Prediction of O ₂ dissociation kinetics on LaMnO ₃-based cathode materials for solid oxide fuel cells

First-principles and statistical-theory calculations were applied to examine the interactions between oxygen molecules and the (100) surfaces of LaMnO ₃ and La _0.5Sr _0.5MnO _2.75, one of the most-used cathode materials in solid oxide fuel cells (SOFCs). To predict the rate constants for the interactions between O ₂ and LaMnO ₃ or La _0.5Sr _0.5MnO _2.75, potential energy profiles were constructed using the nudged elastic band (NEB) method. Predicted rate constants for the dissociation of adsorbed oxygen species on LaMnO ₃ (lm) and La _0.5Sr _0.5MnO _2.75 (lsm) can be expressed as k _diss,Im) 2.35 × 10 ¹² exp(-0.50 eV/RT) s ^-1 and k _diss,lsm) 2.15 × 10 ¹² exp(-0.23 eV/RT) s ^-1, respectively, in the temperature range of 873-1273 K at 1 atm. Because the activation energy for oxygen dissociation on La _0.5Sr _0.5MnO _2.75 (0.23 eV) is much smaller than that on LaMnO ₃ (0.50 eV), oxygen vacancies greatly enhance O ₂ dissociation kinetics. The kinetic and mechanistic studies for the interactions at the molecular level are imperative to gaining a fundamental understanding of oxygen reduction kinetics on cathode materials and to providing important insight into the rational design of more catalytically active cathode materials for SOFCs.