High-performance asymmetric supercapacitor based on urchin-like cobalt manganese oxide nanoneedles and biomass-derived carbon nanosheet electrode materials

A novel high-performance asymmetric supercapacitor (ASC) has been fabricated based on the cobalt manganese oxide (Co2Mn3O8) nanoneedles as a positive electrode and the hibiscus fruits-based carbon nanosheet (HBFC) as a negative electrode. The Co2Mn3O8 nanoneedles are synthesized by employing a one-step hydrothermal procedure using nickel foam as a support framework for the nanoneedle growth. The Co2Mn3O8 sample shows a distinct urchin-like morphology structure consisting of uniform nanoneedle arrays. The HBFC is prepared by chemical activation of the hibiscus fruits biomass carbon precursor using NH4Cl and KOH activation reagents. The as-prepared Co2Mn3O8 nanoneedles exhibited the highest specific capacity of 238 mAh g(-1) at a current density of 1 A g(-1). Moreover, the novel Co2Mn3O8//HBFC ASC device assembled based on those electrode materials at a maximum operating potential of 1.7 V shows an excellent energy density of 24.3 Wh kg(-1) at a power density of 850 W kg(-1). Besides, long-term cycling stability of 91.7% capacitance retention after 10,000 cycles in 2 M KOH electrolyte.