High water pressure - high temperature autoclave for in situ Raman study of fuel cell/electrolyser materials
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High water pressure - high temperature autoclave for in situ Raman study of fuel cell/electrolyser materials. Aneta Slodczyk1, Oumaya Zaafrani1 and Philippe Colomban1 1
LADIR, UMR7075 CNRS & UPMC, 4 Place Jussieu, Paris, 75005, France.
ABSTRACT According to the recent hydrogen and methanol economy, the proton conducting materials appear very interesting as an electrolytic membrane and/or an electrode component of fuel cells, CO2/Syngas converters and water steam electrolysers. Prior to the long lifetime requirements their structural and mechanical behaviors as a function of operating condition: high temperature and high water vapor pressure, have to be well determined. Consequently, we designed the autoclave working till 620°C and 50 bars of H2O pressure equipped with a sapphire window allowing in situ Raman scattering measurements. It should be stressed that Raman scattering is an optical technique very efficient to detect both long and short range order structural modifications. The technical and scientific challenges/difficulties encountered during the studies performed on proton conducting zirconates are discussed. INTRODUCTION The ceramics showing significant proton conduction in a medium temperature range (400-700°C) appear as an important potential pillar of the hydrogen and methanol economy [15]. Different Ln/RE-modified, protonated (the proton content is not intrinsic to the pristine structure) perovskite ceramics, i.e. A(Sr,Ba,La)B(Zr, Ce, Ti, Sn, Ta, Nb,W)O3-δHε, are widely investigated [3-15] prior to the application as an electrolytic membrane and/or electrode components of fuel cells, water electrolysers and CO2/syngas converters [1-4]. In order to be used in an industrial device, a ceramic membrane should exhibit significant mechanical and (electro)chemical stability to guaranty a long lifetime, ~ 10000 hours. Therefore, the structural and chemical stability of a membrane should be determined as a function of operating condition: temperature and water vapor pressure. Obviously, the higher the chemical gradient / higher the (partial) pressures, the faster the (electro)chemical membrane degradation. Since direct in situ measurements are difficult when a high temperature is combined with a high water pressure, most of necessary experiments are actually performed ex situ, far from working conditions, and/or a device is studied after dismounting or post mortem. The reliability of such ex situ experiments should be validated by the comparison with the in situ ones. Within indirect methods allowing a study of proton conducting frameworks, Raman scattering appears extremely well suited. This method, already tested on different ordered or disordered perovskites such as ferroelectrics, relaxor ferroelectrics or proton/oxygen conductors [11-16], allows the determination of both long and short range order structural modifications. Note, in the case of proton conducting perovskites, the host structure is perturbed by the Ln/RE substitution, consequently by the oxygen vacancy presence and then by the incorporatio
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