Determination of surface exchange and diffusion coefficient in mixed conductors using EMF measurements

Abstract

We discuss a new technique for determining the chemical diffusion coefficient, D chem , as well as the coefficient K chem of surface chemical exchange, in mixed ionic electronic conductors (MIECs). The method is based on EMF measurements following the response to chemical step changes. Expressions for the dependence of V OC ( t), the open circuit voltage (EMF), on time after chemical step are developed. The interpretation of D chem and K chem depends on the defect model of the MIEC and the surface reaction process. The analytic solution for V OC ( t) assumes constant D chem and K chem . However, the solution can be applied to cases with non-constant D chem and K chem provided the composition changes are done in small steps. The method is demonstrated by applying it to LSM (La 0.8Sr 0.2MnO 3 − x ) as the MIEC.