Effect of the Hydrophobic Component on the Properties of Sulfonated Poly(arylene ether sulfone)s

Preparation of Sulfonated Poly(arylene ether)/SiO2 Composite Membranes with Enhanced Proton Selectivity for Vanadium Redox Flow Batteries

Proton exchange membranes (PEMs) are an important type of vanadium redox flow battery (VRFB) separator that play the key role of separating positive and negative electrolytes while transporting protons. In order to lower the vanadium ion permeability and improve the proton selectivity of PEMs for enhancing the Coulombic efficiency of VRFBs, herein, various amounts of nano-sized SiO2 particles were introduced into a previously optimized sulfonated poly(arylene ether) (SPAE) PEMs through the acid-catalyzed sol-gel reaction of tetraethyl orthosilicate (TEOS). The successful incorporation of SiO2 was confirmed by FT-IR spectra. The scanning electron microscopy (SEM) images revealed that the SiO2 particles were well distributed in the SPAE membrane. The ion exchange capacity, water uptake, and swelling ratio of the PEMs were decreased with the increasing amount of SiO2, while the mechanical properties and thermal stability were improved significantly. The proton conductivity was reduced gradually from 93.4 to 76.9 mS cm−1 at room temperature as the loading amount of SiO2 was increased from 0 to 16 wt.%; however, the VO2+ permeability was decreased dramatically after the incorporation of SiO2 and reached a minimum value of 2.57 × 10−12 m2 s−1 at 12 wt.% of SiO2. As a result, the H+/VO2+ selectivity achieved a maximum value of 51.82 S min cm−3 for the composite PEM containing 12 wt.% of SiO2. This study demonstrates that the properties of PEMs can be largely tuned by the introduction of SiO2 with low cost for VRFB applications.

Multi-Block Copolymer Membranes Consisting of Sulfonated Poly(p-Phenylene) and Naphthalene Containing Poly(Arylene Ether Ketone) for Proton Exchange Membrane Water Electrolysis

Glassy hydrocarbon-based membranes are being researched as a replacement for perfluorosulfonic acid (PFSA) membranes in proton exchange membrane water electrolysis (PEMWE). Here, naphthalene containing poly(arylene ether ketone) was introduced into the poly(p-phenylene)-based multi-block copolymers through Ni(0)-catalyzed coupling reaction to enhance π-π interactions of the naphthalene units. It is discovered that there is an optimum input ratio of the hydrophilic monomer and NBP oligomer for the multi-block copolymers with high ion exchange capacity (IEC) and polymerization yield. With the optimum input ratio, the naphthalene containing copolymer exhibits good hydrogen gas barrier property, chemical stability, and mechanical toughness, even with its high IEC value over 2.4 meq g−1. The membrane shows 3.6 times higher proton selectivity to hydrogen gas than Nafion 212. The PEMWE single cells using the membrane performed better (5.5 A cm−2) than Nafion 212 (4.75 A cm−2) at 1.9 V and 80 °C. These findings suggest that naphthalene containing copolymer membranes are a promising replacement for PFSA membranes in PEMWE.

Ameliorated Performance of Sulfonated Poly(Arylene Ether Sulfone) Block Copolymers with Increased Hydrophilic Oligomer Ratio in Proton-Exchange Membrane Fuel Cells Operating at 80% Relative Humidity

We designed and synthesized a series of sulfonated poly(arylene ether sulfone) (SPES) with different hydrophilic or hydrophobic oligomer ratios using poly-condensation strategy. Afterward, we fabricated the corresponding membranes via a solution-casting approach. We verified the SPES membrane chemical structure using nuclear magnetic resonance (¹H NMR) and confirmed the resulting oligomer ratio. Field-emission scanning electron microscope (FE-SEM) and atomic force microscope (AFM) results revealed that we effectively attained phase separation of the SPES membrane along with an increased hydrophilic oligomer ratio. Thermal stability, glass transition temperature (T_g) and membrane elongation increased with the ratio of hydrophilic oligomers. SPES membranes with higher hydrophilic oligomer ratios exhibited superior water uptake, ion-exchange capacity, contact angle and water sorption, while retaining reasonable swelling degree. The proton conductivity results showed that SPES containing higher amounts of hydrophilic oligomers provided a 74.7 mS cm⁻¹ proton conductivity at 90 °C, which is better than other SPES membranes, but slightly lower than that of Nafion-117 membrane. When integrating SPES membranes with proton-exchange membrane fuel cells (PEMFCs) at 60 °C and 80% relative humidity (RH), the PEMFC power density exhibited a similar increment-pattern like proton conductivity pattern.

Synthesis and investigation of sulfonated poly(p-phenylene)-based ionomers with precisely controlled ion exchange capacity for use as polymer electrolyte membranes

To achieve precise control of sulfonated polymer structures, a series of poly(p-phenylene)-based ionomers with well-controlled ion exchange capacities (IECs) were synthesised via a three-step technique: (1) preceding sulfonation of the monomer with a protecting group, (2) nickel(0) catalysed coupling polymerisation, and (3) cleavage of the protecting group of the polymers. 2,2-Dimethylpropyl-4-[4-(2,5-dichlorobenzoyl)phenoxy]benzenesulfonate (NS-DPBP) was synthesised as the preceding sulfonated monomer by treatment with chlorosulfuric acid and neopentyl alcohol. NS-DPBP was readily soluble in various organic solvents and stable during the nickel(0) catalysed coupling reaction. Sulfonated poly(4-phenoxybenzoyl-1,4-phenylene) (S-PPBP) homopolymer and seven types of random copolymers (S-PPBP-co-PPBP) with different IECs were obtained by varying the stoichiometry of NS-DPBP. The IECs and weight average molecular weights (M_ws) of ionomers were in the range of 0.41–2.84 meq. g⁻¹ and 143 000–465 000 g mol⁻¹, respectively. The water uptake, proton conductivities, and water diffusion properties of ionomers exhibited a strong IEC dependence. Upon increasing the IEC of S-PPBP-co-PPBPs from 0.86 to 2.40 meq. g⁻¹, the conductivities increased from 6.9 × 10⁻⁶ S cm⁻¹ to 1.8 × 10⁻¹ S cm⁻¹ at 90% RH. S-PPBP and S-PPBP-co-PPBP (4 : 1) with IEC values >2.40 meq. g⁻¹ exhibited fast water diffusion (1.6 × 10⁻¹¹ to 8.0 × 10⁻¹⁰ m² s⁻¹), and were comparable to commercial perfluorosulfuric acid polymers. When fully hydrated, the maximum power density and the limiting current density of membrane electrode assemblies (MEAs) prepared with S-PPBP-co-PPBP (4 : 1) were 712 mW cm⁻² and 1840 mA cm⁻², respectively.

Poly(p-phenylene)-based sulfonated polymers with well-controlled IECs were synthesized via a three-step procedure including preceding sulfonation of precursor monomers.

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).

Considerations of the Effects of Naphthalene Moieties on the Design of Proton-Conductive Poly(arylene ether ketone) Membranes for Direct Methanol Fuel Cells

Novel sulfonated poly(arylene ether ketones) (SDN-PAEK-x), consisting of dual naphthalene and flexible sulfoalkyl groups, were prepared via polycondensation, demethylation, and sulfobutylation grafting reaction. Among them, SDN-PAEK-1.94 membrane with the highest ion exchange capacity (IEC = 2.46 mequiv·g(-1)) exhibited the highest proton conductivity, which was 0.147 S· cm(-1) at 25 °C and 0.271 S·cm(-1) at 80 °C, respectively. The introduction of dual naphthalene moieties is expected to achieve much enhanced properties compared to those of sulfonated poly(arylene ether ketones) (SNPAEK-x), consisting of single naphthalene and flexible sulfoalkyl groups. Compared with SNPAEK-1.60 with a similar IEC, SDN-PAEK-1.74 membrane showed higher proton conductivity, higher IEC normalized conductivity, and higher effective proton mobility, although it had lower analytical acid concentration. The SDN-PAEK-x membranes with IECs higher than 1.96 mequiv·g(-1) also exhibited higher proton conductivity than that of recast Nafion membrane. Furthermore, SDN-PAEK-1.94 displayed a better single cell performance with a maximum power density of 60 mW·cm(-2) at 80 °C. Considering its high proton conductivity, excellent single cell performance, good mechanical stabilities, low membrane swelling, and methanol permeability, SDN-PAEK-x membranes are promising candidates as alternative polymer electrolyte membranes to Nafion for direct methanol fuel cell applications.

New sulfonated poly(arylene ether sulfone) copolymers containing phenyl side chains as proton exchange membranes

The chemical structure and phase images of the SPAES-PQ-40 membrane.