Fabrication of an Efficient N, S Co-Doped WO(3) Operated in Wide-Range of Visible-Light for Photoelectrochemical Water Oxidation

In this work, a highly efficient wide-visible-light-driven photoanode, namely, nitrogen and sulfur co-doped tungsten trioxide (S-N-WO(3)), was synthesized using tungstic acid (H(2)WO(4)) as W source and ammonium sulfide ((NH(4))(2)S), which functioned simultaneously as a sulfur source and as a nitrogen source for the co-doping of nitrogen and sulfur. The EDS and XPS results indicated that the controllable formation of either N-doped WO(3) (N-WO(3)) or S-N-WO(3) by changing the n(W):n((NH4)2S) ratio below or above 1:5. Both N and S contents increased when increasing the n(W):n((NH4)2S) ratio from 1:0 to 1:15 and thereafter decreased up to 1:25. The UV-visible diffuse reflectance spectra (DRS) of S-N-WO(3) exhibited a significant redshift of the absorption edge with new shoulders appearing at 470–650 nm, which became more intense as the n(W):n((NH4)2S) ratio increased from 1:5 and then decreased up to 1:25, with the maximum at 1:15. The values of n(W):n((NH4)2S) ratio dependence is consistent with the cases of the S and N contents. This suggests that S and N co-doped into the WO(3) lattice are responsible for the considerable redshift in the absorption edge, with a new shoulder appearing at 470–650 nm owing to the intrabandgap formation above the valence band (VB) edge and a dopant energy level below the conduction band (CB) of WO(3). Therefore, benefiting from the S and N co-doping, the S-N-WO(3) photoanode generated a photoanodic current under visible light irradiation below 580 nm due to the photoelectrochemical (PEC) water oxidation, compared with pure WO(3) doing so below 470 nm.