organic linkers with a periodic, nanoscaled structure and ultrahigh surface areas. With their tunable pore/cage sizes, flexible skeleton, and large surface-to-volume ratio, [13][14][15][16][17][18][19] MOFs have a large potential for a wide range of applications, including gas storage and separation, rechargeable batteries, supercapacitors, solar cells, nanoreactors, heterogeneous catalysis, or drug delivery. [20][21][22][23][24][25][26][27] Recently, significant efforts have been devoted to the design and synthesis of new MOFs structures and the investigation of their physical or chemical properties. MOFs are generally prepared as bulk form through traditional hydrothermal or solvothermal synthesis. [28][29][30][31] In order to expand the application range, suitable pathways for the structuring of MOF powders into a functional architecture or devices are highly desirable.Currently, intensive efforts are focusing on the structuring of MOFs at the mesoscopic/macroscopic scale for the use as coatings, membranes, or sophisticated architectures in specific devices and applications. [32][33][34][35] A major difference in the structuring of MOFs into complex shapes compared to inorganic microporous materials, such as zeolites or silica, is the fact that most inorganic binders cannot be used for MOFs as these binders usually require heat treatment. The intrinsic fragility of MOFs needs to be considered which is related to the inorganic/organic hybrid character of this class of materials and the resulting limited thermal and mechanical stability. Alternatively, a more effective way to structure MOFs is the combination with polymer materials. The polymer which acts as a binder improves the mechanical flexibility and ensures chemical stability. Numerous methods have been developed for structuring MOF-polymer compositions including hard or soft templates, spin-or dip-coating, spray-drying, printing, or lithography approaches. [36][37][38] The integration of MOFs into a polymer matrix can result in poor MOF-polymer dispersion and compatibility issues owing to the different physical and chemical properties for the two kinds of materials and this is a challenge in some applications, e.g., in MOF-based mixed matrix membranes for gas separation. [39][40][41][42] The poor interfacial compatibility would lead to agglomeration of MOF particles, causing the formation of nonselective voids between the MOFs particles and the polymer.Electrospinning is a fabrication method to produce continuous ultrafine fibers with diameters in the range of a few tens of nanometers to a few micrometers in the form of nonwoven mats, yarns, etc. The mechanism of electrospinning is based Herein, recent developments of metal-organic frameworks (MOFs) structured into nanofibers by electrospinning are summarized, including the fabrication, post-treatment via pyrolysis, properties, and use of the resulting MOF nanofiber architectures. The fabrication and post-treatment of the MOF nanofiber architectures are described systematically by two routes: i) the dire...

A nanofiber electrode is fabricated by electrospinning an ink composed of Pt/C catalyst particles in a solution of Nafion and poly(acrylic acid). Exceptionally high power densities and platinum mass activity are achieved when using the mat as cathode in H2/air and H2/O2 fuel cell membrane–electrode assemblies. The nanofiber cathode also exhibits outstanding stability in accelerated durability tests.

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There is a need for polymeric hydrogen/air fuel-cell membranes that can efficiently conduct protons at moderate to high temperatures for wet and dry gas feeds. The US Department of Energy (DOE), for example, set an exceedingly stringent preliminary target for membrane conductivity, 0.10 S cm À1 at 120 8C and 50 % relative humidity (RH).[1] Herein, we describe the fabrication and basic properties of one membrane that exhibits outstanding proton conductivity over a wide range of humidity conditions at temperatures of 80 8C and 120 8C. The membrane is based on a nanofiber network composite design [2] with precise topological separation of the proton transporting and mechanically reinforcing polymer components. This desirable morphology is created via electrospinning, an electrostatic fiber processing technique that has been known for more than one hundred years and underwent a renaissance in the early 1990s, mainly due to the work of Reneker et al. [3,4] The use of electrospinning for membrane and porous filter fabrication is not yet widespread, but interest in this technique is growing. Nanofiber air filters with highly desirable retention characteristics have recently been commercialized. [5, 6] Electrospinning of ionic polymers, on the other hand, is quite new and the data on these systems are very scarce.The present implementation of electrospinning, leading to a functional proton conducting membrane, is unique and involves a sequence of four processing steps: 1) electrospinning a proton conductive blend containing a negatively charged polymer and a sulfonated molecular silica (silsesquioxane) to create a nanofiber mat, 2) welding of intersecting nanofibers to improve the connectivity of the protonic pathways, 3) compacting the mat to increase the volumetric density of the proton conductive fibers, and 4) impregnating the processed nanofiber network with an inert, hydrophobic (uncharged) polymer to fill the pores between fibers, reinforcing the membrane, and limiting ionomer swelling.The new ion-exchange membrane differs from alternative approaches, such as those based on block copolymers, [7,8] in that it combines two separate materials: one for proton conduction and the other as a reinforcement and for stabilizing ionomer swelling, which allows for better control of the nanostructure and properties. Thus, the submicron component (i.e., the "mixing" of the constituent electrospun nanofibers and inert, uncharged polymer matrix) produces a co-continuous morphology similar to that of a polymer blend at the point of phase inversion. Initial experiments focused on the highly charged 825 equivalent weight (EW) perfluorosulfonic acid (PFSA) polymer from 3M Corporation, with an ion-exchange capacity (IEC) of 1.21 mmol g À1 (i.e., 33 % more ÀSO 3 H proton exchange groups per unit weight than commercially available 1100 EW Nafion). Data on electrospinning of PFSA polymers is sparse and limited to Nafion. [9][10][11] Researchers have been unable to electrospin neat Nafion fibers from a Nafion/alcohol solution due to the ...

Separating low/high-valent ions with sub-nanometer sizes is a crucial yet challenging task in various areas (e.g., within environmental, healthcare, chemical, and energy engineering). Satisfying high separation precision requires membranes with exceptionally high selectivity. One way to realize this is constructing well-designed ion-selective nanochannels in pressure-driven membranes where the separation mechanism relies on combined steric, dielectric exclusion, and Donnan effects. To this aim, charged nanochannels in polyamide (PA) membranes are created by incorporating ionic polyamidoamine (PAMAM) dendrimers via interfacial polymerization. Both sub-10 nm sizes of the ionic PAMAM dendrimer molecules and their gradient distributions in the PA nanofilms contribute to the successful formation of defect-free PA nanofilms, containing both internal (intramolecular voids) and external (interfacial voids between the ionic PAMAM dendrimers and the PA matrix) nanochannels for fast transport of water molecules. The external nanochannels with tunable ionizable groups endow the PA membranes with both high low/high-valent co-ion selectivity and chemical cleaning tolerance, while the ion sieving/transport mechanism was analyzed by employing the Donnan steric pore model with dielectric exclusion.