Hierarchically N/O-enriched nanoporous carbon for supercapacitor application: Simply adjusting the composition of deep eutectic solvent as well as the ratio with phenol-formaldehyde resin

In present work, we demonstrate the synthesis of hierarchically nanoporous carbon materials using deep eutectic solvent by urea and ZnCl2 and phenol-formaldehyde resin as starting materials via direct carbonization process. Notably, the largest surface area can reach up to 1414 m2 g−1, coexistent with high nitrogen (8.09 at. %) and oxygen (14.77 at. %) contents. Moreover, we use density functional theory theoretical calculation to determine the optimum molar ratio of deep eutectic solvent (the optimum molar ratio between urea and ZnCl2 is 1:1). As a consequence, it delivers large specific capacitance (204 F g−1), superior cycling stability (96.97%) and excellent energy density (5.28 Wh kg−1) in alkaline KOH electrolyte. For further increasing energy density, we employ an ionic liquid electrolyte consisting of 1-ethyl-3-methylimidazolium tetrafluoroborate and acetonitrile in an equivalent mass into a symmetric supercapacitor configuration. Resultantly, the energy density is as high as 40.13 Wh kg−1 due to large voltage window (3 V). The present deep eutectic solvent carbonization method opens an avenue for producing carbon materials especially possessing with porosities and functionalities for favorable of achieving superior supercapacitor.