Heterogeneous molecular catalysts (HMCs) with cobalt (Co) active sites are potent for electrochemical oxygen evolution reaction (OER) in the energy conversion applications. Such catalysts are typically operative through the classical redox mediated mechanism, where dynamic equilibriums of Co2+/3+ and Co3+/4+ redox are present before and throughout the OER cycle. The generation of low-valent Co2+ sites is however disadvantageous for proceeding the catalysis. To this end, sulfate groups embedded in graphene were developed to link a model Co-2, 2′-bipyridine complex toward synthesis of a novel Co based HMC, generating a specific CoN2O4S1 coordination moiety. Such molecular Co sites were induced to convert from +2 to +3 oxidation state at the open circuit condition through their proton coupled electron transfer nature. This process ultimately eliminated the generation of Co2+ state from its redox equilibrium, and efficiently improved the turnover frequencies of Co sites toward OER with two-order dependence on the concentrations of OH− ions. This work provides a novel mechanistic perspective for the rational design of high-performance HMCs.
