Fabrication of an Efficient N, S Co-Doped WO3 Operated in Wide-Range of Visible-Light for Photoelectrochemical Water Oxidation

Abstract

In this work, a highly efficient wide-visible-light-driven photoanode, namely, nitrogen and sulfur co-doped tungsten trioxide (S-N-WO3), was synthesized using tungstic acid (H2WO4) as W source and ammonium sulfide ((NH4)2S), 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 WO3 (N-WO3) or S-N-WO3 by changing the nW:n(NH4)2S ratio below or above 1:5. Both N and S contents increased when increasing the nW: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-WO3 exhibited a significant redshift of the absorption edge with new shoulders appearing at 470–650 nm, which became more intense as the nW:n(NH4)2S ratio increased from 1:5 and then decreased up to 1:25, with the maximum at 1:15. The values of nW: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 WO3 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 WO3. Therefore, benefiting from the S and N co-doping, the S-N-WO3 photoanode generated a photoanodic current under visible light irradiation below 580 nm due to the photoelectrochemical (PEC) water oxidation, compared with pure WO3 doing so below 470 nm.

Co3O4/WO3/C Nanorods with Porous Structures as High-Performance Electrocatalysts for Water Splitting

“…Particularly, the vibrational peaks at 127 and 179 cm –1 are the lattice modes corresponding to the (W 2 O 2 )­n chains . Whereas the peaks appearing in pairs at 266 and 320 cm –1 result from the bending reverberation of the bridging oxygens (δ W–O–W ) . And the other two pairs of peaks with peak broadening at 711 and 801 cm –1 are the distinctive characteristic Raman modes of the monoclinic phase WO 3 crystallites and arising from the stretching vibration of the bridging oxygens (ν W–O–W ) .…”

“…55 Whereas the peaks appearing in pairs at 266 and 320 cm −1 result from the bending reverberation of the bridging oxygens (δ W−O−W ). 56 And the other two pairs of peaks with peak broadening at 711 and 801 cm −1 are the distinctive characteristic Raman modes of the monoclinic phase WO 3 crystallites and arising from the stretching vibration of the bridging oxygens (ν W−O−W ). 57 This appearance of a significant number of active Raman modes is attributed to the distortions in ReO 3 -type structure in original monoclinic phase, as the group theory suggests that two active modes must be demonstrated in this type of structure always.…”

Controllable Synthesis of N2-Intercalated WO3 Nanorod Photoanode Harvesting a Wide Range of Visible Light for Photoelectrochemical Water Oxidation

“…Since TiO 2 was first reported as photoanode by Fujishima and Honda in 1972 [ 5 ], numerous semiconductors (WO 3 , Fe 2 O 3 , Ta 3 N 5 , TaON, etc.) have been employed for photoanode materials [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ].…”

Vapor Deposition-Assisted Sulfurization Synthesis of S-doped WO3 Nanorods and Their Enhanced Photoactivity

“…Several impurity-doped oxides have shown that impurity doping can improve the conductivity and narrow band gap of oxide nanostructures; moreover, impurity doping can increase the roughness and active site number of nanostructures and improve the activity of photocatalysts. [15][16][17] Several works on synthesizing metaldoped WO 3 nanostructures demonstrate an enhanced photocatalytic activity compared to pristine WO 3 . The Nb-doped WO 3 nanoparticles have higher solar energy conversion efficiency than the pristine WO 3, thus enhancing photoactive properties.…”

“…20 Notably, compared with metal doping, several examples of non-metallic doped oxides show better charge separation efficiency and higher efficiency in narrowing optical gaps, contributing to photoactivity enhancement. 15,17,21 Recently, sulfur atoms have been doped into oxide semiconductors with various methods to improve photocatalytic activity. For example, sulfur-doped TiO 2 through different chemical methods has been proposed to significantly enhance the photocatalytic activity compared with pristine TiO 2 .…”