Journal
APPLIED SURFACE SCIENCE
Volume 303, Issue -, Pages 406-418Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.apsusc.2014.03.016
Keywords
Anodic oxide; Oxide nanotubes; Mixed oxide of ZrO2-WO3; Supercapacitor
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Funding
- Defense Advanced Research Projects Agency (DARPA) [YFA N66001-12-1-4252]
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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 10(21) 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/cm(2) at a scan rate of 10 mV/s and the lowest was 1.93 mF/cm(2) at 1 V/s in 1 M sulfuric acid solution. Published by Elsevier B. V.
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