Mechanically Robust Nafion-Based Anhydrous Proton Exchange Membranes with High Proton Conductivity and Efficient In Situ Self-Healing Capacities

There is increasing demand for self-healing high-temperature proton exchange membranes (HT-PEMs) with superior mechanical robustness and proton conductivity. In this study, the fabrication of mechanically robust HT-PEMs (denoted as N-IL-PW) is demonstrated by integrating high proton conductivity and the ability to in situ heal fatigue and damage during operation via the complexation of Nafion, phosphotungstic acid (PW) clusters, and ionic liquids (ILs). Originating from the synergistic effect of high-density electrostatic interactions as well as hydrogen bonds in ionic domains and stable crystalline domains, the N-IL-PW membranes are highly resilient and fatigue resistant, and display excellent creep resistance even at 170 °C. Under an anhydrous condition of ≈170 °C, the N-IL-PW membranes have a high proton conductivity of ≈18.86 mS cm-1. Meanwhile, the hydrogen-powered HT-PEM fuel cells assembled with N-IL-PW membranes exhibit good cell performance under an anhydrous condition of ≈120 °C. More importantly, the reversibility of electrostatic and hydrogen bonding interactions enables the membranes in situ to heal fatigue and mechanical damages under fuel cell operation conditions. Healed membranes can regain their pristine mechanical properties, proton conductivity, hydrogen barrier property, and cell performance. Excellent high-temperature creep resistance, fatigue resistance, and healing capability can work in concert to enhance the reliability of N-IL-PW membranes.

Degradation of a Bipolar Membrane in a Hybrid Acid/Alkali Electrolyzer Studied by X-ray Computed Tomography

The use of a bipolar membrane (BPM) in a hybrid acid/alkali electrolyzer is widely considered as a promising energy technology for efficient hydrogen production. The stability of a BPM is often believed to be largely limited by the anion exchange layer (AEL) due to the hydrophilic attack of AEL polymers by hydroxide groups in alkaline. In this study, we employ X-ray computed tomography (CT) to investigate the degradation behaviors of BPM and found that the cation exchange layer (CEL) experiences more pronounced degradation compared with the AEL during water splitting operations. Despite its chemical stability in both acidic and alkaline environments, the CEL is more prone to electrochemical corrosion under the influence of applied voltages. This susceptibility leads to the formation of micropores and a consequent increase in the porosity. The results of this work provide a new perspective on and highlight the complexity of the degradation behaviors of BPMs in hybrid acid/alkali electrolyzers.

Tetrafluorophenylene-Containing Vinylbenzyl Ether-Terminated Oligo(2,6-dimethyl-1,4-phenylene ether) with Better Thermal, Dielectric, and Flame-Retardant Properties for Application in High-Frequency Communication

In an integrated circuit, signal propagation loss is proportional to the frequency, dissipation factor (D _f), and square root of dielectric constant (D _k). The loss becomes obvious as we move to high-frequency communication. Therefore, a polymer having low D _k and D _f is critical for copper-clad laminates at higher frequencies. For this purpose, a 4-vinylbenzyl ether phenoxy-2,3,5,6-tetrafluorophenylene-terminated OPE (VT-OPE) resin was synthesized and its properties were compared with the thermoset of commercial OPE-2St resin. The thermoset of VT-OPE shows a higher T _g (242 vs 229 °C), a relatively high cross-linking density (1.59 vs 1.41 mmole cm^-3), a lower coefficient of thermal expansion (55 vs 76 ppm/°C), better dielectric characteristic at 10 GHz (D _k values of 2.58 vs 2.75, D _f values of 0.005 vs 0.006), lower water absorption (0.135 vs 0.312 wt %), and better flame retardancy (UL-94 VTM-0 vs VTM-1 with dropping seriously) than the thermoset of OPE-2St. To verify the practicability of VT-OPE for copper-clad laminate, a laboratory process was also performed to prepare a copper-clad laminate, which shows a high peeling strength with copper foil (5.5 lb/in), high thermal reliability with a solder dipping test at 288 °C (>600 s), and the time for delamination of the laminate in thermal mechanical analysis (TMA) at 288 °C is over 60 min.

Composite Anion-Exchange Membrane Fabricated by UV Cross-Linking Vinyl Imidazolium Poly(Phenylene Oxide) with Polyacrylamides and Their Testing for Use in Redox Flow Batteries

Composite anion-exchange membranes (AEMs) consisting of a porous substrate and a vinyl imidazolium poly(phenylene oxide) (VIMPPO)/acrylamide copolymer layer were fabricated in a straightforward process, for use in redox flow batteries. The porous substrate was coated with a mixture of VIMPPO and acrylamide monomers, then subsequently exposed to UV irradiation, in order to obtain a radically cured ion-exchange coating. Combining VIMPPO with low-value reagents allowed to significantly reduce the amount of synthesized ionomer used to fabricate the mem- brane down to 15%. Varying the VIMPPO content also allowed tuning the ionic transport properties of the resulting AEM. A series of membranes with different VIMPPO/acrylamides ratios were prepared to assess the optimal composition by studying the changes of membranes properties-water uptake, area resistivity, permeability, and chemical stability. Characterization of the membranes was followed by cycling experiments in a vanadium RFB (VRFB) cell. Among three composite membranes, the one with VIMPPO 15% w/w-reached the highest energy efficiency (75.1%) matching the performance of commercial ion-exchange membranes (IEMs) used in VRFBs (Nafion® N 115: 75.0% and Fumasep® FAP 450: 73.0%). These results showed that the proposed composite AEM, fabricated in an industrially oriented process, could be considered to be a lower-cost alternative to the benchmarked IEMs.

Dually cross-linked single networks: structures and applications

Cross-linked polymers have attracted an immense attention over the years, however, there are many flaws of these systems, e.g. softness and brittleness; such materials possess non-adjustable properties and cannot recover from damage and thus are limited in their practical applications. Supramolecular chemistry offers a variety of dynamic interactions that when integrated into polymeric gels endow the systems with reversibility and responsiveness to external stimuli. A combination of different cross-links in a single gel could be the key to tackle these drawbacks, since covalent or chemical cross-linking serve to maintain the permanent shape of the material and to improve overall mechanical performance, whereas non-covalent cross-links impart dynamicity, reversibility, stimuli-responsiveness and often toughness to the material. In the present review we sought to give a comprehensive overview of the progress in design strategies of different types of dually cross-linked single gels made by researchers over the past decade as well as the successful implementations of these advances in many demanding fields where versatile multifunctional materials are required, such as tissue engineering, drug delivery, self-healing and adhesive systems, sensors as well as shape memory materials and actuators.

Advancements in proton exchange membranes for high-performance high-temperature proton exchange membrane fuel cells (HT-PEMFC)

The high-temperature proton exchange membrane fuel cell (HT-PEMFC) offers several advantages, such as high proton conductivity, high CO tolerance, good chemical/thermal stability, good mechanical properties, and low cost. The proton exchange membrane (PEM) is the critical component of HT-PEMFC. This work discusses the methods of current PEMs development for HT-PEMFC including modifications of Nafion® membranes and the advancement in composite PEMs based on non-fluorinated polymers. The modified Nafion®-based membranes can be used at temperatures up to 140 °C. Nevertheless, the application of Nafion®-based membranes is limited by their humidification with water molecules acting as proton carriers and, thus, by the operation conditions of membranes under a relative humidity below 20%. To obtain PEMs applied at higher temperatures under non-humidified conditions, phosphoric acid (PA) or ionic liquids (ILs) are used as proton carriers in PEMs based on non-fluorinated polymers. The research discussed in this work provides the approaches to improving the physicochemical properties and performance fuel cell of PEMs. The effects of polymer blending, crosslinking, and the incorporation of inorganic particles on the membrane properties and fuel cell performance have been scrutinized. The incorporation of inorganic particles modified with ILs might be an effective approach to designing high-performance PEMs for HT-PEMFC.

Micro-block versus random quaternized poly(arylene ether sulfones) with highly dense quaternization units for anion exchange membranes

A systematic study was carried out to investigate the effect of different distributions of conducting groups in segments for poly(arylene ether sulfone)s.