Humidification strategy for polymer electrolyte membrane fuel cells - A review

Polymer electrolyte membrane fuel cells are promising power sources because of their advantage such as high efficiency, zero emission and low operating temperature. Water management is one of the critical issues for polymer electrolyte membrane fuel cells and has received significant attention. The membrane within the fuel cell needs to stay in hydrated state to have high ion conductivity and durability, which requires proper humidification. Both internal and external methods have been utilized to humidify the polymer electrolyte membrane. Numerous studies on fuel cell humidification have been conducted in the past decades, especially in recent years. This review aims to summarize the main humidification methods and the related studies. The internal humidification methods are classified as physical methods and chemical methods. The external humidification methods include gas bubbling humidification, direct water injection, enthalpy wheel humidification, membrane humidifiers, and exhaust gas recirculation. The working principle and performance of each method are introduced and the advantage and drawback are summarized. Further, the humidification methods for alkaline anion exchange membrane fuel cells are also briefly reviewed, because of more recent studies showing their potential of using non-precious metal catalysts. This review can help to choose proper humidification strategy for specific polymer electrolyte membrane fuel cell application and may inspire further investigations.