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NOVEL ION-CONDUCTING PERFLUORINATED MULTIBLOCK COPOLYMER AND METHODS OF MAKING

IP.com Disclosure Number: IPCOM000183539D
Publication Date: 2009-May-26

Publishing Venue

The IP.com Prior Art Database

Related People

Jing Li: AUTHOR [+4]

Abstract

An ion-conducting perfluorinated multiblock copolymer having the formula E-{-[-(A)a-CF(X)CF2-]b-Z-[-(B)c-CF(Y)CF2-]d-Z-}e-F wherein A and B are perfluorinated monomer units; E and F are terminal groups; X is a first perfluorinated side chain comprising a first acid-functionalized pendent group; Y is a second perfluorinated side chain having a chain length that is different from X and comprising a second acid-functionalized pendent group; Z is an ether, phenyl, hydrocarbon, fluorocarbon, or combination thereof; a and c are 0 to 10; and b, d and e are 1 to 50. A method of making the ion-conducting perfluorinated multiblock copolymer is also provided.

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Novel ion-conducting perfluorinated
multiblock copolymer and methods of making

BACKGROUND

Technical Field

This invention generally relates to a novel ion-conducting perfluorinated multiblock copolymer, in particular, for proton exchange membrane fuel cells, and methods for making the same.

Description of the Related Art

In general terms, an electrochemical fuel cell converts a fuel and oxygen into electricity and water.  Fundamental components of proton exchange membrane (“PEM”) fuel cells include two electrodes – the anode and cathode – separated by the PEM.  Each electrode is coated on one side with a thin layer of catalyst, with the PEM being "sandwiched" between the two electrodes and in contact with the catalyst layers.  Alternatively, one or both sides of the PEM may be coated with a catalyst layer, and the catalyzed PEM is sandwiched between a pair of porous electrically conductive electrode substrates.  The anode/PEM/cathode combination is referred to as a membrane electrode assembly or "MEA." Hydrogen fuel, typically in the form of a gas, dissociates into electrons and protons upon contact with the catalyst on the anode-side of the MEA.  The protons migrate through the PEM, while the free electrons are conducted from the anode, in the form of usable electric current, through an external circuit to the cathode.  Upon contact with the catalyst on the cathode-side of the MEA, oxygen, electrons from the external circuit, and protons that pass through the PEM combine to form water.

Desirable characteristics of a PEM include good mechanical properties, high conductivity, resistance to oxidative and thermal degradation, and dimensional stability upon hydration and dehydration.  Hydrocarbon-based (non-fluorinated) materials are advantageous due to lower costs, but such materials are prone to oxidative degradation.  As a result, perfluorinated materials have been employed, including perfluorinated sulfonic acid aliphatic polymers.  One example is a product sold by DuPont under the trade name Nafion®, a polytetrafluoroethylene-based ionomer containing sulfonic acid groups to provide proton conductivity.  This material has been used effectively in PEM fuel cells due to its acceptable proton conductivity and chemical resistance characteristics. 

Perfluorinated ionomers such as Nafion®, however, have many drawbacks.  For instance, Nafion® membranes do not have a high tensile strength, which is important from a manufacturing and handling perspective, particularly for thin membranes.  Furthermore, such ion-exchange materials must remain well hydrated in order to retain their ionic conductivity.  Accordingly, operation of PEM fuel cells containing such membranes has largely been limited to operational temperatures below 100ºC to limit dehydration of the ion-exchange membrane.    

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