UC Davis

Water splitting is a promising but challenging solution to alleviate the urgent fuel crisis. While the hydrogen-evolution reaction provides the powerful hydrogen gas as a renewable energy source, the high energy barrier of the anodic oxygen-evolution reaction (OER) limits the overall water splitting efficiency. While heavy metal oxides have been found to be the highly efficient OER catalysts, nature employs the oxygen-evolving complex (OEC) in the photosystem II, which consists of a Mn4O5Ca cluster. It generates most of the O2 in the world in a highly efficient and persistent manner. Inspired by the OEC cluster, in this dissertation, we synthesized biogenic manganese oxides (BioMnOx) using a multicopper oxidase Mnx for OER catalysts. Chapter 1 will provide background information about the OER catalysts, the Mnx protein and Electron Paramagnetic Resonance (EPR) spectroscopy. Chapter 2 will explore the potential of the BioMnOx as OER catalysts and the structure- function relationship. Chapter 3 will investigate Co-doping effect of BioMnOx as well as the structural elucidation of Co-doped BioMnOx using X-ray Absorption Spectroscopy (XAS). On the mechanistic side of the story, Chapter 4 investigates the first row transition-metal ion-inhibition effect of Mnx. EPR spectroscopy has been proven to be a powerful tool to selectively probe the active sites and the metal binding sites of Mnx. Understanding the mechanism of the inhibition effect provides fundamental knowledge about the Mnx mecha- nism and provide information for formulating and optimizing BioMnOx synthesis. Chapter 5 extends the usage of EPR spectroscopy to other metalloprotein and inorganic systems.