Photoelectrochemical activity of visible light-responsive BiVO4@La1-xSrxFeO3-δ (x = 0, 0.2, 0.4) heterojunction architectures – Optimizing activity by tuning Fe[sbnd]O bond in perovskites

Abstract

Understanding the mechanism of charge transfer in the straddle heterojunction architecture is the key to designing active materials. To address this issue, BiVO4, La1-xSrxFeO3-δ (x = 0, 0.2, and 0.4) perovskites, and BiVO4@La1-xSrxFeO3-δ straddle heterojunction architectures were synthesized and thoroughly studied. Insertion of Sr2+ ions into A-sites implied the increasing content of Fe4+ ions at B-sites, which increased the strength of the FeO bond, proven by X-ray photoelectron and 57Fe Mössbauer spectroscopies. The improved FeO bond strength in the perovskites had a significant impact on their electrocatalytic activity (La0.8Sr0.2FeO3-δ, 110 mA cm−2; LaFeO3-δ, 20 mA cm−2) and therefore on the photoelectrocatalytic activity of their heterojunction architectures. The increased Fermi levels diminished the band bending degree, which controls the drift direction of the photoinduced charges. Under 1 sun irradiation BiVO4@La0.8Sr0.2FeO3-δ reached 3.2 mA cm−2, indicating 16 times higher photocurrent compared to BiVO4 (0.2 mA cm−2). Based on the results (surface photovoltage, ultraviolet photoelectron spectroscopy, electrochemical impedance spectroscopy, incident photon to current efficiency, and oxygen evolution reaction), the mechanism of photoinduced charge transfer was elucidated. It was concluded that concerted band engineering and enhanced electrocatalytic activity are crucial to reaching an optimal PEC performance.