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

A highly efficient visible-light-driven photoanode, N-2-intercalated tungsten trioxide (WO3) nanorod, has been controllably synthesized by using the dual role of hydrazine (N2H4), which functioned simultaneously as a structure directing agent and as a nitrogen source for N-2 intercalation. The SEM results indicated that the controllable formation of WO3 nanorod by changing the amount of N2H4. The b values of lattice parameters of the monoclinic phase and the lattice volume changed significantly with the n(W): n(N2H4) ratio. This is consistent with the addition of N2H4 dependence of the N content, clarifying the intercalation of N-2 in the WO3 lattice. The UV-visible diffuse reflectance spectra (DRS) of N-2-intercalated exhibited a significant redshift in the absorption edge with new shoulders appearing at 470-600 nm, which became more intense as the n(W):n(N2H4) ratio increased from 1:1.2 and then decreased up to 1:5 through the maximum at 1:2.5. This addition of N2H4 dependence is consistent with the case of the N contents. This suggests that N-2 intercalating into the WO3 lattice is responsible for the considerable red shift in the absorption edge, with a new shoulder appearing at 470-600 nm owing to formation of an intra-bandgap above the VB edges and a dopant energy level below the CB of WO3. The N-2 intercalated WO3 photoanode generated a photoanodic current under visible light irradiation below 530 nm due to the photoelectrochemical (PEC) water oxidation, compared with pure WO3 doing so below 470 nm. The high incident photon-to-current conversion efficiency (IPCE) of the WO3-2.5 photoanode is due to efficient electron transport through the WO3 nanorod film.

Automated summary

A highly efficient visible-light-driven photoanode, N-2-intercalated tungsten trioxide (WO3) nanorod, was successfully synthesized by using hydrazine (N2H4) as a structure directing agent and as a nitrogen source for N-2 intercalation. Controllable formation of WO3 nanorod was achieved by changing the amount of N2H4. The addition of N2H4 resulted in a redshift in absorption edge and the appearance of new shoulders in the UV-visible diffuse reflectance spectra.