Enhanced accuracy of electrochemical kinetic parameters determined by electrical conductivity relaxation

Abstract

Electrical conductivity relaxation (ECR) is a widely adopted technique for determination of oxygen surface exchange coefficient (kchem) and chemical oxygen diffusivity (Dchem) of mixed ionic and electronic conductors (MIECs). However, it has been argued that the fitting process of determining two kinetic parameters from a single conductivity relaxation curve inevitably leads to high error in the determined values. In this research, we demonstrate experiment-based analytical approaches to overcome the issue and obtain highly reliable kinetic parameters using ECR for the case of (La0.6Sr0.4)0.95Co0.2Fe0.8O3-δ (LSCF), a representative MIEC. As a baseline, kinetic parameters of a standard LSCF bar sample with the thickness close to the critical thickness are obtained using a conventional ECR method along with error range and sensitivity analysis at oxygen partial pressures of 0.2–3.125 × 10−3 atm. Dchem with improved accuracy is obtained by ECR under primarily bulk diffusion-controlled condition, which is achieved by either increasing the thickness or coating porous LSCF on the baseline sample. With the Dchem determined, the baseline data are further refined to obtain kchem as the sole fitting parameter and the error range is reduced more than 70% of the original value under all test conditions. With the significantly improved accuracy and sensitivity of both kchem and Dchem, this demonstrated method is proven to be a practical approach to advance the application of ECR.