More interestingly, Fan et al. produced the N-doped graphene hollow nanospheres by layer-by-layer assembly of GO and PANI over polystyrene spheres accompanied by the calcination under nitrogen atmosphere at 800 °C about 2 h [544]. Among the different bilayers, the optimized sample (NGHS-4bi) has attained the nitrogen content of 8.7 at. % along with the maximum specific capacitance of 381 F g -1 at 1 A g -1 in 6 M KOH aqueous solution and also the 96% of capacitance retained after 5000 cycles. It has been mentioned that hollow nanospheres deliver electroactive regions that promote the kinetics for both charge transport as well as ion transport. Simultaneously, higher space charge capacitance was obtained as a result of enhanced electron mobility due to the incorporation of nitrogen atoms over graphene. .03 at% and demonstrated the high specific capacitance of 481 F g -1 at 1 A g -1 which is four-fold higher than reduced graphene oxide electrode (127. 5 F g -1 ) in 2 M KOH solution.