Abstract:

Nitrogen/oxygen co-doped porous carbons were prepared for supercapacitor electrode using waste crab shells as the carbon source and KOH as the activated agent. The effects of the pyrolysis temperature on the yield, the porous structures and the nitrogen/oxygen content of the obtained carbons were investigated with the fixed mass ratio of crab shells and KOH as 5:3. The results show that the specific surface area and pore volume of the as-synthesized carbons are increased, while their nitrogen/oxygen contents are decreased when the pyrolysis temperature is increased from 500 to 700 ℃. Electrochemical behaviors were determined using cyclic voltammetry and galvanostatic charge-discharge measurements. The results demonstrate that the nitrogen/oxygen content and the porosity of the carbons have important effects on their electrochemical performances. The sample with the pyrolysis temperature fixed at 600 ℃ exhibits the specific surface area of 612 m²/g, the nitrogen content of 3.53% as well as the oxygen content of 32.8%. Its specific capacitance reaches 310 F/g at the current density of 50 mA/g and exhibits the long-term stability with 95% capacitance retention after 1000 cycles. It is obvious that the porous structure and the nitrogen/oxygen contents of the obtained carbons can be controlled by adjusting the pyrolysis temperature, and their electrochemical performances depend on the synergistic effects of the porosity and the surface properties.

Key words: biomass, porous carbon, crab shells, nitrogen doped, supercapacitor