Semi-interpenetrating anion exchange membranes using hydrophobic microporous linear poly(ether ketone)

In order to realise high ionic conductivity and improved chemical stability, a series of anion exchange membranes (AEMs) with semi-interpenetrating polymer network (sIPN) has been prepared via the incorporation of crosslinked poly(biphenyl N-methylpiperidine) (PBP) and spirobisindane-based intrinsically microporous poly(ether ketone) (PEK-SBI). The formation of phase separated structures as a result of the incompatibility between the hydrophilic PBP network and the hydrophobic PEK-SBI segment, has successfully promoted the hydroxide ion conductivity of AEMs. A swelling ratio (SR) as low as 12.2 % at 80 °C was recorded for the sIPN containing hydrophobic PEK-SBI as the linear polymer and crosslinked structure with a mass ratio of PBP to PEK-SBI of 90/10 (sIPN-90/10(PEK-SBI)). The sIPN-90/10(PEK-SBI) AEM achieved the highest hydroxide ion conductivity of 122.4 mS cm-1 at 80 °C and a recorded ion exchange capacity (IEC) of 2.26 meq g-1. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) clearly revealed the improved phase separation structure of sIPN-90/10(PEK-SBI). N2 adsorption isotherm indicated that the Brunauer-Emmett-Teller (BET) surface area of the AEMs increased with the increase of microporous PEK-SBI content. Interestingly, the sIPN-90/10(PEK-SBI) AEM showed good alkaline stability for being able to maintain a conductivity of 94.7 % despite being soaked in a 1 M sodium hydroxide solution at 80 °C for 30 days. Meanwhile, a peak power density of 481 mW cm-2 can be achieved by the hydrogen/oxygen single cell using sIPN-90/10(PEK-SBI) as the AEM.