Fuel Cell Efficiency
The fuel cell thermodynamic efficiency
is given by the ratio of the Gibbs function change to the Enthalpy change in
the overall cell reaction. The Gibbs function change measures the electrical
work and the enthalpy change is a measure of the heating value of the fuel.
Efficiency = (dG/dH)
For the hydrogen -oxygen
reaction: dH = - 68,317 cal/g mole of H2,
and dG = - 56,690 cal/g mole of H2 .
The efficiency of the Ideal Fuel Cell is therefore:
Efficiency = (56,690/68,317) = 83%
measure of the fuel cell efficiency is known as the "Voltage Efficiency" and
is the ratio of the actual voltage under operating conditions to the theoretical
Voltage Efficiency = (Actual Voltage)/(Theoretical
Voltage) = (VA / 1.23)