Anion Conductive Triblock Copolymer Membranes with Flexible Multication Side Chain

Durable Multiblock Poly(biphenyl alkylene) Anion Exchange Membranes with Microphase Separation for Hydrogen Energy Conversion

Anion exchange membrane fuel cells (AEMFCs) and water electrolysis (AEMWE) show great application potential in the field of hydrogen energy conversion technology. However, scalable anion exchange membranes (AEMs) with desirable properties are still lacking, which greatly hampers the commercialization of this technology. Herein, we propose a series of novel multiblock AEMs based on ether-free poly(biphenyl ammonium-b-biphenyl phenyl)s (PBPA-b-BPPs) that are suitable for use in high performance AEMFC and AEMWE systems because of their well-formed microphase separation structures. The developed AEMs achieved outstanding OH- conductivity (162.2 mS cm-1 at 80 °C) with a low swelling ratio, good alkaline stability, and excellent mechanical durability (tensile strength >31 MPa and elongation at break >147 % after treatment in 2 M NaOH at 80 °C for 3750 h). A PBPA-b-BPP-based AEMFC demonstrated a remarkable peak power density of 2.41 W cm-2 and in situ durability for 330 h under 0.6 A cm-2 at 70 °C. An AEMWE device showed a promising performance (6.25 A cm-2 at 2 V, 80 °C) and outstanding in situ durability for 3250 h with a low voltage decay rate (<28 μV h-1 ). The newly developed PBPA-b-BPP AEMs thus show great application prospects for energy conversion devices.

Nanofiltration Membranes Modified with a Clustered Multiquaternary Ammonium-Based Ionic Liquid for Improved Magnesium/Lithium Separation

Lithium separation is of great significance to overcome the lithium supply shortage resulting from a heightened demand in the energy sector. The low selectivity of polymer nanofiltration membranes for lithium extraction from concentrated Mg/Li mixtures caused by miniaturized pore structures and weak and unstable positive surface charges limits their practical implementation. To address the surface charge strength and stability, a novel ionic liquid monomer, N¹-(6-aminohexyl)-N¹,N¹,N⁶,N⁶,N⁶-pentamethylhexane-1,6-diaminium bromide (denoted as DABIL), is first synthesized and covalently anchored on a pristine polyamide thin-film composite (TFC) membrane via a secondary amidation reaction for improved selective lithium separation from Mg/Li mixtures. DABIL modification of the polyamide network contributes to increased surface hydrophilicity, an enlarged membrane pore structure, and reinforced Donnan exclusion effects. Molecular dynamics simulation confirmed that the difference of the interaction energies between water and the multication groups dominates the surface properties. The DABIL membrane exhibits sixfold enhancement of water permeability compared to the unmodified membrane and outperforms the recently reported state-of-the-art positively charged membranes. It presents an improved Li⁺/Mg²⁺ selectivity of 26.49, suggesting the membranes' potential for lithium recovery. Moreover, the membrane shows efficient antibacterial activity for mitigating biofilm formation. We establish that functionalization of TFC membranes with ionic liquids containing multication side chains could be a promising approach to achieve improved and sustainable permselectivity for the recovery of critical metal resources.

Preparation and Properties of Sulfonated Poly(phthalazinone ether ketone) Membranes for Electrodialysis

Sulfonated poly(phthalazinone ether ketones) (SPPEK) with ion exchange capacities from 0.77 to 1.82 mmol·g⁻¹ are synthesized via an electrophilic substitution reaction. Nuclear magnetic resonance and infrared absorption spectroscopy are used to characterize the chemical structure of the obtained polymers for confirming the successful introduction of sulfonic groups. SPPEKs show excellent thermal stability; their temperature required to achieve 5% weight loss is about 360 °C. Accordingly, the obtained membranes possess high ion perm-selectivity, proton conductivity, and low area resistance. Regarding the electrodialysis-related performance of the membranes, the SPPEK-4 membrane has the highest limiting current density (39.8 mA·cm²), resulting from its high content of sulfonic groups. In a desalination test of standard solution, SPPEK-3 and SPPEK-4 membranes exhibit both better salt removal rate and acceptable energy consumption than commercial membrane. Additionally, SPPEK-3 membrane shows outstanding performance in terms of high concentration rate and low energy consumption during saline water treatment, which indicates the feasibility of novel membranes in electrodialysis application.

Clustered piperidinium-functionalized poly(terphenylene) anion exchange membranes with well-developed conductive nanochannels

Anion exchange membrane fuel cells (AEMFCs) attract considerable attention owing to their high-power density and potential utilization of cheap non-noble metal catalysts. However, anion exchange membranes (AEMs) still face the problems of low conductivity, poor dimensional and chemical stability. To address these issues, AEMs with clustered piperidinium groups and ether-bond-free poly(terphenylene) backbone (3QPAP-x, x = 0.3, 0.4, and 0.5) were designed. Transmission electron microscope results show that the clustered ionic groups are responsible for fabricating well-developed conductive nanochannels and restraining the swelling behavior of the membranes. 3QPAP-0.4 and 3QPAP-0.5 AEMs exhibit higher conductivity (117.5 mS cm^-1, 80 °C) and lower swelling ratio than that of commercial FAA-3-50 (80.4 mS cm^-1, 80 °C). The conductivity of 3QPAP-0.5 only decreased by 10.4% after treating with 1 M NaOH at 80 °C for 720 h. The Hofmann elimination degradation of the cationic groups is restrained by the long flexible alkyl chain between cations. Based on the high performance of 3QPAP-0.5, an H₂-O₂-type AEMFC reaches 291.2 mW cm^-2 (60 °C), which demonstrates that the as-prepared AEMs are promising for application in fuel cells.

Polybenzimidazole Ultrathin Anion Exchange Membrane with Comb-Shape Amphiphilic Microphase Networks for a High-Performance Fuel Cell

A comb-shape amphiphilic cationic side chain is proposed to well-balance the water sorption in anion exchange membranes (AEMs), in which the cationic group is in between of an ether-containing hydrophilic spacer and an alkyl hydrophobic spacer. By fully grafting the amphiphilic side chains onto polybenzimidazole (PBI), comb-shape amphiphilic microphase networks are well-developed in the AEMs, in which the alkyl hydrophobic network greatly restricts water swelling and the ether-containing hydrophilic network keeps the hydration of the cationic groups and enlarges the ion conductive channel. The as-prepared membranes achieve a high conductivity of about 91.2 mS cm^-1, an extremely low swelling ratio of about 8.1% at 80 °C, and good mechanical properties at a hydrated state (tensile strength and elongation at a break of about 14.6 MPa and 77.5%, respectively). Benefits from the balanced water sorption in AEMs, the H₂/O₂ fuel cell with a 10 μm ultrathin membrane could withstand 80 °C and 0.1 MPa back pressure and achieve a high open circuit voltage of about 1.0 V and a high peak power density of about 631.5 mW cm^-2. This work provides a new insight into the design of high-performance AEM.

Highly Durable Ether-Free Polyfluorene-Based Anion Exchange Membranes for Fuel Cell Applications

The preparation of anion exchange membranes (AEMs) with excellent chemical and dimensional stability and high conductivity faces several challenges. In the present work, a novel ether-free durable polyfluorene (PF) without fluorine-bearing pendant piperidinium groups was synthesized by the Suzuki cross-coupling reaction. Alkyl groups were introduced into the backbone of PF to enhance the solubility and flexibility of PF-based AEMs, and the transparent and flexible polymer membrane showed a high conductivity of 80.44 mS cm^-1 and excellent alkaline stability in 2 M KOH solution at 80 °C. Although the membrane possesses a high ion exchange capacity (IEC) (2.49 mequiv g^-1), it exhibits a low swelling ratio (9.4% at 80 °C), excellent mechanical properties, and dimensional stability. The H₂/O₂ single cell assembled with PFPE-Pi exhibited a maximum power density of 661 mW cm^-2 at a current density of 1280 mA cm^-2 at 80 °C. The present work provides a simple and effective strategy for the preparation of ether-free polyfluorene-based AEMs with high conductivity, excellent mechanical properties, and dimensional stability for application in alkaline fuel cells.

Fast Bulky Anion Conduction Enabled by Free Shuttling Phosphonium Cations

Highly conductive anion-exchange membranes (AEMs) are desirable for applications in various energy storage and conversion technologies. However, conventional AEMs with bulky HCO₃ ^- or Br^- as counterion generally exhibit low conductivity because the covalent bonding restrains the tethered cationic group's mobility and rotation. Here, we report an alternative polyrotaxane AEM with nontethered and free-shuttling phosphonium cation. As proved by temperature-dependent NMR, solid-state NMR, and molecular dynamics simulation, the phosphonium cation possesses a thermally trigged shuttling behavior, broader extension range, and greater mobility, thus accelerating the diffusion conduction of bulky anions. Owing to this striking feature, high HCO₃ ^- conductivity of 105 mS cm^-1 at 90°C was obtained at a relatively lower ion-exchange capacity of 1.17 mmol g^-1. This study provides a new concept for developing highly conductive anion-exchange membranes and will catalyze the exploration of new applications for polyrotaxanes in ion conduction processes.

Phenolphthalein Anilide Based Poly(Ether Sulfone) Block Copolymers Containing Quaternary Ammonium and Imidazolium Cations: Anion Exchange Membrane Materials for Microbial Fuel Cell

A class of phenolphthalein anilide (PA)-based poly(ether sulfone) multiblock copolymers containing pendant quaternary ammonium (QA) and imidazolium (IM) groups were synthesized and evaluated as anion exchange membrane (AEM) materials. The AEMs were flexible and mechanically strong with good thermal stability. The ionomeric multiblock copolymer AEMs exhibited well-defined hydrophobic/hydrophilic phase-separated morphology in small-angle X-ray scattering and atomic force microscopy. The distinct nanophase separated membrane morphology in the AEMs resulted in higher conductivity (IECw = 1.3-1.5 mequiv./g, σ(OH^-) = 30-38 mS/cm at 20 °C), lower water uptake and swelling. Finally, the membranes were compared in terms of microbial fuel cell performances with the commercial cation and anion exchange membranes. The membranes showed a maximum power density of ~310 mW/m² (at 0.82 A/m²); 1.7 and 2.8 times higher than the Nafion 117 and FAB-PK-130 membranes, respectively. These results demonstrated that the synthesized AEMs were superior to Nafion 117 and FAB-PK-130 membranes.

Multiple Enhancement Effects of Crown Ether in Tröger's Base Polymers on the Performance of Anion Exchange Membranes

The development of anion exchange membranes (AEMs) is hindered by the trade-off of ionic conductivity, alkaline stability, and mechanical properties. Tröger's base polymers (Tb-polymers) are recognized as promising membrane materials to overcome these obstacles. Herein, the AEMs made from Tb-poly(crown ether)s (Tb-PCEs) show good comprehensive performance. The influence of crown ether on the conductivity and alkaline stability of AEMs has been investigated in detail. The formation of hydronium ion-crown ether complexes and an obvious microphase-separated structure formed by the existence of crown ether can enhance the conductivity of the AEMs. The maximum OH^- conductivity of 141.5 mS cm^-1 is achieved from the Tb-PCEs based AEM (Tb-PCE-1) at 80 °C in ultrapure water. The ion-dipole interaction of the Na⁺ with crown ether can protect the quaternary ammonium from the attack of OH^- to improve the alkaline stability of AEMs. After 675 h of alkaline treatment, the OH^- conductivity of Tb-PCE-1 decreases by only 6%. The Tb-PCE-1-based single cell shows a peak power density of 0.202 W cm^-2 at 80 °C. The prominent physicochemical properties are attributed to the well-developed microstructure of the Tb-PCEs, as revealed by TEM, AFM, and SAXS observations.

Highly Conductive and Water-Swelling Resistant Anion Exchange Membrane for Alkaline Fuel Cells

To ameliorate the trade-off effect between ionic conductivity and water swelling of anion exchange membranes (AEMs), a crosslinked, hyperbranched membrane (C-HBM) combining the advantages of densely functionalization architecture and crosslinking structure was fabricated by the quaternization of the hyperbranched poly(4-vinylbenzyl chloride) (HB-PVBC) with a multiamine oligomer poly(N,N-Dimethylbenzylamine). The membrane displayed well-developed microphase separation morphology, as confirmed by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Moreover, the corresponding high ionic conductivity, strongly depressed water swelling, high thermal stability, and acceptable alkaline stability were achieved. Of special note is the much higher ratio of hydroxide conductivity to water swelling (33.0) than that of most published side-chain type, block, and densely functionalized AEMs, implying its higher potential for application in fuel cells.

Boosting the performance of an anion exchange membrane by the formation of well-connected ion conducting channels

Enlarging the discrepancies between hydrophilic/hydrophobic segments in the chemical structure of an ionomer proved to be an efficient strategy to induce the formation of a microphase-separated morphology of the resulting anion exchange membrane.