N, P co-doped porous carbon from cross-linking cyclophosphazene for high-performance supercapacitors

Nitrogen and phosphorus heteroatoms-doped carbon materials were prepared by carbonization of cross-linking cyclophosphazene from 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-HQ) and Hexachlorocyclotriphosphazene (HCCP) as reactant, followed by activation with KOH as activator. The carbon materials possess a high specific surface area (up to 1342.328 m(2) g(-1)), pore volume with a well-balanced microporosity (up to 0.7289 cm(3) g(-1)), moderate heteroatom content and micrometer-sized morphology. Moreover, the heteroatom contents and porosity parameters (e.g. surface area and pore volume) can be easily controlled by the activation temperature in the range of 700-900 degrees C. When tested as a supercapacitor electrode in a three-electrode system using 6 M KOH solution as the electrolyte, the typical sample (DP-900) displays a high specific capacitance (265.8 F g(-1) at 0.2 A g(-1)), excellent rate capability (155 F g(-1) at 10 A g(-1)) and outstanding cycling stability (98% capacity retention after 10,000 charge/discharge cycles at 10 A g(-1)). Furthermore, high energy density of 14.912 Wh kg(-1) at 1 A g(-1) with a power density of 800 W kg(-1) can be achieved in a two-electrode cell originating from the microporous structure as well as the excellent synergistic effect of N, P co-doping. These encouraging results demonstrate that the DPs electrode materials with high current charge and discharge capability show great potential for supercapacitor applications, where a fast charge/discharge is required.