Use our glossary to find clear definitions of terms and abbreviations (including acronyms) commonly used in relation to fuel cells. If there are any other words or phrases that you would like to see explained on these pages, please contact us.


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Active area
The area of a fuel cell electrode which is electrochemically active and able to produce electricity from the supplied fuel.

Alkaline fuel cell (AFC)
A type of fuel cell containing a potassium hydroxide electrolyte to react hydrogen and oxygen forming water, heat and electricity.

The fuel electrode in a fuel cell at which oxidation occurs.

An auxiliary power unit (for example a fuel cell) provides electricity and is supplemental to the main power source of a vehicle (such as an internal combustion engine).





The balance of plant in a fuel cell system is the auxiliary equipment required to ensure the fuel cell operates as a reliable power source. This may include fuel reformers and pumps, for example.

Bipolar plate
A fuel cell stack component which allows electricity to be conducted between adjacent fuel cell membrane electrode assemblies in a stack. They are often designed to channel the flow of gases and heat to and from the cell.

Fuel cell (German).





The California Fuel Cell Partnership is a collaboration of organisations, including automotive manufacturers, energy providers, government agencies and fuel cell technology companies, promoting the commercialisation of hydrogen fuel cell vehicles.

A catalyst increases the rate of a reaction without itself being consumed. In a fuel cell catalysts are used for the electrodes (to break down hydrogen into electrons and protons).

Catalyst loading
This refers to the mass of catalyst per unit area of a fuel cell electrode.

The oxygen/air electrode in a fuel cell where reduction occurs.

Combined cooling, heat and power utilises the waste heat from the fuel cell with absorption chillers to provide air conditioning and hot or cold water alongside electricity.

The Canadian Hydrogen and Fuel Cell Association was formed in 2009 from the merger between the Canadian Hydrogen Association (CHA) and Hydrogen & Fuel Cells Canada (H2FCC):

Combined heat and power is a way to make even more efficient use of fuel cells. The waste heat from the electricity production is used to heat water or for space heating.

Commercially available
Fuel Cell Today considers a fuel cell commercially available if it is:

  • Offered for sale to the public.
  • Offered with a written warranty, supported by service capability.
  • Meets approved industry standards or is certified by an established industry body.

Combined water and power is similar to CHP, but in this instance the waste heat is used to produce potable water.


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Direct methanol fuel cell (DMFC)
A direct methanol fuel cell functions in a similar way to a PEMFC and uses the same electrolyte, but reforms methanol directly on its electrode to form hydrogen.

Distributed generation
The production of electrical power close to the end user.


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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.

An electrochemical device which works like a fuel cell in reverse and can split water into its constituent molecules, hydrogen and oxygen, by passing an electric current through it.

A substance which carries charge via the migration of ions; together with the external connections of a fuel cell, an electrical circuit can be created.


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Fuel cell electric vehicle.

The Fuel Cell and Hydrogen Energy Association, formed in 2010 from the merger of the US Fuel Cell Council and the National Hydrogen Association, is a US-based industry organisation supporting the Fuel Cell and Hydrogen industries:

The Fuel Cells and Hydrogen Joint Undertaking (FCH JU) is a European partnership supporting research, technological development and demonstration activities in fuel cell and hydrogen energy technologies:

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 and the catalyst remains active.


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Gas diffusion layers, typically made out of carbon paper or cloth, play a number of important roles in a fuel cell, such as structural support, reactant transport, water removal, and heat conduction.


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Hydrogen is the fuel most commonly used in fuel cells.

High temperature proton exhange membrane fuel cell (HT PEMFC)
A variant of the PEMFC which uses a mineral acid based electrolyte rather than an aqueous one and can operate at temperatures up to 200°C. These cells are more tolerant to impurities in the fuel as a result.

Hydrogen economy
The hydrogen economy is a scenario where the world uses hydrogen as the primary energy carrier in place of fossil fuels. Hydrogen would be used to provide electrical power, heat homes and power vehicles. Ideally this hydrogen would be generated from renewable energy, resulting in zero emissions.


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Relates to distributed generation where local generators continue to power a location when power from the electricity grid is no longer present. When a fuel cell is grid-connected, islanding (isolation) of the fuel cell is required to allow safe work at that location.


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Kilowatt, a unit of power equal to 1,000 watts. 

Kilowatt electric, a measure of electric power output.

kWth or kWt
Kilowatt thermal, a unit of thermal (heat) power output.

Kilowatt-hour, a unit of energy. A device with a power output of one kilowatt running for one hour would generate one kilowatt-hour of energy.


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The London Hydrogen Partnership was set up in 2002 to work towards the establishment of a hydrogen economy for London and the UK.

Load following
A load-following fuel cell generates variable amounts of electrical power depending on the requirements of the devices it is powering.

Low emission vehicles are light duty passenger vehicles meeting strict emissions regulations in California. These can be divided into a number of sub-categories including ultra-low emissions vehicles (ULEV), super-ultra-low emissions vehicles (SULEV), partial zero emissions vehicles (PZEV) or zero emission vehicles (ZEV).


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Membrane electrode assembly, a structured component in a PEMFC and DMFC, consisting of a membrane with an electrode on each side.

This separates two electrodes of a fuel cell, acting as the electrolyte and allowing passage of ions between the electrodes.

Methanol is a fuel used in DMFCs.

Micro-combined heat and power fuel cells refer to stationary units designed to provide electricity, hot water and sometimes space heating. These can either be for residential use or for small offices and commercial buildings.

Molten carbonate fuel cell (MCFC)
Molten carbonate fuel cells have an electrolyte of molten carbonate salt and operate at temperatures in the region of 600°C to 700°C. Negatively charged carbonate ions carry the current through the membrane separating the electrodes, which have a standard electrical connection. MCFC systems are fuelled by hydrogen.


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Nationale Organisation Wasserstoff- und Brennstoffzellentechnologie. Based in Germany and founded in 2008, this state organisation coordinates and manages market preparation programmes for products and applications based on hydrogen, fuel cell and battery electric powertrain technology.


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Palladium is one of the platinum group metals and can be used for the purification of reformed hydrogen for fuel cells.

Phosphoric acid fuel cell (PAFC)

Phosphoric acid fuel cells use phosphoric acid as the electrolyte. Their operating temperature is typically higher than for polymer electrolyte fuel cells, at around 200°C.

Pile a combustibile
Fuel cell (Italian).

Pile à combustible
Fuel cell (French).

Planar Solid Oxide Fuel Cell
SOFCs can have multiple geometries. The planar geometry is the typical sandwich type geometry employed by most other fuel cells, where the electrolyte is sandwiched in between the electrodes.

Polarisation curve
A measure of cell performance that indicates the relationship between current density and voltage across a fuel cell.

Proton exchange membrane (PEM)
Proton exchange membranes, also referred to as polymer electrolyte membranes due to their composition, separate the feed gases in a PEMFC or DMFC and act as the electrolyte by allowing the passage of protons.

Proton exchange membrane fuel cell (PEMFC)
Proton exchange or polymer electrolyte membrane fuel cells use a solid acid membrane as the electrolyte. PEMFC operate at low temperatures (100°C) and use platinum-containing electrodes.

Power density
The power density of a fuel cell is the power produced in relation to the active area or volume of the cell, expressed in W/m2 or W/m respectively.

Platinum is a commonly used catalyst material for PEMFC and DMFC technologies.

Partial zero emissions vehicle, see LEV.


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Reformate is the output of a fuel reformer. Such a gas stream often contains hydrogen, carbon monoxide and carbon dioxide. This reformate gas can be fed to a fuel cell, generally after some degree of cleanup.

Reversible fuel cell
A reversible, or regenerative, fuel cell can operate as a fuel cell, or in reverse like an electrolyser.

Ruthenium is a member of the platinum group of metals and is used in DMFC to assist with internal fuel reforming.

Regulations, codes and standards.


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Solid Energy Conversion Alliance was founded in 1999. A collaboration between the US Federal Government, private industry, academic institutions and national laboratories to develop low-cost, fuel-flexible solid oxide fuel cells (SOFC).

Separator plate
Separator plates are used to physically separate individual fuel cells in a stack.

The Scottish Hydrogen and Fuel Cell Association promotes and develops Scottish expertise in fuel cell and hydrogen technologies:

Single cell
A single cell is the smallest and most basic form of fuel cell. It is useful for testing and development purposes to predict how stacks will perform.

Solid oxide fuel cell (SOFC)
Solid oxide fuel cells have a solid metal oxide as the electrolyte and can exist in multiple geometries including planar and tubular. They function at the highest temperature of the different types of fuel cell (about 900°C to 1,000°C) and can reform most fuels internally.

A fuel cell stack is an arrangement of individual fuel cells, usually in series to provide a useful output voltage.


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Thermal efficiency
The thermal efficiency of a fuel cell system is the ratio between the output of the system (as heat and power) and the heat-content of the input fuel.

Tubular solid oxide fuel cell
SOFC can have multiple geometries. The tubular geometry is where either air or fuel is passed through the inside of a tube and the other gas is passed along the outside of the tube.


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Unmanned aerial vehicle.

The UK Hydrogen and Fuel Cell Association launched in summer 2010 following the merger of Fuel Cells UK and the UK Hydrogen Association. It acts on behalf of its members to accelerate the commercialization of fuel cell and hydrogen energy technologies in the UK:

Ultra-low emission vehicle, see LEV.

Uninterruptible power supply.

A unitised regenerative fuel cell is a reversible fuel cell which can operate either as a fuel cell, or in reverse like an electrolyser.

Unmanned underwater vehicle.


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Watt, a unit of power. It is a measure of the rate of energy conversion or generation, equivalent to one joule per second.

Hydrogen (German)


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A zero emission vehicle is one which has no tailpipe exhaust or evaporative emissions of fuel; hydrogen fuel cell cars count as zero emission vehicles. Their only output is water.


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If you have a simple query about fuel cell technology, take a look at our list of frequently asked questions here.

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