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

Water oxidation is the primary step in both natural and artificial photosynthesis to convert solar energy in into chemical fuels. Herein, we report the first cobalt-based pincer catalyst for electrolytic water oxidation at neutral pH with high efficiency under electrochemical conditions. Most importantly, ligand (pseudo)aromaticity is identified to play an important role in the electrocatalysis. A significant potential jump (~300 mV) was achieved towards a lower positive value when the aromatized cobalt complex was transformed to a (pseudo)dearomatized cobalt species. This complex catalyzes the water oxidation in its high valent oxidation state at a much lower overpotential (~ 340 mV vs. NHE) based on the onset potential (0.5 mA/cm2) of catalysis at pH 10.5, outperforming all the other literature systems. These observations may provide a new strategy for the design of earth-abundant transition metal-based water oxidation catalysts.