Facile synthesis of N, S co-doped hierarchical porous carbon/MnO2 composites for supercapacitor electrodes via sodium alginate crosslinking

Porous carbon materials have been widely used as electrode materials for supercapacitors . However, low specific capacitance severely hinders the practical application. To further improve the capacitance, this work reports a facile approach to prepare N, S co-doped hierarchical porous carbon/MnO 2 composites (NSPC/MnO 2 ). Acidified thiourea, acting as N and S source, is used to crosslink sodium alginate (SA) to give SA-based composite gels which are pyrolyzed to produce NSPC/MnO 2 . X-ray diffraction and X-ray photoelectron spectra proved that manganese exists in the porous carbon in the form of MnO 2 . The obtained NSPC/MnO 2 exhibit hierarchical porous structure, remarkable mesoporous feature (the proportion of mesopores and macropores reached 32.69%), and high specific surface area of 1701 m 2 g −1 . Meanwhile, NSPC/MnO 2 show abundant heteroatom doping, i.e. Mn (2.05 at%), N (6.76 at%), and S (2.16 at%), which provided plenty of pseudocapacitance. The electrochemical tests show that NSPC/MnO 2 as electrode material can reach a high specific capacity of 281.1 F g −1 at 1 A g −1 (which is almost 1.85 times higher than the comparative sample), with good cycling stability (86.02% after 5000 cycles at 10 A g −1 ).