Origins of rapid aging of Ba-based proton conducting perovskites
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Origins of rapid aging of Ba-based proton conducting perovskites Aneta Slodczyk1, Bogdan Dabrowski2, Natalie Malikova3 and Philippe Colomban1 1 LADIR UMR7075 CNRS, UPMC, Thiais, 94320, France. 2 Department of Physics, Northern Illinois University, DeKalb, IL, USA. 3 Laboratoire Leon Brillouin CNRS-CEA, CEA Saclay, 91191 Gif-sur-Yvette, France. ABSTRACT Proton conducting ceramics are considered as promising membranes for medium temperature fuel cells, water stream electrolyzers and CO2/syngas converters. Materials for these applications have to be mechanically and chemically stable at corrosive conditions of temperature and water vapor pressure in order to ensure the long life-time operation. Our comprehensive Raman, infrared, thermogravimetric, thermal expansion and neutron diffraction studies have shown that the choice of A and B elements as well as the material processing (synthesis, geometry, density, etc.) are crucial to control aging of material. We will consider an example of BaZr0.25In0.75O3 perovskite to show that several factors such as the carbonation, the traces of secondary AO phases at the grain boundaries as well as the use of samples with highly active surface, i.e. powders or lightly densified ceramics can cause: i) preferential adsorption of surface protonic species such as hydroxides, (hydro)carbonates, water, ii) decreased incorporation of bulk protonic species responsible for the proton conduction, iii) significant modification of the host perovskite structure up to complete crumbling of the material. We will show how to improve potential application of perovskites by understanding and controlling these processes. INTRODUCTION A2+(Sr,Ba)B4+(Zr,Ce,Ti,Sn,In,Ta,Nb)O3-δ perovskites substituted with Rare Earths (RE3+) or Lanthanides (Ln3+) appear as very interesting intermediate temperature proton conductors with huge possibility of applications as electrolytic membranes of water steam electrolysers, fuel cell electrolytes and CO2/syngas convertors [1-3]. Consequently, several oxygen-deficient perovskites such as cerates, zirconates or titanates have been widely investigated when substituted with lower valence elements from a few up to 75% [2-9]. Note that the higher the doping content, the higher the oxygen vacancy content and consequently the higher the content of bulk protonic species. Since the presence of protonic species is not intrinsic to the perovskite structure, it is necessary to hydrate/protonate them. The challenge is to obtain perovskites with the highest possible proton conduction while assuring mechanical and chemical stability over long life-time (~10.000 hours) at the operating temperatures under corrosive conditions of high water vapor pressure. Recently, we showed the high mechanical and chemical stability of SrZr0.9Ln0.1O3-δ dense ceramic [8]. However due to the low substitution level, this system has a very small content of bulk protonic species, as confirmed by neutron measurements [8]. In order to maximize the content of the bulk protonic species we prepared the 75% In substitu
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