Mechanistic insights into the roles of precursor content, synthesis time, and dispersive solvent in maximizing supercapacitance of N-rGO sheets

Graphene oxide (GO) sheets were prepared using the improved Hummers' method, followed by simultaneous reduction and nitrogen doping using an easy solvothermal route to obtain Nitrogen-doped reduced graphene oxide (N-rGO) sheets. The amount of N-doping was controlled using the different amounts of GO and Urea, keeping the ratio of the two (1:3) fixed. Here, we examined several variations in synthesis parameters, viz. change in precursor content, variation in synthesis time, and volume of dispersive solvent. The N-rGO sample prepared with 250 mg GO and 750 mg urea at 24-hour synthesis time in 80 ml dispersive solvent exhibits a superlative specific capacitance of 1244 F/g at 0.5 A/g using 3-electrode measurements in an acidic medium. The high value can be understood via the synergistic roles of optimum defects, degree of reduction, and types of Nenvironments. The symmetric 2-electrode device prepared by depositing the synthesized material onto carbon cloth exhibits supercapacitance of 635 F/g at 1 A/g current density and high cyclic constancy with capacitive retention of similar to 96% after 10000 charge-discharge cycles. Our work provides critical mechanistic insights on the complex intermingling of an optimum N-content, the relative amount of the different N-environments, degree of reduction, and disorder to generate a high specific capacitance, remarkably better than previously reported works on similar materials. Notably, a relatively high graphitic-N, with moderate surface N-content (4.64%) and a moderate degree of reduction, leads to this higher specific capacitance.

Automated summary

Graphene oxide (GO) sheets were prepared using the improved Hummers' method and then simultaneously reduced and nitrogen-doped using a simple solvothermal route to obtain Nitrogen-doped reduced graphene oxide (N-rGO) sheets. The amount of nitrogen doping was controlled by adjusting the ratio of GO and urea. The study investigated the effect of different synthesis parameters on the specific capacitance and revealed that the N-rGO sample prepared with 250 mg GO and 750 mg urea at 24-hour synthesis time in 80 ml dispersive solvent exhibited the highest specific capacitance.