Investigation of interfacial charge transfer kinetics of photocharged Co-Bi modified BiVO4 using scanning electrochemical microscopy (SECM)

Bismuth vanadate (BiVO4) is a promising photoanode for photoelectrochemical (PEC) water oxidation process. However, fast charge recombination and sluggish surface kinetics limit its application. Here, we demonstrate improvement in the PEC performance due to cobalt borate (Co-Bi) incorporation in BiVO4 and due to prolonged exposure in 1 sun illumination. Photocurrent is improved from 0.96 mAcm−2 to 1.95 mAcm−2 at 0.8 V upon Co-Bi incorporation, which plays as a hole collector and hole reservoir. Photocharging treatment leads to further improvements in the photocurrent from 0.96 mAcm−2 to 1.31 mAcm−2 and 1.95 mA cm−2 to 2.63 mAcm−2 for BV and BV/Co-Bi-3 respectively. The scanning electrochemical microscope (SECM) study reveals the improvement in the interfacial hole transfer kinetics from 7.23 × 10−3 to 9.05 × 10−3 cm s−1 and 9.61 × 10−3 to 11.76 × 10−3 cm s−1 for BV and BV/Co-Bi -3, respectively, upon photocharging. The SECM mapping of the interface reflects the localized photoelectrochemical activity of photoanodes. The improvements in the feedback photocurrents upon the Co-Bi incorporation confirm the improved interfacial charge transfer kinetics. Photocharging leads to further improve in the photocurrent for BV and BV/Co-Bi.