First principle study of transition metal oxide (catalytic) electrodes for electrochemical energy technologies

TTo 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.