What Are Fuel Cells Used For

Fuel Cell Basics

Through this website we are seeking historical materials relating to fuel cells. We have constructed the site to gather information from people already familiar with the technology–people such equally inventors, researchers, manufacturers, electricians, and marketers. This Basics section presents a general overview of fuel cells for casual visitors.

What is a fuel cell?

A fuel cell is a device that generates electricity by a chemical reaction. Every fuel cell has two electrodes called, respectively, the anode and cathode. The reactions that produce electricity take place at the electrodes.

Every fuel cell also has an electrolyte, which carries electrically charged particles from ane electrode to the other, and a goad, which speeds the reactions at the electrodes.

Hydrogen is the bones fuel, simply fuel cells also require oxygen. One great entreatment of fuel cells is that they generate electricity with very picayune pollution–much of the hydrogen and oxygen used in generating electricity ultimately combine to course a harmless byproduct, namely water.

I item of terminology: a single fuel cell generates a tiny corporeality of directly current (DC) electricity. In practice, many fuel cells are usually assembled into a stack. Prison cell or stack, the principles are the same.

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How do fuel cells work?

The purpose of a fuel cell is to produce an electric current that can exist directed outside the jail cell to do piece of work, such as powering an electric motor or illuminating a light bulb or a city. Because of the way electricity behaves, this electric current returns to the fuel cell, completing an electrical circuit. (To learn more about electricity and electric power, visit "Throw The Switch" on the Smithsonian website Powering a Generation of Alter.) The chemic reactions that produce this current are the central to how a fuel prison cell works.

There are several kinds of fuel cells, and each operates a bit differently. But in full general terms, hydrogen atoms enter a fuel cell at the anode where a chemical reaction strips them of their electrons. The hydrogen atoms are at present "ionized," and deport a positive electrical charge. The negatively charged electrons provide the current through wires to exercise work. If alternate current (AC) is needed, the DC output of the fuel cell must be routed through a conversion device called an inverter.

animated image showing the function of a PEM fuel cell
Graphic past Marc Marshall, Schatz Energy Research Center

Oxygen enters the fuel prison cell at the cathode and, in some cell types (similar the one illustrated above), information technology there combines with electrons returning from the electric circuit and hydrogen ions that have traveled through the electrolyte from the anode. In other cell types the oxygen picks up electrons and then travels through the electrolyte to the anode, where it combines with hydrogen ions.

The electrolyte plays a key role. It must permit just the appropriate ions to laissez passer betwixt the anode and cathode. If gratis electrons or other substances could travel through the electrolyte, they would disrupt the chemical reaction.

Whether they combine at anode or cathode, together hydrogen and oxygen class h2o, which drains from the jail cell. As long equally a fuel cell is supplied with hydrogen and oxygen, it will generate electricity.

Even improve, since fuel cells create electricity chemically, rather than by combustion, they are not subject to the thermodynamic laws that limit a conventional power plant (see "Carnot Limit" in the glossary). Therefore, fuel cells are more efficient in extracting free energy from a fuel. Waste material heat from some cells can too be harnessed, boosting arrangement efficiency still further.

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And then why can't I exit and purchase a fuel cell?

The basic workings of a fuel cell may non be hard to illustrate. But edifice inexpensive, efficient, reliable fuel cells is a far more complicated business.

Scientists and inventors have designed many dissimilar types and sizes of fuel cells in the search for greater efficiency, and the technical details of each kind vary. Many of the choices facing fuel jail cell developers are constrained by the choice of electrolyte. The design of electrodes, for case, and the materials used to make them depend on the electrolyte. Today, the main electrolyte types are alkali, molten carbonate, phosphoric acid, proton exchange membrane (PEM) and solid oxide. The kickoff iii are liquid electrolytes; the last 2 are solids.

The type of fuel likewise depends on the electrolyte. Some cells need pure hydrogen, and therefore need extra equipment such every bit a "reformer" to purify the fuel. Other cells can tolerate some impurities, just might need higher temperatures to run efficiently. Liquid electrolytes circulate in some cells, which requires pumps. The type of electrolyte as well dictates a cell's operating temperature–"molten" carbonate cells run hot, just as the proper noun implies.

Each type of fuel cell has advantages and drawbacks compared to the others, and none is however cheap and efficient plenty to widely replace traditional ways of generating power, such coal-fired, hydroelectric, or even nuclear power plants.

The following list describes the 5 main types of fuel cells. More than detailed information tin can be found in those specific areas of this site.

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Different types of fuel cells.

drawing of an Alkali fuel cell
Drawing of an alkali cell.

Brine fuel cells operate on compressed hydrogen and oxygen. They generally employ a solution of potassium hydroxide (chemically, KOH) in water as their electrolyte. Efficiency is most 70 percentage, and operating temperature is 150 to 200 degrees C, (nearly 300 to 400 degrees F). Cell output ranges from 300 watts (West) to 5 kilowatts (kW). Alkali cells were used in Apollo spacecraft to provide both electricity and drinking water. They crave pure hydrogen fuel, however, and their platinum electrode catalysts are expensive. And similar any container filled with liquid, they tin leak.

drawing of molten carbonate fuel cell
Drawing of a molten carbonate prison cell

Molten Carbonate fuel cells (MCFC) use high-temperature compounds of salt (similar sodium or magnesium) carbonates (chemically, CO ₃ ) as the electrolyte. Efficiency ranges from sixty to 80 pct, and operating temperature is well-nigh 650 degrees C (1,200 degrees F). Units with output upwards to ii megawatts (MW) take been constructed, and designs exist for units up to 100 MW. The high temperature limits harm from carbon monoxide "poisoning" of the jail cell and waste product heat can be recycled to make additional electricity. Their nickel electrode-catalysts are inexpensive compared to the platinum used in other cells. Merely the loftier temperature too limits the materials and safe uses of MCFCs–they would probably be as well hot for home employ. Also, carbonate ions from the electrolyte are used up in the reactions, making it necessary to inject carbon dioxide to compensate.

Phosphoric Acid fuel cells (PAFC) utilise phosphoric acid as the electrolyte. Efficiency ranges from 40 to 80 percentage, and operating temperature is between 150 to 200 degrees C (well-nigh 300 to 400 degrees F). Existing phosphoric acid cells accept outputs up to 200 kW, and 11 MW units have been tested. PAFCs tolerate a carbon monoxide concentration of about 1.v percent, which broadens the choice of fuels they can use. If gasoline is used, the sulfur must be removed. Platinum electrode-catalysts are needed, and internal parts must be able to withstand the corrosive acid.

drawing of how both phosphoric acid and PEM fuel cells operate
Cartoon of how both phosphoric acid and PEM fuel cells operate.

Proton Exchange Membrane (PEM) fuel cells work with a polymer electrolyte in the course of a sparse, permeable sheet. Efficiency is about forty to 50 per centum, and operating temperature is nigh 80 degrees C (nearly 175 degrees F). Cell outputs generally range from l to 250 kW. The solid, flexible electrolyte will not leak or crack, and these cells operate at a low plenty temperature to make them suitable for homes and cars. Merely their fuels must exist purified, and a platinum goad is used on both sides of the membrane, raising costs.

drawing of solid oxide fuel cell
Drawing of a solid oxide prison cell

Solid Oxide fuel cells (SOFC) utilize a difficult, ceramic chemical compound of metal (like calcium or zirconium) oxides (chemically, O ₂ ) as electrolyte. Efficiency is about sixty percentage, and operating temperatures are nigh one,000 degrees C (nearly ane,800 degrees F). Cells output is up to 100 kW. At such high temperatures a reformer is not required to extract hydrogen from the fuel, and waste estrus can be recycled to make additional electricity. Notwithstanding, the loftier temperature limits applications of SOFC units and they tend to be rather large. While solid electrolytes cannot leak, they tin cleft.

More detailed data about each fuel cell blazon, including histories and current applications, can exist constitute on their specific parts of this site. Nosotros have as well provided a glossary of technical terms–a link is provided at the acme of each engineering page.

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