Tailoring of microstructural evolution in impregnated SOFC electrodes

Lead Research Organisation: University of St Andrews
Department Name: Chemistry

Abstract

Solid oxide fuel cells are highly intricate devices with many interfaces which are typically formed at high temperatures. This places many constraints in terms of chemical and physical compatibility upon such devices limiting both performance and durability. Such problems strongly restrict materials choice and impose significant cost penalties on SOFC manufacture.

The utilisation of solution methods to introduce part of the SOFCs active constituents is a highly attractive approach that has gained much interest in recent years. This can involve infiltration of nanoparticles or impregnation of precursor solutions to form phases in situ. Much lower reaction temperatures can be utilised avoiding problems with compatibility and affording wider materials choice.

Typically such process involves formation of a scaffold structure by high temperature processing and then impregnation of an electrode by lower temperature methods. We have successfully applied this approach to three different novel variants of SOFC architectures. These are electrolyte supported oxide anodes, oxide anode supported and metal anode supported cells. Excellent performances can be obtained and good redox properties demonstrated; however, progress needs to be made to ensure high durability. The impregnates tend to form well dispersed nanoparticles, but these might be expected to agglomerate over time, in fuel cell operating conditions, to reduce overall performance.

Through the national and European projects where we applied the impregnation concept, we have learned much about impregnation and how to develop appropriately dispersed electrode structures. The electrode structure is seen to evolve with use and clear opportunities exist to optimise structures through improved processing. Most important has been the realisation that there are strong interplays between the materials impregnated, the substrate and the solvent utilised. Even subtle changes in electrode composition, demand significant changes in impregnation chemistry to maintain the maximum levels of performance.

In this project we seek to further develop control of this impregnation chemistry and hence to develop generic methods for developing controlled microstructures via solution routes across several platforms. These new chemistries will be applied to electrolyte- and anode-supported SOFC geometries and properties optimised for performance, durability and redox tolerance.

The overall objective is to develop and demonstrate this new approach as one that can be successfully applied to manufacture of fuel cells that combine high performance with durability and resistance to contaminants. We will apply this approach typically for an impregnated oxide electrode with metallic catalyst to zirconia, strontium titanate and metal supports and develop our understanding of the fundamental chemistry across this range of platforms. By so doing we will develop methodologies to tailor impregnations over a broad range of composition space. Studies of performance, durability and resistance to contaminants utilising electrochemical, spectroscopic and microstructural techniques will be used to inform choice of impregnate systems.

Final outcomes will be delivery of novel tailored chemistries for different SOFC application modes and geometries, demonstration of novel cell technologies with robust, high performance characteristics at SOFC developer ready scales and development of new routes and instrumentation for SOFC manufacture.

Planned Impact

There is also considerable economic potential in these new SOFC technologies and we are carefully directing our efforts towards technologies that can be exploited to the benefit of the UK economy. In particular our findings will be of particular interest our UK and EU Industry partners who sit on the steering group. A key challenge for fuel cell deployment is the ability to achieve low cost, durable and efficient systems, this project seeks to strongly address these aspects. Success will have significant positive impacts on society and the economy.

The findings obtained in this project will be widely disseminated in the peer reviewed journals, open access where possible, as well as at national and international conferences and meetings usually having significant industrial presence, such as the SUPERGEN hydrogen and fuel cells annual meeting. When potential commercial exploitation opportunities arise, the publication will be delayed to allow for IP protection via conventional procedures. A direct output of this project will be researchers developing interdisciplinary skills in chemistry, advanced characterisation techniques, manufacturing and energy research areas, capable of becoming leaders in the energy materials field. We will continue collaboration with the research groups involved in common research projects on this topic and seek for further links and interdisciplinary applications of the concept studied here.

Publications

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Connor P (2018) Tailoring SOFC Electrode Microstructures for Improved Performance in Advanced Energy Materials

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Mitchell-Williams T (2017) Infiltration of commercially available, anode supported SOFC's via inkjet printing in Materials for Renewable and Sustainable Energy

 
Title SOFC infiltration 
Description Video for advanced energy materials article. https://v.qq.com/x/page/y0845hfz1gm.html 
Type Of Art Film/Video/Animation 
Year Produced 2019 
Impact just released 
URL https://v.qq.com/x/page/y0845hfz1gm.html
 
Description We have correlated the evolution of electrode microstructures with surface energy changes on redox via wetting angle measurements. Redox characteristics of various ceria derivates have been investigated by XPS and Raman spectroscopy confirming that Zr doped ceria is easier to reduce than ceria which is easier to reduce than gadolinia ceria
Exploitation Route We are working closely with industry, A high impact review paper has been published in Advanced Energy Materials. Some concepts have been transferred to Li-ion batteries and have contributed to a successful Faraday Challenge application
Sectors Energy

URL https://v.qq.com/x/page/y0845hfz1gm.html
 
Description A follow on project has been supported by Hexis
First Year Of Impact 2018
Sector Energy
Impact Types Economic

 
Title Data underpinning - Demonstration of high performance in a perovskite oxide supported solid oxide fuel cell based on La and Ca co-doped SrTiO3 
Description Perovskite electrodes have been considered as an alternative to Ni-YSZ cermet-based anodes as they afford better tolerance towards coking and impurities and due to redox stability can allow very high levels of fuel utilisation. Unfortunately performance levels have rarely been sufficient, especially for a second generation anode supported concept. A-site deficient lanthanum and calcium co-doped SrTiO3, La0.2Sr0.25Ca0.45TiO3 (LSCTA-) shows promising thermal, mechanical and electrical properties and has been investigated in this study as a potential anode support material for SOFCs. Flat multilayer ceramics cells were fabricated by aqueous tape casting and co-sintering, comprising a 450-?m thick porous LSCTA- scaffold support, a dense YSZ electrolyte and a thin layer of La0.8Sr0.2CoO3-d (LSC)-La0.8Sr0.2FeO3-d ( LSF)-YSZ cathode. Impregnation of a small content of Ni significantly enhanced fuel cell performance over naked LSCTA-. Use of ceria as a co-catalyst was found to improve the microstructure and stability of impregnated Ni and this in combination with the catalytic enhancement from ceria significantly improved performance over Ni impregnation alone. With addition of CeO2 and Ni to a titanate scaffold anode that had been pre-reduced at 1000oC, a maximum powder density of 0.96Wcm-2 can be achieved at 800oC using humidified hydrogen as fuel. The encouraging results show that an oxide anode material, LSCTA- can be used as anode support with YSZ electrolyte heralding a new option for SOFC development. 
Type Of Material Database/Collection of data 
Year Produced 2016 
Provided To Others? Yes  
 
Title Data underpinning : Wetting and interactions of Ag-Cu-Ti and Ag-Cu-Ni alloys with ceramic and steel substrates for use as sealing materials in a DCFC stack 
Description  
Type Of Material Database/Collection of data 
Year Produced 2015 
Provided To Others? Yes  
 
Title METHOD FOR PRODUCING AN ELECTRODE CATALYST FROM A PEROVSKITE METAL OXIDE 
Description The invention relates to a method of producing electrode materials for solid oxide cells which comprises applying an electric potential to a metal oxide which has a perovskite crystal structure. The resultant electrode catalyst exhibits excellent electrochemical performance. The invention extends to the electrode catalyst itself, and to electrodes and solid oxide cells comprising the electrode catalyst. 
IP Reference CA3030088 
Protection Patent application published
Year Protection Granted 2018
Licensed Commercial In Confidence
Impact -