Screening mixed conducting oxide storage electrodes via chemical capacitance measurements

Abstract

Solid Mixed Ionic Electronic Conductors (MIECs) are frequently used in energy applications, such as high temperature Solid Oxide Fuel Cells (SOFC), Solid Oxide Electrolysis Cells (SOEC) and oxygen permeation membranes. However, their ability to conduct both ionic oxygen va cancies and electronic charge carriers and the resulting variability of the oxygen non-stoichio metry also makes them attractive oxide ion battery anode and cathode materials. Those are based on the transport of O 2– ions between the anode and cathode through an electrolyte via oxygen vacancies. Therefore, suitable electrode materials not only need good ion and electron conductivity, but also a highly variable oxygen non-stoichiometry (𝛿) to chemically store large amounts of charge. In this work, several candidates (La0.6Sr0.4FeO3–𝛿 (LSF), Gd:CeO2 (GDC), La0.5Sr0.5Cr0.2Mn0.8O3–𝛿 (LSCrMn), La2NiO4+𝛿 (LNO), YBaCo4O7–𝛿 (YBCo4O7) and SrTiO3 Strontium Titanate (STO), La0.8Ca0.2FeO3– (LCF)) are investigated for their usability as electrode materials in oxide ion batteries. Thin film microelectrodes were prepared on Yttrium stabilized Zirconia (YSZ) single crystal solid electrolytes. Electrochemical Impedance Spectroscopy (EIS) measurements were conducted over a wide range of temperatures (𝑇 = 300 – 600 °C) and frequencies (𝑓 = 10 6 – 4 · 10−3 Hz). The chemical capacitance extracted from the impedance spectra allow predicting the charge/discharge characteristics of the corresponding electrode. These were then compared with charge/discharge characteristics obtained by DC voltage measurements.