Control of crystallization dynamics via vanadium–polyethylene glycol interactions toward high-performance BiVO4 photoanodes

Abstract

BiVO₄ is a promising photoanode material for photoelectrochemical (PEC) water splitting, but its short hole diffusion length significantly limits charge separation efficiency in thick films, which otherwise offer superior light absorption. To overcome this limitation polyethylene glycol (PEG) assisted metal–organic deposition (MOD) has been widely employed to create nanostructured BiVO₄ films. However, reproducibility of morphology and PEC performance under identical PEG conditions remains challenging. Here, we reveal that such reproducibility issues stem from changes in PEG-V ion interactions due to variations in the vanadium oxidation state (V⁴⁺ → V⁵⁺), affecting crystallization kinetics. By developing an Acoustic Energy Assisted Aging (AEA) process to precisely control V oxidation states, we achieved reproducible morphology control from nanoporous structures to isolated large-grain morphologies under identical PEG conditions. Optimized isolated large-grain BiVO₄ films exhibited outstanding crystallinity, ideal composition, enhanced optical absorption, and superior charge transport, delivering high photocurrent densities of 5.8 mA cm⁻² (SOR, 1.23 V vs. RHE) and 5.4 mA cm⁻² (OER with NiFeOOH catalyst). These results represent the highest PEC performance reported for MOD-derived BiVO₄ films, highlighting a novel strategy for highly reproducible and efficient nanostructured photoanodes.