Mixed proton-electron-oxide ion triple conducting manganite as an efficient cobalt-free cathode for protonic ceramic fuel cells

It is challenging for materials chemists to develop efficient, cobalt-free cathode materials for solid oxide fuel cells mainly because of the resource scarcity. This study demonstrates that a cubic-type La0.7Sr0.3Mn0.7Ni0.3O3-delta (C-LSMN7373) perovskite is promising for intermediate-temperature protonic ceramic fuel cells (PCFCs) because of the sufficient H+/e(-)/O2- triple conductivity. The oxide can be hydrated by gaining 0.1 molar fraction of H2O under wet air at 415 degrees C, as confirmed by thermogravimetry analysis. An in situ extended X-ray absorption fine structure (EXAFS) analysis shows that the hydration reaction takes place via the association between H2O and oxygen vacancies, coupled with the redox of Mn and O atoms. Rhombohedral-type La0.7Sr0.3Mn1-xNixO3-delta cannot undergo hydration because the oxygen vacancy concentration required for water association is lower than the cubic phase concentration. The cathode performances of various PCFCs are examined by fabricating thin-film cells based on a Ba(Zr0.4Ce0.4Y0.2)O-3 electrolyte. The peak power density of the PCFCs with the cubic-type LSMN7373 cathode is 386 mW cm(-2) at 600 degrees C, which is much higher than the reported values for Zr-rich side electrolytes. Moreover, the cathodic polarization resistance is lower than that of a cell with the widely used La0.6Sr0.4Co0.2Fe0.8O3 cathode below 550 degrees C.