Structure Of Carbon Nanofibers Research Articles

Elucidating the Chemical Pre-Lithiation Mechanism of Hard Carbon Anodes for Ultra-high Stability Lithium-Ion Batteries.

The hard carbon (HC) anode materials demonstrate high capacity and excellent rate performance in lithium-ion batteries. However, HC anodes suffer from excessive loss of Li+ ions during the formation of the solid electrolyte interphase (SEI) film, leading to poor cycling stability, which hinders their large-scale applications. Herein, a facile pre-lithiation strategy is proposed to achieve multi-functional precompensation of carbon nanofibers (CNFs) anodes. Both experimental and density functional theory (DFT) calculation results revealed that the strategy compensated for the loss of Li+ ions and reacted with four structures of CNFs during pre-lithiation, including tiny graphite domains, CO-containing functional groups, defects, and micropores. Furthermore, the lithium in pre-lithiated carbon nanofibers (pCNFs) existed in various forms, consisting of LiC24 and LiC18, Li─O─C, quasi-metallic lithium, and Li+ ions. Moreover, the uniformly distributed lithium on the surface of pCNFs induced the formation of denser and more robust LiF/Li2CO3-rich SEI film, which promoted Li+ ions transport. As a result, pCNFs showed more stable cycling performance (369.8mAhg-1, almost no decay for 1500 cycles). This work provides deeper insight into chemical pre-lithiation and offers a simple and mild strategy for highly stable batteries.

Free‐Standing Si@C/CNFs Prepared by Simple Electrospinning as a Stable Anode for Lithium‐Ion Batteries

AbstractThe development of free‐standing and foldable electrodes with excellent electrochemical performance is paramount for flexible electronic devices. However, the silicon‐based free‐standing anodes lack a straightforward preparation process. Herein, we successfully designed a hierarchical Si@C/CNFs composite material by combining hydrothermal and electrospinning techniques, in which the carbon‐coated silicon (Si@C) is served as the primary nanostructure and carbon nanofibers (CNFs) from electrospinning are maintained as the network matrix, resulting in a free‐standing anode. Owing to the amorphous carbon coating on Si nanoparticles and the formation of a 3D network structure of CNFs, which tightly encases the primary Si@C nanostructure, the Si@C/CNFs electrode demonstrates exceptional conductivity and flexibility. This dual carbon‐layer structure further enhances kinetics and mitigates the volume expansion of Si nanoparticles. The Si@C/CNFs electrode exhibits a high specific capacity (1573 mAh g−1 at 0.1 A g−1), exceptional rate capability, and excellent cycling stability (78.5 % capacity retention after 100 cycles). Thus, Si@C/CNFs can be a promising material for the anode electrode in flexible lithium‐ion batteries.

Tailoring Single‐Atom Coordination Environments in Carbon Nanofibers via Flash Heating for Highly Efficient Bifunctional Oxygen Electrocatalysis

The rational design of carbon‐supported transition metal single‐atom catalysts necessitates precise atomic positioning within the precursor. However, structural collapse during pyrolysis can occlude single atoms, posing significant challenges in controlling both their utilization and coordination environment. Herein, we present a surface atom adsorption‐flash heating (FH) strategy, which ensures that the pre‐designed carbon nanofiber structure remains intact during heating, preventing unforeseen collapse effects and enabling the formation of metal atoms in nano‐environments with either tetra‐nitrogen or penta‐nitrogen coordination at different flash heating temperatures. Theoretical calculations and in situ Raman spectroscopy reveal that penta‐nitrogen coordinated cobalt atoms (Co‐N5) promote a lower energy pathway for oxygen reduction and oxygen evolution reactions compared to the commonly formed Co‐N4 sites. This strategy ensures that Co‐N5 sites are fully exposed on the surface, achieving exceptionally high atomic utilization. The turnover frequency (65.33 s‐1) is 47.4 times higher than that of 20% Pt/C under alkaline conditions. The porous, flexible carbon nanofibers significantly enhance zinc‐air battery performance, with a high peak power density (273.8 mW cm‐2), large specific capacity (784.2 mA h g‐1), and long‐term cycling stability over 600 h. Additionally, the flexible fiber‐shaped zinc‐air battery can power wearable devices, demonstrating significant potential in flexible electronics applications.

Tailoring Single-Atom Coordination Environments in Carbon Nanofibers via Flash Heating for Highly Efficient Bifunctional Oxygen Electrocatalysis.

The rational design of carbon-supported transition metal single-atom catalysts necessitates precise atomic positioning within the precursor. However, structural collapse during pyrolysis can occlude single atoms, posing significant challenges in controlling both their utilization and coordination environment. Herein, we present a surface atom adsorption-flash heating (FH) strategy, which ensures that the pre-designed carbon nanofiber structure remains intact during heating, preventing unforeseen collapse effects and enabling the formation of metal atoms in nano-environments with either tetra-nitrogen or penta-nitrogen coordination at different flash heating temperatures. Theoretical calculations and in situ Raman spectroscopy reveal that penta-nitrogen coordinated cobalt atoms (Co-N5) promote a lower energy pathway for oxygen reduction and oxygen evolution reactions compared to the commonly formed Co-N4 sites. This strategy ensures that Co-N5 sites are fully exposed on the surface, achieving exceptionally high atomic utilization. The turnover frequency (65.33 s-1) is 47.4 times higher than that of 20 % Pt/C under alkaline conditions. The porous, flexible carbon nanofibers significantly enhance zinc-air battery performance, with a high peak power density (273.8 mW cm-2), large specific capacity (784.2 mAh g-1), and long-term cycling stability over 600 h. Additionally, the flexible fiber-shaped zinc-air battery can power wearable devices, demonstrating significant potential in flexible electronics applications.

Lignin regulating the active sites and peroxymonosulfate activation capacities of iron incorporated 1D carbon nanofiber for efficient organic pollutant degradation

In this study, 1D iron incorporated carbon nanofiber composite catalysts (PLCF-Fe) were prepared by pyrolyzing iron nitrate embedded polyacrylonitrile/lignin electrospun nanofiber. PLCF-Fe exhibited prominent peroxymonosulfate (PMS) activation capability for organic pollutant degradation, in which 1D structured carbon nanofiber effectively inhibited the aggregation of iron moieties. The introduction of lignin could modulate the oxidation capacities of the prepared PLCF-Fe through regulating both the graphitic degree as well as the oxygen-containing group distributions of the carbon nanofiber, and the crystalline phase composition of the iron compounds in PLCF-Fe. The existence of multiple active sites could concertedly trigger radical and non-radical PMS activation for high-efficient pollutant degradations, during which process negligible iron ions were leached. It was also found that pollutant degradation rate in PLCF-Fe/PMS system was correlated well with their highest occupied molecular orbital positions. Additionally, PLCF-Fe/PMS system could maintain conspicuous catalytic performance in a variety of water matrices with wide pH application range. This study provides an applicable structure and active sites regulating approach to prepare high-efficiency heterogeneous catalyst for PMS based Fenton-like organic decontamination processes.

Synthesis and Characterization of Nanocellulose/Polyacrylonitrile‐based Carbon Nanofibers: An Approach toward Low Cost and Sustainable Agro Waste based Carbon Nanomaterials

AbstractThe cost of polymer precursors and high energy need in carbonization for the preparation of carbon materials are two limiting factors in the commercialization of carbon‐based materials. In this study, carbon nanofiber films were prepared by adding a very small concentration of polymer polyacrylonitrile in nanocellulose (extracted from agro waste i.e., rice straws) with an overall aim of producing carbon nanomaterials with cost effective, renewable and sustainable carbon source. Polyacrylonitrile (PAN) added nanocellulose solution was drop‐casted to prepare Nanocellulose/Polyacrylonitrile‐based nanofibers film (NC/PAN). It was further stabilized in air atmosphere at 280 °C followed by carbonized in nitrogen atmosphere at 700 °C. It was found that addition of NC/PAN have 18 % lower activation energies than PAN. Results of tunneling electron microscopy showed that polyacrylonitrile/nanocellulose films carbonized at 700 °C temperature exhibited amorphous carbon nanofibers structure similar to bare polyacrylonitrile based carbon film carbonized at higher temperature of 1000 °C‐1200 °C. Furthermore, polyacrylonitrile/nanocellulose based carbon nanofibers have showed high degree of carbonization ((ID)/(IG)=0.87) as compared to bare polyacrylonitrile based carbon nanofibers film ((ID)/(IG)=1.02). This may be attributed to chiral nature of nanocellulose which served as a template to orientation of graphene planes and showed efficient carbonization.

The influence of structure of carbon nanofibers on their interaction with polyethylene matrix

The development of methods for purposeful modification of the polyethylene matrix with carbon nanostructures to create stronger and more durable pipe composites is an important direction in polymer science. Carbon nanofibers (CNFs) of three types, obtained via catalytic chemical vapor deposition of ethylene (Type I), trichloroethylene (Type II), and a mixture of ethylene and acetonitrile (Type III), were applied as modifying additives to improve the physical and mechanical characteristics of polyethylene. The polyethylene/CNF composites were prepared using a laboratory plasticizer. The introduction of CNFs (Type I) with a densely packed structure into the polymer matrix was found to provide the formation of a uniform fine-spherulitic structure that results in increased tensile strength, yield strength, elastic modulus, and abrasive wear. Such a positive effect is observed when the CNF content in the composite does not exceed 1.0 wt%. An increase in the abrasion resistance by a factor of 1.6 was observed.

Pore-confined strategy to achieve controllable growth of Co/CoO in carbon nanofibers for the fabrication of lightweight and enhanced microwave absorbers

In recent years, magnetic metal nanoparticles (NPs)/carbon nanofibers (CNFs) composites have become very promising electromagnetic waves (EMWs) absorbers. However, how to achieve controllable growth of magnetic metals in CNFs is still an urgent problem to be solved. Herein, we reported a pore-confined strategy for constructing the porous Co/CoO/CNFs. By introducing different amounts of acetone (0.20 g, 0.30 g and 0.40 g) into the aqueous phase spinning solution to construct the porous structure, we achieved uniform distribution of Co/CoO NPs and ultimately obtained the porous Co/CoO/CNFs microwave absorbers (MAs) with excellent microwave absorption performance. Thanks to the excellent impedance matching and enhanced polarization loss, the porous Co/CoO/CNFs obtained the minimum reflection loss (RL) of −52.2 dB with a thickness of 3.0 mm, and the effective bandwidth (EBW) was 3.02 GHz when the acetone addition in the spinning solution was 0.30 g. Therefore, the pore-confined strategy proposed herein is conducive to the design of the MAs with excellent performance and low infilling rates based on CNFs. Furthermore, the porous structure of CNFs also improves the lightweight performance of the MAs.

Synergistic Engineering of CoO/MnO Heterostructures Integrated with Nitrogen-Doped Carbon Nanofibers for Lithium-Ion Batteries.

The integration of heterostructures within electrode materials is pivotal for enhancing electron and Li-ion diffusion kinetics. In this study, we synthesized CoO/MnO heterostructures to enhance the electrochemical performance of MnO using a straightforward electrostatic spinning technique followed by a meticulously controlled carbonization process, which results in embedding heterostructured CoO/MnO nanoparticles within porous nitrogen-doped carbon nanofibers (CoO/MnO/NC). As confirmed by density functional theory calculations and experimental results, CoO/MnO heterostructures play a significant role in promoting Li+ ion and charge transfer, improving electronic conductivity, and reducing the adsorption energy. The accelerated electron and Li-ion diffusion kinetics, coupled with the porous nitrogen-doped carbon nanofiber structure, contribute to the exceptional electrochemical performance of the CoO/MnO/NC electrode. Specifically, the as-prepared CoO/MnO/NC exhibits a high reversible specific capacity of 936 mA h g-1 at 0.1 A g-1 after 200 cycles and an excellent high-rate capacity of 560 mA h g-1 at 5 A g-1, positioning it as a competitive anode material for lithium-ion batteries. This study underscores the critical role of electronic and Li-ion regulation facilitated by heterostructures, offering a promising pathway for designing transition metal oxide-based anode materials with high performances for lithium-ion batteries.

Nitrogen-Doped, Vertically Aligned Structures of Graphene and Carbon Nanofibers for Energy Storage Applications

Nitrogen-Doped, Vertically Aligned Structures of Graphene and Carbon Nanofibers for Energy Storage Applications

Accelerating lithium-sulfur battery reaction kinetics and inducing 3D deposition of Li2S using interactions between Fe3Se4 and lithium polysulfides

Although lithium-sulfur batteries (LSBs) exhibit high theoretical energy density, their practical application is hindered by poor conductivity of the sulfur cathode, the shuttle effect, and the irreversible deposition of Li2S. To address these issues, a novel composite, using electrospinning technology, consisting of Fe3Se4 and porous nitrogen-doped carbon nanofibers was designed for the interlayer of LSBs. The porous carbon nanofiber structure facilitates the transport of ions and electrons, while the Fe3Se4 material adsorbs lithium polysulfides (LiPSs) and accelerates its catalytic conversion process. Furthermore, the Fe3Se4 material interacts with soluble LiPSs to generate a new polysulfide intermediate, LixFeSy complex, which changes the electrochemical reaction pathway and facilitates the three-dimensional deposition of Li2S, enhancing the reversibility of LSBs. The designed LSB demonstrates a high specific capacity of 1529.6 mA h g−1 in the first cycle at 0.2 C. The rate performance is also excellent, maintaining an ultra-high specific capacity of 779.7 mA h g−1 at a high rate of 8 C. This investigation explores the mechanism of the interaction between the interlayer and LiPSs, and provides a new strategy to regulate the reaction kinetics and Li2S deposition in LSBs.

Transforming Disposed Face Masks into S‐Doped Carbon Nanofibers for High Performance Supercapacitors

AbstractThe substantial increase in discarded face masks since the onset of the COVID‐19 pandemic has resulted in extensive environmental pollution from plastic waste. This study presents a novel upcycling method to repurpose disposable face masks into a carbon‐based nanomaterial for use in supercapacitors. The upcycled sample, CSDFM@800, demonstrates very good supercapacitor properties, boasting a high specific capacitance of 234 F g−1 at a current density of 0.5 A g−1. Additionally, the symmetric coin cell supercapacitor constructed from this material exhibits excellent performance, achieving a high energy density of 8.54 Wh kg−1 at a low current density of 0.5 A g−1, and maintaining superior capacitance retention of 96.8 % after 15,000 charge/discharge cycles at a current density of 10 A g−1. Materials characterisation results and electrochemical analysis reveal that this upcycling process not only preserves the carbon nanofiber structure but also introduces highly reactive sulfur as a heteroatom doping element.

Effect of etchant gases on the structure and properties of carbon nanofibers

The utilization of plasma-enhanced chemical vapor deposition (PECVD) for carbon nanofiber (CNF) growth using NH3 as the etchant gas has been extensively documented. Notably, NH3 serves a dual role by etching excess carbon and providing N heteroatoms. Most studies neglect to address this phenomenon, despite the well-known impact of N-doping on CNF properties. Furthermore, NH3 exhibits specific interactions with C2H2—it not only etches excess carbon, but also suppresses the dissociation of C2H2. The implications of this phenomenon on CNF micro- and macroscale morphology have not been comprehensively investigated. To elucidate the influence of etchant gases on CNF structure and properties, we fabricated two types of CNFs - N-doped CNFs (N-CNF) and undoped CNFs (U-CNF). Both were grown on identical substrates using the same carbon source (C2H2) but different etchants (NH3 and H2). Their microstructure and surface chemistry were analyzed using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). Electrochemical properties were investigated using cyclic voltammetry (CV). U-CNFs were found to have a larger population density and a more disordered structure than N-CNFs. N-doping was confirmed in N-CNFs using XPS analysis, which also revealed differences in relative amounts of sp2 C and O functional groups. U-CNFs exhibited distinct electrochemical properties, including smaller pseudocapacitance, larger potential window, slower outer sphere redox (OSR) kinetics, and diminished dopamine sensitivity. Electrochemical differences were rationalized based on CNF structure and surface chemistry, which, in turn, were attributed to how different etchant gases influence the PECVD process.

Well-Dispersed Fluorine-doped Tin Oxide Nanoparticles on the One-Dimensional Network Structure of Carbon Nanofibers for Enabling Ultrafast Lithium Storage

Well-Dispersed Fluorine-doped Tin Oxide Nanoparticles on the One-Dimensional Network Structure of Carbon Nanofibers for Enabling Ultrafast Lithium Storage

Super-sensitive nanobrush-based carbon nanofiber aggregates

A carbon nanofiber aggregate of exceptional sensitivity is developed. Our approach involves the development and utilization of a novel nanobrush structure of carbon nanofiber within the mortar matrix. The high number of nanostructures in the nanobrush, particularly near the electrodes, results in a greater number of nanogaps, leading to a substantial improvement in sensitivity. We are able to detect forces as small as 1 N using this sensor. The carbon nanofiber brush (CNFB) provides a well-defined conductive path for the piezoresistive functioning of the super-sensitive carbon nanofiber aggregate (SSCNFA) with significantly reduced cost. The influence of scanning frequency in impedance is rigorously investigated with alternating current (AC) based on two methods. SSCNFAs are tested in uniaxial compression to determine the highly sensitive face of cube sensor. An SSCNFA (0.05 % CNFs, dense electrodes) and a CNFA (0.5 % CNFs, wide-spaced electrodes) were tested in a sweep-frequency test under parallel compression to compare the super-sensitive performance of the new sensor. The gauge factors at various frequencies were determined. The electrical impedance measured at various frequencies provides versatility to the SSCNFA for stress monitoring. Four fixed-frequency tests were conducted to determine the resolution under uniaxial compression and examine repeatability.

Lure the “enemy” deep: an innovative biomimetic strategy for enhancing the microwave absorption performance of carbon nanofibers

The high conductivity inherent to the dense graphite structures of carbon nanofibers (CNFs) results in microwave reflection, making it a noteworthy topic to design structures that endow CNFs with microwave absorption capabilities.

Iron nanoparticle embedded carbon nanofibers as flexible electrodes for selective chloride ions capture in capacitive deionization

Developing steady material for selective chloride ion capture is a challenging task to match the high capacity of counterparts during the practice of capacitive deionization (CDI). Iron-based materials have presented great potential for its environmentally friendly and low-cost features as chloride ion trapping electrodes. However, the severe capacity fading occurs due to the uncontrollable aggregation during cycling. Herein, iron nanoparticles embedded carbon fibers are creatively fabricated via an electrospinning technology followed by an anneal treatment. The presence of iron greatly increases the capacity of the electrode, while the coating structure of carbon nanofibers improves stability. Due to the synergistic effect of the electric double layer and the pseudocapacitance behavior, when employed as an anode for capacitive deionization device, this material shows an excellent adsorption capacity (82.5 mg g−1) and fast adsorption rate (20.4 mg g−1 min−1) during the desalting process. Meanwhile, the carbon-coated structure greatly prevents the dissolution or aggregation of iron nanoparticles in the reaction process, so that the electrode displays a splendid cycle stability and there is still a 93 % capacity retention rate after 30 cycles. In short, this work provides a new strategy for capacitive desalination of chloride ion trapping electrode with excellent performance by means of encapsulating iron nanoparticles into carbon nanofibers.

Modulation of Si-O Structure in Uniformly Ultrasmall Silicon Oxycarbide for Superior Lifespan of Lithium Metal Anodes.

Utilizing nanoseeds guiding homogeneous deposition of lithium is an effective strategy to inhibit disorderly growth of lithium, where silicon oxide has been attracting attention as a transform seed. However, the research on silicon-oxide-based seeds has concentrated more on utilizing their lithiophilicity but less on their Si-O structures, which could result in different failure mechanisms. In this study, various Si-O structures of silicon oxycarbide carbon nanofibers are prepared by adjusting the content of octa(aminopropylsilsesquioxane). According to XANES and experimental observations, the C-rich SiOC has an active Si-O-C structure but generates a larger volume variation during lithiation, while in the O-rich phase, the silica-oxygen tetrahedral structure can contribute to alleviate the volume expansion but has poor electrochemical activity. SiOC, which is dominated by SiO3C, has a suitable Si-O and silica-oxygen tetrahedral-structure distribution, which balances the electrochemical activity and volume expansion. This allows the host to demonstrate an excellent lifespan over 3740 h with a tiny voltage hysteresis (22 mV) at 2 mA cm-2, and it retains a favorable capacity of 97 mA h g-1 after 630 cycles with a high Coulombic efficiency of 99.7% in full cells. This study experiences the influence of various Si-O structures on lithium metal anodes.

Elucidating the role of Fe-Mo interactions in the metal oxide precursors for Fe promoted Mo/ZSM-5 catalysts in non-oxidative methane dehydroaromatization

Literature shows that adding Fe as a separate phase to MoO3/ZSM-5 catalysts can improve benzene selectivity in methane dehydroaromatization (MDA), but only when added in small quantities, making it difficult to characterize the state of Fe in the catalyst and understand the role of Fe-Mo interactions on the catalytic properties. Here, we explore how the nature of the Mo-Fe interactions in the catalyst precursor can influence the stability and product selectivity in MDA, by employing for the first time Fe2(MoO4)3/ZSM-5 as a catalyst precursor in MDA. We have compared the activity of Fe2(MoO4)3/ZSM-5 with monometallic MoO3/ZSM-5 and mixed MoO3 + Fe2O3/ZSM-5 containing equivalent Mo and Fe loadings and found that Fe2(MoO4)3/ZSM-5 shows higher benzene selectivity than the mixed MoO3 + Fe2O3/ZSM-5 catalyst and exhibits higher stability in reaction compared to the monometallic MoO3/ZSM-5 catalyst. Structural characterization suggests that Fe2(MoO4)3 partially segregates to Fe2O3 and amorphous MoOx during thermal pretreatment. The MoOx species migrate into the zeolite channels during pretreatment, while Fe oxides remain on the external surface of the zeolite. Gas adsorption/desorption techniques and density functional theory calculations demonstrate that the preexisting Fe2O3 phases on the external surface of the zeolite in the mixed MoO3 + Fe2O3/ZSM-5 precursor trap (MoO3)3 clusters preventing them from migrating into the zeolite channels during pretreatment, whereas gradual formation of amorphous MoOx together with the segregation of the Fe2O3 phase when using the Fe2(MoO4)3 precursor diminishes trapping of (MoO3)3 and consequently enhances migration and anchoring of the MoOx species in the zeolite channels, boosting selectivity to benzene. Characterization of used catalysts suggests that the presence of Fe promotes formation of structured carbon nanofibers which reduce the rate of catalyst deactivation.

In-situ growth of magnetic nanoparticles on honeycomb-like porous carbon nanofibers as lightweight and efficient microwave absorbers

To achieve the goal of both lightweight and strong absorption, tailoring the microstructure and components of microwave absorber had been regarded as a promising method. Herein, in-situ growth of magnetic Ni nanoparticles on honeycomb-like porous carbon nanofibers were prepared by electro-blowing spinning and subsequent high-temperature pyrolysis technique. The honeycomb-like porous structure of carbon nanofibers was formed by the decomposition of pore forming agent PTFE nanoparticles during carbonization process, and the effects of PTFE content on the specific surface area and pore size distribution were systematically studied. Simultaneously, the magnetic Ni nanoparticles were in-situ formed and homogenously dispersed in the fiber skeleton. The obtained fibers were connected into a three-dimensional (3D) interconnected macroscopic network, which could form an electrically conductive network to enhance the conductive loss, and induce multiple reflecting and scattering to consume electromagnetic waves. The honeycomb-like porous structure with large specific surface area could shorten the impedance gap with free space and endow the absorber with light-weight feature. In addition, the in-situ growth magnetic Ni nanoparticles introduced additional magnetic loss, which was also benefit to improve the impedance matching. Moreover, the formed heterojunctions at the interface of magnetic Ni nanoparticles and carbon nanofibers triggered intensive interfacial polarization. Under the synergistic effect of magnetic-dielectric loss, appropriate impedance matching, strong interfacial polarization and multiple reflecting and scattering, the optimal sample of Ni/PCNF-2 presented an excellent microwave absorption performance with the minimum RL of −40.48 dB at 1.5 mm thickness, and the effective absorption bandwidth reached to 4.0 GHz.