Mixed Ionic-Electronic Conductivity, Redox Behavior and Thermochemical Expansion of Mn-Substituted 5YSZ as an Interlayer Material for Reversible Solid Oxide Cells

Alejandro Natoli; Blanca I Arias-Serrano; Enrique Rodríguez-Castellón; Agnieszka Żurawska; Jorge R Frade; Aleksey A Yaremchenko

doi:10.3390/ma14030641

Mixed Ionic-Electronic Conductivity, Redox Behavior and Thermochemical Expansion of Mn-Substituted 5YSZ as an Interlayer Material for Reversible Solid Oxide Cells

Materials (Basel). 2021 Jan 30;14(3):641. doi: 10.3390/ma14030641.

Authors

Alejandro Natoli¹, Blanca I Arias-Serrano^{1

2}, Enrique Rodríguez-Castellón³, Agnieszka Żurawska^{4

5}, Jorge R Frade¹, Aleksey A Yaremchenko¹

Affiliations

¹ CICECO-Aveiro Institute of Materials, Department of Materials and Ceramic Engineering, University of Aveiro, 3810-193 Aveiro, Portugal.
² Leibniz Institute for Plasma Science and Technology, Felix-Hausdorff-Street 2, 17489 Greifswald, Germany.
³ Department of Inorganic Chemistry, Faculty of Science, University of Malaga, Campus de Teatinos, 29071 Málaga, Spain.
⁴ Institute of Power Engineering-Research Institute, Mory 8 Street, 01-330 Warsaw, Poland.
⁵ CTH2-Center for Hydrogen Technologies, Institute of Power Engineering, Augustówka 36 Street, 02-981 Warsaw, Poland.

Abstract

Manganese-substituted 5 mol.% yttria-stabilized zirconia (5YSZ) was explored as a prospective material for protective interlayers between electrolyte and oxygen electrodes in reversible solid oxide fuel/electrolysis cells. [(ZrO₂)_0.95(Y₂O₃)_0.05]_1-x[MnO_y]_x (x = 0.05, 0.10 and 0.15) ceramics with cubic fluorite structure were sintered in air at 1600 °C. The characterization included X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), thermogravimetry and dilatometry in controlled atmospheres, electrical conductivity measurements, and determination of oxygen-ion transference numbers by the electromotive force (EMF) technique. Mn-substituted 5YSZ solid solutions exhibit variable oxygen nonstoichiometry with manganese cations in a mixed 2+/3+ oxidation state under oxidizing conditions. Substitution by manganese gradually increases the extent of oxygen content variation on thermal/redox cycling, chemical contribution to thermal expansion and dimensional changes on reduction. It also deteriorates oxygen-ionic conductivity and improves p-type electronic conductivity under oxidizing conditions, leading to a gradual transformation from predominantly ionic to prevailing electronic transport with increasing x. Mn^2+/3+→Mn²⁺ transformation under reducing atmospheres is accompanied by the suppression of electronic transport and an increase in ionic conductivity. All Mn-substituted 5YSZ ceramics are solid electrolytes under reducing conditions. Prolonged treatments in reducing atmospheres, however, promote microstructural changes at the surface of bulk ceramics and Mn exsolution. Mn-substituted 5YSZ with 0.05 ≤ x < 0.10 is considered the most suitable for the interlayer application, due to the best combination of relevant factors, including oxygen content variations, levels of ionic/electronic conductivity and thermochemical expansion.

Keywords: buffer layer; ionic conductivity; manganese oxide; mixed conductor; oxygen nonstoichiometry; solid oxide electrolysis cell; solid oxide fuel cell; thermochemical expansion; zirconia.

Abstract

Grants and funding