Gd, Sm, and Yb Co-Doped Proton-Conducting Electrolytes for an Intermediate-Temperature Solid Oxide Fuel Cell

Strontium-based perovskite-type proton-conducting SrCe_0.5Zr_0.3Y_0.1Gd_0.05Zn_0.05O_3−δ (SrCZYGdZn), SrCe_0.5Zr_0.3Y_0.1Sm_0.05Zn_0.05O_3−δ (SrCZYSmZn), and SrCe_0.5Zr_0.3Y_0.1Yb_0.05Zn_0.05O_3−δ (SrCZYYbZn) have been synthesized by a solid-state reaction method. The studied materials were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and electrochemical impedance spectroscopy (EIS). All the materials showed tetragonal symmetry with the P4mm space group. SEM image analysis confirms the well-crystallized high-density materials with good grain size, and TGA shows the thermal stability up to 800°C. In wet 5% H₂, the ionic conductivities of SrCZYGdZn, SrCZYSmZn, and SrCZYYbZn were 2.36 × 10⁻⁴ Scm⁻¹, 9.33 × 10⁻⁵ Scm⁻¹, and 1.17 × 10⁻³ Scm⁻¹, respectively, at 700°C. On the other hand, in a dry H₂ atmosphere, the ionic conductivities were 2.33 × 10⁻⁴ Scm⁻¹, 8.97 × 10⁻⁵ Scm⁻¹, and 9.17 × 10⁻⁴ Scm⁻¹, respectively, at the same temperature. The calculated activation energies of SrCZYGdZn, SrCZYSmZn, and SrCZYYbZn were 0.90 eV, 0.41 eV, and 0.31 eV, respectively, in wet 5% H₂. Reasonable conductivity and low activation energy makes these electrolytes promising for IT-SOFC.