Nanophase-Separated Block-co-Polymers Based on Phosphonated Pentafluorostyrene and Octylstyrene for Proton-Exchange Membranes

Nanophase separation into hydrophobic and hydrophilic domains in commercial perfluorosulfonic acid polymers promotes high conductivity by forming proton-conductive channels within a matrix. To transfer this beneficial phase separation to phosphonic acid functionalized ionomers, we combine phosphonated polypentafluorostyrene and flexible polyoctylstyrene in a di-block-co-polymer. We introduce a stepwise approach, including mesophase simulations, synthesis, and spectroscopic imaging. After the required block lengths were calculated, controlled radical polymerization led to a narrowly distributed block-co-polymer. The respective block-co-polymer membrane outperforms a phosphonated pentafluorostyrene blend concerning conductivity and water uptake. Stained membrane cross-sections revealed bicontinuous nanophase separation in the 13 to 25 nm range in transmission electron microscopy. The ion-conducting phosphonated polymer block assembled into an isotropic, three-dimensional gyroidal network across the membrane. Our stepwise approach is transferable toward other block-co-polymer systems featuring different monomers or functional groups. Applying the proposed principles allows for the prediction of structure-related phase separation while reducing the amount of synthesis work

Seawater Electrolysis Using All-PGM-Free Catalysts and Cell Components in an Asymmetric Feed

In arid coastal zones, direct seawater electrolysis appears particularly intriguing for green hydrogen production. State-of-the-art direct seawater electrolyzers, however, show unsatisfactory performance and rely on large amounts of platinum-group metals (PGMs) in the electrodes or hidden as transport layer coatings. Herein, we report an asymmetric-feed electrolyzer design, in which all cell components consist of PGM-free materials. Cobalt- and nickel-based phosphides/chalcogenides not only serve as active and robust electrocatalysts but also are put forth as porous transport layer (PTL) surface coatings enhancing selective seawater splitting performance. In a systematic design study at the single-cell level, we report the integration of our catalysts and PTLs into a membrane–electrode assembly (MEA) using a customized, terphenyl-based anion-exchange membrane (AEM). The presented entirely PGM-free electrolyzer achieves industrially relevant current densities of up to 1.0 A cm–2 below 2.0 Vcell in standardized alkaline seawater and dry cathode operation