Surface chemistry of carbon electrodes in 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid – an in situ infrared study

Abstract Three different carbon materials were studied in very dry 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) ionic liquid using infrared and electrochemical spectroscopy methods. Advantages of in situ infrared measurements with magnetron sputtered thin carbon films are demonstrated over thicker porous carbide-derived carbon and pyrolytic graphite electrodes. Differences in the double layer structure exist for the three carbon materials, confirmed by the different shape of capacitance-potential curves and infrared spectra. It was established that imidazolium cation dimerizes at potential E E > +1.6 V. An explanation is given why EMImBF4 with a potential window of 4.1 V for the carbon film electrode gives symmetric supercapacitor voltage of only 2.8 V.