Enhanced Photoelectrochemical Water-Splitting Reaction by a Nano-dendritic BiVO ₄ Photoanode Coupled with Nanoparticles of β-FeOOH

In response to the urgent demand for sustainable and clean energy solutions, photoelectrochemical (PEC) water splitting is a leading approach for effectively producing green hydrogen (H 2 ). BiVO 4 photoanodes are among the best materials available for visible-light-driven water oxidation. However, their performance is hindered by rapid charge-carrier recombination and inadequate photostability. Therefore, the surface of nanodendritic BiVO 4 is modified with an iron oxyhydroxide (β-FeOOH) cocatalyst, which is obtained via a pH-controlled dip-coating method. A saturation photocurrent density of 2.73 mA cm –2 at +1.4 V versus RHE under AM 1.5 G illumination is observed, which shows a 1.8-fold enhancement over that of pristine BiVO 4 . The applied bias photon-to-current efficiency (ABPE) reflects a striking 3.45-fold increment for the heterojunction. The incident photon-to-current conversion efficiency (IPCE) measurements indicate that the heterojunction is twice as efficient as pristine BiVO 4 . The BiVO 4 /β-FeOOH heterojunction has significantly facilitated interfacial charge transfer, resulting in an increase in charge transfer efficiency from 35.73% to 58.24%, which reflects a noticeable reduction in electron–hole recombination. The oxidation of water molecules proceeds via a peroxo intermediate, which is confirmed by Fourier transform infrared (FTIR) spectroscopy. The Mott–Schottky analysis shows an enhanced charge carrier density, 3.61 times for the optimized BiVO 4 /FeOOH heterostructure. According to the band edge alignment determined by ultraviolet photoelectron spectroscopy (UPS) analysis, a type-II heterojunction is formed between BiVO 4 and β-FeOOH, which efficiently separates the photogenerated excitons and promotes water oxidation, boosting its PEC performance. Hence, this study demonstrates that integrating the β-FeOOH cocatalyst is an effective strategy for overcoming the intrinsic limitations of BiVO 4, paving the way for advancing the development of efficient photoanodes for solar-driven H 2 production.