Fluorinated Aromatic Polyether Ionomers Containing Perfluorocyclobutyl as Cross-Link Groups for Fuel Cell Applications

The cross-linkable copolymers (SHQ<i>x</i>-TFV<i>y</i>s) with varying degrees of sulfonation (DS) from 70 to 95% were prepared from potassium-2,5-dihydroxybenzenesulfonate (SHQ), decafluorobiphenyl (DFBP), and 4-(trifluorovinyloxy)-biphenyl-2,5-diol (TFVOH) as a cross-linkable moiety. To develop a highly stable polymer electrolyte membrane (PEM) for application in polymer electrolyte fuel cells (PEFC)­s, cross-linked membranes were prepared by chemical cross-linking. The cross-linked membranes were synthesized by varying the amount of TFVOH (5–30 mol %) in order to achieve desirable PEM properties. The structures of the cross-linkable monomer and polymers were investigated by ¹H and ¹⁹F NMR and FT-IR spectra. The cross-linked membranes exhibited good glass transition temperature and thermal stability up to 239–271 °C and 290–312 °C, respectively. The crosslinked membranes (DS range 80–95%) exhibited higher proton conductivity (0.098–0.151 S/cm) than Nafion 212 (0.092 S/cm). Moreover, all membranes possessed lower methanol permeability (13–132 × 10^–8 cm²/s) compared with Nafion 212 (163 × 10^–8 cm²/s) under the same measurement conditions. The H₂/O₂ single cell performance tests of the cross-linked membranes and Nafion 212 were performed. The CSHQ90-TFV10 exhibited the higher maximum power density (1.053 W/cm²) than that of Nafion 212 (0.844 W/cm²)

Anion Engineering for Stabilizing Li Interstitial Sites in Halide Solid Electrolytes for All-Solid-State Li Batteries

Halide solid electrolytes (SEs) have been highlighted for their high-voltage stability. Among the halide SEs, the ionic conductivity has been improved by aliovalent metal substitutions or choosing a ccp-like anion-arranged monoclinic structure (C2/m) over hcp- or bcc-like anion-arranged structures. Here, we present a new approach, hard-base substitution, and its underlying mechanism to increase the ionic conductivity of halide SEs. The oxygen substitution to Li2ZrCl6 (trigonal, hcp) increased the ionic conductivity from 0.33 to 1.3 mS cm–1 at Li3.1ZrCl4.9O1.1 (monoclinic, ccp), while the sulfur and fluorine substitutions were not effective. A systematic comparison study revealed that the energetic stabilization of interstitial sites for Li migration plays a key role in improving the ionic conductivity, and the ccp-like anion sublattice is not sufficient to achieve high ionic conductivity. We further examined the feasibility of the oxyhalide SE for practical and all-solid-state battery applications