Facile morphology control strategy to enhance charge separation efficiency of Mo:BiVO₄ photoanodes for efficient photoelectrochemical water splitting

Bismuth vanadate (BiVO₄) is one of the promising earth-abundant semiconducting materials for photoelectrochemical (PEC) water splitting. However, BiVO₄ suffers from poor charge separation efficiency due to its low carrier mobility and short minority carrier diffusion length. Nanostructured BiVO₄ photoanodes provide a simple way to improve charge separation efficiency. Here, we propose a facile nanostructuring strategy for enhancing the PEC performance of molybdenum-doped BiVO₄ (Mo:BiVO₄) photoanodes by varying the molecular weight of poly(ethylene glycol) (PEG) as a pore former. It was demonstrated that the grain and pore sizes of Mo:BiVO₄ could be controlled by changing the molecular weight of PEG. Nanoporous Mo:BiVO₄ photoanodes with optimized grain and pore sizes revealed an effective charge separation efficiency of 72% and showed the highest photocurrent density of 2.2 mA cm⁻² at 1.23 V versus the reversible hydrogen electrode (V_RHE). After hydrogen treatment and decoration of nickel iron (oxy)hydroxide (NiFeOOH) as an oxygen evolution catalyst, a stable photocurrent density of 4.5 mA cm⁻² with a 10-h duration was achieved at 1.23 V_RHE under standard 1-sun illumination. Our findings clearly suggest new insights on a simple strategy to improve the PEC performance of nanostructured Mo:BiVO₄ photoanodes.