Page 114 - Introduction to Transfer Phenomena in PEM Fuel Cells

and:
c
c O 2 = Px ⋅ O 2 O 2 Mass Transfer Phenomena 103
[3.45]
K
KH 2, KO 2 are the Henry constants of hydrogen and oxygen. In equations
[3.42] and [3.43], the activation overpotentials ( a,c) in [V] are determined
from the local potentials of the membrane electrodes:

η a,c = φ a,c − φ − E eq [3.46]
m
a,c
where E eq is the equilibrium potential of the anode and the cathode [WAN 06].
a,c
The equilibrium potential of the anode is zero, and that of the cathode
depends on the fuel cell temperature (in Kelvin) according to the expression:

×
E eq = 1.23 − 0.9 10 − 3 × (T − 298 ) [3.47]
c

3.5.2. Agglomerate model with strong current

To integrate the transport of the reactants in the activation layers into the
simulation, Gloaguen et al. [GLO 98] noted that the agglomerate model was
more accurate than the macro-homogeneous model. As a result, this
agglomerate model describes two processes of transporting the reactants to
the catalyst sites. The first process presents the diffusion of gases through the
secondary pores between the agglomerates. The second integrates the
dissolution of the reactants in the electrolyte before reaching the reaction
layers. Applying this type of model, Siegel et al. [SIE 03] showed that the
performance of the fuel cell depended considerably on the catalyst structure.
–2
Ion current densities (j a,c) in [A.m ] are related to the average current densities
(i a,c ) on the surface of the agglomerate particles [MAH 06,
agg
SHI 06]:

j a,c = L act ⋅ (1− ε CL ) j⋅ agg [3.48]
a,c