Synthesis of hierarchically porous carbon spheres by an emulsification-crosslinking method and their application in supercapacitors

Porous carbon materials have greatly developed as promising electrode materials for electric double-layer capacitors (EDLCs). Herein, hierarchically porous carbon spheres (HPCSs) were synthesized by using chitosan, glutaraldehyde and KOH as the carbon source, crosslinking agent and chemical activating agent, respectively. The morphology of the HPCSs was characterized by scanning electron microscopy and transmission electron microscopy, while the porous structural features, including high specific surface area (1974 m(2) g(-1)), total pore volume (2.52 cm(3) g(-1)) and wide pore-size distribution, were measured by nitrogen sorption technology. Electrochemical tests in a three-electrode cell indicated that the prepared HPCSs displayed excellent capacitive performances (328 F g(-1)), and good cycling stability with approximately 9% of capacitance reduction after 10 000 times of cycling. Moreover, the electrochemical properties characterized in a two-electrode system indicated that the specific capacitance is 66.1 F g(-1) at a current density of 0.5 A g(-1), and the energy density is 8.3 W h kg(-1) at a power density of 6 kW kg(-1), demonstrating that the obtained HPCSs are a potential electrode material and met well the practical requirement for an EDLC.