Single-Site Copper(II) Water Oxidation Electrocatalysis: Rate Enhancements with HPO42- as a Proton Acceptor at pH 8

The complex Cu-II(Py3P) (1) is an electrocatalyst for water oxidation to dioxygen in H2PO4-/HPO42- buffered aqueous solutions. Controlled potential electrolysis experiments with 1 at pH 8.0 at an applied potential of 1.40 V versus the normal hydrogen electrode resulted in the formation of dioxygen (84% Faradaic yield) through multiple catalyst turnovers with minimal catalyst deactivation. The results of an electrochemical kinetics study point to a single-site mechanism for water oxidation catalysis with involvement of phosphate buffer anions either through atom-proton transfer in a rate-limiting O-O bond-forming step with HPO42- as the acceptor base or by concerted electron-proton transfer with electron transfer to the electrode and proton transfer to the HPO42- base.