Development and Mechanistic Study of Copper-Based Water Oxidation Catalysts

Abstract

Water oxidation is a challenging reaction that has great importance for alternative energy and fuel generation. Although several water oxidation catalysts have been discovered, much improvement is needed for the technology to be viable on a global scale. In recent years, there has been focus in the development of catalysts with earth-abundant elements and, subsequently, cobalt, nickel, manganese, and iron catalysts have been reported. This dissertation discusses the discovery and study of the first reported copper-based water oxidation electrocatalyst. This catalyst is a molecular species with bipyridine and hydroxide ligands. Study of this catalyst has shown that it is among the fastest homogeneous water oxidation catalysts yet reported, with a turnover frequency of ~100 s-1. The catalyst is also relatively robust and can undergo at least 30 turnovers. Solutions of the catalyst are generated easily by reaction of bipyridine and a copper salt in a 1:1 ratio in water, followed by addition of hydroxide to obtain a solution between pH 11 and 13. The catalytic mechanism has been investigated through spectroscopic analysis to understand the speciation, electrochemical kinetics, a ligand study, and reactivity studies. While further work is still needed, these investigations have laid the groundwork for a basic understanding of the mechanism. A phenanthroline-based catalyst has also been successfully immobilized on a pyrolytic graphite electrode through physisorption. The heterogeneous catalyst shows remarkable similarities to its homogeneous counterpart. It operates at the same overpotential and activity level and displays similar pH dependent behavior. This system has important implications for catalyst immobilization in general, which is an important area of study for the development of more industrially relevant catalysts.