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 (VRHE). 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 VRHE 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.