INTRODUCTION TO FUEL CELLS
A fuel cell produces electricity by means of an electrochemical reaction much like a battery. But there is an important difference. Rather than extracting the chemical reactants from the plates inside the cells, a fuel cell uses hydrogen fuel and oxygen extracted from the air to produce electricity. As long as these substances are fed into the fuel cell, it will continue to generate electric power.
Different types of fuel cells work with different electrochemical reactions. The following is a basic description of how a phosphoric acid fuel cell generates electric power.
1. Hydrogen gas is extracted from natural gas or other hydrocarbon fuels and permeates the anode. Oxygen from the air permeates the cathode.
2. Aided by a catalyst in the anode, electrons are stripped from the hydrogen. Hydrogen ions pass into the electrolyte.
3. Electrons cannot enter the electrolyte. They travel through an external circuit, producing electricity.
4. Electrons travel back to the cathode where they combine with hydrogen ions and oxygen to form water.
A fuel cell provides DC (direct current) voltage that can be used to power motors, lights or other electrical appliances. To supply electricity for homes, businesses, and buildings, however, the direct current must be changed into AC (alternating current). A device called an "inverter" makes this conversion.
Hydrogen needed by a fuel cell can be extracted from a variety of fuels. Natural gas - a chemical combination of carbon and hydrogen atoms - is perhaps the most common fuel, but other hydrocarbon fuels can also be used. For example, some fuel cells operate on gases released from wasterwater digesters or from landfills. In the future, gas made from coal or biomass might be candidate fuels. Some types of fuel cells extract the hydrogen in a separate fuel processor called a "reformer;" other fuel cells incorporate reforming inside the cell stack itself.
Written by: Office of Fossil Energy, U.S. Department of Energy
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