Chemical stability and proton conductivity of doped BaCeO3-BaZrO3 solid solutions

Barium cerate has a high proton conductivity but rather poor chemical stabi lity in CO2-containing atmospheres. Barium zirconate, in contrast, is a rat her stable material but one that exhibits low proton conductivity. In the p resent work, the conductivity and chemical stability of solid solutions bet ween these compounds have been investigated, in an attempt to find a compos ition exhibiting both high conductivity and good stability. Compounds of ge neral formula BaCe(0.9-x)ZrxM(0.1)O(3-delta), where M was Gd or Nd and x ra nged from 0 to 0.4, were prepared by solid state reaction and characterized by X-ray powder diffraction, thermal gravimetric analysis (TGA) in flowing CO2, differential thermal analysis (DTA) in flowing CO2, and AC impedance spectroscopy in dry and H2O-saturated argon. Introduction of Zr into doped barium cerate greatly enhanced the chemical stability: for the Nd-doped sys tem, compositions with x = 0.2 or higher did not react with CO2 (under the experimental, non-equilibrium conditions), whereas for the Gd-doped system, the composition with x = 0.4 did not react. Not unexpectedly, introduction of Zr also led to a decrease in conductivity and an increase in the activa tion energy for proton transport. Overall, Nd-doped samples exhibited highe r chemical stability and lower conductivity than those doped with Gd. The c omposition BaCe0.7Zr0.2Nd0.1O3-delta appears to give a good compromise betw een conductivity and stability for fuel cell applications. (C) 1999 Elsevie r Science B.V. All rights reserved.