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. SrZr 0.8 Y 0.2 O 3- δ exhibits a high ionic conductivity of approximately 0.01 S cm −1 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 SrZr 0.8 Y 0.2 O 3- δ . The OH − ionic conduction of CaZr 0.8 Y 0.2 O 3- δ in water was demonstrated by electrolysis of both H 2 18 O and D 2 O. The ionic conductivity of CaZr 0.8 Y 0.2 O 3- δ in 6 M KOH solution is around 0.1 S cm −1 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.