W kg -1 and the capacitance retention of 87.7% after 5000 cycles at 4 A g -1 were achieved. The challenging task is the transformation of waste PET bottles into supercapacitor electrode material via simple and lucrative one-step thermal decomposition strategy which was established using urea. g -1 at 0.5 A g -1 in 1 M H2SO4 solution) is higher than N-doped graphene without nitric acid because of the increase in the pseudocapacitance by nitric acid incorporation under supercritical condition. In another report, the same group demonstrated the electrochemical capacitive performance of N-doped graphene prepared via supercritical fluid method (SCDGO) was compared with hydrothermal (HTDGO) using dimethyl glyoxime (DMG) as the nitrogen source . The calculated specific capacitance of SCDGO is 286 F g -1 at 0.5 A g -1 in 1 M H2SO4 solution which is significantly superior compared to HTDGO (170 F g -1 ) and RGO (143 F g -1 ). The drastic variation in capacitance is attributed to the difference in the existence of nitrogen and their relative intensities. On comparing the deconvoluted N 1s spectra of SCDGO and HTDGO as displayed in Fig. and, the pyridinic nitrogen is existed in the SCDGO but not in HTDGO. In general, the pyridinic nitrogen is more supportive for supercapacitor applications because it easily utilizes its unshared pair of electrons with H + from H2SO4 electrolyte. Additionally, the intensity of quarternary nitrogen is higher than nitrile nitrogen in SCDGO but reverse is the case of HTDGO. The conductivity of the electrode is generally enhanced to the greater extent owing to the presence of quarternary nitrogen which was clearly observed from the EIS investigations that the charge transfer resistance (Ω) of SCDGO (2.2) is lower than HTDGO (4.9). Also, the order of knee frequency factor (Hz) obtained from the Nyquist plot is SCDGO (6.26)> HTDGO (0.74)>RGO (0.51) implying that the rate performance of the SCDGO electrode is more pronounced among the three samples.