Bipolar pump cell

Fig.4 Bipolar Pump-Cell employs a magnetically driven rotor on ceramic shaft 1- rotor, 2- stator, 3- current connections, and 4-flow direction...

Furan was dimethoxylated to give 2,5-dihydro-2,5-dimethoxyfuran, using electrogenerated bromine molecules generated from bromide salts in electrolyte solutions [71]. This reaction was characterized in classical electrochemical reactors such as pump cells, packed bipolar cells and solid polymer electrolyte cells. In the last type of reactor, no bromide salt or electrolyte was used rather, the furan was oxidized directly at the anode. H owever, high consumption of the order of 5-9 kWh kg (at 8-20 V cell voltage) was needed to reach a current efficiency of 75%. 

The pump-cell concept (32) devised by Jansson and coworkers in Southampton Is another variant of the rotating cell. In the simplest version (Fig.4) the process stream enters the thin layer between the rotating disc cathode and the stationary cell body. The electrolyte Is accelerated to high mass transfer rates and the cell becomes self priming. In metal recovery applications the deposited metal film is discharged from the cell in the form of fine powder. It is also relatively straightforward to scale-up this cell design to produce a multiplate bipolar stack a 500-amp version of this cell has been tested. 

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]. 

Fig. 2,34 The electrochemical pump cell, (a) A monopolar cell for production of metal powders. After Jansson, R. E. W. and Ashworth, G. A., (1977) J. Appl. Electrochem., 7, 309). (b) Bipolar rotor cell for electrosynthesis. After Jansson, R. E. W., Marshall, R. J. and Rizzo, J. E. J., (1978) J. Appl Electrochem., 8, 281). (c) An improved version of (b) which incorporates facilities for adjustment of the rotor position, a reference electrode probe and enhanced mass transport. The bipolar rotor has a diameter of 10 cm and rotates at 2800 rev min" ...

A detailed cost analysis for a polymer electrolyte membrane fuel cell power plant of 5 kW was provided in 2006 by Kamarudin et al. According to their data, the total cost of such a plant will be about 1200 of which 500 is for the actual fuel-cell stack and 700 for the auxiliary equipment (pumps, heat exchangers, etc.). The cost of the fuel-cell stack is derived from the components as 55 /kW for the membranes, 52 /kW for the platinum, 128 /kW for the electrodes, and 148 /kW for the bipolar plates. 

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. 

BASF in Germany considered the use of the capillary gap cell (see Fig. 2.16 in Chapter 2) for this electrolysis. The cell consists of a stack of carbon discs closely spaced by 0.2 mm thick strips of an insulator. The electrolyte is pumped through the inter-electrode gaps and a voltage is applied to endplates so that a bipolar cell is formed. The cell design is compact, simple and cheap compared with a filter press cell and the tetraalkylammonium concentration could be reduced to below 0.5% without loss of yield and with an energy consumption below 3000 kWh ton . ... 

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 ... 

Trends in short- and lOTiger-term directions for key fuel cell components including electrocatalysts/supports, membranes, and bipolar plates have been elaborated in this section improvement of the performance and durability of these components will directly impact the entire automotive fuel cell system requirements, complexity, and cost. Durable catalysts with enhanced ORR activity, durable membranes that perform at very low humidity and durable bipolar plates that have low contact resistance will not only increase the power density and cost of the fuel cell stack but also simplify and lower/eliminate system component costs of the air compressor, humidification systems, recycle pumps, radiator, start-up/shutdown and freeze-start-related components, etc. A combination of advances in all the fuel cell components discussed above, system simplification, governmental policies that are sensitive to sustainable clean energy, and development of a hydrogen infrastructure will enable achieving the projected technical and cost targets needed for automotive fuel cell commercialization. 

The internal humidifier takes external liquid into the cell interior through a pump. Liquid water is then allocated according to the internal structure. Usually, the bipolar plate structure or the diffusion layer designs perform this function. 

Also, in selecting materials for theconstniction of cells it must be remembered that the concentrated electrolyte solutions used for electrolysis arc corrosive and even pumps, pipework and cell bodies must be selected with oorrosiotl resistance in mind. Indeed, whenever it is feasible, non-eleciroda components should be fabricated from (or coated with) an electrically insulating material (usually a polymer but possibly a ceramic), in particular it is wise to avoid the problem of bipolar MTodon (Chapter 0) which may arise if a conductive material interrupts the usual current path between anode and cathode It is essential to test all components in the system for corrosion resistance, with the cell on load and under open-ciTCuit conditions ... 

Figure 4.17 The Ballard Nexa fuel cell is an example of a commercial PEM fuel cell that uses air cooling. The blower for the cooling air can clearly be seen at the bottom left of the unit, and it blows air up through channels in the bipolar plates as per Figure 4.16. The reactant air passes through the humidifier on the front of the unit and is driven by a pump in the box on the top left of the system. (Reproduced by kind permission of Ballard Power Systems.)...

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