Combined effect of nitrogen-doped functional groups and porosity of porous carbons on electrochemical performance of supercapacitors.

In this work, nitrogen-doped porous carbons obtained from chitosan, gelatine, and green algae were investigated in their role as supercapacitor electrodes. The effects of three factors on electrochemical performance have been studied-of the specific surface area, functional groups, and a porous structure. Varying nitrogen contents (from 5.46 to 10.08 wt.%) and specific surface areas (from 532 to 1095 m2 g-1) were obtained by modifying the carbon precursor and the carbonization temperature. Doping nitrogen into carbon at a level of 5.74-7.09 wt.% appears to be the optimum for obtaining high electrochemical capacitance. The obtained carbons exhibited high capacitance (231 F g-1 at 0.1 A g-1) and cycle durability in a 0.2 mol L-1 K2SO4 electrolyte. Capacitance retention was equal to 91% at 5 A g-1 after 10,000 chronopotentiometry cycles. An analysis of electrochemical behaviour reveals the influence that nitrogen functional groups have on pseudocapacitance. While quaternary-N and pyrrolic-N nitrogen groups have an enhancing effect, due to the presence of a positive charge and thus improved electron transfer at high current loads, the most important functional group affecting energy storage performance is graphite-N/quaternary-N. The study points out that the search for the most favourable organic precursors is as important as the process of converting precursors to carbon-based electrode materials.