Screen-printed ruthenium dioxide pH-electrodes

The alternative use of metal oxide electrodes instead of glass electrodes for pH-measurements is reported. This study is focused on screen printed potentiometric pH-electrodes - which consists of a ruthenium dioxide - glass composite. The electrode will be used in a sensor for carbon dioxide measurements. This sensor will contain an electrolyte of alkaline NaHC03 solution, so the pH-properties of the electrodes in this buffer are from large interest. Former investigations have shown good results in pH-measurement, without detailed statements about the stability of electrode potentials. In this report the sensor properties, like pH-sensitivity, pH-response and especially the stability of potentials are characterized. The examined electrodes were made by thick-film technology. The ruthenium-glass inks were printed on alumina substrates. Two sorts of glass, which were selected for their behaviour in several solutions, were used. Different series of pH-electrodes were tested, one with lead oxide glass and one with lead free glass. The electrodes were treated in different solutions and measurements were taken in weekly time steps. The sensory properties are examined by potentiometric measurements. The dependence of electrode behaviour on surface structure was characterized by microscopic observation. The electrodes show a near-Nernstian dependence of potential upon pH in aqueous buffer between pH 4 and 9. Especially in alkaline buffer solutions the pH-data are very stable. Different behaviour of pH-response during the testing time could be explained with structural changing of the electrode surfaces. The best results have shown the ruthenium lead free electrodes in alkaline NaHCO3-solution, which can be used in carbon dioxide sensors in the future. Entnommen aus TEMA