Porous nitrogen-doped hollow carbon spheres derived from polyaniline for high performance supercapacitors

Porous nitrogen-doped hollow carbon spheres (PNHCS) had been prepared by pyrolysis of hollow polyaniline spheres (HPS), which were synthesized by the use of sulfonated polystyrene spheres (SPS) as a hard template. PNHCS have a specific surface area of 213 m(2) g(-1) and a pore volume of 0.24 cm(3) g(-1). At a current density of 0.5 A g(-1), the specific capacitance of the PNHCS prepared is ca. 213 F g(-1). The capacity retention after 5000 charge/discharge cycles at a current density of 1 A g(-1) is more than 91%. The enhanced electrochemical performance can be attributed to the unique carbon nanostructure and nitrogen-doping of the PNHCS electrodes. The hollow macro-structure plays the role of an ion-buffering reservoir. The micropores of the PNHCS enlarge the specific surface area, while the mesopores offer larger channels for liquid electrolyte penetration. Nitrogen groups in the PNHCS not only improve the wettability of the carbon surface, but also enhance the capacitance by addition of a pseudocapacitive redox process.