Face to face with enemy - analysis of aqua carbonate hydroxide second surface phases in proton conducting perovskite ceramic electrolytic membrane

摘要

The various perovskite ceramic electrolytic membranes, (Ba,Sr)(Zr,Ce,Nb,In,Sn)O_3 modified by incorporation of Ln/RE elements, are widely investigated due to their high industrial potential for H2 production and CO_2 conversion. One of the most important criteria to classify such ceramic as a good membrane is its high mechanical and chemical stability over thousands hours in severe operating conditions: high temperature and (high water) vapour pressure cycling. It is well known that the Ba- and Sr-based materials can easily form the mixed carbonates, hydroxides, hydrates, hydroxycarbonates, ... The presence of undesirable phases, even limited to traces, on the ceramic surface, and/or at the grain boundary, may lead directly to the premature degradation. Since such mixed, hydrated, poorly crystallized phases cannot be detected by diffraction experiments, we have performed thermogravimetric analysis as well as IR and Raman spectroscopic study. The comparison of vibrational and TGA signatures characteristic of complex secondary phases i.e. (Sr/Ba)(OH)_x(CO_3)_y, nH_2O and of proton conducting perovskite reveals that the ignorance of a second phase presence can lead to wrong conclusion concerning the bulk proton nature and understanding of associated conductivity mechanisms.