Gallium-doped tungsten trioxide thin film photoelectrodes for photoelectrochemical water splitting

A sol–gel method was used to synthesise different compositions of Ga-doped tungsten trioxide thin films using tungstic acid and gallium(III) nitrate as starting materials. The precursor solutions were drop-casted on FTO glass and annealed at 500 °C for 30 min, and the resulting materials were characterised with SEM, XRD, UV/Vis spectrophotometry and photoelectrochemical analysis. The Ga-doped WO3 samples exhibited a greater grain than undoped WO3, and a monoclinic structure was observed for all WO3 samples. The band gap reduction of WO3 from 2.74 to 2.60 eV indicated the red-shift of light absorption towards the visible light region in the solar spectrum. The donor carrier density for the doped WO3 increased, and the conduction band edge position exhibited a positive shift. The photoactivity of WO3 increased threefold when the photoanode was 20% doped with gallium.