Enhancing the supercapacitive properties of SnO2 through W5+/W6+ redox pairs

This research underscores the promising potential of SnO 2 -based materials in high-performance supercapacitor applications, with and ions serving as dopants. A range of characterization and testing was performed to examine SnO 2 as an electrode material, focusing on understanding the influence of W ions on its electrochemical properties. Techniques such as scanning and transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and photoluminescence spectroscopy were employed to analyze the morphology and structure. Changes in defect structures due to W-doping and its oxidation state were detected via electron paramagnetic resonance and X-ray photoelectron spectroscopy, confirming the presence of / redox pairs. An exhaustive electrochemical examination of undoped and W-doped SnO 2 was performed, tested as electrodes in all-in-one symmetrical supercapacitor setups, with detailed performance assessments following. Results indicated that W addition significantly enhanced the specific capacitance of the host material, achieving a specific capacitance of 268 F/g at a 0.5% W ion concentration, along with improved energy and power densities of 36.8 Wh/kg and 2650 W/kg, respectively. This enhancement is attributed to the variable valence states of W ions, with the mixed / state enhancing faradaic reactions and facilitating rapid charge transfer through hopping processes between different cation valence states at relatively low activation energies. Dunn’s analysis of the best-performing supercapacitor device indicated that, at higher scan rates, capacitive processes dominate the energy storage mechanism, with electric double-layer capacitance and rapid surface redox reactions playing a key role, while at lower scan rates, diffusion-based processes become more significant. This suggests that, at lower scan rates, electrolyte ions can penetrate deeper pores and interact with the / redox-active sites introduced into the SnO 2 host.