Image analysis of porous yttria-stabilized zirconia structure for a lanthanum ferrite-impregnated solid oxide fuel cell electrode

Significance 

Lanthanum-based perovskites are widely used cathode materials. Normally, very high sintering temperature is usually used for densification of the YSZ. Consequently, such temperatures prevent the use of many potential La-based perovskites, as they tend to react with YSZ to form the insulating La2Zr2O7, or worse, cause chemical/physical process instability at such temperatures. Several measures can be taken to avoid exposure of these more reactive materials to the high temperature sintering process.

One interesting measure that has caught the attention of many scholars is the impregnation of perovskites materials into a porous well-sintered YSZ scaffold. This technique offers a feasible way to fabricate the composite electrode at low temperatures. This approach has been explored far and wide, with different investigators reporting varying or conflicting results. Within the haystack, the needle has been found and it involves optimization of the microstructure of the YSZ Scaffold. Better still, the optimization of microstructure, across length scales has proven to be particularly useful in promoting and understanding the performance of electrodes. However, thorough characterization of porous scaffolds for building SOFC cathodes is still required.

Recently, University of St Andrews researchers Dr. Chengsheng Ni, Dr. Mark Cassidy and Professor John Irvine conducted a study high-resolution SEM imaging in a bid to better understand the effect of particle size of YSZ on the microstructure of porous scaffold. In addition, the electrochemical performance of the impregnated LSF-YSZ composite electrode was also evaluated by AC impedance. Their work is currently published in Journal of the European Ceramic Society.

In their studies two types of YSZ powders, U1 and U2, were used to quantify the porous scaffolds. Specifically, AC impedance on symmetrical cells was also applied to evaluate the performance of the electrode impregnated with 35-wt.% La0.8Sr0.2FeO3. Lastly, scanning electron microscopy (SEM) images were analyzed.

The authors observed that the powder with 9 vol. % particles smaller than 0.3μm and bimodal distribution in the powder (U1 powder) induced the faster YSZ grain growth and decreased in surface area when compared to powders (U2 powder). Moreover, the electrode using scaffolds made from U2 powder with narrow particle size distribution showed the respective polarization and series resistance that were in agreement with the prediction of the image analysis.

In summary, University of St Andrews study presented the application of two types of powders, of different sintering behaviors, in the preparation of porous YSZ scaffolds for impregnation. Generally, SEM image quantification was reported to be consistent with the sintering behavior of the YSZ powder as was the performance of the impregnated electrode. Altogether, the quantitative study on image of the sintered scaffold indicates that U2 powder is better at producing architecture of high porosity or long triple phase boundary (TPB), which is attributed as the reason for the higher performance of the LaFeO3 (LSF)-impregnated electrode.

Image analysis of   porous yttria-stabilized zirconia (YSZ) structure for a lanthanum ferrite-impregnated solid oxide fuel cell  electrode - Advances in Engineering

About the author

Mark Cassidy has been involved in Fuel Cell R&D for over 25 years, commencing doctoral studies into the design and fabrication of solid oxide fuel cells at Edinburgh Napier University in 1993. Following the award of his PhD in 1997 he held a number of research positions with leading international fuel cell companies. In 2006 he joined the University of St Andrews as a Senior Research Fellow in the Energy Materials Group of the School of Chemistry, where his research centred on advanced materials and processing to optimise the microstructure of SOFC components to enhance performance, durability and robustness. He also facilitated communication and collaboration with industry.

He has over 70 publications across journals, conference contributions, book chapters and patents and in 2016 was elected as a Fellow of the Institute of Materials, Minerals and Mining. More recently his research interests have focused on how new energy technologies develop from the laboratory to wider deployment, the nature of the innovation dynamics around this and how society can interact with and influence the transitions to new technologies. He is currently co-ordinator for low carbon transitions with Perth and Kinross Council in Scotland.

About the author

John Irvine FRSE, FRSC has made a unique and world-leading contribution to the science of energy materials, especially fuel cell and energy conversion technologies. This research has ranged from detailed fundamental to strategic and applied science and has had major impact across academia, industry and government. Irvine’s science is highly interdisciplinary extending from Chemistry and Materials through physics, bioenergy, geoscience, engineering, economics and policy.

The quality and impact of Irvine’s research has been recognised by a number of national and international awards, including the Lord Kelvin Medal from the Royal Society of Edinburgh in 2018, the Schönbeim gold medal from the European Fuel Cell Forum in 2016, the RSC Sustainable Energy Award in 2015, with earlier RSC recognition via Materials Chemistry, Bacon and Beilby awards/medals.

Irvine has almost 500 publications and has an WoS h-index of 64. He has strong international standing having held senior visiting appointments in the US, Australia and China and has strong links with a number of leading laboratories across the Chinese Academy of Science including being Thousand Talents professor at Fujian Institute of Research on the Structure of Matter.

About the author

Dr. Chengsheng Ni currently holds an associate professorship at Southwest University, Chongqing, China. He had been a research fellow and PhD candidate at University of St Andrews under the supervision of Professor John Irvine during 2010-2016, followed by the installation of an associate professor at Southwest University in 2017.

His worked on several topics but focused mainly on electrochemical characterization of solid-state materials, including electrochemical corrosion of metals, solid-state ionics and photocatalysis. After joining Southwest University, he is working on solid oxide fuel cells for efficient electricity generation from carbonaceous fuel and energy storage using the back and forth conversion between H2 and H2O. At the same time, he is also interested the solar-energy driving pollutant removal and hydrogen production using photocatalysts absorbing the visible light.

He authored/co-authored more than 30 peer-reviewed publications in the above areas in journals like Nature Communication, Journal of Materials Chemistry A, Chemical Engineering Journal and et al. His lab is based in the Testing & Analysis Center at the College of Resources and Environment, Southwest University and is now supervising more than 10 research students.

College of Resources and Environment, Southwest University, Beibei, Chongqing, 400715.

Email: [email protected]

Reference

Chengsheng Ni, Mark Cassidy, John T.S. Irvine. Image analysis of the porous yttria-stabilized zirconia (YSZ) structure for a lanthanum ferrite-impregnated solid oxide fuel cell (SOFC) electrode. Journal of the European Ceramic Society, volume 38 (2018), page 5463–5470.

Go To Journal of the European Ceramic Society

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