1. Unit 6
Fuel Cells

2. The fuel cell is a unique power converter
That is efficient, nonpolluting, and flexible.
For many, it is the technology that will wean
Us from our strong dependence upon
Imported oil, especially the transportation sector.
It combines a fuel (usually natural gas or hydrogen)
With oxygen from the air by an electrochemical
Process to produce electricity.

3. Fuel cells are being developed to power passenger
Vehicles, commercial buildings, homes, and
Even small devices such as laptop computers.
These systems are effective over a large range
Of sizes, from 1kW to hundreds of MW, with
Over all efficiencies of 80% or more!
(when heat production is combined with
The power generation)
They are clean, highly reliable (no moving parts),
And offer a unique opportunity for energy
Independence.

4. The fuel cell was invented more than a hundred
Years ago, but didn’t come of age in
The 1970’s when it was first used on space missions.
They offer a large power-to-weight ratio,
Compactness, and reliability.
This makes it a popular power source for such
Uses as vehicle propulsion, and
Small scale electric facilities.

5. The high cost of fuel cells and future
Unknowns have hindered their commercialization.
The present price of about $4000 per kilowatt
Can be offset by fading government grants.
In its most basic form, it is a battery
That has a constant supply of fuel to
Always “recharge” it.
It provides direct current through an
Electro-chemical process.

6. H2 + ½ 02  H22+ 02- + energy The 2 chemical reactants in a fuel cell
Are generally hydrogen and oxygen, which
Are fed into the cell through
Porous electrodes.
The fuel cell reaction can be thought of as
A very slow hydrogen gas combustion process.
H2 + ½ 02  H energy

7. In a fuel cell the electrons are transferred
Slowly to the oxygen via an external circuit.
At the positive electrode, hydrogen atoms are
Stripped of their electrons and enter into the
Electrolyte.
At the negative electrode, the hydrogen ions
Combine with the oxygen atoms and electrons to
Form water and heat.

8. The electrons flow through an external circuit
Connecting the electrodes.
The net result is the reaction of
Oxygen and hydrogen to form
Water.

10. There are 5 different types of fuel cells that
Are in research, testing, or development stages.
The proton exchange membrane (PEM), the
Molten carbonate cell, the solid-oxide ceramic
Cells are all in the demonstration stage.
The phosphoric acid cell has been operated
In a commercial size of 200 kW and tested
With an 11MW unit.

11. The alkaline process has been used by
NASA in its space program, in the
Gemini space capsules in the 1960s.

12. The phosphoric acid cell (PAFC) is considered to
Be the “1st” generation of fuel cells.
It was also the first to be used commercially
With over 200 units currently in use.
They are usually used for stationary power generation
Since they are heavy.
They are 85% efficient when used for
Electricity and heat.

13. Polymer electrolyte membrane (PEM) fuel cells
Deliver high power density and are lower in
Weight compared to other types.
PEM uses a solid polymer as an electrolyte and
Porous carbon electrodes containing a platinum catalyst.
They require only hydrogen, oxygen from the air
And water to operate.
Can also use methane and methanol but a
Fuel processor is necessary.
These are the most popular choice for small
Electronics and vehicle propulsion.

15. Alkaline fuel cells were the first to be used in the
Space program to produce electricity and
Onboard spacecraft.
They use a solution of potassium hydroxide in
Water as the electrolyte and a variety of precious
Metals as the anode and cathode.
They have demonstrated efficiencies as
High as 60%.

16. Molten metal carbonate fuel cells use an
Electrolyte of molten carbonate salt mixture in
A porous, chemically inert ceramic lithium
Aluminum oxide (LiAlO2).
They operate at a high temperature, so they
Can use lower quality fuels.
Efficiencies reach 60%.

17. Solid Oxide fuel cells (SOFC) use a hard, nonporous
Ceramic compound as the electrolyte, allowing
Solid construction.
These also operate at a very high temperature,
So they require a long start up time, making
Them more suitable for stationary functions.
Efficiencies of around 50%.

18. Potassium hydroxide solution Hydrogen Oxygen 60-90
Fuel Cell Type
Electrolyte
Anode Fuel
Cathode Fuel
Operating Temp. (°C)
Applications
Alkaline
(AFC)
Potassium hydroxide solution
Hydrogen
Oxygen
60-90
Spacecraft Submarines
Proton exchange membrane (PEMFC) 50%
Proton-conductive polymer electrolyte
(in air)
Transportation
Stationary power plants
Direct methanol
(DMFC)
Proton-conductive polymer
Methanol
90-120
Phosphoric-acid (PAFC) 50%
Phosphoric acid
200
Molten carbonate (MCFC)60+%
Molten alkaline carbonate
Hydrogen, methane
650
Solid oxide
(SOFC) 60+%
Ceramic solid electrolyte
Hydrogen, natural gas

19. Direct methanol fuel cell (DMFC) And regenerative fuel cells.
There are more types:
Direct methanol fuel cell (DMFC)
And regenerative fuel cells.
Methanol uses methanol, which has a
Higher energy density than H2.
Regenerative fuel cells use solar panels to
Split water through electrolysis and use
Those gases to run the fuel cell.

20. The fuel stack is the heart of the system.
A single cell produces only about 1 volt DC and
A small current.
Therefore, fuel cells use layers of cells to
Produce the desired voltage and current needed.

21. The costs of fuel cells are not yet competitive with
Conventional power technologies.
In general, they are $30/kW, so they
Cannot replace the ICE.
At the moment, there are only a handful of
Fuel cell systems in the U.S.
The largest one being in Anchorage, Alaska.

23. Questions?

24. THE END