Proton Exchange Membrane Fuel Cell

1. PROTON EXCHANGE MEMBRANE
FUEL CELL : POWERING AVIATION
Understanding PEM Fuel Cell: Thermodynamic Analysis

2. Introduction
• A fuel cell is a device that converts the chemical energy from a fuel
into electricity through a chemical reaction

4. THERMODYNAMIC ANALYSIS
ΔHr = ΔHp + Qsys + Poutput power + Qloss
Fuel Cell Module

5. Theoretical and Real Fuel Cell Efficiency
• Assuming that all the Gibbs free energy of hydrogen, ΔG, can be
converted into electrical energy, the maximum possible (theoretical)
efficiency of a fuel cell is
Where ΔHHHV is Higher Heating Value which is The energy
content of an energy carrier
ΔHLHV is used very often to express the fuel cell efficiency to compare it with the
internal combustion engine, whose efficiency has traditionally been expressed using the
fuel ΔHLHV

6. The fuel cell efficiency ηFC can also be defined as the ratio between the power
produced and the power of hydrogen consumed
Where Vfc is the generated voltage and
Ifc is the fuel cell current
Thus, the FC efficiency is related to
the actual voltage, which is related
to the fuel cell current through the
polarization curve.

7. In a real system it is necessary to incorporate some auxiliary systems which consume a
fraction of the generated power. As a result, the efficiency of the fuel cell system, ηfcs,
is even lower than that expressed in previous Eq
Where Pnet is the net power output, Pfc is the fuel cell power, and
Paux is the power consumed by the auxiliary components, which
include, in particular, the air compressor

8. • the efficiency of the fuel cell system, ηfcs,
Pnet is the net power output, Pfc is the fuel cell power, and Paux is the
power consumed by the auxiliary components, which include, in
particular, the air compressor

9. Exergetic efficiency
• is defined as the second law efficiency
Where
Ėair;R, ĖH2;R,  total exergies of the reactants, air and fuel (H2),
Ėair;P and ĖH2O;P total exergies of the products air and water

10. • the total exergy transfer per unit mass of each reactant and product
consists of the combination of both physical and chemical exergies
Physical exergy
h0 and s0 denote the specific enthalpy and entropy evaluated at
standard conditions
The physical exergy of an ideal gas with constant specific heat Cp and specific
heat ratio k can be written as:
The physical exergy is expressed in terms of the differences of enthalpy from those
and entropy from those at standard conditions.
The general expression of the physical exergy can be described as

11. • The chemical exergy is associated with the departure of the chemical
composition of a system from that of the environment
• the chemical exergy of air can be calculated in terms of the mole
fraction by the equation under standard condition
Chemical exergy

12. Mass flow rates of the products and the reactants in the fuel cell
• The mass flow rates of the inlet air and fuel, hydrogen, can be evaluated through
the following equations
Where power output Ẇ
fuel cell voltage V
stoichiometry of air λ,
The mass flow rate of the product air can be defined as
The amount of water produced by the fuel cell is given by

13. the total exergy of the reactants and the products can be determined through