Abstract
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 LiCoO 2 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.