Electrochemical properties of activated carbon supercapacitors prepared with solid state electrolytes based deep eutectic solvents

Current environmental problems and the need for efficient devices for capturing and storing energy have boosted research in this area, focused mainly on photovoltaic cells, batteries and double-layer electrical capacitors, currently known as electrochemical supercapacitors. The energy in the supercapacitor is stored through polarization followed by the migration of ionic charges on the surface of the electrodes. Due to the high surface area, porous structure and good conductivity, carbon-based electrodes are promising for application in supercapacitors. Traditional electrolytes are aqueous or organic, however electrolytes based on ionic liquids have also been used in electrochemical supercapacitors as they have a higher maximum operating potential (3.0 - 4.0 V), but may present some toxicity. An alternative class of ionic liquid is that of deep eutectic solvents (DES) which is based on a mixture of two compounds HBA and HBD (hydrogen bond acceptor and hydrogen bond donor). Eutectic solvents are compounds of natural origin such as: organic acids, amino acids, sugars, choline chloride and urea. Based on the individual properties of each component it is possible to state that they are considered non-toxic and biodegradable. In this study, propylene glycol, glycerol, choline chloride, tetraethylammonium bromide and benzoic acid have been used as chemical starters reactants to DES preparation. (author)