Improving the photoelectrochemical catalytic ability of bismuth vanadate electrodes by depositing efficient Co-catalysts

Depositing effective co-catalysts with an excellent electrocatalytic ability is one of the most efficient ways to solve the serious surface charge recombination for BiVO₄ as the photocatalyst toward water oxidation. Five cheap co-catalysts based on nickel, cobalt and iron were synthesized and deposited on BiVO₄ electrodes using hydrothermal synthesis and electrodeposition methods. The negatively shifted onset potentials and higher photocurrent densities were obtained for the BiVO₄ electrodes with co-catalyst depositions. The best photoelectrochemical performance toward catalysing water oxidation was attained for the NiOOH/BiVO₄ electrode, owing to the better intrinsic properties of NiOOH and the continuous film on the BiVO₄ surface to improve the connection between nanoparticles. The loading amount of NiOOH on the BiVO₄ electrode was optimized by varying the photo-assisted electrodeposition times. The NiOOH/BiVO₄ electrode prepared using 15 min for the photo-assisted electrodeposition showed the highest photocurrent density of 2.10 mA/cm² at 1.23 V versus reversible hydrogen electrode under air mass 1.5 global illumination. The BiVO₄ electrode without the co-catalyst deposition only presented a photocurrent density of 0.30 mA/cm² measured at the same conditions. The negatively shifted onset potential, smaller charge transfer resistance and the better long-term stability were also attained for the NiOOH/BiVO₄ electrode. The excellent photoelectrochemical catalytic ability for the NiOOH/BiVO₄ electrode is primarily owing to the reduced surface charge recombination and the continuous film of NiOOH on the BiVO₄ electrode for achieving better connection between nanoparticles. This study confirms the function of co-catalysts and provides a systematic comparison of cheap co-catalysts deposited on the promising monoclinic BiVO₄ electrode on the enhancement of the photoelectrochemical catalytic performance toward water oxidation. It is also suggested that the adequate deposition amount of the co-catalyst is of the great importance for improving the catalytic ability of the co-catalyst/photocatalyst system.