Enhanced energy storage of a UV-irradiated three-dimensional nanostructured TiO2–Ni(OH)2 composite film and its electrochemical discharge in the dark

Oriented rutile TiO2 nanoarrays on transparent conductive fluorine-doped tin oxide (FTO) substrates were prepared by a facile hydrothermal synthesis. A three-dimensional (3D) nanostructured TiO2–Ni(OH)2 composite film was further constructed by a novel electrochemical procedure using the obtained TiO2 nanorod array as substrate. A photosensitized electrolytic oxidation phenomenon was observed for the as-prepared TiO2–Ni(OH)2 composite film electrode under UV irradiation. It was found that the photosensitized electrolytic oxidation of Ni(OH)2 exhibited a much lower rate than the corresponding electrochemical oxidation. The as-prepared 3D nanostructured TiO2–Ni(OH)2 composite film electrode, coupled with platinum, showed excellent UV-induced oxidative energy storage ability, and the apparent quantum yield was as high as 10.6%. The nanostructured composite film electrode still delivered a discharge capacity of 5.45 mC cm−2 after 45 irradiation–discharge cycles, manifesting the good reversibility of the UV-induced oxidative energy storage and conversion. It was concluded that the enhanced UV-induced oxidative energy storage of the TiO2–Ni(OH)2 composite film can be ascribed to its unique nanostructured characteristics.