Heptanuclear Co, Ni and mixed Co-Ni clusters as high-performance water oxidation electrocatalysts

Herein we report a comparative study for a series of cheap, robust, and efficient water oxidation electrocatalysts made up of the heptanuclear disk clusters ([M7(OH)6L6](ClO4)2·solvent (M = Co, Ni or mixed Co-Ni) and L = 2-ethoxy-6-(N-methyl-iminomethyl)phenolate) for renewable energy production. Experiments performed on the three complexes immobilized on conductive substrates reveal the catalytic efficiency in the order Co-Ni > Ni > Co based on threshold and overpotentials as well as electro-impedance parameters. Remarkably, the Co-Ni mixed metal cluster shows low onset overpotential of only 270 mV and a small Tafel slop of 53.4 mV/dec. Moreover, the Faradaic efficiency exceeds 90% for the Co-Ni cluster. Their characteristics are major improvements on those reported for transition metal complexes. These complexes could be proposed as promising electrocatalysts for water oxidation reaction.