The role of nitrogen-doping on the electrochemical behavior of MOF-derived carbons in ionic liquid electrolytes

Metal-organic frameworks (MOFs) derived nanoporous carbons have been intensively studied as electrode materials for electric double-layer capacitors. However, the current research on MOF-derived carbons were mainly focused on investigating electrochemical performances of supercapacitors in aqueous electrolytes, and there were only a few studies involved ionic liquids electrolytes. In addition, the research of nitrogen doping effect on MOF-derived carbons in ionic liquids electrolytes has rarely been reported. Nitrogen doping is considered to be the common and effective way to improve the electrochemical performances of carbonaceous electrodes because it can not only enhance the electrical conductivity but also bring about pseudocapacitances in aqueous electrolytes. However, the nitrogen doping effect in ionic liquids electrolytes need to be further investigated especially for MOF-derived carbons with large quantities of micropores. In this study, MOF-derived nitrogen-doped carbons were synthesized by carbonization of urea functionalized Zn-MOF-74, and their electrochemical behavior in EMIMBF4 and EMIMTFSI ionic liquid electrolytes were investigated. The nitrogen-doping degree was tuned by adjusting the amount of urea. Electrochemical test showed that nitrogen-doped carbons exhibited a maximum capacitance enhancement of 24.4 % than pristine sample in ionic liquid electrolytes. Nevertheless, nitrogen-doping contributed few pseudocapacitances in ionic liquid electrolytes, and the enhanced electrochemical performances could be ascribed to the increased electrical conductivity and the matched pore structures.