Membrane electrode assembly
Encyclopedia
A membrane electrode assembly (MEA) is an assembled stack of proton exchange membrane
s (PEMs) or alkali anion exchange membrane
(AAEMs), catalyst and flat plate electrode used in a fuel cell
.
s which have the catalyst embedded in them. The electrodes are electrically insulated from each other by the PEM. These two electrodes make up the anode
and cathode
respectively.
The PEM is a proton permeable but electrical insulator
barrier. This barrier allows the transport of the protons from the anode to the cathode through the membrane but forces the electrons to travel around a conductive path to the cathode. Companies such as DuPont
, Dow and E-TEK produce PEMs. DuPont's PEM offering can be found under the trade name
Nafion
. The most commonly used Nafion PEMs are Nafion 112, 115, 117, and 105.
The electrodes are heat pressed onto the PEM. Commonly used materials for these electrodes are carbon cloth or Toray carbon fiber paper . E-TEK produce a carbon cloth called ELAT which maximizes gas transport to the PEM as well as moves water vapor
away from the PEM. Imbedding ELAT with Noble metal
catalyst allows this carbon cloth to also act as the electrode.
Complete MEAs are made by several companies, including PEMEAS (now a division of BASF Fuel Cell). Many of these companies specialize in high volume products. There are companies which produce custom or low quantity MEAs, allowing different shapes, catalysts or membranes to be evaluated. There are hands-on workshops focused on preparation and evaluation of membrane electrode assemblies as well as fuel cell testing.
Platinum is one of the most commonly used catalysts, however other platinum group
metals are also used. Ruthenium and platinum are often used together, if CO is a product of the electro chemical reaction
as CO poisons the PEM and impacts the efficiency of the fuel cell. Due to the high cost of these and other similar materials, research is being undertaken to develop catalysts that use lower cost materials as the high costs are still a hindering factor in the wide spread economical acceptance of fuel cell technology.
Current service life
is 7,300 hours under cycling conditions, while at the same time reducing platinum group metal loading to 0.2 mg/cm2.
Proton exchange membrane
A proton exchange membrane or polymer electrolyte membrane is a semipermeable membrane generally made from ionomers and designed to conduct protons while being impermeable to gases such as oxygen or hydrogen...
s (PEMs) or alkali anion exchange membrane
Alkali anion exchange membrane
An alkali anion exchange membrane is a semipermeable membrane generally made from ionomers and designed to conduct anions while being impermeable to gases such as oxygen or hydrogen...
(AAEMs), catalyst and flat plate electrode used in a fuel cell
Fuel cell
A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. Hydrogen is the most common fuel, but hydrocarbons such as natural gas and alcohols like methanol are sometimes used...
.
PEM-MEA
The PEM is sandwiched between two electrodeElectrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
s which have the catalyst embedded in them. The electrodes are electrically insulated from each other by the PEM. These two electrodes make up the anode
Anode
An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....
and cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
respectively.
The PEM is a proton permeable but electrical insulator
Electrical insulation
thumb|250px|[[Coaxial Cable]] with dielectric insulator supporting a central coreThis article refers to electrical insulation. For insulation of heat, see Thermal insulation...
barrier. This barrier allows the transport of the protons from the anode to the cathode through the membrane but forces the electrons to travel around a conductive path to the cathode. Companies such as DuPont
DuPont
E. I. du Pont de Nemours and Company , commonly referred to as DuPont, is an American chemical company that was founded in July 1802 as a gunpowder mill by Eleuthère Irénée du Pont. DuPont was the world's third largest chemical company based on market capitalization and ninth based on revenue in 2009...
, Dow and E-TEK produce PEMs. DuPont's PEM offering can be found under the trade name
Trade name
A trade name, also known as a trading name or a business name, is the name which a business trades under for commercial purposes, although its registered, legal name, used for contracts and other formal situations, may be another....
Nafion
Nafion
Nafion is a sulfonated tetrafluoroethylene based fluoropolymer-copolymer discovered in the late 1960s by Walther Grot of DuPont. It is the first of a class of synthetic polymers with ionic properties which are called ionomers...
. The most commonly used Nafion PEMs are Nafion 112, 115, 117, and 105.
The electrodes are heat pressed onto the PEM. Commonly used materials for these electrodes are carbon cloth or Toray carbon fiber paper . E-TEK produce a carbon cloth called ELAT which maximizes gas transport to the PEM as well as moves water vapor
Water vapor
Water vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...
away from the PEM. Imbedding ELAT with Noble metal
Noble metal
Noble metals are metals that are resistant to corrosion and oxidation in moist air, unlike most base metals. They tend to be precious, often due to their rarity in the Earth's crust...
catalyst allows this carbon cloth to also act as the electrode.
Complete MEAs are made by several companies, including PEMEAS (now a division of BASF Fuel Cell). Many of these companies specialize in high volume products. There are companies which produce custom or low quantity MEAs, allowing different shapes, catalysts or membranes to be evaluated. There are hands-on workshops focused on preparation and evaluation of membrane electrode assemblies as well as fuel cell testing.
Platinum is one of the most commonly used catalysts, however other platinum group
Platinum group
The platinum group metals is a term used sometimes to collectively refer to six metallic elements clustered together in the periodic table.These elements are all transition metals, lying in the d-block .The six...
metals are also used. Ruthenium and platinum are often used together, if CO is a product of the electro chemical reaction
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
as CO poisons the PEM and impacts the efficiency of the fuel cell. Due to the high cost of these and other similar materials, research is being undertaken to develop catalysts that use lower cost materials as the high costs are still a hindering factor in the wide spread economical acceptance of fuel cell technology.
Current service life
Service life
A product's service life is its expected lifetime, or the acceptable period of use in service. It is the time that any manufactured item can be expected to be 'serviceable' or supported by its manufacturer....
is 7,300 hours under cycling conditions, while at the same time reducing platinum group metal loading to 0.2 mg/cm2.
Research
- 2009 - Research is ongoing at the Fuel Cell Research Center, Korea Institute of Energy Research to enhance the performance of the MEA.
- 2009 - EMSL/PNNL-Functionalized graphene sheets with a Pt layer
See also
- Electrochemical hydrogen compressorElectrochemical hydrogen compressorAn electrochemical hydrogen compressor is a hydrogen compressor where hydrogen is supplied to the anode, and compressed hydrogen is collected at the cathode with an exergy efficiency of 70 to 80% for pressures up to 10,000 psi or 700 bars.-Principle:...
- Electroosmotic pumpElectroosmotic pumpAn electroosmotic pump , or EO pump, is used for generating flow or pressure by use of an electric field. One application of this is removing liquid flooding water from channels and gas diffusion layers and direct hydration of the proton exchange membrane in the membrane electrode assembly of the...
- Gas diffusion electrodeGas diffusion electrodeGas diffusion electrodes are electrodes with a conjunction of a solid, liquid and gaseous interface, and an electrical conducting catalyst supporting an electrochemical reaction between the liquid and the gaseous phase...
- Glossary of fuel cell termsGlossary of fuel cell termsThe Glossary of fuel cell terms lists the definitions of many terms used within the fuel cell industry. The terms in this fuel cell glossary may be used by fuel cell industry associations, in education material and fuel cell codes and standards to name but a few. –...