A Maximization of the Proton Conductivity of Sulfonated Poly(Ether Ether Ketone) with Grafted Segments Containing Multiple, Flexible Propanesulfonic Acid Groups

Fabrication of a High Proton-Conducting Sulfonated Fe-Metal Organic Framework-Polytriazole Composite Membranes: Study of Proton Exchange Membrane Properties

A series of hybrid composite membranes including polymer-metal-organic frameworks (MOFs), are synthesized using sulfonated Fe-MOF and sulfonated polytriazole (PTSF). After being post-modified by 1,3-propane sultone, the obtained Fe-S MOF is incorporated into the polytriazole polymer matrix through the solution blending method. Additionally, a series of polytriazole with a degree of sulfonation of 60 is prepared, with the percentage of the Fe-S MOF ranging from 3 to 9 weight percent. A comparison is made between the properties of these hybrid membranes and those of the pristine membranes. The hybrid membranes demonstrate a high degree of solubility in every solvent that is employed. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) confirm that the MOF is distributed uniformly throughout the polymer matrix. Moreover, well-separated morphologies are confirmed by transmission electron microscopy (TEM). The prepared hybrid membranes demonstrate enhanced proton conductivities, water absorption, and swelling, all of which are accomplished without influencing the oxidative stability values.

Dual Free Radical Synergism for Enhancing Proton Conductivity in Photochromism iHOFs

Stimuli-responsive smart materials, as an emerging material, can fulfill reversible transformation of chemical/physical properties under external stimuli such as mechanical stress, light, and electricity, which has the highlights of rapid response, designable structure, and function. Two ionic hydrogen-bonded organic frameworks (iHOFs 36-37) were synthesized by self-assembly of bis(benzene-o/p-sulfonic acid)-naphthalenediimide (o/p-H2BSNDI) and two basic ligands. The naphthalenediimide (NDI) was introduced into the material to equip iHOFs 36-37 with radical-driven photochromic behavior. The proton conductivity of iHOF-37 demonstrated a maximum of 6.50 × 10-4 S·cm-1 at 98% RH and 100 °C, and it increased to 9.10 × 10-3 S·cm-1 due to dual free radical synergism following UV irradiation (NDI and viologen), which represents a significant 14-fold enhancement. Furthermore, the incorporation of iHOF-37 into the chitosan (CS) matrix forms photochromic composite membranes. The proton conductivity of the 5%-iHOF-37/CS composite membrane reached up to 5.70 × 10-2 S·cm-1 at 98% RH and 90 °C, and reached 8.08 × 10-2 S·cm-1 after UV irradiation. This work reveals the dual radicals generated by NDI and viologen derivatives, whose synergistic action plays a significant role in enhancing the proton conductivity in iHOFs and composite membranes, rendering the rational design of stimuli-responsive smart materials feasible.

Construction of Successive Proton Conduction Channels to Accelerate the Proton Conduction Process in Flexible Proton Exchange Membranes

Successive proton conduction channels are constructed with the spin coating method in flexible proton exchange membranes (PEMs). In this research, phosphoric acid (PA) molecules are immobilized in the multilayered microstructure of Kevlar nanofibers and polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) polymer molecular chains. As a result, successive proton conduction channels can accelerate the proton conduction process in the prepared membrane with the multilayered microstructure. Additionally, the microstructure fractures of the composite membranes from the external force of folding and stretching operations are modified by the inner PA molecules. Notably, numerous PA molecules are further combined through formed intermolecular hydrogen bonding. The stretched membrane absorbs more PA molecules owing to the arrangement of PA molecules, Kevlar nanofibers, and SEBS molecular chains. The stretched membrane thus exhibits the enhanced proton conduction ability, such as the through-plane proton conductivity of 1.81 × 10-1 S cm-1 at 160 °C and that of 4.53 × 10-2 S cm-1 at 120 °C lasting for 600 h. Furthermore, the tensile stress of PA-doped stretched membranes reaches (3.91 ± 0.40)-(6.15 ± 0.43) MPa. A single proton exchange membrane fuel cell exhibits a peak power density of 483.3 mW cm-2 at 120 °C.