Tailoring surface states in WO3 photoanodes for efficient photoelectrochemical water splitting

The dynamics of photo-induced charge carriers are significantly influenced by the surface states of WO3 thin films, which were synthesized by reactive sputtering of tungsten substrates in oxygen plasma. Tailoring the surface properties by (i) hydrogen plasma treatment and (ii) anchoring plasmonic nanoparticles (Au and Ag) altered the light harvesting and charge separation/transport processes of WO3 photoanodes. Upon hydrogen plasma-treatment and coating of noble metal clusters, WO3 films showed enhanced visible light absorption and consequently higher photocurrent density (1.4 mA cm−2) compared to pristine WO3 (0.2 mA cm−2). Enhancement in hydrogen treated WO3 sample was found to be due to the reduction of W(VI) into W(V) centers, which produced substoichiometric WO3−x phases, whereas noble metal particles contributed towards both resonant and non-resonant scattering of incident light thereby increasing photon-to-current conversion efficiency.