Reference electrode-induced surface poisoning of thin-film electrodes

The effect of reference electrode (RE)-induced surface poisoning of magnesium-scandium (MgSc) thin-film electrodes has been investigated. A comparison is made between various electrochemical responses of identical MgSc thin-film electrodes. The measurements were performed in two separate three-electrode setups containing REs from different manufacturers, the first of which contained a radiometer Hg/HgO RE that consists of a glass construction. The second setup contained a Hg/HgO RE from Koslow Scientific Company, which has a polyethylene housing. It was found that lead (Pb) species originating from the radiometer RE readily dissolves into the alkaline electrolyte. These dissolved species could be deposited on the surface of thin film electrodes, both as metallic Pb and Pb oxides, during electrochemical hydrogen loading/unloading of the MgSc alloys. This surface poisoning prohibits accurate determination of kinetic parameters related to the hydrogen adsorption reaction. The electrochemical measurements showed inferior electrode kinetics when using a radiometer RE as compared to a Koslow RE. The electrode kinetics could be linked directly to the amount of Pb deposited on the metal hydride thin film by means of electrochemical impedance spectroscopy and analytical techniques. (c) 2005 The Electrochemical Society.