Metallo-Polyelectrolyte-Based Robust Anion Exchange Membranes via Acetalation of a Commodity Polymer

Anion Exchange Membranes with Tuned Hydrophilic-Hydrophobic Phase Separation for Efficient Ion Transportation

The development of high-performance anion exchange membranes (AEMs) remains a major challenge in commercializing alkaline fuel cells. Significant efforts have been directed toward enhancing the ionic conductivity, mechanical strength, and alkaline stability of AEMs. Among various strategies, modifying commercially available polymers has emerged as an effective and straightforward approach. In this work, we focused on fabricating an eco-friendly polymer membrane using poly(vinyl alcohol) (PVA). Specifically, two polymer membranes, poly[vinyl alcohol-co-4-(1-methylpiperidinium iodide) benzylidene acetal] (PVA-PB-MI) and poly[vinyl alcohol-co-4,4'-(1,6-hexanediylbis(1-piperidinium) benzylidene acetal) dibromide] (PVA-PB-DBH), were synthesized through the acetylation of PVA with 4-(1-piperidinyl)benzaldehyde, followed by quaternization using methyl iodide and 1,6-dibromohexane. Structural confirmation of the synthesized membranes was carried out using 1H NMR and FTIR spectroscopy. The resulting cross-linked PVA-PB-DBH membrane exhibited superior hydroxide ion conductivity that reached 72.5 mS cm-1 at 90 °C and maintained lower water uptake and swelling ratio in comparison to those of non-cross-linked PVA-PB-MI, which displayed a conductivity of 49.7 mS cm-1. The reduced water uptake and improved ion conductivity of the cross-linked membrane were due to the hydrophobic nature and microphase separation within the polymer matrix, which was confirmed by contact angle and atomic force microscopy (AFM) analysis. A theoretical study of the alkaline stability of polymer membranes was carried out by using density functional theory (DFT).

Metallo-Polyampholyte Hydrogel Based on a Y-Shaped Amphoteric Monomer with Robust Antibacterial and Antifouling Performance

A Y-shaped metallo-amphoteric monomer with cobaltocenium as the cation and sulfonyl as the anion was synthesized and used to prepare the corresponding metallo-polyampholyte hydrogel (PAH). The cobaltocenium in the amphoteric system and its Y-shape may introduce tunable supramolecular interactions, providing regulation of hydration properties and biomedical performance. Such metallo-PAH showed a higher water swelling ratio and comparable mechanical performance in comparison with its organic counterpart, polysulfobetaine methacrylate hydrogel (SBMA-PAH). Moreover, the metallo-PAH showed a good inhibitory effect against Gram-negative bacteria, Gram-positive bacteria, as well as corresponding drug-resistant bacteria. Interestingly, it was found that the metallo-PAH achieved as high as 95% antifouling property against different proteins in both short-term (2 h) and long-term (24 h) tests, which is much better than that of the SBMA-PAH (<50%). It is believed that the concept of "metallo-polyampholyte" may expand the field of classical polyampholytes and related materials, thus opening up a new avenue to design powerful antifouling materials.

Diamine Crosslinked Addition-Type Diblock Poly(Norbornene)s-Based Anion Exchange Membranes with High Conductivity and Stability for Fuel Cell Applications

Anion exchange membranes (AEMs) as a kind of important functional material are widely used in fuel cells. However, synthetic AEMs generally suffer from low conductivity, poor alkaline stability, and poor dimensional stability. Constructing efficient ion transport channels is widely regarded as one of the most effective strategies for developing AEMs with high conductivity and low swelling ratio. Herein we demonstrate a versatile strategy to prepare the AEMs with both high conductivity and excellent alkali stability via all-carbon hydrogen block copolymer backbone hydrophilic crosslinking and introducing flexible alkoxy spacer chains. Additionally, we investigated the impact of the crosslinking degree on the AEMs' performances. It was found that the dosage of the hydrophilic crosslinker has a significant impact on the construction of efficient ion transport channels in the AEMs. Amazingly, the CL30-aPNB-TMHDA-TMA exhibited the highest hydroxide conductivity (138.84 mS cm-1), reasonable water uptake (54.96%), and a low swelling ratio (14.07%) at 80 °C. Meanwhile, the membrane showed an excellent alkaline stability in a 1 M NaOH solution at 80 °C for 1008 h (ion exchange capacity (IEC) and OH- conductivity remained at 91.9% and 89.12%, respectively). The single cells assembled with CL30-aPNB-TMHDA-TMA exhibited a peak power density of 266.2 mW cm-2 under a current density of 608 mA cm-2 at 80 °C. The novel developed composite strategy of flexible alkoxy side chains with hydrophilic crosslinking modification is potentially promised to be an effective approach to develop the high-performance AEMs.

Theoretical Examination of the Hydroxide Transport in Cobaltocenium-Containing Polyelectrolytes

Polymers incorporating cobaltocenium groups have received attention as promising components of anion-exchange membranes (AEMs), exhibiting a good balance of chemical stability and high ionic conductivity. In this work, we analyze the hydroxide diffusion in the presence of cobaltocenium cations in an aqueous environment based on the molecular dynamics of model systems confined in one dimension to mimic the AEM channels. In order to describe the proton hopping mechanism, the forces are obtained from the electronic structure computed at the density-functional tight-binding level. We find that the hydroxide diffusion depends on the channel size, modulation of the electrostatic interactions by the solvation shell, and its rearrangement ability. Hydroxide diffusion proceeds via both the vehicular and structural diffusion mechanisms with the latter playing a larger role at low diffusion coefficients. The highest diffusion coefficient is observed under moderate water densities (around half the density of liquid water) when there are enough water molecules to form the solvation shell, reducing the electrostatic interaction between ions, yet there is enough space for the water rearrangements during the proton hopping. The effects of cobaltocenium separation, orientation, chemical modifications, and the role of nuclear quantum effects are also discussed.

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.

A Brief Review of Poly(Vinyl Alcohol)-Based Anion Exchange Membranes for Alkaline Fuel Cells

Anion exchange membrane fuel cells have unique advantages and are thus gaining increasing attention. Poly(vinyl alcohol) (PVA) is one of the potential polymers for the development of anion exchange membranes. This review provides recent studies on PVA-based membranes as alternative anion exchange membranes for alkaline fuel cells. The development of anion exchange membranes in general, including the types, materials, and preparation of anion exchange membranes in the last years, are discussed. The performances and characteristics of recently reported PVA-based membranes are highlighted, including hydroxide conductivity, water uptake, swelling degree, tensile strength, and fuel permeabilities. Finally, some challenging issues and perspectives for the future study of anion exchange membranes are discussed.