Boosting charge transport in the BiVO4 photoanode interface modified with an aluminum hydroxide layer for solar water oxidation

Abstract

Solar light-driven photoelectrochemical (PEC) water splitting into hydrogen (H₂) and oxygen (O₂) is a promising technology for the conversion of light energy to clean chemical energy. However, practical applications are currently limited by the slow rate of its oxygen evolution reaction. In this study, n-type monoclinic BiVO₄ photoelectrodes fabricated by a non-vacuum deposition method was developed for an effective PEC system of water oxidation into O₂. Doping Mo ions inside the BiVO₄ bulk and modifying the surface with redox-inert aluminum hydroxide, Al(OH)₃ successfully improved the anodic photocurrent density. The resulting Al-modified Mo:BiVO₄ exhibited a highly efficient anodic photocurrent density of 2.48 mA cm⁻² at +1.23 V vs. RHE, and an applied bias photon-to-current efficiency (ABPE) of 0.65% at +0.8 V vs. RHE was achieved. Thus, this work is unprecedented in finding that modifying the surface of BiVO₄ with an Al species improves its PEC properties and yields high photocurrent density. In fact, surface modification of BiVO₄ with Al(OH)₃ layers significantly increased surface wettability, indicating the strong interaction of H₂O with the BiVO₄ surface. Moreover, Al(OH)₃ as the passivation layers were found to play a significant role in efficient charge carrier transportation on the BiVO₄ interface.