Aqua oxyhydroxycarbonate second phases at the surface of Ba/Sr‐based proton conducting perovskites: a source of confusion in the understanding of proton conduction

Abstract

Ba/Sr‐based zirconates and cerates appear as potential proton conducting electrolytes for water electrolysers, hydrogen fuel cells and CO2/syngas converters. Such application requires long lifetime of each components: a good chemical and thermal stability of the device core and a low reactivity of the electrolyte membrane. It has been recently revealed that the complex infrared (IR) and Raman signatures observed for series of zirconates, cerates and/or titanates, assigned by some authors to the bulk protonic species actually arose from the surface species in the form of second undesirable phases: the high dense proton conducting ceramics being free from such signatures. In order to contribute to a better characterization of the phases that can be formed on the surface of proton conducting ceramics, we analysed the IR and Raman spectra of Ba/SrO, Ba/Sr(OH)2, Ba/SrCO3 in their dry and hydrated/deuterated forms in combination with thermogravimetric analysis. The results allowed us to confirm the above claim and to re‐assign the vibrational spectra of perovskite materials wrongly attributed to the bulk protonic species. Since these second phases exhibit a high proton conductivity, their presence is very detrimental in the determination of intrinsic electrolyte bulk properties and interpretation of the conduction mechanisms. Copyright © 2012 John Wiley & Sons, Ltd.

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

“…The as-prepared ceramic was treated under high/medium water vapor pressure (20/40 bar, 550 1C, CO 2 -free and CO 2 -saturated water) for period of 8-47 days using the home designed autoclave device [20,[28][29][30][31][32]. This device is equipped with a temperature and pressure controller, which allows us to follow the protonation process/incorporation of water/protonic species from the pressure drop.…”

“…The protonation process leads to subtle modifications of a material structure whatever the small amount of incorporated protons [28][29][30][31][32][33][34][35]. The quantity of CO 2 dissolved in the water used is one of the stringent parameters.…”

“…Careful analysis of the secondary phases with usual analytical techniques permits the study of the corrosion mechanism. Following the procedure of the previous studies, the LSCF6428 ceramic sample was treated under medium/high water vapor pressure ($ 20 and $ 40 bar) at 550 1C for several days using a home-designed autoclave device [20,[28][29][30][31][32]. Two kinds of water were used: i) CO 2 -free water and ii) CO 2 -saturated water.…”

Sr1−xBaxSnO3 system applied in the photocatalytic discoloration of an azo-dye

“…This band can be assigned to the hydration of the perovskite structure [37]; however, the presence of non-ordered reduced tin oxide (SnO) cannot be excluded [38][39][40].…”

Crystal Structure, Hydration, and Two-Fold/Single-Fold Diffusion Kinetics in Proton-Conducting Ba0.9La0.1Zr0.25Sn0.25In0.5O3−a Oxide

“…It should be emphasized that (Ba,La)-O distance can be derived as equal to a √ 2/2, while (Zr,Sn,In)-O bond length equals a/2 in the cubic perovskite structure. Stored [39]. An approximate value of proton conductivity (σ H ) was obtained as a difference between the recorded conductivity in wet and dry atmospheres: σ H = σ wet − σ dry .…”