Filter press design

The first water electrolyzers used the tank design and an alkaline electrolyte.20 These electrolyzers can be configured as unipolar (tank) or bipolar (filter press) designs. In the unipolar design (see Figure 1), electrodes, anodes, and cathodes are alternatively suspended in a tank. In this design, each cell is connected in parallel and the entire system operated at 1.9-2.5 Vac. 

A common design is the so-called filter-press design of stacks built up of bipolar electrodes, one side of such electrodes working as the anode of one cell and the other side working as cathode of the neighboring cell (Fig. 16.3). 

So far the vast majority of PEFC are built in the form of bipolar stacks consisting of flat components in a filter press design. Other forms such as tubular designs have not yet found acceptance outside the research community. 

The most widely used design for high power applications is the bipolar configuration in a filter press design causing minimum losses due to electric resistances. The main components in the stack are... 

Three types of water electrolyser based on a tank cell, a filter press design and the use of elevated pressure are presently manufactured in various sizes to meet the various markets described above. In addition, a solid electrolyte cell is expected to become available by the mid-1980s. All these cells are described below. 

Large filter-press designs are normally assembled in the cell room. The frame is erected and the elements placed within. Membrane fitting is carried out in situ as discussed in Section 13.7.2 before compressing the whole pack to seal the gaskets. 

The Allis-Chalmers battery had a filter-press design. It contained a 5 M KOH solntion in asbestos diaphragms 0.75 mm thick. The working temperature was 65°C, much lower than that in the batteries described above. At a current density of 200 mA/cm and a gas pressure of 1.35 bar, the voltage per cell was 0.75 V, which is somewhat lower fiian in battery types working at higher temperatures. 

The most convenient way to establish a series connection of individual fuel cells in stacks and batteries is to use the filter-press design with bipolar electrodes and bipolar plates between two adjacent individual cells (as described in Section 1.2.2). 

It is possible that the filtration cycle should be stopped short of maximum cake thickness, since the pressure starts to iuCTease well before that point, and filtrate rate may fall to an unacceptable level. The question of optimum cake thickness is an important parameter in filter press design. The plate and frame and recessed plate presses do not allow much freedom to vary cake thickness, very much decided by the width of the recess, should a very dry cake be required. 

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