Membrane electrode assembly, a sandwich structure that contains the the ion conducting elements of any fuel cell: cathode electrode, anode electrode, and electrolyte. In PEMFCs, this polymer membrane can be made from DuPont’s Nafion. W.L. Gore’s Gore-Select and PRIMEA, Asahi Glass Co. Ltd.’s Flemion and Aciplex, Celanese’s PBI material, and others. Fuel Cells: Green Power states that the membrane of a PEMFC resembles multiple layers of an extremely thin film, ranges in thickness from 50 to 175 microns and is water absorptive, appearing similar to a moist piece of plastic wrap. (See FCIR online, August 2003) A report from the Fuel Cell Seminar 2004 conference discusses upgrades and new materials used in fuel cell membranes (FCIR online December 2004), including non-fluorinated membranes from Polyfuel, www.polyfuel.com. (In the May 2005 issue of FCIR, Polyfuel announces a "drop in" nonfluorinated membrane for portable applications capable of easily replacing Nafion in performance.) In the September 2003 issue of FCIR, the polymer blend membrane capable of operating at 200°C from Danish Power Systems is explained, www.daposy.dk. Within an individual PEMFC MEA, the membrane is usually layered between a gas diffusion medium (GDM) such as porous carbon paper or carbon cloth, catalyst coating the membrane, and the separator/current collector or bipolar plates. This gas diffusion layer (GDL) provides a passageway for the gases and optimizes diffusion of reactant gases to the catalyst. These elements of the MEA are also important for water management. Multiple factors must be taken into account in GDM manufacture, such as porosity, pore size control, wettability, flexibility and strength. For electrode supports within PEMFC MEAs, carbon fabric supplied by Zoltek is being used by Ballard Power Systems, www.zoltek.com. Ballard has also signed an agreement with Victrex Partners to exploit the latter’s sulfonated polyether-ether ketone (PEEK) copolymer in the proton-conducting (ionomer) technology applicable to MEAs, www.victrex.com, www.ballard.com. For SOFC MEAs, Honeywell has been successful in creating a design where the anode supports are porous but the ceramic electrolytic membrane exhibits full density, with matching CTEs between the membrane and metal interconnects (FCIR online February 2001). Altair Technologies makes ceramic oxide membranes and reactive crystalline catalyst support structures based in nanoparticle technology (FCIR online September 2000), www.altairinc.com. SOFCo has a membrane and stack design that isolates electrical interconnects from the hot gas streams and eliminates formation of insulating layers and spinnel structures that inhibit gas flow (FCIR online May 2001). Materials and Systems Research chemically bonds its SOFC ceramic membrane to the anode support to improve the interface and ensure durability and mechanical strength (FCIR online February 2001), www.msrihome.com. Source : Fuel cell glossary. http://www.sanewsletters.com/FCIR/glossary1.asp |
