A Mixed-Potential Sensor Based on a Ce[sub 0.8]Gd[sub 0.2]O[sub 1.9] Electrolyte and Platinum and Gold Electrodes

A Pt/Ce0.8Gd0.2O1.9/Au mixed-potential sensor was constructed and its response to reducing gases in an oxygen containing stream was measured at T = 550 and 600 degrees C. The sensor response was maximum for H-2 and negligible for methane; other gases followed the trend methane < propane < CO, propylene < hydrogen. The mixed potentials developed at the Au and Pt electrodes were also independently monitored with respect to Pt air-reference electrodes. The mixed potential at the Au electrode was always higher (more negative) than that at the Pt electrode irrespective of the type of reducing gas used. 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 oxidation of reducing gas and the overpotential for oxygen reduction. While the response of the Pt electrode was found to be stable at both 600 and 550 degrees C, the Au electrode had stability problems at 600 degrees C due to the changing morphology of the gold him. (C) 2000 The Electrochemical Society. S0013-3651 (99)06-033-4. All rights reserved.