Proton conductivity, perovskite

Key words membrane reactor, perovskite, proton conducting membrane, mixed ionic-electronic conductor (MIEC), partial oxidation of methane... 

Proton conduction at high temperatures occurs in certain perovskites such as doped strontium cerate, Sr Ceo.95Ybo.o503 t. In air, this material is primarily an electronic conductor due to the mixed valence of Ce. In the presence of moisture, water is absorbed by the reaction with positive holes to generate protons ... 

Figure 25. Proton conductivity of various oxides, as calculated from data on proton concentrations and mobilities, according to Norby and Larring (the type of dopant is not indicated see ref 187 for source data). The conductivity of oxides with a perovskite-type structure are shown by bold lines, and the conductivity of the oxide ion conductor YSZ (yttria-stabilized zirconia) is shown for comparison, (reproduced with the kind permission of Annual Reviews, http //www.AnnualReviews.org).

Haile, S. M., Staneff, G., and Ryu, K. H. Non-stoichiometry, Grain Boundary Transport and Chemical Stability of Proton Conducting Perovskites, Journal of Materials Science, 36, 1149 (2001). 

More recently, H. Iwahara et al. [20] reported that some compounds having the perovskite structure (see Section 2.7.3) become proton conductors if hydrogen is introduced into the crystal, and the solubility of water and proton mobility in perovskites are now actively researched topics [21]. The perovskites which can be tailored to exhibit high protonic conductivity have compositions of the type... 

Fig. 4.42 Electrical conductivities of modified perovskite proton conductors (adapted from...

In Chapter 10, the use of membranes for different applications are described. One of the possible membranes for hydrogen cleaning is an asymmetric membrane comprised of the dense end of a proton conduction perovskite such as BaCe0 95 Yb0 05O3 5 and a porous end to bring mechanical stability to the membrane. In this case, it is possible to take from the slurry, obtained by the acetate procedure, several drops to be released over a porous ceramic membrane, located in the spinning bar of a spin-coating machine. Thereafter, the assembly powder, thin film porous membrane is heated from room temperature up to 1573 K at a rate of 2K/min, kept at this temperature for 12 h, and then cooled at the same rate in order to get the perovskite end film over the porous membrane [50],... 

The defects in doped BaCe03 perovskites, which are good proton conductors, are described here [32,33,48-54]. It has been recognized that temperature and atmosphere significantly affect the transport properties of the majority of protonic conductors [33], Certainly, under a definite temperature range and specific atmosphere, doped BaCe03 has significant protonic conductivity [48-54],... 

The introduction of defects into the perovskite structure and their distribution in the structure are key factors that determine the protonic conductivity [50,51], The inclusion of trivalent dopants ideally takes place, as described in the Kroger-Vink notation, [43] by... 

Absorption and Diffusion of Hydrogen in Nanocrystals of the BaCe095Yb0 05O3 8 Proton-Conducting Perovskite... 

J. Wu, Defect chemistry and proton conductivity in Ba-based perovskites, PhD thesis, California Institute of Technology, Pasadena, CA (2005). 

In the 1960s, all the tools needed to treat hydrogen defects in oxides [41-43] were fundamentally developed by Wagner and collaborators. However, up to the end of the 1970s, real developments in the field did not take place. During the last years of this decade, some significant studies were carried out [44-48], After that, it was realized that the introduction of defects in some perovskite structures determine the protonic conductivity of these materials. In this regard, Iwahara and... 

Hydrogen-permselective silica membranes [8,10] can be, as well, synthesized by a particular application of solgel techniques [142,143], Additionally, hydrogen permselective asymmetric membranes composed of a dense ceramic of a proton-conducting perovskite over a porous support have been developed [40], However, some difficulties with respect to their stability is possible in certain reactive environments [121],... 

Development of compact fuel cells, created by combining proton conductive perovskite-type oxide ceramics with metal-hydride materials, has been already proposed [1], Our group expects that the compact fuel cells can be utilized under radiation environments such as fission and fusion reactors or cosmic [2], Therefore, it is very important to understand behaviors of electron and proton conductions under radiation environments. 

A point defect model has been proposed for the brownmillerite structure, based on a study of electrical conductivity and em/measurements of Ba2ln205 [236]. The experimental results matched well with modelling, while evidence was found for protonic conduction at low temperatures. In modelling, the unoccupied oxygen sites relative to the perovskite structure, below Tj, are regarded as structural units and therefore are potential interstitial sites for... 

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