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.

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.

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 microstructures could be formed permitting shortened diffusion lengths between the electrolyte and the electrode surface being necessary for increased exchange current densities

The development of synthetic methods for the fabrications of new bimetallic platinum-based nanocrystals (PtM) with high catalytic activity is one of the essential subjects in fuel cell research. Our study demonstated that three different types of alloyed FePt nanstructures, nanodendrites, nanospheres and nanocubes, were prepared and their catalytic activities for oxygen reduction reaction (ORR) were studied. The ORR catalytic activity of the nanostructures were increased in the order of E-TEK Pt/C < FePt nanospheres < FePt nanocubes < FePt nanodendrites. The FePt nanostructures were analyzed by high-resolution transmission electron microscopy (HRTEM), high angle annular dark field (HAADF), scanning transmission electron microscopy (STEM) and electron energy loss spectrum (EELS) mapping. The HRTEM images revealed that the large surface area of FePt nanodendrites with a high density of atomic steps was enclosed by high-index {311} facet. The density functional theory simulation was performed to understand the origins of the enhanced electrochemical activity of FePt nanodendrites. The enhancement could be attributed to the exposure of high-index {311} facet of the nanodendrite with high surface energy in comparison to that low-index {111} and {200} facets of FePt nanospheres and nanocubes, respectively. Our experimental and theoretical studies have opened a route toward the syntheses of new nonprecious alloyed nanostructures to replace Pt as active fuel cell catalysts.

The synthesis of high energy-faceted alloy nanoparticles has been zealously pursued for the development of high performing nanocatalysts. While the facet-control of alloy nanoparticles, namely the organization of surface atoms, is attained by understanding the growth kinetics and surface-stabilizing effects of surfactants, little is known for the atomistic organization within the matrix of a nanoparticle. Herein we report that the atomistic organization within the alloy nanoparticle matrix is greatly affected by the surface energies which are governed by the geometrical parameters of the nanoparticle and the identities of surface bound moieties. With this understanding, we could prepare phase-segregated binary nanoparticles that exhibit excellent electrocatalytic activities relevant to the fuel cell applications.

Facet-controlled nanoparticles are expected to exhibit varying reactivity dependent on the type of facets and nanostructural features. On the other hand, the composition of alloy nanoparticle could be dynamically varied by understanding the nature of metal-surface binding moiety interaction. The successful formation of alloy nanoparticles requires the kinetic and thermodynamical control. Therefore, a new alloy phase, obtained from regioselective impurity doping of facet-controlled nanoparticles, might exhibit a surface-stabilization behavior which is completely different from that of the original nanoparticle, leading to different facets and completely new nanocrystal shapes. Herein we report an unusual post-synthetic doping-induced novel nanostructure transformation process, leading the unique nanostructures.

There are a lot efforts to synthesize new Pt-based nanoparticles for the improvement of electro-catalytic activity in oxygen reduction reaction and methanol oxidation reaction. Because core-shell structure has already proved its excellent activity due to the lattice mismatch between the core and the shell, we have strived to find a synthetic route for a highly efficient electro-catalytic 1-D nanostructure with a core-shell structure. Herein we report the facile one pot synthesis of coaxial nanocables with Pt shell, which exhibits catalytic performance enhancing numerous twinning boundaries. The combination of the core-shell effect and high activity of twinning boundary resulted in a great surface energy elevation, which in turn led to a great improvement in electro-catalytic activity.

Synthesis of facet-controlled nanoparticle is receiving a great attention as promising materials for catalyst, optoelectronics, and nanobio applications. However, synthesis of facet-controlled Ru and Ir nanoparticles has not been reported thus far, probably due to the difficulty in atomic packing; the Ru and Ir precursors are thermodynamically very stable and thermal decomposition of them usually lead to the formation of only very small spherical nanoparticles. In order to prepare facet-controlled Ru and Ir nanocrystal, it is necessary to speed up the decomposition kinetics for the precursors. The different decomposition kinetics of Cu and M (M=Ru, Ir) precursors leads to the formation of core-shell type nanoparticles. However, the disparate dissolution of Cu phase leads to different nanocrystal morphologies, namely, facet-controlled hollow octahedral Ru nanocage and CuIr@Ir core-shell octahedral nanoparticle.

Dendritic Pt catalysts are one of superb candidates in the proton exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) due to high surface-area-to-volume ratio, plenty of adsorption site, and surface permeability. However, monometallic Pt catalyst suffers from poisoning associated with intermediates adsorbates, which limits methanol oxidation reaction (MOR) or oxygen reduction reaction (ORR) kinetics and long-term stability. To improve electocatalytic properties of Pt, morphology control of the Pt particles and using Pt-based bimetallic alloy nanoparticles instead of pure Pt as the electrocatalyst have been extensively studied for the past decade. In this regard, we developed a facile aqueous synthesis method for preparation of Au@Pt core-shell and Pd@Pt core-shell nanostructures based on Pt dendritic shell. As a results, prepared bimetallic core-shell nanostructures have exhibited higher electrocatalytic activity, stability, and durability than those of the monometallic Pt dendritic catalysts toward ORR and MOR because bimetallic core-shell nanostructures can be finely tuned by manipulating their core and shell structures. In this reason, core effect was investigated via synthesized Au@Pt core-shell nanostructures consisting of a dendritic Pt shell and structured Au cores (nanocubes, nanorods, and nanooctahedra) toward ORR. And also, we found that the electrocatalytic activity and stability of the prepared Pd@Pt core-shell nanostructures for the MOR were highly dependent on their Pt shell thicknesses.

We demonstrate a highly efficient synthesis of palladium-tungsten bimetallic nanoparticles supported on ordered mesoporous carbon (Pd-W/OMCs) and their use as high performance electrocatalysts for oxygen reduction reactions (ORR) in fuel cells. The synthesis is performed in an ordinary kitchen microwave oven in less than one minute by a direct mixing of precursor materials. Even at a very low percentage of noble metal (Pd:W=1:8), the hybrid catalyst material exhibit a current density equal to commercial 60% Pt/Vulcan. This is explained by a partial segregation and the formation of catalytic hot spots at small Pd-islands embedded in the Pd-W bimetallic nanoparticles. The formation of the Pd-islands is supported by high resolution STEM and high resolution energy dispersive X-ray spectroscopy (EDS) mapping, and unambiguously confirmed by extended x-ray fine structure absorption spectroscopy (EXAFS) which based on a coordination number analysis demonstrate that the embedded Pd-islands contain 10 atoms on average. By electron energy loss spectroscopy, x-ray photo-electron spectroscopy (XPS) and EXAFS we find that the Pd-islands embedded in the W-matrix are metallic, and despite their small size they are remarkable stable, explained by the reducing environment of the W-matrix. The long term stability of the Pd-islands is manifested by EELS and EXAFS measurement showing that the Pd-islands exhibit metallic character even in samples stored for more than one year at ambient conditions. In addition the oxygen reduction activity measured by cyclic voltammetry shows negligible decrease after 53 hours of continuous testing. Density functional theory calculations show that the Pd-islands form due to higher energetic stability compared to a fully homogeneous alloy particle. Concurrently, a complete segregation is hindered by quenching the samples during synthesis. Theoretical analysis of ORR and activity Volcano plots show that the catalytic efficiency of the atomic Pd-islands in the W-matrix depends strongly on both the number of Pd-atoms as well as their structural configuration in the nanoparticle, and that for some configurations the ORR proceeds as efficiently as on Pt(111) surface. Our results give important insight into the formations, stabilization and performance of bimetallic nanoparticles for catalytic reactions. Furthermore, our study show that the complete formation of core-shell nanoparticles is not crucial for high performance cost efficient electrocatalysts. As a matter of fact; the island structure exhibit several advantages over core-shell structures, and hence opens the field to other designs of bimetallic nanoparticles.

Polymer exchange membrane (PEM) fuel cell technology is one of the promising fields of clean and sustainable power, which is based on direct conversation of fuel into electricity. However, at the present moment PEM fuel cell is unable to be successful commercialization. The main factor is the high cost of materials in catalyst layer which is a core part of PEM fuel cell. In order to reduce the overall system cost, developing active, inexpensive non-precious metal (non-PGM) electrode catalysts to replace currently used Platinum (Pt)-based catalysts is a necessary and essential requirement. The purpose of my research is using Graphene oxide, melamine, ferrous salt and metal organic frameworks (MOF) to synthesize a new Non-PGM catalyst. This catalyst will be a transition metal nitrogen-containing complex supported on carbon material (M-N/C). The main synthetic methods are high temperature heat treating (800-1000 #8451;) and ball milling. RRDE test will be used to measure electron transfer number and ORR reactivity, which are the most important electrochemical properties of the new catalyst. So far the experimental setup is almost finished and some precursor samples are prepared by different treatment methods. And a better treatment method is designed from the analysis of precursor samples. The next step will be doping Fe and MOF to synthesize M-N/C catalyst.

A series of CoSe₂/C nanoparticles were prepared by a simple microwave method using different molar ratios of Se/Co=2.0~4.0. The surface morphology, crystal structure, chemical composition and electrocatalytic activity toward oxygen reduction reaction (ORR) of CoSe₂/C catalyst nanoparticles were systematically investigated. The major phases of CoSe₂/C nanoparticles were identified to be orthorhombic CoSe₂ with minor cubic CoSe₂. The potentials corresponding to ORR (E_ORR) reached 0.6~0.7 V, while the electron transfer numbers (n) were 3.1~4.0 in oxygen saturated sulfuric acid solutions. The presence of excessive Se on the catalyst surface was confirmed at Se/Cosup3;2.5, which significantly influenced the ORR activities. Slightly excess amount of Se oxide presented in CoSe₂/C would prevent CoSe₂ nanoparticles from growing and smaller sizes with less agglomerated Se-rich CoSe₂/C were obtained, resulting in good ORR activity. However, too much Se oxide would cause severe aggregation of CoSe₂ nanoparticles, leading to poor ORR activity. The best ORR activities with E_ORR=0.705 V and n=4.0 could be achieved with Se/Co=3.0.

CeO₂ is an attractive material for various applications due to its physical, chemical and electrical properties. For example, CeO₂ is a basic component in oxidative catalysis as well as sensors and fuel cell technology, where catalytically active surfaces and high ionic conductivity, well-known for CeO₂, are essential. These applications are based on the easily formed oxygen vacancies in the fluorite structure of ceria due to the variable oxidation state of Ce ions (3+ and 4+). Doping ceria with aliovalent cations to some extent may increase the oxygen vacancies while maintaining the cubic fluorite structure. These ceria-based materials are found to have high ionic conductivities and enhance catalytically active surface. In the present study, the effect of Nd³⁺ on the surface energy and water adsorption enthalpy of CeO₂ was investigated. Neodymium doped nano CeO₂ powders, with 0 to 10 wt% Nd were synthesized by non-aqueous sol-gel method with oleylamine as a surfactant and diphenyl-ether as an aging agent, in vacuum. The water adsorption enthalpy was measured using a custom combination of gas dosing system and micro-calorimeter. The interfacial energies were assessed using differential scanning calorimetry. The effect of Nd on the energetics will be discussed.

Inexpensive, abundant, efficient and stable materials for oxygen evolution reaction catalysis are needed to enhance the production of H₂ via electricity- or solar- driven water electrolysis. First row transition metals are an ideal candidate for oxygen evolution reaction (OER) catalysts in alkaline media. To develop these materials and create highly efficient catalysts that work in anion exchange membrane (AEM) electrolysis systems we aim to 1) understand the intrinsic activity and stability of each catalyst and 2) understand how that knowledge relates to AEM cell performance and durability.
We demonstrated that a simple Fe impurity dramatically increases the activity of Ni- and Co-(oxy)hydroxide materials.^1,2 Prior to this analysis the commonly cited activity trend of 1^st row (oxy)hydroxides was Ni > Co > Fe.^3,4 Our new results indicate that by removing this impurity, the revised activity trend of 1^st row transition metals in 1 M KOH is Ni-Fe > Co-Fe > Fe > Co > Ni.⁵ This new activity trend is the opposite of those previously reported. By using a quartz crystal microbalance to measure the electrode mass in situ during catalysis and an interdigitated array electrode to measure conductivity in situ we also report new insight into the origin of these OER trends.
With this developed understanding of the fundamental properties of our materials, we will also report progress on their integration into AEM test cells. There are many challenges in taking a catalyst from a lab test cell (stirred, 1 M KOH) and putting it into a practical solid-electrolyte electrolysis system where one needs also to consider ion, gas and liquid transport, as well as catalyst adhesion and electrode mechanical robustness. To address these challenges we have focused specifically on understanding the role that catalyst deposition method, electrode thickness, conductivity and composition play on performance and durability. Several promising integration methods will be presented that enable relatively high-performance AEM hydrogen production using earth abundant oxygen evolution electrocatalysts.
1)Trotochaud, L.; Young, S. L.; Ranney, J. K.; Boettcher, S.W. J. Am. Chem. Soc.2014, 136, 6744.
Burke, M.S.; Kast, M.; Trotochaud, L.; Boettcher, S.W. manuscript near submission to JACS.
2)Subbaraman, R.; Tripkovic, D.; Chan, K.-C.; Strmcnik, D.; Paulikas, A.P.; Hirunsit, P.; Chan, M.; Greeley, J.; Stamenkovic, V.; Markovic, N.M. Nat. Mater.2012, 11, 550.
3)Trotochaud, L.; Ranney, J.K.; Williams, K.N.; Boettcher, S.W. J. Am. Chem. Soc. 2012, 134, 17253.
4)Burke, M.S.; Gaber, C.; Zou, S.; Kellon, J.; Pledger, E.; Boettcher, S.W. manuscript in progress.

Renewable power sources become essential in modern society. Due to the irreplaceability of hydrogen as future energy carrier for mobile, mass and buffer energy storage [1, 2] electrochemical water splitting is the most reliable technology which has the potential to be optimized for more efficient conversion and energy storage. While the hydrogen evolution reaction (HER) is well optimized, the oxygen evolution reaction (OER) is intensively studied by both academia and industry because of the potential to increase the reaction rate. As a matter of fact, HER and OER cannot be treated separately in the electrolytic cell, the slower rate of the OER determines the overall reaction rate. Although the electrochemistry of oxygen was researched intensively [3], the reactions on the electrode surface have not been related to the defect structure and chemistry. Oxygen electrocatalysis is the operative point, where more efficient, chemically stable and economically reasonable electrode materials are required. (Double) perovskite materials have been reported to be good electrocatalysts [1,2]. The chemistry of the interface layers of the electrocatalytic films can be examined by state of the art methods like in situ high pressure ETEM, XPS and SEM [4,5] to achieve a better understanding how to improve oxygen evolution. Here, we report the assembly and characterization of perovskite Pr_xCo_1-xMnO₃ (PCMO) epitaxial thin film electrodes, which are promising as electrocatalysts for the OER. For comparison, epitaxial PCMO thin films as well as polycrystalline films on titanium substrates are characterized by potentiostatic and potentiodynamic methods. Systematically, the Pr content in the electrodes is varied and the dependence of oxygen activity on noble metal content is shown.
References:
1. A. Grimaud; K. J. May; C. E. Carlton; Y. L. Lee; M. Risch; W. T. Hong; J. Zhou; Y. Shao-Horn. Double perovskites as a family of highly active catalysts for oxygen evolution in alkaline solution. Nat. Commun., 4, 2439/1-7 (2013)
2. J. Suntivich; K. J. May; H. A. Gasteiger; J. B. Goodenough; Y. Shao-Horn. A Perovskite Oxide Optimized for Oxygen Evolution Catalysis from Molecular Orbital Principles. Science, 334, 1383-1385 (2011)
3. J.P. Hoare. Electrochemistry of Oxygen. Wiley (1968)
4. S. Raabe; D. Mierwaldt; J. Ciston; M. Uijttewaal; H. Stein; J. Hoffmann; Y. Zhu; P. Bloechl; C. Jooss. In Situ Electrochemical Electron Microscopy Study of Oxygen Evolution Activity of Doped Manganite Perovskites. Adv. Funct. Mater., 22, 3378-3388 (2012)
5. D. Mierwaldt; S. Mildner; R. Arrigo; A. Knop-Gericke; E. Franke; A. Blumenstein; J. Hoffmann; C. Jooss. In Situ XANES/XPS Investigation of Doped Manganese Perovskite Catalysts. Catalysts, 4, 129-145 (2014)

Spent coffee grounds, the solid residual wastes from coffee industry is an inexpensive, abundantly available renewable resource material. Every year about 6 million tons of this waste is generated worldwide. This work represents an efficient way of transforming spent coffee grounds to hetero-atom doped carbon to replace expensive metal based catalysts as electrodes in fuel cells. Unlike other techniques for preparing heteroatom doped carbon which involves prolonged time, special apparatus and reducing gases, the microwave technique employed for the synthesis affords unique high surface area carbon structures with exceptional properties. Also there is no need for the use of reducing or inert gases during the carbonization process. Ammonium polyphosphate is utilized to aid in the carbonization process and also to create defects in carbon lattice. The as-synthesized P, N co-doped carbon (PNDC) exhibited high BET surface area of ~507 m²/g. XPS revealed the material to contain about 1.90 % N and 3.02 % P. PNDC exhibited an intense O₂ reduction peak in alkaline media. The mechanism of O₂ reduction was discovered to be a 4 e-mediated process based on Rotating Disk Electrode studies. Also, the material exhibited good electrochemical stability which enables it to find practical applications in fuel cells.

To date, carbon-based materials including various carbon nanostructured materials have been extensively used as the most practical catalyst supports for fuel cell applications. However, carbon dissolution or corrosion caused by high electrode potential in the presence of O₂ and/or water has been identified as one of the main failure modes for the device operation. To address these issues, in recent years there has been a growing interest in developing alternative non-carbon-based materials for catalyst supports for the manufacture of fuel cell devices in order to improve their durability while simultaneously keeping catalysts activity efficient. Titanium nitride (TiN) has been attractive as a promising support material for the various dynamic operating conditions required in fuel cell applications. Its high electrical conductivity and outstanding electrochemical corrosion resistance makes it a promising candidate for the highly efficient and durable catalyst support. Recently, we developed a facile synthetic method to prepare TiN nanofibers directly by electrospin method. The control of surface structure of TiN, size distribution of the prepared nanofibers and Pt catalyst distribution over the individual nanofiber enable manipulation of the catalytic and electrochemical properties of the final catalyst/TiN nanostructures. Experimentally, when compared to commercial carbon-supported Pt catalysts, our optimized TiN nanofiber-supported Pt catalysts showed better catalytic performance and the improved stability against catalyst or Pt dissolution under potential cycling regimes. In this talk, we will illustrate how these new TiN support materials yields superior performance fuel cell devices. Specifically, effect of the TiN support on catalytic stability and activity as well as the physicochemical and electronic interaction of Pt catalysts with the TiN support will be presented by experimental results and model analysis.

Finding cost-effective alternative electrocatalysts for oxygen reduction reaction (ORR) is considered as one of the most overriding challenges in the development of electrochemical technologies such as fuel cell and metal-air batteries. Although significant progress has been made in developing carbon-based ORR catalysts as cost-effective alternative to platinum, most of alternative electrocatalysts have been synthesized via heat treatment of mixture of carbon, heteroatom, and transition metal precursors in trial and error. Therefore, it is necessary to investigate factors that can affect to electrocatalysts during synthesis process and how the difference in electrocatalysts can influence the ORR activity. In this study, we investigated effect of transition metal on carbon structure formation and ORR activity depending on different physicochemical properties of carbon. Based on the detailed physicochemical analysis with electrospun transition metal containing carbon nanofibers (TM-N-CNFs), we reveal that the ORR activity was totally different in various TM-N-CNFs due to difference in surface area, pore size distribution, and conductivity. Moreover, the reason of different carbon structure formation might be catalytic graphitization that generally occurs during heat treatment of mixture of carbon and transition metal at high temperature.^[1,2] Such knowledge is important for the understanding of carbon-based ORR catalysts and the knowledge should attribute the rational design of other carbon-based ORR catalysts to improve performance of them as alternative catalysts.
References
[1] K. Kinoshita, Carbon: Electrochemical and Physicochemical Properties, Wiley, Berkeley, 1988.
[2] X. An, D. Shin, J. D. Ocon, J. K. Lee, Y. Son, J. Lee, Chinese Journal of Catalysis2014, 35, 891-895.

Highly active, durable, and cost-effective transition metal based electrocatalysts for oxygen evolution reaction (OER) in efficient electrochemical energy conversion and storage processes have been developed in recent years. Moreover, there is a growing interest in nitrogen doped carbon materials as non-metal OER electrocatalysts although the transition metal and their oxide have been considered unique active species in OER electrocatalysts.^1,2 However, its mechanistic origin of active species in non-metal OER electrocatalysts is still undefined. In order to investigate catalytic active site and the function of transition metal, we synthesized transition metal N-C catalysts (TM-N-CNFs) via a facile route of electrospinning and pyrolysis, and the electrospun N-C species (N-CNFs) were prepared by removing the metal with carbon etching and acid metal leaching. Following detailed physico-chemical and electrochemical characterizations, N-CNFs exhibit comparable activity and stability than TM-N-CNFs and 20 wt% Ir on Vulcan carbon black. We revealed that the N-C related active site might be mainly responsible for OER activity of non-metal N-C catalysts. This result is important for understanding the non-metal OER catalysts, and it should be attributed to other N-C catalysts with further improved performance.
References
1. Zhao, Y., Nakamura, R., Kamiya, K., Nakanishi, S. & Hashimoto, K. Nitrogen-doped carbon nanomaterials as non-metal electrocatalysts for water oxidation. Nat. Commun. 4, (2013).
2. Ma, T. Y., Dai, S., Jaroniec, M. & Qiao, S. Z. Graphitic carbon nitride nanosheet-carbon nanotube three-dimensional porous composites as high-performance oxygen evolution electrocatalysts. Angew. Chem. Int. Ed. 53, (2014).

Density functional theory (DFT) in conjunction with virtual crystal approximation are used to study the catalytic activity of Pd-Cu disordered binary alloy metal surfaces towards the oxygen reduction reaction (ORR) as a function of the cooper concentration in the alloy. Reactivity is evaluated on the basis of an oxygen reduction reaction (ORR) dissociative mechanism of four steps, it involves the splitting of the O-O bond in O₂ after its adsorption, followed by hydrogenation of atomic O to OH. Then, the OH species undergoes another hydrogenation to yield H₂O. For each concentration of Cu, results for low oxygen coverage are presented at zero cell potential (U = 0), at the equilibrium potential (U = 1.23 V), and at the highest potential (U = 0.80 V) where all reaction steps are exothermic. The results indicate that at the ORR equilibrium potential of 1.23 V, the reactivity of all surfaces is shown to be limited by the rate of OH removal from the surface, while that at a cell potential of 0.80 V, the ORR reactivity of different surfaces is dictated by the strength of oxygen adsorption. The results are compared with other of other non-Pt alloys.

Catalytic electroreduction of carbon dioxide to useful chemical feedstocks is an environmentally and technologically important process, yet the low energy efficiency and difficulty of controlling product selectivity is a big challenge. A part of the latter reasons is that there are presently no catalyst design principles to selectively control CO₂ electroreduction toward a desired product. In this work, we suggest to combine a few activity criteria (CO binding energy, OH binding energy, and H binding energy) that can be collectively used as activity & selectivity determining descriptors to preferentially produce methanol over methane from CO₂ electroreduction. We then apply these concepts to near-surface alloys (NSAs) to propose efficient and selective CO₂ electrochemcial reduction catalysts to produce methanol. The W/Au alloy is identified as a promising candidate to have increased catalyst efficiency (decreased CO₂ reduction overpotential & increased overpotential for unwanted hydrogen evolution) as well as improved product selectivity toward methanol, as compared to conventional Cu catalyst.

Fuel cells are widely considered as a promising source of clean energy. Inadequate device efficiencies and expensive Pt electrocatalysts, however, present technological and economic hurdles that currently restrict the widespread commercialization of fuel cell technology. To overcome these barriers, considerable research has focused on developing more active, lower Pt content electrocatalysts for the kinetically slow oxygen reduction reaction (ORR) at the fuel cell cathode. Recently, researchers have looked to reduce Pt loading via core-shell nanostructures where a Pt shell surrounds the core of a different metal or alloy. In addition to increasing Pt surface area, the core material allows for the tuning of electronic properties of the catalyst by altering the binding energies of reaction intermediates. To select a core material, we utilized a systematic approach for catalyst design developed in our previous study in which it was shown that catalytic activity could be enhanced by properly balancing weakening and strengthening forces of oxygen binding.¹ By selecting a core material that is theoretically predicted to over-weaken the oxygen binding energy on a Pt monolayer on a flat metal surface, the binding energy can then be strengthened towards its optimum value through nanoscale effects and by adjusting shell thickness. Through this approach, iridium was identified as a promising core material. Therefore, this work focuses on examining the performance and properties of Ir-Pt core-shell nanoparticles. Ir-Pt nanoparticles with several shell thicknesses and core sizes were synthesized using a highly scalable, inexpensive polyol method. Particle size and composition were characterized using TEM and STEM-EDS. Electrochemical activities of the Ir-Pt catalysts were compared to synthesized Ir-only and Pt-only nanoparticles as well as to the state-of-the-art commercial standard Pt catalyst, TKK. It was found that activity is affected by the composition of the particles with the best Ir-Pt catalysts achieving specific activities of 680 mA cm^-2_Pt at 0.9 V vs. RHE, on par with state-of-the-art commercial TKK.
1. A. Jackson et al., ChemElectroChem1, 67-71 (2014).

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.

High conductivity and surface area are the most anticipated properties of an electrocatalyst [1]. Herein, we report a noble technique to synthesize highly conductive and microporous N and S-doped carbon from polyaniline (PANI) via a simple template-free hydrothermal method followed by carbonization in presence of iodine. Iodine treatment removes large amount of attached oxygen and other heteroatoms, and as a consequence increases the carbon content. Thus, the iodine treatment decreases catalytically active heteroatom doping, which is unfavourable for oxygen reduction reaction (ORR), but at the same time, significantly increases the electrical conductivity, which is beneficial for ORR [2,3]. In particular, iodine-treated carbonized PANI (CPANI) shows exceptionally high conductivity, about 3 times that of untreated CPANI. Iodine treatment is also found to enhance the micropore surface area of the PANI during carbonization without using any activating agent or hard template. Electrocatalytic study indicates that amazingly the activity of the iodine-treated sample is found to be much better than that of untreated sample. This remarkable upsurge in activity is mainly attributed to the high increase in conductivity and surface area of the iodine-treated sample. The ORR activity is discussed in terms of heteroatom content, surface area and conductivity of the carbon. This convenient innovative approach can open up a window for the designing of highly efficient future fuel cell electrocatalysts.
Reference
[1] B. Fang, M. S. Kim, J. H. Kim and J. S. Yu, Acc. Chem. Res., 2013, 46, 1397.
[2] D.S. Yang, S. Chaudhari, K. P. Rajesh and J. S. Yu, ChemCatChem, 2014, 6, 1236.
[3] D. S. Yang, D. Bhattacharjya, S. Inamdar, J. Park and J. S. Yu, J. Am. Chem. Soc. 2012, 134, 16127

Recently a novel ORR catalyst is reported consisting of uniform Fe₃C nanoparticles wrapped by graphitic layers. Volatile precursors, e.g. cyanamide and ferrocene are used and the synthesis was performed by high pressure pyrolysis. The catalyst in form of hollow porous microspheres is a result of the atom-reorganization process from the vapor phase. More detailed studies are carried out in terms of synthetic parameters, nanostructure formation and ORR active sites. A series of pyrolytic temperatures ranging from 500^oC to 800^oC are employed in the synthesis allowing for the formation of catalysts with tailored structures. Below 500^oC, melamine-rich microspheres were first formed with uniformly dispersed amorphous Fe species. At temperatures above 600^oC, the melamine-rich phase started to evaporate while the initially formed sphere structure confine the following growth of the graphitic phases as well as the encapsulated Fe₃C nanoparticles. Simultaneous formation of Fe₃C nanoparticles and electronically conductive graphitic phases occurred at 700^oC. Around this temperature the synthesized catalysts, with negligible surface nitrogen or iron functionalities, exhibit superior ORR activity and stability. A new type of ORR active sites is proposed originating from the synergies between the carbide nanoparticles and protective graphitic layers. Fuel cell evaluation of the catalysts is conducted using both Nafion- and PBI-based membranes in an operating temperature range from 80 to 180 ^oC with demonstrated activity and durability.

In proton exchange membrane (PEM) fuel cells, carbon supported Pt and Pt alloys are usually used as electrocatalysts. Carbon support is critical to ensure highly dispersion of metal catalyst nanoparticles and high conductivity through the electrode. However, carbon itself is not stable and can be oxidized into carbon-oxygen groups or even to CO₂/CO under PEM fuel cell environment. Once carbon is oxidized, electrocatlysts will degrades. It also causes electric contact issues since electrode thickness may be decreased. Significant efforts have been made to increase the properties of carbon supports. In this talk, we will discuss the design, synthesis and characterization of durable nanocomposite electrocatalysts for oxygen reduction. We first used graphene as a model support, and above it a triple-junction structured nanocatalyst is constructed. This nanocatalyst was tested using our new electrochemical protocol. It demonstrated significantly enhanced durability and activity for oxygen reduction. In combination of characterization and theoretical calculation, the mechanisms behind will be discussed. Based on this model system, we further develop new durable electrocatalysts.

Water splitting for hydrogen fuel generation is considered as a viable pathway to fulfill the demanding energy. Catalysts play a significant role for the water splitting reactions, hydrogen or oxygen evolution reaction (HER or OER), to provide efficient and enough gas evolutions. Among different catalysts, semiconductor-based catalysts are very promising owing to their abundance, low cost, chemical stability, facile and scalable techniques to synthesize them, etc. Between the HER and OER, the OER is more challenging to achieve efficient and durable gas evolution. Co-based catalysts have attracted considerable attention for the OER due to their unique properties. On the other hand, the size and morphology of catalyst is crucial and having high surface area to provide more gas evolution reaction is necessary. Moreover, the facile catalyst synthesis is also important facilitating the practical application. In this talk, we present hydrothermally-grown CoFe₂O₄ nanoparticles (NPs) on 3D carbon fiber papers (CFPs) for highly efficient and durable OER. The CoFe₂O₄ NPs on CFPs show high current with a low onset potential and a very low Tafel slope; orders of magnitude higher current than the CoFe₂O₄ NPs grown on the FTO substrate or the bare CFP substrate with a much lower Tafel slope. Very remarkably, the CoFe₂O₄ NPs on CFPs exhibit very long-time stability of over 15 hours without any morphological change and with preservation of all materials within the electrode. The CoFe₂O₄ NP CFP electrodes were then coupled with a synthesized HER electrode (working as cathode) for overall water splitting in a full system/device. The achieved results show promising potential for practical clean, efficient, cost-effective and durable solar hydrogen generation at large scales using earth-abundant materials with cheap fabrication processes.

Non-precious Fe/N co-modified carbon electrocatalysts have attracted great attention due to their high activity and stability in oxygen reduction reaction (ORR). Compared to iron-free N-doped carbon electrocatalysts, Fe/N-modified electrocatalysts show four-electron selectivity with better activity in acid electrolytes. This is believed relevant to the unique Fe-N complexes, however, the Fe-N structure remains an issue of discussion. We used o,m,p-phenylenediamine as nitrogen precursors to tailor the Fe-N structures in heterogeneous electrocatalysts which contain FeS and Fe3C phases. The electro- catalysts have been operated for 5000 cycles with a small 39 mV shift in half-wave potential. By combining advanced electron microscopy and Mccedil;ssbauer spectroscopy, we have identified the electrocatalytically active Fe-N6 complexes (FeN6,[FeIII (porphyrin)(pyridine)2]). We expect the understanding of the FeN6 structure as a possible acitve site for ORR will pave the way towards new advanced Fe-N based electrocatalysts.

Carbon nano-onions (CNOs) are an emerging class of carbon nanomaterials. CNOs are comprised of concentric graphene shells surrounding a hollow core. The high surface reactivity of CNOs enables their surface modification which is essential for enhanced electrocatalytic activity. In the present study, CNOs were synthesized by thermally annealing detonation nanodiamond powders under helium flow at 1600 °C. Nitrogen-doping was conducted by thermal annealing of CNOs with urea. For the successful doping of nitrogen, CNOs were chemically oxidized by HNO₃ prior to the thermal treatment. This pre-oxidation of CNO was a key step to obtain efficient nitrogen-incorporation. The morphology, microstructure, and chemical states of nitrogen-incorporated CNOs were probed by TEM, Raman and XPS characterizations. The electro-catalytic activity for oxygen reduction reaction was studied using rotating disk electrode (RDE) and rotating ring disk electrode (RRDE) measurements. It was found 3-4% N doped CNOs exhibited a remarkable ORR catalytic activity, which is comparable to commercial Pt/C catalysts.

In this work, we report the synthesis and assessment of a novel non-precious-metal oxygen reduction reaction (ORR) catalyst from pyrolysis of an iron coordinated complex, which manifests superior activity in both alkaline and acidic media. 11,11'-bis(dipyrido[3,2-a:2',3'-c]phenazinyl (bidppz) was selected as a ligand for the formation of a nitrogen-rich iron coordinated coordination polymer (Fe-bidppz), which forms a self-supporting catalyst containing high densities of nitrogen and iron doping by pyrolysis. The catalyst pyrolyzed at 800 0C (Fe-N/C-800) shows the highest ORR activity with onset and half-wave potentials of 923 mV and 809 mV in 0.1 M KOH, respectively, which are comparable to that of Pt/C (half-wave potential 818 mV vs. RHE) at the same catalyst loading. Besides, Fe-N/C-800 catalyst has an excellent ORR activity with the onset and half-wave potential is only 38 mV and 59 mV less than that of the Pt/C catalyst in 0.1 M HClO₄. The optimal Fe-N/C-800 catalyst displays much greater durability and tolerance to methanol than Pt/C. We propose that Fe-N/C-800 catalyst has a considerably high density of surface active sites, because Fe-N/C-800 possesses excellent ORR activity while its specific surface area is not so high. Electrochemical measurements show that Fe-N/C-800 catalyst in KOH and HClO₄ follow the effective four-electrons transfer pathway.

M-N-C structures (M=Fe, Co or Ni) have been extensively explored as electrocatalysts for oxygen reduction reaction (ORR) to substitute expensive Pt based catalysts. In recent days, it is generally accepted that an efficient binding of transition metals with N (M-N_x, x=2 or 4) is a key factor for excellent ORR performance. Nevertheless, control of such binding configurations is not straightfoward, thus expensive metal complexes such as metal-porphyrins or metla-phthalocyanines were often employed. Graphitic carbon nitride (g-C₃N₄) is another candidate that generates M-N structures since it contains a number of N sites that could possibly interact with transition metals. However, the low electrical conductivity and its densely packed structure limit electrocatalytic applications. To overcome those limitations, we employed exfoliated g-C₃N₄ nanosheets to synthesize Co-N-C catalysts. Interconnected hollow Co-N-C nano-composites were prepared by pyrolysis of exfoliated g-C₃N₄ nanosheets containing Co with carbon black. Numerous N moieties of g-C₃N₄ nanosheets act as coordination sites for Co ions to give Co-N_x structures and the exfoliated g-C₃N₄ nanosheets were preferentially assembled on the carbon surface by p-p interactions to direct an efficient incorporation of Co-N to carbon structures. As obtained nano-composites have well dispersed Co-N_x structures over carbon surface and showed high electrical conductivity and surface area stemmed from their interconnected arrangement. This unique approach allowed the materials as excellent electrocatalysts for ORR which exhibit superior catalytic activity and durability comparable to Pt/C.

Fe- and N-doped CNT and graphene are very promising ORR electrocatalyst which could be alternative to Pt/C based electrocatalysts. However, synthesis of CNT and graphene is requires significant elaboration to control the material quality and it is difficult to produce large amount of sample in a single batch. We introduce Fe- and N-containing electrospun carbon nanofibers (Fe-N-CNF) as an ORR electrocatalyst. Electrospinning is suitable for the mass production of ultrathin fibers with the diameter in the range of 100 ~ 300 nm, and it provides a facile method for synthesis of inherently Fe- and N-doped carbon nanofibers by choosing appropriate polymer solution and metal precursor. In addition, we present ball-milling and water vapor activation methods to excavate the more number of active sites buried inside Fe-N-CNFs. Ball-milling process delaminates carbon layers surrounding the embedded metal particles and improved ORR activity by enhanced exposure of Fe-N_x based active sites. In particular, water vapor activation resulted in a substantial improvement of ORR activity up to the level comparable to Pt/C, confirmed via half- and single-cell tests. Embedded iron carbide particles and water vapor synergistically created a hierarchical structure comprising macro-, meso-pores, and graphitic edge defects at a high temperature, which may lead widely exposed Fe-based ORR active sites. Due to the possibility of continuous role-to-role production and high ORR activity performance, it is expected that Fe- and N-modified electrospun carbon nanofiber can be another promising ORR electrocatalyst.

In recent years, the growing scarcity of easily accessible oil and the environmental concerns related to the exploitation of non-conventional oil fields led to intensified efforts to find alternatives for the gasoline-fuelled internal combustion engine currently used in most transportation applications. The proton-exchange membrane (PEM) fuel cell fueled by hydrogen from renewable sources constitutes an efficient and environmentally-harmless alternative to this gasoline-dependent technology, but has yet to overcome a number of challenges to reach full commercialization potential. One of these major hurdles is the excessive cost of the platinum-based catalysts currently used to boost the kinetics of the two half-reactions that occur inside the cell, i.e. the oxidation of H₂ at its anode and the complementary O₂ reduction reaction (ORR) at its cathode. Currently, Pt electrocatalysts account for about 1/3 of the fuel cell stack cost. As ORR is a much slower reaction, even on Pt, compared with the rate of H₂ oxidation on the same metal, the Pt content at the cathode is usually 5 to 10 times that at the anode.
Eliminating Pt from cathode catalysts has been challenging due to the limited number of catalyst candidates with decent prospects for high ORR activity, performance, and durability in acidic medium. Today, Fe/N/C-catalysts obtained from the pyrolysis of molecular precursors are the most promising non-platinum-group-metal (non-PGM) catalysts for the ORR in PEM fuel cells. In Fe/N/C catalysts, the ORR-active metal is in ionic form. The choice of an iron ion at the heart of the main catalytic sites in Fe/N/C catalysts is inspired by the occurrence of the same ion in efficient biological oxido-reductases. Fe/N/C catalysts for PEM fuel cells have been produced according to many synthesis procedures, all of them using iron and nitrogen molecular precursors adsorbed on a carbon support before being pyrolyzed at high temperature. However, the best performing catalysts to date are made using a molecular precursor that decomposes into the carbon support itself concurrently with the active catalytic sites during the pyrolysis step.
One of such family of Fe/N/C catalysts made with iron acetate and ZIF-8, a zinc-methylimidazolate framework, will be analyzed in detail. Particularly, we will report on the effect of increasing the synthesis temperature on their durability in H₂/O₂ and H₂/Air fuel cells. We will also report on the consequences of increasing the synthesis temperature on their ORR activity and performance in fuel cell.

In the field of fuel cell technology one major challenge is to develop efficient and durable non precious metal catalysts (NMPC) for the Oxygen Reduction Reaction (ORR), as an alternative to current bench-mark electrocatalysts based on expensive and limited platinum^[1]. Nitrogen doped carbons (C-N) and especially nitrogen doped carbons modified with transition metals (C-N-M) - such as iron or cobalt - have been shown to be promising candidates as platinum-free catalyst for the oxygen reduction reaction (ORR).^[2-3]
In here, we present a simple and scalable synthetic approach for the synthesis of highly active C-N-Fe catalysts. The synthetic route is based on the use of a polymer network as nitrogen-rich carbon source, which once pyrolyzed in the presence of an iron precursor, leads to the formation porous N-enriched Fe₃C/Fe/C composites. Based on this approach we are able to obtain composites with all the desirable features for efficient ORR catalysis, i.e. high surface area, well interconnected porosity for a good diffusion and high amounts of C-N-Fe sites. The influence of the iron loading and temperature of pyrolysis on the attained structural features and resulting ORR activity was investigated, allowing obtaining highly active and stable catalysts both in alkaline and acid media.
References:
[1] Z. Chen, D. Higgins, A. Yu, L. Zhang, J. Zhang, Energy & Environmental Science2011, 4, 3167.
[2] G. Wu, K. L. More, C. M. Johnston, P. Zelenay, Science 2011, 332, 443.
[3] F. Jaouen, E. Proietti, M. Lefèvre, R. Chenitz, J.-P. Dodelet, G. Wu, H. T. Chung, C. M. Johnston, P. Zelenay, Energy Environ. Sci. 2011, 4, 114.

The sluggish oxygen reduction reaction (ORR) in both proton exchange membrane and anion exchange membrane fuel cells, imposes the need for a catalyst to increase the reaction rate and overall cell efficiency. Pt, due to its high catalytic activity and relative stability, is currently the most used ORR catalyst. However, as a precious metal, Pt is expensive and a limited resource, greatly impacting the fuel cell&’s cost and, as a consequence limiting its mass commercialization.
An advantage of alkaline fuel cells (AFCs) over proton exchange membrane fuel cells (PEMFCs) is that non-precious metals catalysts (NPMC) that are not very efficient for the ORR in acidic environment present higher catalytic activity and stability in alkaline media, even comparable to Pt. Synthesis of NPMCs is often inspired by natural systems. Enzymes, such as laccase, are very efficient ORR catalysts and are known to reduce oxygen at approximately 1.2 V vs. the reversible hydrogen electrode (RHE) under mild pH conditions.
We have synthesized a series of pyrolyzed NPMCs based on Cu, Co, Fe and their bimetallic combinations, and a phthalocyanine-like ligand supported on a carbon black. Catalysts are prepared by covalently attaching a triazolophthalocyanine (TrPc) ligand to the surface of BP2000 carbon black via diazonium coupling, and then adding metal acetate salts. The as prepared catalysts are then pyrolyzed at temperatures ranging from 600 ^oC to 1000 ^oC, treated with diluted H₂SO₄ to remove excess metal, followed by a second pyrolysis step. Catalyst ORR activity and stability in 0.1 M KOH were tested by rotating ring disk electrode (RRDE) experiment.
The bimetallic catalysts based on CoFe and CuFe surpassed the ORR activity of commercial Pt/C, reaching half way potentials E_1/2 of 0.832 V and 0.815 V respectively, compared to 0.808 V vs. RHE of Pt/C.
The samples were characterized using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and x-ray powder diffraction (XRD). RRDE experiments were used to study the effect of catalyst loading, to determine the reaction order and catalyst stability. Ongoing experiments study the performance of the catalysts on a single cell using various anion exchange membranes.

In order to reduce the Pt loading in PEM fuel cell cathodes there are three widely studied options: (1) enhancing Pt mass activity for ORR via alloying or core-shell nanostructuring, (2) improving mass-transport properties of Pt-based cathodes, and (3) developing high performance non-precious metal catalysts (NPMCs) for ORR. In the latter case, studies to date have focused on obtaining high performance in pure oxygen, thereby overstating the case relative to the likely conditions in real fuel cells.
To describe an NPM catalyst layer, we need to identify and obtain estimates of the main parameters such as catalyst loading and thickness, diffusion coefficients, active catalyst surface area, volume fraction of polymer in the agglomerate. It is also critical to use adequately complex experimental data sets to be analyzed and to include as many independently and experimentally determined parameters as are available to reduce the degrees of freedom for fitting. Only then will a modeling study serve to reveal the physical basis of the important performance differences resulting from the use of given catalyst layer structures, on one hand, and different non-precious reaction pathways on the other. Polarization curves measured under a single experimental condition are woefully inadequate as sufficient data sets for most models. Though such curves can be fit (quite easily), the values of physical parameters derived from the fit are not reliable.
In this work, we describe work designed to extend the discussion of NPM-based catalyst layer performance to include the rather significant mass transfer effects that arise from the need to use thicker layers. First, we measure a family of curves obtained for different oxygen partial pressures using catalyst layers of different thicknesses. Then we use simultaneous fits of all of the family of course with only a single variable (and directly derived properties) allowed to be different for the different curves. For this purpose we will evaluate two models as starting points and then compare and interpret the results in light of catalyst characterization and structure measurements. Firstly, a Springer-type cathode model was used to calculate the overpotential, current and concentration distribution inside the catalyst layer. A second approach uses a Sandwich Fuel Cell model, in which we solve the transport equations through the different components of the fuel cell. We provide a reflection on the meaning and statistical robustness of such fits.

The sluggish oxygen reduction reaction (ORR) rate in concentrated phosphoric acid remains a major technological challenge for development of phosphoric acid fuel cells (PAFCs) as well as its congener the high-temperature proton exchange membrane fuel cells (HT-PEMFCs). Despite good physical and chemical properties, phosphoric acid electrolyte adsorbs on the surface of the platinum catalyst and blocks therefore the catalytic active sites for the ORR.
Fluoroalkyl phosphoric acid derivatives as alternative electrolytes might hold the key to overcoming this obstacle. We evaluated commercial fluoroalkyl phosphonic acids as potential electrolytes for PAFCs and HT-PEMFCs. They exhibit high proton conductivity under anhydrous condition and high oxygen solubility. We used theses acids as model systems to study the effect of adsorbates on the selectivity and electrochemical activity of ORR. For our investigations, small amounts of trifluoromethyl phosphonic acid (TFMPA), pentafluoroethyl phosphonic acid (PFEPA), and for comparison phosphoric acid were added into the perchloric acid host solution. Noticeable differences in the Pt voltammograms and significant impact on the kinetic current were observed. The voltammograms for TFMPA and PFEPA show a negative shift of the onset potential of the oxide formation peak. In rotating disk (RDE) and flow cell experiments, an improved ORR activity was measured. Substituting a hydroxyl-group in phosphoric acid by a perfluoroalkyl group reduces the affinity of the electrolyte to specifically adsorb on platinum. Impedance data further supported the findings even for elevated temperatures (60°C and 80°C). The less adsorbing nature of fluoroalkyl phosphoric acid derivatives was also confirmed by in-situ FTIR experiments.

This presentation will provide an overview of the recent progress achieved at Los Alamos National Laboratory in oxygen reduction reaction (ORR) electrocatalysis for polymer electrolyte fuel cells (PEFCs). Since the early work of Jasinski in the 1960s [1], non-precious metal ORR catalysts have received much attention as a possible replacement of Pt-based formulations in both hydrogen and other types of polymer electrolyte fuel cells. Recent breakthroughs in the synthesis of NPMCs, achieved via the use of high-temperature approach (e.g., Lefevre et al. [2]; Wu et al. [3]) make replacement of Pt in ORR catalysts with earth-abundant elements, such as Fe, Co, N, and C, a realistic possibility. A successful ORR catalyst must combine high activity with good long-term stability - a major challenge in the strongly acidic environment of the polymer electrolyte cathode. The NPMC performance depends on the selection of precursors, synthesis chemistry, and catalyst nanostructure. Apart from possible direct participat