Polymer electrolyte membranes based on cross-linked highly sulfonated co-polyimides

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.

Branched Poly(arylene ether ketone sulfone)s with Ultradensely Sulfonated Branched Centers for Proton Exchange Membranes: Effect of the Positions of the Sulfonic Acid Groups

Branched sulfonated polymers present considerable potential for application as proton exchange membranes, yet investigation of branched polymers containing sulfonated branched centers remains to be advanced. Herein, we report a series of polymers with ultradensely sulfonated branched centers, namely, B-x-SPAEKS, where x represents the degree of branching. In comparison with the analogous polymers bearing sulfonated branched arms, B-x-SPAEKS showed a reduced water affinity, resulting in less swelling and lower proton conductivity. The water uptake, swelling ratio (in-plane), and proton conductivity of B-10-SPAEKS at 80 °C were 52.2%, 57.7%, and 23.6% lower than their counterparts, respectively. However, further analysis revealed that B-x-SPAEKS featured significantly better proton conduction under the same water content due to the formation of larger hydrophilic clusters (∼10 nm) that promoted efficient proton transportation. B-12.5-SPAEKS exhibited a proton conductivity of 138.8 mS cm^-1 and a swelling ratio (in-plane) of only 11.6% at 80 °C, both of which were superior to Nafion 117. In addition, a decent single-cell performance of B-12.5-SPAEKS was also achieved. Consequently, the decoration of sulfonic acid groups on the branched centers represents a very promising strategy, enabling outstanding proton conductivity and dimensional stability simultaneously even with low water content.

Sulfonated co‐poly(ether imide)s with alkyne groups: Fabrication of crosslinked membranes and studies on PEM properties including MFC performance

A new diamine monomer having alkyne side‐groups (DADAF) has been successfully synthesized, and it was used to prepare a series of sulfonated co‐polyimides (DFN‐XX) when reacted with 1,4,5,8‐naphthalenetetracarboxylic dianhydride along with different mole% of 4,4′‐diaminostilbene‐2,2′‐disulfonic acid. The membrane was made from the copolymers by solution casting route, and one of the copolymers DFN‐70 was used to prepare crosslinked membranes by adding a different amount of 1,6‐hexanediazide during solution casting step. The morphological transformation from non‐crosslinked S‐coPI to crosslinked S‐coPI was observed by employing transmission electron microscopy, atomic force microscopy, and small‐angle X‐ray scattering analyses. Compared to the non‐crosslinked DFN‐XX membranes, crosslinked DFN‐70 copolymer membranes showed low water uptake and improved mechanical and peroxide radical stability. Also, crosslinked DFN‐70 copolymer membranes showed significantly higher proton conductivities (0.004‐0.06 S cm−1) compared to those of DFN‐70 (0.003‐0.05 S cm−1) particularly, at 80°C when the relative humidity increased from 40% to 98%. Furthermore, crosslinked DFN‐70 copolymer membranes exhibited significantly enhanced performance in a microbial fuel cell (MFC) as compared to those of non‐crosslinked DFN‐70 membrane.

The design, preparation, and properties of dual-crosslinking copolymerized systems based on hemp oil

Novel, dual-crosslinking, resin monomers of MAHHAGMA and HHAGE were synthesized using hemp oil.

Proton-conducting poly(ether sulfone ketone)s containing a high density of pendant sulfonic groups by a convenient and mild post-sulfonation

A class of new poly(ether sulfone ketone)s containing a high density of pendant sulfonic groups on the sulfonated structural units were designed and the resulting membranes exhibited overall good performance at low IEC levels.