Surface modification of carbon materials by nitrogen/phosphorus co-doping as well as redox additive of ferrous ion for cooperatively boosting the performance of supercapacitors

In this work, we demonstrate a cooperative strategy of surface modification of carbon materials by N/P co-doping and redox additive of Fe2+ ion for boosting the performance of supercapacitors. Using NH4HCO3 or NH4H2PO4 as N/P dopants, the modified carbon materials have increased concerning the electrical conductivity, porosity, and N/P contents. Furthermore, Fe2+ ion serving as redox additive has been incorporated. In a three-electrode configuration, the C-N-P-Fe sample exhibits capacitance of 371 F g−1, which is 2.38 times larger than the C-Blank-Fe sample; the redox process of Fe2+ ions is controlled by the diffusion. In a two-electrode configuration, the C-N-P-Fe sample delivers energy density of 7.7 Wh kg−1, almost 2.33 times higher than the C-Blank-Fe sample. Moreover, it unveils that the pseudo-capacitance contribution has been improved with increasing N/P doping by Trasatti method; the redox process of Fe2+ ions predominantly happens on negative electrode.