Improving the Charge Kinetics of BiVO4-Based Photocatalysts by Surface Modification

Abstract

Solar energy conversion efficiency can be determined by the properties of a photocatalyst. Recently, bismuth vanadate (BiVO4) has emerged as a potential photocatalyst due to its suitable band structure and superior visible light response. However, severe charge recombination, poor electron transportation and sluggish surface reaction kinetics prevent BiVO4 from reaching its potential. Herein, different tactics regarding its modification were employed to improve the photocatalytic capability of BiVO4. The research initially investigated the interfacial contact between BiVO4 and reduced graphene oxide (rGO). Two BiVO4/rGO composites with BiVO4 particles extensively or insufficiently contacted with rGO sheets were fabricated. An enlarged interfacial contact greatly improved charge separation and electron transfer efficiency as well as band alignment within the BiVO4/rGO composite, hence delivering a greater photocurrent during photoelectrochemical (PEC) testing. However, an excessive rGO coverage also resulted in higher hydrophobicity, which reduced the water miscibility and lowered the capability toward photocatalytic O2 production. Consequently, the balance between electron shuttling and the water miscibility should be considered depending on the photoreaction mode. Subsequently, a CoOx co-catalyst was loaded onto a dual-faceted BiVO4 which possessed distinct levels of exposed {010} and {110} facets. Enhancement provided by the co-catalyst was depended on both its deposit location and the ratio of {010}/{110} facet exposure. When selectively deposited on the hole-accumulating {110} facet or loaded on {010}-dominant BiVO4 particles, CoOx functioned more effectively in alleviating surface hole trapping and reducing the charge recombination, thus delivering a higher photocatalytic activity. Finally, the bimetallic phosphide, NiFePx, was studied as a BiVO4 co-catalyst for PEC performance. NiFePx was immobilized onto a BiVO4 photoanode via a hydrothermal method followed by a phosphorization process. The NiFePx passivated the surface states of BiVO4 and provided a greater driving force to initiate water oxidation. Accordingly, surface charge recombination was suppressed, and charge transfer and charge injection efficiency were promoted. In summary, surface modification strategies can endow BiVO4-based photocatalysts with a good capacity for water splitting with rational manipulation of their interfacial properties providing even greater benefits.