Improved, Low-Cost, Durable Fuel Cell Membranes

Improved, Low-Cost, Durable Fuel Cell Membranes

J. Goldbach, D. Mountz, J. Yi, T. Zhang, W. He, S. Gaboury and M. Foure

Arkema Inc.

King of Prussia, PA

A typical polymer electrolyte membrane (PEM) is composed of a single copolymer, such as is present in the well-known perfluorinated sulfonic acid polymer (PFSA) based membranes. This copolymer must meet the demanding conductivity, gas barrier, mechanical, and electrochemical requirements for a desirable fuel cell membrane.  Effectively satisfying all of these properties is complex, costly, and generally leads to trade-offs in desired properties.

Researchers at Arkema have taken a new approach to PEM design whereby the mechanical property requirements are decoupled from the other desired properties.  This decoupling is accomplished by blending two very dissimilar polymers, a fluoropolymer such as Kynar^® PVDF with any one of a variety of highly sulfonated polyelectrolytes.  Using this blending process along with inexpensive starting materials, many different membrane compositions can be produced at significantly reduced cost over traditional methodologies.

One major drawback of current fuel cell membrane technology is poor proton conductivity at reduced relative humidity.  To meet the US Department of Energy 2010 performance targets, a membrane that efficiently retains water, and conducts protons mainly through a hopping, or ‘Grotthus' type mechanism is necessary.  One approach to such a membrane is to incorporate phosphonic acid functionality.  In a fashion analogous to phosphoric acid-imbibed membranes, it is hypothesized that phosphonic acid functionality will promote water retention and proton conduction at reduced RH.  In the case of a Kynar-polyelectrolyte blend membrane, the phosphonic acid groups can be covalently bound to the polyelectrolyte phase, and undesirable acid leaching effects are likely to be eliminated.

The ongoing drive toward continuous operation at ultra-low relative humidities and/or higher temperatures requires performance and durability optimization of all major fuel cell components under these more harsh conditions.  The flexibility and rapid development cycle possible with Arkema's blended membrane approach is well suited to meet these new challenges.