Air management in PEM fuel cells: State-of-the-art and prospectives

This paper deals with the state-of-the-art of air management in PEM fuel cell which is a challenge because commercial compressors and humidification systems are not suitable for automotive applications. Major tasks and requirements for compression and humidication subsystems have been introduced showing that compression and humidiation subsytems cannot be decoupled. A higher working pressure around 2.5 bar is recommended, because it permits the PEMFC to have a higher efficiency, as well as a lighter stack and a lower volume than an equivalent PEMFC working at a lower pressure, moreover the water necessary for humidifying the membrane decreases, resulting in a simple management. For high pressure fuel cells, centrifugal compressors or positive displacement compressors with internal compression have to be preferred to those with external compression, because they offer a better efficiency. The built-in compression ratio has to be as close as possible to the fuel cell working pressure to ensure maximum efficiency. Downstream or integrated direct water injection, has shown many advantages for air humidication compared to other methods, because of its controllability, low power consumption and compactness.