Dual Functions of Optimized FeCo Oxyhydroxide Composition in BiVO₄ Photoanodes with Bi Vacancy for Photocorrosion Inhibition and Improved Photoelectrochemical Performance

Excessive hole-accumulation-induced photocorrosion is considered a key factor that limits the activity of the photoelectrochemical water splitting reaction. In this study, a heterogeneous catalyst was prepared by a simple impregnation method, i.e., modification of different ratios of heterometallic oxyhydroxides (Fe_<i>x</i>Co_1-<i>x</i>OOH) on in situ photoreduction-treated BiVO₄ (Bi-BVO). This work demonstrates for the first time that adjusting the FeCo ratio can greatly enhance the separation, transport, and directional control of electron-hole pairs, thus inhibiting photocorrosion. The Bi-BVO/Fe_0.7Co_0.3OOH composite exhibited a photocurrent density of 0.243 mA cm^-2 at 1.23 V_RHE (4.5 times that of pure BiVO₄ under 1.5 G AM illumination) in a sacrificial agent-free Na₂SO₄ electrolyte. After 20 h of continuous illumination, the photocurrent density of the optimized samples showed negligible attenuation (7.2%). The strong stability under light conditions can be attributed to Fe and Co acting as hole shuttling mediators, which efficiently match the hole generation rate of Bi-BVO and enhance hole transport to the surface active sites. Furthermore, formation of Co-O-V bonds and passivation of surface states, which immobilize V⁵⁺ in the lattice, further inhibit photocorrosion. This bimetallic oxyhydroxide modification strategy provides valuable insights into mitigating photocorrosion and offers an optimization approach for photoelectrochemical water splitting.