N/P Codoped Porous Carbon/One-Dimensional Hollow Tubular Carbon Heterojunction from Biomass Inherent Structure for Supercapacitors

A N/P codoped porous carbon/one-dimensional (1D) hollow tubular carbon heterojunction was successfully fabricated from waste biomass. 1D carbon microtube (CMT) originating from the inherent biological structure of enteromorpha prolifera (EP) was used for constructing the heterojunction with uniform heteroatom distribution and good conductivity by pyrolyzing the chitosan dihydrogen phosphate protic salt (CDPPS)-coated CMT, in which CMT was used as conductive substrate and CDPPS as carbon, nitrogen, phosphorus sources, and “soft” activating agent. The optimized heterojunction (NPEPC-6-900) possesses a large specific surface area (1220 m 2 g –1 ) and high content of heteroatom functionalities (4.50 at. % N and 2.36 at. % P). A similar effect also occurs on cotton with analogous 1D hollow tubular architecture structure, and the sample presents a specific surface area (766 m 2 g –1 ) and chemical composition (3.75 at. % N and 1.34 at. % P). Benefiting from the distinctive structural feature and desirable heteroatom doping, the NPEPC-6-900-based electrode indicates high capacitance of 324 F g –1 at 1 A g –1, and still maintains the capacitance of 231 F g –1 even at 20 A g –1 (ca. 71.3% capacitance retention). Moreover, it also possesses good cycling stability with only a loss of 2% after 5000 cycles.