Effect of TiO2 nanostructures on specific capacitance of Al2O3–TiO2 composite film on etched aluminum foil formed by the sol–gel and anodizing

Nano-thin TiO2 film on etched aluminum foil was prepared by the Sol–gel dip-coating method and annealing post-treatment at different temperatures; then, Al2O3–TiO2 composite oxide film on etched aluminum foil was fabricated by anodization in 13 wt% ammonium adipate solution. Nanostructures of TiO2 film were characterized by means of X-ray Diffraction (XRD), Raman Spectroscopy (RS), and Atomic Force Microscope (AFM). TiO2 nanostructured films are composed of anatase nanopartilces in size of 5–12 nm as annealed at 400 °C and 500 °C, and anatase-rutile complex nanopartilces in 5–15 nm at 600 °C. Compared with pure anodic aluminum oxide film, TiO2 nanostructures effectively improved specific capacitance of the Al2O3–TiO2 composite oxide film on etched aluminum foil, with an increment ratio of about 8.6%, 24.6%, and 33.3%, caused by anatase and rutile content increasing with annealing temperature from 400 °C, 500 °C to 600 °C, respectively. The specific capacitance of dip-coated etched aluminum foil annealed at 500 °C reached to a maximum after two dip-coating times with 28.3% enhancement.