Niobium pentoxide nanoparticles @ multi-walled carbon nanotubes and activated carbon composite material as electrodes for electrochemical capacitors

We report here on a novel method to produce nanostructured porous carbon composite electrodes decorated with niobium pentoxide nanoparticles. The carbon support is composed of multiwalled carbon nanotubes and activated carbon composite material. Nanotubes work simultaneously as binder and additive for activated carbon supported on the nickel-aluminide current collector. The hydrated niobium pentoxide nanoparticles attached on the carbon surface improved the charge storage process, introducing Faradaic reactions (pseudocapacitance) to the storage mechanism. The pseudocapacitive process involving the niobium pentoxide was stable since the oxide nanoparticles partially covered with a porous carbon layer were not deactivated. This approach improved the electrical conductivity and chemical stability and also avoided reaggregation and deactivation of niobium pentoxide nanoparticles by passivation. The electrochemical performance of the symmetric coin cell using an aqueous lithium sulfate solution was evaluated by cyclic voltammetry, galvanostatic (re)charge/discharge curves, and the electrochemical impedance spectroscopy techniques. In short, our results showed that the composite material has good electrochemical properties, including high specific capacitance (similar to 220 F g(-1)), long lifespan (more than 200 thousand cycles), and high energy (0.11-6.5 kW kg(-1)) and power (3.1-6.1 Wh kg(-1)) densities for the applied gravimetric currents in the range of 0.5-30 A g(-1). We additionally performed in situ Raman analyses (operando studies) using the composite electrode under dynamic potential conditions. We observed reversible shift on the D band position, and the intensity of the Raman signal decreased during cycling due to SO42- adsorption.