Challenges for PEM fuel cell membranes

Proton Exchange Membrane (PEM) fuel cells have been developed extensively since their introduction over thirty years ago. A key component, the polymer electrolyte membrane, acts as both a separator and an electrolyte in the operating fuel cell. Composite membranes offer the capability of using a wide variety of ionomeric polymers that may be mechanically too weak to use as freestanding films. These thinner membranes can replace thicker non-reinforced membranes, thereby increasing performance while simultaneously increasing durability. However, additional advancements will be necessary to meet aggressive operating conditions of higher temperatures and/or lower humidities, as well as longer operating lifetimes demanded in both stationary and automotive applications. In this paper, these challenges for fuel cell membranes are considered. PEM membrane requirements are discussed in terms of two different parameters: temperature and relative humidity. The effect of these two operating parameters on the proton conductivity of PEM fuel cell membranes and the resulting effect on fuel cell performance are examined using experimental observations. Numerical simulations are used to assess the influence of water transport properties on the local hydration state of the membrane inside the running fuel cell. Finally, the challenge of longer membrane life is explored by examination of recent studies on reinforced and non-reinforced membranes. These results illustrate the benefit of reinforced membranes in terms of membrane durability and therefore cell lifetime. Copyright (c) 2005 John Wiley & Sons, Ltd.