Bio-Inspired Calcium-Containing Manganese Catalysts for Water Oxidation

Increasing concerns on the anthropogenic climate change, rising global energy demands, and diminishing fossil fuels have urged the search of alternative carbon-neutral and sustainable energy resources, among which solar energy stands out as the most promising target since it is the largest exploitable resource. However, its nature of diurnal variation, intermittence, and unequal distribution requires efficient and cost-effective capture, conversion, and storage. Generation of chemical fuels, such as hydrogen, from solar energy input represents an appealing approach to meet this goal. An ideal scheme would tap hydrogen from the splitting of water with concomitant evolution of oxygen. Due to the nature of the four-proton and four-electron process, water oxidation is the bottleneck of the overall water splitting process. Nature catalyzes water oxidation using an oxygen-evolving complex (OEC) in Photosystem II. This project aims at mimicking the OEC center to prepare and investigate bimetallic Mn-Ca catalysts for water oxidation catalysis. Calcium has been reported to be critical in water oxidation by OEC, however its functional role has not been well studied. By positioning a calcium atom in the secondary coordination sphere of manganese in molecular scaffolds, we are able to systematically probe the functional role of calcium at the molecular level. Our project will prompt the development of water oxidation catalysis and benefit artificial photosynthesis at large