Polymer Electrolyte Membrane Technology for Fuel Cells
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Polymer Electrolyte
Membrane Technology for Fuel Cells Raj G. Rajendran
PEM Requirements
Abstract The concept of using an ion-exchange membrane as an electrolyte separator for polymer electrolyte membrane (PEM) fuel cells was first reported by General Electric in 1955. However, a real breakthrough in PEM fuel cell technology occurred in the mid1960s after DuPont introduced Nafion, a perfluorosulfonic acid membrane. Due to their inherent chemical, thermal, and oxidative stability, perfluorosulfonic acid membranes displaced unstable polystyrene sulfonic acid membranes. Today, Nafion and other related perfluorosulfonic acid membranes are considered to be the state of the art for PEM fuel cell technology. Although perfluorosulfonic acid membrane structures are preferred today, structural improvements are still needed to accommodate the increasing demands of fuel cell systems for specific applications. Higher performance, lower cost, greater durability, better water management, the ability to perform at higher temperatures, and flexibility in operating with a wide range of fuels are some of the challenges that need to be overcome before widespread commercial adoption of the technology can be realized. The present article will highlight the membrane properties relevant to PEM fuel cell systems, the development history of perfluorosulfonic acid membranes, and the current status of R&D activities in PEM technology. Keywords: ionic conductivity, Nafion, perfluorosulfonic acid membranes, PEM fuel cells, polymer electrolyte membranes, proton-exchange membranes.
Introduction Among the various fuel cell systems known today, the proton-exchange membrane fuel cell system has proven to be an attractive and more promising option than alkaline, solid oxide, or molten carbonate fuel cell systems for power generation in portable, stationary, and mobile (automotive) applications. The use of proton-exchange membranes as an electrolyte separator in fuel cell applications offers several advantages, such as selectivity, system simplicity, and improved reliability compared with systems based on a liquid electrolyte. An early breakthrough in proton-exchange membrane technology occurred in 1955 when General Electric announced their successful demonstration
MRS BULLETIN • VOLUME 30 • AUGUST 2005
brane material provided superior mechanical and electrochemical properties and represented the first durable and stable polymer electrolyte membrane (PEM) fuel cell system. After extensive evaluation, Nafion was first used by GE in 1966 for NASA’s space mission work.5,6 In extended operation, a multicell stack constructed with Nafion membranes demonstrated more than 60,000 h of stable operation, thereby providing the exceptional lifetime needed for commercial fuel cells.7 This advance resulted in worldwide acceptance of PEM fuel cells as a viable technology option. This article will highlight the membrane properties relevant to PEM fuel cell systems, the development of perfluorosulfonic acid membranes, and the current status of research and
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