Enhanced Ionic Transport and Interfacial Properties of Sr/Gd Co-doped CeO2 Electrolytes for IT-SOFCs

The Gd 0.1 Ce 0.9- x Sr x O 2-δ ( x = 0, 0.01, 0.04, 0.07) electrolytes were synthesized via the citric acid-EDTA combustion method as electrolyte materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs), aiming to enhance ionic conductivity and mechanical stability of SOFCs at intermediate-to-high temperatures. Sr²⁺ doping improved electrolyte densification, increased grain volume, and reduced grain boundary density, thereby enhancing the dielectric constant. These modifications decreased both intragrain and grain boundary resistances and facilitated oxygen ion migration. At 500°C, the optimized Gd 0.1 Ce 0.86 Sr 0.04 O 2-δ exhibited a 6.4-fold increase in ionic conductivity and a 50% reduction in activation energy compared to Gd 0.1 Ce 0.9 O 1.95 . This enhancement was partially attributed to the improved scavenging coefficient of Gd 0.1 Ce 0.86 Sr 0.04 O 2-δ , whose blocking factor decreased by approximately 43% relative to Gd 0.1 Ce 0.9 O 1.95 . Dielectric property analysis elucidated the contribution of Gd-Sr synergistic effects to interfacial polarization.In terms of mechanical properties, the 4GSDC sample demonstrated a 13.5% increase in Vickers hardness, 69.7% improvement in fracture toughness, and 24.91% enhancement in flexural strength compared to GDC. At 750°C, single cells with the 4GSDC electrolyte achieved a power density of 1100   mW/cm², representing a 55.4% improvement over GDC. Density functional theory (DFT) calculations revealed that Sr²⁺ incorporation effectively reduced binding energy and migration barriers. Therefore, Sr-Gd co-doping can be regarded as an effective strategy to enhance the performance of ceria-based electrolytes in IT-SOFCs.