Electrochemical properties of Pr-doped Ce(Gd)O2-δ

Substitution of 2% gadolinium in the fluorite-type lattice of Ce0.80Gd0.20O2-delta with praseodymium cations was found to increase the p-type electronic conductivity by 2.5-4 times, whereas the activation energy for the electron-hole transport decreases from 145 to 125 kJ/mol. The polarization resistance of porous Pt electrodes in contact with Ge0.80Gd0.18Pr0.02O2-delta solid electrolyte, determined by impedance spectroscopy at 723-1073 K in air, is 0.5-3 times lower than that for Ce0.80Gd0.20O2-delta ceramics. This behavior, indicating an active role of the surface of the ceria-based electrolytes in electrochemical processes, was attributed to the larger p-type conductivity as well as to the high electrocatalytic activity of praseodymium cations, Further decrease in polarization resistance can be achieved by incorporation of praseodymium oxide into the Pt metal electrode matrix. Microstructural studies of Ce0.80Gd0.18Pr0.02O2-delta ceramics showed that Pr doping increases the tendency for segregation of rare-earth dopants at the grain boundaries; the segregated Pr-enriched phase may have a positive effect on electrochemical activity. (C) 2002 Elsevier Science B.V. All rights reserved.