Rectangular microscale carbon tubes with protuberant wall for high-rate electrochemical capacitors

A series of novel rectangular microscale carbon tubes with protuberant wall are prepared by polyaniline with hollow carbon nanospheres (HCNSs) as templates. By changing mass ratio of ammonium persulfate to HCNSs, the morphology and the tube dimension of those samples can be controlled. Chemical activation with KOH at 1123 K results in a large specific surface area (SSA), ranging from 1680 to 2415 m2 g−1, and big pore volumes, ranging from 1.274 to 1.550 cm3 g−1. Electrochemical tests show that the special morphology effectively increases charge–discharge rate. The maximum capacitance reaches 230 F g−1 at a potential scan rate of 50 mV s−1, and 50% of which even can be remained at a scan rate of 1000 mV s−1. The electrochemical impedance tests show that the frequency exceeds 10 Hz and even reaches up to 15 Hz for the optimum sample corresponding to the 50% of the maximum capacitance, which is intensely higher than 1 Hz for common porous carbon.