
138 Fuel Cells
n
I
f
e
= . (4.23b)
The current efciency, η
I
, is then dened as the ratio of the mass of fuel con-
sumed in the reaction to the mass of fuel supplied to the cell and expressed
as
η
I
e
f,in
/
=
InF
n
. (4.63)
Substituting Equation 4.23b into Equation 4.62, the current or fuel utilization
efciency can be expressed as a function of the stoichiometric factor
ηη
ξ
Ifc,fuel
1
. (4.64)
Equation 4.64 shows that for a fuel stoichiometric factor greater than one,
the current efciency of the fuel cell is less than 100%.
Physically, a current or fuel utilization efciency value represents the
fraction of the fuel converted into current. The rema ...