Preparation of high-capacitance N,S co-doped carbon nanospheres with hierarchical pores as supercapacitors

The N, S co-doped carbon nanospheres with/without hierarchical pores (N, S-HPCNs/N, S-CNs) are prepared by the pyrolysis of polypyrrole and (NH4)(2)S2O8 with/without F127 as the pore-foaming agent in flowing N-2. The results show that the combination of the hierarchical pores and N, S co-doping improves the electrochemical properties of carbon materials. As a result, the specific capacitance of N, S-HPCNs is as high as 416 F g(-1) at a current density of 0.2 A g(-1), which is much higher than that of N, S-CNs (138 F g(-1)). At a current density of 10 A g(-1), the specific capacitance of 313 F g(-1) for N, S-HPCNs is obtained, which keeps a capacitance retention of 75.2%, while the N, S-CNs has only the capacitance retention of 44.2%. After 5000 cycles, the retention ratio of N, S-HPCNs as high as 95.8% is obtained and the columbic efficiency of N, S-HPCNs is close to 100%. The symmetric supercapacitor device assembled using N, S-HPCNs exhibited a high energy density of 18.1Wh kg(-1) at a power density of 100Wkg(-1). The exhibited excellent electrochemical performances of N, S-HPCNs are attributed to a high content of doped heteroatoms N and S and the hierarchical pore structure. (C) 2018 Elsevier Ltd. All rights reserved.