Exploring supercapacitance of solvothermally synthesized N-rGO sheet: role of N-doping and the insight mechanism

We demonstrate the method of achieving excellent supercapacitance in nitrogen-doped reduced graphene oxide (N-rGO) sheets by controlling the amount of N-content through the use of different ratios of GO and urea during solvothermal synthesis. Here, urea plays a dual role in reducing GO and simultaneously doping nitrogen into the GO flakes forming exfoliated N-rGO sheets. The nitrogen content in N-rGO samples rises with an increase in the amounts of urea and saturates at a value of similar to 14% for the GO : urea ratios beyond 1 : 8. The obtained N-rGO sheets with similar to 5% N-content (obtained for GO : urea ratio of 1 : 3) were demonstrated as excellent supercapacitor materials. Using a 3-electrode setup, the maximum specific capacitance obtained for this sample was 514 F g(-1) at a current density of 0.5 A g(-1) (mass normalized current). The insights into the origin of this excellent supercapacitive behavior are explained through our results on optimum N-content, the relative amount of different N-environments, defects/disorders, and the degree of reduction of GO. Importantly, a proper stacking of rGO sheets with moderate N-content (similar to 5-6%) and a moderate amount of defects is the key to achieve high specific-capacitance. Furthermore, our 2-electrode device demonstrates the excellence of our samples with a C-sp of 237 F g(-1), a power density of 225 W kg(-1), and an energy density of 6.7 W h kg(-1) at 0.5 A g(-1), exhibiting a high cyclic constancy with high capacitive retention of similar to 82% even after 8000 cycles. Hence, our work provides a way to control the properties of N-rGO in achieving excellent supercapacitive performance.

Automated summary

In this study, excellent supercapacitance was achieved in nitrogen-doped reduced graphene oxide (N-rGO) sheets by controlling the amount of nitrogen content through the use of different ratios of GO and urea during solvothermal synthesis. The N-content in N-rGO samples increased with the amounts of urea and stabilized at around 14% for GO : urea ratios beyond 1 : 8. The obtained N-rGO sheets with 5% N-content showed excellent supercapacitor properties, with a maximum specific capacitance of 514 F g(-1) at a current density of 0.5 A g(-1). The study highlights the importance of proper stacking of rGO sheets with moderate N-content and defects in achieving high specific capacitance and excellent cyclic stability.