“…[8,9] Photoelectrochemical (PEC) water splitting is a promising method for converting endless solar energy into available hydrogen energy in an environmentally friendly way. [10][11][12][13] As the most important component of PEC water splitting, numerous photoelectrodes including n-type semiconductors and p-type semiconductors have been developed, such as TiO 2 , [14,15] BiVO 4 , [16,17] ZnO, [18,19] ZnIn 2 S 4 , [20,21] Fe 2 O 3 , [22,23] WO 3 , [24,25] CdS, [26,27] Cu 2 O [28,29] and CuO. [30,31] In particular, WO 3 has captured wide attention as an outstanding semiconductor photoanode among these photoelectrodes due to the moderate hole diffusion length of about 150 nm, satisfactory electron transmission capability of about 12 cm 2 V À 1 s À 1 and opportune band gap of 2.5~2.8 eV.…”