Proton‐Conducting Amorphous Alumina Electrolytes for Low‐Temperature Ceramic Fuel Cells

The development of high-performance electrolytes enabling rapid ionic transport represents a critical pathway for operational temperature reduction in solid oxide fuel cells (SOFCs). This study introduces amorphous alumina (AlO_x) as a novel electrolyte material, systematically investigating its structural characteristics and charge transport mechanisms through comparative analysis with crystalline alumina (α-Al₂O₃, γ-Al₂O₃) and conventional gadolinium-doped ceria (GDC). It is found that AlO_x possesses a notable enrichment of oxygen vacancy concentration. Its unique disordered atomic configuration plays a vital role in facilitating multiple pathways to enable fast ionic transport, resulting in high ionic conductivity of 0.08-0.12 S/cm at 480-540 °C, as evidenced by electrochemical impedance spectroscopy (EIS), which is one order of magnitude superior to its crystalline counterpart. When implemented in symmetrical SOFC configurations, the AlO_x electrolyte demonstrates unprecedented power density of 677 mW/cm² at 540 °C. Further distribution of relaxation times (DRT) analysis confirms the predominance of protonic conduction pathways in AlO_x while providing discernment of its electrochemical sub-processes. This work thus provides a new advanced electrolyte for low-temperature SOFCs while providing insights into amorphous ceramic.