An Unusual O-O Bond Formation Route Results in Low Overpotential Water Oxidation at Neutral pH by a Cu <sup>II</sup> Catalyst

Abstract

Low overpotential water oxidation under mild conditions is required for new energy conversion technologies with potential application prospects. Extensive studies on molecular catalysis have been performed to gain fundamental knowledge for rational design of cheap, efficient and robust catalysts. We herein report a CuII complex of tetrakis(4-N-methylpyridyl)porphyrin (1), which catalyzes the oxygen evolution reaction (OER) in neutral aqueous solution with a small onset overpotential of 290 mV. An unusual coupling of two [Por• −CuII−OH] units is proposed. Experimental and theoretical studies verified that such new O−O bond formation strategy accounts for the observed low overpotential water oxidation. In addition to the 4e water oxidation to O2 at neutral pH, 1 catalyzes the 2e water oxidation to H2O2 in acidic solutions. This work presents an efficient and robust Cu-based catalyst for water oxidation in both neutral and acidic solutions. The proposed O−O bond formation mechanism will enrich the knowledge of molecular catalysis.