Reinforcement of a BiVO4 anode with an Fe2O3 underlayer for photoelectrochemical water splitting

Abstract

To understand the consequence of an Fe₂O₃/BiVO₄ heterojunction simply, we fabricated an FTO/Fe₂O₃/BiVO₄ composite photoanode for photoelectrochemical (PEC) water oxidation. We discovered that forming a heterojunction between the Fe₂O₃ underlayer and BiVO₄ upper layer dramatically increased the photocurrent in the low bias region. This photocurrent density increased six-fold from 0.15 mA cm⁻² at 0.6 V vs. the reversible hydrogen electrode (RHE) for BiVO₄ to 0.95 mA cm⁻² at 0.6 V vs. RHE for BiVO₄ with the Fe₂O₃ underlayer. The faradaic efficiency of PEC water splitting was close to 100%, and the molar ratio of the generated hydrogen to oxygen was 2 : 1. However, the photocurrent did not improve in the high bias region; at higher than 1.23 V vs. RHE, the photocurrent density of the FTO/Fe₂O₃/BiVO₄ electrode was lower than that of the bare BiVO₄ electrode. The effects of the Fe₂O₃ underlayer greatly improved the charge separation efficiency, but such improvements were noted only in the low bias region. In addition, the PEC performance was observed to depend on the thickness of the Fe₂O₃ underlayer. The optimised FTO/Fe₂O₃/BiVO₄ electrode was achieved when the Fe₂O₃ underlayer was approximately 350 nm thick and when the BiVO₄ upper layer had approximately the same thickness as the underlayer.