Impact of nitrogen functionalization and porosity on the electrosorption of ionic liquids on templated porous carbons

• Systematic investigation of nitrogen functionalities and content in nitrogen-rich carbon/carbon nitride nanohybrids as electrode materials for ionic liquid-based electric double-layer capacitors (EDLCs). • Pyridinic nitrogen species enhance area-normalized capacitance, while mass-specific capacitance is primarily governed by specific surface area. • Reduced total pore volume results in higher active material loadings and minimizes dead volume, lowering electrolyte requirements in IL-based EDLCs. • Infiltration-condensation synthesis effectively incorporates carbon nitride into ZTC pores, outperforming physical mixtures in EDLC electrode performance. This study systematically investigates the influence of nitrogen functionalities and their content in nitrogen-rich carbon materials, specifically carbon/carbon nitride nanohybrids, on their performance as electrode materials in electric double-layer capacitors (EDLCs) operated with ionic liquid electrolyte (1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide). The loading amounts of cyanamide as carbon nitride precursor as well as the condensation temperature are varied over a wide range to obtain materials with significantly different porosity, nitrogen contents, and chemical properties of the nitrogen species. Thermogravimetric analysis, combustion elemental analysis, gas physisorption, and X-ray photoelectron spectroscopy measurements show that the nitrogen loss from carbon nitride starts to become significant between 500 and 600 °C and that different nitrogen species are created shifting from more pyridinic forms to graphitic and oxidized nitrogen. For the EDLC application, it is found that the mass-specific capacitance is dictated by the specific surface area whereas the capacitance normalized to the specific surface area determined by gas physisorption can be slightly enhanced by the presence of pyridinic nitrogen species. In addition, lowering of the total pore volume leads to higher areal active material loadings and lower dead volume which needs to be filled with electrolyte.