Lanthanum Ferrite-Based Mixed-Conducting Electrodes for Solid Oxide Fuel Cells and Electrolyzers

Abstract

Intermediate temperature solid oxide fuel cells (SOFCs) and electrolysis cells (SOECs) potentially facilitate efficient, decentralized, and environmentally sustainable interconversion of electricity and carbon-containing fuels. However, the phenomena limiting performance of the associated oxygen and fuel electrodes are poorly understood, particularly for the class of mixed ionic and electronic conducting (MIEC) electrodes gaining interest for their performance and stability. This work investigates thermodynamic, kinetic, and transport processes affecting the performance of La_0.9Ca_0.1FeO_3-δ (LCF) and La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) electrodes. Thermodynamic measurements on LCF reveal semiconducting behavior across a wide range of temperature and oxygen partial pressure, while also showing stability in both oxidizing and reducing conditions. Linear and nonlinear electrochemical impedance spectroscopy (EIS, NLEIS) were used to identify rate-limiting processes occurring on LCF and LSCF cells in oxygen by comparison with porous electrode models. In both cases, results suggest the electrode surface to play a dominant role, behaving more reduced than expected from bulk measurements. Additionally, impedance measurements of LCF-91 electrodes in reducing hydrogen-water environments highlight the difficulties, both thermodynamic and transport-related, that arise when studying n-type MIECs under these conditions.