PNNL

Abstract

First-principles and statistical-theory calculations were applied to examine the interactions between oxygen molecules and the (100) surfaces of LaMnO3 and La0.5Sr0.5MnO2.75, one of the most-used cathode materials in solid oxide fuel cells (SOFCs). To predict the rate constants for the interactions between O2 and LaMnO3 or La0.5Sr0.5MnO2.75, potential energy profiles were constructed using the nudged elastic band (NEB) method. Predicted rate constants for the dissociation of adsorbed oxygen species on LaMnO3 (lm) and La0.5Sr0.5MnO2.75 (lsm) can be expressed as kdiss,lm ) 2.35 × 1012 exp(-0.50 eV/RT) s-1 and kdiss,lsm ) 2.15 × 1012 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 La0.5Sr0.5MnO2.75 (0.23 eV) is much smaller than that on LaMnO3 (0.50 eV), oxygen vacancies greatly enhance O2 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.