Hydrogen enters a PEM fuel cell on the anode side and it is exposed to platinum which acts as a catalyst to separate the proton (ion) and electron. The chemical structure of the polymer electrolyte membrane (PEM) in the fuel cell allows the positively charged proton to pass through the membrane while the negatively charged electron is not able to pass through. The electrons are directed through a circuit where we are able to use the electricity generated to do work before it reaches the cathode side of the fuel cell. When the electrons reach the oxygen-rich cathode side of the fuel cell, they recombine with protons to form hydrogen which then joins with oxygen to produce water. The electro-chemical reactions in the fuel cell also produce heat which can be used to heat water for cogeneration applications.
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The amount of current produced by one cell of a fuel cell varies based on the size of the active area of the membrane, the amount of catalyst loaded on the membrane, and the thickness and conductivity of the polymer electrolyte membrane. The voltage provided by a single cell is limited to about .7 volts. To increase voltage, cells must be joined electrically in series into fuel cell stacks. Graphite plates are used in fuel cell stacks to direct hydrogen through the fuel cell and to help manage water. Gasketing is an important component in PEM fuel cells because hydrogen is so small it can be difficult to achieve a tight bond between cells. In higher temperature fuel cells, such as Solid Oxide or Molten Carbonate fuel cells, the co-generation of heat directly heats water in pipes.
The output of the stack can be adjusted by changing the number of individual cells.
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