Pulsed polarization of platinum electrodes on YSZ

Pulsed polarization is employed for NO x detection using thimble-type standard lambda probes. The model system Pt l YSZ is investigated to understand the reactions occurring at electrodes during alternating pulsed voltages and self discharge. For that purpose, the atmosphere is varied and different pulse parameters like pulse duration and pause between the pulses with opposite sign are evaluated. During polarization in oxygen rich atmosphere, it appears that platinum oxide is formed at one electrode and reduced due by the following pulse with opposite sign at this electrode. At the other electrode, this reaction also takes place, but one pulse delayed. With increasing pulse duration, more platinum is oxidized. According to this, the polarization current of the subsequent pulse grows clearly due to the reduction of the formed oxide and therefore more charge is transferred in contrast to a short polarization pulse duration. Higher oxygen content affects the polarization current in the same way. The theory of platinum oxidation and reduction during alternating polarization is in good agreement to cyclic voltammetry investigations.