Improving the electrochemical performance of flexible carbon nanotubes based supercapacitors by depositing Ni@TiO2:W nanoparticles on their anodes

Abstract The fabrication and electrochemical characterization of flexible carbon nanotube (CNT) based supercapacitors (SCs) with and without Ni@TiO2:W (TiNiW) nanoparticles (NPs) are reported. The TiNiW NPs had an average size of 37 ± 2 nm and were deposited on the CNT fibers using the Dr. Blade technique. The analysis by X-ray diffraction determined that such NPs presented a mixture of anatase and rutile phases. The electrochemical studies indicate that the capacitance and energy density of the SCs increase by ≈ 46.2% and ≈348%, respectively, after adding the TiNiW NPs on their anodes. In fact, a stable output voltage of 1.24 V is observed after 550 min of continuous discharge. This battery-like behavior has not been observed previously in solid state SCs fabricated with electrodes of CNTs/TiO2. The maximum capacitance and energy density values were 549.1 F g−1 and 336.7 Wh kg−1, respectively. Those values are among the highest reported so far for flexible CNT based SCs. The optical absorbance and XPS spectra demonstrated the presence of oxygen vacancy defects and Ti3+/Ti4+ ions, which acted as redox centers for the charge storage in the SC devices. Measurements of impedance were carried out and a reduction of the electrical resistance (≈39%) at the electrode/electrolyte interface was observed after adding the TiNiW NPs, which facilitated the ion diffusion/storage in the SCs’ electrodes. Thus, the results obtained in this work are useful to improve the performance of flexible SCs, paving the way for their use in portable or wearable applications.