Some Considerations on the Use of Platinum Electrodes in Chloride Solutions

Abstract

As part of some studies on the passivity of iron‐chromium alloys, experiments were performed to determine under which conditions platinum pre‐electrolysis electrodes and auxiliary electrodes will dissolve anodically in chloride solutions and cause interference with subsequent measurements due to the cathodic redeposition on the alloy of the dissolved platinum. For these experiments potential‐current relationships were measured and thin foils of the alloy were examined by transmission electron microscopy and by selected‐area electron diffraction for the presence of deposited platinum. Even when the anolyte and catholyte were separated by a fine‐porosity fritted disk during pre‐electrolysis, platinum subsequently deposited on the working electrode. Platinum will also dissolve anodically from the auxiliary electrode when a net cathodic current flows at the working electrode; if the electrochemical measurements are not sufficiently fast, the dissolved platinum will diffuse to the working electrode and deposit on it. The presence of dissolved platinum can usually be detected electrochemically. However, an examination of the material under study by transmission electron microscopy and electron diffraction is the most certain means to determine whether platinum will re‐deposit under the conditions of the experiment.