The Kinetics of Hydration and H/D Isotope Exchange of Y-Doped Barium Cerate and Lanthanum Tungstate Studied by Transient Thermogravimetry

The surface and bulk kinetic properties of BaCe0.9Y0.1O2.95 (BCO) and La(27.15)W(4.85)O(55.28)v(0.73) (LWO) have been studied by means of transient thermogravimetry. Dissolution and diffusion of water have been determined from step changes in the water vapor pressure, and dissolution and diffusion of protons from H-D isotope exchange. The hydrogen tracer diffusion in BCO is about one order of magnitude faster than that in LWO, and the enthalpy of mobility of protons is 43 +/- 3 and 66 +/- 5 kJ mol(-1), respectively, for the two materials. Chemical and tracer surface exchange rates at BCO and LWO surfaces are of similar magnitudes and have activation energies in the range of 25-50 kJ mol(-1). We speculate that the surface exchange rate on BCO is limited by dissociative adsorption of water catalyzed by oxygen vacancies, whereas incorporation of hydroxide groups is limiting for LWO under oxidizing conditions. The applicability of thermogravimetry with respect to differentiating between one-fold and two-fold bulk hydration mechanisms is moreover discussed. (C) 2013 The Electrochemical Society. All rights reserved.