Do You Know Fuel Cells?

Do You Know Fuel Cells?

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Description: According to the rate of consuming the non-renewable fossil fuels such as oil, coal, and natural grasses, in our earth, the reserve of such fossil fuels in the world is estimated to run out over the next 100 years. A worldwide energy crisis in the future is unavoidable if we do not develop alternative renewable energy sources in time. Upon exhaustion of fossil fuels and the search for new energy sources is fruitless, can you image what our future will be? Will our world be in total darkness?.

 
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Domain:  Green Tech Category: Battery & Fuel Cell 
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Contents:
Reading to Learn Activity (2)

Fuel Cells
Do you know?

What is a fuel cell?

According to the rate of consuming the
non-renewable fossil fuels such as oil,
coal, and natural gases, in our earth, the
reserve of such fossil fuels in the world is
estimated to run out over the next 100
years. A worldwide energy crisis in the
future is unavoidable if we do not
develop alternative renewable energy
sources in time. Upon exhaustion of fossil
fuels and the search for new energy
sources is fruitless, can you image what
our future will be? Will our world be in
total darkness?

Similar to a battery, a fuel cell is a device
that converts chemical energy directly
into electrical energy. However, unlike
batteries, with non-stop supply of fuels,
fuel cell can run forever and produce
steady supply of electrical energy. The
two basic components used to run a fuel
cell are hydrogen and oxygen. They react
inside the fuel cell to generate electricity,
heat and water. This new energy source
will never be used up as we have
unlimited supply of oxygen on Earth.
Hydrogen can be produced from water,
gasoline, natural gas, landfill gas, coalbased gas, methane, methanol and
ethanol.

Therefore, scientists have been urged to
look for alternative energy sources that
are renewable. Among all the possible
choices, such as solar energy, hydropower, nuclear power, geothermal
energy etc, there is a promising energy
source called the fuel cell which has
recently attracted the attention of people
from all kinds of background. The
invention of this technology has caused a
great impact on various industries, as fuel
cell is quiet, flexible, highly efficient and
exceptionally clean.

-

e

How does a fuel cell work?
A fuel cell consists of two electrodes, the
anode and the cathode, separated by an
electrolyte. Thin layer of platinum or
other metals, depending on the type of
the fuel cell, is coated on each electrode to
activate the reaction between oxygen and
hydrogen when they pass through the
electrodes. The overall reaction is shown
by the equation below:
-

e

V

O2 (g) → H2O(l)
∆H=-287 kJ mol-1

O2

2H+

H2(g)→2H+(aq)+2eAnode

1
2

e-

eH2

H2(g) +

1
2

H2O
Solid
Polymer
Electrolyte

Cathode
H2O
Exhaust

A hydrogen-oxygen fuel cell

140

O2(g)+2H+(aq)+2e-→H2O(l)

Reading to Learn Activity (2)

How many types of fuel cell are there?

Apart from the five of types fuel cell
mentioned above, there is a new type of
fuel cell called Direct Methanol Fuel Cell
(DMFC) which is being under vigorous
on-going research. This type of fuel cell
has the same operating mechanism as
PEMFC, but instead of using pure
hydrogen, it is able to use methanol
directly as the basic fuel. A reformer is
therefore not essential in this fuel cell
system to reform complex hydrocarbons
into pure hydrogen. Several companies
around the world are presently working
on DMFC to power electronic equipments.
The DMFC appears to be the most
promising alternative electric source to
replace the battery used in portable
electronics such as mobile phones and
laptop computers.

There are five major types of fuel cells
being known or used in the market. They
all have the same basic design as
mentioned above, but with different
chemicals used as the electrolyte. These
fuel cells are:






Alkaline Fuel Cell (AFC)
Phosphoric Acid Fuel Cell (PAFC)
Molten Carbonate Fuel Cell (MCFC)
Solid Oxide Fuel Cell (SOFC)
Proton Exchange Membrane Fuel
Cell (PEMFC)

All the above fuel cells require fairly pure
hydrogen fuel to run. However, large
amount of hydrogen gas is difficult to
transport and store. Therefore, a reformer
is normally equipped inside these fuel
cells to generate hydrogen gas from liquid
fuels such as gasoline or methanol.

Why are fuel cells being developed so
fast?

Among these five types of fuel cell,
PEMFC has the highest potential for
widespread use.
PEMFC is getting
cheaper to manufacture and easier to
handle. It operates at relatively low
temperature when compared with other
types of fuel cell. Alkaline Fuel Cell (AFC)
has the highest efficiency and is therefore
being used to generate electricity in space
craft for more than thirty years.
However, it requires very pure hydrogen
and oxygen to operate and thus the
running cost is very expensive. As a
result, AFC is unlikely to be used
extensively for general purposes, such as
in vehicles and in our homes. In contrast,
the Molten Carbonate Fuel Cell (MCFC)
and the Solid Oxide Fuel Cell (SOFC) are
specially designed to be used in power
stations to generate electricity in largescale. Nevertheless, there are still a lot of
technical and safety problems associated
with the use of these fuel cells (MCFC and
SOFC) in the long term.

141

With the ever increasing world
consumption of fossil fuels, sooner or
later the reserve of fossil fuels will be
used up. We should look for a renewable
energy source to resolve this problem.
Besides, the burning of fossil fuels has
caused serious environmental problems
such as air pollution, oil spillage and
global warming. Using fuel cells to
replace fossil fuels as our primary energy
source can solve these problems because
fuel cells:







are clean energy source
have high efficiency, 40-50% of the
chemical energy being converted to
electrical energy
use a variety of fuels e.g. hydrogen
or natural gas or methanol or
hydrocarbons
are reliable, maintainable and
durable

Reading to Learn Activity (2)

What are the applications of fuel cells?

Fuel cell system is ideally to be used for
residential and stationary applications
because it operates silently with low level
of noise and air pollution, also the heat it
releases during operation can be used to
boil water for shower and central heating
system inside the house.

Space Exploration
In the late 1950’s, NASA began
experiments with the fuel cell technology
to develop power source required for
space travel. Fuel cell technology is also
used in space shuttles and the new
international space station. Electrical
power for NASA's Space Shuttle Orbiter
is provided by fuel cells. Each fuel cell is
a self-contained unit with size 14x15x45
inches, weighs 260 pounds and is capable
of providing 12 kW of electricity
continuously, and up to 16 kW for short
period of time.

Portable Power for Electronics
In the near future, it will be of no surprise
that miniature fuel cell power generators
suitable for use in portable electronics
such as PDAs, notebook computers and
cellular phones will be pervaded in the
electronic world. Researchers have been
trying to invent fuel cells that are small,
lightweight, refillable, low operating
temperature and having higher energy
density to replace the lithium batteries
that are now being used in notebook
computers and cellular phones. The most
promising fuel cell type for portable
applications is the direct methanol fuel
cells (DMFC). These fuel cells have been
estimated by scientists to have energy
storage that is ten times that of the
lithium batteries.

Transportation
Most vehicles today use internal
combustion engines that burn fossil fuels
to generate energy. However, such
system has many unpleasant side-effects
including air-pollution and low efficiency.
Therefore, in order to replace the internal
combustion engine, a fuel cell has to be
safe to operate with high efficiency and
low cost, it must also be fairly light with
high power densities. Most of the leading
automotive manufacturers have been
focusing on building fuel cell vehicles for
some time. As a matter of fact, some
major automotive companies have
already begun to rent out vehicles that
used fuel cell as the energy source.
However, this is only limited to Japan and
California at the moment. Automakers
and experts speculate that it will be
another few years before fuel cell vehicle
can be fully commercialized. Nowadays,
fuel cells are also being installed in bikes,
scooters, and airplanes.

How far has the development of fuel cell
gone?
Although the development of fuel cell is
fast, fuel cell has not yet reached its
potential level of commercial success due
to high material costs (Pt electrode) and
market barriers. To tackle the electrode
problem, platinum or platinum-based
nanoparticles are coated on the surface of
carbon black. This porous electrode used
in fuel cells can give higher current
densities than geometric plate electrode.
More importantly, it can reduce the
quantity of platinum used.

Stationary and Residential Applications
At present, thousands of fuel cell systems
have been incorporated into hospitals,
nursing homes, hotels, commercial
buildings, schools, power stations,
airports as principal electric generator or
to provide backup power when necessary.

To be successful in the marketplace, fuel
cells have to attain a number of
requirements.
Firstly, its cost of
investments must not be too high.
According to a report, current fuel cell
power plants cost about $3000/kW.
142

Reading to Learn Activity (2)

be gained by generating electricity in
fuel cells rather than in the thermal
power stations used at present.

Therefore, to increase the competitiveness
of the fuel cells in the market, it is
necessary for this price to be reduced to
$1500/kW or less in order to fit in the
utility and commercial on-site market.
Secondly, better designs including size
and weight are essential to fit the actual
market needs. Other factors, such as
efficiency, high power output, ease of use
and maintenance etc, are also important.

3.

What are the advantages and
disadvantages of using fuel cells in
portable electronic devices?

4.

Write half-equations for the reactions
that would occur at the anode and
cathode in a Direct Methanol Fuel
Cell. Use these half-equations to
produce an overall equation showing
the net reaction occurring in the cell.

5.

Electrical power for space shuttles is
provided by fuel cells for about forty
years. Write a précis on the fuel cells
used and their future development.

Questions
1.

2.

What are the major differences
between a fuel cell and a
conventional electrochemical cell like
a zinc-carbon cell?
Outline the advantages that would

References
http://www.fuel-cell-bus-club.de/html/body_new_generation_fuel_cell_buses.html
http://ne.nikkeibp.co.jp/english/2002/02/0130toshiba_device.html
http://www.me.umn.edu/courses/me4054/dfe/power.html
http://www.labs.nec.co.jp/Eng/innovative/E1/03.html
http://www.nec.co.jp/press/en/0108/3001.html
http://www.utcfuelcells.com/space/spaceshuttle.shtm
http://www.nasa.gov/missions/science/focus_fuel_cell.html
http://www.staff.ncl.ac.uk/p.a.christensen/dmfc1.htm

143