POTENTIOMETRIC SENSOR FOR OXYGEN BASED ON O-2-H-2 MIXED POTENTIAL OF A COMPOSITE PT-METAL HYDRIDE ELECTRODE

A very simple potentiometric sensor for oxygen operating at room temperature is described. This sensor is based on the variation of the oxygen-hydrogen mixed potential established at the sensing electrode when a constant activity of the hydrogen adsorbed on the catalytic metal (usually platinum) is maintained. This constant activity of the adsorbed hydrogen was obtained simply by sputtering a thin layer of platinum directly over a suitable metal hydride (ZrHx, ZrH2, NbH). Sheets of titanium covered by a layer of TiHx were used as reference electrodes, while pellicular a-zirconium phosphate was preferred as the solid protonic conductor. Preliminary experiments showed that these sensors are sensitive and very fast. However, a gradual worsening of the properties was noted, essentially due to the formation of an oxide layer at the hydride-proton conductor interface. This problem has been solved by protecting the surface of the metal hydride with a layer of palladium.