Enhanced electrochemical performance of nitrogen-doped graphene and poly[Ni(salen)] composite electrodes for supercapacitors

High electric conductivity and great specific capacitance are demanded for supercapacitor electrodes. In this paper, N-doped graphene (NDG) was synthesized and polymerized with Schiff base transition metal conductive polymer–poly[Ni(salen)] (P@NDG) via a cyclic voltammetry method to address the issues above. The microstructure of different support electrodes and composite electrodes was observed by field emission scanning electron microscopy (FESEM). It is demonstrated that GO is reduced and nitrogen-doped by urea successfully under solvothermal condition. According to the EDS elemental mapping analysis, nitrogen atomic percentages are 5.1 and 7.5% for NDG-30 and NDG-60, respectively. Diffusion coefficient of the composite electrode was calculated in order to interpret the effect of nitrogen doping on the kinetics of the composite electrode. The result shows that optimized P@NDG-60 provides better charge transfer ability. Moreover, NDG-60 shows a BET surface area of 553.8 m2 g−1, much higher than that of NDG-30 (375.2 m2 g−1) and GO (25.7 m2 g−1). Correspondingly, P@NDG-60 exhibits the highest specific capacity of 169.8 C g−1 which is higher than that of P@NDG-30 (138.0 C g−1), P@GO (59.4 C g−1), and poly[Ni(salen)] (27.7 C g−1). The enhanced specific capacity is attributed to the nitrogen doping of graphene, which is more conductive to the growth of the polymer and the reversible redox transition between Ni(III) and Ni(II). It testifies that nitrogen doping not only induces the electropolymerization of poly[Ni(salen)] but also facilitates the kinetics in the composite electrodes for symmetric supercapacitor and thus enhances the electrochemical performance.