Improved bi-layer electrolytes of solid oxide cells: the role of a Sm0.2Ce0.8O2−δ diffusion barrier layer

Abstract

The Y₂O₃-stabilized ZrO₂ (YSZ)/ceria bi-layer electrolyte is a key component in recent solid oxide fuel cells and electrolyzers. An industrially viable route for its effective implementation involves reduced-temperature co-sintering; however, this is a multistep process, often requiring precise control due to the poor sinterability of conventional gadolinia-doped ceria (GDC). Here we demonstrate a bi-layer electrolyte in a single-step 1250 °C co-sintering with Sm_0.2Ce_0.8O_2−δ (SDC) as a key solution, and verify the performance of the resultant bi-layer electrolyte in a Ni–YSZ fuel electrode supported cell. This approach, proven to be scalable, delivers a satisfactory cell performance, such as a fuel cell power density of ∼2.15 W cm⁻² and a steam electrolysis current density of ∼2.95 A cm⁻² at 800 °C. Even without adding the Fe₂O₃ aid to SDC, the YSZ/SDC electrolyte remains reasonably dense, free from resistive phases, and exhibits a higher interdiffusion conductivity than that of the benchmark YSZ/GDC. Furthermore, the strategic addition of Fe₂O₃ improves the shrinkage compatibility of YSZ and SDC, enhancing the integrity of the bi-layer structure. The optimal electrolytes show a remarkable stability across 300 h of typical fuel cell operation. These results suggest important strategic modifications in bi-layer electrolyte compositions and processing.