LiCo Dual‐Doped Ceria‐Based Composite as a Promising Low‐Temperature Electrolyte for Metal‐Supported Solid Oxide Electrolyzers

Solid oxide electrolysis cells (SOECs) are among the most efficient energy-conversion devices for power-to-X applications in green energy technologies. Here, we report a high-level (5 mol%) Li- and Co-dual-doped gadolinium-doped ceria (GDC) electrolyte synthesized under an inert atmosphere, suitable for fabricating SOECs using conventional ferritic steel supports. The doped GDC exhibits uniform dopant incorporation and a single-phase cubic fluorite structure, achieving 98.18% relative density at 950 °C. Dilatometry and microstructural analyses reveal that Li-Co codoping significantly reduces sintering temperature and improves grain connectivity. Time-of-flight secondary ion mass spectrometry shows a Li,Co-rich surface layer whose thickness depends on sintering conditions, while Raman spectroscopy confirms the presence of a LiCoO₂ phase and temperature-dependent oxygen-vacancy concentration. Electrochemical impedance spectroscopy demonstrates enhanced ionic conductivity, particularly for the sample sintered at 950 °C (denoted 5LC-4), which achieves increases of 269.5% at 450 °C and 138.85% at 750 °C compared with commercial GDC. The ionic conductivity reaches 2.17 × 10^-2 S cm^-1 with an activation energy of 0.32 eV. A symmetric five-layer SOEC integrating 5LC-GDC exhibits superior electrochemical performance to yttria-stabilized zirconia (YSZ) support, achieving a peak power density of 267.5 mW cm^-2 at 850 °C.