Electrospun Carbon Nanofibers Research Articles

Atomic Engineering of 3D Self‐Supported Bifunctional Oxygen Electrodes for Rechargeable Zinc‐Air Batteries and Fuel Cell Applications

AbstractThe oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are cornerstone half reactions involved in many renewable energy technologies. High‐density single‐atom catalysts maximize the atom utilization and isolated active sites. Furthermore, introduction of pyri‐N into the carbon‐based nanostructures as an oxygen electrocatalyst creates an abundance of active sites. Here, an innovative strategy is reported based on atomic scale dispersion of Co atoms into the pyri‐N enriched carbon nanotube encapsulated Ni nanoparticles grown on 3D electrospun carbon nanofiber nano‐assemblies. Notably, the CoSANi‐NCNT/CNF electrocatalyst exhibited excellent OER and ORR activity in terms of low overpotentials and higher half‐wave potentials. The atomically distributed Co allows the maximum exposure of active sites on the pyri‐N dominated multidimensional carbon skeleton, and synergistic effects with Ni nanoparticles greatly reduced the delocalization around the metal centers and provided an ideal environment for interactions with oxygen intermediates, thus facilitating the 4e− pathway, as evidenced by the DFT calculations. Moreover, Zn‐air batteries using a CoSANi‐NCNT/CNF air cathode exhibited a high‐power density and admirable specific capacity. This studies may provide an avenue for the rational modulation of single‐atom catalysts and cost‐effective, large‐scale synthesis of bifunctional oxygen electrocatalysts for rechargeable Zn‐air batteries and anion exchange membrane fuel cell.

Effect of stabilization and carbonization treatment on the chemical and physical transformation of polyacrylonitrile (PAN) based electrospun carbon nanofibers

The present study delves into the production of carbon nanofibers (CNFs) utilising electrospun polyacrylonitrile (PAN) nanofiber mats, with a specific focus on the influence of oxidative stabilisation and carbonisation treatments. This research aims to thoroughly understand how variations in stabilisation time and temperature, as well as carbonisation temperature, impact the CNFs properties. These properties include fiber size, morphology, chemical and crystal structure transformation, thermal behaviour, and surface characteristics. Our methodology involved a detailed examination of the thermal treatment processes, where we observed a significant decrease in fiber size, though the surface morphology of the fibers remained largely unaffected. We employed Fourier-transform infrared (FTIR) spectroscopy to track the transformation of nitrile groups in PAN to imine groups, which indicated the progression of cyclisation reactions. Complementary analyses through differential scanning calorimetry (DSC) confirmed a high degree of these reactions, particularly at stabilisation temperatures extending to 250 °C and beyond. The cyclisation process was found to be complete during the carbonisation phase, at temperatures reaching 450 °C and above. Further, x-ray diffraction (XRD) patterns offered insight into the changes in the crystal structure, particularly in the packing of the d(002) spacing because of the stabilisation and carbonisation processes. This findings from this study not only elucidate the intricate process of CNFs production from electrospun PAN nanofiber mats but also highlight the critical factors that influence their final properties. These insights are invaluable for the development of advanced CNFs with tailored properties suitable for a range of applications, including but not limited to energy storage, electronics, and as supporting materials in various technological domains.

Copper Nanoparticles Modified Superhydrophobic Electrospun Carbon Nanofiber Membranes with Enhanced the Oil–water Separation Performance

Copper Nanoparticles Modified Superhydrophobic Electrospun Carbon Nanofiber Membranes with Enhanced the Oil–water Separation Performance

Silk derived electrospun carbon nanofibers loaded with CoS nanoparticles as efficient hydrogen evolution reaction catalysts in acidic and alkaline media

The design of a stable and efficient hydrogen evolution catalyst across the entire pH range is of significant importance for the development of hydrogen production technology by electrocatalytic water splitting. This study chose biomass silk fibroin protein as the electrospinning raw material, synthesizing a hybrid membrane of CoS@carbon nanofibers (CNF) with a layered core–shell structure through simple carbonization and hydrothermal treatment. The CoS nanoparticles can grow uniformly and densely on the CNF. By varying the concentrations of hexahydrate cobalt nitrate (Co(NO3)2·6H2O) and thiourea (CH4N2S), the morphology of the synthesized CoS nanoparticles on CNF can be controlled. Different microscopic morphologies lead to differences in the activity of the hydrogen evolution reaction (HER), attributed to variations in the exposed active sites for different morphologies. Compared to pure CNF, the CoS-2@CNF hybrid membrane exhibits excellent HER activity in both acidic and alkaline electrolytes. This highlights the synergistic catalytic effect between CNF and CoS particles. This work provides guidance for the rational design of bio-based catalysts with excellent performance.

Spatially Confined in Situ Formed Sodiophilic-Conductive Network for High-Performance Sodium Metal Batteries.

The sodium (Na) metal anode encounters issues such as volume expansion and dendrite growth during cycling. Herein, a novel three-dimensional flexible composite Na metal anode was constructed through the conversion-alloying reaction between Na and ultrafine Sb2S3 nanoparticles encapsulated within the electrospun carbon nanofibers (Sb2S3@CNFs). The formed sodiophilic Na3Sb sites and the high Na+-conducting Na2S matrix, coupled with CNFs, establish a spatially confined "sodiophilic-conductive" network, which effectively reduces the Na nucleation barrier, improves the Na+ diffusion kinetics, and suppresses the volume expansion, thereby inhibiting the Na dendrite growth. Consequently, the Na/Sb2S3@CNFs electrode exhibits a high Coulombic efficiency (99.94%), exceptional lifespan (up to 2800 h) at high current densities (up to 5 mA cm-2), and high areal capacities (up to 5 mAh cm-2) in symmetric cells. The coin-type full cells assembled with a Na3V2(PO4)3/C cathode demonstrate significant enhancement in electrochemical performance. The flexible pouch cell achieves an excellent energy density of 301 Wh kg-1.

Highly crystalline Prussian blue anchored on electrospun carbon nanofibers as flexible electrode for high power sodium-ion batteries

Highly crystalline Prussian blue anchored on electrospun carbon nanofibers as flexible electrode for high power sodium-ion batteries

Simple and rapid determination of tartrazine in fake saffron using the metal organic framework (Fe SA MOF@CNF) by HPLC/PDA

The present study of a novel metal–organic framework containing Fe single atoms doped on electrospun carbon nanofibers (Fe SA-MOF@CNF) based on dispersive micro solid phase extraction (D-μ-SPE) using HPLC–PDA for detection tartrazine in fake saffron samples was designed. The Fe SA-MOF@CNF sorbent was extensively characterized through various techniques including N2 adsorption–desorption isotherms, X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The specific area of surface of the sorbent was 577.384 m2/g. The study variables were optimized via the central composite design (CCD), which included a sorbent mass of 15 mg, a contact time of 6 min, a pH of 7.56, and a tartrazine concentration of 300 ng/ml. Under the optimum condition, the calibration curve of this method was linear in the range of 5–1000 ng/mL, with a correlation coefficient of 0.992. The LOD and LOQ values were ranged 0.38–0.74 and 1.34–2.42 ng/ml, respectively. This approach revealed significant improvements, including high extraction recovery (98.64), recovery rates (98.43–102.72%), and accuracy (RSDs < 0.75 to 3.6%). the enrichment factors were obtained in the range of 80.6–86.4 with preconcentration factor of 22.3. Consequently, the D-μ-SPE method based on synthesized Fe SA-MOF@CNF could be recommended as a sustainable sorbent for detecting tartrazine in saffron samples.

Supercapacitor Performance of MXene-Coated Carbon Nanofiber Electrodes

MXenes consisting of thin layers of transition metal carbides or nitrides are good candidates for electrode materials due to their excellent electrical conductivity and fast ion transfer. Electrospun carbon nanofibers are highly porous and electrically conductive, making them attractive for electrode materials. In this study, free-standing electrodes were prepared by the dip-coating of carbon nanofibers (CNFs) in the MXene (Ti3C2) colloidal solution, which was synthesized via the wet-etching of MAX (Ti3AlC2) phase, and their chemical structures were investigated by X-ray diffraction and Fourier transform infrared spectroscopy. In addition, scanning and transmission electron microscopy were used to investigate the morphological and crystallographic features of MXene-coated CNFs. Surface area and pore volumes were investigated by nitrogen adsorption/desorption measurements. Supercapacitor performance was studied by assembling a 3-electrode system with 1M aqueous sodium sulfate solution as an electrolyte. MXene-coated CNFs exhibited a maximum specific capacitance of 514 F/g at 0.5 A/g, with energy and power densities of 71.4 Wh/kg at 0.5 A/g and 2.3 kW/kg at 5 A/g, respectively, which are relevantly higher compared to the pristine CNFs due to the pseudocapacitive behavior of MXenes. They also showed comparable cyclic stability during 5000 cycles with the CNFs. This result indicates that MXene-coated carbon nanofibers can be effective electrode materials for electrochemical energy storage.

Rational fabrication of metal phosphide nanoparticles immobilized in electrospun carbon nanofibers for efficient pH-universal hydrogen evolution and overall water splitting

Design and preparation of bifunctional electrocatalysts with optimized structures and abundant electrocatalytic active sites are significant for hydrogen generation in electrocatalytic water splitting. Herein, we have elaborately prepared Fe-doped CoP nanoparticles encapsulated in porous electrospun carbon nanofibers for bifunctional electrocatalysis on both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The morphologies, components, and properties of the prepared electrocatalysts are influenced by the introduction of a facile air calcination treatment. Porous nanostructure as well as the full conversion of metal active sites are simultaneously achieved. Owing to the protective electrospun carbon nanofibers as well as the abundant exposed active sites, the optimized electrocatalyst exhibits excellent pH-universal HER activities with small overpotentials (99 mV, 159 mV, and 185 mV) at 10 mA cm−2 in acidic, alkaline, and neutral electrolytes, and also presents remarkable OER performance. Moreover, a water electrolyzer cell, using the optimized electrocatalyst as the electrodes, manifests both a high efficiency (1.63 V@10 mA cm−2) and robust stability. This work provides a convenient route for the controllable fabrication of transition metal-based electrocatalysts toward energy conversion.

Vanadium nitride-vanadium oxide-carbon nanofiber hybrids for high performance supercapacitors

Vanadium Nitride (VN) is attractive for energy storage due to its high conductivity (1.6 × 106 S/m) and specific capacitance (1350 F/g) but limited to alkaline electrolytes for redox. In contrast, V2O3 is redox active but not very conductive. In these hybrids a mixture of VN and vanadium oxide (V2O3) were encapsulated in electrospun carbon-nanofibers. A combination of VN and V2O3 takes advantage of the high conductivity from VN and the redox activity from V2O3. Additionally, having the vanadium encapsulated within the carbon can help with the stability as the electrolyte will not have direct interaction with the surface. These hybrids were made by in-situ nitridation of the encapsulated V2O5 followed by ex-situ activation with carbon dioxide. The hybrids were characterized by XPS and Raman spectroscopy. Hybrids of VN/V2O3-CNF showed increased capacitance of 245 Fg−1 with energy and power densities of 70.2 Wh kg−1 and 1751 W kg−1 in ionic liquid electrolyte. The devices showed good cycle stability with ∼90 % retention after 10,000 cycles at a current density of 1 Ag−1. These findings highlight the potential of VN/V2O3-CNF hybrids as high-performance supercapacitor electrodes. The combination of high conductivity and redox activity, along with encapsulation within CNFs, opens promising avenues for advanced energy storage.

Understanding the behaviors of ZIF-67 reinforced electrospun carbon nanofibers in the preparation and stabilization

MOFs-reinforced electrospun carbon nanofibers offer a wide range of applications in the field of energy storage. In this study, ZIF-67 nanoparticles were produced and combined with polyacrylonitrile for electrospinning before being stabilized and carbonized to form a carbon nanofiber. BET, FT-IR, EA, DSC, and other techniques were used to investigate the stabilizing behaviors of PAN electrospun fiber with varying ZIF-67 concentrations at different temperatures. Under the same stabilizing settings, it was discovered that PAN electrospun fiber containing ZIF-67 nanoparticles could absorb more oxygen, promoting a higher degree of cyclization and crosslinking. Therefore, it was preferred to prepare carbon nanofibers at a lower stabilization temperature. Importantly, the degree of stability and disorder of the PAN/ZIF-67 stabilized fiber has been described by the FT-IR and the Raman spectra. This research deepens understanding about the formation of MOF-reinforced carbon nanofibers and expands our knowledge of the stability of PAN/MOF hybrid fibers.

Porous Prussian Blue Analogs Decorated Electrospun Carbon Nanofibers as Efficient Electrocatalyst for Overall Water Splitting

Metal-organic frameworks are becoming increasingly important in electrocatalysis as the hydrogen production sector grows. However, their electrocatalytic capability is limited by their inclination to agglomerate and the insufficient exposure of active sites. In this work, a three-step strategy was used to develop a bifunctional electrocatalyst with porous Prussian blue analogs supported on carbon nanofibers. The use of electrospun carbon nanofibers as conductive substrates can successfully address the problem of easy aggregation. Moreover, the etching procedure with tannic acid creates a porous structure that effectively regulates the electrical structure and exposes additional active sites. The resulting catalyst performs well in both the hydrogen evolution reaction and the oxygen evolution reaction, and also exhibits good stability in overall water splitting. The findings of this study present new concepts for the design and fabrication of metal-organic frameworks-based materials in the realm of electrocatalysis.

Crystalline and amorphous Fe2O3 nanocubes grown on electrospun carbon nanofibers for lithium-ion batteries and lithium-sulfur batteries: A comparative study

Amorphous transition metal oxides have recently received particular research interests in electrochemical energy storage. However, there is still a lack of direct comparisons between amorphous materials and their crystalline counterparts. Here, we demonstrate the rational synthesis of crystalline and amorphous Fe2O3 nanocubes uniformly grown on carbon nanofibers (denoted as CNFs@C-Fe2O3 and CNFs@A-Fe2O3, respectively) for lithium-ion batteries (LIBs) and lithium-sulfur batteries (LSBs). In such a structure, the Fe2O3 nanocubes possess strong interfacial bonding with CNFs, which can ensure rapid electron transportation. Besides, these Fe2O3 nanocubes are highly porous, which can effectively alleviate the volume change, enlarge the surface area, increase active sites and facilitate ion diffusion. When employed as freestanding anode for LIBs, the CNFs@C-Fe2O3 electrode delivers much improved lithium ion storage performance compared to that of CNFs@A-Fe2O3. When evaluated as interlayers for LSBs, instead, the batteries with CNFs@A-Fe2O3 exhibit better rate performance cycling stability than that of with CNFs@C-Fe2O3. Moreover, theoretical calculations elucidate the amorphous Fe2O3 has stronger adsorption ability toward the soluble lithium polysulfides. This work would provide new insights into the reasonably development of crystalline and amorphous transition metal oxides toward electrochemical energy storage.

Polyacrylonitrile-based carbon nanofiber electrode fabricated via electrospun for supercapacitor application

The versatile properties of electrospun carbon nanofibers gaining attention for electrode materials for supercapacitors. The heat treatment process of stabilization played an important role before the carbonization process in electrode fabrication. In the present study, electrospun stabilized polyacrylonitrile nanofiber (St PAN) and carbonized Polyacrylonitrile nanofiber (CNF) at minimum temperature were used as active mass for supercapacitor electrodes. Stabilized CNF nanofiber sample showed a reduction in nanofiber diameter with increased carbon percentage. XRD results showed increased crystallinity in the CNF sample as compared with the Stabilized PAN sample. Electrochemical characterization was performed to measure specific capacitance and to analyze the charge storage mechanism. The proportion of capacitive and diffusion-controlled contributions to energy storage was estimated using Dunn’s model. The results obtained demonstrated that, in comparison to the St PAN electrode, the CNF electrode exhibited a greater capacitive-controlled contribution. The CNF sample has shown an increased capacitive contribution of 82.3% as compared with the St PAN sample. This work provides a method for making electrospun carbon nanofiber-based electrodes as well as a methodical methodology for examining the charge storage process.

Controlled Alignment of Carbon Black Nanoparticles in Electrospun Carbon Nanofibers for Flexible Films.

Carbon nanofiber (CNF) films or mats have great conductivity and thermal stability and are widely used in different technological processes. Among all the fabrication methods, electrospinning is a simple yet effective technique for preparing CNF mats, but the electrospun CNF mats are often brittle. Here, we report a feasible protocol by which to control the alignment of carbon black nanoparticles (CB NPs) within CNF to enhance the flexibility. The CB NPs (~45 nm) are treated with non-ionic surfactant Triton-X 100 (TX) prior to being blended with a solution containing poly(vinyl butyral) and polyacrylonitrile, followed by electrospinning and then carbonization. The optimized CB-TX@CNF mat has a boosted elongation from 2.25% of pure CNF to 2.49%. On the contrary, the untreated CB loaded in CNF displayed a lower elongation of 1.85% because of the aggregated CB spots created weak joints. The controlled and uniform dispersion of CB NPs helped to scatter the applied bending force in the softness test. This feasible protocol paves the way for using these facile surface-treated CB NPs as a commercial reinforcement for producing flexible CNF films.

In situ assembly of well-dispersed Fe0.64Ni0.36 nanoparticles on electro-spun carbon nanofibers (CNFs) for efficient microwave absorption

In situ assembly of well-dispersed Fe0.64Ni0.36 nanoparticles on electro-spun carbon nanofibers (CNFs) for efficient microwave absorption

Electrospun carbon nanofibers embedded with heterostructured NiFe2O4/Fe0.64Ni0.36 nanoparticles as an anode for high-performance lithium-ion battery

Binary transition metal compounds exhibit promising application potential as anode materials in the field of lithium-ion batteries (LIBs) due to their high theoretical specific capacity. However, their poor electrical conductivity and drastic volume expansion during charge and discharge pocesses limit their high-performance applications. Herein, we have synthesized carbon nanofibers (CNFs) loaded with heterostructured NiFe based nanoparticles (NiFe2O4/Fe0.64Ni0.36@CNFs) using electrospinning, and explore their cyclic stability and rate performances. By subjecting the electrospun membranes to thermal treatment at different annealing temperatures, three distinct phases of NiFe compounds embedded in CNFs, i.e., NiFe2O4 (400 °C), NiFe2O4/Fe0.64Ni0.36 (500 °C) and Fe0.64Ni0.36 (800 °C), are obtained. When they are used as anode materials, the electrochemical properties are investigated. The NiFe2O4/Fe0.64Ni0.36@CNFs anode material exhibits the best cycling and rate performances, with a capacity of 431.1 mAh g−1 achieved after 200 cycles at a current density of 0.2 A g−1. Moreover, its specific capacities are 558.9, 400.1, 272.4, 178.1 and 89.5 mAh g−1 at current densities of 0.1, 0.2, 0.5, 1.0 and 2.0 A g−1, respectively. As the current density returns to 0.1 A g−1, its specific discharge capacity can reach 527.5 mAh g−1. The excellent cycling and rate performances of NiFe2O4/Fe0.64Ni0.36@CNFs are mainly attributed to the following reasons: i) the carbon fibers can effectively alleviate volume expansion and structural stress during cycling; ii) Fe0.64Ni0.36 alloy can inhibit the formation of lithium dendrites and effectively reduce the nucleation overpotential of metallic lithium, thereby improving the electrochemical stability; iii) the heterostructure can improve electrochemical properties through the synergistic interaction between NiFe2O4 and Fe0.64Ni0.36. The catalytic Fe0.64Ni0.36 not only facilitate the conversion reaction of NiFe2O4, resulting in the high capacity, but also increase the conductivity of the material. This work offers a feasible strategy to significantly improve the electrochemical performance of binary metal compounds, paving the way for their practical applications in the high-performance LIBs.

In situ growth of a redox-active metal-organic framework on electrospun carbon nanofibers as a free-standing electrode for flexible energy storage devices.

The rational construction of free-standing and flexible electrodes for application in electrochemical energy storage devices and next-generation supercapacitors is an emerging research focus. Herein, we prepared a redox-active ferrocene dicarboxylic acid (Fc)-based nickel metal-organic framework (MOF) on electrospun carbon nanofibers (NiFc-MOF@CNFs) via an in situ approach. This in situ approach avoided the aggregation of the MOF. The NiFc-MOF@CNF flexible electrode showed a high redox-active behavior owing to the presence of ferrocene and flexible carbon nanofibers, which led to unique properties, including high flexibility and lightweight. Furthermore, the prepared electrode was utilized in a supercapacitors (SC) without the use of any binder, which achieved a specific capacity of 460 C g-1 at 1 A g-1 with an excellent cyclic retention of 82.2% after 25 000 cycles and a good rate capability. A flexible asymmetric supercapacitor device was assembled, which delivered a high energy density of 56.25 W h kg-1 and a long-lasting cycling performance. Also, the prepared electrode could be used as a freestanding electrode in flexible devices at different bending angles. The obtained cyclic voltammetry curves showed negligible changes, indicating the high stability and good flexibility of the electrode. Thus, the use of the in situ strategy can lead to the uniform growth of redox-active MOFs or other porous materials on CNFs.

Post-treatment strategies for pyrophoric KOH-activated carbon nanofibres.

The effect of two atmospheric post-treatment conditions directly after the KOH activation of polyacrylonitrile-based nanofibres is studied in this work. As post-treatment different N2 : O2 flow conditions, namely high O2-flow and low O2-flow, are applied and their impact on occurring reactions and carbon nanofibres' properties is studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), Raman spectroscopy, elemental analysis and CO2 and Ar gas adsorption. At high O2-flow conditions a pyrophoric effect was observed on the KOH-activated carbon nanofibers. Based on the obtained results from the TGA and DSC the pyrophoric effect is attributed to the oxidation reactions of metallic potassium formed during the KOH activation process and a consequent carbon combustion reaction. Suppression of this pyrophoric effect is achieved using the low O2-flow conditions due to a lower heat formation of the potassium oxidation and the absence of carbon combustion. Compared to the high O2-flow samples no partial destruction of the carbon nanofibers is observed in the SEM images. The determination of the adsorption isotherms, the surface area, the pore size distribution and the isosteric enthalpies of adsorption show the superior properties under low O2-flow conditions. The present micropore volume is increased from 0.424 cm3 g-1 at high O2-flow to 0.806 cm3 g-1 for low O2-flow samples, resulting in an increase of CO2 adsorption capacity of 38% up to 6.6 mmol g-1 at 1 bar. This significant improvement clearly points out the importance of considering highly exothermic potassium oxidation reactions and possible post-treatment strategies when applying KOH activation to electrospun carbon nanofiber materials.

Emerging electrospinning platform toward nanoparticle to single atom transformation for steering selectivity in ammonia synthesis.

The rising top-down synthetic methodologies for transition metal single-atom catalysts (SACs) require controlled movement of metal atoms through the substrates; however, their direct transportation towards the ideal carrier remains a huge challenge. Herein, we showed a "top down" strategy for Co nanoparticles (NPs) to Co SA transformation by employing electrospun carbon nanofibers (CNFs) as atom carriers. Under high-temperature conditions, the Co atoms migrate from the surfaces of Co NPs and are then anchored by the surrounding carbon to form a Co-C3O1 coordination structure. The synthesized Co SAs/CNF electrocatalyst exhibits excellent electrocatalytic nitrate reduction reaction (NO3RR) activity with an NH3 yield of 0.79 mmol h-1 cm-2 and Faraday efficiency (FE) of 91.3% at -0.7 V vs. RHE in 0.1 M KNO3 and 0.1 M K2SO4 electrolytes. The in situ electrochemical characterization suggests that the NOH pathway is preferred by Co SAs/CNFs, and *NO hydrogenation and deoxygenation easily occur on Co SAs due to the small adsorption energy between Co SAs and *NO, as calculated by theoretical calculations. It is revealed that a small energy barrier (0.45 eV) for the rate determining step (RDS) ranges from *NO to *NOH and a strong capability for inhibiting hydrogen evolution (HER) significantly promotes the NH3 selectivity and activity of Co SAs/CNFs.