CW and Pulse EPR Studies of Cobalt-Catalyzed Water Oxidation

Recent reports claim that an "artificial leaf", able to harvest up to 4.7% of incident photonic energy for water-splitting and solar fuel production, has been made using only earth abundant elements. These types of systems have the potential to revolutionize modern energy storage techniques, cheaply converting solar energy into H2-based fuels. They will dictate how effectively solar power can be deployed as a primary source of energy at the local level. At its heart, the system relies on a cobalt-based, water-oxidation catalyst to complete the difficult oxygen half of the water-splitting reaction. In order to make these systems even more efficient and cost-effective -- and enable solar to compete with carbon-based sources of energy -- we must understand how and why they work so well in a rigorous and detailed way.;To gain insight into the structure and mechanism of water oxidation by this material, CW and pulse EPR spectroscopy was used to investigate the cobalt centers of these catalysts and other related Co-based water oxidation materials and model complexes. Chapters 1 and 2 provide an introduction to the system and methods used in this work. Chapter 3 details how we used EPR to identify a rare Co(IV) species only present during and immediately after water splitting takes place.;Chapter 4 of this dissertation builds upon these insights and combines EPR and electrokinetic assays to provide a detailed mechanism and structural description of the system. In chapter 5, we characterized a structural model complex of CoPi. Using a combined spectroscopic and DFT approach, we explored structure-function relationships in this model system and determined that it is probably the highly localized nature of the unpaired electron in CoPi that enables it to oxidize water so well.;Chapter 6 looks at another cobalt-based water oxidation catalyst for the purpose of comparing its properties to CoPi. Finally, Chapter 7 attempts to synthesize the data we have observed to provide a means for improving this important system.