Prediction of O(2) Dissociation Kinetics on LaMnO(3)-Based Cathode Materials for Solid Oxide Fuel Cells

Abstract

First-principles and statistical-theory calculations were applied to examine the interactions between oxygen molecules and the (100) surfaces of LaMnO(3) and La(0.5)Sr(0.5)MnO(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(0.5)Sr(0.5)MnO(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(0.5)Sr(0.5)MnO(2.75) (lsm) can be expressed as k(diss,lm) = 2.35 x 10(12) exp(-0.50 eV/RT) s(-1) and k(diss,lsm) = 2.15 x 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(0.5)Sr(0.5)MnO(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.