In a typical synthetic procedure, a solution of 0.15 M Bi(NO3)3•5H2O (0.2910 g, 0.6 mmol) was prepared in a solvent mixture of 1.5 mL ethylene glycol, 2 mL glacial acetic acid, 100 μL 5 mM CoPOM aqueous solution (0.0027 g, 5×10 -7 mol) and 400 μL deionized water for Composite 1. (For the pure BiVO4 reference, a similar synthetic mixture solvent was used containing 1.5 mL ethylene glycol, 2 mL glacial acetic acid and 500 μL deionized water. Other processes are the same as for Composite 1 samples.) After stirring for 15 min, VO(acac)2 (0.3182 g, 1.2 mmol) was added into the above solution, and the resulting solution was stirred at room temperature for 1 h. Then 0.35 g tri-block copolymer (F-108) as structure-directing agent was added in this solution and the resulting solution was stirred at room temperature for 2 h. The resulting precursor solution was deposited on cleaned fluorinedoped tin oxide (FTO) glasses (2 cm × 2 cm) by spincoating. Spin-coating was performed for the ink precursor solution (75 μL per run) at 50 rps for 30 s, followed by baking at 250 °C for 5 min using a hot plate, and then cooling down to room temperature naturally; the above coating and baking process was repeated five times. Finally, samples were annealed in a muffle oven with a heating rate of 3 °C/min and keeping at 450 °C for 1 hour, cooling down to room temperature naturally. After sintering, the sample was immersed in 1 M aqueous NaOH solution for 40 min to remove the excess V2O5, rinsed with deionized water and dried with air flow. Different CoPOM-doping amount thin films were synthesized via the same procedure, except added amounts (50 μL, 150 μL, 200 μL) of CoPOM aqueous solution (5 mM) in the solvent mixture were used instead of 100 μL. Deionized water and CoPOM aqueous solution in the solvent mixture is total 500 μL, for example, 50 μL CoPOM aqueous solution and 450 μL deionized water in the mixture solvent for CoPOM-BiVO4 (50 μL) sample.