Membrane electrode assembly
A membrane electrode assembly (MEA) is an assembled stack of proton exchange membranes (PEMs) or alkali anion exchange membrane (AAEMs), catalyst and flat plate electrode used in a fuel cell.[1]
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PEM-MEA [edit]
The PEM is sandwiched between two electrodes 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 fluoropolymer (PFSA) 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.[2] 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.[3]
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.[4]
Production of MEAs [edit]
The production of MEAs is on the rise and is a very fast growing and competitive market. There are many companies who offer several competitive advantages, of which include, customization, low to high order volumes, and research and development. Current companies that offer these include FuelCellStore, FuelCellsEtc, and Alfa Aesar.
See also [edit]
- Electrochemical hydrogen compressor
- Electroosmotic pump
- Gas diffusion electrode
- Glossary of fuel cell terms
References [edit]
- ^ Bentham, Daniel WIPO patent WO/2008/007108 Current distribution system for electrochemical cells. Freepatentsonline.com (2008-01-17). Retrieved on 2013-04-19.
- ^ Ge, Jiabin; Higier, Andrew; Liu, Hongtan (2006). "Effect of gas diffusion layer compression on PEM fuel cell performance". Journal of Power Sources 159 (2): 922. doi:10.1016/j.jpowsour.2005.11.069.
- ^ Fuel Cell Short Course. Fsec.ucf.edu. Retrieved on 2013-04-19.
- ^ Fuel Cell School Buses: Report to Congress. US Department of Energy, December 2008, p. 9.
