Poly(isatin-piperidinium-terphenyl) anion exchange membranes with improved performance for direct borohydride fuel cells

In this work, an effective design strategy for anion exchange membranes (AEMs) incorporating ether-bond free and piperidinium cationic groups promote chemical stability. A series of poly (isatin-piperidium-terphenyl) based AEMs were synthesized by superacid catalyzed polymerization reaction, followed by quaternization. The effect of functionalization on the performance of poly (isatin-N-dimethyl piperidinium triphenyl) (PIDPT-x) AEMs was investigated. Highly reactive N-propargylisatin was introduced into the backbone to achieve high molecular weight polymers (ηa = 2.06–3.02 dL g−1) leading to robust mechanical properties, as well as modulating 1.78–2.00 mmol g−1 of the ion exchange capacity (IEC) of the AEMs by feeding. Apart from that, the rigid non-ionized isatin-terphenyl segment provides AEMs improved dimensional stability with a swelling ratio of less than 12% at 80 °C. Among them, PIDPT-90 exhibited a higher OH− conductivity of 105.6 mS cm−1 at 80 °C. The alkali-stabilized PIDPT-85 AEM was presented, in which OH− conductivity retention maintained 85.6% in a 2 M NaOH at 80 °C after 1632 h. Afterward, the direct borohydride fuel cells (DBFC) with PIDPT-90 membrane as a separator showed an open-circuit voltage of 1.63 V and a peak power density of 75.5 mWcm−2 at 20 °C. This work demonstrates the potential of poly (isatin- N-dimethyl piperidinium triphenyl) as AEM for fuel cells.