Superionic Conductivity of Sm³⁺, Pr³⁺, and Nd³⁺ Triple-Doped Ceria through Bulk and Surface Two-Step Doping Approach

Sufficiently high oxygen ion conductivity of electrolyte is critical for good performance of low-temperature solid oxide fuel cells (LT-SOFCs). Notably, material conductivity, reliability, and manufacturing cost are the major barriers hindering LT-SOFC commercialization. Generally, surface properties control the physical and chemical functionalities of materials. Hereby, we report a Sm³⁺, Pr³⁺, and Nd³⁺ triple-doped ceria, exhibiting the highest ionic conductivity among reported doped-ceria oxides, 0.125 S cm^-1 at 600 °C. It was designed using a two-step wet-chemical coprecipitation method to realize a desired doping for Sm³⁺ at the bulk and Pr³⁺/Nd³⁺ at surface domains (abbreviated as PNSDC). The redox couple Pr³⁺/Pr⁴⁺ contributes to the extraordinary ionic conductivity. Moreover, the mechanism for ionic conductivity enhancement is demonstrated. The above findings reveal that a joint bulk and surface doping methodology for ceria is a feasible approach to develop new oxide-ion conductors with high impacts on advanced LT-SOFCs.