A Catalytic Etching-Wetting-Dewetting Mechanism in the Formation of Hollow Graphitic Carbon Fiber

Effect of Sepiolite-Loaded Fe2O3 on Flame Retardancy of Waterborne Polyurethane

In this study, a kind of inorganic composite flame retardant (Sep@Fe2O3) was prepared by combining solution deposition and calcination methods using sepiolite microfiber material as carrier. This inorganic compound flame retardant was combined with waterborne polyurethane (WPU) through layer-by-layer method to prepare WPU composites. The SEM and EDS, TEM, and XRD were used to characterize the microscopic morphology and crystal structure of WPU composites. Thermogravimetric analysis tests confirmed the good thermal stability of WPU/Sep@Fe2O3 composites; at the temperature of 600°C, the carbon residual percentage of WPU/Sep, WPU/Fe2O3, and WPU/Sep@Fe2O3 composites is 7.3%, 12.2%, and 13.4%, respectively, higher than that of WPU (1.4%). Vertical combustion tests proved better flame-retardant property of WPU/Sep@Fe2O3 composite-coated cotton than noncoated cotton. The microcalorimeter test proved that the PHRR of WPU/Sep@Fe2O3 composites decreased by 61% compared with that of WPU. In addition, after combining with Sep@Fe2O3, the breaking strength of WPU increased by 35%.

Outside-in catalytic graphitization method for synthesis of dispersible and uniform graphitic porous carbon nanospheres

Common strategies to synthesize graphitic porous carbon nanospheres suffer from energy consumption, exorbitant cost and harsh condition, and lead to closed pore and polydisperse particles. The successful manipulation of adjustable graphitic skeleton, developed porosity, good monodispersity and dispersity of carbon nanospheres is essential to meet their structural varieties and practical applications. Herein, an outside-in catalytic graphitization method is reported to synthesize carbon nanospheres with abovementioned properties, which involves interfacial assembly between layered double hydroxides nanosheets and polymer nanospheres, in-situ generation of nickel nanoparticles, and outside-in catalytic graphitization. The unusual phenomenon is that the in-situ generated nickel nanoparticles are preferentially oriented to the carbon side rather than to the free open space. The interface reactions between nickel nanoparticles and amorphous carbons drive continuous etching of carbon species to form graphitic structure in the interior of spheres. The graphitic structure can be tuned by changing effective charge ratio and pyrolysis conditions and obtained carbon nanospheres possessed good dispersibility in water and ethanol. Moreover, such carbon nanospheres exhibited good performance when used as anodes in lithium-ion batteries. These findings may pave new ways for synthesizing multifarious carbon nanomaterials with adjustable graphitic skeleton, developed porosity, good monodispersity and dispersibility for various applications.

Loading of individual Se-doped Fe2O3-decorated Ni/NiO particles on carbon cloth: facile synthesis and efficient electrocatalysis for the oxygen evolution reaction

The synthesis of competitive, affordable and sustainable electrocatalysts via simple and scalable methods is highly desirable for the oxygen evolution reaction (OER). Usually, expensive, complex, time-consuming methods are applied to prepared suitable electrocatalysts for the OER. In contrast, a single-step thermal method is simple and inexpensive. Nickel and iron-based composite materials are potential candidates as OER catalysts. Accordingly, herein, Se-doped Fe2O3-decorated Ni/NiO particles on carbon cloth (Se-Fe2O3@Ni/NiO/CC) were synthesized via a facile and scalable one-step thermal method. The individual Se-Fe2O3@Ni/NiO particles were accommodated in holes in the carbon fibers of CC. The optimized Se-Fe2O3@Ni/NiO/CC-2 sample exhibited an outstanding OER performance with an overpotential of 205 mV at the current density 10 mA cm-2, small Tafel slope of 36 mV dec-1, and good stability in 1.0 M KOH electrolyte. The outstanding catalytic performance was mainly attributed to the heterointerfaces between Se-Fe2O3 and Se-Ni/NiO. Moreover, the accommodation of the Se-Fe2O3@Ni/NiO particles in the holes of CC restricted the aggregation of the particles, and CC provided a conductive substrate for the OER process. Thus, this work provides a simple, scalable and effective strategy for designing and engineering of outstanding electrocatalysts for the OER.

Building Carbon-Based Versatile Scaffolds on the Electrode Surface to Boost Capacitive Performance for Fiber Pseudocapacitors

In order to fabricate high performance fiber pseudocapacitors, the trade-off between high mass loading and high utilization efficiency of pseudocapacitive materials should be carefully addressed. Here, a solution that is to construct a carbon-based versatile scaffold is reported for loading pseudocapacitive materials on carbonaceous fibers. The scaffold can be easily built by conformally coating commercial pen ink on the fibers without any destruction to the fiber skeleton. Due to the high electrical conductivity and abundant macropore structure, it can provide sufficient loading room and a high ion/electron conductive network for pseudocapacitive materials. Therefore, their loading mass and utilization efficiency can be increased simultaneously, and thus the as-designed fibrous electrode displays a high areal capacitance of 649 mF cm^-2 (or 122 mF cm^-1 based on length), which is higher than most of the reported fiber pseudocapacitors. The simple and low-cost strategy opens up a new way to prepare high performance portable/wearable energy storage devices.

Development and Applications of MOFs Derivative One-Dimensional Nanofibers via Electrospinning: A Mini-Review

Metal organic frameworks (MOFs) have been exploited for various applications in science and engineering due to the possibility of forming different mesoscopic frameworks and pore structures. To date, further development of MOFs for practical applications in areas such as energy storage and conversion have encountered tremendous challenge owing to the unitary porous structure (almost filled entirely with micropores) and conventional morphology (e.g., sphere, polyhedron, and rod shape). More recently, one-dimensional (1D) MOFs/nanofibers composites emerged as a new molecular system with highly engineered novel structures for tailored applications. In this mini-review, the recent progress in the development of MOFs-based 1D nanofibers via electrospinning will be elaborated. In particular, the promising applications and underlying molecular mechanism of electrospun MOF-derived carbon nanofibers are primarily focused and analyzed here. This review is instrumental in providing certain guiding principles for the preparation and structural analysis of MOFs/electrospun nanofibers (M-NFs) composites and electrospun MOF-derived nanomaterials.

Temperature Effect on the Mechanical Properties of Electrospun PU Nanofibers

Polyurethane (PU) nanofibers were prepared from electrospun method. Atomic force microscopy (AFM) was employed to characterize the mechanical properties of electrospun PU nanofibers. The impact of temperature on the mechanical behavior of PU nanofibers was studied using three-point bending test based on AFM. A Young's modulus of ~ 25 GPa was obtained for PU nanofibers with diameter at ~ 150 nm at room temperature. With decrease in nanofiber's diameter, the increasing Young's modulus can be due to the surface tension effect. The Young's modulus of the PU nanofiber decreased linearly while the fibrous morphology was maintained with the increase of temperature.

Facile Synthesis of Palladium-Nanoparticle-Embedded N-Doped Carbon Fibers for Electrochemical Sensing

In recent years, there have been many studies on metal/carbon hybrid materials for electrochemical applications. However, reducing the metal content in catalysts is still a challenge. Here, a facile synthesis of palladium (Pd) nanoparticle-embedded N-doped carbon fibers (Pd/N-C) through electropolymerization and reduction methods is demonstrated. The as-prepared Pd/N-C contains only 1.5 wt % Pd. Under optimal conditions, bisphenol A is detected by using amperometry in two dynamic ranges from 0.1 to 10 μm and from 10 to 200 μm, and the obtained correlation coefficients are close to 0.9836 and 0.9987, respectively. The detection limit (DL) for bisphenol A is determined to be 29.44 (±0.77) nm.

A highly efficient double-hierarchical sulfur host for advanced lithium-sulfur batteries

Li-S batteries have attracted enormous interest due to their potentially high energy density, non-toxicity and the low cost of sulfur. The main challenges of sulfur cathodes are the short cycling life and limited power density caused by the low conductivity of sulfur and dissolution of Li polysulfides. Here we design a new double-hierarchical sulfur host to address these problems. Hierarchical carbon spheres (HCSs), constructed from building blocks of hollow carbon nanobubbles for loading sulfur, are sealed within a thin, polar MoS2 coating composed of ultrathin nanosheets. Experimental and theoretical studies show a strong absorption of the MoS2 nanoshell to polysulfides, and the excellent stability of the MoS2 nanosheets after the adsorption of polysulfides. Moreover, MoS2 promotes the electrochemical redox kinetics in Li-S batteries. Benefiting from the unique hierarchical, hollow and compositional characteristics of the host, the S/MoS2@HCS composite electrode shows a high capacity of 1048 mA h g-1 at 0.2C, good rate capacity and long cycling life with a slow capacity decay of 0.06% per cycle.

Cobalt Doping To Boost the Electrochemical Properties of Ni@Ni3 S2 Nanowire Films for High-Performance Supercapacitors

Metal sulfides have aroused great interest for energy storage. However, their low specific capacities and inferior rate capabilities hinder their practical applications. In this work, a facile cobalt-doping process is used to boost the electrochemical performance of Ni@Ni₃ S₂ core-sheath nanowire film electrodes for high-performance electrochemical energy storage. Co ions are doped successfully and uniformly into Ni₃ S₂ nanosheets through a facile ion-exchange process. The electrochemical properties of film electrodes are improved greatly, and an ultrahigh volumetric capacity (increased from 105 to 730 C cm^-3 at 0.25 A cm^-3 ) and excellent rate capability are obtained after Co is doped into Ni@Ni₃ S₂ core-sheath nanowires. A hybrid asymmetric supercapacitor with Co-doped Ni@Ni₃ S₂ as the positive electrode and graphene-carbon nanotubes as the negative electrode is assembled and exhibits an ultrahigh volumetric capacitance of 142 F cm^-3 (based on the total volume of both electrodes) at 0.5 A cm^-3 and excellent cycling stability (only 3 % capacitance decrease after 5000 cycles). Moreover, the volumetric energy density can reach 44.5 mWh cm^-3 , which is much larger than those of thin-film lithium batteries (1-10 mWh cm^-3 ). These results may provide useful insights for the fabrication of high-performance film electrodes for energy-storage applications.

Bio-inspired spider-web-like membranes with a hierarchical structure for high performance lithium/sodium ion battery electrodes: the case of 3D freestanding and binder-free bismuth/CNF anodes

High gravimetric energy density and volumetric energy density energy storage devices are highly desirable due to the rapid development of electric vehicles, and portable and wearable electronic equipment. Electrospinning is a promising technology for preparing freestanding electrodes with high gravimetric and volumetric energy density. However, the energy density of the traditional electrospun electrodes is restricted by the low mass loading of active materials (e.g. 20%-30 wt%). Herein, a biomimetic strategy inspired by the phenomenon of the sticky spider web is demonstrated as a high performance anode, which simultaneously improves the gravimetric and volumetric energy density. Freestanding carbon nanofiber (CNF) membranes containing over 50 wt% of bismuth were prepared by electrospinning and subsequent thermal treatment. Membranes consisting of CNF network structures bonded tightly with active Bi cluster materials, resulting in excellent mechanical protection and a fast charge transport path, which are difficult to achieve simultaneously. The composite membrane delivers high reversible capacity (483 mA h g^-1 at 100 mA g^-1 after 200 cycles) and high rate performance (242 mA h g^-1 at 1 A g^-1) as a lithium-ion battery anode. For use as a sodium ion battery, the composite membrane also shows a high reversible specific capacity of 346 mA h g^-1 and outstanding cycling performance (186 mA h g^-1 at 50 mA g^-1 after 100 cycles). This work offers a simple, low cost and eco-friendly method for fabricating free-standing and binder-free composite electrodes with high loading used in LIBs and SIBs.

Facile preparation of a V2O3/carbon fiber composite and its application for long-term performance lithium-ion batteries

A V₂O₃/carbon-nanofiber composite was initially synthesized, which exhibited large reversible capacity and excellent long-term cycling performance for lithium-ion batteries.