Porous Nitrogen-Doped Carbon Nanotubes Derived from Tubular Polypyrrole for Energy-Storage Applications

Porous nitrogen-doped carbon nanotubes (PNCNTs) with a high specific surface area (1765m(2)g(-1)) and a large pore volume (1.28cm(3)g(-1)) have been synthesized from a tubular polypyrrole (T-PPY). The inner diameter and wall thickness of the PNCNTs are about 55nm and 22nm, respectively. This material shows extremely promising properties for both supercapacitors and for encapsulating sulfur as a superior cathode material for high-performance lithium-sulfur (Li-S) batteries. At a current density of 0.5Ag(-1), PNCNT presents a high specific capacitance of 210Fg(-1), as well as excellent cycling stability at a current density of 2Ag(-1). When the S/PNCNT composite was tested as the cathode material for Li-S batteries, the initial discharge capacity was 1341mAhg(-1) at a current rate of 1C and, even after 50cycles at the same rate, the high reversible capacity was retained at 933mAhg(-1). The promising electrochemical energy-storage performance of the PNCNTs can be attributed to their excellent conductivity, large surface area, nitrogen doping, and unique pore-size distribution.