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 as inventors, researchers, manufacturers, electricians, and marketers. This Basics section presents a general overview of fuel cells for casual visitors.

What is a fuel cell?	How do fuel cells work?
Why can't I go out and buy a fuel cell?
Different types of fuel cells.

What is a fuel cell?

A fuel cell is a device that generates electricity by a chemical reaction. Every fuel cell has two electrodes, one positive and one negative, 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 one electrode to the other, and a catalyst, which speeds the reactions at the electrodes.
Hydrogen is the basic fuel, but fuel cells also require oxygen. One great appeal of fuel cells is that they generate electricity with very little pollution–much of the hydrogen and oxygen used in generating electricity ultimately combine to form a harmless byproduct, namely water.
One detail of terminology: a single fuel cell generates a tiny amount of direct current (DC) electricity. In practice, many fuel cells are usually assembled into a stack. 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 electrical current that can be directed outside the cell to do work, such as powering an electric motor or illuminating a light bulb or a city. Because of the way electricity behaves, this 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 Change.) The chemical reactions that produce this current are the key to how a fuel cell works.
There are several kinds of fuel cells, and each operates a bit differently. But in general terms, hydrogen atoms enter a fuel cell at the anode where a chemical reaction strips them of their electrons. The hydrogen atoms are now "ionized," and carry a positive electrical charge. The negatively charged electrons provide the current through wires to do work. If alternating current (AC) is needed, the DC output of the fuel cell must be routed through a conversion device called an inverter.

Graphic by Marc Marshall, Schatz Energy Research Center

Oxygen enters the fuel cell at the cathode and, in some cell types (like the one illustrated above), it there combines with electrons returning from the electrical 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 only the appropriate ions to pass between the anode and cathode. If free 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 form water, which drains from the cell. As long as a fuel cell is supplied with hydrogen and oxygen, it will generate electricity.
Even better, 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 energy from a fuel. Waste heat from some cells can also be harnessed, boosting system efficiency still further.
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So why can't I go out and buy a fuel cell?

The basic workings of a fuel cell may not be difficult to illustrate. But building inexpensive, efficient, reliable fuel cells is a far more complicated business.
Scientists and inventors have designed many different 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 cell developers are constrained by the choice of electrolyte. The design of electrodes, for example, 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 first three are liquid electrolytes; the last two are solids.
The type of fuel also depends on the electrolyte. Some cells need pure hydrogen, and therefore demand extra equipment such as a "reformer" to purify the fuel. Other cells can tolerate some impurities, but might need higher temperatures to run efficiently. Liquid electrolytes circulate in some cells, which requires pumps. The type of electrolyte also dictates a cell's operating temperature–"molten" carbonate cells run hot, just as the name implies.
Each type of fuel cell has advantages and drawbacks compared to the others, and none is yet cheap and efficient enough to widely replace traditional ways of generating power, such coal-fired, hydroelectric, or even nuclear power plants.
The following list describes the five main types of fuel cells. More detailed information can be found in those specific areas of this site.
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Different types of fuel cells.

Drawing of an alkali cell.

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

Drawing of a molten carbonate cell

Molten Carbonate fuel cells (MCFC) use high-temperature compounds of salt (like sodium or magnesium) carbonates (chemically, CO₃) as the electrolyte. Efficiency ranges from 60 to 80 percent, and operating temperature is about 650 degrees C (1,200 degrees F). Units with output up to 2 megawatts (MW) have been constructed, and designs exist for units up to 100 MW. The high temperature limits damage from carbon monoxide "poisoning" of the cell and waste heat can be recycled to make additional electricity. Their nickel electrode-catalysts are inexpensive compared to the platinum used in other cells. But the high temperature also limits the materials and safe uses of MCFCs–they would probably be too hot for home use. 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) use phosphoric acid as the electrolyte. Efficiency ranges from 40 to 80 percent, and operating temperature is between 150 to 200 degrees C (about 300 to 400 degrees F). Existing phosphoric acid cells have outputs up to 200 kW, and 11 MW units have been tested. PAFCs tolerate a carbon monoxide concentration of about 1.5 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.

Proton Exchange Membrane (PEM) fuel cells work with a polymer electrolyte in the form of a thin, permeable sheet. Efficiency is about 40 to 50 percent, and operating temperature is about 80 degrees C (about 175 degrees F). Cell outputs generally range from 50 to 250 kW. The solid, flexible electrolyte will not leak or crack, and these cells operate at a low enough temperature to make them suitable for homes and cars. But their fuels must be purified, and a platinum catalyst is used on both sides of the membrane, raising costs.

Drawing of a solid oxide cell

Solid Oxide fuel cells (SOFC) use a hard, ceramic compound of metal (like calcium or zirconium) oxides (chemically, O₂) as electrolyte. Efficiency is about 60 percent, and operating temperatures are about 1,000 degrees C (about 1,800 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 heat can be recycled to make additional electricity. However, the high temperature limits applications of SOFC units and they tend to be rather large. While solid electrolytes cannot leak, they can crack. More detailed information about each fuel cell type, including histories and current applications, can be found on their specific parts of this site. We have also provided a glossary of technical terms–a link is provided at the top of each technology page.

First Eight CA Dealers Announced For 2016 Toyota Mirai Hydrogen Fuel-Cell Car

2016 Toyota Mirai: 'A car that breathes in air,' posted by Toyota, Feb 2015

With the 2016 Toyota Mirai set to go on sale this October, Toyota has now announced the first eight dealers that will be selling its first production hydrogen fuel-cell vehicle.
Four are in Northern California, four in the southern part of the state.
Production of the Mirai will be limited to about 3,000 vehicles for the U.S. through 2017.

ALSO SEE: 2016 Toyota Mirai: First Drive Of Hydrogen Fuel-Cell Sedan

The Northern California dealerships selling the Mirai are San Francisco Toyota, Roseville Toyota, Stevens Creek Toyota, and Toyota of Sunnyvale.
In the Los Angeles Basin and environs, the dealers are Longo Toyota, Toyota Santa Monica, Toyota of Orange and Tustin Toyota.

2016 Toyota Mirai construction at Motomachi plant

Toyota says it chose the initial dealerships based on both their proximity to hydrogen refueling infrastructure and their previous sales of advanced-technology vehicles, presumably hybrids and plug-in electric vehicles.
Starting this summer, potential Mirai buyers will have to apply to purchase or lease the car online.

DON'T MISS: 10 Questions On Hydrogen Fuel-Cell Cars To Ask Toyota, Honda & Hyundai

Only "select, eligible customers" will be allocated Mirais, largely based on how close they live and work to hydrogen fueling stations.
Accordingly, as Toyota says in its release, "Drivers are encouraged to make their requests early to save a potential parking spot in transportation history."

2016 Toyota Mirai hydrogen fuel-cell car, Newport Beach, CA, Nov 2014

While the reservation and ordering process will be online, sales and delivery of every Mirai must take place through the authorized Mirai dealer of the customer’s choice.
Toyota appears to be marketing the Mirai as the most advanced and technically sophisticated vehicle it sells.

MORE: Lesson Learned In Last Round Of Hydrogen Fueling: Fund Operations Too

Its release calls those potential customers "California trailblazers," echoing an ad last year in which it suggested that drivers who chose not to drive fuel-cell cars would be "roadblocks" to a future world of zero-emission vehicles.
Toyota is one of three carmakers who will sell hydrogen-fueled vehicles in California over the next two years.

2016 Toyota Mirai hydrogen fuel-cell car, Newport Beach, CA, Nov 2014

The Hyundai Tucson Fuel Cell, a compact crossover utility vehicle converted by its Korean maker to hydrogen power, began leasing last summer.
As of December, Hyundai had delivered 54 hydrogen Tucsons.

RELATED: How To Test Hydrogen Vs Electric Cars: A Challenge To Automakers (In Our Dreams)

Then there's the Toyota Mirai, with first deliveries now announced for October.
Finally, Honda will release a production version of its hydrogen-powered FCV Concept sedan sometime this year, with first sales now expected in 2016.
That car will follow the very low-volume Honda FCX Clarity, of which about 60 were delivered in the U.S. from 2008 through 2014.

Powering the future

Hydrogen fuel cell vehicles could change mobility forever

Around the world, efforts are being made to harness the power of hydrogen,
the most abundant element in the universe.
Recognizing hydrogen’s vast potential as a clean energy source,
Toyota is actively developing and producing fuel cell vehicles (FCV).
We believe hydrogen can help us contribute to
the next 100 years of the automobile.

Fuel cell vehicles are leading innovation
in two key areas.

Depending on how we embrace fuel cell vehicles and hydrogen as an energy source,
the potential results could change the world and bring about innovations that far exceed even those of the Prius.

Toyota sees great potential in hydrogen
and fuel cell vehicles.

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What is a fuel cell vehicle?

Through the chemical reaction between hydrogen and oxygen, fuel cell vehicles generate electricity to power a motor. Instead of gasoline they are fuelled by hydrogen, an environment-friendly energy source that can be produced from a variety of raw materials.
Toyota’s efforts to make sustainable mobility a reality with hydrogen started in 1992, even before the release of the Prius. In 2002, Toyota began the world’s first limited sales of a fuel cell vehicle, the “Toyota FCHV”, in Japan and the U.S. Toyota has also made use of its hybrid vehicle technology in the development of fuel cell vehicles.

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Hydrogen and oxygen from the air are pulled into the fuel cells in the FC Stack, and electricity is created through a chemical reaction. The result: a responsive—and emission-free—drive.

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Fuel cell vehicles: not just eco-cars

In addition to excellent environmental credentials, fuel cell vehicles are fun to drive, and also offer convenience and performance.

Pioneering development, starting with the fuel cell manufacturing process.

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The Mirai, the world’s first fuel cell vehicle
for the mass market

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The Toyota Fuel Cell System (TFCS) moves the Mirai

The Mirai features the Toyota Fuel Cell System, which combines fuel cell technology with hybrid technology.
The system is more energy efficient than internal combustion engines, and offers excellent environmental performance without emitting CO₂ or other harmful substances during driving. At the same time, the system gives vehicles convenience on a par with conventional gasoline engine vehicles, thanks to a cruising range^*1 of roughly 650 km and a refueling time of about three minutes^*2.
In addition, the Mirai can serve as a high capacity power supply during emergencies. It is capable of supplying roughly 60 kWh^*3 of electricity, with a maximum DC power output of 9 kW^*4. When a separately-sold power supply unit is connected, the Mirai converts the DC power from the CHAdeMO power socket located inside the trunk to AC power and can power a vehicle-to-home^*5 system or a vehicle-to-load system. Consumer electronics can also be connected directly and used from the interior accessory socket (AC 100 V, 1,500 W).

*1 According to Toyota measurements based on the Japanese Ministry of Land, Infrastructure, Transport and Tourism's JC08 test cycle; measured by Toyota when refueling at a hydrogen station supplying hydrogen at a pressure of 70 MPa under the SAEe J2601 standard conditions (ambient temperature: 20° C, hydrogen tank pressure when fueled: 10 MPa). Differing amounts of hydrogen will be supplied to the tank if refueling is carried out at hydrogen stations with differing specifications, and the cruising range will therefore also differ accordingly. It is estimated that a cruising range of approximately 700 km can be achieved when fueled under the conditions above at new hydrogen stations scheduled to begin operation from FY2016. Possible cruising range may vary considerably due to usage conditions (weather, traffic congestion, etc.) and driving methods (quick starts, air conditioning, etc.).
*2 As measured by Toyota when refueling at a hydrogen station supplying hydrogen at a pressure of 70 MPa under the SAEe J2601 Standard conditions (ambient temperature: 20°C, hydrogen tank pressure when fueled: 10 MPa). Time will vary depending on hydrogen fueling pressure and ambient temperature.
*3 After DC/AC conversion by power supply unit. Power supply capacity varies according to power supply unit conversion efficiency, amount of remaining hydrogen and power consumption.
*4 Power supply capability varies according to power supply unit specifications (amount of power supplied cannot exceed power supply unit specifications).
*5 Specific residential wiring is required.

A new driving sensation

Fuel cell vehicles offer excellent drivability. This is the result of the fusion of a painstaking design process. The Mirai offers a low center of gravity, aerodynamic performance, optimal weight layout, and a highly rigid body. These features, combined with the car’s engineless, motor-driven performance, create a driving experience that is smooth, safe, quiet and fun.

Design based on experience and knowledge

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The unique and impressive design of the Mirai is perfect for a fuel cell vehicle:
it reflects the revolutionary nature of the technology.

Toyota’s in-house fuel cell technology development

Whereas many manufacturers procure high-pressure hydrogen tanks, etc., from outside sources, Toyota is developing its FC system (including the FC stack) in-house.
Our dedication to manufacturing always drives us to do as much as we can ourselves.

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FCV video gallery

• Driving Performance
• FC Stack and Technical Information