An Efficient Photocatalytic Oxygen Evolution System with the Coupling of Polyoxometalates with Bismuth Vanadate

Abstract

In this work, a coupling system consisting of bismuth vanadate (BiVO4) and cobalt-based polyoxometalates (Co-POMs) was developed to enhance the oxygen evolution reaction. Crystallization-driven self-assembly and the wet chemical synthesis method were deployed in synthesizing Co-POMs and monoclinic–tetragonal mixed–phase BiVO4, respectively. The introduction of Co-POMs into a BiVO4-containing mixture significantly enhanced the water oxidation reaction, with a more than twofold increment in the total amount of oxygen evolved. For instance, 461.2 µmol of oxygen was evolved from the system containing 20 mg of Co-POMs compared to 195 µmol of oxygen produced from a pristine BiVO4 system. This extraordinary improvement in the oxygen evolution reaction indicates the existence of a positive synergic effect between BiVO4 and Co-POMs, in which Co-POMs could act as effective cocatalysts to extract photogenerated charge carriers generated by BiVO4 and improve the charge transfer process. However, the amount of oxygen produced was slightly reduced to 440.7 µmol with an increase in AgNO3 loading from 30 mg to 60 mg. This unforeseen phenomenon could be elucidated by the shielding effect of silver particles, in which a higher AgNO3 loading led to a more prominent shielding effect. The presence of silver nanoparticles on post-reaction BiVO4 was confirmed by TEM and XPS analysis. This newly established process scheme provides an insight into the development of an efficient photocatalytic oxygen evolution system in realizing future commercial applications toward green energy production.