Cation–dipole interaction that creates ordered ion channels in an anion exchange membrane for fastOH⁻conduction

Abstract

Precise control over polyelectrolyte architecture, engineered for self-assembly of ion-conducting channels, is of fundamental and technological importance to many fields, for example, fuel cells and redox flow batteries and electrodialysis. Building on recent advances with the supramolecular chemistry, we introduce inter/intramolecular cation-dipole interactions between pendent quaternary ammoniums cations and polar polyethylene glycol grafts in an anion-exchange membrane (AEM). Such interactions lead to desirable, ordered ion-conducting pathways when in the membrane form. Comparison of the results of molecular dynamics simulation with 1 H NMR and nano-scale microscopy analyses show that the cation-dipole interactions enhance self-assembly and the formation of interconnected ionic network domains, providing three-dimensional pathways for both water and ion transport. The resultant AEM exhibits high OH − conductivity (49 mS cm −1 at 30 C) and a completive peak power density of 622 mW cm −2 at 70 C when tested in a H 2 /O 2 single-cell alkaline membrane fuel cell.

Flexible Bis-piperidinium Side Chains Construct Highly Conductive and Robust Anion-Exchange Membranes

“…Generally, the AEMs are fabricated by amorphous polymers, with so many structural disorders hindering efficient ion transport, therefore showing low conductivity. Precise control over AEM structures to form the desired microphase separation morphology is believed to accelerate ion transport across the membrane through the continuous ionic channels. − Over the past decades, AEMs featuring the block, − clustered, , side-chain, − or graft/comb-shaped structure , have been successfully designed to construct the aforementioned ionic channels.…”

Cross-Linked Anion-Exchange Membranes with Dipole-Containing Cross-Linkers Based on Poly(terphenyl isatin piperidinium) Copolymers

“…Many researchers usually enhance ion conductivity by increasing the ion-exchange capacity (IEC). ,, However, high IEC often leads to excessive water uptake, which easily deteriorates the mechanical stabilities of membranes. , The difference in polarity of the hydrophilic/hydrophobic regions in membranes can induce ion aggregation and promote the formation of ion transport channels, which improves the ion conductivity of AEMs . Furthermore, introducing spontaneous intermolecular interactions, such as a hydrogen bond, dipolar interactions, and a π–π stacking interaction, can further accelerate the self-aggregation of hydrophilic cations in AEMs. , Xu et.al reported a PPO-based AEM grafted with a PEG homopolymer, which can form an abundant cation–dipole interaction network. The resulting membrane showed that cation–dipole interactions (between quaternary ammonium cations and PEG moieties) provide an additional driving force for hydrophilic QA self-aggregation, promoting the formation of a well-defined microphase separation.…”

Dual-Cation Interpenetrating Polymer Network Anion Exchange Membrane for Fuel Cells and Water Electrolyzers

“…However, low ionic conductivity and poor stability, especially poor chemical stability, have always been the major problems that lie in the way of AEM development. To address the above problems, several strategies have been proposed, including the design of stable cation exchange groups, − alkaline-resistant polymer backbone (e.g., without the benzyl- ether group), − microphase separation, − semi-interpenetrating polymer network (IPN)/IPN structure, cross-linking, − blending, − and hybridization. − Encouraging results have been achieved, for instance, a cross-linked poly­(norbornene) PTFE-supported membrane showed a high conductivity of 198 mS cm –1 @80 °C, with no significant decay after 1000 h under 1 mol L –1 KOH at 80 °C . The poly­(aryl piperidinium) membrane was prepared by inducing the strong basic piperidinium cationic group onto the rigid hydrophobic aryl backbone without the ether bond, which showed conductivity of 170 mS cm –1 @80 °C and durability of over 2000 h …”