Photoelectrochemical (PEC) water splitting is a promising route for direct solar-to-hydrogen (STH) conversion efficiency, but its efficiency is limited by the performance of available photoanodes. Bismuth vanadate (BiVO4), with its ideal ∼2.4 eV bandgap for visible-light absorption, is a leading candidate, yet its practical application is constrained by severe charge carrier separation and sluggish charge transfer kinetics. To this end, we engineered an optimized BiVO4 photoanode by precisely controlling the electrodeposition pathway of the BiOI precursor. This singular parameter governed the formation of compact, uniform BiVO4 films upon annealing, yielding superior PEC performance via a maximized charge separation yield and enhanced surface kinetics. As a result, the FTO/BiVO4/CoPi photoanode achieved a photocurrent density of 5.51 mA cm-2 at 1.23 VRHE, and an applied bias photon-to-current efficiency (ABPE) of 1.58%. Harnessing this optimized photoanode, we constructed a bias-free tandem device by integrating it with a Cu2ZnSnS4 (CZTS) photocathode. This integrated system achieved a solar-to-hydrogen (STH) conversion efficiency of 2.10% with an operating current density of 1.71 mA cm-2. This work provides a viable strategy for developing efficient and stable PEC systems for solar hydrogen production.
Xie et al. (Mon,) studied this question.