Samples of Ba1-xSrxCe0.9Y0.1O3-δ, 0 < x < 0.1, with Improved Chemical Stability in CO2-H2 Gas-Involving Atmospheres as Potential Electrolytes for a Proton Ceramic Fuel Cell.

Magdalena Dudek,Przemysław Grzywacz,Salius Daugėla,Radosław Lach,Algimantas Kežionis,Bartłomiej Lis,Maciej Sitarz,Tomas Šalkus,Alicja Rapacz-Kmita,Michał Mosiałek

doi:10.3390/ma13081874

Abstract

Comparative studies were performed on variations in the ABO3 perovskite structure, chemical stability in a CO2-H2 gas atmosphere, and electrical conductivity measurements in air, hydrogen, and humidity-involving gas atmospheres of monophase orthorhombic Ba1−xSrxCe0.9Y0.1O3−δ samples, where 0 < x < 0.1. The substitution of strontium with barium resulting in Ba1−xSrxCe0.9Y0.1O3−δ led to an increase in the specific free volume and global instability index when compared to BaCe0.9Y0.1O3−δ. Reductions in the tolerance factor and cell volume were found with increases in the value of x in Ba1−xSrxCe0.9Y0.1O3−δ. Based on the thermogravimetric studies performed for Ba1−xSrxCe0.9Y0.1O3−δ, where 0 < x < 0.1, it was found that modified samples of this type exhibited superior chemical resistance in a CO2 gas atmosphere when compared to BaCe0.9Y0.1O3−δ. The application of broadband impedance spectroscopy enabled the determination of the bulk and grain boundary conductivity of Ba1−xSrxCe0.9Y0.1O3−δ samples within the temperature range 25–730 °C. It was found that Ba0.98Sr0.02Ce0.9Y0.1O3−δ exhibited a slightly higher grain interior and grain boundary conductivity when compared to BaCe0.9Y0.1O3−δ. The Ba0.95Sr0.05Ce0.9Y0.1O3−δ sample also exhibited improved electrical conductivity in hydrogen gas atmospheres or atmospheres involving humidity. The greater chemical resistance of Ba1−xSrxCe0.9Y0.1O3−δ, where x = 0.02 or 0.05, in a CO2 gas atmosphere is desirable for application in proton ceramic fuel cells supplied by rich hydrogen processing gases.

Highlights

One promising group of ceramic proton conductors is composed of perovskite (ABO3 )-based oxides.The Y2 O3 -doped zirconates BaZr1−x Yx O3−δ or cerates BaCe1−x Yx O3−δ, where 0 < x < 0.3, Materials 2020, 13, 1874; doi:10.3390/ma13081874 www.mdpi.com/journal/materialsMaterials 2020, 13, 1874 are currently considered to be suitable materials for ceramic proton-conducting fuel cells operating at reduced temperatures
In order to find the impact of the incorporation of strontium resulting in Ba1−x Srx Ce0.9 Y0.1 O3−δ on variations in its structure compared to the BaCe0.9 Y0.1 O3−δ sample, the Goldschmidt tolerance factor (t), specific free volume (SFV), and global instability index (GII) were calculated using the SPuDS software package
In the case of SBCY samples with increased SrO content in Ba1−x Srx Ce0.9 Y0.1 O3−δ the diffraction peaks shifted towards greater diffraction angles in the recorded XRD patterns; a decrease was found in the cell volume of Ba1−x Srx Ce0.9 Y0.1 O3−δ samples when compared to BaCe0.9 Y0.1 O3−δ

Summary

Introduction

One promising group of ceramic proton conductors is composed of perovskite (ABO3 )-based oxides.The Y2 O3 -doped zirconates BaZr1−x Yx O3−δ or cerates BaCe1−x Yx O3−δ , where 0 < x < 0.3, Materials 2020, 13, 1874; doi:10.3390/ma13081874 www.mdpi.com/journal/materialsMaterials 2020, 13, 1874 are currently considered to be suitable materials for ceramic proton-conducting fuel cells operating at reduced temperatures. One promising group of ceramic proton conductors is composed of perovskite (ABO3 )-based oxides. The Y2 O3 -doped zirconates BaZr1−x Yx O3−δ or cerates BaCe1−x Yx O3−δ , where 0 < x < 0.3, Materials 2020, 13, 1874; doi:10.3390/ma13081874 www.mdpi.com/journal/materials. Materials 2020, 13, 1874 are currently considered to be suitable materials for ceramic proton-conducting fuel cells operating at reduced temperatures. Ceramic proton-conducting fuel cells (PCFCs) and solid oxide fuel cells (SOFCs) are being intensively studied with the aim of constructing power sources which can be operated within a temperature range of 400–700 ◦ C [1,2]. Ceramic proton conductors can be applied to the construction of other electrochemical devices important for hydrogen infrastructures. Y2 O3 -doped cerates exhibit higher levels of ionic conductivity than BaZr1−x Yx O3−δ Classic electrochemical devices for this technology include solid oxide electrolyzers, hydrogen or hydrocarbon sensors, hydrogen units for gas purification processes, and reactors for the hydrogenation of compounds [3,4,5].

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