Surface hole polaron site tuning governs charge carrier separation in BiVO₄ photoanodes

The self-trapping of charge carriers, resulting in the formation of polarons, significantly restricts the separation and transport of charge carriers in photoelectrochemical systems. Herein, using bismuth vanadate as a model photoanode, we propose a surface-selective strategy to regulate hole polarons. Density functional theory calculations predict that substituting bismuth ions with indium ions suppresses hole polaron formation by weakening electron-phonon coupling. This substitution is achieved through a liquid-phase cation exchange method, enabling precise surface modification. The electron paramagnetic resonance, temperature-dependent photoluminescence spectroscopy, in situ irradiation X-ray photoelectron spectroscopy, and femtosecond time-resolved absorption spectroscopy all confirm the suppression of hole polaron formation. After loading co-catalyst, the optimized photoanode achieves a water-splitting photocurrent density of 6.46 mA cm^-2 at 1.23 V versus the reversible hydrogen electrode, with an applied bias photo-to-current efficiency of 2.19%. The unbiased tandem system exhibits a solar-to-hydrogen conversion efficiency of 6%. Here, we show that suppressing surface hole polaron formation facilitates hole carrier release, offering a pathway for enhancing photoelectrochemical performance.