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Results for “Nanofibers”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Characterization of the thermal conductivity of La 0.95 Sr 0.05 CoO 3 thermoelectric oxide nanofibers

Thermoelectric oxide nanofibers prepared by electrospinning are expected to have reduced thermal conductivity when compared to bulk samples. Measurements of nanofibers’ thermal conductivity is challenging since it involves sophisticated sample preparation methods. In this work, we present a novel method suitable for measurements of thermal conductivity of a single nanofiber. A microelectro-mechanical (MEMS) device has been designed and fabricated to perform thermal conductivity measurements on a single nanofiber. A special Si template was designed to collect and transfer individual nanofibers onto a MEMS device. Pt was deposited by a focused ion beam to reduce the effective length of a prepared nanofiber. La 0.95 Sr 0.05 CoO 3 nanofibers with diameters of 140 nm and 290 nm were studied and characterized using this approach at room temperature. Measured thermal conductivities yielded values of 0.7 W·m -1 ·K -1 and 2.1 W·m -1 ·K -1 , respectively. Our measurements in La 0.95 Sr 0.05 CoO 3 nanofibers confirmed that a decrease of linear dimensions has a profound effect on its thermal conductivity.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Preparation of Porous Nanofibers from Electrospun Polyacrylonitrile/Polyvinylidene Fluoride Composite Nanofibers by Inexpensive Salt Using for Dye Adsorption

The high surface area of porous nanofibers enhances their performance for many applications. The present study investigated electrospinning and dye adsorption properties of polymeric nanofibers which were porous by various types of salts. The salt/polyacrylonitrile/polyvinylidene fluoride composite nanofibers were electrospun, and the inexpensive salts such as sodium chloride (NaCl), sodium bicarbonate (NaHCO{sub 3}), or calcium chloride (CaCl{sub 2}) was used to manufacture the porous fibers. Subsequently, the salt was removed by a selective dissolution, and salt extraction of nanofibers was performed with the solution of hydrochloric acid (10 wt%). Salt/PVDF/PAN and porous PVDF/PAN composite nanofibers have been applied to dye adsorption of solution. The characteristics of nanofibers were studied by Fourier transform infrared microscopy (FTIR) and scanning electron microscopy (SEM) analysis. FTIR showed that the salt was extracted from PVDF/PAN nanofibers successfully, and SEM indicated that many pores were aligned with the nanofibers. The adsorption capacity of salt nanofibers webs and porous nanofibers webs for Basic Blue 41 were compared with each other, and porous fibers were obtained from NaHCO{sub 3} having the highest dye adsorption value. Adsorption of dyes follows the Langmuir isotherm and pseudo-second order kinetics.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Computational study of the effect of core–skin structure on the mechanical properties of carbon nanofibers

The effect of the core–skin structure on the mechanical properties of carbon nanofibers is investigated in large-scale molecular dynamics simulations of tensile deformation of carbon nanofibers with the core–skin and homogeneous structures. Contrary to an established notion of the deleterious effect of the skin layer on the strength of carbon fibers, the presence of a high-quality skin layer is found to increase both the Young’s modulus and tensile strength of the nanofiber. A detailed analysis of the fracture process indicates that the nanofiber strengthening is related to the ability of skin layer to suppress crack nucleation at the core–skin interface. Furthermore, the computational predictions suggest that the design of new approaches to carbon fiber manufacturing and processing leading to the generation of a high-quality skin layer while avoiding the introduction of structural defects at the core–skin interface may yield a significant enhancement of the mechanical properties of carbon fibers.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Improving microstructure of silicon/carbon nanofiber composites as a Li battery anode

We report the interfacial study of a silicon/carbon nanofiber (Si/CNF) nanocomposite material as a potentially high performance anode for rechargeable lithium ion batteries. The carbon nanofiber is hollow, with a graphitic interior and turbostratic exterior. Amorphous silicon layers were uniformly coated via chemical vapor deposition on both the exterior and interior surfaces of the CNF. The resulting Si/CNF composites were tested as anodes for Li ion batteries and exhibited capacities near 800 mAh g1 for 100 cycles. After cycling, we found that more Si had fallen off from the outer wall than from the innerwall of CNF. Theoretical calculations confirmed that this is due to a higher interfacial strength at the Si/Cedge interface at the inner wall than that of the Si/C-basal interface at the outer wall. Based upon the experimental analysis and theoretical calculation, we have proposed several interfacial engineering approaches to improve the performance of the electrodes by optimizing the microstructure of this nanocomposite.

Howe, Jane Y↗
DOE OSTI2016

Potassium-Based alpha-Manganese Dioxide Nanofiber BinderFree Self-Supporting Electrodes: A Design Strategy for High Energy Density Batteries

This work minimizes electrode passive components and moves toward bridging the gap between actual and theoretical battery gravimetric energy density. Binder-free self-supporting (BFSS) cathodes were prepared from redox-active, high aspect ratio, potassium α-MnO2 nanofibers (K-OMS-2), eliminating the binder and current collector. The electroactive and structural element, K-OMS-2, was prepared using a scalable, moderate temperature, aqueous synthesis. The BFFS electrode approach allows fabrication of thick, high energy density electrodes with low impedance, with up to 10 fold improvement in delivered specific energy relative to conventional cathodes. This could enable high capacity large form factor cell designs, as required for applications demanding high energy content. In principle, this approach suggests a widely applicable paradigm for the construction of other BFFS electrodes through the targeted synthesis of other transition metal oxides with high aspect, fibrous morphologies. Introduction

25 ENERGY STORAGE↗
DOE OSTI2013

Carbon nanofibers derived from cellulose nanofibers as a long-life anode material for rechargeable sodium-ion batteries

A highly reversible anode is indispensable to the future success of sodium-ion batteries (SIBs). Herein, carbon nanofibers (CNFs) derived from cellulose nanofibers are investigated as an anode material for SIBs. The CNFs exhibit very promising electrochemical properties, including a high reversible capacity (255 mA h g(-1) at 40 mA g(-1)), good rate capability (85 mA h g(-1) at 2000 mA g(-1)), and excellent cycling stability (176 mA h g(-1) at 200 mA g(-1) over 600 cycles).

Luo, W↗
DOE OSTI2017

Stable Low-Current Electrodeposition of α-MnO 2 on Superaligned Electrospun Carbon Nanofibers for High-Performance Energy Storage

Metal oxide/carbonaceous nanomaterials are promising candidates for energy-storage applications. Yet, inhomogeneous mass and charge transfer across the electrode/electrolyte interface due to unstable metal oxide/carbonaceous nanomaterial synthesis limit their performance in supercapacitors. Here, it is shown that the above problems can be mitigated through stable low-current electrodeposition of MnO 2 on superaligned electrospun carbon nanofibers (ECNFs). The key to this method is coupling a self-designed four steel poles collector for aligned ECNFs and a constant lowcurrent (40 μA) electrodeposition technique to form a uniform Na + -induced α-MnO 2 film which proceeds by a time-dependent growth mechanism involving cluster-“kebab” structures and ending with a compact, uniform MnO 2 film for high-performance energy storage.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Yield strength dependence on strain rate of molybdenum-alloy nanofibers

The yield strength dependence on strain rate was studied for molybdenum-alloy nanofibers with varying initial dislocation density at three different pre-strain levels. In-situ tensile experiments at three displacement rates were carried out in a scanning electron microscope. Yield strength and its scatter decreased as a function of the pre-strain level for different displacement rates. A statistical model was used to analyze the results, and a negative strain rate dependence was inferred from the yield experiments. This finding suggests the need for theoretical investigations since classical models such as dynamic strain aging may have limitations at such nanoscales.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A 3D Lithiophilic Mo 2 N–Modified Carbon Nanofiber Architecture for Dendrite–Free Lithium–Metal Anodes in a Full Cell

The pursuit for high-energy-density batteries has inspired the resurgence of metallic lithium (Li) as a promising anode, yet its practical viability is restricted by the uncontrollable Li dendrite growth and huge volume changes during repeated cycling. Herein, a new 3D framework configured with Mo 2 N-mofidied carbon nanofiber (CNF) architecture is established as a Li host via a facile fabrication method. The lithiophilic Mo 2 N acts as a homogeneously pre-planted seed with ultralow Li nucleation overpotential, thus spatially guiding a uniform Li nucleation and deposition in the matrix. The conductive CNF skeleton effectively homogenizes the current distribution and Li-ion flux, further suppressing Li-dendrite formation. As a result, the 3D hybrid Mo 2 N@CNF structure facilitates a dendrite-free morphology with greatly alleviated volume expansion, delivering a significantly improved Coulombic efficiency of ≈99.2% over 150 cycles at 4 mA cm –2 . Symmetric cells with Mo 2 N@CNF substrates stably operate over 1500 h at 6 mA cm –2 for 6 mA h cm –2 . Furthermore, full cells paired with LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NMC811) cathodes in conventional carbonate electrolytes achieve a remarkable capacity retention of 90% over 150 cycles. Finally, this work sheds new light on the facile design of 3D lithiophilic hosts for dendrite-free lithium-metal anodes.

25 ENERGY STORAGE↗
DOE OSTI2016

What does nitric acid really do to carbon nanofibers? [What nitric acid really does to carbon nanofibers]

Understanding the chemical nature of the surface of carbon nanofibers (CNF) is critical in assessing their fundamental properties and tailoring them for the right application. To gain such knowledge, we present here a detailed X-ray adsorption spectroscopy (XAS) study accompanied by high resolution transmission electron microscopy (TEM) micrographs of two morphologically different CNF pairs (tetrahedral amorphous carbon (ta-C) grown “open structured” fibers and traditional bamboo-like “closed structured” fibers), where the surface chemical properties and structural features of the fibers are investigated in depth and the effects of nitric acid treatment on the fibers are revealed. The morphology of the fiber and/or the original seed- and adhesion layers markedly affect the response of the fibers to the acid treatment. Results also show that the nitric acid treatment increases the observed sp 2 intensity and modifies the two types of fibers to become more-alike both structurally and with respect to their oxygen functionalities. Furthermore, the XAS and HRTEM results confirm that a short nitric acid treatment does not remove the Ni catalyst particle but, instead, oxidizes their surfaces, especially in the case of ta-C grown fibers.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Transparent, Anisotropic Biofilm with Aligned Bacterial Cellulose Nanofibers

Abstract Cellulose nanofibrils are attractive as building blocks for advanced photonic, optoelectronic, microfluidic, and bio‐based devices ranging from transistors and solar cells to fluidic and biocompatible injectable devices. For the first time, an ultrastrong and ultratough cellulose film, which is composed of densely packed bacterial cellulose (BC) nanofibrils with hierarchical fibril alignments, is successfully demonstrated. The molecular level alignment stems from the intrinsic parallel orientation of crystalline cellulose molecules produced by Acetobacter xylinum. These aligned long‐chain cellulose molecules form subfibrils with a diameter of 2–4 nm, which are further aligned to form nanofibril bundles. The BC film yields a record‐high tensile strength (≈1.0 GPa) and toughness (≈25 MJ m −3 ). Being ultrastrong and ultratough, yet the BC film is also highly flexible and can be folded into desirable shapes. The BC film exhibits a controllable manner of alignment and is highly transparent with modulated optical properties, paving the way to enabling new functionalities in mechanical, electrical, fluidic, photonics, and biocompatible applications.

Wang, Sha↗