Hysteresis in the measurement of double-layer capacitance at the gold–ionic liquid interface

The capacitance of the polycrystalline gold electrode–ionic liquid BMIMTf [1-butyl-3- methyl imidazolium trifluoromethanesulfonate (triflate)] interface has been studied using ac voltammetry and electrochemical impedance spectroscopy (EIS). Slow potential scanning reveals a massive hysteresis between potential scans toward negative or positive directions and provides a distorted C(E) curve. Kinetic studies indicate that 10 min wait times are required after each potential step for system relaxation. EIS resolves the overall series capacitance into contributions from ion adsorption and double-layer capacitance, CDL. Isolation of CDL reveals that even 10 min of equilibration time is insufficient to completely remove the hysteresis. The shape of the negative-going CDL(E) curve is camel-shaped whereas the shape of the positive-going curve is bell-shaped.