superior cycle stability with the capacitance retention of 98.9% in 2 M KOH solution and 99.2% in 1 M H2SO4 after 8000 cycles. From Fig. , it is strongly evident that the capacitive performance in alkaline medium is preferred over acidic medium due to the relative higher contribution from pyridinic N that effectively participated the faradaic interaction with hydroxide ions compered to H + ions. Also, the very high energy density of 42.8 Wh kg -1 at power density of 500 W kg -1 in 2 M KOH aqueous electrolyte was obtained for N-doped graphene which is three-fold greater than RGO Wh kg -1 ) as displayed in Fig. . The very high capacitance is attributed to the high surface area of 438.7 m 2 g -1 which is significantly greater than RGO (108.6 m 2 g -1 ). Furthermore, the bubble-like morphology generates greater number of active sites which is reliable for facile ion transport. Elessaway et al. prepared the 3D N-doped graphene by mixing of urea and raw PET waste in different weight ratios in teflon lined autoclave under thermal heat-treatment two various temperatures (600 and 800 °C) for 5 h [549]. Among the various samples, the obtained N-doped graphene derived from PET and urea in the ratio 1:2 with 2.514 at% of nitrogen has got the specific capacitance of 405 F g -1 at