Planar stacked fuel cells

Malzbender, J., Wakui, T., and Steinbrech, R.W. (2006) Curvature of planar solid oxide fuel cells during sealing and cooling of stacks. Fuel Cells, 6, 123-129. 

SOFC are produced with either tubular or planar stack configurations investments for planar design are a rough estimate, as no prototypes exist. Specific investments for PAFC are in the range 4000- 4500/kW (IEA, 2007). For further fuel-cell R D needs see IEA (2005). 

M. Hsu, "Zirconia Fuel Cell Power System Planar Stack Development," Fuel Cell Abstracts, 1986 Fuel Cell Seminar, Tucson, AZ, October 26-29, 1986. 

Fig. 1.6 Illustration of a planar-stack, solid-oxide fuel cell (SOFC), where an membrane-electrode assembly (MEA) is sandwiched between an interconnect structure that forms fuel and air channels. There is homogeneous chemical reaction within the flow channels, as well as heterogeneous cehmistry at the channel walls. There are also electrochemical reactions at the electrode interfaces of the channels. A counter-flow situation is illustrated here, but co-flow and cross-flow configurations are also common. Channel cross section dimensions are typically on the order of a millimeter.

Planar SOFC, in particular, monolithic designs (MHI) are capable of high (volumetric) power densities most favoured by direct and short current paths across the stack components. The PEN is principally square, rectangular and circular (Ceramic Fuel Cells Limited (CFCL), Mitsubishi Materials Corp., SulzerHexis) in shape with active surface areas of 100-200 cm2 (15.5-31 in2). A drawback of this design is that it often necessitates the use of high temperature sealants for application at the in-... 

AchenbachE., 1994. Three-dimensional and time dependent simulation ofa planar solid oxide fuel cell stack. Journal of Power Sources 49, 333-348. 

O Brien, J.E., C.M. Stoots, J.S. Herring, J.J. Hartvigsen (2006), Hydrogen Production Performance of a 10-cell Planar Solid-oxide Electrolysis Stack , Journal of Fuel Cell Science and Technology, Vol. 3, pp. 213-219, May. 

The interconnect normally links the anode of one cell to the cathode of the next. It must, of course, be an electronic conductor and also a gas barrier preventing the direct meeting of fuel and oxidant gases. Fig. 4.27 illustrates how the interconnection is achieved in the case of the so-called planar fuel cell stack. In the later discussion of the ceramics-based cells a tubular configuration is described, but the principles are the same. 

The design of BP for PEMFCs is dependent on the cell architecture, on the fuel to be used, and on the method of stack cooling (e.g., water or air-cooling). To date, most of the fuel cells have employed traditional filter-press architecture, so that the cells are planar and reactant flow distribution to the cells is provided by the bipolar plate. The bipolar plate therefore incorporates reactant channels machined or etched into the surface. These supply the fuel and oxidant and also provide... 

Figure 3.9. Visualisation of the physical structure of a planar fuel cell stack...

The beginnings of the SOFC are recorded in an early East German University patent (Mobius and Roland, 1968) which shows awareness of many of the variables still being worked upon today. The oxides of lanthanum, zirconium, yttrium, samarium, europium, terbium, ytterbium, cerium and calcium are mentioned as candidate electrolyte materials. The proposed monolithic planar arrangement has, however, been abandoned by many companies, on the example of Allied Signal. One notable exception is a reversion to a circular planar concept by Ceramic Fuel Cells of Australia, UK (Section 4.7). The Rolls-Royce all-ceramic fuel cell (Section 4.3), which is monolithic and has one compliant feature, namely a gap, is a major exception. One modern trend is towards lower SOFC temperatures, with the intermediate-temperature IT/SOFC allowing the use of cell and stack arrangements with some flexibility and manoeuvrability based on new electrolytes, metallic flow plates, electrodes and interconnects. 

The Rolls-Royce fuel cell modules and stacks are devoid of compliant features, as the cross-section in Figure 4.3 shows, unless one counts the gap as compliant. Cell improvement is clearly possible via thin (say 6 p.m) electrolyte layers, as employed in a planar IT/SOFC by Global Thermoelectric (Section 4.9) and Steele etal. (2000a, b). Alternatively, modern reduced temperature electrolytes could be used. 

FIGURE 11.1 Planar design of solid-oxide fuel cell (a) a stack repeat unit and (b) details of a possible design. 

Figure 3.20 shows a cylindrical layout often used for high-temperature SOFCs. Alternatives are a stack of planar cells or a disk concept with feed tubes in the centre. A consideration of efficient heat exchange is the cormnon design strategy for the high-temperature fuel cell geometry. 

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