In Situ Derived CoB Nanoarray: A High‐Efficiency and Durable 3D Bifunctional Electrocatalyst for Overall Alkaline Water Splitting

The development of efficient bifunctional catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of extreme importance for future renewable energy systems. This Communication reports the recent finding that room-temperature treatment of CoO nanowire array on Ti mesh by NaBH₄ in alkaline media leads to in situ development of CoB nanoparticles on nanowire surface. The resulting self-supported CoB@CoO nanoarray behaves as a 3D bifunctional electrocatalyst with high activity and durability for both HER (<17% current density degradation after 20 h electrolysis) and OER (<14% current density degradation after 20 h electrolysis) with the need of the overpotentials of 102 and 290 mV to drive 50 mA cm^-2 in 1.0 m KOH, respectively. Moreover, its two-electrode alkaline water electrolyzer also shows remarkably high durability and only demands a cell voltage of 1.67 V to deliver 50 mA cm^-2 water-splitting current with a current density retention of 81% after 20 h electrolysis. This work provides a promising methodology for the designing and fabricating of metal-boride based nanoarray as a high-active water-splitting catalyst electrode for applications.