Proton Conductivity in Perovskite Oxides

Perovskite oxides offer in almost all respects a wide variety of properties because of the structure s ability to host varying cations, substitutions, nonstoichiometry, and defects of many kinds. Proton conduction, resulting from oxide ability to dissolve protons from water vapor or hydrogen, is no exception Some perovskites contain virtually no protons at all and are thus barriers to protons, hydrogen, and water vapor. Other perovskites are dominated by proton defects to high temperatures and are predominantly proton conductors. 

The proton conductivity can if relatively pure be used in galvanic sensors for hydrogen or water vapor activity, usually at elevated temperatures. These sensors ntilize hydrogen activity gradients between the tested environment and a reference electrode. An example is In-doped CaZr03 used for probing hydrogen in molten alnmininm [7]. 

In many perovskites, the proton condnctivity is high enough to be utilized in high-drain applications, snch as fnel cells, steam electrolyzers, hydrogen pumps, and varions hydrogenation/dehydrogenation electrochemical reactors [8]. 

Department of Chemistry, Centre for Materials Science and Nanotechnology, University of Oslo, FERMiO, Gaustadalleen 21, NO-0349 Oslo, Norway e-mail t.e.norby kjemi.uio.no 

Ishihara (ed.), Perovskite Oxide for Solid Oxide Fuel Cells, 

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Fig. 9 Comparison of proton conduction in perovskite oxides (Ishihara et al. 2003).

Takahashi, T., and Iwahara, H. (1980). Solid-state ionics protonic conduction in perovskite type oxide solid solutions. Revue de Chimie minerale 17 243-233. 

Mechanisms of Proton Conduction in Perovskite-Type Oxides... 

Acceptor doping in perovskite oxides gives materials with a vacancy population that can act as proton conductors in moist atmospheres (Section 6.9). In addition, the doped materials are generally p-type semiconductors. This means that in moist atmospheres there is the possibility of mixed conductivity involving three charge carriers (H+, O2-, and h ) or four if electrons, e, are included. 

Sata N, Yugami H, Akiyama Y, Sone H, Kitamura N, Hattori T, Ishigame M. Proton conduction in mixed perovskite type oxides. Solid State Ionics. 1999 125 383-387. 

The oxide Ba Inp adopts the brownmillerite structure at lower temperatures (Section 2.4). The structure begins to disorder at approximately 900°C and forms a cubic perovskite phase with a high concentration of oxygen vacancies somewhere above this temperature. Proton conduction in the solid is brought about by the incorporation of water molecules. Water vapour can react directly with the oxide at higher temperatures, following disproportionation at the oxide surface ... 

These studies on the above materials did not however, provide a direct evidence for high-temperature protonic conduction in oxide materials. A conclusive demonstration for high-temperature protonic conduction in oxides was first reported in 1981 by Iwahara et al. (1981a) for rare-earth doped perovskite oxides. 

Many perovskite-type (ABO3) oxides show high proton conductivity in a reducing atmosphere. The most common proton-conducting oxide is BaCeOs, which has been doped with various oxides, including those of samarium (Ranran et al, 2006), neodymium (Schober, 2003 Kobayashi et al, 2005 Gorbova et al, 2006 Su et al, 2006) and ytterbium (Taherparvar et al,... 

Shimura, T., Fujimoto, S., Iwahara, H. (2001). Proton conduction in non-perovskite-t)fpe oxides at elevated temperatures. Solid State Ionics, 143, 117—123. 

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