La2CuO4 (LCO) powders were used to fabricate electrodes for solid-state potentiometric NOx sensors [LCO vertical bar yttria-stabilized zirconia (YSZ)vertical bar Pt], and symmetrical Pt (Pt vertical bar YSZ vertical bar Pt) and La2CuO4 (LCO vertical bar YSZ vertical bar LCO) cells. The impedances of the sensors and symmetrical cells were measured. Three phenomena were observed in the impedance spectra: O-2 ion conduction in the YSZ electrolyte, surface conduction on the La2CuO4 electrode, and the electrochemical reaction of O-2 at the electrode/electrolyte/gas interface. The impedance associated with O-2 reduction/oxidation decreased in the presence of O-2, NO, and NO2, in contrast to the potentiometric response which increased in NO, decreased in NO2, and was unaffected by changes in O-2 concentration. The impedance associated with surface conduction on the La2CuO4 electrode was affected by NO and NO2 in much the same way as the previously reported potentiometric sensor response (Delta OCP) in terms of temperature and concentration dependencies providing evidence for an adsorption mechanism for the potentiometric response. (c) 2007 The Electrochemical Society.