Visible light photoelectrochemical responsiveness of self-organized nanoporous WO3 films

Visible light-responsive WO3 nanoporous films with preferential orientation of the (0 0 2) planes were prepared by anodization in neutral F−-containing strong electrolytes. The pore diameter of the self-organized structure was estimated to be in the region of 70–90 nm. Voltages were applied by stepping, which positively influenced passivity breakdown and played a significant role in the formation of self-organized nanoporous films. Under visible light irradiation, the photocurrent density (at 1.6 V vs. Ag/AgCl) and maximum photoconversion efficiency generated by the annealed nanoporous film were 3.45 mA/cm2 and 0.91%, respectively. The annealed nanoporous WO3 films show maximum incident photon-to-current conversion efficiency of 92% at 340 nm at 1.2 V vs. Ag/AgCl. These values are higher than that of annealed compact WO3 film due to the large interfacial heterojunction area. The photoelectrochemical activities and electronic conductivities were also enhanced by annealing crystallization, which removed the recombination centers.