Mitigating Electronic Conduction in Ceria‐Based Electrolytes via External Structure Design

Doped ceria electrolytes are the state of the art low‐temperature solid oxide electrolytes because of their high ionic conductivity and good material compatibility. However, cerium tends to reduce once exposed to reducing environments, leading to an increase in electronic conduction and a decrease in efficiency. Here, the leakage current is mitigated in ceria‐based electrolytes by controlling the defect chemistry through an engineered cathode side microstructure. This functional layer effectively addresses the problematic electronic conduction issue in ceria‐based electrolytes without adding significant ohmic resistance and increases the ionic transference tO2−$t_{{{\mathrm{O}}}^{2 - }}$ number to over 0.93 in a thin 20 µm ceria‐based electrolyte at 500 °C, compared to a tO2−$t_{{{\mathrm{O}}}^{2 - }}$ of 0.8 for an unmodified one. Based on this design, solid oxide fuel cells (SOFCs) are further demonstrated with the remarkable peak power density of 550 mW at 500 °C and excellent stability for over 2000 h. This approach enables a potential breakthrough in the development of ceria‐based low‐temperature solid oxide electrolytes. Herein a simple porous functional layer that mitigates the problematic electronic conduction issue of ceria‐based electrolytes is demonstrated, increasing the ionic transference number without adding significant ohmic resistance. The resulting low‐temperature SOFCs exhibit remarkable power density and stability, thus enabling a potential breakthrough in the development of ceria‐based SOFCs and SOECs.