We present calorimetric measurements on a single isothermal polymer electrolyte fuel cell, operated on dry hydrogen and oxygen at 50 °C. The measured heat production of the complete cell was decomposed into ohmic and non-ohmic heat effects. The results predicted the thermo-neutral potential of the cell within 7% error. The part of the heat production that originated mainly from the cathode overpotential, was analyzed in terms of standard overpotential theory, giving an exchange current density of the bulk cathode overpotential of 6×10−4 A/cm2 and a transfer factor of 0.27. (The cathode catalyst surface area was not determined.) This is the first time an overpotential of an electrode has been determined from its heat production.

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