Page 73 - Introduction to Transfer Phenomena in PEM Fuel Cells

62 Introduction to Transfer Phenomena in PEM Fuel Cells
which means we will have at the anode:
– for the enthalpy:
Δ H anode = 0 − Δ H 0 H 2 [2.36]
– for the entropy:
Δ S anode = 0 − Δ S 0 H 2 [2.37]

then, for the enthalpy at the cathode:

1
Δ H cathode = Δ H 0 H O − Δ H 0 O 2 [2.38]
2
2
and for the entropy at the cathode:

1
Δ S cathode = Δ S 0 H O − Δ S 0 O 2 [2.39]
2
2
For temperatures below 100°C, the variation in the value of (C p), (ΔH)
and (ΔS) is not very significant, but at high temperatures (in some types of
fuel cell such as SOFC), this change should not be negligible.

The above equations and tables allow us to calculate the theoretical anode
and cathode potentials for any given temperature [PER 08, SAI 06].

For the anode:
( )
Δ
TS 0 H − Δ H 0 H − RTln P H
E = 2 2 2 [2.40]
theo _ anode
2F
and for the cathode:

Δ H 0 H 2 O + 1 Δ S 0 O − 1 Δ H 0 O − TΔ S 0 H 2 O − RT ln ( )
P
2 0
E = 2 2 2 2 2 [2.41]
theo
cathode
_
2 F