Enhancing Oxygen Evolution Catalytic Performance of Nickel Borate with Cobalt Doping and Carbon Nanotubes

Abstract Metal borates have recently been recognized as alternative earth‐abundant water oxidation catalysts. Herein, we employed solid‐state synthesis to prepare a series of Ni−Co borates, Ni a Co (3‐a) (BO 3 ) 2 , with a Kotoite structure to elucidate the effect of the metal‐doping on the water oxidation activity of metal borates. We performed electrocatalytic and photocatalytic studies to reveal that the catalytic activity could be enhanced with cobalt doping and by using carbon nanotubes (CNTs) as the substrate. Ni 3 B 2 O 6 exhibits an overpotential of 525 mV to reach current densities of 10 mA cm −2 in 1 M KOH solution, while it is 355 mV for Co 2 NiB 2 O 6 _CNT@CC. The overpotential is also 100 mV lower than the pure catalyst (Co 2 NiB 2 O 6 @CC, 445 mV). The as‐prepared samples exhibit significantly enhanced photocatalytic activities for water oxidation under visible‐light irradiation with an increasing cobalt ratio, and an average O 2 evolution rate of up to 1822 μmol h −1 g −1 is obtained for Co 3 B 2 O 6 , which is nearly 1.78, 4.25, and 4.90 times higher than the rates obtained for Co 2 NiB 2 O 6 , CoNi 2 B 2 O 6 , and Ni 3 B 2 O 6 , respectively.