Engineering Fuel Cells

1. Energy Storage Components
MRE 505 FUEL CELL

2. FUEL CELL
OVERVIEW
1. Introduction
2. Issues with Fuel cell
3. Hydrogen Fuel Cell
4. Fuel Cell Thermodynamics
5. Main reasons for loss in voltage

3. 1. Introduction
• Fuel cells were invented in 1840. However, they are
yet to make an impact as a source of energy.
• The basic principle of a fuel cell is that it uses
hydrogen fuel to produce electricity.
• The basic chemical reaction is:
2H2 + O2 2H2O ………………………(1)
• The products are thus water and energy.

4. 2. Main issues with the Fuel cell
(i) Cost: Fuel cells are far more expensive compared to
other energy storage systems
(ii) Cooling: Thermal management is an issue with fuel
cells
(iii)Hydrogen supply: Hydrogen is the preferred fuel.
However, it is difficult to transport and store.
(iv)Water management: This is an issue especially with
automotive fuel cells.

5. 3. Hydrogen Fuel Cells – Basic principles
Electrode reactions: The basic principle of the fuel cell
is the release of energy following a chemical reaction
between hydrogen & oxygen.
The difference between the fuel cell & simply burning
the gas is that the energy is released as an electric
current, rather than heat.
• The simplest & most common type of fuel cell is based
on an acid electrolyte.

6. Hydrogen Fuel cell

7. Basic principles
• At the anode of an acid electrolyte fuel cell the hydrogen gas ionizes,
releasing electrons & creating H+ ions (or protons).
2H2 4H+ + 4e- ………………………………….(2)
This reaction releases energy.
• At the cathode, oxygen reacts with electrons taken from the anode, &
H+ ions from the electrolyte to form water.
O2 + 4e- + 4H+ 2H2O …………………………(3)

8. Basic principles
• For both of the reactions (2) & (3) to proceed
continuously, electrons from the anode must pass
through an electrical circuit to the cathode. Also H+
ions must pass through the electrolyte. An acid is a
fluid with the H+ ions, & so serves this purpose very
well.
• Certain polymers can also be made to contain H+ ions.

9. Electrolytes
• The reactions given in the previous section may seem
very simple, but they do not proceed rapidly. Also the
fact that hydrogen has to be used as a fuel is a
disadvantage. To solve these & other problems
different fuel types have been tried. The different
types are usually distinguished by the electrolyte
used, though there are other important differences as
well.

10. Table: Data for different types of Fuel cells
Fuel Cell Type Mobile ion Operating
Temp.
Application & Notes
Alkaline (AFC) OH- 50 – 200 ˚C Used in space vehicles e.g
shuttles
Proton Exchange Membrane
(PEMFC)
H+ 30 - 100 ˚C Vehicles & mobile applications
for lower power CHP systems
Direct Methanol (DMFC) H+ 20 -90 ˚C Portable electronic systems
running for long times
Phosphoric Acid (PAFC) H+ 220 ˚C 200 kW systems in use
Molten Carbonate (MCFC) 𝐶𝑂3
2−
650 ˚C Medium to large scale CHP
systems, up to MW capacity
Solid Oxide (SOFC) 𝑂2− 500 – 1000 ˚C All sizes of CHP systems, 2 kW to
multi MW.

11. Different types of Fuel cells
• The PEMFC capitalises on the essential simplicity of
the cell. The electrolyte is a solid polymer, in which
protons are mobile. The chemistry is the same as the
acid electrolyte fuel cell.
• The PEMFC operates at low temperatures, so the
problem of slow reaction rates has to be addressed by
using sophisticated catalysts & electrodes. Platinum is
the catalyst

12. Fuel cell electrodes

13. Fuel cell electrodes
• Figure shows another representation of a Fuel cell.
However, a Fuel cell is much more complex than this.
• Normally the rate of reaction of both hydrogen & oxygen
is very slow, which results in a low current, & low power.
• The three main ways to deal with the slow reaction rates
are: use of suitable catalysts on the electrodes, raising
the temperature, & increasing the electrode area.

14. Fuel cell electrodes
• The first two can be applied to any chemical reaction.
However, the third is very special to Fuel cells. Performance
of a Fuel cell design is often quoted in terms of the current
per cm2.
• Structure of the electrode is also important. It is made highly
porous so that the real surface is much greater than the
normal length x width. The electrode must also be coated
with a catalyst layer. In the case of PEMFC this is platinum,
which is very expensive.

15. Fuel cell electrodes
• Very fine particles of catalyst are normally supported on
carbon particles & then spread finely on the electrode.
• A good electrical contact needs to be made with the
electrode surface. Also, in the case of the cathode the
product, water, needs to be removed. These tasks are
performed by the gas diffusion layer, a porous & highly
conductive material such as carbon felt or carbon paper,
which is layered on the electrode surface.

16. Fuel cell Thermodynamics: Introduction:
Fuel cell efficiency & efficiency limits:
Fuel cells are more efficient than the IC engines & other types of