Crosslinked poly (ether ether ketone) hydroxide exchange membranes with improved conductivity

Crosslinked poly (ether ether ketone) (PEEK) hydroxide exchange membranes are prepared using bi-functional cyclic ammonium, 1,4-diazabicyclo [2,2,2] octane (DABCO), as simultaneous quaternization and crosslinking reagent. Hydroxide conductivity and ion mobility are evaluated as a function of ion concentration, which integrates the counteracting effects of the hydroxide ion amount and crosslinking degree. With the increase of ion concentration, effective mobility of hydroxide ion increases to a high level and then levels off or slightly goes down, suggesting a balance existed between ion concentration and mobility in the crosslinked membranes. As a result, hydroxide conductivity increases rapidly to a high stable level, indicating the applicable range of ion concentration (up to 1.0 mol L−1) for improving hydroxide conductivity. The crosslinked membranes exhibit high hydroxide conductivity of 33.4 mS cm−1 at 25 °C and low swelling ratio of 48.2% at 60 °C. Thermal stability (Tonset: 176 °C) of the crosslinked membranes is better as compared with the non-crosslinked (Tonset: 165 °C) and trimethylamine quaternized PEEK membranes.