Unveiling the Potential of Natural Deep Eutectic Solvents in Electrochemical Energy Storage Applications

Supercapacitors are key to sustainable energy storage due to their high power density and long lifespan, though their energy density remains limited. This study explores natural deep eutectic solvents (NADES) as alternative electrolytes for graphene-based supercapacitors via molecular dynamics simulations. Three NADEScomposed of betaine chloride and the amino acids arginine, histidine, or lysineare assessed for their biocompatibility, cost-effectiveness, and hydrogen-bonding capabilities. Simulations at 300 and 600 K reveal distinct physicochemical behaviors: histidine-based NADES shows the highest density and cohesive energy, attributed to imidazole-mediated interactions, while lysine-based NADES offers the greatest ionic mobility. In supercapacitor models, asymmetric electric double layers (EDLs) form, with amino acids dominating the positive EDL and betaine the negative. Interaction energy analyses underscore the stabilizing role of amino acids in the EDL structure. Capacitance values range from 2.2 to 2.8 μF/cm2, aligning with those of conventional electrolytes. These results highlight the promise of NADES as sustainable and tunable electrolytes, offering a viable route to enhance the performance of next-generation supercapacitors.