Understanding the fundamentals of electrochemical interfaces will undoubtedly reveal a path forward towards a society based on clean and renewable energy. In particular, it has been proposed that hydrogen can play a major role as an energy carrier of the future. To fully utilize the clean energy potential of a hydrogen economy, it is vital to produce hydrogen via water electrolysis, thus avoiding co-production of CO2 inherent to reformate hydrogen. While significant research efforts elsewhere are focused on photo-chemical hydrogen production from water, the inherent low efficiency of this method would require a massive land-use footprint to achieve sufficient hydrogen production rates to integrate hydrogen into energy markets. Thus, this research has primarily focused on the water splitting reactions on base-metal catalysts in the alkaline environment. Development of high-performance base-metal catalysts will help move alkaline water electrolysis to the forefront of hydrogen production methods, and when paired with solar and wind energy production, represents a clean and renewable energy economy. In addition to the water electrolysis reactions, research was conducted to understand the de-activation of reversible hydrogen electrodes in the corrosive environment of the hydrogen-bromine redox flow battery. Redox flow batteries represent a promising energy storage option to overcome the intermittency challenge of wind and solar energy production methods. Optimization of modular and scalable energy storage technology will allow higher penetration of renewable wind and solar energy into the grid. In Chapter 1, an overview of renewable energy production methods and energy storage options is presented. In addition, the fundamentals of electrochemical analysis and physical characterization of the catalysts are discussed. Chapter 2 reports the development of a Ni-Cr/C electrocatalyst with unprecedented mass-activity for the hydrogen evolution reaction (HER) in alkaline electrolyte. The HER kinetics of numerous binary & ternary Ni-alloys and composite Ni/metal-oxide/C samples were evaluated in aqueous 0.1 M KOH electrolyte. The highest HER mass-activity was observed for Ni-Cr materials which exhibit metallic Ni as well as NiOx and Cr2O3 phases as determined by ex-situ XRD and in-situ XAS analysis. The on-set of the HER is significantly improved compared to numerous binary and ternary Ni-alloys - including state-of-the-art Ni-Mo materials. It is likely that at adjacent Ni/NiOx sites, the oxide site facilitates formation of adsorbed hydroxide (OHads) from the reactant (H2O) thus minimizing the high activation energy of cleaving the H-OH bond to form the Hads HER intermediate on the metallic Ni site. This is confirmed by in-situ XAS studies which show that the synergistic HER enhancement is due to NiOx content and that the Cr2O3 appears to stabilize the composite NiOx component under HER conditions (where NiOx would typically be reduced to metallic Ni0) Furthermore in contrast to Pt, the Ni(Ox)/Cr2O3 catalyst appears resistant to poisoning by the anion exchange ionomer (AEI), a serious consideration when applied to an anionic polymer electrolyte interface. Furthermore a model of the double layer interface is proposed, which helps explain the observed ensemble effect in the presence of AEI. In Chapter 3, Ni-Fe and Ni-Fe-Co mixed-metal-oxide (MMO) films were investigated for oxygen evolution reaction (OER) activity in 0.1M KOH on high surface area Raney-Nickel supports. During investigations of MMO activity, aniline was identified as a useful "capping agent" for synthesis of high-surface area MMO-polyaniline (PANI) composite materials. A Ni-Fe-Co/PANI-Raney-Ni catalyst was developed which exhibits enhanced mass-activity compared to state-of-the-art Ni-Fe OER electrocatalysts reported to date. Furthermore, in-situ XAS analysis revealed charge-transfer effects of MMOs in which the average oxidation state of the OER-active NiOx(OH)y sites is affected by the binary or ternary components (Fe &/or Co). Cyclic voltammetry results show changes in the potential of the Ni2+/3+ transitions in the presence of binary or ternary metals. In-situ XAS analysis confirms that the redox peaks can be attributed to the Ni sites and the shifts in the XANES peak as a function of applied potential indicates that Fe acts to stabilize Ni in the 2+ oxidation state, while Co facilitates oxidation to the 3+ state. The enhanced OER activity of the ternary Ni-Fe-Co/PANI-Raney catalyst is likely due to "activation" of the conductive Ni(III)OOH phase at lower overpotential due to the charge-transfer effects of the cobalt component. The morphology of the MMO catalyst film on PANI/Raney-Ni support provides excellent dispersion of active-sites and should maintain high active-site utilization for catalyst loading on gas-diffusion electrodes. In Chapter 4, the de-activation of reversible-hydrogen electrode catalysts was investigated and the development of a Pt-Ir-Nx/C catalyst is reported, which exhibits significantly increased stability in the HBr/Br2 electrolyte. Initial screening of Rh- and Ru-chalcogenides (oxides, sulfides and selenides) indicates that these non-Pt catalysts do not exhibit sufficient hydrogen reaction kinetics for use in the hydrogen electrode of a H2-Br2 redox flow battery (RFB). However, a standard Pt/C catalyst suffered from rapid and irreversible de-activation upon high-voltage cycling or exposure to Br2. In contrast a Pt-Ir/C catalyst exhibited increased tolerance to high-voltage cycling and in particular showed recovery of electrocatalytic activity after reversible de-activation (presumably from bromide adsorption and subsequent oxidative bromide stripping). Under the harshest testing conditions of high-voltage cycling or exposure to Br2 the Pt-based catalyst showed a trend in stability: Pt

This book covers the recent development of metal oxides, hydroxides and their carbon composites for electrochemical oxidation of water in the production of hydrogen and oxygen as fuels. It includes a detailed discussion on synthesis methodologies for the metal oxides/hydroxides, structural/morphological characterizations, and the key parameters (Tafel plot, Turnover frequency, Faradic efficiency, overpotential, long cycle life etc.) needed to evaluate the electrocatalytic activity of the materials. Additionally, the mechanism behind the electro oxidation process is presented. Readers will find a comprehensive source on the close correlation between metal oxides, hydroxides, composites, and their properties and importance in the generation of hydrogen and oxygen from water. The depletion of fossil fuels from the earth’s crust, and related environmental issues such as climate change, demand that we search for alternative energy resources to achieve some form of sustainable future. In this regard, much scientific research has been devoted to technologies such as solar cells, wind turbines, fuel cells etc. Among them fuel cells attract much attention because of their versatility and efficiency. In fuel cells, different fuels such as hydrogen, CO2, alcohols, acids, methane, oxygen/air, etc. are used as the fuel, and catalysts are employed to produce a chemical reaction for generating electricity. Hence, it is very important to produce these fuels in an efficient, eco-friendly, and cost effective manner. The electrochemical splitting of water is an environmentally friendly process to produce hydrogen (the greener fuel used in fuel cells), but the efficiencies of these hydrogen evolution reactions (cathodic half reaction) are strongly dependent on the anodic half reaction (oxygen evolution reaction), i.e., the better the anodic half, the better will be the cathodic reaction. Further, this oxygen evolution reaction depends on the types of active electrocatalysts used. Though many more synthetic approaches have been explored and different electrocatalysts developed, oxide and hydroxide-based nanomaterials and composites (with graphene, carbon nanotubes etc.) show better performance. This may be due to the availability of more catalytic surface area and electro active centers to carry out the catalysis process.

Fuel cells, one of the most widely studied electrochemical energy conversion devices, together with electrolyzers, a promising energy storage system for natural renewable energy and source of purified hydrogen, have attracted significant research attention in recent years as the demand for energy continues to increase with no end to this energy expansion in sight. However, electrochemical reactions occurring at oxygen electrodes such as the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have very slow kinetics, which has limited the industrialization of both fuel cells and electrolyzers because slow kinetics leads directly high reaction overpotentials. Metal oxides have been widely adopted in terms of electrocatalysts for these oxygen reactions, either as as a support to enhance the stability or activity of platinum, or as the direct catalysts for ORR and OER in alkaline media. However, what is not known is how and why metal oxides as support materials can influence the performance of precious metals through their interactions, what the active sites are for different electrochemical reactions and how to control the desired phases by manipulating the synthesis conditions. This study will probe these very important questions. Chapter 1 of this work provides a background into the ORR/OER mechanism, active sites, and catalyst candidates in electrochemical devices. Chapter 2 presents experimental approaches including material synthesis, and both physical and electrochemical characterization. Chapters 3 and 4 of this study investigate doped metal carbides and metal oxides as support materials for platinum and iridium catalysts for the ORR and OER, respectively, in acidic electrolytes. The Chapter 3 is an investigation of tungsten carbide modified with titanium as a potential non-carbon support for platinum during the ORR in acid media. Chapter 4 discusses the relationship between the synthesis parameters of iridium/iridium oxide supported on titanium-doped tungsten oxide and its durability both ex-situ in a three-electrode cell on a rotating disk electrode (RDE) and in-situ in an operating electrolyzer. Chapter 5 discusses a new method to determine the electrochemically active area of iridium oxide, one of the most common anode catalysts in commercial PEM electrolyzers, in-situ through its electrochemical psuedocapacitance. Chapter 6 probes the performance and function of tin-doped indium oxides (ITO) as a support for platinum ORR catalyst in alkaline media. Metal-support interactions were studied mainly through X-ray photoelectron spectroscopy and electrochemical measurements. Chapter 7 focuses on the electrocatalysis of carbon nanotube (CNT)-supported cobalt oxide for both oxygen reduction and evolution reactions in alkaline media. An optimized procedure to produce a highly stable and active bifunctional ORR/OER hybrid catalyst was developed along with an understanding of the impact of metal oxide anchoring sites and synthesis parameters on catalyst durability. This part of the study provides novel perspectives for the design of carbon-based, hybrid materials and insight into the synthesis-property relationships for these and future electrocatalysts. In summary, this work has studied metal oxides as catalysts and support materials for precious metals during aqueous oxygen reactions. Wherever possible, the fundamental cause for their behavior, including enhanced electrocatalytic activity and durability, was probed thoroughly through physical and electrochemical characterization.

To fulfill the needs for developing the alternative energy technologies, searching for the adequate electrode materials which catalyze the electrochemical reactions utilized in devices such as fuel cell, Li-ion batteries, and related applications such as hydrogen generation and storage, has been a longstanding challenge. Among various catalysts, transition metal oxides (TMO) draw great attentions due to their low-cost, high stability, and, most importantly, a great variety of structures and electrical properties. Nonetheless, studying electrochemical reactions catalyzed by TMO is a challenging task due to the possible multivalent systems, flexible coordinations of lattice atoms, adjustable surface structures and diverse surface species. In the past decades, many innovative approaches have been explored with encouraging results; however, the mechanisms of incorporating the bulk/surface TMO structures in various chemical reactions still remain unclear. In this dissertation, using quantum mechanical calculations, we attempt to improve the fundamental understandings of how structures and electronic properties of TMO materials facilitate the electrochemical reactions of interest. To identify the possible causes for CuO and Cu structures having different selectivity in catalysis, in Chapter 3, we study the CO2 reduction reaction (CO2RR) catalyzed by CuO (111) surface structure, and compare the results with the more widely studied Cu (100) surface. The roles played by the electronic properties of two materials in their selectivity are elucidated. In Chapter 4 and 5, we study the oxygen evolution reaction (OER) for LiCoO2 surface structure. The structures and stabilities of Li-, O-, and H-terminated surface are investigated comprehensively. Based on the results, the formation of H-terminated surface results from Li/H exchange at the solid/liquid interface is proposed (Chapter 4). Along with the findings, we explore the possible mechanisms for the OER for non-metal terminated LiCoO2 surface (Chapter 5). In Chapter 6, we study the oxygen reduction reaction (ORR) for Co3O4 (111) H-terminated surface structure. The possible reaction steps for both four-electron and two-electron pathway are investigated. In Chapter 7, the PO4-decicient LiFePO4/FePO4 structures are investigated to understand how the presence of polyanion defects in the matrices could potentially improve the performance of the materials as electrodes in Li-ion batteries

The oxygen evolution reaction (OER) is the ideal anodic reaction for a photoelectrochemical cell that converts solar energy into chemical fuels; however it is currently limited by catalyst efficiency and cost. In order to overcome these limitations, much effort has been devoted to the discovery of more efficient earth-abundant metal oxide electrocatalysts, particularly mixed-metals oxides, as well as understanding their mechanisms. This thesis addresses both of these challenges. An O2-sensitive fluorescence-based screening assay was developed and arrays of ternary oxide electrocatalysts were examined. Analysis of the intensity of the resulting fluorescence signal allowed for the identification of compositions with high activity. Compositions exhibiting the highest activities were validated through Tafel analyses, and good qualitative agreement was observed between screening results and electrochemical measurements. While Fe is known to improve the activity of Ni oxide catalysts, the incorporation of a third metal into Ni-Fe binary oxides was often observed to further enhance OER activity, with Ni-Fe-Al amorphous oxide showing the highest activity during our initial screening. The previously observed instability led to the investigation of a well-defined NiFeAlO4 inverse spinel oxide as a water oxidation electrocatalyst, where structural analyses confirmed the substitution of Al for Fe lattice sites. A comparison of electrochemical activity against compositionally and structurally relevant oxides, including the known OER catalysts NiO, NiFe 9:1, and NiFe2O4 established NiFeAlO4 as a superior electrocatalyst with no Al leaching, and cyclic voltammograms of the oxides indicated that the electron-withdrawing M+3 ions in the inverse spinels make Ni+2 sites more difficult to oxidize. Furthermore, it was observed that neither of the bimetallic spinel oxides (NiFe2O4 & NiAl2O4) outperformed NiFeAlO4, suggesting a unique synergistic effect between all three metal sites that influences the OER rate determining step. In addition to catalyst discovery, we also pursued mechanistic studies to better understand the dramatic activity enhancement that results when Fe is added to various Ni oxide electrocatalysts. Operando Mössbaurer spectroscopic studies of a 3:1 Ni:Fe layered oxide and anhydrous Fe oxide electrocatalyst was performed. Catalyst materials were prepared by a hydrothermal precipitation method that enabled growth of the oxide catalysts directly on a carbon paper electrode, thereby enhancing charge transport and mechanical stability needed for the operando studies. Fe+4 species are evident in the NiFe-oxide catalyst during steady-state water oxidation, accounting for up to 21% of the total Fe in the catalyst. No Fe+4 is detected under any conditions in the Fe-oxide catalyst. The lifetime of the observed Fe+4 species suggests they do not participate directly in water oxidation; however, their presence has important implications for the promoting effect of Fe in NiFe-oxide electrocatalysts.