A mixed-potential sensor based on a Ce0.8Gd0.2O1.9 electrolyte and platinum and gold electrodes

A Pt/Ce0.8Gd0.2O1.9/Au mixed-potential sensor was constructed and its respo nse to reducing gases in an oxygen containing stream was measured at T = 55 0 and 600 degrees C. The sensor response was maximum for H-2 and negligible for methane; other gases followed the trend methane < propane < CO, propyl ene < hydrogen. The mixed potentials developed at the Au and Pt electrodes were also independently monitored with respect to Pt air-reference electrod es. The mixed potential at the Au electrode was always higher (more negativ e) than that at the Pt electrode irrespective of the type of reducing gas u sed. The polarization curves of the two electrodes during oxygen reduction were also measured. These measurements revealed that the mixed potential at the electrodes was dependent on both the amount of electrochemical oxidati on of reducing gas and the overpotential for oxygen reduction. While the re sponse of the Pt electrode was found to be stable at both 600 and 550 degre es C, the Au electrode had stability problems at 600 degrees C due to the c hanging morphology of the gold him. (C) 2000 The Electrochemical Society. S 0013-3651 (99)06-033-4. All rights reserved.