Fuel cells without searing heat: new material conducts oxide ions at just 233 degrees
Solid oxide fuel cells usually run at 700 to 1,000 degrees. A team in Tokyo has found a material that conducts oxide ions very well at just 233 degrees – while remaining stable.
Symbolic image · Photo: Jakub.kupecki / Wikimedia Commons, CC BY-SA 4.0 (cropped and resized)
Solid oxide fuel cells (SOFCs) generate electricity directly from hydrogen, natural gas or biogas. Their usual electrolytes, such as yttria-stabilised zirconia, need temperatures of around 700 to 1,000 degrees Celsius, which ages the materials and raises costs. Researchers are therefore looking for electrolytes that work well between 200 and 500 degrees – a range experts call the "Norby gap".
A team led by Professor Masatomo Yashima of the Institute of Science Tokyo has now presented a new Sillén oxybromide with the formula Bi1.9Te0.1LaO4.05Br. It reaches a bulk oxide-ion conductivity of 0.01 siemens per centimetre at just 233 degrees. Established electrolytes such as YSZ and LSGM need 644 and 534 degrees respectively to do the same. The material also remained chemically stable in various atmospheres up to 300 degrees, and its chemical expansion is negligible. The mechanism is surprising: the ions move via vacancies in the crystal lattice even though the material contains excess oxygen. The study was published in Nature Communications on 14 October, with Kyushu University, Imperial College London and Japan's KEK research centre also involved.
More work is needed before it can be used: because of resistance at the grain boundaries, the total conductivity is lower than the bulk value. The researchers therefore plan to further optimise the material's microstructure.