Hydration and Proton Kinetics in Ce-Doped Co-Free Perovskite for the Triple-Conducting Cathode in Solid Oxide Fuel Cells

Perovskite-type oxides (ABO3) possess beneficial cathode characteristics for solid oxide fuel cells because of quick oxide ion transport through the octahedral structures. However, mixed proton-electron conducting Co-free perovskites, which extend the electrode reactions from the electrolyte interface to the whole electrode, are still in urgent need of development. Herein, the hydration and proton kinetics in Ce-doped BaFeO3-delta are explored by using first-principles calculations. In our study, we have defined two parameters to characterize the symmetry and investigate the formation and motion of protons in cathode materials of perovskite from the perspective of reaction thermodynamics and dynamics. The results demonstrated that Ce exhibited the most favorable equilibrium property at a low concentration of 12.5%, characterized by an oxygen vacancy formation energy of 0.55 eV, hydration energy of -1.06 eV, and a migration energy barrier of 0.15 eV, thereby facilitating the overall reaction process. The transition state calculation elucidates the influence of lattice distortion and lattice oxidation environment on proton migration. Specifically, a decrease in lattice distortion facilitates proton hydration and reduces proton migration. As lattice distortion increases, the energy barrier gradually rises from 0.076 to 0.4 eV. Moreover, in crystals with second-class symmetry, reducing lattice distortion is more favorable for promoting proton migration than increasing free volume. The reliability of the calculated parameters is validated through comparison with experimental and computational studies. This study provides a theoretical foundation for developing Co-free perovskite cathodes with triple conductivity through doping.