Moo2 acac 2

Bi(NO₃)₃·5H₂O, VO(acac)₂, MoO₂(acac)₂, oleic acid, oleyl amine, and octadecyl amine were obtained from Sigma Aldrich in Switzerland. Dried ethanol and tetrahydrofuran are the solvents used for this purpose and are procured from Sigma Aldrich and Merck. All chemicals obtained are 99.9% pure and can be used without further purification. The glycerol and potassium phosphate (K₂HPO₄) used to make the phosphate buffer for electrochemical measurement is 99% pure and can be procured from Sigma Aldrich and Fischer in Switzerland. The water used to make the electrolyte has been double distilled.

All chemicals used in this study were of analytical grade and used without further purification. BiVO₄ film was prepared by a modified metal-organic decomposition method with a slight modification from our previous procedure8 (link). Thus, 0.2 M Bi(NO₃)·5H₂O (99.8%; Kanto Chemicals) dissolved in acetic acid (99.7%; Kanto Chemicals), 0.03 M VO(acac)₂ (98.0%; Sigma Aldrich) and 0.03 M MoO₂(acac)₂ (98.0%; Sigma Aldrich) in acetyl acetone (>99.0%; Kanto Chemicals) were prepared as a precursor solution. Then stoichiometric amount of each precursor was mixed to complete a precursor solution. For Mo doping, Bi:(V+Mo)=1:1 atomic ratio was applied for 1% Mo:BiVO₄ films. For fabrication of a BiVO₄ film, 60 μl of solution was dropped on a fluorine doped tin oxide (FTO) glass (2 cm × 2.5 cm) and dried for 15 min in Ar atmosphere. Depending on synthesis condition, 10–80 μl of precursor was used. The FTO glass (TEC 8; Pilkington) was cleaned by using KOH (0.1 M)+ethanol with ratio of 1:5, and washed with copious amount of deionized water and finally stored in acetone before usage. The greenish transparent precursor film was calcined at 550 °C for 25 min to form a yellow BiVO₄ film. After annealing process, 2 cm × 2.5 cm BiVO₄/FTO was split to obtain photoanodes with a net irradiation area of 0.24 cm² connected by silver paste and copper wire and sealed with epoxy resin.