Enhanced water oxidation reaction kinetics on a BiVO ₄ photoanode by surface modification with Ni ₄ O ₄ cubane

Transition-metal-organic molecular catalysts have been regarded as novel, promising and high-efficiency water oxidation cocatalysts for photoelectrochemistry. Here, molecular Ni ₄ O ₄ cubane was prepared and combined with a BiVO ₄ nanoplate photoanode to generate a water oxidation cocatalyst. Intensity modulated photocurrent spectroscopy tests verify that the Ni ₄ O ₄ cubane catalyst not only facilitates the kinetics of water oxidation, but also suppresses the recombination of carriers at the electrolyte/photoanode interface. As expected, the BiVO ₄ nanoplates modified with Ni ₄ O ₄ cubane show superior activity (3.9 mA cm ^-2 at 1.23 V vs. RHE), with a more than twice increased activity compared to the BiVO ₄ nanoplates. Meanwhile, the onset potential also generates a 350 mV cathodic shift. In order to prevent desorption of the molecular catalyst due to the weak binding between the semiconductor and molecular catalyst, an Al ₂ O ₃ adsorbed layer is constructed on the surface of the nanoplates. Consequently, Ni ₄ O ₄ /Al ₂ O ₃ /BiVO ₄ shows a significant improvement in PEC stability.