Zr and Gd co-doped ceria oxide conductor with low electronic conductivity in reducing atmosphere

The Gd and Zr co-doped ceria electrolyte Gd_0.1Ce_0.9-xZr_xO_1.95 (x = 0, 0.03, 0.06, 0.09, 0.12, 0.15, labeled as GDC, Zr0.03GDC, Zr0.06GDC, Zr0.09GDC, Zr0.12GDC, Zr0.15GDC) was synthesized by solid-state reaction. The XRD and Rietveld refinements reveal that ZrxGDC is in a cubic fluorite phase with the cell parameters a decrease from 5.4186(1) to 5.3728(1) Å and cell volume V decreases 159.10(2) to 155.09(2) ų as the x increases from 0 to 0.15. SEM studies confirm a dense microstructure with well-defined grains in a size of 10–20 μm. The Raman spectra agree with the fact that a solid solution is formed and the blue-shift of Raman modes is observed as expected. XPS analysis shows that Ce⁴⁺ is more stable in Zr doped GDC. The conductivity of Zr0.03GDC reaches 1.2 × 10⁻³ S/cm at 450 °C. The bond valence of Ce⁴⁺ is constrained to a higher one as the Ce⁴⁺ is substituted by Zr⁴⁺ in the solid solution, and a higher stability in the reducing atmosphere was achieved. The electronic conductivity decreases from 14.8% of GDC to 0.1% of Zr0.03GDC at 400 °C. The oxygen ion transference number of Zr0.03GDC is improved significantly to > 0.93 in 3% H₂/Ar at 700 °C.