Membranes with good water vapor permeability and high selectivity towards air are interesting for humidification or dehumidification applications. Dehydration of gases such as flue gas, natural gas or compressed air are some fields of application. Another sector is in air conditioning of buildings where, besides water vapor transport, a heat transfer is also often required. Such membrane systems are known as enthalpy exchangers or energy recovery ventilators. Membranes for humidification are also of major interest for external humidifiers, a component of polymer electrolyte membrane fuel cells (PEMFC).
For optimum performance of the PEMFC, hydration of its ionomeric membrane is essential. If the ionomeric membrane is not fully hydrated a loss of proton conductivity occurs which reduces the performance and durability.