Evaluating and Developing a Reliable Reference Electrode for Choline Chloride Based Deep Eutectic Solvents

The Ag/AgCl reference electrode is commonly used in choline chloride based deep eutectic solvents. However, we found it undergoes significant potential shifts in electrochemical tests which previous reports largely ignored. In this work, we studied the degradation mechanism leading to its instability. Results show that due to the high Cl−concentration in ethaline, the AgCl film easily dissolves and forms AgCl2−species causing a potential shift. Therefore, we suggest a [Fe(CN)6]3−/[Fe(CN)6]4−reference electrode based on the reversibility and low diffusivity of [Fe(CN)6]3−/[Fe(CN)6]4−redox couple in ethaline, which was demonstrated to be reliable and stable over weeks of operation.