Oxidative energy storage behavior of a porous nanostructured TiO2-Ni(OH)2 bilayer photocatalysis system

TiO2-Ni(OH)2 bilayer electrodes were prepared by the cathodic electrodeposition of Ni(OH)2 layer on a TiO2/ITO substrate. The porous Ni(OH)2 layers were obtained at relatively high current densities (≥1.0 mA cm-2), and the particle size increased with increasing the deposition current density. A porous nanostructured TiO2-Ni(OH)2 bilayer was obtained at a current density of 1.0 mA cm-2. The effects of OH- concentration in the electrolyte and surface structure in the Ni(OH)2 layer on storage of the oxidative energy of TiO2 were investigated. In our experimental conditions the oxidative energy storage of an UV-irradiated TiO2 photocatalyst in Ni(OH)2 was obviously enhanced in the electrolyte with 1.0 M OH-. The porous nanostructured TiO2-Ni(OH)2 bilayer electrode showed the notably improved oxidative energy storage performance, resulting from its porous structure and nanostructured Ni(OH)2 particles. The TiO2-Ni(OH)2 bilayer electrode during UV irradiation exhibited much higher potentials and larger photocurrent than the TiO2/ITO electrode. The transition from Ni(OH)2 to NiOOH under UV irradiation proceeded in the potential range of -0.5 to -0.2 V, much more negative than the Ni(OH)2/NiOOH redox potential. A possible mechanism on the oxidative energy storage of an UV-irradiated TiO2 photocatalyst in Ni(OH)2 was proposed, and the related experimental results were discussed in terms of the suggested model.