Pendant-group cross-linked highly sulfonated co-polyimides for proton exchange membranes

Sulfonated Polyimide Membranes Constructed by Main-Chain and Molecular-Network Engineering Strategy for Direct Methanol Fuel Cell

Excessive swelling is one important factor that leads to high fuel permeability and limited operating concentration of methanol for proton exchange membranes. Herein, a collaborative strategy of main-chain and molecular-network engineering is applied to lower swelling ratio and improve methanol resistance for highly sulfonated polyimide. Two m-phenylenediamine monomers (4-(2,3,5,6-tetrafluoro-4-vinylphenoxy)benzene-1,3-diamine and 4,6-bis(2,3,5,6-tetrafluoro-4-vinylphenoxy)benzene-1,3-diamine) with tetrafluorostyrol groups are designed and synthesized. Two series of cross-linked sulfonated polyimides (CSPI-Ts, CSPI-Bs) are prepared from the two diamines, 4,4'-diaminostilbene-2,2'-disulfonic acid and 1,4,5,8-naphthalenetetracarboxylicdianhydride. The rigid main-chain structure is cornerstone for wet CSPI-Ts and CSPI-Bs remaining stable at elevated temperatures. The introduction of hydrophobic cross-linked network further improves their dimensional stability and methanol resistance. CSPI-Ts and CSPI-Bs show obviously improved performances containing high proton conductivity (121 ± 0.27-158 ± 0.35 S cm-1 ), low swelling ratio (9.6 ± 0.40%-16.1 ± 0.01%) and methanol permeability (4.14-7.69 × 10-7 cm2 s-1 ) at 80 °C. The direct methanol fuel cell (DMFC) is assembled from CSPI-T-10 with balanced properties, and it exhibits high maximum power density (PDmax ) of 82.3 and 72.6 mW cm-2 in 2 and 10 m methanol solution, respectively. The ratio of PDmax in 10 m methanol solution to the value in 2 m methanol solution is as high as 88%. The CSPI-T-10 is promising proton exchange membrane candidate for DMFC application.

Tuning Alkaline Anion Exchange Membranes through Crosslinking: A Review of Synthetic Strategies and Property Relationships

Alkaline anion exchange membranes (AAEMs) are an enabling component for next-generation electrochemical devices, including alkaline fuel cells, water and CO2 electrolyzers, and flow batteries. While commercial systems, notably fuel cells, have traditionally relied on proton-exchange membranes, hydroxide-ion conducting AAEMs hold promise as a method to reduce cost-per-device by enabling the use of non-platinum group electrodes and cell components. AAEMs have undergone significant material development over the past two decades; however, challenges remain in the areas of durability, water management, high temperature performance, and selectivity. In this review, we survey crosslinking as a tool capable of tuning AAEM properties. While crosslinking implementations vary, they generally result in reduced water uptake and increased transport selectivity and alkaline stability. We survey synthetic methodologies for incorporating crosslinks during AAEM fabrication and highlight necessary precautions for each approach.

Microporous polyimides with high surface area and CO2 selectivity fabricated from cross-linkable linear polyimides

Linear polyimides of intrinsic microporosity have been intensively investigated for gas separation due to their microporous structure and high surface area. The microporous structure in the linear polyimides of intrinsic microporosity comes from their contorted structure. Therefore, most linear polyimides without contorted structure do not have micropores. In this work, the microporous polyimides are constructed through the condensation of a cross-linkable dianhydride monomer with two novel nitrogen-rich diamine monomers and post crosslinking reaction. The linear polyimide precursors without contorted structure have the same main-chain structure. The introduction of crosslinked structure endow the crosslinked polyimides (PI-CLs) with microporous structure. The microporous structure in PI-CLs can be tuned by changing the substituents of the linear polyimide precursors. The PI-CLs have competitive CO₂ uptake capacity (7.3-9.4 wt%) at 273 K and 1 bar. Particularly, the crosslinked polyimide containing trifluoromethyl groups (CF₃-PI-CL) shows high CO₂/N₂ and CO₂/CH₄ selectivity (72 and 22) at 273 K, which are among the best results for reported porous materials. This work reveals that the introduction of crosslinked structure and changing substituents is an efficient method for constructing microporous polyimides with abundant micropores and excellent CO₂ selective adsorption capacity. This method also has great potential for fabricating high-performance microporous polymers based on other linear polymers without rigid contorted structure.

Preparation of Covalent-Ionically Cross-Linked UiO-66-NH2/Sulfonated Aromatic Composite Proton Exchange Membranes With Excellent Performance

Metal-organic frameworks (MOFs), as newly emerging filler materials for polyelectrolytes, show many compelling intrinsic features, such as variable structural designability and modifiability of proton conductivity. In this manuscript, UiO-66-NH₂, a stable MOF with -NH₂ functional groups in its ligands, was selected to achieve a high-performance sulfonated poly(arylene ether nitrile)s (SPENs)/UiO-66-NH₂-x covalent-ionically cross-linked composite membrane. Simultaneously, the obtained composite membranes displayed excellent thermal stability and dimensional stability. The as-prepared SPEN/UiO-66-NH₂-x cross-linked membranes exhibited higher proton conductivity than recast SPENs, which can be attributed to the construction of ionic clusters and well-connected ionic nanochannels along the interface between UiO-66-NH₂-x and SPEN matrix via molecular interactions. Meanwhile, the methanol permeability of the SPEN/UiO-66-NH₂-x composite membrane had been effectively reduced due to the barrier effect of cross-linking and the addition of UiO-66-NH₂-x. The SPEN/UiO-66-NH₂-5 composite membrane had the highest selectivity of 6.42 × 10⁵ S·s·cm⁻³: 14.3-times higher than that of Nafion 117. The preparation of cross-linked UiO-66-NH₂/SPEN composite was facile, which provides a new strategy for preparing high performance proton exchange membrane.

Preparation of Graft Poly(Arylene Ether Sulfone)s-Based Copolymer with Enhanced Phase-Separated Morphology as Proton Exchange Membranes via Atom Transfer Radical Polymerization

Novel proton exchange membranes (PEMs) based on graft copoly(arylene ether sulfone)s with enhanced phase-separated morphology were prepared using atom transfer radical polymerization (ATRP). A series of PEMs with different graft lengths and sulfonation degrees were prepared. The phase-separated morphologies were confirmed by transmission electron microscopy. Among the membranes prepared and evaluated, PAESPS18S2 exhibited considerably high proton conductivity (0.151 S/cm, 85 °C), benefitting from the graft polymer architecture and phase-separated morphology. The membranes also possessed excellent thermal and chemical stabilities. Highly conductive and stable copoly(arylene ether sulfone)-based membranes would be promising candidates as polymer electrolytes for fuel cell applications.

Synthesis and Characterization of Highly Proton Conducting Sulfonated Polytriazoles

This article describes the synthesis and characterization of highly sulfonated polytriazole copolymers (PTSQSH-I to IV) with IEC_w values ranging from 2.41 to 3.49 mequiv g^-1. The copolymers were synthesized by click reaction between equimolar amount of a dialkyne monomer, potassium 2,5-bis(2-propyn-1-yloxy)benzenesulfonate, and a mixture of two different diazide monomers, 4,4-bis[3'-trifluoromethyl-4'(4-azidobenzoxy)benzyl]biphenyl and 4,4'-diazido-2,2'-stilbene disulfonic acid disodium salt. The copolymers were characterized by Fourier transform infrared and NMR spectroscopy techniques. The membranes were prepared by dissolving the salt form of the copolymers in dimethyl sulfoxide. The copolymers showed high thermal, mechanical, and oxidative stabilities, and the acidified membranes showed very high proton conductivity (43-173 and 132-304 mS cm^-1 at 30 and 80 °C, respectively). Transmission electron microscopy images confirmed the formation of well-phase-separated morphology with interconnected hydrophilic domains (20-150 nm).

New sulfonated copoly(triazole imide)s synthesized by a click chemistry reaction with improved oxidative stability

New sulfonated copoly(triazole imide)s synthesized by a click chemistry reaction with improved oxidative stability.

Phosphine oxide based polyimides: structure–property relationships

The PI flame retardance has been influenced by the variation of flexible segments leading to a reduction of THR.

Direct polymerization of novel functional sulfonated poly(arylene ether ketone sulfone)/sulfonated poly(vinyl alcohol) with high selectivity for fuel cells

The acid–base pairs (–SO₃H⋯H₂N–) formed between –SO₃H and –NH₂ can promote protons transport.

Highly sulfonated co-polyimides containing hydrophobic cross-linked networks as proton exchange membranes

The cross-linked highly sulfonated co-polyimides based on novel diamine monomer containing double hydrophobic cross-linkable tetrafluorostyrol side-groups showed improved enhanced dimensional stability and superior proton conductivity.

Synthesis and properties of sulfonated poly(arylene ether ketone sulfone) copolymer

A series of novel sulfonated poly(arylene ether ketone sulfone)s copolymer (SPAEKS- x) were synthesized by polycondensation reaction of commercial 2,2-bis(4-hydroxyphenyl)propane, 4,4′-dichlorodiphenylsulfone, 4,4′-dihydroxydiphenylether, and 3,3′disulfonate-4,4′-difluorobenzophenone. The degree of sulfonation was realized by controlling quantities of the sulfonated monomer. The structure of SPAEKS- x was confirmed by proton nuclear magnetic resonance and Fourier transform infrared instrument. The tough, flexible, and transparent films of SPAEKS- x were obtained by solution casting. These membranes with desired ion-exchange capacity (IEC) values showed good thermal stability and mechanical properties. The proton conductivity of SPAEKS- x with the IEC of 1.44 meq. g−1 is very close to that of Nafion 117 in a temperature range from 20°C to 100°C. SPAEKS- x copolymers, which combine the advantages of the sufficiently high proton transport conductivity and enhanced physical properties, will be the potential alternative materials to Nafion for proton exchange membrane fuel cell.