Hydrogen EconomyFuel Cells PGCC Honors Program Project Presented by QueenetIbekweh 7 December 2007 Academic Advisor: Prof. William Antonio Boyle, PhD
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 charges. • 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 cell (PEMFC) • 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 turbines to generate more electricity. Drawing of a solid oxide cell
Drawing of a molten carbonate cell Molten Carbonate Fuel Cells 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.
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 • Cost • Durability • Infrastructure
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 mechanical work. • 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.
Literature Cited CBC News, Technology and Science Research boosts potential of hydrogen fuel. http://www.cbc.ca/technology/story/2007/11/13/hydrogen.html#skip300x250 The Lugar Energy Initiative. http://lugar.senate.gov/.../fuel/electricity.htm The Time to Care. http://thetimetocare.blogspot.com/ How Stuff Works. It’s good to know. http://auto.howstuffworks.com/fuel-cell2.htm Fuell Cells: Fuel Cell Basics http://americanhistory.si.edu/fuelcells/basics.htm