Differentiate the pseudocapacitance and double-layer capacitance contributions for nitrogen-doped reduced graphene oxide in acidic and alkaline electrolytes

Nitrogen-doped reduced graphene oxide (N-RGO) and reduced graphene oxide (RGO) have been synthesized by microwave-assisted hydrothermal method to discern the actual contribution of nitrogen-containing functional groups on the specific capacitance (CS,T) in acidic and alkaline electrolytes. Material characterization reveals similar porosity, electrolyte-accessible surface area, element composition, and graphitic crystallinity between N-RGO and RGO except the difference in the nitrogen content. In 1 M H2SO4, additional pseudocapacitance provided by pyridinic-N and pyrrolic-N/pyridone-N is clearly observed at the potential negative to 0.6 V (vs. RHE) while this contribution in pseudocapacitance diminishes in 1 M KOH due to the lack of proton in the electrolyte for these basic functional groups to undergo redox reactions. The double-layer capacitance of N-RGO in 1 M H2SO4 in higher than that in 1 M KOH owing to the presence of N-containing functional groups which increase the electronic charge density of graphene and favor proton adsorption in the acidic electrolyte. The contribution of nitrogen-containing functional groups on CS,T in acidic media is more pronounced than that in the alkaline electrolyte. This finding is crucial for the future application of N-doped carbons in supercapacitors to achieve full utilization.