Dual-Functional Surfactant-Templated Strategy for Synthesis of an In Situ N -Intercalated Mesoporous WO Photoanode for Efficient Visible-Light-Driven Water Oxidation.

N -Intercalated crystalline mesoporous tungsten trioxide (WO ) was synthesized by a thermal decomposition technique with dodecylamine (DDA) as a surfactant template with a dual role as an N-atom source for N intercalation, alongside its conventional structure-directing role (by micelle formation) to induce a mesoporous structure. N physisorption analysis showed that the specific surface area (57.3 m  g ) of WO templated with DDA (WO -DDA) is 2.3 times higher than that of 24.5 m  g for WO prepared without DDA (WO -bulk), due to the mesoporous structure of WO -DDA. The Raman and X-ray photoelectron spectra of WO -DDA indicated intercalation of N into the WO lattice above 450 °C. The UV/Vis diffuse-reflectance spectra exhibited a significant shift of the absorption edge by 28 nm, from 459 nm (2.70 eV) to 487 nm (2.54 eV), due to N intercalation. This could be explained by the bandgap narrowing of WO -DDA by formation of a new intermediate N 2p orbital between the conduction and valance bands of WO . A WO -DDA-coated indium tin oxide (ITO) electrode calcined at 450 °C generated a photoanodic current under visible-light irradiation below 490 nm due to photoelectrochemical water oxidation, as opposed to below 470 nm for ITO/WO -bulk. The incident photon-to-current conversion efficiency (IPCE=24.5 %) at 420 nm and 0.5 V versus Ag/AgCl was higher than that of 2.5 % for ITO/WO -bulk by one order of magnitude due to N intercalation and the mesoporous structure of WO -DDA.