Improvement of transport properties and hydrogen permeation of chemically-stable proton-conducting oxides based on the system BaZr1-x-yYxMyO3-δ

Abstract

The structural and transport properties as well as the chemical stability of a series of proton-conducting oxides based on yttrium-doped barium zirconate were investigated. Specifically, Pr-, Fe- and Mn-doped BaZr_1-x-yY_xM_yO_3-δ compounds were prepared by solid state reaction. The compound exhibiting the highest total and protonic conductivity at elevated temperatures under reducing atmospheres was BaZr_0.8Y_0.15Mn_0.05O_3-δ. Temperature-programmed reduction experiments revealed a particular redox behavior related to the Mn-species under selected conditions. The hydrogen permeation was thoroughly studied as a function of the temperature, hydrogen concentration and the humidification degree in the sweep gas. Moreover, the transient processes induced by alternate step changes in the humidification degree of the sweep gas were analysed. The highest steady hydrogen evolution flow exceeded 0.03 ml min⁻¹ cm⁻² (0.9 mm-thick membrane) at 1000 °C for the humidified sweep gas. The stability of BaZr_0.8Y_0.15M_0.05O_3-δ under operation-relevant atmospheres (CO₂-rich reducing atmosphere at high temperature) was tested using different techniques (X-ray diffraction (XRD), Raman, SEM, TEM and TG) and the results showed that this material is stable even when exposed to 115 ppm H₂S.