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fuel cell
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An electrochemical system in which the chemical energy of a fuel is converted directly into electrical energy. A fuel cell works in a similar way to a primary battery with the difference that the energy is not stored between the electrodes, but is instead transferred from an external tank. Because there is no combustion, fuel cells give off few emissions. Also, having no moving parts, they are quiet.
Fuel cell technology dates back to the 1800s, but it wasn't until the end of the 20th century that it was used successfully in spacecraft to provide electricity and water. The technology can be used to make electricity to power vehicles, homes, and businesses. And if a renewable energy source is used as the main source of hydrogen, a fuel cell can be considered a renewable energy source.
Today the technology is used for the production of electric and thermal energy in power-heat coupling systems (see block-type thermal power station) and it is also the source of electricity in electric automobiles. Unlike battery-powered electric automobiles, fuel cell powered automobiles achieve similar ranges and load-carrying capacities to conventional automobiles with combustion engines. In the past few decades, significant advances in the materials sciences have helped spur the breakthrough of fuel cell technology.
How fuel cells work
Unlike conventional technologies, fuel is not "burned" but is combined in a chemical process. A fuel cell consists of two electrodes sandwiched around an electrolyte. Oxygen passes over one electrode and hydrogen over the other, generating electricity, water, and heat.
Hydrogen fuel is fed into the anode of the fuel cell. Oxygen (or air) enters the fuel cell through the cathode. Encouraged by a catalyst, the hydrogen atom splits into a proton and an electron, which take different paths to the cathode. The proton passes through the electrolyte. The electrons create a separate current that can be utilized before they return to the cathode, to be reunited with the hydrogen and oxygen in a molecule of water.
A fuel cell system that includes a fuel reformer can obtain hydrogen from any hydrocarbon fuel – from natural gas, methanol, and even gasoline. Other possible fuels include propane, hydrogen, anaerobic digester gas from wastewater treatment facilities, and landfill gas.
Fuel cell types
Fuel cells are categorized according to the type of electrolyte used. Some of the these include:
- Proton Exchange Membrane (PEM) fuel cells were used in the Gemini spacecraft missions and designed by DuPont. A solid polymer ion exchange membrane is used as an electrolyte. Platinum ruthenium is used as the catalyst. PEM fuel cells are being tested in mobile sources such as buses and smaller vehicles.
- Platinum is used as the catalyst in phosphoric acid fuel cells, one of the most mature fuel cells (and which relies upon aqueous phosphoric acid as an electrolyte).
- Alkaline fuel cells are one of the oldest types of fuel cells. They, too, rely upon platinum (or palladium) as the catalyst for a potassium hydroxide electrolyte.
- Molten carbonate fuel cells rely upon nickel-based catalysts (and molten carbonates as electrolytes) and can operate at higher temperatures. Reforming the fuel into hydrogen can occur inside the fuel cell. Most of the larger fuel cells on the market today rely upon this approach.
- Solid oxide fuel cells rely upon a coated zirconia ceramic as the electrolyte, which translates into the ability to operate at even higher temperatures that can support fuel formulation within the fuel cell. No catalyst at all is required. This technology is the least mature of the fuel cell types currently on the market. Nevertheless, it offers the promise of reduced cost and greater quantities of thermal heat for use at the installation site.
Related categories
• FUELS
• BATTERIES
Source: California Energy Commission
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Encyclopedia of Science
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