Multi-cation alkoxy chains with high ion conductivity and durability in cross-linked poly (aryl piperidinium) anion exchange membranes

Abstract

AEMs with high ionic conductivity and excellent alkali stability are one of the cores to ensure that AEMWE achieves high performance. For the current problems of AEMs, multi-cation side chain crosslinkers present a mitigation strategy for the inherent “trade-off” between ion conductivity and mechanical strength and ensure exceptional alkali resistance. Herein, we introduced the first report on cross-linked AEMs with several hydrophilic multi-cation alkoxy chains, featuring ethylene oxide (EO). The differentiation in the hydrophilic/hydrophobic microphase separation structures, characterized by varying positions of the alkoxy chains within the three-stage multi-cation crosslinker, was explored by experiments and simulation, as well as bearing on the comprehensive performance of AEMs. Notably, EO located in the middle of multi-cations crosslinker was found to establish a coherent and ordered ion channel. QPTP-NOBN15 AEM exhibited the highest OH− conductivity (166.6 mS cm−1) and demonstrated lower water uptake (44.4 %) and swelling ratio (14.5 %) at 80°C. And meticulously designed cross-linked structures, along with ether-free backbones, bestowed upon QPTP-NOBN15 impressive alkali stability. After being retained in 1 M KOH solutions for 1200 h, ion conductivity of QPTP-NOBN15 remained largely unaffected. Furthermore, QPTP-NOBN15-MEA was evaluated by water electrolysis in 1 M KOH solutions at 60°C and found that the current density reached 1.8 A cm−2 at 2.99 V.