Tubular SOFC, structure

SOFC electrodes are commonly produced in two layers an anode or cathode functional layer (AFL or CFL), and a current collector layer that can also serve as a mechanical or structural support layer or gas diffusion layer. The support layer is often an anode composite plate for planar SOFCs and a cathode composite tube for tubular SOFCs. Typically the functional layers are produced with a higher surface area and finer microstructure to maximize the electrochemical activity of the layer nearest the electrolyte where the reaction takes place. A coarser structure is generally used near the electrode surface in contact with the current collector or interconnect to allow more rapid diffusion of reactant gases to, and product gases from, the reaction sites. A typical microstructure of an SOFC cross-section showing both an anode support layer and an AFL is shown in Figure 6.4 [24],... 

The micro-tubular SOFCs considered are depicted in Figure 4.19. Specifically, Figure 4.19 shows the anode (supporting structure), the anode plus the electrolyte, and the final single cells. More details about the production process, the cell properties and characteristics can be found in [13-15],... 

From the structure point of view, there are two types of structures of SOFC tubular and planar. Tubular SOFCs have shown some desirable characteristics over systems with planar SOFCs [4]. Tubular SOFCs can alleviate the sealing problem arose by CTE mismatch of planar SOFC therefore, they are robust for repeated cycling under rapid changes in electrical load and in cell operating temperatures. The large form factor tubular SOFC built by Siemens Westinghouse has successfully conducted long-term operation over 70,000 h. Small-scale tubular SOFCs could... 

A single planar or tubular SOFC generally produces a low voltage and power and the connection into a stack is needed in order to give higher power. Electrochemical performance, structural and mechanical integrity gas manifold and ease of fabrication are important targets for the improvements of cell performances [176,186]. 

Both tubular and planar SOFCs are typically fabricated using one of the cell layers as the structural support layer with a fairly large thickness, on the order of millimeters or hundreds of micrometers, with the other components present as thinner layers of 10s of micrometers for the electrodes and 5 to 40 micrometers for the electrolyte. 

Arthur D. Little has carried out cost structure studies for a variety of fuel cell technologies for a wide range of applications, including SOFC tubular, planar and PEM technologies. Because phenomena at many levels of abstraction have a significant impact on performance and cost, they have developed a multi-level system performance and cost modeling approach (see Figure 1-15). At the most elementary level, it includes fundamental chemical reachon/reactor models for the fuel processor and fuel cell as one-dimensional systems. 

Figure 12.18 Example of SOFC geometries, (a) Tubular geometry ofthe Siemens-Westinghouse system (b) Planar structure ofthe Sulzer-Hexis SOFC (for details, see the text).

SOFCs have largely converged on standard configurations, such as tubular or planar, with the structural support provided by the electrolyte, the anode, the metallic intercormector, or an inert porous support material. Each of these concepts has its own combination of advantages and disadvantages. In this section, some unconventional SOFC configurations and devices are discussed, and their performance and potential applications are considered in comparison with the more conventional approaches. This will include microtubular fuel cells, mixed reactant fuel cells, micro-planar fuel cells, and dual proton-oxygen ion fuel cells. 

Figure 3.11. Diagram of the principle of a tubular structure SOFC...

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