Properties of composite proton-conducting membranes prepared from three-dimensionally ordered macroporous polyimide matrix and polyelectrolyte

Inverse opal-inspired, nanoscaffold battery separators: a new membrane opportunity for high-performance energy storage systems

The facilitation of ion/electron transport, along with ever-increasing demand for high-energy density, is a key to boosting the development of energy storage systems such as lithium-ion batteries. Among major battery components, separator membranes have not been the center of attention compared to other electrochemically active materials, despite their important roles in allowing ionic flow and preventing electrical contact between electrodes. Here, we present a new class of battery separator based on inverse opal-inspired, seamless nanoscaffold structure ("IO separator"), as an unprecedented membrane opportunity to enable remarkable advances in cell performance far beyond those accessible with conventional battery separators. The IO separator is easily fabricated through one-pot, evaporation-induced self-assembly of colloidal silica nanoparticles in the presence of ultraviolet (UV)-curable triacrylate monomer inside a nonwoven substrate, followed by UV-cross-linking and selective removal of the silica nanoparticle superlattices. The precisely ordered/well-reticulated nanoporous structure of IO separator allows significant improvement in ion transfer toward electrodes. The IO separator-driven facilitation of the ion transport phenomena is expected to play a critical role in the realization of high-performance batteries (in particular, under harsh conditions such as high-mass-loading electrodes, fast charging/discharging, and highly polar liquid electrolyte). Moreover, the IO separator enables the movement of the Ragone plot curves to a more desirable position representing high-energy/high-power density, without tailoring other battery materials and configurations. This study provides a new perspective on battery separators: a paradigm shift from plain porous films to pseudoelectrochemically active nanomembranes that can influence the charge/discharge reaction.

Simple method for preparation of porous polyimide film with an ordered surface based on in situ self-assembly of polyamic acid and silica microspheres

In this Article, we addressed a facile method for the fabrication of porous polyimide film with an ordered surface based on the solvent-evaporation-assisted in situ self-assembly of polyamic acid (PAA, precursor of polyimide) and silica microspheres during vacuum-drying of PAA/silica colloid solution. Hydroxyl groups on the surface of silica microspheres have strong hydrogen-bonding with PAA chains, which improve the dispersion of silica microspheres in PAA/DMF solution and further help the self-assembly of PAA/silica colloid solution via solvent evaporation. The approach is simple, neither the preparation of special template nor complex preparation process and precise control over condition is necessary. Furthermore, the method could be employed for mass production of ordered porous polyimide films, and by changing the content and size of silica microspheres, the pore size and porous structure of the porous polyimide films could be tunable. The wettability behavior of the as-prepared porous polyimide films is also studied; the ordered surface topography of the porous polyimide films could change the wettability from hydrophilicity to hydrophobicity.

Hybrid polymer-silicon proton conducting membranes via a pore-filling surface-initiated polymerization approach

An alternative approach for the creation of proton conducting platforms is presented. The methodology is based on the so-called "pore-filling concept", which relies on the filling of porous matrices with polyelectrolytes to obtain proton conducting platforms with high dimensional stability. Polymer-silicon composite membranes, with well-defined polyelectrolyte microdomains oriented normal to the plane of the membrane, were prepared using photoelectrochemically etched silicon as a microstructured scaffold. Ordered two-dimensional macroporous silicon structures were rendered proton conducting by filling the micropores via a surface-initiated atom transfer radical polymerization process. The morphological aspects, chemical stability, and performance of the hybrid assemblies were characterized by a set of techniques including scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, nuclear magnetic resonance and impedance spectroscopy, among others. The fabricated silicon-poly(sodium 2-acrylamide-2-methylpropane sulfonate) hybrid membranes displayed proton conductivities in the range of 1x10(-2) S/cm. This work illustrates the potential of hybrid polymer-silicon composite membranes synthesized by pore-filling surface-initiated polymerization to create proton conducting platforms in a simple and straightforward manner. Versatility and relative ease of preparation are two key aspects that make this approach an attractive alternative for the molecular design and preparation of proton conducting systems.