Synthesis of biomass-based porous graphitic carbon combining chemical treatment and hydrothermal carbonization as promising electrode materials for supercapacitors

A synthesis strategy was developed for preparing porous graphitic carbon with high electrochemical performance from peanut shell through chemical treatment by NH4OH, HNO3, and H2SO4, subsequent hydrothermal carbonization, and ZnCl2 activation under CO2 atmosphere. At a certain activation temperature of 700 °C, the carbon sample after NH4OH pretreatment (NHAC-700) achieved the highest specific capacitance of 256.05 F/g at the current density of 0.5 A/g due to its high surface area and good pore size distribution. The porosity and electrochemical performance of NH4OH-pretreated carbon was further improved by improving the activation temperature to 800 °C (NHAC-800). The NHAC-800 possessed a large surface area of 2129.5 m2/g with a high proportion of mesopores in the pore size range of 2–5 nm. Electrochemical analysis in the three-electrode system showed that NHAC-800 electrode exhibited a high specific capacitance of 266.06 F/g at 0.5 A/g. In the two-electrode system, the symmetric supercapacitor assembled by NHAC-800 delivered an energy density of 32.08 Wh/kg at a power density of 1000 W/kg and maintained 25.63 Wh/kg at 20000 W/kg. NHAC-800 also displayed excellent cycle stability with the capacitance retention rate of 93.76% after 5000 cycles at a constant current density of 2 A/g.