Although fuel cells have been around for more than 150 years, it is only in recent years that they have become a hot area of research and development. In 2003, President Bush announced the Hydrogen Fuel Initiative (HFI) in his State of the Union Address. This initiative is intended to make fuel cell-powered automobiles practical and cost effective by the year 2020. The government has invested more than a billion dollars in fuel cell research to date.
Fuel cells have the potential to do much more than power automobiles. Solar energy fuel cells would have the potential to reduce or even eliminate our dependence on fossil fuels, eliminating our dependence on foreign oil. Moreover, fuel cells produce little or no pollution and will not contribute to global warming. Fuel cell-powered cars are being developed by a number of manufacturers, and fuel cell-powered buses are already in operation in a growing number of countries.
What Is a Fuel Cell?
Much like the batteries that power flashlights, cell phones, and wristwatches, a fuel cell is a device that produces electricity through a chemical reaction. The main difference is that in a battery all the chemicals needed to make a battery work are contained inside it. Once those chemicals are used up, the battery stops working. Fuel cells are fed a constant flow of chemicals, so they can continue to work indefinitely. Although individual fuel cells provide relatively little power, combining several of them in “stacks” produces a substantial direct current.
The First Fuel Cell
The fuel cell was invented by William Robert Grove in 1839. Grove placed two platinum electrodes in sulfuric acid, which acted as the electrolyte. The first electrode held a sealed container of hydrogen and water while the second held a container of oxygen and water. When the two electrodes were connected, a current flowed between them. Grove also noticed that the water level rose in both the container holding hydrogen and the one holding oxygen. Although it had been shown in 1800 that electricity could cause water to decompose into hydrogen and oxygen, Grove’s experiment reversed the process — combining hydrogen and oxygen to produce water and electricity.
It wasn’t until the 1890s that scientists figured out how fuel cells work. Scientists created new types of fuel cells using different materials in the years leading up to World War II. Emil Bauer, of Switzerland, developed a fuel cell that used molten silver as the electrolyte, and another that used an electrolyte made of clay and metal oxides. Others employed electrolytes made of tungsten trioxide, solid oxide, and nickel. But the seemingly limitless supplies of fossil fuels and the expense of producing fuel cells severely limited their use.
Francis Thomas Bacon began experimenting with alkali electrolyte fuel cells in the late 1930s, and in 1958 he demonstrated a fuel cell made from a stack of electrodes 10 inches in diameter that used potassium hydroxide (KOH) as the electrolyte. Unlike the acid electrolytes used since Grove, KOH did not corrode the electrodes and worked just as well. Meanwhile, the late 1950s and 1960s saw the emergence of a new field where fuel cells would prove essential: space flight. Bacon’s design became the basis for fuel cells used in the Apollo spacecraft.
Types of Fuel Cells
- Alkali fuel cell. The fuel cells used on Apollo spacecraft provided both electricity and drinking water and were fueled with compressed hydrogen and oxygen. The electrolyte was a solution of KOH and water. Alkali fuel cells operate at a temperature of 300 to 400 degrees Fahrenheit.
- Molten carbonate fuel cell. As the name implies, these fuel cells are hot. Using molten sodium or magnesium and carbonates as an electrolyte, they operate at a temperature of 1,200 degrees Fahrenheit. The heat they produce can be used to generate additional electricity. These fuel cells are most appropriate for large stationary power generators.
- Phosphoric acid fuel cell. These cells use phosphoric acid as the electrolyte and operate at temperatures between 300 and 400 degrees Fahrenheit. Platinum electrode-catalysts are required. Internal parts of the fuel cell must be able to withstand the phosphoric acid. These fuel cells may be appropriate for small-scale stationary power systems.
- Proton exchange membrane fuel cell. Also known as polymer exchange membrane fuel cells, these were singled out by the Department of Energy as the most likely fuel cell for use in automobiles. The electrolyte in these fuel cells is a thin, permeable sheet of polymer. They operate at a temperature of about 175 degrees Fahrenheit. Fuel for these cells must be purified, and platinum catalysts would make them expensive.
- Solid oxide fuel cell. Using calcium oxide or zirconium oxide as the electrolyte, these fuel cells operate at a temperature of 1,800 degrees Fahrenheit. The heat can be recycled to produce additional electricity. Due to their heat and large size, these fuel cells would be most useful in large-scale power generators for factories or towns.