Electrolyzers unipolar

Water electrolyzer units typically consist of several cells or electrodes arranged in two basic configurations, tank type operated in unipolar configuration, or filter press type operated in bipolar configuration. Tbe most common configuration, see Fig. 2.1, is the unipolar tank type where each electrode has only one polarity and all the electrodes of the same polarity are connected in parallel. The anodes and cathodes are alternately connected, with the... 

See color insert following page 140.) Unipolar (left) and bipolar (right) alkaline electrolyzers. 

Electrolytic vessels for unipolar electrodes have usually rectangular or square cross sections. These electrolyzers oan be either closed or open. This depends on whether gaseous products are to be collected or not. 

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. 

There are essentially two types of industrial electrolyzers the unipolar (tank-type) electrolyzer and the bipolar (filter-press) type. Though there have been improvements in materials, in design, and in conversion efficiency (from about 70-75 percent in the 1970s to about 80-90 percent now, based on the higher heating value of hydrogen4), the basic concept has not changed in about 70 years. 

In a bipolar electrolyzer, each electrode has both a positive and a negative face, with the positive face in one cell and the negative face in the adjacent cell. Proponents say that bipolar electrolyzers take up less floor space than unipolar ones and that they are better suited to high-pressure and high-temperature operation (which is more efficient). Their drawbacks are that they require much more precise tolerances in construction and that they are more difficult to maintain. (If one cell fails, the entire assembly has to be shut down.)... 

Figure 4.3 Performance (voltage v. current density) of a basic (unactivated), unipolar electrolyzer running at 90 °C.

Electrolyzer, Inc. has been a principal developer and supplier of unipolar electrolyzers since the 1940s. The electrodes are supported in containers (cells) filled with concentrated KOH. The cells are connected in parallel and operate at voltages in the range of 1.5-2 V. Experimental results indicate that energy conversion efficiencies of 85% or above will be possible in commercial units. A layout for a planned 35-MWe installation is 29 m wide and 95 m long. With these dimensions, a 350-MWe electrolyzer for an OTEC plantship would occupy an area of 2750 m. ... 

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