Synthesis of Highly Ion-Conductive Lignin Eutectogels in a Ternary Deep Eutectic Solvent and Nitrogen-Doped 3D Hierarchical Porous Carbons for Supercapacitors

A new strategy has been developed to synthesize deep eutectic solvent (DES)-based lignin eutectogels by the chemical crosslinking of homogeneously dispersed lignin with poly(ethylene glycol)diglycidyl ether (PEGDE) in a ternary DES of choline chloride (ChCl)/urea/glycerol. The as-prepared lignin eutectogels have high ionic conductivity, high strength, and extreme temperature stability, which can be used as sensors for flexible electronics. N-doped hierarchical porous carbons (HPCs) are prepared when the eutectogels were solvent-replaced and sintered in the atmosphere of N₂ and CO₂, which results in the formation of porous carbon with a sufficient specific surface area and a three-dimensional framework composed of a hierarchical porous structure. They were used as electrodes with excellent capacitance performance attributed to the synergy of reasonable pore size distribution and excellent nitrogen doping efficiency. The electrode displayed a significantly enhanced specific capacitance (270 F g^-1 at a current density of 1.0 A g^-1 in a three-electrode system and 224 F g^-1 at 0.5 A g^-1 in a two-electrode system) and high-performance stability (7% capacitance loss over 10,000 cycles at 8 A g^-1) as a supercapacitor electrode. It indicates the great promise of the lignin eutectogels for both sensing and energy storage applications.