Development of bio-gel electrolyte with wide potential range

Bio-based gel electrolytes were developed and evaluated using carrageenan polymers (kappa, iota, and lambda) combined with various inorganic salts (LiCl, NaCl, KCl, Li2SO4, and Na2SO4). The study explored the maximum salt concentrations that can form homogeneous and mechanically stable gels, followed by detailed electrochemical characterization through cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and thermal analyses. Among all combinations, kappa carrageenan with LiCl exhibited the highest salt compatibility, maintaining homogeneity and structural integrity up to 5 M. Chloride-based salts generally enabled higher concentration thresholds compared to sulfate-based salts, attributed to differences in ionic radius and charge density.Electrochemical analysis showed that increasing salt concentration broadened the electrochemical stability window and enhanced specific capacitance. The 5 M LiCl–kappa carrageenan gel demonstrated superior performance, including high ionic conductivity and favorable thermal stability. Electrode modification with anthraquinone further increased capacitance due to enhanced pseudocapacitive behavior. Two-electrode cell measurements confirmed the practical applicability of the system, achieving an energy density of 17.65 Wh/kg within a stable operating window of 1.6 V.The influence of external conditions, such as pH and temperature, was also investigated. Near-neutral pH and ambient temperatures were optimal for maintaining gel structure and facilitating ion transport. Overall, the results highlight the strong potential of carrageenan-based gels for use in eco-friendly energy storage systems, especially when optimized with appropriate salt type, concentration, and structural modification.