Sputtered WO3 films for water splitting applications

Abstract Tungsten oxide films with different thickness were grown by sputtering deposition. Analysis of sample morphology showed that the films were constituted by sub-micrometric columnar structures, with diameters in the range 100–500 nm. As-deposited films revealed an almost-amorphous crystal structure and a wide optical band-gap of about 3.28 eV. Thermal annealing at 500 °C was used to promote the formation of a monoclinic WO 3 crystal structure and the reduction of the band-gap. Photo-electrochemical characterizations were used to compare the responses of the different films and to evaluate their possible use in water splitting applications.