New anion exchange membranes based on long side-chain piperidinium cation grafted poly(ether ketone-cardo)

The synthesis of high-performance membranes is one of the most momentous issues for alkaline energy devices. To develop anion exchange membranes (AEMs) that combine high chemical stability and ionic conductivity, we have designed and prepared a series of AEMs based on poly(ether ketone cardo) (PEKC). Through a facile lactamization procedure between the cardo phenolphthalein group in PEKC and the amino group in 1-(2-aminoethyl)-4-methylpiperazine (AP), the flexible side-chain methylpiperazine group is introduced into the PEKC backbone. By using iodomethane (Me), 1-bromopentane (Pe) and 1-(5-bromopentyl)-1-methylpiperdinium bromide (Pip) as the quaternized regents for the methylpiperazine group, three different AEMs (named PEKC-AP-Me, PEKC-AP-Pe and PEKC-AP-Pip, respectively) are developed. Comparing with alkyl side chain grafted membranes, the PEKC-AP-Pip membrane with bis-cation groups exhibits the highest OH− conductivity of 60.3 mS cm−1 (80 °C) when its corresponding IEC is 1.13 mmol g−1. Meanwhile, the PEKC-AP-Me, PEKC-AP-Pe and PEKC-AP-Pip membranes show excellent mechanical strengths of 36.2 MPa, 32.3 MPa and 26.3 MPa, respectively. Due to the good chemical stability of piperdinium cation and PEKC-AP main chain, the long side chain grafted AEMs also demonstrate good alkaline stability. When submersing in 1 M KOH solution at 80 °C, PEKC-AP-x membranes maintain their conductivities up to 1200 h. These good comprehensive properties grant the prepared PEKC-AP-x membranes ambitious future for alkaline energy devices.