A fuel cell is a device that produces electricity through a chemical reaction between a source fuel and an oxidant. The source fuel could be almost anything that can be oxidized, including hydrogen, methane, propane, methanol, diesel fuel or gasoline. The only byproducts are water and a small amount of nitrous oxide if air is used as the oxidizer.
Fuel cells can be used to power just about anything conceivable, from cars to mobile phones to space vehicles. In February 2010, Bloom Energy announced their fuel cell product, Bloom Boxes. Bloom Boxes are modular constructions of fuel cells that can be used in combination to produce the amount of electricity required for a given application. A single fuel cell could power a light bulb; a stack about the size of a loaf of bread could power the average home. At the time of the announcement, five Bloom Boxes the size of a parking spot were providing 15% of the electricity for eBay's campus. Other beta customers for Bloom's product included Coca-Cola, FedEx, Google and Wal-Mart. Bloom is calling the boxes "energy servers," a reference to the modular capability similar to that of servers in data center.
Fuel cells offer several advantages over conventional power sources. These include:
- Reduced dependence on fossil fuels
- Long useful life
- High efficiency
- Relative safety
- Essentially zero toxicity
- Minimal maintenance costs
- Reduced pollution, particularly carbon emissions
- Tax breaks for users and producers.
How do fuel cells work?
A fuel cell does not actually burn its fuel. The oxidation process occurs at a far lower temperature than that produced by active combustion. A fuel cell can be recharged by filling a tank or from a continuously available external supply of fuel. In a common form of hydrogen fuel cell, known as the proton exchange membrane (PEM), hydrogen is delivered to a positive electrode called the anode. At the anode, hydrogen atoms are broken down or ionized into their constituent protons and electrons. The protons permeate through an electrolyte membrane to a negative electrode called the cathode. Electrons travel from the cathode to the anode through an external load, which converts the resulting current to useful power. Within the cell, oxygen molecules react with the protons permeating through electrolyte membrane and the electrons arriving through the external load. The result is water, the principal byproduct of all hydrogen-based energy sources.
A single PEM hydrogen fuel cell generates approximately 0.7 direct-current (DC) volts of electricity. The voltage decreases as the current demand increases. Combinations of cells in series and parallel can produce higher voltage and deliver more current than a single cell. A set of fuel cells connected together to obtain useful power is called a stack. A typical stack, capable of powering a small electric vehicle or large home appliance, is roughly the size and mass of a small tank full of gasoline. Fuel cells can be used to provide power for most electrical or electronic devices designed for operation from batteries or from conventional utility power sources.
The fuel cell was originally conceived by a German scientist, Christian Schoenbein, in the middle of the 19th century. A Welsh physicist, William Grove, developed a working device in 1843. More than a century later in the 1950s, the American scientists Thomas Grubb and Leonard Niedrach improved on the design by incorporating an ion-exchange membrane and making use of hydrogen as the fuel source. Fuel cells of this type were used in some of the American space missions conducted by the National Aeronautics and Space Administration (NASA) during the 1960s.