An Artificial Interface for High Cell Voltage Aqueous-Based Electrochemical Capacitors

Abstract

Aqueous electrolytes are very effective for supercapacitor applications but their narrow electrochemical potential window (∼1 V) and associated limited energy currently limits their use. Here, we demonstrate a new strategy to enlarge the potential window by designing an artificial interface (ai). An effective ai was achieved via a mixture of siloxanes doped with an ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI TFSI). Indeed, the as-deposited ai on the carbon-based electrode hinders the electron charge transfer but not the ionic charge transfer, making the ai ionic conductive. As a result, a cell voltage of about 1.8 V was obtained in aqueous electrolyte-EMI HSO4 1 mol l−1 in water. Used as a membrane, the ai was found to be ionically specific to EMI+; the proton transference number being close to zero. These results show the strategy of developing an ai at the electrode/electrolyte interface could represent a new path for aqueous-based carbon-carbon supercapacitors to reach higher cell voltages, providing both higher specific energy and power.