Alternative Sources of Energy— 

An Introduction to Fuel Cells 

By E.A. Merewether 

U.S. Geological Survey Bulletin 2179

U.S. Department of the Interior

U.S. Geological Survey
Alternative Sources of Energy— 

An Introduction to Fuel Cells 

By E.A. Merewether 

U.S. Geological Survey Bulletin 2179

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Gale A. Norton, Secretary 

U.S. Geological Survey

Charles G. Groat, Director 

U.S. Geological Survey, Reston, Virginia: 2003 

Version 1.0, 2003 

This publication is available only online at: http://pubs.usgs.gov/bul/b2179


For more information about the USGS and its products:


Telephone: 1-888-ASK-USGS


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Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 


endorsement by the U.S. Government.

iii 

Contents 

Abstract ............................................................................................................................................................


Introduction ....................................................................................................................................................


History ........................................................................................................................................................... 3


Components .................................................................................................................................................. 3


New Developments ...................................................................................................................................... 5


Evaluations..................................................................................................................................................... 5


Conclusion ..................................................................................................................................................... 6


References..................................................................................................................................................... 6


Glossary ......................................................................................................................................................... 9


Figure 

1. 	 A schema for a typical fuel cell wherein the electrolyte is a proton exchange


membrane (PEM) and the catalysts are platinum.................................................................. 2 


Table 

1. Types of fuel cells—their components and characteristics ................................................ 4 

Alternative Sources of Energy—


An Introduction to Fuel Cells 

By E.A. Merewether 

Abstract 

Fuel cells are important future sources of electrical power 

and could contribute to a reduction in the amount of petroleum imported by the United States. They are electrochemical devices similar to a battery and consist of a container, an 

anode, a cathode, catalysts, an intervening electrolyte, and an 

attached electrical circuit. In most fuel cell systems, hydrogen is supplied to the anode and oxygen to the cathode which 

results in the production of electricity, water, and heat. Fuel 

cells are comparatively efficient and reliable, have no moving 

parts, operate without combustion, and are modular and scaleable. Their size and shape are flexible and adaptable. In operation, they are nearly silent, are relatively safe, and generally do 

not pollute the environment. 

During recent years, scientists and engineers have 

developed and refined technologies relevant to a variety of 

fuel cells. Types of fuel cells are commonly identified by 

the composition of their electrolyte, which could be either 

phosphoric acid, an alkaline solution, a molten carbonate, a 

solid metal oxide, or a solid polymer membrane. The electrolyte in stationary power plants could be phosphoric acid, 

molten carbonates, or solid metal oxides. For vehicles and 

smaller devices, the electrolyte could be an alkaline solution 

or a solid polymer membrane. For most fuel cell systems, the 

fuel is hydrogen, which can be extracted by several procedures 

from many hydrogen-bearing substances, including alcohols, 

natural gas (mainly methane), gasoline, and water. 

There are important and perhaps unresolved technical 

problems associated with using fuel cells to power vehicles. 

The catalysts required in several systems are expensive metals 

of the platinum group. Moreover, fuel cells can freeze and not 

work in cold weather and can be damaged by impacts. Storage 

tanks for the fuels, particularly hydrogen, must be safe, inexpensive, of a reasonable size, and contain a supply sufficient 

for a trip of several hundred miles. Additional major problems 

will be the extensive and costly changes in the national infrastructure to obtain, store, and distribute large amounts of the 

fuels, and in related manufacturing. 

Introduction 

This report describes and compares fuel cells and is one 

of a series of reports from the Energy Program of the U.S. 

Geological Survey prepared in response to requests from the 

public for information regarding contemporary sources of 

power and unconventional sources of electricity. The Energy 

Program is concerned mainly with resources of natural, 

energy-rich materials, particularly with accumulations of 

coal, crude oil, natural gas, and uranium minerals. However, 

the Program also includes investigations of less developed 

sources of energy, including deposits of tar sand, oil shale, 

and biomass. Additionally, there are tentative plans to review 

the energy potential of hydropower and gas-to-liquids technology as well as areas that might supply geothermal, solar, 

or wind power. 

A fuel cell is an electrochemical device, similar to a battery, that generally combines hydrogen from any of several 

sources and oxygen (which can come from air) to produce 

electricity, heat, and water (Baird and Hayhoe, 1993). Basically, a fuel cell is composed of an anode (a negative electrode) and a cathode (a positive electrode), which are separated by a liquid or solid electrolyte (fig. 1). Generally, the 

electrodes are permeable or contain channels that distribute 

hydrogen or other substances and oxygen. The electrodes are 

frequently accompanied by catalysts, commonly platinum or 

palladium (Geyer, 2000). In most fuel cells, hydrogen atoms 

enter the cell at the anode where their electrons are removed, 

producing direct current electricity and positively charged 

hydrogen ions (cations). Direct current can be converted to 

alternating current by an inverter. The electrons flow through 

an external circuit that extends from the anode to the cathode. The external circuit can include electric motors, lighting 

systems, or other electrical devices. The hydrogen ions travel 

through the electrolyte to the cathode where they recombine 

with the electrons and oxygen to produce water and heat 

(Smithsonian Institution, 2001). 

Fuel cells are almost endlessly rechargeable and productive, operate without combustion, have no moving parts, 

are nearly silent, and have an excellent safety record. Those 
2 Alternative Sources of Energy—An Introduction to Fuel Cells 

hydrogen

 ions 

electrons 

oxygen 

water 

and 

heat 

hydrogen 

electrons 

2H2 

4H+ 

+ 

4eO2 

+ 

4H+ 

+ 

4e2H2O 

H+ 

H+ 

H+ 

H+ 

H+ 

H+ 

anode (-) catalyst electrolyte catalyst cathode (+) 

Figure 1. A schema for a typical fuel cell wherein the electrolyte is a proton exchange membrane (PEM) and 

the catalysts are platinum. Hydrogen molecules when added to the anode and a catalyst lose their electrons, 

which travel through an external circuit from the anode to the cathode, activating electrical devices enroute. 

Hydrogen ions formed at the anode and a catalyst move through the electrolyte to the cathode and another 

catalyst where they combine with the electrons and oxygen to produce water and heat. 

recently developed for powering automobiles have an estimated life span of decades (Baum, 2002). Fuel cells can be 

modular and scaleable; many joined together are called a fuelcell stack. These characteristics allow the gradual addition of 

electrical capacity in response to increases in demand, as well 

as flexibility in the selection of sizes and locations for new 

stationary power plants. If stationary power plants are built at 

sites of electrical need, less of the electricity generated is lost 

during transmission and distribution (Geyer, 2000). Presently, 

the main planned uses of fuel cells are for the production of 

electricity at stationary power plants and to supply electricity 

for motors that move buses, trucks, and cars. Other contemplated applications include power for dwellings, trains, 

motorcycles, snowmobiles, watercraft, aircraft, and assorted 

electronic equipment (Jacobson, 1999). 

Hydrogen for fuel cells that power vehicles is derived 

from external sources and thereafter placed in onboard storage 

systems or is provided by an onboard “fuel reformer” that 

extracts hydrogen from accompanying supplies of methanol, 

gasoline, or other substances (Geyer, 2000). Pure hydrogen for 

the storage systems can be obtained from alcohols, naphtha, 

benzene, methane, propane, gasoline, and diesel fuel. Hydrogen is released when hydrocarbon-bearing materials in the 

presence of catalysts are subjected to pressurized steam (gasification) (U.S. Department of Energy, 1999, 2002). It can also 

be obtained from water by electrolysis, where the electricity 

could be supplied by hydroelectric generators, wind turbines, 

solar cells, or other producers of power. Hydrogen can also be 

generated by photoelectrochemical and photobiological procedures (U.S. Department of Energy, 2002). In a few commercial 

fuel cells, gaseous mixtures of hydrogen and carbon dioxide 

are extracted from fossil fuels or biomass and used instead of 

pure hydrogen (Baird and Hayhoe, 1993). 

When converting the chemical energy in hydrogenrich materials into electricity, efficiencies are as much as 80 

percent for fuel cells and a maximum of only 40 percent for 
3 

conventional thermal power plants (International Fuel Cells, 

2000a, 2000b). Power plants based on fuel cells are more 

dependable than diesel-powered generators (Beardsley, 1996). 

They have lower maintenance costs and longer life expectancies than the alternatives (Baird and Hayhoe, 1993). The 

operation of fuel cells provides heat for space heating and 

is virtually pollution free, although when fueled by natural 

gas, fuel cells can produce a small amount of carbon dioxide. 

Compared with combustion-based processes for generating 

electricity, a one-megawatt fuel cell system would save more 

than 200,000 pounds of air pollutants and 11 million pounds 

of carbon dioxide from the atmosphere during each year of 

operation (International Fuel Cells, 2000a, 2000b). A typical, 

medium-sized car powered by fuel cells using hydrogen will 

have a system efficiency of more than 50 percent (Bellona 

Foundation, 2000). The same car with an internal combustion 

engine has an average fuel efficiency of 12 percent. 

History 

The possibility of generating electricity by reversing the 

electrolysis of water was discovered by Sir William Grove in 

about 1839 (Society of Automotive Engineers, 2001). Charles 

Langer and Ludwig Mond first used the term “fuel cell” in 

1889 while attempting to create a practical fuel cell using 

coal gas (a mixture of hydrogen, methane, carbon monoxide, 

other hydrocarbons, carbon dioxide, nitrogen, and oxygen) 

and air. In the first few years of the 20th century, there were 

efforts to develop a fuel cell that would use carbon or coal to 

produce electricity. Francis Bacon developed a usable hydrogen-oxygen cell containing an alkaline electrolyte and nickel 

electrodes in 1932. However, a practical system was not demonstrated by Bacon and his associates until 1959. In the same 

year, Harry Karl Ihrig presented a tractor of 20 horsepower 

that was powered by fuel cells (Society of Automotive Engineers, 2001). NASA began developing a compact generator of 

electricity for use on space missions in the late 1950s and fuel 

cells have been providing electricity and water on spacecraft 

since the 1960s. More recently, many companies and governmental agencies have supported research concerning fuel cell 

technology for possible use in stationary power plants, homes, 

vehicles, water craft, and small electronic devices including 

cell phones. Mainly because of the dependence of the United 

States and other nations on imported crude oil, research to 

develop less conventional sources of energy has accelerated 

during the past decade. 

Components 

The electrolyte in a fuel cell can be phosphoric acid, 

alkaline solutions (generally potassium hydroxide in water), 

molten carbonate (sodium, potassium, lithium, or magnesium carbonate), a solid metal oxide (commonly calcium or 

Components 

zirconium oxide), or a solid polymer membrane [the protonexchange membrane (PEM), a thin permeable sheet] (table 1). 

Using phosphoric acid, a silicon carbide matrix holds the electrolyte, and the electrodes are composed of finely dispersed 

platinum on carbon paper (U.S. Department of Energy, 2002). 

This type of fuel cell requires relatively pure hydrogen for the 

anode, operates at temperatures of 150–200 degrees Celsius 

(C) [about 300–400 degrees Fahrenheit (F)] (U.S. Department of Energy, 2002), and has an electrical output of as much 

as 200 kilowatts. This fuel cell is comparatively heavy and 

inappropriate for use in vehicles but can be used in stationary 

installations such as power plants. 

Fuel cells containing molten carbonate and solid metal 

oxide electrolytes can be used as highly efficient power-generating stations, although these fuel cells are not portable and 

operate at much higher temperatures than cells using phosphoric acid or PEM. The high temperatures enable hydrogen 

and carbon monoxide to be electrochemically oxidized at 

the anode (Steele and Heinzel, 2001). Potential fuels include 

natural gas and coal-derived gas. Existing units using molten 

carbonate electrolytes have electrical outputs of as much as 

two megawatts and their nickel electrode catalysts are inexpensive compared to the platinum or palladium used in other 

cells. A pilot plant for the city of Santa Clara, California, that 

uses a molten carbonate electrolyte, operates at a temperature 

of 650 degrees C (1202 degrees F). Molten carbonate salts are 

highly corrosive and require carefully designed and maintained facilities. 

If the electrolyte is a solid metal oxide, commonly a thin 

ceramic layer of zirconium oxide, the cathode is usually composed of lanthanum manganate and the anode is composed of 

nickel-zirconia (U.S. Department of Energy, 2002). This fuel 

cell (a direct fuel cell) is a promising option for high-powered applications, such as industrial uses or central electricity 

generating stations. The cell operates at temperatures of nearly 

1000 degrees C (1,832 degrees F) and has an electrical output 

of as much as 100 kilowatts. The high operating temperature 

allows the extraction of hydrogen from fuels without the use 

of a reformer. However, where the electrolyte consists of solid 

metal oxides, the fuel cells can suffer from leakage and sealing 

problems (Beardsley, 1996). 

In lightweight fuel cells for use mainly in automobiles, 

buses, and trucks, the electrolyte can be an alkaline solution 

or a solid polymer membrane [the proton-exchange membrane 

(PEM)]. These cells require relatively pure hydrogen for the 

anode (Steele and Heinzel, 2001). In alkaline electrolytes, the 

operating temperature is 150–200 degrees C (about 300–400 

degrees F) and the electrical output ranges from 300 watts to 

5 kilowatts (Smithsonian Institution, 2001; Society of Automotive Engineers, 2001). Alkaline cells were used in Apollo 

spacecraft to provide both electricity and drinking water. 

However, one disadvantage is that containers filled with liquid 

can leak. 

The PEM electrolyte is a solid, flexible, fluoride polymer 

film, a fluorocarbon ion exchange with a polymeric membrane 

(U.S. Department of Energy, 2002). This fuel cell will not leak 
Table 1. Types of fuel cells— t h eir components and characteristics. 

Type of fuel cell Electrode composition Electrolyte composition Operating Fuel Elecrical output Portability of fuel Potential proble

temperature cell 

Phosphoric acid Platinum on carbon Phosphoric acid 150–200°C Hydrogen As much as 200 Not portable Too heavy for 

paper kilowatts many uses 

Alkaline Insufficient Alkaline solution— 150–200°C Hydrogen 300 watts to 5 Portable Containers of 

solution information potassium hydroxide in kilowatts liquids can 

water leak 

Molten Anode: nickel- Molten carbonate salt— About 650°C Methane As much as 2 Not portable Too heavy for 

carbonate chromium. Cathode: sodium, potassium, megawatts many uses; 

nickel oxide (lithium lithium, or magnesium salts are doped) carbonate highly 

corrosive 

Solid metal Anode: nickel zirconia. Solid metal oxide— Nearly 1,000°C Methane As much as 100 Not portable Too heavy for 

oxide Cathode: lanthanum calcium or zirconium kilowatts many uses; 

manganate oxide leakage and 

sealing pro- blems 

PEM (proton- Unknown Solid, fluorocarbon– About 80°C Hydrogen Unknown Portable Unknown 

exchange polymer film (a thin, membrane) flexible, permeable 

sheet) 

Direct methanol Unknown Polymer membrane 50–100°C Methanol Unknown Portable Unknown 

Reversible— Unknown PEM (proton-exchange Unknown Hydrogen Unknown Portable Unknown 

unitized membrane) in water regenerative 
5 

or crack and operates at a temperature of about 80 degrees C 

(176 degrees F) which is low enough for the cell to be suitable 

for vehicles and homes. Nevertheless, the platinum catalyst 

used on both sides of the membrane is costly and the hydrogen 

for fuel must be purified. 

The direct methanol fuel cell is similar to the PEM cell 

because the electrolyte is a polymer membrane. However, the 

fuel is methanol instead of hydrogen. A catalyst on the anode 

draws hydrogen from liquid methanol, eliminating the need 

for a fuel reformer. This cell has an operating temperature of 

50–100 degrees C (122–212 degrees F) (Society of Automotive Engineers, 2001) and has considerable potential value for 

use in vehicles. 

The unitized regenerative or reversible fuel cell functions 

alternately as a fuel cell, producing electricity and water, and 

as an electrolyzer, generating hydrogen and oxygen. This cell 

has a PEM electrolyte and “oxidation and reduction electrodes 

that reverse roles when switching from charge to discharge” 

(Walter, 1997). Water is moved from the anode to the cathode. A major advantage of the regenerative fuel cell, where 

combined with a lightweight hydrogen storage unit, is the 

comparatively low total weight, which is appropriate for use in 

a variety of vehicles. 

New Developments 

The widely recognized potential of fuel cells as sources 

of electricity for stationary power plants, for motors in 

vehicles, and for other purposes has encouraged investigations 

by government agencies and by large and small companies in 

several nations. Prototypes of micro fuel cells, which can be 

smaller than a deck of cards, are being prepared by several 

companies (Hill, 2002). Studies during the past decade have 

developed and described a variety of components and systems. 

One company produces an assortment of small fuel cells, 

one of which has an alkaline electrolyte and will function 

when any of several liquid or solid hydrogen-rich materials 

are dissolved in the electrolyte. They also offer the unusual 

aluminum/air cell that contains an aluminum anode, which is 

fuel for the cell, and an electrolyte consisting of salt water. In 

the fuel cell system of a recent concept-vehicle from a major 

manufacturer, the required hydrogen is extracted from sodium 

borohydride, a compound related to borax (Brown, 2002). 

For hydrogen storage, solid state materials include metal 

hydride alloys that reportedly absorb and desorb hydrogen 

rapidly at low pressures and at temperatures of 0–200 degrees 

C (0–392 degrees F) (Fuel cell investors portal, 2002). Carbon 

nanotubes, which are carbon molecules in the form of long 

thin tubes, are another potential hydrogen storage medium. 

They are also suitable for electrodes and can be used in sensors for hydrogen, especially for the smallest fuel cells (NEC 

Corporation press release, 2001). Another potential storage 

material is glass microspheres that will fill with hydrogen 

when their permeability is modified by changes in temperature 

(U.S. Department of Energy, 2002). 

Evaluations 

Several major manufacturers have developed fuel cell 

systems that will produce enough hydrogen and electricity to 

power vehicles. The two systems commonly proposed include 

either an onboard fuel processor (fuel reformer) or the direct 

hydrogen system. The feedstocks currently preferred for these 

systems are gasoline or methanol for the onboard processor 

and natural gas for the direct hydrogen system (U.S. Department of Energy, 1999). A system using an onboard processor 

and gasoline is favored by many because a new and widespread infrastructure would not be required. The option of 

an onboard processor and methanol would need additional 

infrastructure but would be more readily implemented than 

the direct hydrogen system. However, present fuel reformers, which can extract hydrogen from several hydrogen-rich 

materials, increase the cost of the system, reduce the overall efficiency, and produce carbon dioxide (Brown, 2002; 

Schrope, 2001). They also must be heated for several minutes 

before they can function. These characteristics contribute to 

a common opinion that fuel reformers would be part of an 

interim technology. 

Using the direct hydrogen system for passenger vehicles 

will require the development of a new national infrastructure 

for generating and supplying this gas. Hydrogen generators, which can be steam reformers, partial oxidation units, 

or electrolyzers, will probably be widely distributed and can 

obtain hydrogen from natural gas, propane, alcohol, gasoline, 

or water (U.S. Department of Energy, 1999). 

Evaluations 

Several practical and fundamental issues concerning 

the applications of fuel cells have not been resolved. In cold 

weather, fuel cells can freeze and stop working (Baum, 2002). 

They are also fragile and could be damaged when powering 

vehicles on rough roads. Furthermore, the catalysts required in 

several fuel cell systems are expensive metals of the platinum 

group. For fuel cells that require pure hydrogen, the associated 

gas storage devices must be safe, efficient, and relatively inexpensive. Storing and supplying hydrogen for cells in vehicles 

and in smaller mechanisms is a current technical problem. For 

a trip of 373 miles (600 kilometers) in the family car, using 

hydrogen and without refueling, a conventional pressurized 

storage tank would need to be much too large for the vehicle 

(Schrope, 2001). However, promising, newly developed, 

smaller storage tanks contain either metal hydride alloys, 

carbon nanotubes, or glass microspheres. Nevertheless, replacing most of the present combustion-based, energy-producing 

mechanisms throughout the world with less conventional, 

power-producing devices will probably require extensive and 

costly changes in sources of fuels, in the related national infrastructure for storage and distribution of fuels, and in associated 

manufacturing. 

Steele and Heinzel (2001) assumed “that fuel cells have 

to be designed for operation on hydrocarbon or alcohol fuels 
6 Alternative Sources of Energy—An Introduction to Fuel Cells 

to ensure that the technology” will penetrate the relevant 

markets. If hydrogen is essential for fuel cells, which of the 

potential materials will be used as sources and how will the 

gas be extracted? For the large-scale production of hydrogen, 

the currently cheapest method is “steam reforming of natural gas, which produces significant emissions of greenhouse 

gases” (Steele and Heinzel, 2001). Additionally, using present 

technology, more energy is required to extract hydrogen from 

natural gas and other fuels than can be obtained from the 

hydrogen (Baum, 2002). 

Another technical challenge in obtaining electricity from 

fuel cells, according to Beardsley (1996), is the high cost of 

their manufacture. David Brown (2002) reported that “fuel 

cells are relatively expensive to manufacture and operate, in 

relation to their output.” In a column in a financial magazine, 

Jerry Flint (2002) stated that hydrogen fuel cell engines would 

function for vehicles but are not currently available by means 

of mass-production technology. Consequently, those engines 

will be too costly for powering cars during the next twenty 

or more years. However, in a description of an automobile 

powered by fuel cells that was recently developed by a major 

corporation, Baum (2002) indicated that the cost of manufacturing this new vehicle will be much less than the cost of 

building a new traditional car. Baum (2002) also proposed that 

this unconventional new automobile would be ready for mass 

production in about the year 2010. 

Conclusion 

Fuel cells could be a major and necessary source of 

energy within a decade. They have great potential as the basic 

elements of large and small stationary power plants and as the 

source of electricity for vehicles and smaller devices. Their 

size and shape are flexible and adaptable. They are modular, 

have no moving parts, operate without combustion, are comparatively efficient and reliable, are nearly silent, generally do 

not pollute the environment, and are quite safe. The byproducts of the operation of fuel cells using pure hydrogen are only 

water and heat. Hydrogen for most of the cell systems can be 

extracted from many hydrogen-bearing materials by gasification and other procedures and from water by electrolysis. 

A fuel cell installation in Groton, Conn., consumes methane 

from a nearby landfill to produce electricity and heat. Nevertheless, preparing the infrastructures required for extracting, storing, and distributing hydrogen for use in many of the 

vehicles in the U.S.A. will be a major achievement. 

Stationary power plants based on fuel cells are now 

feasible and are economically and environmentally appealing. As a source of power for transportation, fuel cell systems 

have been improved recently by means of intensive development and probably will soon be used in the larger vehicles. 

The systems for vehicles might include fuel reformers for 

extracting hydrogen, first from gasoline and later perhaps 

from natural gas, propane, or alcohols. Eventually, when pure 

hydrogen is widely available, fuel reformers will be unnecessary. The electrical requirements of many small mechanisms 

could be satisfied by micro fuel cells which presently are 

being developed. In recent years, scientists and engineers have 

been devising and refining technologies relevant to fuel cells 

and have suggested new applications. They have proposed a 

variety of materials for use as electrodes, catalysts, electrolyes, 

and fuel. 

References 

Baird, Stuart, and Hayhoe, Douglas, 1993, Fuel cells: 

Energy educators of Ontario, Energy fact sheet, http: 

//www.iclei.org/efacts/fuelcell.htm 

Baum, Dan, 2002, Object in mirror may be closer than it 

appears: WIRED, August, 2002, p. 100–107. 

Beardsley, Tim, 1996, Beyond batteries: Scientific American, Explorations, http://www.sciam.com/explorations/ 

122396explorations.html 

Bellona Foundation, 2000, The future’s energy solutions: 

Fact sheet, http://www.bellona.no/en/energy/hydrogen/ 

11576.html 

Brown, David, 2002, If fuel cells are the future...the future 

isn’t here—yet: AAPG Explorer, March 2002, p. 6, 8, and 

12. 

Electro-Chem-Technic, 2001, Fuel Cells: http:// 

www.ectechnic.co.UK/FCS.HTML 

Flint, Jerry, 2002, Hydrogen bomb: Forbes, March 4, 2002, p. 

100. 

Fuel cell investors portal, 2002, Hydrogen storage and safety: 

http://www.loonycat.com/fc_tech.htm 

Geyer, B. K., 2000, Developments in fuel cell technology: 

Breakthrough Technologies Institute, Fuel Cells 2000, 

http://www.sustdev.org/journals/edition.01/download/ 

01.103.pdf 

Hill, Michael, 2002, Companies work on micro fuel cell: 

Associated Press, Rocky Mountain News, released Sept. 21, 

2002. 

International Fuel Cells, A United Technologies Company, 

2000a, How does a fuel cell work?: http://www.internationationalfuelcells.com/fuelcell/how_fl.shtml 

International Fuel Cells, A United Technologies Company, 

2000b, Nation’s largest commercial fuel cell system dedicated in Anchorage today: Press release. http://www.internationalfuelcells.com/news/archive/080900.shtml 
References 7 

Jacobson, Roger, 1999, Energy advances at DRI: 2nd Annual 

Lake Tahoe Fuel Cell Conference, http://www.dri.edu/ 

projects/energy/fuelcells/fuelcells.html 

NEC Corporation, 2001, NEC uses carbon nanotubes to 

develop a tiny fuel cell for mobile applications: Press 

release, August 30, 2001; http://www.nec.co.jp/press/en/ 

0108/3001.html 

Nelson, A., 1965, Dictionary of mining: New York, Philosophical library. 

Office of Fossil Energy, U.S. Department of Energy, 2002, 

Advanced fuel cells for stationary electric power generation: http://www.fe.doe.gov/coal_power/fuelcells/ 

Schrope, Mark, 2001, Which way to energy utopia: Nature, 13 

December 2001, v. 414, p. 682–684. 

Smithsonian Institution, 2001, Fuel cells: http:// 

americanhistory.si.edu/csr/fuelcells/basics.htm 

Society of Automotive Engineers, 2001, Fuel cell technology 

showcase: http://fuelcells.sae.org/ 

Steele, B.C.H., and Heinzel, Angelika, 2001, Materials for 

fuel-cell technologies: Nature, v. 414, p. 345–352. 

U.S. Department of Energy, 1999, Fuel choice for fuel cell 

vehicles: An overview by the DOE Hydrogen Technical 

Advisory Panel, May 1999, http://www.eren.doe.gov/ 

hydrogen/pdfs/fuel_choice_overview.pdf 

U.S. Department of Energy, 2002, Information network: http: 

//www.eren.doe.gov/RE/hydrogen_production.html 

Walter, Katie, 1997, The unitized regenerative fuel cell: 

Science and technology review, May 1997, p. 13, http: 

//www.llnl.gov/str/Mitlit.html 

Manuscript approved for publication April 14, 2003 

Published in the Central Region, Denver, Colorado 

Page layout by Norma J. Maes 

Edited by F. Craig Brunstein 
8 

9 

C 

Glossary 

Glossary 

A


Alkali: A basic substance (the opposite of an 

acidic substance) such as a hydroxide or carbonate of an alkali metal (commonly sodium 

or potassium). 

Anion: A negative ion. In anion-mobile fuel 

cells, anions move through the electrolyte 

toward the anode. 

Anode: One of two terminals (electrodes) in 

a fuel cell or battery. In a fuel cell, it is where 

the fuel reacts and releases electrons. 

Carbonate: An electro-negative part of a 

compound. Composed of carbon and oxygen. 

Catalyst: A substance that initiates a chemical reaction and enables it to proceed but is 

not affected by the reaction. 

Cathode: One of two terminals (electrodes) 

in a fuel cell or battery. In a fuel cell, it is 

where oxygen combines with hydrogen ions 

and electrons to produce water. 

Cation: A positive ion. In cation-mobil fuel 

cells, cations move through the electrolyte 

toward the cathode. 

Coal gas: A fuel gas produced from coal. Its 

average composition, by volume, is 50 percent hydrogen, 30 percent methane, 8 percent 

carbon monoxide, 4 percent other hydrocarbons, and 8 percent carbon dioxide, nitrogen, 

and oxygen (Nelson, 1965). 

Combustion: An act or instance of burning 

or oxidation accompanied by the generation 

of light and heat. 

D


Direct fuel cell: A type of fuel cell in which 

a hydrocarbon fuel is fed directly to the fuel 

cell stack; an external reformer to generate 

hydrogen is not required. 

E


Electrochemistry: A science that deals with 

the relation of electricity to chemical changes 

and with the interconversion of chemical and 

electrical energy. 

Electrode: An electrical terminal (anode or 

cathode) that conducts an electric current into 

or out of a battery or fuel cell. 

Electrolysis: The producing of chemical 

changes by the passage of an electric current 

through an electrolyte. 

Electrolyte: One or more chemical compounds that conduct ions from one electrode 

to the other inside a battery or fuel cell. 

Electron: An elementary subatomic particle 

that carries a negative electrical charge. 

F 

Fuel cell: A device for generating electricity 

by chemically combining a fuel (commonly 

hydrogen) and oxygen. 

H 

Hydrogen: A nonmetallic chemical element, normally a gas, composed of one 

proton and one electron. It is the fuel for 

most fuel cells. 

I 

Inverter: A device for converting direct current electricity to alternating current electricity. 

Ion: An atom or group of atoms that carries 

a positive or negative electric charge as a 

result of having gained or lost one or more 

electrons. 

K 

Kilowatt: 1,000 watts—a measure of electric power. 

M 

Matrix: A framework within which something else functions. 

Molten carbonate: In one type of fuel cell, 

a molten electrolyte that consists of carbon, 

oxygen, and another element, such as sodium, 

potassium, lithium, or magnesium. 

Megawatt: 1,000,000 watts—a measure of 

electric power. 

N


Natural gas: Hydrocarbons that exist as a 

gas or vapor, usually consisting of methane 

and lesser amounts of propane and ethane. 
10 Alternative Sources of Energy—An Introduction to Fuel Cells 

Impurities in natural gas commonly include 

nitrogen, carbon dioxide, and hydrogen 

sulfide. 

O


Oxygen: A nonmetallic chemical element, 

normally a gas, composed of eight protons, 

eight neutrons, and eight electrons. 

P


Phosphoric acid: A solution of a combination of the elements phosphorus, hydrogen, 

and oxygen that can serve as the electrolyte in 

a fuel cell. 

Polymer: A solid, natural or synthetic 

chemical compound or mixture of compounds 

composed essentially of repeating molecular 

units. 

Potassium hydroxide: A compound composed of potassium, hydrogen, and oxygen 

that when dissolved in water forms a basic 

solution, which can serve as the electrolyte in 

a fuel cell. 

Proton exchange membrane (PEM): A polymer sheet or membrane that can serve as the 

electrolyte in a fuel cell. 

R 

Reformer: A device that extracts hydrogen 

from hydrocarbons. 

Regenerative fuel cells: Types of fuel cells in 

which the fuel and, in several types of cells, the oxidant are regenerated from the oxidation products. 

S 

Solid oxide: A combination of oxygen and 

another element (commonly calcium or zirconium) that forms a solid electrolyte for one 

type of fuel cell. 

Stack: A series of individual fuel cells connected within an electricity generating system. 

W 

Watt: A unit of power equal to the work done 

at the rate of one absolute joule per second or to 

the rate of work represented by a current of one 

ampere under a pressure of one volt.