ELECTROCHEMICAL INVESTIGATIONS OF A CARBON-MONOXIDE OXYGEN SENSOR

The CO, O2, PtAu/ZrO2(0.92)Y203(0.04)YbO3(0.04)/Pt, air system has bee n recently proposed as CO, O2 sensor. Thermodynamic measurements of th e open-circuit potential, E0, of the interphase CO, O2, PtAu/ZrO2(0.92 )Y2O3(0.04)Yb2O3(0.04) as a function of the carbon monoxide/oxygen pre ssure ratio were carried out at T = 773 K and T = 873 K and confirmed the recently obtained results that the cell operates as a reproducible and CO-sensitive sensor. To clarify whether the carbon monoxide takes part in an electrochemical reaction step or is oxidized only in a che mical step, i.e. in a heterogeneous catalytic reaction, dynamic measur ements using electrochemical impedance spectroscopy (EIS) were per-for med. They show a mixed charge transfer and transport controlled kineti c behavior. The polarization resistance, R(p), decreases with increasi ng P(CO)/P(O2) ratio at constant P(O2). This clearly indicates an elec trochemical step of carbon monoxide oxidation in the overall reaction in agreement with previous results obtained for pure platinum paint el ectrodes.