The Hydrogen Economy:
PGCC Honors Academy Project
7 December 2007
Prof. William A. Boyle
What Is A Fuel Cell?
A fuel cell, also known as a flow battery, is
an electrochemical device that combines a
fuel and an oxidizer such hydrogen and
oxygen to produce electricity.
Purpose of a Fuel Cell
It is used to produce electrical current that
can be directed outside the cell to perform
work, such as powering an electric motor
or illuminating a light bulb or a city.
Due to the way electricity behaves, this
current returns to the fuel cell, completing
an electric circuit.
How the Fuel Cell Works
Hydrogen molecules enter the fuel cell at the anode and
are stripped of their electrons.
Hydrogen atoms become “ionized” and carry positive
Negative charged electrons provide current through the
electrical circuit to perform work.
Oxygen enters at the cathode and combines with the
electrons returning from the electric circuit and the
hydrogen ions that have traveled through the electrolyte
to the anode.
Types of Fuel Cells
Proton exchange membrane fuel
Solid oxide fuel cell (SOFC)
Alkali fuel cell (AFC)
Molten-carbonate fuel cell (MCFC)
Phosphoric-acid fuel cell (PAFC)
Direct-methanol fuel cell (DMFC)
Alkali Fuel Cell
Reactants: Pure hydrogen and oxygen (compressed)
Electrolyte: Potassium hydroxide (KOH) in water.
Its operating temperature is 150 to 200 degrees C.
Alkali cells were used in the Apollo spacecraft to provide both electricity and
drinking water. It has an efficiency of about 70%. It is very susceptible to
contamination, so it requires very pure hydrogen and oxygen. It is also very
expensive, so this type of fuel cell is unlikely to be commercialized.
Solid Oxide Fuel Cell
These fuel cells are best suited for large-scale
stationary power generators that could provide
electricity for factories or towns. They operate at a
temperature of about 700-1000 degrees C. The high
temperature also has an advantage: the steam
produced by the fuel cell can be channeled into
Drawing of a solid oxide cell
turbines to generate more electricity.
Molten Carbonate Fuel Cells
Drawing of a molten carbonate cell
This type of fuel cells use high temperature compounds of
salts such as sodium or magnesium carbonate. Its
efficiency ranges from 60-80% and it operates at a
temperature of about 650 degrees C.
PEM Fuel Cells
The Proton Exchange Membrane Fuel Cell (PEMFC) is
the most likely candidate for transportation applications
due to its high power density and low operating
temperature which ranges from 60-80 degrees Celsius.
With its low operating temperature, it does not take a
long time for the fuel cell to warm up and start generating
energy. The solid, flexible electrolyte will not leak or
crack, and these cells operate at a low enough
temperature to make them suitable for homes and cars.
Hydrogen Fuel Cell
Purpose of Electrolyte
Electrolyte permits the appropriate ions to
pass between the anode and the cathode.
It acts as the proton exchange membrane
which only conducts positively charged
ions and blocks the electrons.
Fuel Cell Problems
Why Use Fuel Cells?
The efficiency of a gasoline-powered car is surprisingly low
and all the heat that comes out in the exhaust or goes
into the radiator is wasted energy. The overall efficiency
of a gas engine is around 20% which refers to the
thermal-energy content of the gasoline converted into
Fuel-cell vehicles are potentially as efficient as a battery-
powered car that relies on a non-fuel-burning power
plant, therefore, decreasing our dependency on oil and
atmospheric deterioration (“pollution”) due to the
combustion of fossil fuels.
Gas prices from 1990-2004
CBC News, Technology and Science. Research boosts potential of
The Lugar Energy Initiative.
The Time to Care.
How Stuff Works. It’s good to know.
Fuell Cells: Fuel Cell Basics