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PEM Fuel Cells by Ken S. Chen, Yun Wang

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8.2 HEATING MECHANISMS

In PEM fuel cells, the chemical energy stored in hydrogen gas is converted to electricity by the electrochemical HOR and ORR reactions at efficiency possibly over 60%. The rest is released as waste heat through four major mechanisms: the reversible entropic heat, irreversible reaction heat, ohmic or Joules heat, and latent heat release/absorption during phase change. The details on latent heat release or absorption during ice–liquid, liquid–vapor, vapor–ice phase changes, or membrane hydration/dehydration will be discussed in Chapter 9. The amount of the entropic heat is evaluated from the entropy change of the electrochemical reaction in a reversible way, generally referred to as the reversible heating. Any irreversibility ...

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