Possibilities of NOx and CHx determination using galvanic cells with perovskite-electrodes on YSZ

Perovskite-type mixed oxides with the formula La_1−xA_xMe_1−yB_yO_3±δ (x=0.01...0.2; y=0.01...0.5; A=Ca, Sr; Me=Cr, Mn, Fe, Co; B=Mg, Ga) were investigated with the aim to use the oxides as electrode materials for galvanic cells with Y₂O₃-stabilized ZrO₂ solid electrolytes (YSZ). The catalytic activity of the oxides for the oxidation, reduction and decomposition of gas components was varied by changing the transition metal and by partial substitution of lanthanum and the metal. The behaviour of different substituted lanthanum chromite/YSZ and manganite/YSZ electrodes in the presence of nitric oxides (NO_x) and combustible components (CH_x) in gases containing oxygen was investigated. Various electrode combinations were tested in gas-symmetrical cells. For the NO determination cells with a catalytically active Pt electrode and a La_0.8Sr_0.2MnO₃ electrode with a low catalytic activity for the decomposition of NO were used. The results show the possible quantitative measurement at low and constant p(O₂) on the basis of a calibration. For the determination of C₃H₆ a CH_x-sensitive Au and an O₂-sensitive La_0.99Sr_0.01CrO₃ electrode were combined in a potentiometric thick film sensor. In gases containing oxygen with small amounts of C₃H₆ the sensor provided a utilizable voltage in dependence of the C₃H₆ concentration. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996