It has been reported in the literature that the electrochemical hydrogen storage is chiefly responsible for the broad working voltage in carbon based aqueous supercapacitors. For instance, the P-doped graphene having 1.3 at% of phosphorus was obtained by H3PO4 activation and demonstrated the energy density of 11.63 Wh Kg -1 at the cell voltage of 1.7 V which is three-fold higher than the working voltage of . Therefore, the P-doping is helpful for increment in the energy density by broadening operating voltage. It might be attributed to the fact that the P-doped carbon or graphene-based materials are electrochemically stable at positive potential limit because of the blockage of active sites by phosphate functionalities that can suppress the evolution of hydrogen . Interestingly, the loading of the electrode has significant impact on the electrochemical performance. For instance, the Pdoped hierarchical carbon shown the specific capacitance of 406.2 F g -1 in 6 M KOH solution at 2 mg cm -2 while the specific capacitance is faintly reduced to 348.8 F g -1 if the mass loading increased to 60 mg cm -2 [195]. This might be ascribed to the fact that the materials possess good conductivity and rapid ion diffusion. In general, porosity of the any heteroatom doped carbon has shown appreciable influence on the electrochemical performance which is also determined by optimization of reaction temperature. For instance, the P-doped porous carbon obtained by the H3PO4 activation of saw dust at 900 °C has delivered the high specific capacitance of 292 F g -1 in 1 M H2SO4 . It is interesting to note that the SBET and total pore volume for biomass derived carbon are higher than the P-doped biomass derived porous carbon when the temperatures are 700 and 1000 °C. However, the reverse trend is followed if the temperature was 800 and 900 °C. This is because of the fact that at temperatures beyond 750 °C, the gas generated as a result of partial decomposition of H3PO4 will end up with the formation of pore structure. On the other hand, if the temperature is lower than 750 °C, then the decomposition of H3PO4 would not occur and thereby it cannot promote the pore formation.