N/B codoped porous carbon electrode and electrolyte derived from amino acid based deep eutectic solvent for high capacitive performance

Abstract

In this work, N/B codoped hierarchical porous carbons (BNCs) were prepared by the polymerization reaction in an amino acid-urea deep eutectic solvent (DES) and carbonization process. During the polymerization process, amino acid-urea DES not only acts as a structure directing agent, but also as the reaction solvent to ensure homogenization of the reagents and promote polymerization of reaction monomer. Specifically, l-aspartic acid and urea composed DES were used as monomers and reacted with formaldehyde and boric acid, after the high temperature carbonization the BNCs were obtained. The optimized materials of BNC-900-3, which possesses high nitrogen (N) content (11.51 at%) and boron (B) content (7.01 at%), exhibits an excellent electrochemical performance with a specific capacitance (330 F g−1 at a current density of 1.0 A g−1) in 6 M KOH electrolytes and displays a long-term cycling stability with 91% after 80,000 charge–discharge cycles. Meanwhile, the assembled symmetric solid KOH/PVA supercapacitor exhibits an energy density of 13.5 Wh kg−1. In addition, a new DES electrolyte was prepared, which also uses DES composed of l-aspartic acid and urea. The fabricated DES electrolyte based symmetric capacitor exhibits a large energy density of 14.5 Wh kg−1 at a power density of 398.8 W kg−1. This work provides a new way for the preparation of porous carbon not only using DES as a precursor but as an electrolyte, and also demonstrates its possible application in supercapacitor electrode materials.