Monopolar stack

Fig. 9.3 Top scheme of a passive monopolar stack with built-in methanol reservoir [24]. Bottom MEMS-based micro DMFC [25] (Reprinted from Refs. [24] and [25] with permission)...

Electrode Materials The AFCs developed by F. Bacon utilized nonnoble sintered nickel metal catalysts. The high electrical conductivity of these porous electrodes permits use of current collection from monopolar stack plates [62]. The sintered metal is often applied in two separate layers, with large pores on the channel side, so that control of the hquid electrolyte-gas phase interface can be achieved by capillary and gas-phase pressure forces. 

Two distinct classes of cell design exist the monopolar and the bipolar. Most commercial stacks have the bipolar design, which means that the single cells are connected in series both electrically and geometrically. The bipolar cell design has the advantages of compactness and shorter current paths with lower voltage losses. 

Figure 19.16. Basic designs of electrolytic cells, (a) Basic type of two-compartment cell used when mixing of anolyte and catholyte is to be minimized the partition may be a porous diaphragm or an ion exchange membrane that allows only selected ions to pass, (b) Mercury cell for brine electrolysis. The released Na dissolves in the Hg and is withdrawn to another zone where it forms salt-free NaOH with water, (c) Monopolar electrical connections each cell is connected separately to the power supply so they are in parallel at low voltage, (d) Bipolar electrical connections 50 or more cells may be series and may require supply at several hundred volts, (e) Bipolar-connected cells for the Monsanto adiponitrile process. Spacings between electrodes and membrane are 0.8-3.2 mm. (f) New type of cell for the Monsanto adiponitrile process, without partitions the stack consists of 50-200 steel plates with 0.0-0.2 ram coating of Cd. Electrolyte velocity of l-2 m/sec sweeps out generated Oz.

Electrodialysis is a well-proven technology with a multitude of systems operating worldwide. In Europe and Japan, electrodialysis dominates as a desalting process with total plant capacity exceeding that of reverse osmosis and distillation [3]. Electrodialysis with monopolar membranes is applied to different food systems, to demineralization of whey [5-8], organic acids [9], and sugar [10,11], separation of amino acids [12] and blood treatments [13], wine stabilization [14—16], fruit juice deacidification [17-19], and separation of proteins [20-22]. These applications use the sole property of dilution-concentration of monopolar lEMs in a stack of as many as 300 in an electrodialysis cell. 

A traditional, monopolar electrolyzer is built up by coupling tank units in series electrically L By contrast, a bipolar unit uses a metal sheet (or bipole ) to join adjacent cells, as depicted in Figure 4.5(b). The electrocatalyst for the negative electrode is coated on one face of the bipole and that for the positive electrode of the adjacent cell is on the reverse face. A series-connected stack of such cells forms a module that operates at a higher voltage and lower current... 

When a cell or cell stack contains more than two electrodes, there are two ways of making the electrical connection the cell may be monopolar (Fig. 2.10(a)) or bipolar (Fig. 2.10(b)). In the monopolar cell there is an external electrical contact to each electrode and the cell voltage is applied between each cathode and anode. 

AEG stacks are frequently designed with a monopolar concept for which single cells are externally connected. Eor PEFCs, a bipolar configuration is commonly... 

The electrical connection to electrolysis cells can be either monopolar or bipolar [1,3]. Monopolar cell stacks require electrical connection to each electfode and expensive control equipment (low voltage, high current), whereas bipolar stacks have electrical connection only to end plates and employ cheaper control equipment (mains supply voltage, lower currents). In addition, a bipolar connection eases the problems of uneven current distfibution. 

Electrode plates or grids are assembled in stack of cells (see Fig. 2). There is no membrane separation between the electrodes. The electrodes are inserted inline directly into the water flow after the filtering unit. Monopolar, bipolar, and combined bipolar-monopolar electrode configurations are used. The required maximum chlorine production rate, for residential pools 2-3 g of CI2 per hour per 10 m of water, defines the size and number of cells. 

Concerning to the movement of the electrode can be cited the rotating cylinder electrode [5-8], the electrochemical pump cell in monopolar [9] and bipolar [10] electrical connection, and the multiplate bipolar stack [11]. 

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