Stability of preplated mercury coated platinum and carbon fibre microelectrodes

Abstract

The stability of preplated mercury coatings on platinum and carbon fibre microelectrodes has been studied both after transfer of the electrodes to a mercury free solution and at open circuit in Hg(I) and Hg(II) solutions. While significant amounts of mercury were found to be lost upon transfer of mercury coated platinum electrodes, the recovery after transfer was often higher than 100% for mercury coated carbon fibre electrodes. The losses observed with the platinum electrodes were shown to be caused by mechanical detachment of mercury during the handling of the electrode. No losses of mercury due to oxidation by oxygen could be detected either for mercury coated carbon fibre or platinum electrodes. For carbon fibre electrodes (and also for platinum electrodes under some experimental conditions), additional mercury deposition was found to take place in the mercury plating solutions at open circuit. The effect was most pronounced for depositions at negative potentials in acidic solutions indicating that the reproducibility in the preparation of mercury coated electrodes should be improved by avoiding conditions during which hydrogen evolution occurs. In solutions of Hg(II), the reaction Hg 2+ + Hg→ Hg 2+ 2 resulted in a gradual loss of the mercury coatings after sufficiently long times at open circuit.