Page 152 - Introduction to Transfer Phenomena in PEM Fuel Cells
P. 152
Heat Transfer Phenomena 141
where:
– R is the electrical resistance of the membrane, in [Ω.cm²];
m
– e is the thickness of the membrane, in [cm].
m
4.5.2. At the electrodes
The hydrogen oxidation and oxygen reduction reactions at the cathode
are exothermic and the production of heat is assumed to be homogeneous.
The water is produced by the reaction agglomerates and it is assumed to be
in liquid form. However, three heat sources are observed at the electrodes:
– heat flow (reversible) released by the electrochemical reaction
(variation in entropy of each half-reaction);
– heat flow (irreversible) of the electrochemical activation of reactions;
– phase change heat flow (sorption).
For the anode, we write:
Q = Q reac + Q act + Q sorp [4.27]
a
a
a
a
and for the cathode :
Q = Q reac + Q act + Q sorp [4.28]
c
c
c
c
4.5.2.1. Heat flow of the reaction
The total heat released by the reaction at the two electrodes Q reac in
[J.mol ] is expressed according to the variation in entropy SΔ rev [ROS 99],
–1
such that:
Q reac =− T ⋅Δ S rev [4.29]
