EAPSI: Directly Measuring the Surface Reaction Constant of Solid Oxide Fuel Cell Cathodes

Khan Anupama Q, Pasadena CA

Investigators

Abstract

Solid oxide fuel cells (SOFCs) are a promising alternative technology for stationary electricity generation. To improve performance and bring down cost, it is necessary to study the chemical reactions occurring at the device electrodes. These reactions are not well understood, even for the most common commercial SOFC cathode material, Sr-doped lanthanum manganite (LSM). This project will use a novel experimental geometry to measure the surface reaction constant of LSM using Electrical Conductivity Relaxation (ECR). Without the unique geometry described in this work, it is difficult to directly measure this important parameter for LSM and other electrode materials under SOFC operating conditions. Results from this work will 1) improve fundamental understanding of the chemistry of LSM and 2) demonstrate a new way to measure kinetics of electrode materials that was previously inaccessible. This work will be conducted with Dr. Ji-Won Son at the Korea Institute of Science and Technology. Dr. Son has extensive experience with solid oxide fuel cell electrode materials. In an ECR experiment, the gas composition around a sample of material is rapidly changed and the conductivity of the material is recorded as a function of time. This conductivity relaxation profile can be used to determine the kinetic parameters (diffusion coefficient and/or surface reaction rate constant, depending on the limiting step) of the material. This method is a fast, reliable, and direct way to study kinetics. However, this technique does not work if the material does not change conductivity as a function of gas composition under device relevant conditions. LSM is one such material. To work around this limitation of the technique, this project will use a unique sample geometry. A thin film of LSM will be deposited on a thick layer of Zr-doped ceria, ZDC. It is known that ZDC changes conductivity as a function of oxygen partial pressure and that this change is limited by the surface reaction rate. In this new geometry, the surface reaction rate will be controlled by the LSM layer. Therefore, the conductivity relaxation profile can be used to determine the surface reaction constant of LSM. This award is funded in collaboration with the National Research Foundation of Korea.