Proton exchange membranes for fuel cell operation at low relative humidity and intermediate temperature: An updated review

Low proton conduction, resulting from interrupted H+ hopping between water molecules to form H3O+ ions, significantly complicates the operation of proton exchange membrane fuel cells at intermediate temperatures (80-120°C) and low relative humidities (<50%), which are the conditions imposed by thermal and water management considerations. Importantly, the performance of the above cells is influenced by water channeling in proton exchangeable polymers, since high ionic conductivities at intermediate temperatures and low relative humidities are achieved due to the high water retention and good hydrophobic/hydrophilic segregation ability of these polymers. Therefore, to summarize the current state-of-the-art, this review focuses on the recently developed approaches to preserving good ionic conductivity under the aforementioned conditions or maintaining good ionic conductivity and preventing excessive water swelling under other ones.