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

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-delta (x = 0, 0.2, and 0.4) perovskites, and BiVO4@La1-xSrxFeO3-delta 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 Fe-O bond, proven by X-ray photoelectron and 57Fe Mo center dot ssbauer spectroscopies. The improved Fe-O bond strength in the perovskites had a significant impact on their electrocatalytic activity (La0.8Sr0.2FeO3-delta, 110 mA cm-2; LaFeO3-delta, 20 mA cm-2) and therefore on the photoelectrocatalytic activity of their heterojunction archi-tectures. 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-delta 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, ul-traviolet photoelectron spectroscopy, electrochemical impedance spectroscopy, incident photon to current effi-ciency, 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.

Automated summary

Understanding the charge transfer mechanism in the straddle heterojunction architecture is crucial for designing active materials. The synthesis and thorough study of BiVO4, La1-xSrxFeO3-delta perovskites, and BiVO4@La1-xSrxFeO3-delta straddle heterojunction architectures addressed this issue. The insertion of Sr2+ ions into A-sites increased the Fe4+ ions at B-sites, strengthening the Fe-O bond and improving electrocatalytic activity. The increased Fermi levels reduced band bending and enhanced the drift direction of photoinduced charges, leading to significantly higher photocurrent in the heterojunction architecture.