A high-strength Sm-doped CeO₂ oxide-ion conducting electrolyte membrane for solid oxide fuel cell application

Nano-sized Ce_0.79Sm_0.2Cu_0.01O _2-δ (CSCO) and Ce_0.80Sm_0.2O _2-δ (CSO) electrolyte powders were synthesized by the PVA-assisted combustion method, sintered at various temperatures and electrochemical properties, mechanical properties and microstructures were characterized in detail. The results demonstrate that besides a considerable lowering of sintering temperature to achieve high levels of densification, the addition of very minor amounts of CuO as a co-dopant to CSO significantly enhanced mechanical properties (strength and hardness) without great degradation in electrochemical performance. The CSCO sintered at 1100 °C exhibits a biaxial flexural strength of 319 ± 41 MPa which compared with 194 ± 57 MPa for CSO with a slightly lower relative density sintered at 1400 °C. The enhancement of biaxial flexural strength is due to the formation of stronger CuO-rich grain boundaries during sintering as a consequence of the slight modification in grain boundary chemistry which leads to changes in fracture mode from intergranular to transgranular.