Preparation of a Hierarchical Porous Carbon Material Derived from Starch and its Application in Asymmetrical Supercapacitors

Abstract

A novel core-shell structure hierarchical porous carbon-based material derived from starch, doped with oxygen and nitrogen, is described. The synthesis involves utilizing SiO2 microspheres as templates to create a porous surface, H2SO4 is employed as a dehydrating agent during the carbonization at 100°C for 6 hours to synthesis a high degree of graphitization carbon substrate (SSO-2:1). By employing dual cyanamide and cobalt compounds, a Co@C type of carbon nanotubes with nitrogen doped (Co@NCNTs) are grown on the surface of SSO-2:1 to establish a core-shell structure carbon composite (SSON) with hierarchical pores. The SSON has a specific surface area of 479.56 m2/g. In the electrolyte of 3 M KOH, the specific capacitance of SSON is measured at 790 F/g, with a 98.3% capacitance retention rate until 10,000 cycles. The numerous active sites on SSON promote the absorption of pseudocapacitance materials, such as cobalt and nickel layered double hydroxides (NiCo-LDH), resulting in the formation of NiCo-LDH@SSON. An asymmetrical solid state super capacitor is then fabricated using SSON as the negative electrode, NiCo-LDH@SSON as the positive electrode, PVA-KOH (3 M) as the electrolyte, which delivered a specific capacitance of 194.4 F/g under the voltage window of 0 V ~ 1.6 V. Even after 30000 charge / discharge cycles, the capacitance value remains at a retention rate of 88.3%, while the energy density can achieve to 71.09 Wh/kg under the high power density of 821.9 W/kg.

Keywords: Porous carbon, SiO2, starch, Co@NCNTs, Asymmetrical super capacitor