Investigation of diluted ionic liquid 1-ethyl-3-methyl-imidazolium tetrafluoroborate electrolytes for intercalation-like electrodes used in supercapacitors

The activation behavior and achievable specific capacitance of intercalation-like carbon materials, like partially reduced graphite oxide (GOpr), employing pure and diluted ionic liquids was investigated. The electrochemical activation of two different GOprs with interlayer distances of 3.9 and 4.4 Å and a graphite was studied with the ionic liquid 1-ethyl-3-methyl-imidazolium tetrafluoroborate (EMIMBF4). Furthermore, the effect of the organic solvent acetonitrile (AN) on the activation was tested by a stepwise dilution of the ionic liquid. It is shown that a rudimentary electrochemical activation of GOpr is possible with EMIMBF4. However, the resulting specific capacitance was below 100 F g−1 indicating an incomplete activation reaction. By stepwise dilution of EMIMBF4 with AN the specific capacitance was increased up to approximately 180 F g−1. Therefore, it seems that the electrochemical activation of intercalation-like carbon materials is based on both a reaction with the ions as well as with the employed solvent. Moreover, this experimental study indicates that an increased molarity of organic electrolytes has no influence on the maximum achievable specific capacitance