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 atomic %), N (6.76 atomic %), and S (2.16 atomic %), 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). • NSPC-MnO 2 was prepared from sodium alginate by the one-step carbonization method. • The loaded MnO 2 brought rich mesoporous structure and a large amount of pseudocapacitance to the porous carbon. • NSPC-MnO2 exhibited excellent electrochemical performance (specific capacitance of 281.1 F g -1 at 1 A g -1 ）.