Formation and electrochemical characterization of anodic ZrO₂–WO₃mixed oxide nanotubular arrays
By Whitman, Stuart R. & Raja, Krishnan S.
Published in Applied Surface Science
2014
Abstract
ZrO₂–WO₃ mixed oxide nanotubes were synthesized by a simple electrochemical anodization route. The oxide nanotubes contained a mixture of metastable hexagonal WO₃ and monoclinic (and orthorhombic) ZrO₂ phases, as well as a mixed-oxide ZrW₂O₈ phase that showed a metastable tetragonal symmetry. Evaluation of photo-activity of the materials showed generation of photo-potentials of -85 mV and -230 mV in the as-anodized and annealed conditions. Because of the mismatch in the band edge positions of the WO₃ and ZrO₂ phases and the resultant relaxation of photo-generated charge carriers, no significant photo-current density could be observed. The arrays of oxide nanotubes are considered for electrochemical capacitor application because of their morphology-assisted fast charge/discharge kinetics and large surface area. Presence of a large concentration of charge defects (on the order of 10²¹ cm⁻³) and the reported high proton conductivity of the ZrO₂–WO₃ mixed oxide rendered high capacitance, which decreased with an increase in the scan rate of cyclic voltammetry. The highest measured capacitance was 40.03 mF/cm² at a scan rate of 10 mV/s and the lowest was 1.93 mF/cm² at 1 V/s in 1 M sulfuric acid solution.