Mechanistic Insights into Light-Activated Catalysis for Water Oxidation

The development of catalysts for water oxidation to oxygen has been the subject of intense investigation in the last decade. In parallel to the search for high catalytic performance, many works have focused on the mechanistic analysis of the process. In this perspective, the oxidation of water through light-assisted cycles composed of an electron acceptor (EA), a photosensitizer (PS), and a water oxidation catalyst (WOC) can provide insightful and complementary information with respect to the use of chemical oxidants or to electrochemical techniques. In this minireview, we discuss the mechanistic aspects of the EA/PS/WOC photoactivated cycles, and in particular: (i) the general elementary steps; (ii) the required features and the nature of the PS employed; (iii) the electron transfer processes and kinetics from the WOC to PS+ (hole scavenging); (iv) the detrimental quenching of the PS by the WOC and the alternative mechanistic routes; (v) the identification of WOC intermediates and, finally, (vi) the transposition of the above processes into a dye-sensitized photoanode embedding a WOC.