A fast stabliization technique for oxygen sensors with low cathode current densities.

After application of the polarization voltage to a newly prepared oxygen sensor, an initial stabilization of several minutes to a few hours is required. The electrochemical phenomena accounting for this stabilization process are discussed. By far the slowest reaction is the change of the oxidation state of the noble metal cathode after application of the polarization voltage. During this process, reduction of surface oxides at the cathode causes a transient current. The contribution of this reaction to the total current is proportionately higher in the case of oxygen sensors with low cathode current densities (large cathode, membrane of low oxygen permeability) than in the case of sensors with microcathodes. For the first type of sensor, a technique has been developed which allows acceleration of this surface reaction by passing a high constant current across the cathode. With this technique, the stabilization time can be considerably shortened in a reproducible manner, and the sensor is ready to be used within 15 to 30 min of its preparation. This time is comparable to the stabilization time needed for sensors with microcathodes.