A synthesis study of phosphonated PSEBS for high temperature proton exchange membrane fuel cells

Effect of ionic groups on the morphology and transport properties in a novel perfluorinated ionomer containing sulfonic and phosphonic acid groups: a molecular dynamics study

Combining the phosphonic acid group with the sulfonic acid group in PEMs has been shown to be an effective strategy for improving the fuel cell performance. However, the interplay of two different ionic groups and the resulting effect on the membrane properties have not been fully elucidated. Here, we used classical molecular dynamics simulation to investigate the morphologies, transport properties and effects of ionic groups in a novel perfluorinated PEM containing two ionic groups (PFSA-PFPA) in comparison to the corresponding homopolymers. Phase separations between hydrophilic and hydrophobic domains are confirmed in these PEMs and result from the evolution of water clusters formed around the ionic groups. The combination of both ionic groups brings a complicated morphological feature in PFSA-PFPA, with near-cylindrical aqueous domains of large length scales interconnected by tortuous domains of small sizes. And we found that the self-diffusion coefficients of water molecules are strongly related to morphologies, with the water transport in PFSA-PFPA lying between two analogous homopolymers. At the molecular level, we found that the sulfonic and phosphonic acid groups have distinct effects on the coordination behaviors and the dynamics of water molecules and hydronium ions. Strong electrostatic interactions lead to compact coordination structures and sluggish dynamics of hydronium ions around phosphonic acid groups, which determine the morphological evolution and transport properties in PFSA-PFPA. Our study affords insights into the relationship between molecular characteristics and transport properties bridged by phase-separated morphologies in a novel PEM containing both sulfonic acid and phosphonic acid groups, which deepens the understanding of the interplay between two ionic groups and may inspire the rational design of high-performance PEMs.

Phosphonate poly(vinylbenzyl chloride)-Modified Sulfonated poly(aryl ether nitrile) for Blend Proton Exchange Membranes: Enhanced Mechanical and Electrochemical Properties

Blend proton exchange membranes (BPEMs) were prepared by blending sulfonated poly(aryl ether nitrile) (SPAEN) with phosphorylated poly(vinylbenzyl chloride) (PPVBC) and named as SPM-x%, where x refers to the proportion of PPVBC to the weight of SPAEN. The chemical complexation interaction between the phosphoric acid and sulfonic acid groups in the PPVBC-SPAEN system resulted in BPEMs with reduced water uptake and enhanced mechanical properties compared to SPAEN proton exchange membranes. Furthermore, the flame retardancy of the PPVBC improved the thermal stability of the BPEMs. Despite a decrease in ion exchange capacity, the proton conductivity of the BPEMs in the through-plane direction was significantly enhanced due to the introduction of phosphoric acid groups, especially in low relative humidity (RH) environments. The measured proton conductivity of SPM-8% was 147, 98, and 28 mS cm-1 under 95%, 70%, and 50% RH, respectively, which is higher than that of the unmodified SPAEN membrane and other SPM-x% membranes. Additionally, the morphology and anisotropy of the membrane proton conductivities were analyzed and discussed. Overall, the results indicated that PPVBC doping can effectively enhance the mechanical and electrochemical properties of SPAEN membranes.

Design, Synthesis and Actual Applications of the Polymers Containing Acidic P-OH Fragments: Part 2-Sidechain Phosphorus-Containing Polyacids

Macromolecules containing acidic fragments in side-groups—polyacids—occupy a special place among synthetic polymers. Properties and applications of polyacids are directly related to the chemical structure of macromolecules: the nature of the acidic groups, polymer backbone, and spacers between the main chain and acidic groups. The chemical nature of the phosphorus results in the diversity of acidic >P(O)OH fragments in sidechain phosphorus-containing polyacids (PCPAs) that can be derivatives of phosphoric or phosphinic acids. Sidechain PCPAs have many similarities with other polyacids. However, due to the relatively high acidity of −P(O)(OH)2 fragment, bone and mineral affinity, and biocompatibility, sidechain PCPAs have immense potential for diverse applications. Synthetic approaches to sidechain PCPAs also have their own specifics. All these issues are discussed in the present review.

The Synthesis of Poly(Vinyl Alcohol) Grafted with Fluorinated Protic Ionic Liquids Containing Sulfo Functional Groups

There has been an ongoing need to develop polymer materials with increased performance as proton exchange membranes (PEMs) for middle- and high-temperature fuel cells. Poly(vinyl alcohol) (PVA) is a highly hydrophilic and chemically stable polymer bearing hydroxyl groups, which can be further altered. Protic ionic liquids (proticILs) have been found to be an effective modifying polymer agent used as a proton carrier providing PEMs' desirable proton conductivity at high temperatures and under anhydrous conditions. In this study, the novel synthesis route of PVA grafted with fluorinated protic ionic liquids bearing sulfo groups (-SO₃H) was elaborated. The polymer functionalization with fluorinated proticILs was achieved by the following approaches: (i) the PVA acylation and subsequent reaction with fluorinated sultones and (ii) free-radical polymerization reaction of vinyl acetate derivatives modified with 1-methylimidazole and sultones. These modifications resulted in the PVA being chemically modified with ionic liquids of protic character. The successfully grafted PVA has been characterized using ¹H, ¹⁹F, and ¹³C-NMR and FTIR-ATR. The presented synthesis route is a novel approach to PVA functionalization with imidazole-based fluorinated ionic liquids with sulfo groups.

Polyoxadiazoles as proton exchange membranes for fuel cell application

The number of researches on the ion exchange membrane has increased considerably in recent years showing interest in fuel cell technology for the automobile and portable applications. The most promising fuel cell technology for low-temperature operation (80 °C < T < 150 °C) uses a polymer membrane separating the anode and cathode compartments in an electrochemical cell. Polyoxadiazoles (PODs) belong to a class of heterocyclic polymers, which possess a number of unique properties, such as thermal, mechanical, and chemical resistance. In the present review, numerous ways of POD synthesis are discussed in relation to their functional properties. In addition, different approaches to the elaboration of POD-based composite membranes are discussed in details in order to reveal the structure/properties relationship.

100th Anniversary of Macromolecular Science Viewpoint: Block Copolymers with Tethered Acid Groups: Challenges and Opportunities

Scientific research on advanced polymer electrolytes has led to the emergence of all-solid-state energy storage/transfer systems. Early research began with acid-tethered polymers half a century ago, and research interest has gradually shifted to high-precision polymers with controllable acid functional groups and nanoscale morphologies. Consequently, various self-assembled acid-tethered block polymer morphologies have been produced. Their ion properties are profoundly affected by the multiscale intermolecular interactions in confinements. The creation of hierarchically organized ion/dipole arrangements inside the block copolymer nanostructures has been highlighted as a future method for developing advanced single-ion polymers with decoupled ion dynamics and polymer chain relaxation. Several emerging practical applications of the acid-tethered block copolymers have been explored to draw attention to the challenges and opportunities in developing state-of-the-art electrochemical systems.

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.