Mesoporous Carbon Nanofibers Loaded with Ordered PtFe Alloy Nanoparticles for Electrocatalytic Nitrate Reduction to Ammonia

Highly dispersed bimetallic alloy nanoparticle electrocatalysts have been demonstrated to exhibit exceptional performance in driving the nitrate reduction reaction(NO_(3)RR)to generate ammonia(NH_(3)).In this study,we prepared mesoporous carbon nanofibers(mCNFs)functionalized with ordered PtFe alloys(O-PtFe-mCNFs)by a composite micelle interface-induced co-assembly method using poly(ethylene oxide)-block-polystyrene(PEO-b-PS)as a template.When employed as electrocatalysts,O-PtFe-mCNFs exhibited superior electrocatalytic performance for the NO_(3RR)compared to the mCNFs functionalized with disordered PtFe alloys(D-PtFe-mCNFs).Notably,the NH_(3)production performance was particularly outstanding,with a maximum NH_(3)yield of up to 959.6μmol/(h·cm~2).Furthermore,the Faraday efficiency(FE)was even 88.0%at-0.4 V vs.reversible hydrogen electrode(RHE).This finding provides compelling evidence of the potential of ordered PtFe alloy catalysts for the electrocatalytic NO_(3)RR.

Flexural destructive process of unidirectional carbon/carbon composites reinforced with in situ grown carbon nanofibers

Unidirectional carbon/carbon（C/C） composites modified with in situ grown carbon nanofibers（CNFs） were prepared by catalysis chemical vapor deposition. The effect of in situ grown CNFs on the flexural properties of the C/C composites was investigated by detailed analyses of destructive process. The results show that there is a sharp increase in the flexural load-displacement curve in the axial direction of the CNF-C/C composites, followed by a serrated yielding phenomenon similar to the plastic materials. The failure mode of the C/C composites modified with in situ grown CNFs is changed from the pull-out of single fiber to the breaking of fiber bundles. The existence of interfacial layer composed by middle-textured pyrocarbon, CNFs and high-textured pyrocarbon can block the crack propagation and change the propagation direction of the main crack, which leads to the higher flexural strength and modulus of C/C composites.

Flexible, Porous, and Metal–Heteroatom?Doped Carbon Nanofibers as Efficient ORR Electrocatalysts for Zn–Air Battery

Developing an e cient and durable oxygen reduction electrocatalyst is critical for clean-energy technology, such as fuel cells and metal–air batteries. In this study, we developed a facile strategy for the preparation of flexible, porous, and well-dispersed metal–heteroatom-doped carbon nanofibers by direct carbonization of electrospun Zn/Co-ZIFs/PAN nanofibers(Zn/Co-ZIFs/PAN). The obtained Zn/Co and N co-doped porous carbon nanofibers carbonized at 800 °C(Zn/Co–N@PCNFs-800) presented a good flexibility, a continuous porous structure, and a superior oxygen reduction reaction(ORR) catalytic activity to that of commercial 20 wt% Pt/C, in terms of its onset potential(0.98 V vs. RHE), half-wave potential(0.89 V vs. RHE), and limiting current density(-5.26 mA cm^(-2)). In addition, we tested the suitability and durability of Zn/Co–N@PCNFs-800 as the oxygen cathode for a rechargeable Zn–air battery. The prepared Zn–air batteries exhibited a higher power density(83.5 mW cm^(-2)), a higher specific capacity(640.3 mAh g^(-1)), an excellent reversibility, and a better cycling life than the commercial 20 wt% Pt/C + RuO_2 catalysts. This design strategy of flexible porous non-precious metal-doped ORR electrocatalysts obtained from electrospun ZIFs/polymer nanofibers could be extended to fabricate other novel, stable, and easy-to-use multi-functional electrocatalysts for clean-energy technology.

Preparation of a novel PAN/cellulose acetate-Ag based activated carbon nanofiber and its adsorption performance for low-concentration SO_2

Polyacrylonitrile （PAN）, PAN/cellulose acetate （CA）, and PAN/CA-Ag based activated carbon nanofiber （ACNF） were prepared using electrostatic spinning and further heat treatment. Thermogravimetrylifferential scanning calorimetry （TG-DSC） analysis indicated that the addition of CA or Ag did not have a significant impact on the thermal decomposition of PAN materials but the yields of fibers could be improved. Scanning electron microscopy （SEM） analysis showed that the micromorphologies of produced fibers were greatly influenced by the viscosity and conductivity of precursor solutions. Fourier transform infrared spectroscopy （FT-IR） analysis proved that a cyclized or trapezoidal structure could form and the carbon scaffold composed of C=C bonds appeared in the PAN-based ACNFs. The characteristic dif- fraction peaks in X-ray diffraction （XRD） spectra were the evidence of a turbostratic structure and silver existed in the PAN/CA-Ag based ACNF. Brurmer-Emmett-Teller （BET） analysis showed that the doping of CA and Ag increased surface area and micropore volume of fi- bers; particularly, PAN/CA-Ag based ACNF exhibited the best porosity feature. Furthermore, SO2 adsorption experiments indicated that all the three fibers had good adsorption effects on lower concentrations of SO2 at room temperature; especially, the PAN/CA-Ag based ACNF showed the best adsorption performance, and it may be one of the most promising adsorbents used in the fields of chemical industry and en- vironment protection.

Improved Na+/K+ Storage Properties of ReSe2–Carbon Nanofibers Based on Graphene Modifications

Rhenium diselenide(ReSe2) has caused considerable concerns in the field of energy storage because the compound and its composites still suffer from low specific capacity and inferior cyclic stability.In this study,ReSe2 nanoparticles encapsulated in carbon nanofibers were synthesized successfully with simple electrospinning and heat treatment.It was found that graphene modifications could affect considerably the microstructure and electrochemical properties of ReSe2–carbon nanofibers.Accordingly,the modified compound maintained a capacity of 227 mAhg-1 after 500cycles at 200 mAg-1 for Na+storage,230 mAh g-1 after 200 cycles at 200 mAg-1,212 mAh g-1 after 150 cycles at 500 mAg-1 for K+ storage,which corresponded to the capacity retention ratios of 89%,97%,and 86%,respectively.Even in Na+full cells,its capacity was maintained to 82% after 200 cycles at 1 C(117 mAg-1).The superior stability of ReSe2–carbon nanofibers benefitted from the extremely weak van der Waals interactions and large interlayer spacing of ReSe2,in association with the role of graphene-modified carbon nanofibers,in terms of the shortening of electron/ion transport paths and the improvement of structural support.This study may provide a new route for a broadened range of applications of other rhenium-based compounds.

Preparation and electrochemical properties of carbon-coated LiFePO_4 hollow nanofibers

Carbon-coated LiFePO_4 hollow nanofibers as cathode materials for Li-ion batteries were obtained by coaxial electrospinning. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller specific surface area analysis, galvanostatic charge–discharge, and electrochemical impedance spectroscopy（EIS） were employed to investigate the crystalline structure, morphology, and electrochemical performance of the as-prepared hollow nanofibers. The results indicate that the carbon-coated LiFePO_4 hollow nanofibers have good long-term cycling performance and good rate capability： at a current density of 0.2C（1.0C = 170 mA ·g^-1） in the voltage range of 2.5–4.2 V, the cathode materials achieve an initial discharge specific capacity of 153.16 mA h·g^-1 with a first charge–discharge coulombic efficiency of more than 97%, as well as a high capacity retention of 99% after 10 cycles; moreover, the materials can retain a specific capacity of 135.68 mA h·g^-1, even at 2C.

Application of activated carbon-decorated polyacrylonitrile nanofibers as an adsorbent in dispersive solid-phase extraction of fluoroquinolones from wastewater

A cheap and simple sample preparation method, consisting of a dispersive solid-phase method and an adsorbent, activated carbon decorated PAN nanofibers, was employed and used for the extraction of antibiotics(ciprofloxacin, danofloxacin, and enrofloxacin) in wastewater. Electrospun PAN nanofibers that were decorated with activated carbon produced from waste tires were used as the solid phase and the antibiotics analyzed by using high-performance liquid chromatography. Parameters such as pH, mass of adsorbent(MA),extraction volume(EV), and extraction time(ET) were optimized owing to their potential effect on the extraction of antibiotics from water. The recovery of all antibiotics was satisfactory, in the range of 90%–99%.The limits of detection and quantification were 0.05, 0.11, 0.20, and 0.53, 1.21, 2.17 mg/L, respectively. The precision was determined from the repeatability and reproducibility and expressed as the intra-day(n=20)and inter-day(n=5) precision. The intra-day and inter-day precision was reported in terms of the percentage relative standard deviation, which was 3% and 4%, respectively. The adsorption capacity of the activated carbon-decorated PAN nanofibers was satisfactory, and the reusability of the adsorbent was impressive when reused ten times. The accuracy of the dispersive solid phase extraction(DSPE) was validated by spike recovery tests; the results proved the reliability and efficiency of adsorbing antibiotics from wastewater. Finally, the proposed method was applied to wastewater samples collected from a wastewater treatment plant, which included influent, secondary, and effluent wastewater.

N, F?Codoped Microporous Carbon Nanofibers as Efficient Metal?Free Electrocatalysts for ORR

Currently, the oxygen reduction reaction(ORR) mainly depends on precious metal platinum(Pt) catalysts. However, Pt-based catalysts have several shortcomings, such as high cost, scarcity, and poor long-term stability. Therefore, development of e cient metal-free electrocatalysts to replace Pt-based electrocatalysts is important. In this study, we successfully prepared nitrogen-and fluorinecodoped microporous carbon nanofibers(N, F-MCFs) via electrospinning polyacrylonitrile/polyvinylidene fluoride/polyvinylpyrrolidone(PAN/PVDF/PVP) tricomponent polymers followed by a hydrothermal process and thermal treatment, which was achieved for the first time in the literature. The results indicated that N, F-MCFs exhibit a high catalytic activity(E_(onset): 0.94 V vs. RHE, E_(1/2): 0.81 V vs. RHE, and electron transfer number: 4.0) and considerably better stability and methanol tolerance for ORR in alkaline solutions as compared to commercial Pt/carbon(Pt/C, 20 wt%) catalysts. Furthermore, in acidic media, N, F-MCFs showed a four-electron transfer pathway for ORR. This study provides a new strategy for in situ synthesis of N, F-MCFs as highly e cient metal-free electrocatalysts for ORR in fuel cells.

Porosity and Pore Size Distribution Measurement of Cement/Carbon Nanofiber Composites by ~1H Low Field Nuclear Magnetic Resonance

The dispersion effect of carbon nanofibers （CNFs） in aqueous solution and the mechanical properties, porosity, pore size distribution and microstructure of CNFs reinforced cement-based composites were investigated in this paper. To achieve effective dispersion of CNFs, a method utilizing ultrasonic processing and a commercially surfactant were employed. CNFs were incorporated to cementitious materials with the addition of 0.1 wt% and 0.2 wt% of cement with a water/cement ratio of 0.35. The mechanical properties of CNFs/ cement composites were analyzed, the porosity and pore size distribution were characterized by ^1H low field nuclear magnetic resonance （NMR）, and the microstructure was observed by scanning electron microscopy （SEM）. The results indicate that the optimum concentration ratio of MC to CNFs is 2：1 for dispersing in aqueous solution. Moreover, in the field of mechanical properties, CNFs can improve the flexural strength and compressive strength. The increased mechanical properties and the decreased porosity of the matrices correspond to the increasing CNFs content and CNFs act as bridges and networks across cracks and voids.

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, 3 D 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 k Hz, respectively. At 120 Hz, the electrode capacitance density was 0.37 and 0.16 m F 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 promisingpotential of this technology for compact power supply design and other applications.

N-doped porous carbon nanofibers sheathed pumpkin-like Si/C composites as free-standing anodes for lithium-ion batteries

Dramatic capacity fading and poor rate performance are two main obstacles that severely hamper the widespread application of the Si anode owing to its large volume variation during cycling and low intrinsic electrical conductivity.To mitigate these issues,free-standing N-doped porous carbon nanofibers sheathed pumpkin-like Si/C composites(Si/C-ZIF-8/CNFs)are designed and synthesized by electrospinning and carbonization methods,which present greatly enhanced electrochemical properties for lithium-ion battery anodes.This particular structure alleviates the volume variation,promotes the formation of stable solid electrolyte interphase(SEI)film,and improves the electrical conductivity.As a result,the as-obtained free-standing Si/C-ZIF-8/CNFs electrode delivers a high reversible capacity of 945.5 mAh g^(-1) at 0.2 A g^(-1) with a capacity retention of 64% for 150 cycles,and exhibits a reversible capacity of 538.6 mA h g^(-1) at 0.5 A g^(-1) over 500 cycles.Moreover,the full cell composed of a freestanding Si/C-ZIF-8/CNFs anode and commercial LiNi_(1/3)Co_(1/3)Mn_(1/3)O_(2)(NCM)cathode shows a capacity of 63.4 mA h g^(-1) after 100 cycles at 0.2 C,which corresponds to a capacity retention of 60%.This rational design could provide a new path for the development of high-performance Si-based anodes.

Stepwise Fabrication of Co-Embedded Porous Multichannel Carbon Nanofibers for High-Efficiency Oxygen Reduction

A novel nonprecious metal material consisting of Coembedded porous interconnected multichannel carbon nanofibers(Co/IMCCNFs) was rationally designed for oxygen reduction reaction(ORR)electrocatalysis.In the synthesis,ZnCo2O4 was employed to form interconnected mesoporous channels and provide highly active Co3O4/Co core–shell nanoparticle-based sites for the ORR.The IMC structure with a large synergistic effect of the N and Co active sites provided fast ORR electrocatalysis kinetics.The Co/IMCCNFs exhibited a high half-wave potential of 0.82 V(vs.reversible hydrogen electrode) and excellent stability with a current retention up to 88% after 12,000 cycles in a current–time test,which is only 55% for 30 wt% Pt/C.

Effective Modified Carbon Nanofibers as Electrodes for Capacitive Deionization Process

Carbon materials have the advantages of good electrical conductivity and excellent chemical stability, so many carbon materials have been introduced as electrodes for the capacitive deionization (CDI) process. Due to the low surface area compared to the other nanocarbonaceous materials, CNFs performance as electrode in the CDI units is comparatively low. This problem has been overcome by preparing high surface area carbon nanofibers and by creating numerous long pores on the nanofibers surface. The modified CNFs have been synthesized using low cost, high yield and facile method;electrospinning technique. Stabilization and graphitization of electrospun nanofiber mats composed of polyacrylonitrile (PAN) and poly (methyl methacrylate) (PMMA) leads form longitudinal pores CNFs. The utilized characterizations indicated that the CNFs obtained from electrospun solution having 50% PMMA have surface area of 181 m2/g which are more than the conventional CNFs. Accordingly, these nanofibers revealed salt removal efficiency of ~90% and specific capacitance of 237 F/g.

Porous nitrogen-enriched hollow carbon nanofibers as freestanding electrode for enhanced lithium storage

Onedimensional porous carbons bearing high surface areas and sufficient heteroatom doped functionalities are essential for advanced electrochemical energy storage devices,especially for developing freestanding film electrodes.Here we develop a porous,nitrogenenriched,freestanding hollow carbon nanofiber(PNFHCF)electrode material via filtration of polypyrrole(PPy)hollow nanofibers formed by in situ selfdegraded templateassisted strategy,followed by NH3assisted carbonization.The PNFHCF retains the freestanding film morphology that is composed of threedimensional networks from the entanglement of 1D nanofiber and delivers 3.7fold increase in specific surface area(592 m^(2)g^(-1))compared to the carbon without NH_(3)treatment(FHCF).In spite of the enhanced specific surface area,PNFHCF still exhibits comparable high content of surface N functionalities(8.8%,atom fraction)to FHCF.Such developed hierarchical porous structure without sacrificing N doping functionalities together enables the achievement of high capacity,highrate property and good cycling stability when applied as selfsupporting anode in lithiumion batteries,superior to those of FHCF without NH3 treatment.

Functionalized graphene oxide-reinforced electrospun carbon nanofibers as ultrathin supercapacitor electrode

Graphene oxide has been used widely as a starting precursor for applications that cater to the needs of tunable graphene. However, the hydrophilic characteristic limits their application, especially in a hydrophobic condition. Herein, a novel non-covalent surface modification approach towards graphene oxide was conducted via a UV-induced photo-polymerization technique that involves two major routes; a UV-sensitive initiator embedded via pi-pi interactions on the graphene planar rings, and the polymerization of hydrophobic polymeric chains along the surface. The functionalized graphene oxide successfully achieved the desired hydrophobicity as it displayed the characteristic of being readily dissolved in organic solvent. Upon its addition into a polymeric solution and subjected to an electrospinning process,non-woven random nanofibers embedded with graphene oxide sheets were obtained. The prepared polymeric nanofibers were subjected to two-step thermal treatments that eventually converted the polymeric chains into a carbon-rich conductive structure. A unique morphology was observed upon the addition of the functionalized graphene oxide, whereby the sheets were embedded and intercalated within the carbon nanofibers and formed a continuous structure. This reinforcement effectively enhanced the electrochemical performance of the carbon nanofibers by recording a specific capacitance of up to 140.10 F/g at the current density of 1 A/g, which was approximately three folds more than that of pristine nanofibers.It also retained the capacitance up to 96.2% after 1000 vigorous charge/discharge cycles. This functionalization technique opens up a new pathway in tuning the solubility nature of graphene oxide towards the synthesis of a graphene oxide-reinforced polymeric structure.

CO_x-Free Hydrogen and Carbon Nanofibers Produced from Direct Decomposition of Methane on Nickel-Based Catalysts

Direct decomposition of methane was carried out using a fixed-bed reactor at 700 ℃ for the production of COx-free hydrogen and carbon nanofibers. The catalytic performance of NiO-M/SiO2 catalysts （where M=AgO, CoO, CuO, FeO, MnOx and MoO） in methane decomposition was investigated. The experimental results indicate that among the tested catalysts, NiO/SiO2 promoted with CuO give the highest hydrogen yield. In addition, the examination of the most suitable catalyst support, including Al2O3, CeO2, La2O3, SiO2, and TiO2, shows that the decomposition of methane over NiO-CuO favors SiOx support. Furthermore, the optimum ratio of NiO to CuO on SiO2 support for methane decomposition was determined. The experimental results show that the optimum weight ratio of NiO to CuO fell at 8：2 （w/w） since the highest yield of hydrogen was obtained over this catalyst.

CoN_(x)C active sites-rich three-dimensional porous carbon nanofibers network derived from bacterial cellulose and bimetal-ZIFs as efficient multifunctional electrocatalyst for rechargeable Zn–air batteries

In this work, a CoNxC active sites-rich three-dimensional porous carbon nanofibers network derived from bacterial cellulose and bimetal-ZIFs is prepared via a nucleation growth strategy and a pyrolysis process.The material displays excellent electrocatalytic activity for the oxygen reduction reaction, reaching a high limiting diffusion current density of -7.8 mA cm^(-2), outperforming metal–organic frameworks derived multifunctional electrocatalysts, and oxygen evolution reaction and hydrogen evolution reaction with low overpotentials of 380 and 107 mV, respectively. When the electrochemical properties are further evaluated, the electrocatalyst as an air cathode for Zn-air batteries exhibits a high cycling stability for63 h as well as a maximum power density of 308 mW cm^(-2), which is better than those for most Zn-air batteries reported to date. In addition, a power density of 152 mW cm^(-2) is provided by the solid-state Zn-air batteries, and the cycling stability is outstanding for 24 h. The remarkable electrocatalytic properties are attributed to the synergistic effect of the 3 D porous carbon nanofibers network and abundant inserted CoNxC active sites, which enable the fast transmission of ions and mass and simultaneously provide a large contact area for the electrode/electrolyte.

Low-Temperature Carbonized Nitrogen-Doped Hard Carbon Nanofiber Toward High-Performance Sodium-Ion Capacitors

Carbon nanofiber(CNF)was widely utilized in the field of electrochemical energy storage due to its superiority of conductivity and mechanics.However,CNF was generally prepared at relatively high temperature.Herein,nitrogen-doped hard carbon nanofibers(NHCNFs)were prepared by a lowtemperature carbonization treatment assisted with electrospinning technology.Density functional theory analysis elucidates the incorporation of nitrogen heteroatoms with various chemical states into carbon matrix would significantly alter the total electronic configurations,leading to the robust adsorption and efficient diffusion of Na atoms on electrode interface.The obtained material carbonized at 600°C(NHCNF-600)presented a reversible specific capacity of 191.0 mAh g^(−1)and no capacity decay after 200 cycles at 1 A g^(−1).It was found that the sodium-intercalated degree had a correlation with the electrochemical impedance.A sodium-intercalated potential of 0.2 V was adopted to lower the electrochemical impedance.The constructed sodium-ion capacitor with activated carbon cathode and presodiated NHCNF-600 anode can present an energy power density of 82.1 Wh kg^(−1)and a power density of 7.0 kW kg^(−1).

Impregnation of carbonaceous nanofibers into glassy polymer-based composite membrane for CO_2 separation

The development of defect-free composite membrane(CM) is often challenging due to poor dispersion and distribution of filler particles in the polymer matrix. Despite the attractive physicochemical properties and gas separation performance of carbon nanotube(CNT) based CM, CNT displayed poor dispersion characteristics in most polymer matrix domain. Instead of incorporating CNT, a viable alternative, carbon nanofiber(CNF) which exhibits similar properties as CNT, but improved dispersion quality in the polymer matrix is found. In this work,CNF particles were incorporated in poly(2,6-dimethyl-1,4-phenylene oxide)(PPOdm) polymer continuous phase for CM development. The optimum gas separation performance of the PPOdm-CNF CM(11.25 at 197.02 barrer of CO_2 permeability) was obtained at 3 wt% of CNF loading. Compared to pristine PPOdmmembrane,CO_2 permeability and CO_2/CH_4 selectivity of PPOdm-3 wt% CNF CM were enhanced by 180% and 55%, respectively.At 3 wt% CNF loading, the filler particles were dispersed and distributed more homogenously, in which no obvious CNF agglomeration was observed. In addition, the incorporation of CNF particles also enhanced the mechanical and thermal properties of the resultant CM.

A correlation between structural changes in a Ni-Cu catalyst during decomposition of ethylene/ammonia mixture and properties of nitrogen-doped carbon nanofibers

Changes of a 65Ni25Cu10A1203 catalyst consisting of Ni-enriched and Cu-enriched alloys were investigated in the bulk and on the surface during the growth of nitrogen-doped carbon nanofibers （N-CNFs） by decomposition of a 50%C2I-I4/50%NH3 mixture using in situ X-ray diffraction （XRD） analysis, ex situ X-ray photoelectron spectroscopy （XPS） and transmission electron microscopy （TEM） techniques. It was shown that N-CNF growth at 450-650 ℃is accompanied by dissolution of carbon and nitrogen in the Ni-enriched alloy, whereas Cu-enriched alloy remains inactive. A correlation between nickel and copper surface concentrations and properties of N-CNFs in relation to the nitrogen content was found. It was demonstrated that phase composition of the catalyst during N-CNF growth determines the type of N-CNFs structure.