Anion-exchange synthesis of a nanoporous crystalline CoB₂O₄ nanowire array for high-performance water oxidation electrocatalysis in borate solution

Developing nanoporous nanoarray electrocatalysts for efficient water oxidation in environmentally benign media is highly desired but still remains a key challenge. In this communication, we report the fabrication of a nanoporous crystalline CoB₂O₄ nanowire array on Ti mesh (CoB₂O₄/TM) from a Co(OH)F nanowire array on Ti mesh (Co(OH)F/TM) via an anion-exchange reaction. As a three dimensional (3D) catalyst electrode for water oxidation, CoB₂O₄/TM exhibits superior catalytic activity and needs an overpotential of only 446 mV to drive a geometrical catalytic current density of 10 mA cm^-2 in 0.1 M potassium borate (pH = 9.2). Notably, this catalyst also shows strong long-term electrochemical durability with high turnover frequency values of 0.19 and 0.81 mol O₂ per s at overpotentials of 400 and 500 mV, respectively.