Please use our glossary to find definitions of terms, abbreviations and acronyms that are commonly used in relation to fuel cells. Should you require further information, please refer to the Fuel Cell Today website.

	A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z
	A
	Active area	The active area of a fuel cell membrane is the amount which is able to be supplied with hydrogen and to produce electricity.
	AFC	Alkaline fuel cell
	AFV	Alternative fuel vehicle
	Alkaline fuel cell	This is a type of fuel cell which uses a potassium hydroxide electrolyte to assist the reaction of hydrogen and oxygen to form water, heat and electricity.
	Anode	The anode is the electrode in a cell where oxidation occurs.
	APU	Auxiliary power unit
	ATR	Autothermal reforming
	Autothermal reforming	Autothermal reforming is the production of hydrogen from a fuel by the combination of partial oxidation and steam reforming which creates sufficient heat to drive itself but generates more hydrogen than partial oxidation alone.
	Auxiliary power source	A type of power source (for example, a fuel cell) which provides electricity which is supplemental to the main power source for a device (such as car's internal combustion engine).
	Availability	Simply, the ratio of the time for which a power source is functioning to the time for which it should have been functioning.
	B
	Balance of plant	In a fuel cell system, the balance of plant is all the auxiliary equipment required to ensure that the fuel cell can behave as a reliable power source.
	Base load	This is the usual minimum power requirement for a system. In a house, for instance, this might include power required to maintain a refrigerator at constant temperature.
	BEV	Battery electric vehicle
	Bipolar plates	A bipolar plate allows electricity to be conducted between adjacent individual fuel cells. They are often designed to channel the flow of gases and heat to and from the cell.
	Brennstoffzelle	Fuel cell (German)
	Burner	A burner will combust the exhaust gas from a fuel cell to reduce any emissions still further. It may also be used to provide heat during start-up to speed this up.
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	C
	CARB	California Air Resources Board
	Catalyst	A catalyst is a substance which increases the rate of a reaction without being consumed itself. In a fuel cell, there will typically be a catalyst used for the electrodes (to break down hydrogen into electrons and protons). Catalysts are also often used in reforming fuel.
	Catalyst loading	This is related to the amount of catalyst used in a fuel cell or fuel cell system. It often refers specifically to the mass of catalyst per unit area of an electrode.
	Cathode	The cathode is the electrode in a cell where reduction occurs.
	CEC	California energy commission
	CHP	Combined heat and power
	CNG	Compressed natural gas
	CO	Carbon monoxide
	CO2	Carbon dioxide
	Coal gas	Coal gas is a fuel produced by heating coal. It will contain much higher levels of carbon monoxide than would be seen in natural or liquefied petroleum gas.
	cogen	cogeneration
	Cogeneration	A fuel cell produces both heat and electricity. Where it is possible to use both products, this is cogeneration.
	Combustion	This is the reaction of a chemical substance with oxygen to produce heat and light. In a fuel cell, the reaction of hydrogen and oxygen will usually take place at a lower temperature.
	CPA	California Power Administration
	CPO	Catalytic partial oxidation
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	D
	DARPA	United States Defense Advanced Research Projects Agency
	DCX	DaimlerChrysler
	Desulphuriser	Some fuels contain sulphur which can be damaging to fuel cell performance. A desulphuriser may therefore be used to remove sulphur from the gas stream entering the fuel cell stack and maintain peak electrical output.
	DETR	United Kingdom Department of the Environment, Transport and the Regions
	DI	Direct injection
	Diffusion	Diffusion is the movement of a chemical, usually under a pressure differential. In fuel cells, diffusion may happen through a palladium membrane to purify hydrogen or through the fuel cell electrodes before splitting of a hydrogen molecule.
	Direct methanol fuel cell	A DMFC or direct methanol fuel cell functions on methanol which has not been reformed to give hydrogen. It is often a form of PEMFC.
	Distributed generation	Distributed generation involves the production of electrical power much closer to the end user than conventional power supply does. Distributed generation often requires lower power units.
	DMFC	Direct methanol fuel cell
	DOE	Department of Energy
	DTI	United Kingdom Department of Trade and Industry
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	E
	EC	European Commission
	ECJ	European Court of Justice
	Efficiency	The ratio of useful energy produced by a system (such as a fuel cell) compared to the energy supplied (usually chemical energy).
	Electrode	The electrode is where reaction of a chemical species occurs and electrons are either released or accepted. Typically this will be a metal, such as platinum in PEMFC.
	Electrolyte	An electrolyte is a substance which carries electrical current by the migration of ions. Together with the external connections of a fuel cell, this allows the creation of an electrical circuit.
	ELV	End-of-life vehicles
	EPA	United States Environmental Protection Agency
	EU	European Union
	EV	Electric vehicle
	External reforming	External reforming occurs where a fuel is reformed to hydrogen prior to entering a fuel cell stack.
	EZEV	Equivalent to zero emissions vehicle
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	F
	FC	Fuel cell
	FCEV	Fuel cell electric vehicle
	Fuel	A fuel is a chemical which can be used in a fuel cell system to produce electricity. The fuel is typically either hydrogen or something which can produce hydrogen when reformed.
	Fuel cell	A fuel cell is an electrochemical device, which converts chemical energy to electrical energy without combustion. Unlike a battery, a fuel cell will continuously produce electricity as long as fuel is supplied to it.
	Fuel processor	A fuel processor is a device that is capable of reforming a fuel to produce a gas stream containing hydrogen and then clean this up to produce a gas flow of sufficiently high quality to be used as the input for a fuel cell stack.
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	G
	Gas clean-up	When a fuel is reformed, the reformate gas stream will typically contain carbon monoxide which has a negative impact upon fuel cell performance. Gas clean-up will remove this CO and maintain cell performance.
	GDI	Gasoline direct injection
	GDM	Gas Diffusion Media
	GE	General Electric
	GEM	Global electric Motorcars (a subsidiary of DaimlerChrysler)
	GHG	Greenhouse gas
	GM	General Motors
	Grid-connected	A grid-connected fuel cell is designed to function when connected to the electrical grid.
	Grid-independent	A grid-independent fuel cell can operate when not connected to the electrical grid, such as in remote rural areas.
	Grid-parallel	A grid-parallel fuel cell is designed to function when connected to the electrical grid and therefore may not follow the electrical requirements of a device exactly.
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	H
	H2	Hydrogen
	HC	Hydrocarbons
	HDV	Heavy duty vehicle
	HEV	Hybrid electric vehicle
	Hydrocarbon	A hydrocarbon is a chemical compound which consists primarily of hydrogen and carbon. These are often used as fuels.
	Hydrogen economy	The hydrogen economy is a vision of where the world can move to through use of hydrogen as an energy carrier in place of oil and fossil fuels. Here, hydrogen would be used to heat homes and power vehicles (whether with fuel cells or internal combustion engines). Evnetually, this hydrogen would be generated from renewable energy, leading to no emissions even of carbon dioxide.
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	I
	IC	Internal combustion
	ICE	Internal combustion engine
	IEA	International energy agency
	IFC	International Fuel Cells
	IMA	Integrated motor assist
	Internal reforming	Some fuel cells operate at sufficiently high temperatures to be able to convert a hydrocarbon fuel to hydrogen within the fuel cell stack. This is known as internal reforming.
	Islanding	Islanding is the action of separating a power source or device from the electrical grid. When a fuel cell is grid-connected, islanding of the fuel cell is required to allow safe work on the grid.
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	J
	JAMA	Japanese Automotive Manufacturers Association
	JEA	Japanese Environment Agency
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	K
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	L
	LANL	Los Alamos National Laboratories
	LDV	Light duty vehicle
	LEV	Low emissions vehicle
	Liquefied petroleum gas	Liquefied petroleum gas is one of a number of hydrocarbon fuels which can be used to operate fuel cells.
	LNG	Liquefied natural gas
	Load-following	A load-following fuel cell will generate a variable amount of electrical power depending on the requirements of any devices which it is delivering power to.
	Low emission vehicle	Low emission vehicles (LEV) are light duty passenger vehicles which meet strict specific emissions regulations in California. Vehicles meeting tighter standards yet are described as ultra-low emissions vehicles (ULEV), super-ultra-low emissions vehicles (SULEV), partial zero emissions vehicles (PZEV) or zero emission vehicles (ZEV).
	LPG	Liquefied petroleum gas
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	M
	MCFC	Molten carbonate fuel cell
	MEA	Membrane electrode assembly
	Membrane	This separates the two electrodes of a proton exchange membrane fuel cell, acting as an electrolyte, through which hydrogen ions pass.
	Membrane electrode assembly	A structured component in a PEM fuel cell, consisting of a membrane with a catalysed electrode layer on each side.
	MeOH	Methanol
	Molten carbonate fuel cell	Molten carbonate fuel cells have an electrolyte of lithium and sodium carbonate. Carbonate ions carry the current between the electrodes, although the fuel is still hydrogen. Operating temperatures are in the region of 600-700°C.
	MOU	Memorandum of understanding
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	N
	Natural gas	Natural gas (NG) is simply a hydrocarbon fuel which can be used to create electricity from fuel cells. It can be compressed (CNG) or simply carried in a pipeline and is often already supplied to houses and offices.
	NEBUS	New electric bus
	NECAR	New electric car
	NEDO	Japanese New Energy and Industrial Technology Development Organisation
	NEV	Neighbourhood electric vehicle
	NG	Natural gas
	NGV	Natural gas vehicle
	NiMH	Nickel metal hydride
	NLEV	National low emissions vehicle
	NMHC	Non-methane hydrocarbons
	NMOG	Non-methane organic gases
	NOx	Oxides of nitrogen
	NREL	United States National Renewable Energy Laboratory
	NYC	New York City
	NZEV	Near-zero emissions vehicle
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	O
	OAAT	United States Office of Advanced Automotive Technologies
	OECD	Organisation for Economic Cooperation and Development
	OEM	Original equipment manufacturer
	OTT	United States Office of Transport Technologies
	Outage	An outage occurs when a fuel cell or other power source which is producing electricity fails.
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	P
	PAFC	Phosphoric acid fuel cell
	Parallel connection	Where fuel cells are connected in parallel, they are able to supply a higher current than they could individually.
	Partial oxidation	Partial oxidation is used to generate hydrogen from a fuel by reforming. Heat is generated but the amount of hydrogen released is less than with autothermal reforming or steam reforming.
	Pd	Palladium
	PEFC	Polymer electrolyte fuel cell
	PEM	Proton exchange membrane or polymer electrolyte membrane
	PEMFC	Proton exchange membrane fuel cell or polymer electrolyte membrane fuel cell
	Phosphoric acid fuel cell	A phosphoric acid fuel cell (PAFC) has phosphoric acid as the electrolyte between the electrodes. The operating temperature is typically higher than for polymer electrolyte fuel cells, at around 200°C. This is one of the first commercial applications.
	Pile a combustibile	Fuel cell (Italian)
	Pile à combustible	Fuel cell (French)
	PM	Particulate matter
	PNGV	United States Partnership for a New Generation of Vehicles
	Polarisation curve	A polarisation curve indicates the relationship between voltage across a fuel cell and current density. It is a measure of cell performance.
	Polymer electrolyte fuel cell	A type of fuel cell (PEMFC) where the electrolyte is a solid acid membrane. Operating temperature is low, at around 100°C. Typically, precious metal electrodes would be used. (Analogous to proton exchange membrane fuel cells.)
	Polymer electrolyte membrane	This is, as its name suggests, the membrane in a PEMFC which separates the feedgases and allows current to flow across it in order to complete the electrical circuit.
	Portable power plant	A portable power plant is one which can be readily transported but is not designed to provide power for transportation. Such a fuel cell might provide electricity for a mobile phone or a power tool.
	Power conditioning	A fuel cell provides a direct current (dc) output whereas most grid systems operate on alternating current (ac). Power conditioning is used to convert one form to the other.
	Power density	The power density of an individual fuel cell is the power produced related to the active area or volume of the cell.
	Power plant	A power plant is a device capable of generating electrical power for use elsewhere. It may also generate useful heat.
	ppm	Parts per million
	Preferential oxidation	Preferential (or selective) oxidation is used in fuel cells to oxidise carbon dioxide in a gas stream from a fuel reformer but not hydrogen. This may require a catalyst.
	Proton exchange membrane	A proton exchange membrane (or polymer electrolyte membrane) is the film which prevents hydrogen and oxygen meeting and also carries protons across to complete the electrical circuit.
	Proton exchange membrane fuel cell	A type of fuel cell (PEMFC) where the electrolyte is a solid acid membrane. Operating temperature is low, at around 100°C. Typically, precious metal electrodes would be used. (Analogous to polymer electrolyte membrane fuel cells.)
	PROX	Preferential oxidation
	Pt	Platinum
	PZEV	Partial zero emissions vehicle
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	Q
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	R
	Reformate	Reformate is the output of a fuel processor. Such a gas stream will often contain hydrogen, carbon monoxide and carbon dioxide. The reformate gas stream will eventually pass to the fuel cell stack, possibly after some further cleaning.
	Reformer	A fuel reformer produces hydrogen from a hydrogen-containing fuel.
	Reforming	Reforming is the process of producing a hydrogen-rich gas stream for eventual use in a fuel cell from a feedstock.
	Regenerative fuel cell	A regenerative (or reversible) fuel cell is able to react a fuel and an oxidant to produce electricity and other chemical species or operate in reverse. This allows ready production of power when it is economically viable.
	Renewable energy	Renewable energy sources are those which do not require the use of limited fossil fuel resources. They include wind power, hydroelectric or geothermal power and photovoltaics. They can often be used to produce hydrogen for use in fuel cells.
	Residential power plant	A residential power plant (for example, a fuel cell) is used to power a home or a small number of homes. In terms of design it could be identical to a system used to power an office.
	Reversible fuel cell	A reversible, or regenerative, fuel cell is able to react a fuel and an oxidant to produce electricity and other chemical species or operate in reverse. Where hydrogen and water are the fuels, water and electricity are produced. When required, water can be electrolysed, and hydrogen and oxygen produced, upon the input of electricity.
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	S
	SAE	Society of Automotive Engineers
	SCAQMD	South Coast Air Quality Management District (California)
	Selective oxidation	Selective (or preferential) oxidation is used in fuel cells to oxidise carbon dioxide in a gas stream from a fuel reformer but not hydrogen. This may require a catalyst.
	selox	Selective oxidation
	Separator plate	Separator plates are used to physically separate individual fuel cells in a stack.
	Series connection	A fuel cell will only provide electricity at a low voltage. By connecting several in series, similar to batteries, a power source with a higher voltage is effectively produced.
	Shift conversion	Shift conversion (or reaction) is the reaction of carbon monoxide and water to give hydrogen and carbon dioxide. This provides more hydrogen to create power in the fuel cell and removes carbon monoxide which is deleterious to some types of fuel cell.
	Single cell	Most fuel cell technology is first tested on single cells. This gives data which can be used to predict how larger systems or stacks will perform.
	SOFC	Solid oxide fuel cells
	Solid oxide fuel cell	Solid oxide fuel cells have a solid metal oxide as the electrolyte. They function at the highest temperature of the different types of fuel cell (about 900-1000°C) and can reform most fuels internally.
	Specific power	The specific power of a system is the power produced divided by the weight of the system.
	Stack	A fuel cell stack is an arrangement of individual fuel cells, usually in series.
	Stack life	Stack life is similar to the lifetime of any other apparatus and simply means the useful functioning lifetime of a fuel cell.
	Standard Conditions	The performance of most fuel cells will be quoted under standard conditions in order to allow easy comparison.
	Stationary power plant	A stationary power plant is simply a device which produces power but is not designed to be used in portable or transportation activities. One this website, we have split this field into two categories. Small Stationary fuel cells cover units with an output below 10kW, and might be used in residential and remote locations and in UPS and back-up power systems. Large Stationary covers units over 10kW; most of these are infact much larger, with an average size of 200kW.
	Steam reforming	Steam reforming is the reaction of a hydrocarbon fuel with water to produce hydrogen. More hydrogen is produced for the same amount of fuel than by autothermal reforming or partial oxidation but heat input is required to continue the reaction.
	Stoichiometric	A stoichiometric ratio of reactants is one which fits exactly with the chemistry occurring. In the case of a fuel cell, it is typically the ratio of fuel to oxygen required for complete reaction to occur.
	SULEV	Super ultra-low emissions vehicle
	SUV	Sports utility vehicle
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	T
	THC	Total hydrocarbon
	Thermal efficiency	The thermal efficiency of a system is directly analogous to the normal efficiency, being the thermal output of the system compared to the energy input.
	Thermal management	A fuel cell system may require many chemical reactions to occur in order to function correctly. Different reactions consume or produce heat and operate best at different temperatures. Thermal management, which is the redirection of heat into, out of, or around a system, is therefore important in system design.
	Transportation	One of a number of potential applications for fuel cells. The largest of the segments of this market is expected to be light duty automobiles.
	Tubular cells	The two common designs of solid oxide fuel cells are tubular and planar. A tubular system separates the fuel or reformate from the oxidant, inside and outside the tube.
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	U
	ULEV	Ultra-low emissions vehicle
	Ultra-low emission vehicle	An ultra-low emission vehicle (ULEV) is a light duty passenger vehicles which meets strict specific emissions regulations in California. Vehicles meeting tighter standards yet are described as super-ultra-low emissions vehicles (SULEV), partial zero emissions vehicles (PZEV) or zero emission vehicles (ZEV).
	URFC	Unitized regenerative fuel cell
	USABC	United States Advanced Battery Consortium
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	V
	Vaporéformage	Steam reforming (French)
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	W
	Wasserstoff	Hydrogen (German)
	Water-gas shift reaction	This reaction between carbon monoxide and water produces hydrogen and carbon dioxide. It is therefore used after the fuel has been reformed to provide more hydrogen to power a fuel cell and to remove carbon monoxide which may poison performance.
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	X
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	Y
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	Z
	Zero emission vehicle	A zero emission vehicle, or ZEV, is one which has no tailpipe exhaust or evaporative emissions of fuel. A hydrogen fuel cell car would count as a zero emission vehicle.
	ZEV	Zero emissions vehicle
	ZLEV	Zero-level emissions vehicle
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