A fast ceramic mixed OH/H ionic conductor for low temperature fuel cells.

Low temperature ionic conducting materials such as OH and H ionic conductors are important electrolytes for electrochemical devices. Here we show the discovery of mixed OH/H conduction in ceramic materials. SrZrYO exhibits a high ionic conductivity of approximately 0.01 S cm at 90 °C in both water and wet air, which has been demonstrated by direct ammonia fuel cells. Neutron diffraction confirms the presence of OD bonds in the lattice of deuterated SrZrYO. The OH ionic conduction of CaZrYO in water was demonstrated by electrolysis of both HO and DO. The ionic conductivity of CaZrYO in 6 M KOH solution is around 0.1 S cm at 90 °C, 100 times higher than that in pure water, indicating increased OH ionic conductivity with a higher concentration of feed OH ions. Density functional theory calculations suggest the diffusion of OH ions relies on oxygen vacancies and temporarily formed hydrogen bonds. This opens a window to discovering new ceramic ionic conducting materials for near ambient temperature fuel cells, electrolysers and other electrochemical devices.