Sputtered WO3 films for water splitting applications

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 WO3 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.