Molten salt method derived porous carbon with high energy density in KI-additive electrolyte

A series of porous carbons (PCs) with tunable surface areas were prepared by molten salt (NaCl/KCl) method with the assistance of CaCO3. Gas sorption analyses by N2 and CO2 show that the usage of CaCO3 leads to the increasement of in micropores and mesopores, thus enlarging the surface area up to 864 from 425 m2 g−1. Besides, numerous micropores (<0.6 nm) inaccessible to N2 can be detected by CO2. Supercapacitive performance for PCs was also investigated in aqueous KOH, H2SO4 and KI-additive (H2SO4 + KI) electrolytes as well. Combining the results of pore-structure analysis, the investigations on the relationship between specific capacitance and pore-size show that the minimum pore entrance for SO42−, K+ and I− are 0.4, 0.32 and 0.4 nm, respectively. Considering the naked/solvated ionic sizes of SO42− (0.38/0.58 nm), K+ (0.26/0.42 nm) and I− (0.39/0.66 nm), desolvation effect probably occurs in those aqueous electrolytes. Moreover, the effect of oxygen functionalities on the redox reaction was also investigated in this work. It is found that the quinone oxygen species is electrochemically active in both H2SO4 and KI-additive electrolytes. With the addition of KI in electrolyte, the prepared porous carbon-based supercapacitor possesses high specific energy of 55.7 Wh kg−1.