Aromaticity Driven Electrocatalytic Water Oxidation by a Phosphorus-Nitrogen PN3-Pincer Cobalt Complex

Water oxidation is the primary step in bothnatural and artificial photosynthesis to convert solar energy in intochemical fuels. Herein, we report the first cobalt-basedpincer catalyst for electrolytic water oxidation at neutral pH with high efficiencyunder electrochemical conditions. Most importantly, ligand (pseudo)aromaticityis identified to play an important role in the electrocatalysis. A significantpotential jump (~300 mV) was achieved towards a lower positive value when thearomatized cobalt complex was transformed to a (pseudo)dearomatized cobaltspecies. This complex catalyzes the water oxidation in its high valentoxidation state at a much lower overpotential (~ 340 mV vs. NHE) based on theonset potential (0.5 mA/cm2) of catalysis at pH 10.5, outperformingall the other literature systems. These observations may provide a new strategyfor the design of earth-abundant transition metal-based water oxidationcatalysts.