The Journal of Physical Chemistry C116, 8394-8400 (2012).
3. Gorlin, Y. et al. Understanding Interactions between Manganese Oxide and Gold That Lead to Enhanced Activity for Electrocatalytic Water Oxidation. J Am Chem Soc136 (2014).

The oxygen evolution reaction (OER) is regarded as a major bottleneck in the overall water splitting process due to the slow transfer rate of four electrons and the high activation energy barrier for O-O bond formation. For the decades, Ir, Ru and Pt based inorganic materials have presented efficient catalytic activity with high turnover frequency (TOF) under mild conditions. However, its scarcity and high cost still inspire to develop inexpensive and sustainable catalysts. The cubane Mn₄CaO₅ clusters inside biological photosystem II (PS II) can oxidize water using a much smaller overpotential than required by manmade catalysts. Inspired by this attractive feature of Mn₄CaO₅ cluster, intense effort has been dedicated to develop non-precious metal-based water oxidation catalysts. Unfortunately, except for several rare-earth metal-based catalysts, there have been few candidate catalysts that operate under near neutral condition until now.
In this study, we discovered a new Mn-based catalyst that efficiently performs water oxidation catalysis. For conventional manganese oxide catalysts, up to now, the significantly reduced activity under neutral conditions is an unresolved issues. The instability of Mn (III) species at neutral pH is considered as a critical factor in this degradation. Here, we made the breakthrough of a Mn-based water oxidation catalysis that operates under neutral conditions using well-designed monodisperse manganese oxide nanoparticles. Facile surface treatment method was newly adopted and oxidized Mn(III) species were intentionally generated and stabilized on the manganese oxide surface. Various electrochemical methods and in-situ XAS analysis revealed the superior catalytic performance of partially oxidized manganese oxide NCs.

Complex perovskite oxides are considered as the promising candidates of bifunctional catalysts for high catalytic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). As another class of oxide-based catalyst, Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-d (BSCF5582) is a widely known perovskite oxide as a strong candidate of catalyst in solid oxide fuel cell (SOFC) cathode materials, metal-air batteries and other energy related systems. We report herein the heat treating effect of the BSCF5582 in oxygen atmosphere at 950 °C as a function of annealing time on the electrocatalytic performance, compared with pristine BSCF5582. The pristine BSCF5582 sample was calcined at 1050 °C for 5h in air (BSCF5582), and the heated BSCF5582 sample was prepared by heat-heating the pristine BSCF5582 in oxygen atmosphere at 950°C as a function of annealing time (O₂-BSCF5582). The heat treatment effect of the complex Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-d (BSCF5582) perovskite in oxygen atmosphere at 950°C (O₂-BSCF5582) on the electrocatalytic performances of ORR and OER was investigated. During heat-treatment in oxygen atmosphere, the crystallinity of the overall cubic perovskite structure was enhanced, and, most of all, a nanoscale thick surface layer, which is located between ~30 nm thick amorphous surface layer and particle matrix, was not any more observed. The electrocatalytic performance of BSCF5582 catalyst both in oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) was improved significantly. The mechanism of such microstructural- and electrochemical- improvement was explained by correlating with the effect of monitoring the surface chemistry and structure in this paper.

Perovskite (ABO₃) based mixed metal oxides were widely studied over last several decades as electrocatalysts for high-temperature fuel cell electrodes due to their mixed electronic/ionic conductivities at high temperatures (>700^oC). The perovskites formed of lanthanide (at A-site)-transition element (on B-site) metal complex have been recognized as efficient electrocatalysts for Oxygen Reduction Reactions (ORR) and/or Oxygen Evolution Reactions (ORR) in alkaline electrolyte. However, the electrochemical performance and stability of these catalysts depends on the choice of the type of A- and B-cations. Additionally, oxygen deficiencies created in mixed perovskite-phase (AA&’BB&’O_3-δ) by partial substitution of less valent cations on A- and/or B-site are believed to contribute significantly towards ORR/OER due to their oxygen-exchange redox behavior. In this regard, mixed perovskites formed by praseodymium (Pr) and samarium (Sm) based nickel-cobaltites such as PrNi_xCo_1-xO_3-δ and SmNi_xCo_1-xO_3-δ were considered as electrocatalysts for ORR and OER.
Praseodymium and samarium based mixed-perovskites with x= 0.1, 0.5, 0.9 have been synthesized using a modified nitrate-glycine Pechini method and heat-treated in air at 900°C and 1200°C. X-ray diffraction studies of the resultant materials show that a combination of mixed metal oxide structures such as perovskite, layered Ruddleston-Popper (A₂BO_4-δ) and spinel (ABO₃) depend on heat-treatment temperatures and relative composition of Ni and Co. For example, spinel and individual metal oxides were yielded at x=0.1, whereas a combination of perovskite, layered Ruddleston-Popper phases were developed at x=05 and 0.9. A combination of Temperature Programmed Reduction (TPR) and Thermo-Gravimetric (TG) analysis was further employed to understand the structural changes and accurate oxygen content in these materials as a function of the heat-treatment temperature. Scanning Electron Microscopy (SEM) and BET single point specific surface area (SSA) were used to determine morphology of the materials. In order to improve electronic conductivity, the perovskite-graphene composites were synthesized by dispersing metal oxides onto graphene platelets (90 wt. %). Electrochemical performance of these mixed-perovskite/graphene composites towards ORR and OER were studied in three-electrode configuration in alkaline medium. The structure dependent electrochemical behavior of these composites as a function of relative composition of Ni_x-Co_1-x (x= 0.1, 0.5 and 0.9) for the applications of alkaline fuel cells and metal-air battery cathode materials will be presented.

Hydrogen generation via electrolysis is rapidly gaining international interest for energy storage applications due to the ability of this technology to cross-link different infrastructures such as the electrical grid, transportation, and chemical processing. For example, generating hydrogen from peak wind power which would otherwise be a stranded resource can reduce the cost of hydrogen for fuel cell vehicles, in a completely green alternative to reformation of natural gas. Electrolysis based on ion exchange membranes offers several advantages vs. traditional liquid electrolyte systems that use concentrated potassium hydroxide. Proton exchange membrane (PEM)-based electrolysis technology is commercially mature, and can provide higher turndown capability, lack of corrosive electrolyte, and system simplicity and ease of maintenance. PEM electrolysis is already cost competitive on an equal output capacity basis vs. other sources of hydrogen for industrial applications, but overall lifecycle cost needs to be reduced for energy markets.
The oxygen evolution reaction is a key efficiency loss in electrolyzers, typically contributing over 300 mV of overpotential in proton exchange membrane systems. In addition, the catalyst loading is very high, due to the lack of stability of most catalyst supports in acidic environments at electrolysis potentials. While catalyst cost is not currently a key driver in the overall system cost, as other costs are decreased through system scale up and improvement in other processes, improving catalyst utilization needs to be improved in parallel to meet overall cost targets. Therefore, research must focus not only on composition of the catalyst but also electrode structure and application method. Proton has shown that catalyst composition, process conditions, and electrode formulation can all improve performance vs. current commercial baselines. Catalyst loadings also have the potential to be significantly decreased without loss in performance.
Anion exchange membrane (AEM) technology is still immature, but could enable much less expensive materials of construction in the cell stack, such as the bipolar plate and catalyst. Recent work in AEMs has improved durability and provided promise for eventual systems based on this technology as well. In alkaline environments, there should be a substantially larger choice of stable and high activity catalysts for the oxygen evolution reaction. Catalysts based on nickel and other first row transition elements for oxygen evolution in alkaline solution are well known. However, translation from solution data to membrane electrode assemblies with solid electrolyte has been challenging. This talk will describe advancements and potential directions in these areas for electrolysis based on both PEM and AEM systems. Progress and next steps needed in this area of study will also be described.

Nanoparticulate metal-oxide catalysts are among the most prevalent systems for alkaline water oxidation. However, comparisons of the electrochemical performance of these materials has been challenging due to the numerous methods of attachment and catalyst loadings used in the literature. Herein, we have identified a conventional drop-casting method that ensures adhesion of the catalysts and consistently applied to a variety of metal oxides for water oxidation reactions in alkaline condition. The nanoparticulate materials were characterized using XRD, XPS, BET, and SEM. The activity and Tafel slopes of the nanoparticulate catalysts attached by this method have been compared directly to similar systems synthesized by different methods such as electrodeposition, sputtering, etc. A brief discussion of the differences and similarities in the surface area as measured by BET and determined from the double-layer capacitance of the system is also provided.

Fuel cells, including proton-exchange membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC), have recently been considered as potential power sources for both electric vehicles and portable electronics since they could potentially fulfill the requirements of high energy and power density, high efficiency and low or zero emission simultaneously. One current bottleneck for building high energy-conversion efficiency fuel cells lies on the sluggish kinetics of the oxygen reduction reaction (ORR) at the cathode side.^[3] Therefore, development of efficient electrocatalysts for ORR becomes the focal task and main challenge in fuel cells research. Traditionally, platinum (Pt) and Pt-based alloys have been intensively investigated as the most active ORR electrocatalysts. However, Pt-based electrocatalysts suffer from various limiting factors including prohibitive cost, element scarcity and the declining activity caused by methanol crossover, which highly hinder the scalable applications of fuel cells. Therefore, it is highly desirable to develop efficient ORR electrocatalysts based on non-precious metals and with high methanol-tolerance.
Mixed valence oxides involving transition metals have been considered as an important class of possible alternatives that exhibit high ORR catalytic activity in alkaline medium.^[15] In particular, cobalt-based oxides have recently attracted growing interests due to their potentially high activity and relatively easy preparation. For example, Dai et al. fabricated the Co₃O₄/N-doped graphene hybrid structure and observed an enhanced catalytic activity for ORR.^[17] Recently, the partial substitution of cobalt with low cost and environmentally benign elements such as Ni, Cu and Mn has been shown potentially advantageous, while the progress is still quite slow. Moreover, the substituted metal oxides can only deliver much lower mass activity compared with Pt-based materials in most of previous studies. Undoubtedly, it will be of great significance to develop substituted metal oxide electrocatalysts having comparable catalytic performance with Pt-based materials.
In this work, we develop a cost-effective and environmentally benign solution phase method to synthesize hybrid nanosheets by growing well crystalline NiCo₂O₄ nanoparticles on reduced graphene oxide (rGO) sheets through based on a polyol process together with a subsequent thermal annealing treatment. Remarkably, the NiCo₂O₄-rGO hybrid nanosheets exhibit very high catalytic activity for ORR in terms of high current density and low over-potential. More importantly, the NiCo₂O₄-rGO hybrid nanosheets possess very high methanol-tolerance, which is very important for practical applications. The high quality NiCo₂O₄-rGO hybrid nanosheets could find promising use as a noble-metal-free and methanol-tolerant electrocatalyst for fuel cells.

Electrocatalytic water splitting using energy from sunlight represents a promising strategy for clean, low-cost, and environmentally friendly production of H₂. Unfortunately, the oxygen evolution reaction (OER) at the anode is kinetically slow and represents the bottleneck of this process. Transition metal oxides are good candidates for the anode in electrochemical water splitting. Inspired by recent computational work on b-NiOOH, which is the active phase during the charging and discharging process in alkaline batteries, we performed density functional theory calculations with the inclusion of the Hubbard-U correction on selected surfaces of pure and Co-doped b-NiOOH to calculate the energetics of the OER. We explored different reaction mechanisms of the OER for different Co doping levels of the b-NiOOH surface and different surface unit cell sizes. Our results indicate that the most likely reaction mechanism depends on the amount of Co doping. We find that doping the b-NiOOH surface with only 25% Co decreases the overpotential from 0.28 to 0.18 V. We also find that the theoretical overpotential, and which step is the potential limiting step, depends on the size of the surface unit cell selected in the calculations. This work highlights how optimizing the binding energies of the various intermediates (O, OH and H₂O) on the Ni and Co surface sites, may be key to reducing the overpotential.

The oxygen evolution reaction (OER), known for its slow kinetics, is a limiting reaction in several clean energy technologies including rechargeable metal-air batteries, electrolysis cells and solar fuel production.¹ For this reason, considerable effort has been devoted to identify efficient, stable catalysts with earth-abundant first-row transition metals, especially Ni, Co, Fe and Mn.^{2, 3} Fe is particularly well-known for its incorporation as a dopant/impurity into nickel-based OER catalysts while the OER activity of Fe itself is not well understood. ^{4, 5}
Our previous studies show that trace Fe impurities in KOH electrolyte dramatically increase the activity of Ni- and Co- (oxy)hydroxides as well as bare Au substrates. This indicates the importance of Fe, but the real active site in mixed Ni-Fe and Co-Fe (oxy)hydroxide catalysts remains unclear.^{4, 5} To help identify the active site and understand the role of Fe, we examine the intrinsic activity and stability of iron (oxy)hydroxide. By using a quartz crystal microbalance to measure the electrode mass in situ during catalysis, we find that the OER activity of iron (oxy)hydroxide is strongly dependent on film thickness with thinner films exhibiting substantially higher per metal activities than thick films, in some cases approaching those of the Ni-Fe (oxy)hydroxides. This is likely due to the poor conductivity of iron (oxy)hydroxide, with the increase of film thickness, the total resistance increases, resulting in potential drop in transferring electrons to each catalyst site. This hypothesis is confirmed by using an interdigitated array electrode to measure the conductivity in situ. We find the conductivity for FeOOH to be strongly potential dependent and negligible (< 10^-7 S cm^-1) until ~ 400 mV overpotential. We also report the activity of FeOOH on different substrates in order to understand how the substrate affects activity⁶ in ultra thin films that are not substantially affected by conductivity limitations.
1. N. S. Lewis and D. G. Nocera, Proc. Natl. Acad. Sci. U.S.A., 2006, 103, 15729-15735.
2. L. Trotochaud, J. K. Ranney, K. N. Williams and S. W. Boettcher, J. Am. Chem. Soc., 2012, 134, 17253-17261.
3. R. Subbaraman, D. Tripkovic, K.-C. Chang, D. Strmcnik, A. P. Paulikas, P. Hirunsit, M. Chan, J. Greeley, V. Stamenkovic and N. M. Markovic, Nat Mater, 2012, 11, 550-557.
4. L. Trotochaud, S. L. Young, J. K. Ranney and S. W. Boettcher, J. Am. Chem. Soc., 2014, 136, 6744-6753.
5. M. S. Burke, M. Kast, L. Trotochaud and S. W. Boettcher, manuscript near submission to JACS.
6. B. S. Yeo and A. T. Bell, J. Am. Chem. Soc., 2011, 133, 5587-5593.

Li-air batteries have received significant attention as a potential high specific energy alternative to current state-of-the-art rechargeable Li-ion batteries. However, numerous scientific challenges remain unsolved in the pursuit of attaining a battery with high capacity and modest Coulombic efficiency. This presentation will highlight efforts to improve Li-air battery cyclability and capacity through studies that elucidate the nature of Li-O₂ electrochemistry occurring at the positive electrode. Quantitative Differential Electrochemical Mass Spectrometry (DEMS) and electrochemical measurements on flat, nonporous glassy carbon electrodes are coupled with ex-situ chemical analysis of electrodes to better understand factors that control, and hinder, the desired rechargeable cathodic reaction (i.e., 2Li⁺ + O₂ + 2e^- harr; Li₂O₂). Results will be presented confirming that Li-O₂ battery capacity is limited by Li₂O₂-induced cathode electronic insulation and rechargeability is limited by electrolyte and electrode instabilities in the presence of Li₂O₂.

The high demand for new energy storage materials has created a need for experimental techniques that can provide real-time information on the dynamic structural changes/processes that occur locally at the electrode/electrolyte interface during battery operation. In this regard, in-situ electrochemical stages for (scanning) transmission electron microscopes ((S)TEM) enable the fabrication of a real “nano-battery” to study the fundamentals of electrochemical processes under operando conditions with the high spatial and temporal resolution of an electron microscope. Here, we describe quantitative operando observations using an in-situ electrochemical (S)TEM cell to study lithium peroxide (Li₂O₂) formation in rechargeable Li-O₂ battery systems. Currently, Li-O₂ batteries are being considered for application in next generation electric vehicles, due to a theoretical energy density which is comparable to gasoline. The operation of a Li-O₂ battery is based on the reversible formation/oxidation of lithium peroxide (Li₂O₂) at the carbon-based cathode. However, the high energy capacity values are limited to only few full charge-discharge cycles due to the decomposition of both the electrolyte and electrode material during oxygen reduction and evolution. This decomposition leads to the accumulation of insulating side products, causing a high over-potential and fast capacity fading during cycling. The in-situ electrochemical (S)TEM cell can be used to create a rechargeable Li-O₂ “nano-battery” consisting of a carbon-based cathode submersed in high vapor pressure organic battery electrolyte (such as LiTf in tetraglyme). By employing variable scan rate cycling voltammetry, we can gain quantitative insights into the kinetics of nucleation and growth of both Li₂O₂ nanoparticles and Li dendrites. Separation of these two processes allows direct observation of the formation of Li₂O₂ nanoparticles at the glassy carbon/electrolyte interface. Furthermore, the interplay between breakdown products and dendrites can be calibrated directly with standard Li-O₂ battery parameters, permitting this nano-battery to be used to rapidly test for new electrodes and electrolytes.
The research described in this presentation is part of the Chemical Imaging Initiative at Pacific Northwest National Laboratory under Contract DE-AC05-76RL01830 operated for DOE by Battelle. A portion of the research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory.

We present the fabrication of hollow 3-dimensional “microlattices” with a controllable architecture and periodicity, and independently tunable surface composition. The microlattices were fabricated using a self-propagating polymer waveguide technique at Hughes Research Lab, then subsequently conformably coated via a combination of deposition techniques including atomic layer deposition (ALD), sputtering and electrodeposition. The polymer scaffold was then removed via chemical etching, producing a mechanically robust, binder free structure with good electrical conductivity.
These microlattices offer the ability to decouple electrode material from geometry, thereby allowing the investigation of the effects of different material on cell performance. Electrochemically active surface area (true surface area) was measured using cyclic voltammetry (CV), and was found to be in good agreement with CAD software calculations using the microlattice unit cell geometry as input. As proof of feasibility, Au was chosen as the electrode material and 1,2 Dimethoxyethan (DME) as the electrolyte solvent. Discharge rates and capacities were normalized over true surface area. A capacity of 7.0 mu;Ah cm^-2_true was obtained when electrodes were discharged at 70 nA cm^-1_true, and a large number of “toroidal” shaped particles around 500nm in diameter were found covering the surface of the electrode. As the rate increased to 210 nA cm^-1_true, the capacity dropped to 1.0 mu;Ah cm^-2_true and no “toroids” were found. Fourier Transform Infrared (FTIR) and Raman Spectroscopy confirmed the predominant discharge product to be Li₂O₂ after the first discharge. These Li₂O₂ nucleii were fully removed upon subsequent charging. Side reaction products such as Li₂CO₃ , HCO₂Li and CH₃COOLi increased upon cycling, and the morphology of the discharge products turned into clusters of “platelets”, 5 -10 mu;m in diameter. Keeping the electrode geometry constant, several materials, including Ti, TiC and MnO₂ were deposited and tested as candidate electrode materials, and their performance were assessed in terms of chemical stability and catalytic reactivity towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). We demonstrate that the 3-dimensional architected materials provide a powerful vehicle for gaining insight into fundamentals of interface reactions and for a search of optimal positive electrode materials.

Lithium-air batteries are promising energy storage systems for overcoming current challenges in large scale applications such as electric vehicles. The performance of these batteries, however, is highly dependent on the electrochemical stability and physicochemical properties of the electrolyte. The unique properties of ionic liquid solvents, including relatively wide electrochemical stability window and extremely low vapor pressure, have made them promising candidates as electrolytes for improving the cyclic performance and safety of lithium-air batteries. The local current density, which is an important parameter in determining the performance of lithium-air batteries, is directly related to the rate constants of the electron transfer reactions at the surface of the electrodes. In this study, a novel approach is presented to investigate the effect of dielectric constant of the ionic liquid electrolyte and the operating temperature on the kinetics and energetics of electron transfer reactions at the cathode-electrolyte interface. The necessary free energies for all the species involved in the multi-step reduction of oxygen into peroxide ion at the graphitic cathode were calculated using density functional theory (DFT). Our results indicate that the magnitude of the driving force for the cathodic reactions increase with increase in the static dielectric constant of the electrolyte. Moreover, the overall rate constant for the cathodic reaction is inversely proportional to the static dielectric constant of the ionic liquid. Furthermore, it is observed that the increase in the operating temperature results in an increase in the cathodic reaction rates. The presented results provide fundamental understanding of the kinetics and thermodynamics of electron transfer reactions in lithium-air batteries that will help in the identification of appropriate electrolytes.

Due to its high potential, Zn-air battery with a century old technology has been attracted recently. However, it is still under research and development stage so that its maximum application has been significantly limited to small portable device such as just hearing aid. In this talk, we will briefly introduce possible degradation mechanism of each zinc anode and air cathode and then discuss efforts to address these issues. Furthermore, for making Zn-air battery technology more commercialization, we will also discuss which efforts should be more emphasized and which strategy can be possible and alternative for future Zn-air battery technology

Zinc-air batteries are energy-storage devices that provide high mass- and volume-normalized energy density in safe-to-operate configurations, but their broader use is limited by low specific power and limited rechargeability. A major roadblock to pulse-power-enabled, rechargeable Zn-air batteries lies in the multifunctionality required of the air-breathing cathode. This electrode must contain catalysts that promote O₂-reduction reactions (ORR) for battery discharge and O₂-evolution reactions (OER) for recharge, in addition to components that support intermittent high-power demand. We recently demonstrated a “dual-function” air cathode comprising carbon nanofoam paper functionalized with nanoscale MnOx coatings that provide both effective ORR activity and via a capacitive-delivery mechanism, O₂-independent pulse-power capabilities (F cm^-2 over tens of seconds).^1,2 The remaining challenge for our cathode-redesign is to incorporate recharge-enabling OER catalysts such that the resulting “trifunctional” architecture expresses all three functionalities: ORR, OER, and pulse power. In this paper, we present recent progress with OER catalysts that are based on nanostructured iron oxides (e.g., Ni-FeOx) and perovskites (e.g., La_1-xCa_xCoO₃ or LaFeO₃), and describe their integration within our dual-function cathode architectures using grafting and composite layers.
1. J.W. Long, C.N. Chervin, N.W. Kucko, E.S. Nelson, and D.R. Rolison, “Dual-function air cathode nanoarchitectures for metal-air batteries with air-independent pulse power capability.” Adv. Energy Mater. 2013, 3, 584-588; U.S. Patent application filed 27 September 2011.
2. C.N. Chervin, J.W. Long, N.L. Brandell, J.M. Wallace, N.W. Kucko, and D.R. Rolison, “Redesigning air cathodes for metal-air batteries using MnOx-functionalized carbon nanofoam architectures.” J. Power Sources2012, 207, 191-199.

In recent years there has been a marked increased interest in alkaline based energy storage and conversion systems such as anion exchange membrane fuel cells and metal air batteries. Both technologies rely on the reduction and/or evolution of oxygen. The slow kinetics of the oxygen reduction (ORR) and evolution (OER) reactions in alkaline environments necessitate the use of electro catalysts to increase the reaction rate and cell efficiency. Precious metals are most commonly used due to their high activities and relative stabilities.
There has been an extensive search for non-precious metal catalysts (NPMCs) that demonstrate activity and stability for ORR and OER in alkaline environments comparable to precious metal standards. Among the families of materials studied are transition metal oxides, transition metal minerals (perovskites, spinels, pyrochlores, etc.), and organometallic complexes. The latter is the focus of this work.
Organometallic NPMCs are generally synthesized by pyrolysis of a combination of metal salts, a nitrogen source (macromolecules or reactive gas) and a carbon support. State of the art NPMCs are based on Fe and Co and are synthesized in elaborate multi-step processes combining high temperature treatment (900^oC to 1050^oC) with acid wash or reactive gas (NH₃) pyrolysis. These catalysts have proven to have good ORR activity but limited durability.
In this study we report the synthesis and characterization of a new class of NPMCs for ORR and OER based on organometallic complexes of nickel (Ni) and bimetallic complexes of nickel with cobalt (Co), copper (Cu), or iron (Fe). The complexes formed from metals coordinated to substituted triazoles, supported on a carbon black. These catalysts are synthesized by covalently attaching ligands to the carbon surface via diazonium coupling, yielding a phthalocyanine-like molecule.
The as-synthesized catalysts show low catalytic activity for the ORR when compared to Pt. However, after a one step pyrolysis in an inert atmosphere, the activity of catalysts was found to improve dramatically. The NiFe-TrPc catalyst treated at 700°C had an onset potential of 1.03V vs. RHE (measured at 50µA/cm²). The as-synthesized catalysts also generally demonstrate good activity for the OER, significantly surpassing platinum. The activity was also found to increase after pyrolysis.
The samples were characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), thermo gravimetric analysis - mass spectrometry (TGA-MS) and x-ray powder diffraction (XRD). RRDE experiments were used to study the effect of catalyst loading, oxygen concentration and to determine the ORR reaction order and catalyst stability. Optimization approaches to enhance the catalytic performance will also be described. In situ testing of catalysts in Zinc-air batteries was conducted and the performance is compared to precious metals and perovskites.

Significant attention on rechargeable alkali-metal oxygen batteries results from their high theoretical specific energies [1-3] (Li-O₂ 3505 Wh kg^-1, Na-O_2, 1581 Wh kg^-1 and K-O₂, 1323 Wh kg^-1. The main focus of research efforts is on the development of a stable cathode and electrolyte. To assess the viability of such systems fundamental spectroelectrochemistry of electrode interfacial regions is required to reveal mechanistic detail of oxygen reduction and oxygen evolution reactions (ORR/OER) in non-aqueous media. Fundamental studies of dioxygen electrochemistry relevant to metal-air batteries commonly require conductive supporting salts, such as tetraalkylammonium, to sustain redox processes in non-aqueous electrolytes. Electrochemical analysis of the formation and oxidation of superoxide on glassy carbon and gold working electrodes has shown a decrease in reversibility and lowering of the oxygen reduction rate constant when tetraalkylammonium cation alkyl chain length is increased. Probing interfacial regions on Au using in situ surface enhanced Raman spectroscopy (SERS) provides evidence that this is caused by the changing adsorption characteristics of tetralkylammonium cations under negative potentials. These effects are heightened with longer alkyl chain lengths, therefore reducing the reversibility of superoxide formation and dioxygen evolution. From these observations it can be established that shorter chain tetraalkylammonium cations, whilst retaining necessary conductive support: (1) enhance reversibility and rate of superoxide formation and oxidation and (2) for in situ SERS, have lower preference for adsorption, thus improving experimental detection of superoxide at the Au electrode interface [4].
[1] Bruce, P. G.; Freunberger, S. A.; Hardwick; L. J., Tarascon, J.-M. Nat. Mater. 2012, 11, 19-29.
[2] Hartmann, P.; Bender, C. L.; Vra#269;ar, M.; Dürr, A. K.; Garsuch, A.; Janek, J.; Adelhelm, P.. Nat. Mater. 2013, 12, 228-232.
[3] Ren, X.; Wu, Y. J. Am. Chem. Soc. 2013, 135, 2923-2926.
[4] Aldous. I. M.; Hardwick. L. J. J. Phys. Chem. Letts.2014in press DOI 10.1021/jz501850u

A fundamental understanding of oxygen intercalation in metal is important for various applications, including metal-air batteries. Two important factors that are required for metal to act as good candidate for anode of metal-air batteries are: i) ease of oxygen intercalation and ii) small volumetric changes as the concentration of dissolved oxygen is varied. In this study using first-principles density functional theory (DFT) and hybrid-DFT, we study thermodynamic stability of oxygen interstials and corresponding volumetric change in range of metals.
We choose metals from period 4, including K-Ni. We compare oxygen interstial formation energy with formation energy per oxygen of corresponding oxides. As outlier to rest of metals considered, we find that formation energy of oxygen interstial in Sc, Ti and V is lower than corresponding oxides. While for other metals, formation energy of oxides is lower than oxygen interstial. This provides a thermodynamic driving force for oxygen to diffuse into Sc, Ti and V metals rather than forming oxide layer. On the other hand for metals like Fe and Ni, oxides formation is thermodynamically favorable compared to formation of oxygen interstial. Oxygen interstial formation energy is decided by two factors i) ability of metals to take multiple oxidation states and volume of interstitials. For K and Ca higher formation energy is due to ability of metal to take fixed oxidation state. While for Cr, Mn, Fe, Co and Ni higher formation energy is attributed to small interstial spacing. For Sc, Ti, and V unusually lower formation energy is due to both factors, metals take multiple oxidation state and spacing is large as well. Volumetric expansion due to interstials increases as we move from K to Ni. These results suggest that Sc, Ti, V can be suitable candidate for metal-air batteries.

Semiconductor-air batteries - a term we first define as metal-air batteries that use semiconductor anodes such as silicon (Si) and germanium (Ge) - have been introduced in recent years as new high-energy battery chemistries. For instance, p-type Ge behaves extremely better at elevated currents, evident from the higher voltage, more power available, and larger practical energy density from a very long discharge time, possibly arising from high overpotential for surface passivation. Combining the above results with our recently reported Fe-CNF catalysts, which show comparable activity with platinum on carbon (Pt/C), we describe here the oxygen reduction reaction (ORR) performance of two types of activated Fe-N-C electrocatalysts in gelled alkaline electrolyte-based semiconductor-air cells. Consistent with the ORR catalysts&’ performance in linear sweep voltammetry (LSV), ball-milled Fe-CNFs and water activated Fe-CNFs exhibited excellent ORR performances as air cathodes in actual semiconductor-air cells. The present study demonstrates that non-noble based ORR catalysts (e.g. Fe-triad element-based) could indeed successfully replace conventional yet expensive Pt-based catalysts.

We present an overview of our recent work on catalyst materials for the electrochemical oxygen reduction (ORR) and oxygen evolution (OER) reaction.
We address insights in the materials science and catalysis of Pt bimetallic ORR electrocatalysts using aberration-corrected scanning transmission electron microscopy (STEM) and spectroscopic (EELS) studies.We demonstrate how atomic core-shell fine structure,nanoporosity and nanoparticle shape can influence the activity and, more importantly, the stability of Pt-Ni bimetallic nanoparticles for ORR cathode electrocatalysts.
We also discuss recent research on experimental correlations between the geometric and electronic structure of IrO₂ single crystals, thin films and spherical nanoparticles and their OER activity and stability. Starting with pure IrO₂ we move to structure-activity effects of bimetallic IrNiO_x films and IrNiOx core-shell nanoparticles.

A novel Fe-N-C composite material with a hollow graphitized nanostructure is prepared by pyrolyzing iron-chelating, nitrogen-containing precursors adsorbed on carbon black spheres for use in the oxygen reduction reaction (ORR) of polymer electrolyte membrane fuel cells (PEMFCs). The resulting composite hybrid exhibits excellent electrocatalytic activity and a four-electron dominated ORR pathway in an alkaline solution. The efficient catalytic activity of the prepared Fe-N-C is mainly attributed to the effective incorporation of nitrogen and iron atoms into the graphitized matrices and high electrical conductivity due to the interconnected structure. Furthermore, the hybrid material shows superior catalytic durability in the alkaline medium even after 3,000 cyclic voltammetry cycles, making it a good candidate for a cathodic electrocatalyst in PEMFCs.

We present our work on the fabrication of nickel(II) oxide nanoparticles which meet the substantial challenge of an inexpensive, efficient and stable electrocatalyst for water splitting.
We will present a novel synthesis route for the preparation of ultrasmall crystalline highly dispersible nickel(iII) oxide nanoparticles by a solvothermal reaction in tert-butanol. The crystalline nanoparticles are formed already in solution by a chemical reaction with the solvent, without the need for a further high temperature treatment unavoidably leading to irreversible particle agglomeration. The particles prepared in this way are dispersible in ethanol with the addition of very small amounts of acetic acid forming stable colloidal dispersions. Using this approach we have obtained crystalline dispersible nanoparticles of nickel oxide with a narrow particle size distribution. The particle size can be varied from ultra-small 2.5 nm to 6 nm by increasing the reaction duration and can be further tuned by a post-synthesis temperature treatment.
The obtained nickel oxide nanoparticles demonstrate an extremely efficient catalytic behavior of the material in electrochemical water splitting. The nanoparticles show very high turn-over frequencies of 0.49 s^#8209;1 at an overpotential of eta; = 300 mV, even outperforming expensive rare earth iridium oxide catalysts.

Faced-controlled metal alloy nanocrystals has attracted increasing attention due to their use as highly active heterogeneous catalysts in oxygen-involved electrocatalytic reactions in the applications such as fuel cells, batteries, and other alternative energy conversions.¹ Recent studies based on both the theoretic simulation and experiment data on surface of bimetallic catalysts toward oxygen reduction reaction (ORR) show that desorption of OH, which is the determining step in the electro-reduction of oxygen, highly depends on d band structure.^2-3 It is apparent that surface geometry and surface compositions can modulate the d band structure. Recently, we developed a Gas Reducing Agent in Liquid Solution (GRAILS) method for making uniform cubic, octahedral and icosahedral Pt alloy nanocrystals in non-aqueous solutions using carbon monoxide (CO) gas.^4-6
In this presentation, we show that this GRAILS method can be a powerful approach as a platform for making a variety of Pt alloy nanostructures with desired surface compositions, which are designed for highly active and durable ORR catalysts. By using CO gas and organic ligands, we show high-level controls over the growth and facet formation of Pt-based nanocrystals to obtain highly uniform nanocrystals with desired facets. High catalytic activity in ORR was observed in (111) dominated icosahedral and octahedral Pt alloy catalysts. The correlation between the catalytic performance and crystal geometry and surface strain will be discussed based on experiment and simulation data.^6-7 The controlling factors on the growth and stabilizing the formation of Pt icosahedron nanoparticles in solution will also be discussed,⁶ which is in general a type of unstable structure in thermodynamics.
1. J. B. Wu, H. Yang, Acc. Chem. Res., 2013, 46, 1848-1857.
2. V. R. Stamenkovic, B. Fowler, B. S. Mun, G. F. Wang, P. N. Ross, C. A. Lucas, N. M. Markovic, Science2007, 315, 493-497.
3. V. R. Stamenkovic, B. S. Mun, K. J.thinsp;J. Mayrhofer, P. N. Ross, N. M. Markovic, J. Rossmeisl, J. Greeley, J. K. Noslash;rskov, Angew. Chem. Int. Ed., 2006, 45, 2897-2901.
4. J. B. Wu, A. Gross, H. Yang, Nano Lett., 2011, 11, 798-802.
5. J. B. Wu, L. Qi, H. J. You, A. Gross, J. Li, H. Yang, J. Am. Chem. Soc., 2012, 134, 11880-11883.
6. W. Zhou, J. B. Wu, H. Yang, Nano Lett., 2013, 13, 2870-2874.
7. J. B. Wu, P. P. Li, Y.-T. Pan, S. Warren, X. Yin, H. Yang, Chem. Soc. Rev., 2012, 41, 8066-9074.

Fundamental understanding of the processes involved in electrochemical reduction of oxygen and its evolution from water based electrolytes is considered critical for further advancement of materials that could be implemented in technologies such as electrolyzers, batteries and fuel cells. Atomic scale insight at the electrified solid-liquid interfaces provides invaluable guidance to overcome limitations that cause a lower than desired operating efficiency of the devices. All of that highlights the need for development of more active and durable oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts. While the majority of research is placed on the catalyst design and synthesis aiming to improve their efficiency, far less has been done to resolve and understand the impact of the liquid phase of the interface at which reactions are taking place. For that reason, in addition to surface structure, surface and subsurface composition and electronic structure, the role of liquid phase which influences the overall properties of an electrified interface will be emphasized. Molecular species from the electrolyte and the nature of their interaction with the catalyst surface will be demonstrated in tuning the overall catalytic performance. The knowledge acquired from well-defined systems has been further employed to create tailor-made real-world catalysts with advanced properties. It will also be demonstrated how highly diverse multimetallic systems induce additional benefits in enhancing both catalytic activity and durability of solid-liquid interfaces.

The proton exchange membrane (PEM) fuel cell shows tremendous promise and represents a versatile and efficient energy conversion device. However, before the PEM fuel cell can achieve widespread commercial use, improvements in unit cost, fuel cell durability and fuel versatility must be achieved. Key to the PEM fuel cell operation is the catalysis of the oxygen reduction reaction (ORR) on the cathode. A perfect ORR catalyst would very efficiently convert O₂, protons, and electrons to water, have no peroxide byproducts, be inexpensive, and durable. This, however, represents a significant challenge; the sluggish kinetics of the ORR on precious metals have been the subject of extensive studies in electrocatalysis over the last 8 decades and to date no non-platinum or even non-platinum group metal (PGM) based catalyst has been discovered that is more efficient than a PGM based catalyst. And while Pt and Pt alloys offer acceptable ORR performance, the high cost of Pt severely impacts the future commercial viability of current PEM fuel cell technology. Additionally state of the art fuel cell cathodes are inherently thermodynamically unstable in that the preferred catalyst configuration is well dispersed Pt-nanoparticles on a thermally treated carbon support.
A promising alternative approach to Pt alloys or non-precious metal catalysts is the use of metal oxides as co-catalysts and/or sup- ports to Pt catalysts. One class of metal oxides that have received much interest for this application are the heteropoly acids (HPAs), an acid stable subset of the larger group of tungsten or molybdenum based metal oxide clusters termed polyoxometalates. HPAs have been re- peatedly shown to enhance the ORR activity of Pt or Pt alloys, most significantly for HPAs containing tungsten, and even pro- vide limited catalytic activity on their own. Improvements in CO tolerance have also been observed as a result of the addition of various HPAs, presumably by the participation of HPA in the bifunctional mechanism, and provide one mechanism for the activity enhancement. Another mechanism includes the ability of some HPAs to stabilize transition-metal nanoclusters, preventing particle growth/aggregation both during synthesis and potential cycling. Further, modification with HPA has been shown to increase the availability and/or mobility of protons at Pt sites, providing activity advantages at least in membrane electrode assemblies (MEAs).
In this paper we use a dispersed functionalized HPA, 11- silicotungstate (SiW11), covalently attached to the carbon via carbon- carbon bonds prior to the addition of colloidal Pt, so that the HPA would be stable to water dissolution and would not impede mass transport. We quantify the ideal loading of SiW11 on the carbon in terms of maximizing gains in ORR activity catalyzed by the Pt and evaluate the impact of SiW11 on the durability of the Pt catalyst.

Oxygen reduction reaction (ORR) over binary metal alloys has attracted renewed attention due to its technological importance in pollution control and fuel cells. However, the lack of good understanding of how the phase state, chemical composition and atomic-scale structure of the alloys at the nanoscale influence their ORR activity impedes the development of nanoalloy catalysts by rational design. We will show how in situ high-energy synchrotron x-ray diffraction and atomic pair distribution function (PDF) analysis coupled to nanoalloy 3D structure simulations and catalytic activity studies can help in this respect. The great potential of this approach will be demonstrated with results from recent studies on Pd-Ni, Pt-Ru and Pt-Pd nanoalloys post-synthesis treated at elevated temperatures in reactive gas atmosphere as to be optimized for ORR.

Oxygen electrocatalysis is critical to numerous renewable energy technologies, such as fuel cells, metal-air batteries and electrolyzers. The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) exhibit intrinsically slow kinetics and high charge transfer resistances. While effective catalysts have been developed and are commercially available, most are based on precious metals and are not economically viable for widespread application. In addition, commercial catalysts are typically effective at performing either the ORR (e.g. Pt and Pt/C catalysts) or the OER (e.g. Ir and Ir/C catalysts), but not both. Furthermore, these catalysts can still suffer from reaction poisoning, poor electrocatalytic selectivity and stability, further decreasing their utility. An ideal catalyst would be easily prepared, stable, cost effective, and exhibit bi-functional behavior, in that it can efficiently perform both the ORR and the OER. Such catalysts could simplify design protocols for re-chargeable metal-air batteries and fuel cells and lead to the realization of efficient and practical devices.
We have prepared nickel-cobalt oxide (Ni_xCo_3-xO₄) spinel nanostructured films through a simple electro-deposition and annealing process. The Ni_xCo_3-xO₄ catalysts exhibit exemplary performance for both the ORR and OER. Along with an improvement over the parent cobalt oxide (Co₃O₄) catalyst, the Ni_xCo_3-xO₄ films outperform commercial catalysts for both the ORR (e.g. vs. 20% Pt/C), and the OER (e.g. vs. 20% Ir/C). This presentation will demonstrate the synthesis and evaluation of these Ni_xCo_3-xO₄ catalyst films and examine the effect of Ni-doping on composition, metal ion valence, surface area and electrocatalysis. We will also illustrate that these catalysts offer stability and electrocatalytic selectivities greater than or equal to commercial benchmark catalysts. Given that cobalt and nickel are currently about 1,539 and 2,694 times cheaper than platinum, respectively, these catalysts offer promise for widespread next-generation renewal energy technologies.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy&’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

The scalable storage of renewable energy by means of converting water to hydrogen fuels electrochemically hinges on fundamental improvements in catalytic materials. However, many applications exist where an extended lifetime is virtually crucial for their functionality and success, e.g. in case of limited accessibility such as tire pressure sensors or biomedical implants. For these kinds of applications, the ultimate power supply should be a self-renewing energy source. This strategy is pursued by the concept of Micro Energy Harvesting (MEH). Within a MEH system a micro generator converts ambient energy to electrical energy for driving an application. Unfortunately, it is not ensured that the ambient energy level will maintain always high enough to provide sufficient power to the system as harvested energy usually manifests itself in rather irregular, random and low-energy bursts. One appealing form of integrated energy storage is the use of H₂/air, a so called fuel cell type (FC) battery. Such devices promise very high volumetric energy densities of more than 2000 Wh/l. Consequently, this type of battery has recently attracted more and more attention and primary as well as secondary cells have been realized. Alkaline polymer electrolyte fuel cells have been recognized as the most promising solution in order to overcome the dependency on noble metal catalysts. Nevertheless, further improvements for these kinds of fuel cells have to be reached with respect to high power. Therefore, one promising approach is to increase the skin surface of porous chromium decorated nickel electrodes for enhancement of exchange current density by forming three-dimensional (3D) microstructures directly into the electrode. Therefore, a novel laser structuring process was applied using ultrashort laser pulses. Ultrashort laser processing of complex multimaterial systems for energy storage allow for precise material removal without changing the material properties. By applying this novel laser-based structuring technique, 3D microstruc