
143Thermodynamics of Fuel Cells
The water mass production rate is expressed as
m
MP
nFV
HO
HO t
2
kg/s=
2
for a stack (4.85a)
and
m
MP
nFVN
HO
HO t
2
kg/s=
2
for a cell. (4.85b)
In Equations 4.84 and 4.85, the number of electron charge transferred for
each mole of water produced is n
e
= 2 for a hydrogen–oxygen fuel cell.
4.8 Heat Generation in a Fuel Cell
As we have discussed before, the operating voltage (E) of a fuel cell is less
than the open circuit maximum possible voltage as current is drawn from
the cell. This is due to the fact that only a fraction of fuel energy is avail-
able in the form of Gibbs energy for conversion, and the rest represe ...