Review of External Humidifiers for Fuel Cells

The efficient operation of Proton Exchange Membrane Fuel Cells (PEMFCs) relies on precise humidity control, and external humidification technology, which provides humidity management through independent devices, has become a key means to enhance system stability and durability. This article systematically reviews the latest advancements in external humidification technologies for PEMFCs, with a focus on membrane humidifiers, bubble humidifiers and spray humidifiers, analyzing their working principles, performance evaluation metrics and application scenarios. Research indicates that membrane humidifiers, with their low energy consumption and compact structure, hold an advantage in vehicular systems, but their performance is limited by membrane material lifespan and operational condition fluctuations. Bubble humidifiers demonstrate reliability in stationary applications, yet there is a pressing need for deeper research into their dynamic responses and mathematical modeling. Spray humidifiers achieve rapid humidification through direct water injection but are prone to "flooding" issues, necessitating optimization with high-precision control. The article also explores core evaluation metrics for humidifiers (such as dew point approach temperature, water vapor transfer rate, and pressure loss) and their impact on system performance, revealing the potential of novel structural designs like porous metal foams and biomimetic flow channels. Despite the significant improvements in humidity adaptability that external humidification technologies offer to PEMFCs, challenges such as increased system complexity, energy consumption control and long-term durability remain. Future research should focus on the collaborative optimization of various types of humidifiers, the development of intelligent control strategies and cross-disciplinary material innovations to promote their large-scale application in fields such as new energy vehicles and distributed energy systems.