Download Hydrogen Fuel Cells

Hydrogen Fuel Cells
by Ryan, Talha, Jen, Joel
The chemistry behind this technology
Anode  Is being oxidized Is acting as the reducing agent:
+
2H2 => 4H + 4e
Cathode  Is being reduced Is acting as the oxidizing agent:
+
O2 + 4H + 4e => 2H2O
The balanced reaction ends up looking like this:
2H2 + O2 => 2H2O
Image obtained from
http://www.hydrogen.co.uk/earth_again.jpg
A hydrogen fuel cell works due to the reaction between hydrogen molecules and the catalyst. The
catalyst is usually powdered platinum on carbon paper. This reaction breaks the hydrogen into a proton
and an electron. The electron passes through the circuit, generating electricity, while the proton
moves across the electrolyte to an area with oxygen. However, this only produces about 0.7
volts. As a result, hydrogen fuel cells built together in what is known as a stack to increase the
voltage. Once the electron passes through the load, it returns to the cell through the cathode.
Once in the cell, the catalyst fuses the proton, electron, and
oxygen molecules to make water.
The major benefits of Hydrogen Fuels Cells are:
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A 2 to 3 time greater energy efficiency than standard combustion engines
Little or no polluting or environmentally harmful emissions are produced
through the fuel cells use
Low maintenance costs (fuel cells can be monitored remotely) and quiet
operation as very few vibrations are generated
More design freedoms particularly when the fuels cells are used in automobiles
The ability to generate heat and electricity at the point of use
Extremely versatile with many applications including portable, stationary and
transportation power applications
The capability to generate power for a nearly indefinite period provided fuel is readily supplied
Depending on the type of fuel cell, pure hydrogen or hydrocarbons can be used (high fuel flexibility)
Fuel (hydrogen) is a virtually unlimited, easily accessible resource, is safe to store and transport and can be produced
through a variety of means including renewable energy technologies
Social and economic benefits including the creation of jobs, and fiscal growth
The three major disadvantages of Hydrogen Fuel Cells are:
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Hydrogen Fuel Cells are very expensive and inefficient in comparison to normal engines. Usually engines perform
well at 100% load factor; however, a hydrogen fuel cell can only perform well at 30% load factor.
The cost of producing Hydrogen Fuel Cells is more than what is gained out of them. A regular combustion engine
would cost $30 to produce one kilowatt of power. On the other hand, a Hydrogen Fuel Cell would cost $3,000 to
produce the same amount of power.
Extraction of hydrogen through electrolysis is inefficient and expensive.
Hydrogen Fuel cells have three practical problems when used in automobiles: Increased carbon dioxide emissions,
large size of the fuel cell, and sensitivity to extreme conditions. Social and Economic disadvantages include increase
in negative externalities such as pollution through more CO2 emissions.
Different types of Hydrogen fuel cells
Polymer Electrolyte Membrane (PEM) Fuel Cells: Used to backup power or for
portable power use. Also used in transportation and specialty vehicles. Advantages
include: Solid electrolyte reduces corrosion, it maintains a low temperature and starts
up rapidly. Disadvantages include: very expensive catalysts and sensitivity to fuel
impurities.
Alkaline (AFC): Used in military and space
operations. Advantages include: Cathode
reaction faster in alkaline electrolyte; therefore,
high perfor mance and efficiency. Cost of
components is relatively low. Disadvantages
include: sensitivity to CO2 in fuel and air.
Solid Oxide (SOFC): Used in electrical utilities
and for distributed generation (for instance
within power plants). Advantages include: High
efficiency of roughly 60%, flexibility in fuel type
and is able to use a variety of catalysts.
Disadvantages include: A long start up time, and
low power density. Additionally, this cell operates at a very high temperature.
Molten Carbonate (MCFC): Used for auxiliary
power, electrical utilities and for distributed
generation. Advantages include: Can use a solid
electrolyte and a variety of catalysts. Has high
efficiency and greater fuel flexibility than other
fuel cells. Disadvantages include: A long start
up time and high temperature corrosion and
breakdown of the fuel cell components.
Phosphoric Acid Fuel Cell (PAFC): Used for
distributed power generation. Advantages
include: A high tolerance to impurities in fuel,
particularly hydrocarbons. Disadvantages
include: Long start up time
Diagrams obtained from http://www.eere.energy.gov/
Viability for emergency power and remote locations
Hydrogen fuel cells are compact, lightweight, and off-grid power generators. This
makes the ideal for emergency power and remote locations as they are very portable.
Moreover, they can be modified to produce different energy outputs, making them
useful for a wide range of applications. Also, some models only require the addition of water to operate, and thus can be
useful in remote areas where other fuel sources are not available. There have already
been some commercial products for the use of hydrogen fuel cells in these areas. For
example, these cells can be used in spacecraft and rural areas. One specific product
currently on the market is the HydroPak:
The HydroPak
The HydroPak is a portable, off-grid power generator that is lower in cost, weight, and
size when compared to a traditional electric generator. Its ability to produce its own
hydrogen means that all you have to do is add water to use it. Furthermore, it does not
release any emissions.
Image obtained from
http://www.horizonfuelcell.com/portable_power.htm
Background obtained from http://www.stanford.edu/class/history5n/student_work/wang_files/master10_background.jpg