Long side-chain quaternary ammonium group functionalized polybenzimidazole based anion exchange membranes and their applications

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.

Enhanced Vanadium Redox Flow Battery Performance with New Amphoteric Ion Exchange Membranes

Vanadium redox flow batteries (VRFBs) depend on the separator membrane for their efficiency and cycle life. Herein, two amphoteric ion exchange membranes are synthesized, based on sulfonic acid group-grafted poly(p-terphenyl piperidinium), for VRFBs. Using ether-free poly(p-terphenyl piperidine) (PTP) as the polymer matrix, and sodium 2-bromoethanesulphonate (ES) and 1,4-butane sultone (BS) as grafting agents, We achieve quaternization of PTP through an environmentally friendly process without alkaline catalysts. PTP-ES and PTP-BS membranes exhibit low area resistance, high H+ permeability, and significantly reduced vanadium ion permeability, leading to exceptional ion selectivity, which is 3.06 × 106 S min cm-3 and 4.34 × 106 S min cm-3, respectively, three orders of magnitude higher than that of Nafion115 (0.27 × 104 S min cm-3). The VRFB with PTP-BS achieves a self-discharge duration of 190 h, compared to 86 h for Nafion 115. Additionally, under current densities of 40-160 mA cm-2, PTP-BS shows coulombic efficiencies of 98.1-99.1% and energy efficiencies of 92.0-82.1%, outperforming Nafion 115. The VRFB with PTP-BS also demonstrates excellent cycle stability and discharge capacity retention over 300 cycles at 100 mA cm-2. Therefore, the amphoteric PTP-BS membrane shows remarkable performance, offering significant potential for VRFB applications.

Aryl ether-free polymer electrolytes for electrochemical and energy devices

Anion exchange polymers (AEPs) play a crucial role in green hydrogen production through anion exchange membrane water electrolysis. The chemical stability of AEPs is paramount for stable system operation in electrolysers and other electrochemical devices. Given the instability of aryl ether-containing AEPs under high pH conditions, recent research has focused on quaternized aryl ether-free variants. The primary goal of this review is to provide a greater depth of knowledge on the synthesis of aryl ether-free AEPs targeted for electrochemical devices. Synthetic pathways that yield polyaromatic AEPs include acid-catalysed polyhydroxyalkylation, metal-promoted coupling reactions, ionene synthesis via nucleophilic substitution, alkylation of polybenzimidazole, and Diels-Alder polymerization. Polyolefinic AEPs are prepared through addition polymerization, ring-opening metathesis, radiation grafting reactions, and anionic polymerization. Discussions cover structure-property-performance relationships of AEPs in fuel cells, redox flow batteries, and water and CO2 electrolysers, along with the current status of scale-up synthesis and commercialization.