Scientists Synthesize Low-Temperature Oxide-Ion Conductor for Fuel Cells

Solid-oxide fuel cells convert chemical energy from fuels such as hydrogen, natural gas, and biogas directly into electricity. When powered by hydrogen, their primary reaction product is water. However, conventional commercial cells rely on electrolytes like yttria-stabilized zirconia, which require temperatures between 700°C and 1,000°C to conduct oxide ions efficiently. These thermal demands accelerate material degradation, increase manufacturing expenses, and complicate component matching.

To lower those thresholds, researchers have sought electrolytes that function within the 200°C to 500°C range, known as the Norby gap. A research team led by Professor Masatomo Yashima at the Institute of Science Tokyo has synthesized a Sillén oxybromide, Bi₁.₉Te₀.₁LaO₄.₀₅Br, that achieves high bulk oxide-ion conductivity at 233°C, as detailed in a report by TechXplore (https://techxplore.com/news/2026-10-ultrafast-oxide-ion-conductors-route.html) and published in Nature Communications.

The research group substituted the chlorine ion in a previously studied oxychloride with a larger, more polarizable bromide ion. The resulting Bi₁.₉Te₀.₁LaO₄.₀₅Br exhibited a bulk oxide-ion conductivity of 0.01 S cm⁻¹ at 233°C. For the same conductivity, conventional electrolytes such as yttria-stabilized zirconia and lanthanum strontium gallium magnesium oxide require temperatures of 644°C and 534°C, respectively. The material's oxide-ion conductivity also exceeded the values reported for several standard proton-conducting ceramics.

Crystal structure analyses showed that the compound forms triple fluorite-like slabs sandwiched between bromide layers. Using diffraction measurements, first-principles calculations, and ab initio molecular dynamics simulations, the team discovered that oxide ions migrate through lattice vacancies rather than interstitial paths, despite an oxygen excess of 0.05. This vacancy-mediated mechanism runs counter to standard expectations for excess-oxygen conductors.

In lab testing, the material maintained chemical stability up to 300°C across dry and wet oxidizing, reducing, and carbon dioxide environments, alongside negligible chemical expansion. The study involved collaborators from Kyushu University, Imperial College London, and the High Energy Accelerator Research Organization (KEK) at J-PARC.

The researchers noted that total conductivity remains below bulk conductivity due to grain-boundary resistance. Translating the findings into practical fuel cell hardware will require microstructural optimization, such as grain growth and densification. Yashima and colleagues noted that the layered halide architecture could also inform electrolyte designs for solid oxide electrolysis cells and related energy systems.