Synergistic effect of Co doping and borate impregnation on BiVO₄ photoanode for efficient photoelectrochemical water splitting

The performance of photoelectrochemical (PEC) water splitting is hindered by high overpotential and significant recombination of photogenerated charges occurring within the bulk and on the surface of the photoanodes. In this study, we propose a nanoporous photoelectrode, B–Co:BVO, which combines ex-situ Co-doping and surface borate impregnation treatments through simple electrodeposition and immersion methods. As a result, the optimized photocurrent densities of B-BVO and Co:BVO exhibit 1.58 mA/cm² and 1.9 mA/cm², respectively, showing a 1.3 and 1.6-fold increase compared to the bare BVO sample (1.2 mA/cm²) at 1.23 V_RHE. Moreover, the synergistic effect of Co doping and borate impregnation on the BiVO₄ photoanode (B–Co:BVO) achieves the photocurrent density of 2.27 mA/cm², accompanied by a lower onset potential (0.23 V_RHE) and highest IPCE value (42.6 %) at 1.23 V_RHE, maintaining 80.4 % of initial current density value for 18 h in KBi + V electrolyte solution with the enhancement of PEC performance. The proposed charge transfer mechanism in optimum B–Co:BVO photoanodes during the photoelectrochemical water splitting was also studied.