N/O/P co-doped hierarchical porous graphitic carbon materials for high-rate supercapacitors

Heteroatoms-doped hierarchical porous carbons have attracted considerable interest owing to their efficient utility in supercapacitors. However, the increase of defects tends to sacrifice the electrical conductivity of carbon materials. Therefore, it is of great significance to build a good conductive network by increasing the graphitization degree of porous carbons. Here, this study reports the use of serine phosphate protic salt ([Seri][H2PO4]), Pluronic F127 and cobalt nitrate to engineer the N/O/P co-doped hierarchical porous graphitic carbon materials. The Co2+ catalyzes the graphitization of porous carbons under high temperature. A large number of mesopores, highly doped heteroatoms (O: 4.2 wt%, N: 4.07 wt%, P: 0.81 wt%) and conductive carbon skeleton boost the ultrafast transport of electrons and ions, resulting in high specific capacitance, wide operating voltage and outstanding rate performance. The symmetric supercapacitor assembled in KOH electrolyte shows good frequency response with the scan rate up to 1.5 V s−1 on the working voltage of 0–1.3 V. At the same time, when the power density reaches up to 21.3 kW kg−1, its energy density remains 8.74 W h kg−1. Furthermore, the symmetric supercapacitor delivers a high energy density of 81.42 W h kg−1 at the power density of 875 W kg−1 with an ultrahigh working voltage of 3.5 V in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) electrolyte. More promisingly, all-solid device based on the optimized sample exhibits outstanding flexibility, which greatly broadens its practicability. This work marks the importance of the balance between porous structure, heteroatom doping and high conductivity for advanced supercapacitors.