Submersible Reference Electrodes Revisited, October 2007

Th is article examines the status of submersible reference electrodes and presents a new design concept for submersible copper/copper sulfate (Cu/CuSO4) electrodes (CSE). In the new concept, the half-cell potential is independent of the salinity (chlorinity) of the electrolyte, the electrode is not subject to contamination, and structure-to-electrolyte voltages do not require correction to the CSE scale. Although copper/saturated copper sulfate (Cu/CuSO4) solution reference electrodes (CSEs) are the “industry standard” when it comes to measuring metallic structure-toelectrolyte voltages in the corrosion control fi eld, such electrodes are deemed unsuitable for long-term immersion service (submersion applications).1 This is because conventional CSEs have plugs (which make electrical contact with the electrolyte) that are porous. The porous nature of the plugs can lead to contamination of the CuSO4 by chloride ions (in seawater or brackish water applications, for example), particularly when the solution in the electrode is not fully saturated, leading to changes in the half-cell potential of the electrode.2 Contamination of the electrolyte by CuSO4 solution leakage from the electrode might also occur. As indicated in Reference 1, it is recommended that “dry” silver/silver chloride (Ag/AgCl)/seawater reference electrodes be used in submersion applications, rather than CSEs, since such electrodes do not employ porous plugs. Ag/ AgCl/seawater reference electrodes have disadvantages of their own, however.