Available Technology

Silver/Silver Sulfide Reference Electrode

Electrochemical measurements in aqueous solutions are typically measured against a well-characterized and widely used reference electrode (RE), such as silver/silver chloride (Ag/AgCl), saturated calomel electrode (SCE), or reversible hydrogen electrode (RHE). Ag/AgCl reference electrodes can be used in some ionic liquids, however, the high solubility of AgCl in some ionic liquids greatly limits their use. As no other convenient reference electrode currently exists for electrochemistry in ionic liquids, potentials are often measured and reported against a quasi-reference electrode (QRE). In the ionic liquid literature, this QRE is typically a silver or platinum wire, which is immersed directly in the electrolyte. The redox reaction occurring at the surface of the QRE is not known and can vary with wire purity and cleanliness, and therefore the potential of the QRE is likely to vary between labs and experiments. Furthermore, the potential of the QRE can change during the electrochemical experiment due to dissolution, reaction, or polarization, and potential drifts of 10s to 100s of mV throughout experiments are often observed. The potential of the QRE must be reported against a well-defined redox couple (e.g. ferrocene) to allow comparisons of potential to be made between experiments. However, as ferrocene is typically added at the end of the experiment, this one-point calibration of the QRE does not necessarily apply throughout the entire experiment, as the QRE may drift during the measurement. Currently, the only commercially available REs for ionic liquids or other non-aqueous solvents are based on a silver wire in a tube separated with a porous frit, which contains a fixed concentration of Ag+ ions (typically 10 or 100 mM). This Ag/Ag+ RE exhibits good stability, with a variation of only 1–8 mV between measurements made over the course of a few weeks. However, it must be prepared and used in a glove box and protected from light, as the Ag+ salt is air/moisture and light sensitive. This Ag/Ag+ RE must be prepared frequently due to diffusion of the silver ions out of the electrode, and the photoreactivity of the silver ions.
Patent Abstract: 
LLNL has developed a reference electrode that is a great improvement on the widely used silver or platinum wire QRE commonly used in electrochemistry in ionic liquids. This new reference electrode, based on a silver-sulfide coated silver wire, exhibits greatly improved stability over a QRE.
Internal Laboratory Ref #: 
Lab Representatives
Share to Facebook Share to Twitter Share to Google Plus Share to Linkedin