High Charge-Storage Performance of Morphologically Modified Anatase TiO<sub>2</sub>: Experimental and Theoretical Insight
Basudeba Maharana, Satyajit Ratha, Afsal S. Shajahan, Brahmananda Chakraborty, Rajan Jha, Shyamal Chatterjee
Abstract
We report the influence of morphological changes on the process of charge storage for electrode materials based on ${\mathrm{Ti}\mathrm{O}}_{2}$ nanotubes and provide theoretical insights into the electronic properties from density-functional theory (DFT) simulations. ${\mathrm{Ti}\mathrm{O}}_{2}$ nanotubes are synthesized hydrothermally from nanoparticle precursors. Structural characterization analysis reveals excellent phase purity from the XRD peaks and the formation of uniform and homogeneous nanotubes from field-emission SEM images. Interestingly, cyclic voltammetry and charge-discharge measurements demonstrate that these structurally engineered ${\mathrm{Ti}\mathrm{O}}_{2}$ nanotubes exhibit an enhanced specific capacitance of about $1400\phantom{\rule{0.25em}{0ex}}\mathrm{F}\phantom{\rule{0.25em}{0ex}}{\mathrm{g}}^{\ensuremath{-}1}$ compared with $400\phantom{\rule{0.25em}{0ex}}\mathrm{F}\phantom{\rule{0.25em}{0ex}}{\mathrm{g}}^{\ensuremath{-}1}$ for pristine ${\mathrm{Ti}\mathrm{O}}_{2}$ nanoparticles. Employing DFT simulations, we present the electronic and structural properties of the ${\mathrm{Ti}\mathrm{O}}_{2}$ electrode for charge-storage performance. We compute the diffusion barrier of ${\mathrm{K}}^{+}$ ions in the electrolyte ($\mathrm{KOH}$), the accumulated voltage for different ${\mathrm{K}}^{+}$ concentrations, and the quantum capacitance of the ${\mathrm{Ti}\mathrm{O}}_{2}$ surface. A lower diffusion barrier for ${\mathrm{K}}^{+}$ ions and higher accumulated voltage contribute towards a superior charge-storage performance, which supports experimental observations. Hence, detailed experimental and theoretical analyses predict that a larger surface area in the tubular structure, increased number of delocalized carriers, improved conductivity, and enhanced mobility of the electrolytic ions contribute towards a fast and highly reversible electron-transfer process, leading to enhanced charge-storage performance in morphologically engineered ${\mathrm{Ti}\mathrm{O}}_{2}$ nanotube-based electrodes.