Nitrogen doping of mesoporous graphene nanoflakes as a way to enhance their electrochemical performance in ionic liquid-based supercapacitors

Abstract Ionic liquid (IL) electrolytes can enhance specific energy of electrical double layer supercapacitors (EDLCs) due to their large operating voltage. In this work mesoporous nitrogen-doped graphene nanoflakes (NGs) with the high doping level of 9.0 at.% produced by the facile template synthesis were tested as EDLC electrodes in ionic liquid electrolytes. High mesoporosity of NGs provided the rapid transfer of IL ions into electrode pores and the effective charge accumulation, while nitrogen doping improved the wettability of the NG surface with electrolytes and contributed to pseudo-capacitance. The high electrochemical performance of NG-based EDLCs was confirmed by cyclic voltammetry, galvanostatic charge-discharge measurements and impedance spectroscopy. The effect of cation size on the specific capacitance was also analyzed for two pairs of IL electrolytes (N+Et4TFSI− and N+Bu4TFSI−; EMIM+TFSI− and BMIM+TFSI−). The highest specific capacitance of 136 F g−1 was achieved for the optimal combination of NG mesoporous structure and IL cation size.