title: Bidirectional and unidirectional PCET in a molecular model of a cobalt-based oxygen-evolving catalyst.
abstract: The oxidation of water to molecular oxygen is a kinetically demanding reaction that requires efficient coupling of proton and electron transfer. The key proton-coupled electron transfer (PCET) event in water oxidation mediated by a cobalt-phosphate-based heterogeneous catalyst is the one-electron, one-proton conversion of Co(III)-OH to Co(IV)-O. We now isolate the kinetics of this PCET step in a molecular Co(4)O(4) cubane model compound. Detailed electrochemical, stopped-flow, and NMR studies of the Co(III)-OH to Co(IV)-O reaction reveal distinct mechanisms for the unidirectional PCET self-exchange reaction and the corresponding bidirectional PCET. A stepwise mechanism, with rate-limiting electron transfer is observed for the bidirectional PCET at an electrode surface and in solution, whereas a concerted proton-electron transfer displaying a moderate KIE (4.3 ± 0.2), is observed for the unidirectional self-exchange reaction.
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, USA.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Symes
authors.forename: Yogesh
authors.initials: Y
authors.lastname: Surendranath
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Lutterman
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Nocera
mesh_terms: D002384:Catalysis; D003035:Cobalt / Q000737:chemistry*; D004563:Electrochemistry; D004579:Electron Transport; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*
chemical_list: D003035:Cobalt; D010100:Oxygen