Planar cells

Figure C shows an electron photomicrograph of a broken planar SOFC. The thick portion on the left is the porous anode structure. This is an anode-supported cell, meaning that in addition to collecting current and supporting the anode reaction, the anode layer stiffens the whole cell. The layer on the right is the cathode, and the interface between the two is the thin electrolyte. One of the challenges of this design is to ensure that the rates of expansion of the cathode and the anode match. If the anode expands faster than the cathode, the planar cell tends to curl like a potato chip when the temperature changes.

Wnt/non-P-catenin signaling is not as well characterized biochemically as the Wnt/p-catenin-dependent pathway this may reflect that it is molecularly more diverse, at least in vertebrates. In Drosophila the best characterized Wnt/non-P-catenin pathway is planar cell polarity (PCP) signaling. Ironically, although it certainly depends on a Fz receptor, it remains... 

Preliminary Experiments with Self-Supporting Planar Cell... 

Schematic drawing of a self-supporting planar cell (a) and an electrolysis chamber (b).

FIGURE 5.1 Schematics of edge sealing of planar cells (above) and external gas manifold seals (below) used for a simple cross-flow SOFC stack design. 

Once the structural support layers have been fabricated by extrusion or EPD for tubular cells or by tape casting or powder pressing for planar cells, the subsequent cell layers must be deposited to complete the cell. A wide variety of fabrication methods have been utilized for this purpose, with the choice of method or methods depending on the cell geometry (tubular or planar, and overall size) materials to be deposited and support layer material, both in terms of compatibility of the process with the layer to be deposited and with the previously deposited layers, and desired microstructure of the layer being deposited. In general, the methods can be classified into two very broad categories wet-ceramic techniques and direct-deposition techniques. 

A Kelvin foam model with planar cell faces was used (a. 17) to predict the thermal expansion coefficient of LDPE foams as a function of density. The expansion of the heated gas is resisted by biaxial elastic stresses in the cell faces. However SEM shows that the cell faces are slightly wrinkled or buckled as a result of processing. This decreases the bulk modulus of the... 

For reasons already mentioned in Sect. 3.1, cells with finite planar geometry are usually thin cells (i.e. L is small, usually a fraction of a millimetre) and there are only two electrodes. A controlled-potential experiment thus usually involves fixing the potential between the two electrodes, though this does not necessarily mean fixing the potential across either electrode. That is, the way in which the applied potential divides itself between the anode and the cathode will, in general, change with time, even if the total applied potential remains constant. For this reason, the simplification that normally attends experiments carried out at constant applied potential is not achieved with finite planar cells. 

It is only when the electron transfer occurs reversibly (Sect. 3.5) that it is possible to predict the time dependence of the current generated by a finite planar cell in response to an applied potential step of magnitude E. Under reversible conditions, a constant applied potential engenders the constant surface concentrations [80]... 

The active surface to volume ratio of the tubular arrangements previously described is approximately 1 cm2/l cm3. This parameter could be increased with corresponding increases in both volume power density and area power density. New concepts for solid state electrochemical reactors have been proposed based on more or less planar cell structures which can be integrated to make blocks. 

In this section the characteristic phenomena occurring in the tubular cells are shown and the differences with respect to the planar cells are stressed. The model equations are recalled from Chapter 3. 

Fig. 10.1 Pictures for the different designs of SOFCs and the related cross-sectional diagrams (a) electrolyte-supporting planar cell, (b) anode-supported planar cell, (c) tubular cell, (d) segmented cell in-series design.

In the case of cell stacks of planar cells in particular, many cells are piled vertically to obtain a high voltage and a mechanical load is sometimes placed on the cells on top of the stack. This load induces a stress inside the cell stacks. 

Fig. 4.31 Ionic conductivities for candidate electrolyte ceramics. The arbitrary assumption that for a planar cell format a resistance of <15 gQm 2 is required places an upper limit on the permitted thickness of the electrolyte lower values of conductivity demand thinner membranes whilst higher values permit correspondingly thicker membranes. Electrolyte thicknesses greater than approximately 150/an are considered mechanically self-supporting. After B.C.H. Steele [11],...

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