Membrane humidification methods: principles, challenges, and the potential of hollow fiber

Proton Exchange Membrane Fuel Cells (PEMFCs) are a promising power source due to their ability to generate electricity and heat by consuming hydrogen and oxygen with high efficiency and zero point-of-use emissions at low operating temperatures. The membranes require adequate humidification to maintain high proton conductivity without accumulation of excessive water, which can cause flooding in the membrane and flow fields. This review provides an in-depth examination of various state-of-the-art membrane humidification methods, drawing on the latest literature. The methods have been classified into various categories based on their applications, including internal physical and chemical methods, external humidification devices, and novel self-humidifying membranes. For each method’s working principles, efficacy from the recent experiments, advantages, and limitations have been discussed. The paper also includes a categorized table to compare each method in terms of complexity, response time, and suitability for automotive or stationary applications. The external humidification devices, such as bubblers, spray nozzles, membrane humidifiers, enthalpy wheels, and techniques like direct water injection and exhaust water recirculation, have also been assessed. The paper concludes with suggestions for future research directions, emphasizing the need for durable composite membranes, integrated water management, and advanced control strategies.