Nanofiber Framework Research Articles

CoS-interposed and Ketjen black-embedded carbon nanofiber framework as a separator modulation for high performance Li-S batteries

Lithium sulfur batteries are regarded as the promising energy storage device for its high energy density (theoretical: ∼2600 Wh kg−1). In addition, the low cost of sulfur and its small impacts on the environment also arise tremendous interests of industries and governments. However, lithium sulfur batteries are still severely plagued by the free migration of intermediary polysulfides, which are the roots of lithium sulfur batteries' challenges. Besides various cathode design, carbon-based modification layers on the separator are also developed to enhance the electrochemical performance of the lithium sulfur batteries. In this study, carbon nanofiber/CoS/Ketjen black is successfully integrated on the commercial separator as an effective polysulfide blocker. It is demonstrated that the cell with a carbon nanofiber/CoS/Ketjen black-modified separator and high sulfur content (70 wt%) cathode can exhibit excellent stability with a capacity decay of 0.076% per cycle for more than 700 cycles under 1.0 C current density. Especially, the robust and flexible coating strategy can greatly expand the range of materials available to be integrated on the commercial separator.

Surfactant assisted electrospinning of WS2 nanofibers and its promising performance as anode material of sodium-ion batteries

Metal sulfides were considered as a promising anode material for sodium-ion batteries (SIBs). However, volume expansion during charging/discharging is an issue. One dimensional nanofibers are considered here to alleviate the change in stress of the anode's structure. Here we incorporated the nanofibers and WS2 nanosheets which used (DODA)3PW12O40 as the precursor. The precursor was prepared by an ion-exchange method, and then used to fabricate the anode material (denoted as DODA-WS2) via electrospinning. Use of surfactant dimethyldistearylammonium bromide (DODA·Br) disperses the WS2 nanosheets in the nanofibers. Carbonization and decomposition of DODA ligands provides porosity that accommodates volume expansion. The resulting structure of the anode material delivers high capacities of 363 and 318 mAh g−1 with 96% and 91% rate capacity retention after 400 cycles at 200 and 500 mA g−1, respectively. Also, improved rate capabilities (395 and 91 mAh g−1 at 50 and 10000 mA g−1, respectively) and good cycling stability (226.5 mAh g−1 after 800 cycles at 1000 mA g−1). These unique results are ascribed to the well-dispersed WS2 cross-linked nanofiber framework and its conductive network. This structure facilitates the transportation of electrons and Na+ and relieve the stress due to expansion. DODA-WS2 has a high potential for use as anode materials in SIBs.

A carbon-rich nanofiber framework based on a conjugated arylacetylene polymer for photocathodic enzymatic bioanalysis.

Poly(1,3,5-triethynylbenzene) (PTEB), a newly developed conjugated arylacetylene polymer, was utilized for photoelectrochemical (PEC) enzymatic bioanalysis in this work. The porous nanofiber framework of PTEB film which produced an apparent cathodic photocurrent under visible light illumination was fabricated on an indium tin oxide (ITO) electrode via copper-surface mediated interface Glaser polycondensation. As the photocurrent density of the metal-free photocathode displayed a characteristic O2 dependency, the consumption of dissolved oxygen caused by the modified glucose oxidase (GOx) in biocatalysis induced a depressed photoresponse in the presence of glucose. The fabricated PEC transducer exhibited favorable glucose sensing performances in the linear range of 5 μM to 8 mM and with the detection limit of 1.7 μM; it could also be employed in glucose monitoring in human serum. Moreover, the acetylenic carbon-rich polymer possessed the superior features of being cost-effective in preparation and machinable in device development, which sheds light on the exploration of an advanced PEC sensing platform based on conjugated organic polymers for the bioanalysis of valuable analytes.

Highly Dispersed Mn–Ce Binary Metal Oxides Supported on Carbon Nanofibers for Hg0 Removal from Coal-Fired Flue Gas

Highly dispersed Mn–Ce binary metal oxides supported on carbon nanofibers (MnOx–CeO2/CNFs(OX)) were prepared for Hg0 removal from coal-fired flue gas. The loading value of the well-dispersed MnOx–CeO2 was much higher than those of many other reported supports, indicating that more active sites were loaded on the carbon nanofibers. In the present study, 30 wt % metal oxides (15 wt % MnOx and 15 wt % CeO2) were successfully deposited on the carbon nanofibers, and the sorbent yielded the highest Hg0 removal efficiency (>90%) within 120–220 °C under a N2/O2 atmosphere. An increase in the amount of highly dispersed metal oxides provided abundant active species for efficient Hg0 removal, such as active oxygen species and Mn4+ cations. Meanwhile, the carbon nanofiber framework provides the pathway for charge transfer during the heterogeneous Hg0 capture reaction processes. Under a N2+6%O2 atmosphere, a majority of Hg0 was removed via chemisorption reactions. The effects of flue gas composition were also investigated. O2 replenished the active oxygen species on the surface and thus greatly promoted the Hg0 removal efficiency. SO2 had an inhibitory effect on Hg0 removal, but NO facilitated Hg0 capture performance. Overall, carbon nanofibers seems to be a good candidate for the support and MnOx–CeO2/CNFs(OX) may be promising for Hg0 removal from coal-fired flue gas.

A polysulfide-trapping interlayer constructed by boron and nitrogen co-doped carbon nanofibers for long-life lithium sulfur batteries

The shuttle effect of soluble lithium polysulfides (LiPSs) and their insoluble reduction products (Li2S/Li2S2) depositing on the surface of lithium anode are the major drawbacks for the practical application of lithium sulfur (Li-S) batteries. In this work, a thin and light interlayer constructed by boron and nitrogen co-doped carbon nanofibers (BNCNF) has been produced by a facile electrospinning method with following thermal treatment. Through introducing BNCNF film between cathode and separator, the charge transfer resistance decreases largely and the shuttle effect remits to a great extent. The BNCNF exhibits excellent absorption ability for polysulfides under the role of the B⋯S and N⋯Li chemical interaction, and especially the formation of N=B/N-B structure in the carbon nanofiber framework reinforces the electropositive interaction between B atoms and Sx2− and the electronegative interaction between N atoms and Li+ cation, simultaneously. The capacity and cycling life of Li-S batteries are improved significantly due to the BNCNF interlayer. The cell with BNCNF interlayer delivered an initial capacity of 1054.7mAhg−1 at 1.0C over 1000cycles with a decay rate of 0.058%. And even at high current density of 5.0C, it had an initial capacity of 612.2mAhg−1 over 600cycles with a decay rate of 0.085%. The BNCNF interlayer developed here provides a promising methodology to enhance the performance of Li-S batteries.

Polymer modified sulfonated PEEK ionomers membranes and the use of Ru3Pd6Pt as cathode catalyst for H2/O2 fuel cells

Abstract Nanocomposite membranes incorporating electrospun nanofibers of SPEEK, blended with 30 wt% PVB within a water-based matrix of SPEEK with 35 wt% PVA using water as solvent, were prepared and characterized for their application as Polymer Electrolyte Membrane Fuel Cells (PEMFCs) in H2/O2 operating at low temperatures. Compared with a dense bulk phase, an improvement of proton conductivity in the SPEEK-30PVB nanofiber framework was observed. The incorporation of the SPEEK-30PVB nanofibers provides mechanical improvement while the matrix phase of SPEEK-35PVA emphasizes the proton conductivity at crosslinking temperatures up to 140 °C. PEMFC performance tests showed promising results for the use of these novel low cost membranes. The nanocomposite membrane reached a power density which is 25% higher than that of Nafion117 membranes with MEAs constructed with Pt loading in anode and in cathode. However, when the Pt of the cathode is substituted by Ru3Pd6Pt, the power density is lower in Nafion117 MEAs than in the nanocomposite. When used commercial Pt-carbon cloth (Pt-ETEK) for the electrodes, the power density achieved is 1.4 times higher for the Nafion117 MEAs than SPEEK nanocomposites. The differences observed in performance is attributed to the large polarization losses found in the composite membranes because of the interfacial phenomena associated with the use of commercial Nafion-based electrodes.

A Novel Non-Enzymatic Electrochemical Hydrogen Peroxide Sensor Based on a Metal-Organic Framework/Carbon Nanofiber Composite.

A co-based porous metal-organic framework (MOF) of zeolitic imidazolate framework-67 (ZIF-67) and carbon nanofibers (CNFs) was utilized to prepare a ZIF-67/CNFs composite via a one-pot synthesis method. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) were employed to investigate the morphology, structure, and composition of the resulting composite. A novel high-performance non-enzymatic electrochemical sensor was constructed based on the ZIF-67/CNFs composite. The ZIF-67/CNFs based sensor exhibited enhanced electrocatalytic activity towards H2O2 compared to a pure ZIF-67-based sensor, due to the synergistic effects of ZIF-67 and CNFs. Meanwhile, chronoamperometry was utilized to explore the detection performance of the sensor. Results showed the sensor displayed high-efficiency electrocatalysis towards H2O2 with a detection limit of 0.62 μM (S/N = 3), a sensitivity of 323 µA mM−1 cm−2, a linear range from 0.0025 to 0.19 mM, as well as satisfactory selectivity and long-term stability. Furthermore, the sensor demonstrated its application potential in the detection of H2O2 in food.

Encapsulating Silica/Antimony into Porous Electrospun Carbon Nanofibers with Robust Structure Stability for High-Efficiency Lithium Storage.

To address the volume-change-induced pulverization problems of electrode materials, we propose a "silica reinforcement" concept, following which silica-reinforced carbon nanofibers with encapsulated Sb nanoparticles (denoted as SiO2/Sb@CNFs) are fabricated via an electrospinning method. In this composite structure, insulating silica fillers not only reinforce the overall structure but also contribute to additional lithium storage capacity; encapsulation of Sb nanoparticles into the carbon-silica matrices efficiently buffers the volume changes during Li-Sb alloying-dealloying processes upon cycling and alleviates the mechanical stress; the porous carbon nanofiber framework allows for fast charge transfer and electrolyte diffusion. These advantageous characteristics synergistically contribute to the superior lithium storage performance of SiO2/Sb@CNF electrodes, which demonstrate excellent cycling stability and rate capability, delivering reversible discharge capacities of 700 mA h/g at 200 mA/g, 572 mA h/g at 500 mA/g, and 468 mA h/g at 1000 mA/g each after 400 cycles. Ex situ as well as in situ TEM measurements confirm that the structural integrity of silica-reinforced Sb@CNF electrodes can efficiently withstand the mechanical stress induced by the volume changes. Notably, the SiO2/Sb@CNF//LiCoO2 full cell delivers high reversible capacities of ∼400 mA h/g after 800 cycles at 500 mA/g and ∼336 mA h/g after 500 cycles at 1000 mA/g.

Free-Standing Mn3O4@CNF/S Paper Cathodes with High Sulfur Loading for Lithium-Sulfur Batteries.

Free-standing paper cathodes with layer-by-layer structure are synthesized for high-loading lithium-sulfur (Li-S) battery. Sulfur is loaded in a three-dimensional (3D) interconnected nitrogen-doped carbon nanofiber (CNF) framework impregnated with Mn3O4 nanoparticles. The 3D interconnected CNF framework creates an architecture with outstanding mechanical properties. Synergetic effects generated from physical and chemical entrapment could effectively suppress the dissolution and diffusion of the polysulfides. Electrochemical measurements suggest that the rationally designed structure endows the electrode with high utilization of sulfur and good cycle performance. Specifically, the cathode with a high areal sulfur loading of 11 mg cm-2 exhibits a reversible areal capacity over 8 mAh cm-2. The fabrication procedure is of low cost and readily scalable. We believe that this work will provide a promising choice for potential practical applications.

Sulfonated polyimide nanofiber framework: Evaluation of intrinsic proton conductivity and application to composite membranes for fuel cells

A series of proton conductive nanofibers were fabricated by an electrospinning method from various sulfonated polyimides bearing different polymer structures, such as block, graft, and block/graft structures. Except for S-b-PI and S-bg-PI that showed low solubility in the appropriate solvent, the four types of SPIs gave uniaxially-aligned nanofibers along with the nanofibrous mat, which is applicable as nanofiber framework for the composite membranes. The intrinsic proton conductivities of the uniaxially-aligned nanofibers were evaluated to discuss the influence of polymer structures on proton conductivity of the nanofibers. In accord with the result of this study, the S-r-PI nanofiber was selected to fabricate nanofiber framework composite membrane by composing with S-bg-PI that shows high proton conductivity and low gas permeability. The nanofiber framework composite membrane showed good proton conductivity as well as improved gas barrier property and membrane stability. The nanofiber framework composite membrane has a high potential for achieving high proton conductivity, gas barrier property, and membrane stability for future fuel cell application.

Fabrication of Continuous DNA Lattice Structure with Nanofiber Framework

DNA(Deoxyribonucleic acid) is widely used in the fabrication of nanostructures as a nano-material based on the principle of base pair complementarity and has a wide range of applications which involves biology, biophysics, synthetic biology and photonics. However, almost all the structures exhibit a limitation of size which hinders the development of membranes. Here we introduce a new method to manufacturing DNA nanostructures through the combination of DNA lattice and nanofiber. DNA is compiled into a continuous lattice in the size of nanometer and fixed on the framework made up of nanofiber which is also made into grid. We anticipate this method could fabricate a kind of new membranes like nanostructure whose hold size is controllable, and the results of the preliminary experiment reveal the possibility of this method.

Flexible WS2@CNFs Membrane Electrode with Outstanding Lithium Storage Performance Derived from Capacitive Behavior

AbstractFlexible electrodes have recently elicited attention due to their potential to be woven into textiles as flexible power supplies for wearable electronic devices. However, contemporary flexible electrodes generally suffer from the limited reaction kinetics and inferior stability. Here, a flexible WS2@CNFs membrane electrode is facilely fabricated via hydrothermal method and subsequent electrospinning to embed WS2 nanosheets into interconnected framework of carbon nanofibers (CNFs). Benefitting from 3D porous architecture and good conductivity of CNFs, WS2@CNFs composites exhibit outstanding cycling stability and rate capability as self‐supported binder‐free anode for lithium‐ion batteries. Especially, WS2@CNFs with 60.3 wt% of WS2 displays a discharge specific capacity as high as 545 mA h g−1 at 0.5 A g−1 after 800 cycles. Even at 2 A g−1, it maintains 62.4% of specific capacity at 0.1 A g−1, and stably cycles back at 0.1 A g−1. Kinetic analysis confirms that the capacitive mechanism is dominant in the Li‐ion storage process, which is derived mainly from the structure evolution from WS2 nanosheets to WS2/W nanoparticles during extended cycling. The reduced nanoparticles also enhance electrochemical activity, conductivity, and reversibility of the conversion reaction, resulting in the increasing capacity with cycles.

Edge-Oriented Graphene on Carbon Nanofiber for High-Frequency Supercapacitors

High-frequency supercapacitors are being studied with the aim to replace the bulky electrolytic capacitors for current ripple filtering and other functions used in power systems. Here, 3D edge-oriented graphene (EOG) was grown encircling carbon nanofiber (CNF) framework to form a highly conductive electrode with a large surface area. Such EOG/CNF electrodes were tested in aqueous and organic electrolytes for high-frequency supercapacitor development. For the aqueous and the organic cell, the characteristic frequency at − 45° phase angle was found to be as high as 22 and 8.5 kHz, respectively. At 120 Hz, the electrode capacitance density was 0.37 and 0.16 mF cm−2 for the two cells. In particular, the 3 V high-frequency organic cell was successfully tested as filtering capacitor used in AC/DC converter, suggesting the promising potential of this technology for compact power supply design and other applications.

Solid Polymer Electrolytes Based on Ion Conductive Nanofiber Framework for Lithium Ion Battery

Solid polymer electrolyte (SPE) have been expected as high safety and reliable materials compared with conventional organic liquid electrolytes. In order to apply polymer electrolytes to all-solid-state Lithium Ion Battery (LIB), it is essential to improve their lithium ion conductivity and membrane stability. In this study, we focused on polymer nanofibers to overcome these issues on SPEs for LIB applications. Polymer nanofibers have unique characteristics such as high surface area, good mechanical property, and great material transport property [1]. We have reported fabrication, characterizations, and applications of various functional polymer nanofibers prepared by an electrospinning method [2]. Recently, we developed proton or anion conductive polymer nanofibers and revealed their outstanding ion conductive properties [3]. The nanofiber framework (NfF) composite membranes consisting of the ion conductive nanofibers and polymer electrolyte matrix showed remarkable fuel cell properties due to their improved ion conductivity, gas barrier property, and membrane stability [4]. Here presents our recent work on lithium ion conductive polymer nanofibers and their application to all-solid-state LIBs. The electrospinning method was attempted to fabricate lithium ion conductive NfFs composed of lithium salt and polymers bearing ethylene oxide units in their main or side chains. The lithium ion conductive NfF composite membranes were prepared by filling polymer electrolyte matrices into the voids of the NfFs. Electrochemical, thermal, and mechanical properties of the NfFs and NfF composite membranes were evaluated to demonstrate improved electrolyte characteristics. Fabrication and evaluation of all-solid-state LIBs based on the NfF composite membranes will also be reported. Acknowledgements This work is partially supported by JSPS KAKENHI (26410225), and a grant (Platform for Technology and Industry) from Tokyo Metropolitan Government, Japan.

Superior cyclability of branch-like TiO 2 embedded on the mesoporous carbon nanofibers as free-standing anodes for lithium-ion batteries

Abstract For the poor capacity utilization and insufficient cyclability of TiO2/C anodes for lithium-ion batteries, we synthesized branch-like TiO2@mesoporous carbon nanofibers (TiO2@MCNFs) as free-standing anodes via electrospinning technique, hydrothermal treatment and a subsequent carbonization process, where anatase TiO2 branches were densely embedded on the mesoporous carbon nanofiber trunks. Due to the copious highly-exposed TiO2 nanocrystal lattices on the branch except for the trunk support, the abundant intrinsic crystal channels for fluent Li+ transportation, and the interlaced carbon nanofiber framework with a high structural integrity and mechanical flexibility, the branch-like TiO2@MCNFs composites presented a superior initial discharge capacity of 1932 mAhg−1 and an excellent reversible capacity of ∼617 mAhg−1 after 100 cycles. And compared with those of the reported TiO2/C electrodes, the initial discharge capacity and reversible capacity of the branch-like TiO2@MCNFs composites increased by ∼2 times and ∼50%, respectively. Hence, the unique architecture of the branch-like TiO2@MCNFs composites and their superior electrochemical performances may provide new insights for the development of better host materials for practical lithium-ion batteries.

Fabrication and Evaluation of Electrospun, 3D-Bioplotted, and Combination of Electrospun/3D-Bioplotted Scaffolds for Tissue Engineering Applications.

Electrospun scaffolds provide a dense framework of nanofibers with pore sizes and fiber diameters that closely resemble the architecture of native extracellular matrix. However, it generates limited three-dimensional structures of relevant physiological thicknesses. 3D printing allows digitally controlled fabrication of three-dimensional single/multimaterial constructs with precisely ordered fiber and pore architecture in a single build. However, this approach generally lacks the ability to achieve submicron resolution features to mimic native tissue. The goal of this study was to fabricate and evaluate 3D printed, electrospun, and combination of 3D printed/electrospun scaffolds to mimic the native architecture of heterogeneous tissue. We assessed their ability to support viability and proliferation of human adipose derived stem cells (hASC). Cells had increased proliferation and high viability over 21 days on all scaffolds. We further tested implantation of stacked-electrospun scaffold versus combined electrospun/3D scaffold on a cadaveric pig knee model and found that stacked-electrospun scaffold easily delaminated during implantation while the combined scaffold was easier to implant. Our approach combining these two commonly used scaffold fabrication technologies allows for the creation of a scaffold with more close resemblance to heterogeneous tissue architecture, holding great potential for tissue engineering and regenerative medicine applications of osteochondral tissue and other heterogeneous tissues.

ナノファイバーフレームワークを骨格とする新規全固体電解質膜の開発

Environmental problems such as global warming, pollution in our cities and the depletion of fossil fuel resources have conspired to make both the development of renewable energy and the shift to electrical transportation crucial. Proton exchange membrane fuel cells, which efficiently convert chemical energy into electrical energy via oxidation and reduction reactions, are receiving considerable attention as an alternative energy source because of their high energy efficiency and no emissions of pollutants. Electrical transportation applications require the storage of a large amount of energy on board vehicles so as to enable long cruising distances. Recently, we have prepared all solid polymer electrolyte membranes composed of ion conductive nanofibers and revealed that the composite membranes showed a higher ion conductivity (i.e. proton or lithium ions) than the membrane without nanofibers. In this paper, we reported the properties of novel all solid electrolyte membranes comprising an ion conductive nanofiber framework as fuel cells and lithium ion batteries.

Split Sn-Cu Alloys on Carbon Nanofibers by One-step Heat Treatment for Long-Lifespan Lithium-Ion Batteries

To develop next-generation lithium-ion batteries (LIBs) with novel designs, reconsidering traditional materials with enhanced cycle stability and excellent rate performance is crucial. We herein report the successful preparation of three-dimensional (3D) composites in which spilt Sn–Cu alloys are uniformly dispersed in an amorphous carbon nanofiber matrix (Sn–Cu–CNFs) via one-step carbonization-alloying reactions. The spilt Sn–Cu alloys consist of active Cu6Sn5 and inactive Cu3Sn, and are controllable by optimization of the carbonization-alloying reaction temperature. The 3D carbon nanofiber framework allowed the Sn–Cu–CNFs to be used directly as anodes in lithium-ion batteries without the requirement for polymer binders or electrical conductors. These composite electrodes exhibited a stable cyclability with a discharge capacity of 400mA h g−1 at a high current density of 1.0Ag−1 after 1200 cycles, as well as an excellent rate capability, which could be attributed to the improved electrochemical properties of the Sn–Cu–CNFs provided by the buffering effect of Cu3Sn and the 3D carbon nanofiber framework. This one-step synthesis is expected to be widely applicable in the targeted structural design of traditional tin-based anode materials.

Acid-doped polymer nanofiber framework: Three-dimensional proton conductive network for high-performance fuel cells

Abstract High-performance polymer electrolyte membranes (PEMs) with excellent proton conductivity, gas barrier property, and membrane stability are desired for future fuel cells. Here we report the development of PEMs based on our proposed new concept “Nanofiber Framework (NfF).” The NfF composite membranes composed of phytic acid-doped polybenzimidazole nanofibers (PBINf) and Nafion matrix show higher proton conductivity than the recast-Nafion membrane without nanofibers. A series of analyses reveal the formation of three-dimensional network nanostructures to conduct protons and water effectively through acid-condensed layers at the interface of PBINf and Nafion matrix. In addition, the NfF composite membrane achieves high gas barrier property and distinguished membrane stability. The fuel cell performance by the NfF composite membrane, which enables ultra-thin membranes with their thickness less than 5 μm, is superior to that by the recast-Nafion membrane, especially at low relative humidity. Such NfF-based high-performance PEM will be accomplished not only by the Nafion matrix used in this study but also by other polymer electrolyte matrices for future PEFCs.

Rough-surfaced molybdenum carbide nanobeads grown on graphene-coated carbon nanofibers membrane as free-standing hydrogen evolution reaction electrocatalyst

A novel free-standing pie-like paper electrode composed of Mo2C nanobeads on graphene-coated carbon nanofibers (G-CNF) membrane was rationally designed as advanced electrocatalyst for hydrogen evolution reaction (HER). A thin layer of graphene is coated on the surface of CNF membrane, forming a “crust” on fibrous web architecture. The unique design of the all-carbon membrane, which is a 3D interconnected conductive framework of nanofibers, reduces the resistance of electron and ion transport during the electrocatalyzing process. With G-CNF performing as support, well-shaped Mo2C nanobeads were immobilized on the fibers through hydrothermal and calcination procedures, offering rich catalytic sites on the exposed rough surface. Owing to all these merits, the composite membrane of Mo2C-G-CNF exhibits high HER catalytic activity with onset potential of 115 mV in acidic solution and 108 mV in basic solution. Furthermore, the good durability in both acidic and basic environment guarantees its practical application as free-standing electrode material.