Boosting the Photoactivity of BiVO₄ Photoanodes by a ZnCoFe-LDH Thin Layer for Water Oxidation

Monoclinic bismuth vanadate (BiVO₄ ) has been used as an efficient photoanode material for photoelectrochemical water oxidation owing to its suitable band gap and nontoxicity. Nevertheless, the practical application of BiVO₄ photoanode has been severely limited by the surface charge recombination and sluggish kinetic, which leads to the obtained photoactivity of BiVO₄ is much lower than its theoretical value. In this case, ZnCoFe-LDH thin layer is conformally decorated on the porous BiVO₄ photoanode through a simple electrodeposition process. The results show that a boosted photoactivity and a remarkably enhanced photocurrent density (3.43 mA cm^-2 at 1.23 V_RHE ) are attained for BiVO₄ /ZnCoFe-LDH. In addition, the optimized BiVO₄ /ZnCoFe-LDH photoanode exhibits significant negative shift in the onset potential (0.51 V_RHE to 0.21 V_RHE ), promotes charge separation efficiency (49.3% to 60.4% in the bulk, 29.6% to 61.9% on the surface at 1.23 V_RHE ) and enhanced IPCE efficiency (25.5% to 54.7% at 425 nm) compared with that of bare BiVO₄ photoanode. It is demonstrated that the boosted photoactivity of BiVO₄ /ZnCoFe-LDH photoanode is mainly ascribed to the synergy effects of the formation of p-n heterojunction between ZnCoFe-LDH and BiVO₄ to accelerate the photogenerated charge transfer and separation, broaden light absorption, as well as promote the surface water oxidation kinetics.