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Proton Conductivity and Mobility in Triple-Conducting Perovskites Ba0.95La0.05Fe1-x(Y,Zn)xO3-δ

Title data

Berger, Christian ; Merkle, Rotraut ; Exner, Jörg ; Moos, Ralf ; Maier, Joachim:
Proton Conductivity and Mobility in Triple-Conducting Perovskites Ba0.95La0.05Fe1-x(Y,Zn)xO3-δ.
Event: Solid State Ionics 23 , 17.-22.07.2022 , Boston, USA.
(Conference item: Conference , Speech )

Abstract in another language

Barium ferrates from the series Ba0.95La0.05Fe1-xMxO3-δ (BLFM with M=Y, Zn; x=0, 0.2) are mixed proton-, oxide ion-, and electronic conductors and therefore of interest for various applications such as protonic ceramic fuel and electrolyser cells (PCFC and PCEC), or hydrogen separation membranes. Proton concentrations have been measured for a larger range of triple conducting perovskites, and the degree of hydration is significantly lower in such mixed conducting perovskites compared to Ba(Zr,Ce,Y)O3-δ electrolytes. However, the measurement of proton mobility or conductivity is challenging, as it is superimposed by a high electronic and a non-negligible oxygen vacancy ionic conductivity. Nevertheless, its value is important to judge whether it suffices to make the whole surface of a PCFC cathode active for the oxygen reduction reaction. In the current work, Wagner-Hebb DC polarisation measurements with a proton-selective electrode were carried out to obtain the proton conductivity. A pore-free BaCe0.8Y0.2O3-δ layer of approximately 20 micrometer thickness was applied with powder aerosol deposition on dense BLFM pellet samples as an electrode with high proton selectivity. Oxygen vacancies are blocked by operating under conditions of complete hydration of the BaCe0.8Y0.2O3-δ layer (25mbar H2O, T ≤ 450°C). The application of reducing conditions (9×10-27 ≤ pO2/bar ≤ 9×10-22) furthermore suppresses the hole conductivity in the BaCe0.8Y0.2O3-δ layer. The proton conductivity of BLFM obtained from DC polarisation provides values in the range of 4×10-6 ≤ σOHo●/Scm-1 ≤ 2×10-5 at 400°C, with the highest conductivity for Ba0.95La0.05Fe0.8Zn0.2O3-δ. In addition to the proton conductivity, the water chemical diffusion coefficient Dδ H2O can be extracted from the transient behavior of the DC polarization experiment. Within the moderate degree of hydration of BLFM in these experiments, Dδ H2O can be assumed close to the proton diffusion coefficient DOHo●. Values in the order of 4×10-7 ≤ DOHo●/cm^2s-1 ≤ 5×10-6 are obtained at 400°C. The results show that the proton mobility in the investigated barium ferrates is comparable to that in proton conducting electrolytes. The activation energy of ≈0.5 eV for all BLFM samples is in the typical range for proton migration barriers in Ba(Zr,Ce,Y)O3-δ perovskites. The variation of proton mobility with dopants on the iron site will be discussed in this contribution.

Further data

Item Type: Conference item (Speech)
Refereed: Yes
Institutions of the University: Faculties > Faculty of Engineering Science
Faculties > Faculty of Engineering Science > Chair Functional Materials > Chair Functional Materials - Univ.-Prof. Dr.-Ing. Ralf Moos
Profile Fields > Advanced Fields > Advanced Materials
Research Institutions > Research Centres > Bayreuth Center for Material Science and Engineering - BayMAT
Result of work at the UBT: Yes
DDC Subjects: 600 Technology, medicine, applied sciences > 620 Engineering
Date Deposited: 27 Sep 2022 09:01
Last Modified: 27 Sep 2022 09:13
URI: https://eref.uni-bayreuth.de/id/eprint/72000