Carbon Nanofibrous Mats Research Articles

Boron nanosheets induced microstructure and charge transfer tailoring in carbon nanofibrous mats towards highly efficient water splitting

Development of metal-free carbon-based electrocatalysts with high-efficiency and excellent durability towards both oxygen and hydrogen evolution reactions (OER and HER) in a single electrolyte system is crucial yet challenging for sustainable energy generation. In this work, we report a facile and scalable strategy for fabricating self-supporting boron carbon oxynitride nanofibrous (BCNONF) mats with controllable boron contents via electrospinning and subsequent thermal treatment. Notably, the optimal BCNONF mat affords outstanding OER performance in alkaline electrolyte with low overpotential of 403 mV at 10 mA·cm−2, small Tafel slop of 72.9 mV·dec−1, and high stability (88.1% current density retention after 10 h), outperforming the commercial Ir/C benchmark. Moreover, it can serve as a remarkable HER catalyst with better stability than that of the commercial Pt/C counterpart in the same electrolyte, indicating its bifunctional characteristics. When employed as both anode and cathode of an electrolyzer, the self-supporting BCNONF mats exhibit superior activities with a potential of only 1.79 V at 10 mA·cm−2 and high long-term durability (90.6% current density retention after 50 h) for overall water splitting. Furthermore, density functional theory (DFT) calculations reveal that the remarkable OER and HER bifunctional performance of the BCNONF catalyst are originated from the reduced adsorption strength of O atom and the stronger H* adsorption on the BCNO surface as compared to those on CNO surface, which in turn facilitate efficient interfacial charge transfer between the electrocatalytic intermediates and the BCNONF catalyst.

Comparative effects of electrospinning ways for fabricating green, sustainable, flexible, porous, nanofibrous cellulose/chitosan carbon mats as anode materials for lithium-ion batteries

To develop a clean and sustainable carbon anode material derived from biomass with desirable properties for lithium-ion batteries (LIBs), bio-nitrogen (N)-doped composite carbon nanofibrous mats (CNFMs) were made using natural cellulose (CE) and chitosan (CS) by means of two different electrospinning ways (single-nozzle and coaxial-nozzle) coupled with pyrolysis. The conventional CNFMs that had a CE/CS ratio of 5:5 showed the best electrochemical performance, corresponding to a high specific capacity of 327 mAh g−1 at 100 mA g−1, good rate performance with specific capacity of 399 mAh g−1 at 30 mA g−1 and 210 mA g−1 at 1000 mA g−1, as well as excellent cycling stability after 300 cycles. The core–shell CNFMs with a thick outer layer of CS and large average fiber diameter (316 nm) at the same CE/CS ratio had higher pyridinic-N and pyrrolic-N contents but a lower degree of graphitization and BET surface area compared to the conventional CNFMs. It was concluded that the bio-N in CS was more uniformly doped into the CNFMs by the single-nozzle electrospinning way than by the coaxial one, and thus more effectively promoted a comprehensive electrochemical performance.

Preparation of carbon nanofibrous mats encapsulating zero-valent Fe nanoparticles as Fe reservoir for removal of organic pollutants.

Zero-valent iron nanoparticles (ZVI NPs) display promising potential in the removal of organic pollutants and heavy metal ions for environmental remediation. However, it is crucial to prevent the oxidation of ZVI NP and control the release of Fe ions under storage and working conditions. In this study, ZVI NPs are encapsulated in single-axial and co-axial carbon nanofibers by electrospinning polyacrylonitrile (PAN)/Fe3+ nanofibrous mats with different structures and then annealing the PAN nanofibrous mats in reduction atmosphere. SEM images show that the diameter of the carbon nanofibers is affected by the structure of the nanofibers and the ZVI NPs content after the annealing treatment. The formation of ZVI NPs is confirmed through XPS spectra and HRTEM characterization. The catalytic degradation of organic pollutants by ZVI NPs encapsulated in the carbon nanofibrous mats is evaluated using methylene blue (MB). The results show that the degradation rate of MB is significantly improved when the ZVI NP content encapsulated in the nanofibers increased. MB is completely degraded by the nanofibrous mats with either the single-axial structure or the co-axial structure, but at a higher degradation rate by the single-axial structure than that by the co-axial structure. These results provide alternatives to utilize the carbon nanofibrous mats encapsulating ZVI NPs as Fe reservoir for the removal of organic pollutants in an emergent or long-term situation for environmental remediation.

Effects of carbonization temperature on structure and mechanical strength of electrospun carbon nanofibrous mats

Electrospun carbon nanofibrous mat (CNFM) is prepared by the carbonization of stabilized PAN nanofibers under temperatures between 900 °C and 1300 °C. The effects of carbonization temperatures on the structure and mechanical strength of the CNFMs are investigated via Scanning-electron-microscopy, X-ray-diffraction, Raman spectroscopy, and mechanical strength characterizations. Results show that the majority of non-carbon elements are removed from the fibers and that the graphite microstructures are mostly formed below 1100 °C, which led to quickly enhanced conductivity and mechanical strength of CNFMs. When the carbonization temperature further increase to 1300 °C, the graphite crystallite continues to grow and the mechanical strength continues to increase, but at a slower rate. The highest tensile strength of 130.2 ± 16.7 MPa and modulus of 17.53 ± 1.53 GPa were achieved at a carbonization temperature of 1300 °C.

High-strength electrospun carbon nanofibrous mats prepared via rapid stabilization as frameworks for Li-ion battery electrodes

Carbon nanofibrous nonwoven mats (CNFMs) prepared via electrospinning offer excellent electrical and structural properties and have been used as frameworks for electrodes in electrochemical energy storage devices. However, lack of mechanical strength hinders the broad applications of CNFMs in flexible electronics or industry use. In this work, a rapid stabilization method is developed to prepare high-strength and flexible CNFMs. Studies of the effects of stabilization time on the structures of the stabilized polyacrylonitrile (PAN) nanofibers and the subsequent carbon nanofibers reveal that there is an optimal stabilization time for making high-strength CNFMs. Long stabilization time results in excessive oxidation of the stabilized PAN nanofibers and unwanted defects in the carbon nanofibers. Short stabilization time results in carbon nanofibers with less crystalline structures due to insufficient formation of the thermally stable ladder-like structure. Robust and flexible CNFM with the highest tensile strength of 192.7 MPa is obtained using an optimized total stabilization time of 40 min. To demonstrate the application of the flexible CNFMs, they are fabricated as an electrode framework to load TiO2 nanoparticles without use of organic binders. Lithium ion half-cell based on this electrode demonstrates superior rate cycling performance owning to the porous structure and highly conductive fibrous carbon network of CNFM.

Electrospinning preparation of a large surface area, hierarchically porous, and interconnected carbon nanofibrous network using polysulfone as a sacrificial polymer for high performance supercapacitors.

Carbon nanofibrous mats (CNFMs) are prepared by electrospinning of blended precursor of polyacrylonitrile and polysulfone (PSF) followed by pre-oxidation stabilization and carbonization. Addition of PSF as a sacrificial polymer leads to CNFMs with high surface area, large numbers of micropores and mesopores, good degree of carbonization, and interconnected fibrous network, due to the high decomposition temperature, release of SO2 during decomposition, and large amount of carbon residue of PSF during carbonization. The electrochemical characterization shows that the CNFM electrode has a specific capacitance of 272 F g−1 at a current density of 1 A g−1 with 74% of the specific capacitance retained at 50 A g−1 in 2.0 M KOH electrolyte. The CNFM electrodes have excellent cycling durability with 100% capacitance retention after 10 000 cycles.

The fabrication of the elastic zirconium-based carbon nanofibrous mats with three-dimensional macrostructures

Zirconium-based carbon nanofibrous mats (ZrCFs) with three-dimensional macrostructures were prepared by the carbonization of the Polyacrynitrile (PAN) nonwoven mats containing zirconium oxychloride from air jet spinning. ZrCFs exhibited the elastic, flexible and fluffy characteristics, much different from the carbon nanofibres without zirconium. Nano zirconium compounds were uniformly distributed in carbon nanofibres, ascribed to the chelation interaction between Zr+ and PAN precursor. XRD showed that the ZrO2, ZrC and ZrN structures formed in carbon nanofibres of ZrCFs, which could prevent carbon nanofibres from fusing and shrinking. When nitrogen was introduced, ZrCFs could further reduce the charge transfer resistance. The flexible ZrCFs have the potential electric application, which can also be extended to the functional textiles and catalysis.

Liquefied walnut shell-derived carbon nanofibrous mats as highly efficient anode materials for lithium ion batteries

Mechanically flexible walnut shell-derived carbon nanofibers (CNFs) of 175 nm diameter were fabricated from a liquefied walnut shell—polyvinyl alcohol (PVA) hybrid solutionviaconventional electrospinning followed by one-step carbonization.

Hierarchical cellulose-derived CNF/CNT composites for electrostatic energy storage

Today many applications require new effective approaches for energy delivery on demand. Supercapacitors are viewed as essential energy storage devices that can continuously provide quick energy. The performance of supercapacitors is mostly determined by electrode materials that can store energy via electrostatic charge accumulation. This study presents new sustainable cellulose-derived composite electrodes which consist of carbon nanofibrous (CNF) mats covered with vapor-grown carbon nanotubes (CNTs). The CNF/CNT electrodes have high electrical conductivity and surface area: the two most important features that are responsible for good electrochemical performance of supercapacitor electrodes. The results show that the composite electrodes have fairly high values of specific capacitance (101 F g−1 at 5 mV s−1), energy and power density (10.28 W h kg−1 and 1.99 kW kg−1, respectively, at 1 A g−1) and can retain excellent performance over at least 2000 cycles (96.6% retention). These results indicate that sustainable cellulose-derived composites can be extensively used in the future as supercapacitor electrodes.

Direct planting of ultrafine MoO2+δ nanoparticles in carbon nanofibers by electrospinning: self-supported mats as binder-free and long-life anodes for lithium-ion batteries

Three-dimensional (3D) interconnected carbon nanofibrous mats containing well-dispersed MoO2+δ nanocrystals are fabricated through a facile electrospinning route followed by thermal treatment in N2. The resulting nanostructured monolithic hybrid mat made of C/MoO2+δ nanofibers exhibits superior Li-storage performances, when evaluated as a free-standing anode material. At a current density of 200 mA g(-1), a reversible capacity as high as 876.9 mA h g(-1) is achieved after 250 cycles. A capacity of 447.9 mA h g(-1) could still be maintained after 1000 cycles even at a high current density of 2000 mA g(-1), indicating high rate capability and cyclability. The attractive electrochemical performances of the as-obtained 3D C/MoO2+δ networks may benefit from the synergistic effects of the unique nanoarchitectures and the integrity of the electrodes. Monodispersed MoO2+δ nanocrystals encapsulated in carbon nanofibers not only provide interfacial storage but also improve the transport kinetics of electrons and lithium ions.

Thin MoS2 Nanoflakes Encapsulated in Carbon Nanofibers as High-Performance Anodes for Lithium-Ion Batteries

In this work, highly flexible MoS2-based lithium-ion battery anodes composed of disordered thin MoS2 nanoflakes encapsulated in amorphous carbon nanofibrous mats were fabricated for the first time through hydrothermal synthesis of graphene-like MoS2, followed by electrospinning and carbonization. X-ray diffraction as well as scanning and transmission electron microscopic studies show that the as-synthesized MoS2 nanoflakes have a thickness of about 5 nm with an expanded interlayer spacing, and their structure and morphology are well-retained after the electrospinning and carbonization. At relatively low MoS2 contents, the nanoflakes are dispersed and well-embedded in the carbon nanofibers. Consequently, excellent electrochemical performance, including good cyclability and high rate capacity, was achieved with the hybrid nanofibrous mat at the MoS2 content of 47%, which may be attributed to the fine thickness and multilayered structure of the MoS2 sheets with an expanded interlayer spacing, the good charge conduction provided by the high-aspect-ratio carbon nanofibers, and the robustness of the nanofibrous mat.

Ammonium chloride promoted synthesis of carbon nanofibers from electrospun cellulose acetate

Nitrogen-doped carbon nanofibrous mats with the fiber diameters between 70 and 400nm were synthesized from regenerated cellulose impregnated with ammonium chloride. Acting as a flame retardant, ammonium chloride provided the thermal stabilization of incompletely regenerated cellulose fibers, thus allowing their successful carbonization. Besides that, it improved the carbon yield from 13% to 20%. The method of carbon nanofibers (CNF) synthesis reported here is technologically simple and environmentally friendly since it significantly shortens the regeneration step and does not require water consumption for washing of the precursor fibers from deacetylation agents. More than that, introduction of nitrogen via NH4Cl impregnation led to an increase in the electrical conductivity of the obtained CNF samples, a fact which can make them useful for advanced electrochemical applications.

Electrospun carbon nanofibrous mats surface-decorated with Pd nanoparticles via the supercritical CO2 method for sensing of H2

Carbon nanofibers (in the form of an overlaid mat) were prepared by electrospinning of polyacrylonitrile followed by stabilization in air and carbonization in argon. Pd nanoparticles were then deposited on the surface of nanofibers by using Pd(acac)2 as the precursor via the supercritical CO2 method followed by pyrolysis at 600 °C. Structural characterizations indicated that the Pd nanoparticles were composed of single-crystalline clusters with sizes of a few nanometers. The hydrogen sensing properties of electrospun carbon nanofibrous mats surface decorated with Pd nanoparticles were investigated. The results indicated that the resistivity of Pd-decorated nanofibrous mats decreased linearly with the increase of H2 volume fraction from 0 to 0.7 in H2/N2 mixture gas, and the response showed excellent reversibility.

Fabrication of the catalytic electrodes for methanol oxidation on electrospinning-derived carbon fibrous mats

The carbon fibrous mats with high conductivity (50 S cm −1) formed by carbon nanofibers with an average diameter of ∼150 nm have been fabricated by thermally treating the electrospun polyacrylonitrile fibers. The platinum clusters are electrodeposited on the carbon nanofibrous mats (CFMs) by multi-cycle CV method. In contrast to the catalytic peak current of methanol oxidation on commercial catalyst (185 mA mg −1 Pt), the catalytic peak current on optimum Pt/CFM electrode reaches to ∼420 mA mg −1 Pt despite of the large size (50–200 nm) of the Pt clusters, revealing that the special structure of carbon fibrous mats is favorable to improve the performance of catalyst.