Lignin promoted the fast formation of a robust and highly conductive deep eutectic solvent ionic gel at room temperature for a flexible quasi-solid-state supercapacitor and strain sensors

The green synthesis of ionic gels using alternative feedstock enables the preparation of sustainable materials and devices. Due to the excellent solubility of lignin in deep eutectic solvent (DES), lignin was first dissolved into a DES composed of betaine and ethylene glycol (EG) directly, and the dynamic redox reaction between lignin and Fe-2(SO4)(3) was employed in the catalytic polymerization of acrylic acid (AA) in DES at room temperature within minutes. The as-prepared ionic gel had high strength, extreme temperature stability, and good electrical conductivity. The synergistic effect of the dynamic cross-linking of lignin and Fe-2(SO4)(3) gives the gel a high strength of about 1.8 MPa and excellent stretchability, over 1000% strain. Due to the electrical conductivity of Fe-2(SO4)(3) and the DES itself, as well as the stability of the DES, the electrical conductivity of the prepared gel increased from 0.09 mS cm(-1) to 4.07 mS cm(-1) at -20 degrees C to 120 degrees C. Based on these excellent properties, the application of the new ionic gel in a supercapacitor and wearable sensors was demonstrated. This simple gel preparation method has great potential in the future of flexible electronics.

Automated summary

The green synthesis approach of ionic gels using deep eutectic solvent (DES) allowed for the preparation of highly strong and conductive gels by utilizing the dynamic redox reaction between lignin and Fe-2(SO4)(3). These gels demonstrated extreme temperature stability, excellent stretchability, and increased electrical conductivity. The potential applications of these gels in supercapacitors and wearable sensors in flexible electronics were highlighted.