Electrochemical capacitance from carbon nanotubes decorated with titanium dioxide nanoparticles in acid electrolyte

The electrochemical activity of an electrode of carbon nanotubes (CNTs) attached with TiO2 nanoparticles was investigated. A chemical-wet impregnation was used to deposit different TiO2 particle densities onto the CNT surface, which was chemically oxidized by nitric acid. Transmission electron microscopy showed that each TiO2 nanoparticle has an average size of 30–50 nm. Nitrogen physisorption measurement indicated that the porosity of CNTs is partially hindered by some titania aggregations at high surface coverage. Cyclic voltammetry measurements in 1 M H2SO4 showed that (i) an obvious redox peak can be found after the introduction of TiO2 and (ii) the specific peak current is proportional to the TiO2 loading. This enhancement of electrochemical activity was attributed to the fact that TiO2 particles act as a redox site for the improvement of energy storage. According to our calculation, the electrochemical capacitance of TiO2 nanocatalysts in acid electrolyte was estimated to be 180 F/g. Charge–discharge cycling demonstrated that the TiO2-CNT composite electrode maintains stable cycleability of over 200 cycles.