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

•Low proton conduction complicates operation of proton exchange membrane fuel cells.•PEMFC performance is influenced by water channeling in H+-exchangeable polymers.•Good ionic conductivity must be preserved at intermediate temperature/low humidity.•Restricted PEMFC water content preserves their mechanical strength.•Novel methods allow PEMFC thickness to be reduced.