Lignin‐Derived Deep Eutectic Solvent Gel Electrolytes Paired With Porous Carbon Electrodes for Advanced Supercapacitor Application

In the pursuit of enhancing supercapacitor performance, the significance of electrolyte and electrode materials cannot be overstated. A deep eutectic solvent (DES) system comprising K2CO3 and ethylene glycol (EG) is utilized to extract lignin from cotton meal, forming a lignin/agar gel with superior mechanical properties and high liquid retention, which is attributed to the presence of robust intermolecular interactions and enhanced hydrogen bonding interactions within the gel. Notably, the DES gel doubles as a carbon precursor, facilitating the preparation of porous carbon via air combustion carbonization. Furthermore, the formation of the carbonaceous structure of DES gel is elucidated. The Scanning Electrochemical Microscopy (SECM) and Scanning Vibrating Electrode Technique (SVET) confirm that DES gel possesses good ion diffusion ability as an electrolyte and a large electrochemical active area as a porous carbon electrode. The supercapacitor assembled with the prepared DES gel electrolyte and porous carbon electrode exhibits a superior energy density of 30.2 Wh kg-l and operates normally from -25 to 75 °C. This work pioneeringly puts forward the extraction of lignin from biomass for its transformation into gel electrolytes and porous carbon, which may facilitate the fabrication of various biomass-derived gel electrolytes and porous carbon materials.