Enhanced water oxidation reaction kinetics on a BiVO4 photoanode by surface modification with Ni4O4 cubane

Abstract

Transition-metal–organic molecular catalysts have been regarded as novel, promising and high-efficiency water oxidation cocatalysts for photoelectrochemistry. Here, molecular Ni₄O₄ cubane was prepared and combined with a BiVO₄ nanoplate photoanode to generate a water oxidation cocatalyst. Intensity modulated photocurrent spectroscopy tests verify that the Ni₄O₄ 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 BiVO₄ nanoplates modified with Ni₄O₄ 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 BiVO₄ 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 Al₂O₃ adsorbed layer is constructed on the surface of the nanoplates. Consequently, Ni₄O₄/Al₂O₃/BiVO₄ shows a significant improvement in PEC stability.