Testing the Chemical/Structural Stability of Proton Conducting Perovskite Ceramic Membranes by in Situ/ex Situ Autoclave Raman Microscopy

Abstract

Ceramics, which exhibit high proton conductivity at moderate temperatures, are studied as electrolyte membranes or electrode components of fuel cells, electrolysers or CO2 converters. In severe operating conditions (high gas pressure/high temperature), the chemical activity towards potentially reactive atmospheres (water, CO2, etc.) is enhanced. This can lead to mechanical, chemical, and structural instability of the membranes and premature efficiency loss. Since the lifetime duration of a device determines its economical interest, stability/aging tests are essential. Consequently, we have developed autoclaves equipped with a sapphire window, allowing in situ Raman study in the 25–620 °C temperature region under 1–50 bar of water vapor/gas pressure, both with and without the application of an electric field. Taking examples of four widely investigated perovskites (BaZr0.9Yb0.1O3−δ, SrZr0.9Yb0.1O3−δ, BaZr0.25In0.75O3−δ, BaCe0.5Zr0.3Y0.16Zn0.04O3−δ), we demonstrate the high potential of our unique set-up to discriminate between good/stable and instable electrolytes as well as the ability to detect and monitor in situ: (i) the sample surface reaction with surrounding atmospheres and the formation of crystalline or amorphous secondary phases (carbonates, hydroxides, hydrates, etc.); and (ii) the structural modifications as a function of operating conditions. The results of these studies allow us to compare quantitatively the chemical stability versus water (corrosion rate from ~150 µm/day to less than 0.25 µm/day under 200–500 °C/15–80 bar PH2O) and to go further in comprehension of the aging mechanism of the membrane.

Chemical and structural stability of La0.6Sr0.4Co0.2Fe0.8O3− ceramic vs. medium/high water vapor pressure

“…In our previous studies, we demonstrated the potential of the high pressure/middle temperature autoclave to study the chemical stability of various perovskite-type electrolytes and electrodes vs. high pressurized water [20,21]. Such treatment (550-600 1C, 10-40 bar p(H 2 O)) that allows also incorporation of protonic species into a host material structure is called "Protonation".…”

“…The use of high water pressure by industrialists allows an increased efficiency and in consequence decreasing of hydrogen production/conversion cost [22][23][24][25][26][27]. Our previous studies, performed in a strict collaboration with Industrial partner, showed however that high water pressure can significantly accelerate a material ageing [20]. Consequently, our protonation procedure performed under high pressure (40 bar p(H 2 O)) can be considered as an accelerated stability test which allows very fast to choose the most stable material [22,23].…”

Water pressure enhanced sintering of alkaline-earth perovskite ceramics

“…The details related to the recording of Raman and IR spectra can be found in our previous articles [12][13][14][15][16][17].…”

“…Various treatments under high water pressure were performed using home designed temperature and pressure controlled autoclaves [12][13][14][15]. CO 2 -free water was used in order to limit the carbonation.…”

“…Consequently, the ABO 3 perovskite have to be first modified by substituting the B 4+ ion by Ln 3+ one in order to create oxygen vacancies and then exposed to water that allows the partial filling of vacancies by oxygen ions and the incorporation of protons [12,13]. In the case of dense (95-99% theoretical density) ceramic pellets, the most efficient proton-incorporation procedure is the exposition to (pressurized) water [9,[13][14][15][16][17]. Such protonation process requires a few days of treatment at middle or high temperature [14].…”