Mechanism of Proton Conduction in Doped Barium Cerates: A First-Principles Study

Solid oxide fuel cells with high-temperature proton conductors (HTPCs) as the electrolyte have attracted intensive attention for years; however, the mechanism for proton transfer in HTPCs remains uncertain so far. In order to uncover the mechanism, ideal BaCeO3 (BCO) and BaZr0.1Ce0.7Y0.1Yb0.1O3-delta without and with an oxygen vacancy (BZCYYb and BZCYYb_V) are studied at the H-form in BCOT microscopic level by the first-principles approach. Two forms of proton transfer, that is, the H-form and (R-type and S-type) OH-form, are investigated in the aspects of the proton transport path, energy barrier along the path, differential charge density, electrostatic potential, distance between H and O atoms at the transition state of saddle point, as well as the distance between adjacent O atoms. The results indicate that the S- type OH-form in BZCYYb_V is the most favorable realistic mode for proton transfer, which indicates that protons migrate in the form of OH in the presence of oxygen vacancies; doping of Zr, Y, and Yb reduces the electrostatic potential barrier for proton transport, which makes proton transfer much easier in BZCYYb than in BCO, and the introduction of an oxygen vacancy further reduces the electrostatic potential barrier for H- form proton transfer in BZCYYb_V.