Development and Study of Heterogeneous Earth-Abundant Oxygen Evolving Catalysts for Use in Diverse Electrolyte Environments

Abstract

The realization of grid-scale utilization of intermittent, carbon-neutral power sources (such as solar and wind) hinges on the development of efficient methods for interconverting energy between electrical and chemical forms. The electrolysis of water to form H2 and O2 is one of the most extensively studied energy-storing transformations, owing to the large free energy change of the reaction, the ubiquity of water, and the nontoxicity of the products. Water-splitting is composed of two redox half-reactions: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Of these, the latter is more kinetically challenging and thus significant work has been devoted to the development of electrocatalysts to facilitate this oxidation half-reaction. This thesis builds on existing work in the field of OER catalysis by exploring the behavior of OER catalysts across a diverse range of environments, beyond the highly alkaline electrolytes in which the reaction has traditionally been studied. We begin by addressing the challenges faced by OER catalysis in seawater. In particular, strategies for selectively performing OER while suppressing undesirable halide oxidation are explored. As part of this investigation, we study distinct roles played by both electrolyte and catalyst composition. Next, we turn to the study of OER in acid. Here we seek to understand the relationship between the identity of different buffering species in the electrolyte and the long-term stability of a multimetallic oxide catalyst. To develop a better understanding of the rate-limiting chemical step of OER catalysis on cobalt oxide-based catalysts, we develop photocatalyst systems for use in transient absorption spectroscopy. Finally, we use insights gleaned from previous work to propose and explore novel reactivity on cobalt-oxide-based OER catalysts. We demonstrate that these materials are capable of totally oxidizing multi-carbon substrates and show how this reactivity may be exploited for use in biomass fuel cells.