Synergistic Effect of Co Doping and Borate Impregnation on BiVO4 Photoanode for Efficient Photoelectrochemical Water Splitting

Abstract

Photoelectrochemical (PEC) water splitting has become an attractive way to convert solar energy into ecofriendly and green hydrogen energy. Bismuth vanadate (BiVO4) is a promising n-type semiconductor photoanode due to the advantage of the proper band position with a bandgap of ~ 2.4 eV for the water oxidation reaction in the PEC system. However, it needs to overcome the problems such as low electron-hole separation yield, surface charge recombination and slow water oxidation kinetics. Therefore, surface modification by impregnation method and doping strategies can effectively improve the electron-hole separation yield, surface charge recombination, and slow water oxidation kinetics, thereby PEC performance of the BiVO4 photoanodes can be enhanced. In this study, polycrystalline BiVO4 photoanodes were successfully fabricated on FTO substrate by electrodeposition method. Moreover, Co ions doping strategy (Co:BVO) and borate impregnation on BiVO4 (B-BVO) were conducted to enhance the photoelectrochemical performance of BiVO4 photoanode. As a result, the optimized BVO photoanode showed the photocurrent density of 0.58 mA/cm2 and 1.2 mA/cm2 with front-side and back-side illuminations at 1.23 V versus reversible hydrogen electrode (vs. RHE) under AM 1.5 G illumination in 1 M KBi electrolyte (pH-9.3), respectively. Besides, the optimized photocurrent densities of Co:BVO and B-BVO were 1.58 mA/cm2 and 1.9 mA/cm2 , showing which were almost 1.32 and 1.6-times higher than bare BVO sample with the back-side illuminations. In addition, the synergistic effect of those Co doping and borate impregnation on BiVO4 photoanode (B-Co:BVO) achieved the photocurrent density of 2.27 mA/cm2 and highest IPCE value of 42.6% at 1.23 VRHE, keeping 83.5 % of initial current density value for 10 h in KBi + V electrolyte solution with the enhancement of photoelectrochemical performance.