Electrochemical Investigation of Pure and Nitrogen-Doped Graphene Aerogels for Supercapacitor Applications

Graphene aerogels have been a promising electrode material for high-power supercapacitors due to their three-dimensional porous structure and good conductivity. However, enhancing their electrochemical kinetics in a more realistic device setting is still a major challenge. In this work, the effects of nitrogen incorporation on the electrochemical performance of graphene aerogels were systematically examined by direct comparison of the electrochemical performance of pristine graphene aerogel (GA) and nitrogen-doped graphene aerogel (NGA). The materials were synthesized by hydrothermal reduction of graphene oxide and freeze-drying, and the nitrogen doping was made by a post-treatment modification step. Electrochemical characterization was carried out in the form of cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) with a symmetric two-electrode setup and 6M KOH electrolyte. Both the electrodes showed quasi-rectangular CV profiles as well as symmetrical triangular GCD curves, thus representing a predominantly electric double-layer capacitance behavior. The specific capacitance was found to moderately increase from 174.18 F/g for GA to 187.54 F/g for NGA at 5 mA. More importantly, N modification significantly decreased the charge transfer resistance from 9.55 to 2.37 \(\:{\Omega\:}\) and the electrochemical relaxation time constant, leading to improved rate capability. These results show that the nitrogen incorporation mainly leads to an improvement in interfacial charge transfer kinetics and does not result in significant pseudocapacitive contributions to the supercapacitor kinetics, which is a useful insight for the design of high-rate graphene-based supercapacitor electrodes.