High temperature fuel cells (materials, stacks, thermodynamics, electrochemistry, chemistry)
The Module is focused on professional and practical training in field of "Material Science and Engineering".
The Module provides:
- an introduction in renewable energy and FC technology;
- an understanding of physical and chemical processes at the transformation of the chemical energy into electrical and heat ones;
- gaining the skills of purposeful selection of materials and production methods for manufacturing of functional materials with predefined properties;
- deepening and systematizing knowledge provided in other professionally oriented disciplines.
By the end of the module students should be able to:
- explain basics of physical and chemical processes of direct transformation of chemical energy of fuel into electric and thermal within FC, difference between FC types, principles of their working;
- use material science approaches for choice of materials/production methods for creating functional composites with predefined properties for SOFC application;
- apply the knowledge to moderately complex problems;
- communicate information, concepts, problems and solutions to specialists and non-specialists
The module consists of 9 lectures:
Lecture 1: Introduction in SOFC technology (2 hours). In the lecture, the phenomenon of ionic conductivity and the history of solid electrolytes are considered. Some properties of zirconia materials are listed, and the principle of dopant in order to choose structure stabilizers creating maximal number of oxygen vacancies is presented. The dependence of ionic conductivity on structure of electrolyte ceramics, and the test temperature are considered. Few samples of SOFC structures are given. At the end of lection, some requirements of SOFC electrolyte are listed.
Lecture 2: Zirconia powders and their electrolytes (2 hours). Zirconia is the main substance of the whole solid oxide fuel cell. It is not only the electrolyte material. It is added typically into both electrodes (anode and cathode) for spreading the reaction site deeper into them and adjusting thermal expansion coefficient compatibility with electrolyte material. Thus, it is important to understand the relationship between the characteristics of zirconia powder and obtained ceramic, it structures and properties. Three types of zirconia powder with the same chemical composition, but with different powder characteristics (i.e. particle size, specific surface, agglomeration, etc.) were used for preparation of ceramics. Structure, conductivity and mechanical strength of ceramics from different powders were compared.
Lecture 3: Anode component of solid oxide fuel cell, trends in its development (2 hours). In the first part of the lection the solid oxide fuel cell operation principle is briefly considered. After that, the basic geometries and configurations of SOFC are presented. Since the SOFC based on anode support is the most common used configuration, an overview of anode component is carried out. This review includes such the questions: anode requirements, traditional material of anode and its imperfections, alternative anode materials, and the three phase boundaries of anode material. Based on these questions the second part of lecture is devoted to the composition of the traditional nickel-zirconia anode. In this section the detailed overviews on each of anode component phases (nickel, zirconia and porosity) are presented. The third part of lecture is dedicated to trends in anode development. Bi-layered and gradient anode structures are considered. Then, the methods of nickel-zirconia composite preparation and the fabrication processes of anode are given.
Lecture 4: SOFC Cathodes (2 hours). The short explanation of SOFC operation principle is given. After that, the cathode requirements and features of cathode reaction are considered in details. Cathode material should possess the oxygen ion conductivity; it is necessary to understand this process. Furthermore, electronic conductivity is also important requirement for cathode material. Thus, cathode material should demonstrate both ionic and electronic conductivity. Generally, materials that have mixed ionic and electronic conductivity (MIEC) are materials with perovskite structure. Typical cathode materials and some their properties are listed. The problems associated with cathode degradation are considered. At the end of lecture some manufacture technology of cathode is listed.
Lecture 5: Materials for SOFC Interconnect (2 hours). The functions of interconnect are listed. Based on these functions the interconnect requirements are considered. FC interconnect materials can be grouped into two main categories: ceramics and metals (which includes coatings). Advantages and disadvantages of typical ceramic interconnect material (LaCrO3) are presented. Metallic interconnect materials include Cr based alloys, Ni-Fe based superalloys, Fe-Cr based alloys and austenitic and ferritic stainless steels. Composition and properties of metallic interconnects are considered. After that, the tendency of using interconnects coatings is explained. Requirements and types of these coatings, and the methods of their manufacturing are given.
Lecture 6: Impedance spectroscopy (2 hours). Impedance spectroscopy (IS) is non-destructive method for characterization the microstructure of heterogeneous systems. In the first part of the lecture, fundamentals of IS, fields and features of its application are considered. The advantages and disadvantages of IS are listed. Physical principles with mathematical background of IS, and examples of some electrical schemes were given. In the end of first part an exercise accompanied with impedance spectroscopy is presented. Second part of the lecture is dedicated to impedance measurements systems, the difference between them and principles of data analysis. Then, the examples of IS using in material characterization is considered. Impedance spectroscopy can be used for characterization of SOFC electrolyte structure, or even whole fuel cell (interface between components etc.). At the end of the lecture, some results of positive application of the IS method are presented.
Lecture 7: Electrode polarizations (2 hours). The first part of the lecture is dedicated to analysis of overall fuel cell performance. The actual performance of SOFC is differencing from theoretical one. There are few polarizations, that impact on the performance: activation, Ohmic and concentration. The reasons and determination of these polarizations are considered. Then, the ways minimizing fuel cell polarizations are given. In the second part of the lecture, the anode polarization is reviewed. In the section, the influence of anode composition, particle size and distribution of phases (nickel, zirconia and porosity) on electrode polarizations are considered in detail. The third part of the lecture is dedicated to cathode polarizations. The factors that influence on cathode polarizations are listed.
Lecture 8: SOFC testing (2 hours). In introduction of the lecture, the benefits of SOFC, their efficiency, comparison with traditional power generation systems and the operation principle of SOFC are briefly considered. The second part is dedicated to measurements of SOFC electrical properties. The current-voltage (I-V) characteristic of SOFC, typical tests conditions and basic stages of measuring of I-V curve are given. The last section of the lecture is focused on performance analysis of SOFC operation, and few examples of calculation of the SOFC efficiency are listed.
Lecture 9: Tape casting (2 hours). The main purpose of the lecture is to provide an understanding of the well-known high productive industrial method of film manufacturing known as tape casting. The principle of tape casting technique is explained, the advantages and disadvantages of this method are listed. Basic principles of colloidal stabilization of tape casting slurries are shortly presented. Basics of slurry rheology and types of its flow character are represented and explained. The detailed description of relationships about the influence of slurry composition and casting condition on tape properties are given. The post-processing techniques like lamination (assembling a multilayer composite), annealing and sintering reviewed briefly. The last trends and achievements in tape casting technique are reviewed too.