Characterization of (La[sub 1−x]Sr[sub x])[sub s]MnO[sub 3] and Doped Ceria Composite Electrodes in NO[sub x]-Containing Atmosphere with Impedance Spectroscopy

Abstract

This study used electrochemical impedance spectroscopy EIS to characterize composite metal oxide electrodes in atmospheres containing NO, NO 2 , and O 2 . Symmetrical cells with electrodes of La 1-x Sr x s MnO 3 x, s = 0.15, 0.9 and 0.5, 0.99 and doped ceria Ce 0.9 Gd 0.1 O 2 and Ce 1-x Gd x O 2 x = 0.1, 0.2 were subjected to EIS while varying the temperature from 300 to 600C, the composition of the atmosphere, and the gas flow. The impedance spectra were fitted to equivalent circuits, and common arcs were identified and sought related to physical and chemical processes. The electrodes had a much lower polarization resistance R p when NO or NO 2 was present in the atmosphere at low temperatures 300-400C than in air. The impedance spectra for electrodes in 1% NO in Ar were dominated by a low frequency arc at high temperatures 500-600C. This arc seemed to be a type of conversion arc, which is related to a gaseous intermediate possibly NO 2 , formed from NO, through which the electrode reaction occurs. Indications were found that the electrodes are not electrochemically active toward NO around opencircuit voltages.