Preparation of N-doped graphite oxide for supercapacitors by NH₃ cold plasma

In this work, N-doped graphite oxide (GO-P) was prepared by cold plasma treatment of GO using a mixture of NH₃ and Ar as the working gas. When the ratios of NH₃: Ar were 1:2, 1:3, and 1:4, the specific capacitances of the GO-P(NH₃: Ar = 1:2), GO-P(NH₃: Ar = 1:3), and GO-P(NH₃: Ar = 1:4) were 124.5, 187.7, and 134.6 F·g^-1, respectively, which were 4.7, 7.1, and 5.1 times that of GO at the current density of 1 A·g^-1. The capacitance retention of the GO-P(NH₃: Ar = 1:3) was 80% when it was cycled 1000 times. The characterization results showed that the NH₃ cold plasma could effectively produce N-doped GO and generate more active defects. The N/C ratio and the contents of pyridinic nitrogen and graphitic nitrogen of the GO-P(NH₃: Ar = 1:3) were the highest. These were conducive to providing pseudocapacitance and reducing the internal resistance of the electrode. In addition, the I_D/I_G of the GO-P(NH₃: Ar = 1:3) (1.088) was also the highest, indicating the highest number of defects. The results of discharge parameters measurement and in situ optical emission spectroscopy diagnosis of NH₃ plasma showed that the discharge is the strongest when the ratio of NH₃: Ar was 1:3, thereby the generated nitrogen active species can effectively promote N-doping. The N-doping and abundant defects were the keys to the excellent electrochemical performance of the GO-P(NH₃: Ar = 1:3). NH₃ cold plasma is a simple and rapid method to prepare N-doped GO and regulate the N-doping to prepare high-performance supercapacitors.