Zero-gap cells

Another cell design strictly directed toward minimization of the ohmic drop in the electrolyte, especially if gases are developed at the electrodes, is the zero-gap cell, shown in Fig. 8 [17, 93, 94]. The perforated electrodes are pressed directly onto the diaphragm by the current collectors providing optimum contact across the whole electrode area. However, uneven... 

Cell Design. Clearly, low energy consumption requires the interelectrode gap to be minimized. The extreme is the zero gap cell. ... 

Bilayer-SOj" polymer/-COO polymer membrane Zero gap cells... 

The electrodes must be pcnous in zero-gap cells so as to be able to evacuate the gas xoduced. 

Or (he sopited zero gap cell, arhere the electrodes arc in contact with the membrane... 

Narrow-gap or even capillary-gap cells may be required to majntain a moderate cell voltage while proce ing electrolytes of poor conductivity. The need to maintain a uniform capillary gap over large electrodes or multiple electrode stacks requires precise engineering, however, particularly in the case of rotating electrodes or divided cells. Tn, the energy-intensive prooe es such as chlor-alkali production and water electrolysis, the trend ts towards the so-called zero gap cells where the electrodes actually contact the membrane. 

Figure 53 illustrates the effect of hydrophilic cathode surface modification. The surface-modified membrane (Type B) has a lower cell voltage than the conventional membrane (Type A). The voltage of the surface-modified membrane decreases linearly with decreasing gap size. With these advanced membranes, so-called zero-gap cells have been made possible, and the ohmic loss in electrolytes has been reduced to a minimum. 

Fig. 12.8. Chlor-alkali cell configurations (a) gap cell (b) zero gap cell (c) SPE cell.

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