Structure–Property Relationships in the Y2O3–ZrO2 Phase Diagram: Influence of the Y-Content on Reactivity in C1 Gases, Surface Conduction, and Surface Chemistry
2016
Kogler, Michaela | Köck, Eva-Maria | Klötzer, Bernhard | Penner, Simon
The C1 chemistry of Y-doped ZrO₂ samples (3, 8, 20, and 40 mol % Y₂O₃; 3-YSZ, 8-YSZ, 20-YSZ, and 40-YSZ) was comparatively studied with respect to the correlation of electrochemical properties and surface chemistry in CH₄, CO, and CO₂ atmospheres by electrochemical impedance (EIS) and spectroscopic (FT-IR) methods up to 1273 K to unravel the influence of the Y-doping level. A consistent picture with respect to qualitative and quantitative surface modifications as a function of temperature and gas-phase composition evolves by performing highly correlated operando/in situ measurements. A detailed study of carbon deposition in CH₄ and CO and adsorption of CO and CO₂, but also proof of the strong influence of the surface chemistry, is included. Carbon deposition during treatment in CH₄ and CO at temperatures T ≥ 1023 K is a common feature on all materials, irrespective of the Y content. On the 40-YSZ sample, the thinnest, but at the same time fully percolated, carbon layer was generated, and hence, “metallic” conductivity was apparent. This goes along with the fact that 40-YSZ is most unreactive toward adsorption, suggesting a direct link between homogeneous deposition and suppressed reactivity. For all Y-doped samples, temperature regions with different charge carrier activation energies could be identified, perfectly corresponding to significant changes in surface chemistry. Due to the different degree of hydroxylation and the different ability to chemisorb CO and CO₂, the influence of the surface chemistry on the electrochemical properties is varying strongly as a function of Y-content.
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