Progress of synthetic strategies and properties of heteroatoms-doped (N, P, S, O) carbon materials for supercapacitors

Heteroatoms-doped (N, P, S, O) carbon materials used as electrodes can significantly enhance the electro-chemical properties of supercapacitors. Heteroatom doping contributes to enhancing pseudo-capacitance, increasing electrical conductivity, improving wettability and promoting metal ion reversible storage capacity and rate capability. The structural nitrogen usually includes pyridinic N, pyrrolic N, quaternary N (graphitic N) and pyridine N-oxide. Pyrrolic N and pyridinic N enhance the pseudo-capacitance. Graphitic N accelerates the transference of electrons. P can introduce O atoms by forming C-P-O, C-O-P, C3-P--O, C3-P and other groups. S often exists in the edge region or defect site of carbon plane in the form of thiophene and oxidized sulfur species SOx. O exists mainly in the form of C-O-C, -COOH, C--O, C-OH, and other bonds in the carbon skeleton. The synthetic strategies of heteroatoms-doped carbon materials mainly include pyrolysis, chemical activation, and template strategy. This paper intensively summarizes the mechanism of N, P, S and O doping on the performance of heteroatoms-doped carbon materials for supercapacitors. Furthermore, recent progress in the synthetic strategies of heteroatoms-doped carbon materials for supercapacitors is reviewed. Additionally, future developments and directions on heteroatoms-doped carbon materials for supercapacitors have been provided.