Electric vehicle
Connecting Cells in Series – The Bipolar Plate
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| 5.4 Connecting Cells in Series – The Bipolar Plate As has been pointed out in the previous section, the voltage of a working fuel cell is quite small, typically about 0.7 V when drawing a useful current. This means that to produce a useful voltage many cells have to be connected in series. Such a collection of fuel cells in series is known as a stack. The most obvious way to do this is by simply connecting the edge of each anode to the cathode of the next cell all along the line, as in Figure For simplicity, this diagram ignores the problem of supplying gas to the electrodes.) The problem with this method is that the electrons have to flow across the face of the electrode to the current collection point at the edge. The electrodes might be quite good conductors, but if each cell is only operating at about 0.7 V, even a small voltage drop is important. Unless the current flows are very low, and the electrode a particularly good conductor, or very small, this method is not used. The method of connecting to a single cell, allover the electrode surfaces, while at the same time feeding hydrogen to the anode and oxygen to the cathode, is shown in Figure 5.12. The grooved plates are made of a good conductor such as graphite or stainless steel. This idea is then extended to the bipolar plate shown in Figure 5.13. These make connections allover the surface of one cathode and also the anode of the next cell (hence ‘bipolar’). At the same time the bipolar plate serves as a means of feeding oxygen to the cathode and hydrogen to the anode. A good electrical connection must be made between the two electrodes, but the two gas supplies must be strictly separated, otherwise a dangerous hydrogen/oxygen mixture will be produced. Fuel Cells 103 Oxygen fed to each cathode Cathode Electrolyte Anode For reactions in this part the electrons have to pass all along the face of the electrode Hydrogen fed to each enode LOAD Download 3.49 Mb. Share with your friends:
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