Effect of electrochemical treatment in H2SO4 aqueous solution on carbon material derived from cellulose with added guanidine phosphate

► Combination of the addition of guanidine phosphate with electrochemical treatment was proposed. ► The capacitance value in 1 M H2SO4 was greater than 350 F g−1 at 50 mA g−1 after the process. ► The capacitance values at less than 50 mA g−1 were more than 300 F g−1. ► The increment should be related to the reaction of the electrolysis of water. ► The XPS data indicated the increase in both the O atoms and the N atoms after the electrochemical treatment.