Development of a Ag/Ag+ micro-reference electrode for electrochemical measurements in ionic liquids

We report on a novel miniaturized Ag/Ag+ reference electrode (RE) design suitable for electrochemical measurements in room temperature ionic liquids (RTILs). The electrode is based on capillaries with an outer diameter of 365 μm and contains a 10 mmol/l solution of a silver salt in a RTIL. The silver salt bears the same type of anion as the RTIL. While potential shifts of several hundred millivolts have been observed for common platinum or silver pseudo-reference electrodes, our Ag/Ag+ micro electrode provides a stable and reliable reference potential over a period of more than two weeks, if protected from light and stored in a nitrogen atmosphere. Due to the small dimensions of the RE, it can be placed close to the working electrode (WE) and it is well-suited for application in electrochemical micro cells as well as for potential-controlled in situ AFM, STM or electrochemical impedance measurements. The electrode characteristics were determined by voltammetric measurements on ferrocene and cobaltocenium hexafluorophosphate dissolved in a RTIL. The highest expected contamination of the sample with Ag+ ions was calculated and found to be below 4 ppm.

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► Platinum pseudo-reference electrode shows large potential shifts in ionic liquids.
► A miniaturized Ag/Ag+ reference electrode design was developed.
► The new micro-reference electrode shows high potential stability.
► Suitable for potential-controlled in-situ AFM, STM and EIS measurements.