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