Ti3+ in TiO2/Cu2O bilayer film is demonstrated to show energy storage ability. UV-vis absorption spectrum and XPS characterization are carried out to confirm that there are Ti3+ ions formed and that more than 74% Ti4+ ions are reduced to Ti3+ ions after visible-light irradiation. More than 10(-2) C cm(-2) electrons are detected in the bilayer film as determined by H-2 evolution. This study provides a new way to harvest and store excess energy from solar light in the daytime.