
133Thermodynamics of Fuel Cells
∆s
f
kJ
= 174 856.
.
The Gibbs free energy of formation is given as
ΔG
f
= ΔH
f
− TΔS
f
ΔG
f
= −672,599.31 − 400 × 174.856
∆G
f
kJ
=−742 541 71,.
.
Reversible cell voltage
ET
GT
nF
rev
f
()
()
,
=
−
=
×
∆ 672 599 31
696 485
E
rev
= 1.16 V
EE T
RT
nF
YY
YY
n
n
=−
rev
e
A
B
() ln
EE T
RT
nF
YY
=−
rev
e
HO CO
CH OH
O
/
() ln
3
2
21
2
=−
×
×
116
8 314 400
696 485
2
3
1
2
2
5
.
.
,
ln
2
3
5
/
E = 1.158 V.
4.5 Fuel Cell Efficiency
A fuel cell performance may be expressed by considering different quanti-
ties such as thermodynamic efciency based on energy forms; voltage ef-
ciency based on opera