Glossary

IN THIS SECTION:

An explanation of the abbreviations, technical terms and specialist language used on our 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.



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.

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



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



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



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.



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.



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). Eventually, this hydrogen would be generated from renewable energy, leading to no emissions even of carbon dioxide.



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.



JAMA

Japanese Automotive Manufacturers Association

JEA

Japanese Environment Agency



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



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



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



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.



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



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.



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



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.



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



Vaporéformage

Steam reforming (French)



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.







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



© Johnson Matthey 2017