Design, synthesis and characterization of anion exchange membranes containing guanidinium salts with ultrahigh dimensional stability

Chitosan Composite Membrane with Efficient Hydroxide Ion Transport via Nano-Confined Hydrogen Bonding Network for Alkaline Zinc-Based Flow Batteries

The development of membranes with rapid and selective ionic transport is imperative for diverse electrochemical energy conversion and storage systems, including fuel cells and flow batteries. However, the practical application of membranes is significantly hindered by their limited conductivity and stability under strong alkaline conditions. Herein, a unique composite membrane decorated with functional Cu2+ cross-linked chitosan (Cts-Cu-M) is reported and their high hydroxide ion conductivity and stability in alkaline flow batteries are demonstrated. The underlying hydroxide ions transport of the membrane through Cu2+ coordinated nano-confined channels with abundant hydrogen bonding network via Grotthuss (proton hopping) mechanism is proposed. Consequently, the Cts-Cu-M membrane achieves high hydroxide ion conductivity with an area resistance of 0.17 Ω cm2 and enables an alkaline zinc-based flow battery to operate at 320 mA cm-2, along with an energy efficiency of ≈80%. Furthermore, the membrane enables the battery for 200 cycles of long-cycle stability at a current density of 200 mA cm-2. This study offers an in-depth understanding of ion transport for the design and preparation of high-performance membranes for energy storage devices and beyond.

Study on AEMs with Excellent Comprehensive Performance Prepared by Covalently Cross-Linked p-Triphenyl with SEBS Remotely Grafted Piperidine Cations

A series of SEBS-C6-PIP-yPTP (y = 0-15%) AEMs with good mechanical and chemical stability were prepared by combining the strong rigidity of p-triphenyl, good toughness of SEBS, and excellent stability of PIP cations. After the introduction of a p-triphenyl polymer into the main chain, a clear hydrophilic-hydrophobic phase separation structure was constructed within the membrane, forming a continuous and interconnected ion transport channel to improve ion transport efficiency. Moreover, the molecular chains of the cross-linked AEMs change from chain-like to network-like, and the tighter binding between each molecule increases the tensile strength. The special structure of the six-membered ring makes PIP have a significant constraint effect; when nucleophilic substitution and Hoffman elimination occur at the α and β positions, the required transition state potential energy increases, making the reaction difficult to occur and improving the alkaline stability of the polymer membrane. The SEBS-C6-PIP-15%PTP membrane has the best mechanical properties (Ts = 38.79 MPa, Eb = 183.09% at 80 °C, 100% RH), the highest ion conductivity (102.02 mS. cm-1 at 80 °C), and the best alkaline stability (6.23% degradation at 80 °C in a 2 M NaOH solution for 1400 h). It can be seen that organic-organic covalent cross-linking is an effective means to improve the comprehensive performance of AEMs.

Dimensionally Stable Anion Exchange Membranes Based on Macromolecular-Cross-Linked Poly(arylene piperidinium) for Water Electrolysis

The advancement of anion exchange membranes (AEMs) with superior ionic conductivity has been greatly hindered due to the inherent "trade-off" between membrane swelling and ionic conductivity. To resolve this dilemma, macromolecular covalently cross-linked C-FPVBC-x AEMs were fabricated by combining partially functionalized ether-bond-free polystyrene (FPVBC) with poly(arylene piperidinium). The results from atomic force microscopy reveal that an increase in the ratio of FPVBC promotes the fabrication of microphase separation morphology, resulting in a high ionic conductivity of 40.15 mS cm-1 (30 °C) for the C-FPVBC-1.7 membrane. Molecular dynamics simulations further examine the ionic conduction effect of cross-linked AEMs. Besides, the unique cross-linking structure significantly improves mechanical and alkaline stability. After treatment in 1 M KOH at 50 °C for 1200 h, the C-FPVBC-1.7 membrane shows only a 6.9% decrease in conductivity. The C-FPVBC-1.7 AEM-based water electrolyzer achieves a high current density of 890 mA cm-2 at 2.4 V (80 °C) and maintains good stability, enduring over 100 h at 100 mA cm-2 (50 °C). These results demonstrate the significant potential of macromolecularly cross-linked AEMs for practical applications in water electrolysis.

Effects of the crown ether cavity on the performance of anion exchange membranes

Anion exchange membrane fuel cells (AEMFCs) have emerged as a promising alternative to proton exchange membrane fuel cells (PEMFCs) due to their adaptability to low-cost stack components and non-noble-metals catalysts. However, the poor alkaline resistance and low OH^- conductivity of anion exchange membranes (AEMs) have impeded the large-scale implementation of AEMFCs. Herein, the preparation of a new type of AEMs with crown ether macrocycles in their main chains via a one-pot superacid catalyzed reaction was reported. The study aimed to examine the influence of crown ether cavity size on the phase separation structure, ionic conductivity and alkali resistance of anion exchange membranes. Attributed to the self-assembly of crown ethers, the poly (crown ether) (PCE) AEMs with dibenzo-18-crown-6-ether (QAPCE-18-6) exhibit an obvious phase separated structure and a maximum OH^- conductivity of 122.5 mS cm^-1 at 80 °C (ionic exchange capacity is 1.51 meq g^-1). QAPCE-18-6 shows a good alkali resistance with the OH^- conductivity retention of 94.5% albeit being treated in a harsh alkali condition. Moreover, the hydrogen/oxygen single cell equipped with QAPCE-18-6 can achieve a peak power density (PPD) of 574 mW cm^-2 at a current density of 1.39 A cm^-2.

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

To balance the ionic conductivity and dimensional stability of anion-exchange membranes (AEMs), several cross-linked ether-free poly(terphenyl isatin piperidinium) copolymers were synthesized using 1,2-bis(2-aminoethoxy)ethane as a cross-linker. By introducing an alkyl diamine-based hydrophobic cross-linker as a control, the effects of the dipolar-molecule-containing cross-linker on the comprehensive performance of the membranes were investigated. Cation-dipole interactions between the cations and the hydrophilic ethylene oxide cross-linker enhance the self-assembly capability of the cationic groups. The introduction of the rotatable ethylene oxide cross-linker facilitates the flexibility of the cross-linked networks, thereby promoting hydrophilic/hydrophobic phase separation and inhibiting excessive swelling of the corresponding AEMs simultaneously. The resulting PTPBHIN-O₁₉ membrane showed a high hydroxide conductivity (151.69 mS cm^-1) and low swelling ratio (10.53%) at 80 °C. Furthermore, owing to the cross-linked structure and ether-free polymer backbone with high alkali resistance, the membranes treated in 3 M NaOH at 80 °C for 1600 h maintained ≥85% of their hydroxide conductivity, indicating excellent alkaline stability. A H₂/O₂ fuel cell based on the PTPBHIN-O₁₉ AEM exhibited a maximum power density of 398 mW cm^-2 at 515 mA cm^-2.