Sinan Feng

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.

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

A novel diamine monomer bearing double hydrophobic cross-linkable tetrafluorostyrol side-groups has been successfully synthesized. Based on this monomer along with 4,4′-diaminodiphenyl ether-2,2′-disulfonic acid (ODADS) and 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), a series of cross-linked highly sulfonated co-polyimide (CSPIy-6FATFVPx) membranes with IEC values ranging from 2.07 to 2.41 meq g−1 were prepared via a high temperature poly-condensation, followed by a thermal cross-linking reaction. The SPI were synthesized by high temperature polymerization. The CSPI membranes were obtained from the SPI membrane by thermal crosslinking reation. The polymerization and crosslinking reation were not performed in one pot. The CSPIy-6FATFVPx membranes showed significantly excellent performance, especially the high proton conductivity (0.153–0.210 S cm−1 at 80 °C), low water uptake (54.1%–87.1% at 80 °C) and swelling ratio (15.5%–23.0% at 80 °C). Furthermore, the CSPIy-6FATFVPx membranes also exhibited outstanding thermal stability (5% weight loss when the temperature exceed 320 °C), excellent hydrolytic stability and mechanical properties. The results indicate that CSPIy-6FATFVPx are promising candidates as proton exchange membranes in fuel cell technology.

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.