N2-Intercalated WO3 Nanorods for Enhanced Visible Light-Driven Photocatalysis

By utilizing the dual action of hydrazine hydrate (N2H4) as a structure-directing agent and a nitrogen source for N2 intercalation, we successfully synthesized an efficient visible light-driven photoanode with a nanorod-like structure. Scanning electron microscopy (SEM) results showed that the controlled synthesis of WO3 nanorods could be achieved by varying the amount of N2H4 added. The β value and lattice volume of the monoclinic phase varied significantly with the change in nW:nN2H4 ratio. This is consistent with the increase in nitrogen content, indicating the intercalation of N2 in the WO3 lattice. Ultraviolet-visible diffuse reflectance spectroscopy (DRS) of the N2-intercalated photoanode exhibited a significant redshift in the absorption edge, with a new absorption shoulder appearing at 470-600 nm. This increased proportionally with the nW:nN2H4 ratio until reaching a maximum at 1:2.5, and then gradually decreased towards 1:5. The influence of N2H4 addition is consistent with the variation in nitrogen content, suggesting that the intercalation of N2 into the WO3 lattice leads to a significant redshift of the absorption edge, forming a doping level above the valence band (VB) and below the conduction band (CB), resulting in the appearance of a new absorption shoulder at 470-600 nm. Under visible light irradiation, the N2-intercalated WO3 photoanode exhibited anodic current generation under illumination below 530 nm wavelength, while the unmodified WO3 photoanode showed photocatalytic (PEC) water oxidation reaction under illumination below 470 nm wavelength. The high incident photon-to-current conversion efficiency (IPCE) of the WO3-2.5 photoanode is attributed to the efficient electron transfer within the WO3 nanorod film.