Reduced Mesoporous Co3O4 Nanowires as Efficient Water Oxidation Electrocatalysts and Supercapacitor Electrodes

While electrochemical water splitting is one of the most promising methods to store light/electrical energy in chemical bonds, a key challenge remains in the realization of an efficient oxygen evolution reaction catalyst with large surface area, good electrical conductivity, high catalytic properties, and low fabrication cost. Here, a facile solution reduction method is demonstrated for mesoporous Co₃O₄ nanowires treated with NaBH₄. The high‐surface‐area mesopore feature leads to efficient surface reduction in solution at room temperature, which allows for retention of the nanowire morphology and 1D charge transport behavior, while at the same time substantially increasing the oxygen vacancies on the nanowire surface. Compared to pristine Co₃O₄ nanowires, the reduced Co₃O₄ nanowires exhibit a much larger current of 13.1 mA cm^‐2 at 1.65 V vs reversible hydrogen electrode (RHE) and a much lower onset potential of 1.52 V vs RHE. Electrochemical supercapacitors based on the reduced Co₃O₄ nanowires also show a much improved capacitance of 978 F g^‐1 and reduced charge transfer resistance. Density‐functional theory calculations reveal that the existence of oxygen vacancies leads to the formation of new gap states in which the electrons previously associated with the Co‐O bonds tend to be delocalized, resulting in the much higher electrical conductivity and electrocatalytic activity.