Understanding the impact of nitrogen doping and/or amine functionalization of reduced graphene oxide via hydrothermal routes for supercapacitor applications

Nitrogen doping and amine-functionalization have previously been used to improve the capacitance of graphene-based materials, however there is a lack of understanding on the mechanisms by which these modifications impact the electrochemical behavior and electrochemical supercapacitor performance, or if these approaches can be combined to achieve synergistic benefits. Herein, we investigate this by synthesizing reduced graphene oxide (HtrGO) with varying degrees of nitrogen-doping (N-HtrGO), amine-functionalization (NH₃⁺-HtrGO), and a hybrid amine-functionalization and nitrogen-doping (N-NH₃⁺-HtrGO). Synthesized materials were systemically investigated to show the effect of nitrogen-doping and amine-functionalization using electrochemical characterization and rigorous physico-chemical analysis. The capacitance performance was increased in the order of NH₃⁺-HtrGO < HtrGO < N-NH₃⁺-HtrGO < N-HtrGO. The highest capacitance of 244 F/g was observed at 50 mV/s for N-HtrGO. The specific capacitances of NH₃⁺-HtrGO was limited to 179 F/g at 50 mV/s, indicating graphene sheet restacking likely due to interactions between positively charged amine species and oxygen functional groups. Interestingly, the capacitance of N-NH₃⁺-HtrGO was significantly higher as compared to that of NH₃⁺-HtrGO, which was attributed to less agglomeration of GO due to deoxygenation through nitrogen-doping. This work provides fundamental understanding towards nitrogen-based modification of graphene materials and the impact on electrochemical properties that will guide the design of new materials for supercapacitor applications.