Assessment of the electrical properties and chemical stabilities of BaCe _{0 . 9} Y _{0 . 1} O _{3 −δ} and BaCe _{0 . 7} Zr _{0 . 1} Y _{0 . 2} O _{3 −δ} proton ceramic electrolytes at low temperatures, 300 to 600°C

Abstract

The electrochemical promotion of chemical reactions is gaining urgent interest, where proton conducting electrolyte membranes are used to promote industrially important hydrogenation or dehydrogenation reactions toward the desired chemical product. Nonetheless, most of these chemical reactions occur in the low-to-intermediate temperature range (300-600°C), where the overall electrical properties of these membranes become strongly influenced by their grain boundary behavior and where the potential for their phase decomposition also becomes thermodynamically favored. To study these factors, we therefore, compare the stability and electrical properties of the popular electrolyte materials BaCe0.9Y0.1O3−δ (BCY10) and BaCe0.7Zr0.1Y0.2O3−δ (BCZY712) compositions by electrochemical impedance spectroscopy in a reducing H2 atmosphere in both wet (pH2O ~ 10−2 atm) and nominally dry conditions (pH2O ~ 10−4 atm), with special focus on their low-temperature operation, an area of study that is currently lacking adequate information. The results highlight several critical points: (a) The small addition of zirconia is shown to negatively affect the hydration kinetics in the BCZY712 material, which needs at least 60 hours to reach equilibrium at 400°C, in contrast to the BCY10 sample. (b) Due to the increasing role of grain boundary behavior at lower temperatures, the BCY10 sample exhibits significant n-type electronic conductivity in nominally dry conditions, whereas this effect is less noticeable for the BCZY712 sample. (c) Both samples show equivalent and high proton conductivity in nominally dry conditions at 400°C, a factor that can be highly beneficial to avoid potential side reactions in chemical synthesis. (d) Under higher levels of humidity BCY10 is shown to suffer conductivity degradation under prolonged operation at 400°C, corresponding to a change in its crystal structure from the orthorhombic to monoclinic phase. Conversely, BCZY712 does not show any signs of chemical degradation under the same conditions. Overall, the work provides vital information regarding the operation of these materials under low-temperature conditions, providing valuable new insights for membrane selection in chemical synthesis applications.