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Core-shell nanomaterials for enhanced oxygen electrocatalysis

Fuel cells and electrolyzers are emissions-free, electrochemical devices for the interconversion of electricity and chemical energy that hold significant promise towards clean electrification of the transportation sector and carbon-neutral fuel generation, respectively. Unfortunately, both devices suffer from kinetic limitations of the oxygen electrochemical reactions, resulting in performance inefficiency and high catalyst costs and prompting the search for economical, high-performance oxygen electrocatalysts. Core-shell nanostructured catalysts have the potential to decrease precious metal loading requirements over their monometallic counterparts and improve activity via electronic and geometric modifications induced by the core material. This thesis investigates the benefits of the core-shell electrocatalyst motif for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) across several materials systems and electrolyte conditions. First, the performance advantages of Pt-based core-shell nanostructured catalysts for the ORR (occurring at the fuel cell cathode) in acidic media is explored. Utilizing a systematic methodology for catalyst design, we identify Ir@Pt (core@shell) nanoparticles as a promising system for enhanced ORR performance, synthesize Ir@Pt core-shell nanoparticles, and demonstrate an activity and stability enhancement over the commercial state-of-the-art Pt/C catalyst. Building on this demonstration of the core-shell catalyst platform, this thesis further explores core-shell materials for the OER (occurring at the electrolyzer anode). Inspired by the established beneficial effects of Au supports for thin-film OER catalysts, Au@metal-oxide nanoparticles were synthesized and characterized for alkaline OER. These mixed-metal oxide catalysts demonstrated a general activity enhancement with the inclusion of a Au-core, illustrating the successful translation of catalyst/support effects to the core-shell nanoparticle architecture. Finally, the last part of this work focuses on further extending the core-shell morphology to the OER in acidic media. A perspective on the past, present, and future state of OER catalysis in acid is first provided to reveal trends and opportunities for improved catalyst design. Finally, investigations of Sr iridate particles and bimetallic Ir-based thin films are presented and catalysts with significantly improved intrinsic activity over pure Ir-oxide are identified. Overall, this work demonstrates the versatility and promise of the core-shell morphology to achieve high performance catalysts across various reactions, electrolytes, and material chemistries.