Long-branched and densely functionalized anion exchange membranes for fuel cells

Fluorinated Linkers Enable High-Voltage Pyrrolidinium-based Dicationic Ionic Liquid Electrolytes

Novel fluorinated, pyrrolidinium-based dicationic ionic liquids (FDILs) as high-performance electrolytes in energy storage devices have been prepared, displaying unprecedented electrochemical stabilities (up to 7 V); thermal stability (up to 370 °C) and ion transport (up to 1.45 mS cm-1). FDILs were designed with a fluorinated ether linker and paired with TFSI/FSI counterions. To comprehensively assess the impact of the fluorinated spacer on their electrochemical, thermal, and physico-chemical properties, a comparison with their non-fluorinated counterparts was conducted. With a specific focus on their application as electrolytes in next-generation high-voltage lithium-ion batteries, the impact of the Li-salt on the characteristics of dicationic ILs was systematically evaluated. The incorporation of a fluorinated linker demonstrates significantly superior properties compared to their non-fluorinated counterparts, presenting a promising alternative towards next-generation high-voltage energy storage systems.

New block poly(ether sulfone) based anion exchange membranes with rigid side-chains and high-density quaternary ammonium groups for fuel cell application

We report a series of novel poly(ether sulfone) based anion exchange membranes (AEMs) with relatively good stability due to their rigid side-chains and heterocyclic quaternary ammonium groups. The AEMs show appropriate performance in AEM fuel cells.

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.

Anion Exchange Composite Membranes Composed of Quaternary Ammonium-Functionalized Poly(2,6-dimethyl-1,4-phenylene oxide) and Silica for Fuel Cell Application

Anion exchange membranes (AEMs) with good alkaline stability and ion conductivity are fabricated by incorporating quaternary ammonium-modified silica into quaternary ammonium-functionalized poly(2,6-dimethyl-1,4-phenylene oxide) (QPPO). Quaternary ammonium with a long alkyl chain is chemically grafted to the silica in situ during synthesis. Glycidyltrimethylammoniumchloride functionalization on silica (QSiO₂) is characterized by Fourier transform infrared and transmission electron microscopic techniques. The QPPO/QSiO₂ membrane having an ion exchange capacity of 3.21 meq·g^-1 exhibits the maximum hydration number (λ = 11.15) and highest hydroxide ion conductivity of 45.08 × 10^-2 S cm^-1 at 80 °C. In addition to the high ion conductivity, AEMs also exhibit good alkaline stability, and the conductivity retention of the QPPO/QSiO₂-3 membrane after 1200 h of exposure in 1 M potassium hydroxide at room temperature is about 91% ascribed to the steric hindrance offered by the grafted long glycidyl trimethylammonium chain in QSiO₂. The application of the QPPO/QSiO₂-3 membrane to an alkaline fuel cell can yield a peak power density of 142 mW cm^-2 at a current density of 323 mA cm^-2 and 0.44 V, which is higher than those of commercially available FAA-3-50 Fumatech AEM (OCV: 0.91 V; maximum power density: 114 mW cm^-2 at current density: 266 mA cm^-2 and 0.43 V). These membranes provide valuable insights on future directions for advanced AEM development for fuel cells.

Anion Exchange Membranes Obtained from Poly(arylene ether sulfone) Block Copolymers Comprising Hydrophilic and Hydrophobic Segments

The anion exchange membrane may have different physical and chemical properties, electrochemical performance and mechanical stability depending upon the monomer structure, hydrophilicity and hydrophobic repeating unit, surface form and degree of substitution of functional groups. In current work, poly(arylene ether sulfone) (PAES) block copolymer was created and used as the main chain. After controlling the amount of NBS, the degree of bromination (DB) was changed in Br-PAES. Following that, quaternized PAES (Q-PAES) was synthesized through quaternization. Q-PAES showed a tendency of enhancing water content, expansion rate, ion exchange capacity (IEC) as the degree of substitution of functional groups increased. However, it was confirmed that tensile strength and dimensional properties of membrane reduced while swelling degree was increased. In addition, phase separation of membrane was identified by atomic force microscope (AFM) image, while ionic conductivity is greatly affected by phase separation. The Q-PAES membrane demonstrated a reasonable power output of around 64 mW/cm² while employed as electrolyte in fuel cell operation.

Poly(arylene ether sulfone) crosslinked networks with pillar[5]arene units grafted by multiple long-chain quaternary ammonium salts for anion exchange membranes

For the first time, high-molecular-weight pillar[5]arene-containing aromatic polymers were synthesized and further modified for application as anion exchange membranes.

Partially fluorinated copolymers containing pendant piperidinium head groups as anion exchange membranes for alkaline fuel cells

A new series of partially fluorinated copolymers with varying alkyl side chain length (C3, C6 and C9) and piperidinium head groups have been synthesized and characterized in detail in an effort to improve membrane properties for alkaline fuel cell applications. The copolymers (QPAF4-Cx-pip) provided thin and bendable membranes by solution casting, and achieved high hydroxide ion conductivity up to 97 mS cm⁻¹ in water at 80 °C. Membrane properties such as water absorbability, conductivity, and mechanical properties were tunable with the side chain length. The copolymer main chain and the piperidinium groups were both alkaline stable and the membranes retained high conductivity in 4 M KOH at 80 °C for as long as 1000 h, however, conductivity was lost in 8 M KOH due to Hofmann degradation of the side chain. QPAF4-C3-pip copolymer with the best-balanced properties as anion exchange membrane functioned well in a hydrogen/oxygen alkaline fuel cell to achieve 226 mW cm⁻² peak power density at 502 mA cm⁻² current density under fully humidified conditions with no back pressure.

Piperidinium functionalized partially fluorinated copolymers with varying alkyl spacer length were synthesized and evaluated as anion exchange membranes to achieve improved performance in alkaline fuel cells.