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A fuel cell is an electrochemical device in which the energy of a chemical reaction is converted directly into electricity. This electricity can then be used to power an electric motor, or it can be simply supplied to the main electricity grid.
History of the fuel cell
The fuel cell was invented by Sir William Grove in 1839. The fuel cell he made was constructed from similar materials to today's phosphoric-acid fuel cell. In the 1960's, the first application was used in the Gemini and Apollo space programs. Then in the 1970's, a fuel cell was developed to be used on Earth. It eventually was tested to be used with utilities and automobiles in the 1980's.
Types of fuel cells
- Alkaline fuel cells- used by NASA in the Apollo and space shuttle programs, used to power electrical systems on spacecraft
- Phosphoric acid fuel cells- used for stationary power applications, used in hotels, and hospitals in the U.S., Japan, and Europe.
- Molten carbohydrate fuel cells- operate at high temperatures to use fuel directly, built in the U.S. and Japan.
- Solid oxide fuel cells- operate at extremely high temperatures allowing them to tolerate impure fuels, have a simple design.
- Proton exchange membrane (PEM)- use a thin plastic film as an electrolyte, produce a powerful electric current relative to their size, deliver higher power density resulting in reduced weight and improved cost and volume performance. Most PEM fuel cells use hydrogen as the fuel source. To form electricity you thus need to combine H2 fuel with O2 air without combustion of any form. H2O and heat are the only by products when H2 is used as a fuel source.
- Direct-ethanol fuel cell (DEFC); as the name implies, uses ethanol as a fuel source
- Direct-methanol fuel cell (DMFC); as the name implies, uses methanol as a fuel source
- Microbial fuel cells- uses microorganisms to produce electricity
How a basic fuel cell works
Fuel cells come in various types; in order to give an example though, we'll discuss the operation of a PEM fuel cell, operating on hydrogen. This fuel cell combines hydrogen and oxygen to produce electricity, with water and heat as a byproduct. The simplest fuel cell consists of an anode and a cathode. The anode hydrogen reacts with a catalyst creating a positively charged ion and negatively charged electron. The proton passes through an electrolyte, while the electron goes through the circuit. This creates a current. At the cathode, oxygen reacts with the ion and electron forming water and heat. Although most fuel cells are larger than a single cell, they can power a small light bulb or about .7 watts. If these single cells are stacked in series, the energy output can greatly increase from several watts to as high as a few megawatts.
Anode side (external supplies of fuel) 2H2 => 4H+ + 4e-
Cathode side (oxidant) O2 + 4H+ +4e- => 2H2O
Net reaction 2H2 + O2 => 2H2O
Advantages and disadvantages of fuel cells
Because fuel cells don't rely on combustion fuel cells have lower and cleaner emissions. In general fuel cells are durable and highly efficient. Today's fuel cell technology has advanced and some fuel cells can achieve 40-50% efficiency using hydrocarbon fuels like natural gas. To bring these systems to an extremely high efficiency, the wast heat can be captured combining heat and power sometimes called cogeneration. Capturing this heat energy can bring a system to be about 85% efficient.
Fuel cells can also provide energy security because of it eliminates foreign oil imports. Hydrogen aswell as other fuels usable in fuel cells (ie ethanol, methanol, ...) can also be produced domestically.
Since fuel cells don't have moving parts they are generally very quiet and can be stored indoors our outdoors.
Fuel cell applications
- Vehicles (ie automobiles, buses) in environments with air; for this application it's a rather expensive solution though (regular IC engines on biofuel are cheaper and about as emissionless as fuel cells)
- Vehicles in air-less environments (ie spacecraft, underwater vehicles); for this application it's a cost-effective solution
- Portable power (ie for small, energy-intensive devices as cellphones, portable computers, ...). For this application it's a cost-effective solution)
- Home power generation: quite cost-ineffective if hydrogen is used, unless a MEC operating on hydrogen generated from waste plant parts and the power is immediatelly used (see Hydrogen as fuel)
- Mains electricity grid-based power generation
- Landfill Waste Treatment
In regards to home power generation: some groups as Ballard Power Systems are working to develop something called a "regenerative fuel cell". This is a device that can generate hydrogen and oxygen when power is available, and combine these efficiently when power is needed. As hydrogen is very difficult to store for a long time, using and producing it in quick succession seems a good idea (if it can indeed be accomplished fast enough).