Biomass-derived highly porous nitrogen-doped graphene orderly supported NiMn2O4 nanocrystals as efficient electrode materials for asymmetric supercapacitors

Abstract Herein, three-dimensional N-doped porous graphene materials (3DPNG) are successfully synthesized by potassium ferrate (K2FeO4) activation and graphitization using biomass-loofah as carbon source and dicyandiamide as nitrogen source. Furthermore, the mesoporous structure and defects on the surface of 3DPNG can regulate the in-situ growth of NiMn2O4 nanocrystals formation NiMn2O4/3DPNG composite and achieve conductive networks effectively, which not only make electrolyte ions contact with internal NiMn2O4 nanoparticles, but also provide a good electron transport path for electrochemical reaction. Detailed electrochemical characterization indicate that the NiMn2O4/3DPNG electrode exhibits a specific capacitance as high as 1308.2 F g−1 at a current density of 1 A g−1, demonstrates good rate characteristics of 77.9% when current density increased to 15 A g−1. The calculation of contribution rate of pseudocapacitance demonstrate that the behavior of electrode is combining diffusion property and pseudocapacitive property. Besides, a asymmetric supercapacitor (ASC) is assembled using NiMn2O4/3DPNG as positive electrode, 3DPNG as negative electrode, which displays excellent cyclic stability (91.6% retention after 10,000 cycles) and high energy density (45.25 Wh kg−1 at the power density of 11380 W kg−1), implying the great potential application of biomass-derived carbon materials in supercapacitors.