Disordered vacancy-isolated Ce-Gd-O clusters achieve exceptional low-temperature oxygen-ion conductivity for fuel cells.

Oxygen-ion conductors are central to clean energy technologies. Conventional long-range-ordered oxide-ion conductors require high operating temperatures, which increase cost and limit durability; overcoming the low temperature conductivity gap is a long-standing challenge. We created cerium (Ce)-gadolinium (Gd)-oxygen (O) clusters by thermal-shock exfoliation of fluorite Gd0.1Ce0.9O1.95 and examined their structure and ion transport. These disordered, vacancy-isolated clusters form percolative oxygen-ion pathways without long-range order, delivering exceptional conductivity of 2.14 ± 0.09 siemens per centimeter at 400°C-more than 320-fold higher than most previously reported oxide-ion conductors under comparable conditions. Used as a 0.5 weight % cathode additive in solid oxide fuel cells, they tripled the peak power density to 2.87 ± 0.04 watts per square centimeter at 750°C compared with the pristine Pr0.5Ba0.25Ca0.25CoO3-δ/Gd0.1Ce0.9O1.95 cathode and reversed degradation from -13.2 to +3.4% per 100 hours. These findings overturn the paradigm that high oxygen-ion conductivity requires long-range order and highlight Ce-Gd-O clusters as enablers for advanced energy technologies.