doi:10.1021/acscatal.1c01395engGeer, Ana M.Musgrave III, CharlesWebber, ChristopherNielsen, Robert J.McKeown, Bradley A.Liu, ChangSchleker, P. Philipp M.Jakes, PeterJia, XiaofanDickie, Diane A.Granwehr, JosefZhang, SenMachan, Charles W.Goddard, William A.Gunnoe, T. BrentElectrocatalytic Water Oxidation by a Trinuclear Copper(II) ComplexART-2021-135367We report a trinuclear copper(II) complex, [(DAM)Cu3(μ3-O)][Cl]4 (1, DAM = dodecaaza macrotetracycle), as a homogeneous electrocatalyst for water oxidation to dioxygen in phosphate-buffered solutions at pH 7.0, 8.1, and 11.5. Electrocatalytic water oxidation at pH 7 occurs at an overpotential of 550 mV with a turnover frequency of ∼19 s–1 at 1.5 V vs NHE. Controlled potential electrolysis (CPE) experiments at pH 11.5 over 3 h at 1.2 V and at pH 8.1 for 40 min at 1.37 V vs NHE confirm the evolution of dioxygen with Faradaic efficiencies of 81% and 45%, respectively. Rinse tests conducted after CPE studies provide evidence for the homogeneous nature of the catalysis. The linear dependence of the current density on the catalyst concentration indicates a likely first-order dependence on the Cu precatalyst 1, while kinetic isotope studies (H2O versus D2O) point to involvement of a proton in or preceding the rate-determining step. Rotating ring-disk electrode measurements at pH 8.1 and 11.2 show no evidence of H2O2 formation and support selectivity to form dioxygen. Freeze-quench electron paramagnetic resonance studies during electrolysis provide evidence for the formation of a molecular copper intermediate. Experimental and computational studies support a key role of the phosphate as an acceptor base. Moreover, density functional theory calculations highlight the importance of second-sphere interactions and the role of the nitrogen-based ligands to facilitate proton transfer processes.2021http://zaguan.unizar.es/record/13134610.1021/acscatal.1c01395http://zaguan.unizar.es/record/131346oai:zaguan.unizar.es:131346ACS CATALYSIS 11, 12 (2021), 7223-7240All rights reservedhttp://www.europeana.eu/rights/rr-f/info:eu-repo/semantics/openAccess