O–O bond formation in ruthenium-catalyzed water oxidation: single-site nucleophilic attack vs. O–O radical coupling

evolution. A significant portion of the review is dedicated to the O-O bond formation step as the key step in water oxidation catalysis. The two main pathways to accomplish this step, single-site water nucleophilic attack and O-O radical coupling, are discussed in detail and compared in terms of their potential use in photoelectrochemical cells for solar fuels generation.