Structural Characterization and Physicochemical Properties of Functionally Porous Proton-Exchange Membrane Based on PVDF-SPA Graft Copolymers.

Fluorinated proton-exchange membranes (PEMs) based on graft copolymers of dehydrofluorinated polyvinylidene fluoride (D-PVDF), 3-sulfopropyl acrylate (SPA), and 1H, 1H, 2H-perfluoro-1-hexene (PFH) were prepared via free radical copolymerization and characterized for fuel cell application. The membrane morphology and physical properties were studied via small-(SAXS) and wide-angle X-ray scattering (WAXS), SEM, and DSC. It was found that the crystallinity degree is 17% for PEM-RCF (co-polymer with SPA) and 16% for PEM-RCF-2 (copolymer with SPA and PFH). The designed membranes possess crystallite grains of 5-6 nm in diameter. SEM images reveal a structure with open pores on the surface of diameters from 20 to 140 nm. Their transport and electrochemical characterization shows that the lowest membrane area resistance (0.9 Ωcm2) is comparable to perfluorosulfonic acid PEMs (such as Nafion®) and polyvinylidene fluoride (PVDF) based CJMC cation-exchange membranes (ChemJoy Polymer Materials, China). Key transport and physicochemical properties of new and commercial membranes were compared. The PEM-RCF permeability to NaCl diffusion is rather high, which is due to a relatively low concentration of fixed sulfonate groups. Voltammetry confers that the electrochemical behavior of new PEM correlates to that of commercial cation-exchange membranes, while the ionic conductivity reveals an impact of the extended pores, as in track-etched membranes.

Sulfonated Poly(2,6-dimethyl-1,4-phenylene ether)-Modified Mixed-Matrix Bifunctional Polyelectrolyte Membranes for Long-Run Anthrarufin-Based Redox Flow Batteries.

The resurgence in designing polyelectrolyte membrane (PEM) materials has propound grid-scale electrochemical energy storage devices. Herein, we report on studies corroborating the synergistic influence of ionic domain microstructure modification and intercalation of telechelic bis-piperidinium-functionalized graphene oxide (GO) to fabricate stable bifunctional membranes from sulfonated poly(2,6-dimethyl-1,4-phenylene ether) (sPPE) for efficient anthrarufin-based alkaline redox flow batteries. A critically long-lasting quest on alkaline stability and -OH conductivity dilemma in hydrocarbon-based PEMs is meticulously resolved via a bifunctional ion-conducting matrix. Preferential studies on hydrophilic domain distribution in sPPE suggest that, with high microphase homogeneity, higher specific capacity retentions are achievable during galvanostatic charge-discharge (GCD) analysis. Moreover, the low-capacity issues were overcome by improving the redoxolyte-membrane interface affinities incorporating bis-piperidinium-bearing graphene oxide (bis-QGO). Consequently, at 1.0 and 2.0 wt % intercalation of bis-QGO, the bifunctional polyelectrolyte membranes (BFPMs) impart lowest overpotentials of 93 mV (for BFPM-1.0) and ∼100 mV (for BFPM-2.0) which are ∼43 and 40% lower than that of Nafion-117 (i.e., ∼164 mV). Furthermore, the efficiency of BFPMs, viz., the Coulombic, voltage, and energy efficiencies, was ∼95-98%, ∼85%, and ≥80% at 20 mA cm-2, respectively. In long-cycling operations, the GCD profile evidenced ∼99% efficiency retention over 450 cycles and illustrated reproducible rate capability. Finally, the polarization studies of BFPMs revealed ∼54% higher peak power density (87.5 mW cm-2) delivery than Nafion-117 (∼57 mW cm-2). We believe that this strategic designing approach could offer newer and simple avenues to avail high-performance BFPMs at low intercalation loads for alkaline electrochemical energy storage and related applications.