Roles of Bulk and Surface Chemistry in the Oxygen Exchange Kinetics and Related Properties of Mixed Conducting Perovskite Oxide Electrodes

Abstract

Mixed conducting perovskite oxides and related structures serving as electrodes for electrochemical oxygen incorporation and evolution in solid oxide fuel and electrolysis cells, respectively, play a significant role in determining the cell efficiency and lifetime. Desired improvements in catalytic activity for rapid surface oxygen exchange, fast bulk transport (electronic and ionic), and thermo-chemo-mechanical stability of oxygen electrodes will require increased understanding of the impact of both bulk and surface chemistry on these properties. This review highlights selected work at the International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University, set in the context of work in the broader community, aiming to characterize and understand relationships between bulk and surface composition and oxygen electrode performance. Insights into aspects of bulk point defect chemistry, electronic structure, crystal structure, and cation choice that impact carrier concentrations and mobilities, surface exchange kinetics, and chemical expansion coefficients are emerging. At the same time, an understanding of the relationship between bulk and surface chemistry is being developed that may assist design of electrodes with more robust surface chemistries, e.g., impurity tolerance or limited surface segregation. Ion scattering techniques (e.g., secondary ion mass spectrometry, SIMS, or low energy ion scattering spectroscopy, LEIS) with high surface sensitivity and increasing lateral resolution are proving useful for measuring surface exchange kinetics, diffusivity, and corresponding outer monolayer chemistry of electrodes exposed to typical operating conditions. Beyond consideration of chemical composition, the use of strain and/or a high density of active interfaces also show promise for enhancing performance.

Gas Humidification Impact on the Properties and Performance of Perovskite‐Type Functional Materials in Proton‐Conducting Solid Oxide Cells

“…The parameters of the first group lie in the materials science aspect and can be managed by the selection and optimization of electrode compositions; the parameters of the second group can be controlled through the optimization of technological methods. Analysis on the relationship between the electrochemical activity, kinetic and microstructural parameters has been thoroughly carried out . However, the influence of air humidification on the oxygen electrodes' performance was not clear, particularly for the proton‐conducting SOCs.…”

La0.6Sr0.4Co0.2Fe0.8O3-δ nanofiber cathode for intermediate-temperature solid oxide fuel cells by water-based sol-gel electrospinning: Synthesis and electrochemical behaviour

“…Such water-based electrospinning process offers safer operation and cheaper production for industrial applications, as compared to the processes based on toxic and expensive organic solvents. The composition investigated is La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF), which was demonstrated to be of particular interest in a previous study on the La1-xSrxCo1-yFeyO3-δ system [11,33]. Moreover, in this work the electrospun nanofiber electrodes have been directly applied onto the electrolyte disk without being crashed, to preserve the unique 3-dimensional fibrous structure.…”

Effect of sintering temperature on electrochemical performance of porous SrTi1-xFexO3-δ (x = 0.35, 0.5, 0.7) oxygen electrodes for solid oxide cells

“…Also, other materials groups have been studied: double perovskites, Ruddlesden-Popper-type phases [15], and others [16][17][18][19][20][21]. Typical electrode materials have high ionic and electronic conductivity levels, with total conductivities exceeding 100 S cm −1 ; however, the exact role of the influence of the individual partial conductivity levels on the resulting electrode performance is yet to be established, and is currently an active research topic [5,22,23]. In this respect, materials with relatively low total conductivities (or materials with a low electronic-to-ionic conductivity ratio) and good oxygen catalyst properties are very interesting for research.…”