Operating Principles In PEM Fuel Cell

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The polymer membrane is the heart of the PEM fuel cell which has some unique features. It allows protons but it is impermeable to gases, and hence it is known as a Proton Exchange Membrane. The membrane, which is squeezed between two electrodes (electrically conductive carbon cloths or carbon fiber papers) acts as electrolyte. A layer of catalyst particles (platinum) is placed at the interface between the porous electrode and polymer membrane. A schematic diagram of cell configuration and basic operating principles is shown in Fig. 1.1.
Hydrogen, which is fed into one side of the membrane, splits into its primary elements, i.e., one proton and one electron at anode. Protons will pass
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In practice, the fuel cell shown in Figure 1.1 would be combined in series with other cells to produce a fuel cell stack. This fuel cell stack would then be part of a fuel cell system which also includes the fuel pumps, fuel processors, heat exchangers, humidifiers, and other equipment. The power of such PEM fuel cell systems can vary from a few Watts which is suitable for portable applications, up to million Watts such as in the stationary applications in a power plant.

3.1 Components of Fuel Cell
The basic PEM fuel cell consists of a Proton Exchange Membrane or Polymer Electrolyte Membrane (PEM), flow field plates, gas diffusion layer, catalyst layer gaskets and end plates as given in Table 1.1. The actual fuel cell layers are the gas diffusion layer, membrane and catalyst layer. The membrane squeeze in between the two electrodes is called as Membrane Electrode Assembly (MEA). A stack with many cells has MEAs “sandwiched” between bipolar flow field plates and only one set of end plates. Different components of fuel cell are shown in Fig. 1.2. Fig.1.2 Components of PEM Fuel
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The Nafion membrane belongs to a class of poly-perfluoro-sulfonic acids, and consists of a hydrophobic tetrafluoroethylene backbone with pendant side-chains of perfluoronated vinyl-ethers terminated by sulfonic acid groups. Proton conductivity in Naffion and most other polymer electrolytes increases with the water activity and that is the main reason to humidify the incoming gas reactants. Sufficient water must be absorbed into the membrane to ionize the acid groups, whereas excess water can flood the cathode of the fuel cell, diminishing fuel cell performance and limiting the power

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