Covalently crosslinked poly (p-terphenyl N-methylpiperidine) based anion exchange membranes for low temperature direct ammonia fuel cells

Abstract

Low ammonia permeability and stable anion exchange membranes are crucial for the long-term efficient operation of direct ammonia fuel cells . Here, we present a thermal crosslinking strategy to balance ammonia permeation and dimensional stability of crosslinked poly ( p -terphenyl N -methylpiperidine) (PTP-VBC- x ). The cross-linked network and ether-free backbone characteristics endow PTP-VBC-20 with excellent dimensional stability and alkali resistance. The PTP-VBC-20 membrane achieves a high conductivity at low ion exchange capacity (IEC = 1.74 mmol g −1 ), with the conductivity of OH − reaching 100.1 mS cm −1 at 80 °C. Additionally, PTP-VBC-20 exhibits excellent alkaline resistance, with almost no loss of conductivity after 500 h in 1M KOH at 70 °C, and no degradation of cations is detected through infrared characterization. By controlling hydration and swelling through the crosslinking strategy, PTP-VBC-20 exhibits a lower ammonia permeability (P = 2.09 × 10 −7 cm 2 s −1 ) compared to methyl quaternized membrane (PTP-Me) (P = 1.96 × 10 −6 cm 2 s −1 ). Moreover, the direct ammonia fuel cell based on PTP-VBC-20 delivers a peak power density of 201.7 mW cm −2 at 95 °C under an operating pressure of 2 bar when a 3 M NH 3 -KOH solution is fed to anode.