Bismuth Vanadate and 3D Graphene Composite Photoanodes for Enhanced Photoelectrochemical Oxidation of Water

Bismuth vanadate (BiVO₄) has been one of the most promising photoanodes for the photoelectrochemical (PEC) water oxidation process. Efforts are still on to overcome the drawbacks of this photoanode to enhance the catalytic efficiency and improve the stability. In the present work, three-dimensional graphene (3D-G) was incorporated inside the BiVO₄ matrix, primarily to improve the conductivity of the material. The photoanodes are fabricated with the incorporation of a SnO₂ heterojunction and application of cobalt borate (Co-B_i) as a cocatalyst. The incorporation of 3D-G has enhanced the photocurrent from 0.72 o 1.21 mA cm^-2 in ITO/SnO₂/BiVO₄ and ITO/SnO₂/3D-G-BiVO₄ materials; the photocurrent has been improved from 0.89 to 1.52 mA cm^-2 in ITO/SnO₂/BiVO₄/Co-B_i and ITO/SnO₂/3D-G-BiVO₄. Semiconductor properties are evaluated from the Mott-Schottky measurements, and the charge transfer and transport kinetics of the PEC process are measured from several photoelectrochemical investigations. Both the charge transport and the charge transfer efficiencies are enhanced upon inclusion of 3D-G into the catalyst system. The lifetime of the charge carrier is observed to be increased. The decrease in the decay kinetics of the holes, enhancement in the open-circuit photovoltage (OCPV), and the resulting modulation of the surface states are responsible for the enhancement in the surface charge transfer process due to the inclusion of 3D-G into the catalytic system. Therefore, the additional role of 3D-G in the modulation of the surface states and release of the Fermi level pinning has made the band alignment between the semiconductor and the analyte better, which resulted in enhanced catalytic performance in the photoelectrochemical oxidation of water.