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.
Highlights
The use of hydrogen has been increasing over the last decade
This autoclave platform was developed in direct relation with the study of a water steam electrolyser prototype allowing the low cost of hydrogen production [19,20,21]
It should be stressed that the analysis of a ceramic material in its pristine, non-protonated state is crucial in order to detect any small structural and chemical modifications that could appear after autoclave treatment
Summary
The use of hydrogen has been increasing over the last decade. It has been widely considered as a potential energy vector: it can be used in fuel cells to produce electricity or to convert CO2 into Syngas or more complex chemicals [1,2,3,4,5,6,7,8,9]. In the second part of this manuscript, the diffraction, Raman, IR, TGA results obtained for four different proton conducting perovskite high dense ceramics: BaZr0.9Yb0.1O3−δ (BZ:Yb), SrZr0.9Yb0.1O3−δ (SZ:Yb), BaZr0.25In0.75O3−δ (BZ:In) and BaCe0.5Zr0.3Y0.16Zn0.04O3−δ (BCZ:Y,Zn) will be presented in order to compare their stability aspects These perovskite compositions are widely studied by many academic and industrial groups up to the demonstrator scale [6,9,12,13,14,15,16,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36]. Stability evaluation does concern thermodynamic criteria, and those related to kinetics that depends on the whole object: crystallinity, purity, densification, etc The objective of this manuscript is to quantitatively evaluate the aging rates of high quality ceramics in water steam-electrolysis like conditions using a unique autoclave platform
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