Jinhui Pang

Poly(aryl ether ketone) containing flexible tetra-sulfonated side chains as proton exchange membranes

A new difluoride monomer containing electron-rich tetraphenylmethane was designed and synthesized. Based on this monomer along with 4,4′-(hexafluoroisopropylidene)diphenol (6FBPA) and 4,4′-difluorobenzophenone (DFB), a series of tetra-sulfonated poly(aryl ether ketone)s (TS-PAEK-x) were prepared by nucleophilic polycondensation, followed by a sulfonation reaction using chlorosulfonic acid. Tough, flexible, and transparent membranes were obtained by solvent casing. These membranes with ion exchange capacity (IEC) values ranging from 0.85 to 1.43 meq. g−1 exhibited good mechanical properties, excellent dimensional stability, and suitable proton conductivity. The largest swelling ratio (in-plane direction) with a value of 10.3% was observed from TS-PAEK-25 (IEC = 1.43 meq. g−1) membranes at 100 °C, which was much lower than that of Nafion 117 under the same conditions. The highest proton conductivity of 151 mS cm−1 was obtained from the TS-PAEK-25 membrane at 100 °C in the fully hydrated state. Compared to Nafion 117, TS-PAEK-25 with comparable water content exhibited a superior effective proton mobility (μ) value (up to 1.19 × 10−3 cm2 s−1 V−1). Under reduced humidity conditions, TS-PAEK-25 showed desired conductivity considering its lower IEC level. The results indicate that the TS-PAEK-x membranes are promising candidates for application as proton exchange membranes.

Polymer electrolyte membranes based on poly(arylene ether)s with penta-sulfonated pendent groups

The preparation and characterization of new polymeric ionomers based on a fully aromatic poly(arylene ether) backbone with locally pentasulfonated pendent groups for applications as proton exchange membranes is reported. The high molecular weight sulfonated polymers were obtained by the polycondensation of new (2,6-difluorophenyl) (4-(1,2,3,4,5-pentaphenylbenzene)phenyl)methanone, 4,4′-difluorodiphenyl methanone, and 4,4′-dihydroxydiphenylsulfone, followed by sulfonation using sulfuric acid in high yields. The polymers produced tough, flexible, and transparent membranes by solvent casting. Membranes with ion exchange capacities between 0.8 and 1.7 mEq g-1 showed high proton conductivities and low methanol permeabilities. Compared to Nafion 117, these sulfonated membranes exhibited better microphase separation morphologies. The fully humidified membranes also exhibited considerably good mechanical properties, with tensile strengths from 35 to 45 MPa and elongations at break from 23 to 49%. This investigation demonstrates a controllable high density sulfonated side group of a poly(arylene ether sulfone) membrane with tunable and balanced properties, which is promising for proton exchange membrane fuel cell technology.

Synthesis and preparation of sulfonated hyperbranched poly(aryl ether ketone)–sulfonated linear poly(aryl ether ketone) blend membranes for proton exchange membranes

A novel series of sulfonated hyperbranched poly(aryl ether ketone)s (S-HPAEKs) was synthesized based on different post-sulfonation reactions of fluoro-terminated hyperbranched poly(aryl ether ketone). Moreover, the blend membranes of S-HPAEKs with sulfonated linear poly(aryl ether ketone) (S-LPAEK) (S-HPAEK/S-LPAEK) were prepared for proton exchange membrane. All the blends could be cast into tough membranes. The structure of S-HPAEKs was characterized and the thermal stability, water uptake, and proton conductivity of S-HPAEK/S-LPAEK membranes were investigated. The results showed that S-HPAEK/S-LPAEK membranes possessed good thermal stability, better water uptake, and good proton conductivity compared with the S-LPAEK membrane, and their properties depended on the ion exchange capacity and the content of S-HPAEK in the blend membranes.

A Charge-Density-Tunable Three/Two-Dimensional Polymer/Graphene Oxide Heterogeneous Nanoporous Membrane for Ion Transport

The design and fabrication of a robust nanoporous membrane in large scale is still a challenge and is of fundamental importance for practical applications. Here, a robust three/two-dimensional polymer/graphene oxide heterogeneous nanoporous membrane is constructed in large scale via the self-assembly approach by chemically designing a robust charge-density-tunable nanoporous ionomer with uniform pore size. To obtain a nanoporous polymer that maintains high mechanical strength and promotes multifunctionality, we designed a series of amphiphilic copolymers by introducing a positively charged pyridine moiety into the engineered polymer polyphenylsulfone. The multiphysical-chemical properties of the membrane enable it to work as a nanogate switch with synergy between wettability and surface charge change in response to pH. Then we systematically studied the transmembrane ionic transport properties of this two-/three-dimensional porous system. By adjusting the charge density of the copolymer via chemical copolymerization through a controlled design route, the rectifying ratio of this asymmetric membrane could be amplified 4 times. Furthermore, we equipped a concentration-gradient-driven energy harvesting device with this charge-density-tunable nanoporous membrane, and a maximum power of ≈0.76 W m-2 was obtained. We expect this methodology for construction of a charge-density-tunable heterogeneous membrane by chemical design will shed light on the material design, and this membrane may further be used in energy devices, biosensors, and smart gating nanofluidic devices.

Graft octa-sulfonated poly(arylene ether) for high performance proton exchange membrane

A series of octa-sulfonated poly(arylene ether)s (PAEs) was prepared via a low-temperature grafting reaction and subsequent postsulfonation. The rigid backbone with high molecular weight is conducive to higher integrity of the hydrophobic domain. And the grafting ionic clusters are expected to promote the appearance of phase separation. These membranes, with ion exchange capacity (IEC) values ranging from 1.19 to 1.90 meq. g−1, exhibited excellent dimensional stability, mechanical properties and oxidative stability. The membrane with higher IEC (>1.4 meq. g−1) exhibited adequate conductivity (>100 mS cm−1) in water at 80 °C. Furthermore, the membrane with IEC = 1.90 meq. g−1 exhibited comparable conductivity to Nafion 117 under various humidity levels. In addition, SAXS profiles confirmed the well-defined phase-separated morphology of SPAE-x. DMFC single cell performance demonstrates that SPAE-x are good candidates for proton exchange membranes in fuel cell applications.

Synthesis and properties poly(arylene ether sulfone)s with pendant hyper-sulfonic acid

A new class of poly(arylene ether sulfone) with multiple sulfonic acid groups on aromatic side chains (PAES-nS, n = 2 or 3) were prepared from hydroxyphenyl-containing polymer precursors and sulfonated monomer by graft reaction. Those polymers were soluble in the common organic solvents, such as DMAc, DMF, DMSO and NMP, exhibited good thermal stability, the glass transition temperatures ranged from 200 to 240 °C and the 5% weight loss temperatures were higher than 290 °C. Remarkably, all the PAES-nS membranes exhibited high proton conductivity above 10−2 S cm−1 at room temperature, and low swelling ratio below 26% at 80 °C. Compared with Nafion 117, the PAES-3S-40 with high ion exchange capacity (IEC) value (1.89 mequiv. g−1) exhibited higher proton conductivity and appropriate swelling ratio at the same conditions. A combination of good thermal stability, excellent dimensional stability and high proton conductivities indicates these polymers are good candidate materials for proton exchange membrane in fuel cell applications.

Structure–property studies on fluorinated polyimide isomers containing biphenyl moieties

Aimed at clarifying the structure–property relationships of fluorinated high-performance polymers, two series of polyimides were synthesized via a two-step thermal imidization derived from isomeric diamine monomers. Furthermore, comparative studies on their properties including solubility, thermal properties, contact angles, refractive indices, dielectric constants and gas permeability were thoroughly performed. Some property differences of the isomers caused by the sequence changes were found.

High-Performance Semicrystalline Poly(ether ketone)-Based Proton Exchange Membrane

A novel semicrystalline poly(ether ketone) (PEK)-based proton exchange membrane (semi-SPEK-x) has been developed. Through a one-step sulfonation and hydrolysis, a poly(ether ketimine) precursor transforms into PEK and ion-conducting groups are introduced. With an ion-exchange capacity ranging from 1.49 to 2.00 mequiv g-1, the semi-SPEK-x polymers exhibit a semicrystalline feature in both dry and hydrated states. Owing to the semicrystalline domains inside the polymer, the obtained membrane exhibits low water uptake and low volume swelling ratio. More importantly, the semicrystalline structure lowers methanol permeability and, consequently, improves the overall performances of direct methanol fuel cells.

High proton conductivity of sulfonated methoxyphenyl-containing poly(arylene ether ketone) for proton exchange membranes

A series of sulfonated methoxyphenyl-containing poly(arylene ether ketone)s (SMP-PAEKs) were synthesized via polycondensation from 2-(3-methoxy)phenylhydroquinone and other commercial monomers, followed by a postsulfonation approach under mild reaction conditions. Controlled substituted sites and the degree of sulfonation were realized by using various quantities of 2-(3-methoxy)phenylhydroquinone, given that sulfonated polymers (SMP-PAEK) can be soluble in common organic solvents such as DMSO, NMP, and DMAc. The tough and transparent polymer membrane was prepared by a solution casting method, exhibiting excellent mechanical properties and high proton conductivities. The tensile stress at maximum load and elongation at break of these membranes are 30.0–32.4 MPa and 120–171% in a dry state respectively. The proton conductivities of these membranes are higher than that of Nafion 117 in water. In particular, SMP-PAEK-80 with an IEC of 1.62 mequiv. g−1 exhibited the highest proton conductivity of 294 mS cm−1 at 80 °C in water. In addition, SMP-PAEK-90 with an IEC of 1.83 mequiv. g−1 exhibited suitable proton conductivities in different relative humidities (RHs) (30–98%) at 80 °C, which was higher than Nafion 117. The clear micro-phase separation morphology was observed by SAXS, which was powerful evidence to explain their high conductive behaviors. In addition, the current density of the SMP-PAEK-80 membrane was measured to be 235 mA cm−2 at 0.36 voltage (V) under fully hydrated conditions at room temperature with 1.5 bar back pressure during a MEA cell performance test.

Synthesis and characterization of highly branched sulfonated poly(aryl ether ketone) copolymers as proton exchange membranes

Highly branched sulfonated poly(aryl ether ketone) copolymers (Br-SPAEKs) were synthesized based on 4,4′-(hexafluoroisopropylidene) diphenol (A2 monomer), 4,4′-difluorobenzophenone (unsulfonated B2 monomer), 3,3′-disodiumsulfonyl-4,4′-difluorobenzophenone (sulfonated B2 monomer), and 3,4′,5-trifluoro-benzophenone (branched BB2′ monomer). Structures of Br-SPAEKs were confirmed by Fourier transform infrared spectroscopy and nuclear magnetic resonance. Compared to the linear SPAEK (L-SPAEK) copolymer membrane with similar ion exchange capacity, the Br-SPAEK-30 (branched monomer of 20 mol% and sulfonated monomer of 30 mol%) membrane showed higher proton conductivity and lower methanol permeability. This synergistic effect on proton conductivity and methanol permeability was mainly due to the characteristics of large free volume and similar cross-linking architecture arising due to the introduction of the branched monomers. Moreover, the selectivity of the Br-SPAEK-30 membrane is almost three times higher than that of the L-SPAEK membrane. Proton conductivities of Br-SPAEK membranes are higher than 10−2 S cm−1 and increase gradually with increasing temperature. At 80°C, the proton conductivity of the Br-SPAEK-50 (branched monomer of 20 mol% and sulfonated monomer of 50 mol%) membrane reaches 0.127 S cm−1, comparable to that of Nafion-117 (0.139 S cm−1). Additionally, the methanol permeability of Br-SPAEK-50 is one order magnitude lower than that of Nafion-117.