Bipolar cell stacks

A bipolar version of the tank cell design, the Bipolar Stack cell (25). consists of an assembly of parallel, planar electrodes separate by insulating spacers. Flow of electrolyte between electrodes may be either by natural or forced circulation. This design of cell is easy to construct since it simply comprises a Stacie of alternating electrodes and spacers with electrical... 

Fig. 17. Bipolar capillary cell (a) 125 fim gaps, (b) glass vessel, (o) electrical leads, (d) stack of graphite plates, (e) solution flow. (Taken from Beck and Guthke, 1969.)...

Undivided cell bipolar stack of carbon electrodes with a narrow electrode gap... 

Fig. 9.20 Comb-type bipolar electrodes for zinc-chlorine batteries (a) bipolar stack (b) unit cell...

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 The released Na dissolves in the Hg and is withdrawn to another zone where it forms salt-free NaOH with water, (c) Monopolar electrical connections each cell is connected separately to the power supply so they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.

Research and development efforts have been directed toward improved cell designs, theoretical electrochemical studies of magnesium cells, and improved cathode conditions. A stacked-type bipolar electrode cell has been operated on a lab scale (112). Electrochemical studies of the mechanism of magnesium ion reduction have determined that it is a two-electron reversible process that is mass-transfer controlled (113). A review of magnesium production is found in Reference 114. 

Capillary gap cell — The undivided capillary gap (or disc-stack) cell design is frequently used in industrial-scale electroorganic syntheses, but is also applicable for laboratory-scale experiments when a large space-time yield is required. Only the top and bottom electrodes of c.g.c. (see Figure) are electrically connected to - anode and cathode, respectively, whereas the other electrodes are polarized in the electrical field and act as -> bipolar electrodes. This makes c.g.c. s appropriate for dual electrosynthesis, i.e., pro duct-generating on both electrodes. 

Fig. 8 S implified cross section through a single element of a bipolar membrane cell. The electrodes are supported by corrugated bands, which are in turn supported by contact plates. Compression of the single cells together gives the series connections for the stack [14, p. 442],...

The model was first verified for the case of a bipolar stack with fourteen Ni electrodes. " The electrochemical reaction used for the determination of current bypass was the electrolysis of water in alkaline solutions. Good agreement between experimental and estimated current bypass was observed, especially at high current densities. The model was adapted successfully for solid electrolyte cells of bipolar configuration, as discussed below in Section IV.2.i. 

Figure 27. Graphical determination of the current bypass from current-voltage curves. /f d as a function of (a) the cell potential of the bipolar stack with N cells (Kn) and of (b) N times the cell potential of a single cell (NKi).

The cell for the electrolysis consists of a bipolar stack of horizontal carbon anodes with an inter-electrode gap of 1.5 cm. The electrodes and electrolyte flow is designed to ensure the minimum contact between the electrolysis products since the molten aluminium and gaseous chlorine would otherwise react rapidly. The aluminium falls to a pool below the electrodes while the chlorine is pumped out the top of the cell to be used in the reaction with alumina. A simplified cell is shown in Fig. 4.3. It may be noted that the overall process again uses carbon in at least stoichiometric quantities although now in a chemical step. Overall the process run at 1 A cm has an energy efficiency which is currently claimed to be about 10% better than that for the Hall—Heroult process. 

Figure 5.5 View from above of two of a bipolar stack of solid electrolyte water electrolyser cells.

The cell design is very simple. It consists of a bipolar stack of 50—200 rectangular carbon steel sheets whose cathode faces are electroplated with cadmium to a thickness of 0.1—0.2 mm the anode—cathode gap is fixed at about 2 mm by... 

Hence the simplest design is a closely spaced, bipolar stack of electrodes, although control of the hydrodynamics in the cell is essential to prevent cathodic reduction of the hypochlorite. Moreover when the anolyte feed is sea water, an additional... 

BASF in Germany operated a number of commercial, electrolytic processes [44, 56, 57] using a strategy based on the availability of a reliable and simple cell design and then noting the chemistry that can be carried out within this cell. In this cell, a series of horizontal carbon disks (diameter 1 m) were stacked with a separation of 1 mm (maintained by polymer spacers) and the electrolyte was pumped outward from the center of the disks. The cell is operated undivided and as a bipolar stack with bypass currents minimized because the stack is not immersed in electrolyte. The cell is well suited to methoxylation reactions carried out in methanol as the solvent. For example, BASF have carried out the following conversions ... 

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