Photoelectrochromic properties and energy storage of TiO2−xNx/NiO bilayer thin films

N-doped TiO2 film was synthesized on indium-tin oxide (ITO) conducting glass substrate by sol–gel method and characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). As compared to the undoped TiO2, the synthesized N-doped TiO2 had visible-light photoresponse and exhibited a significant increase in the photocurrent under Xe-light irradiation. Then high-porous NiO was deposited onto the N-doped TiO2 layer by chemical bath deposition (CBD) to obtain TiO2−xNx/NiO bilayer thin films. The TiO2−xNx/NiO electrode showed excellent photoelectrochromic properties and energy storage capability. Upon light irradiation, the formed holes gave rise to the oxidation of NiO to NiOOH, and the color of the TiO2−xNx/NiO electrode changed from colorless to brown. After 2 h irradiation, the discharge time was about 4.2 h at the current density of 100 nA cm−2.