An investigation about the cycling stability of supercapacitors containing protic ionic liquids as electrolyte components

In the last years protic ionic liquids (PILs) have been proposed as novel electrolytes for supercapacitors. Nevertheless, so far the long term cycling stability of PIL-based supercapacitors has never been investigated in detail. Since high cycling stability is essential for such devices, a study about this aspect appears therefore of importance to understand the advantages and the limits of PIL-based systems. In this work we showed that using PILs as electrolytes it is possible to realize electrochemical double layer capacitors (EDLCs) with operative voltage as high as 2.4 V, able to feature good cycling stability in a broad range of temperature. Moreover, we also showed that the pseudo-capacitive behavior of activated carbon (ACs) in these electrolytes strongly depends on the water content and on the surface groups present on the ACs. When PILs with a lower content of water were used in combination with AC containing few surface groups, PIL-based supercapacitors exhibit specific capacitance comparable to classical organic electrolytes without any evident pseudo-capacitive contribution.