Learning from Nature How to Make Solar Fuels*

Photosystem II (PSII) uses light energy to split water into protons, electrons and oxygen. In this reaction, Nature has solved the difficult chemical problem of efficient four-electron oxidation of water to yield O₂ without significant side reactions. In order to use Nature’s solution for the design of materials that split water for solar fuel production, it is important to understand the mechanism of the reaction. The X-ray crystal and cryo-electron microscopy structures of cyanobacterial PSII provide information on the structure of the Mn and Ca ions, the redox-active tyrosine called tyrosine-Z, chloride and the surrounding amino acids that comprise the oxygen-evolving complex (OEC). The structure of the OEC in the intermediate oxidation states of the catalytic cycle, the binding of substrate water molecules to the OEC and the water oxidation chemistry of PSII will be discussed in the light of biophysical, spectroscopic and computational studies, inorganic chemistry and X-ray crystallographic information. These insights on the natural photosynthetic system are being applied to develop bioinspired materials for photochemical water oxidation and solar fuel production. Our progress on the development of synthetic water oxidation catalysts and their use in materials for artificial photosynthesis will be discussed.