Electrospun carbon nanofiber web electrode: Supercapacitor behavior in various electrolytes

Carbon nanofibers (CNFs) draw great interest due to their noticeable mechanical, electrochemical, and physical properties. In this study, polyacrylonitrile‐based CNFs are obtained via electrospinning technique. Thermal oxidation and low temperature (950 °C) carbonization are applied to the electrospun web in order to achieve CNF. Through the process, Fourier transform infrared‐attenuated total reflectance spectroscopy and Raman spectroscopic results are investigated. The electrochemical properties of the self‐standing CNF webs are examined with electrochemical impedance spectroscopy and cyclic voltammetry. In addition, various electrolyte solutions are studied to investigate the capacitive behavior of CNF webs. Electrolyte type variation has a significant effect on the capacitance results and high capacitance values are achieved in aqueous solution. According to the differing electrolyte types, specific capacitance values (C_sp) are recorded between 204 and 149 F g^?1 where maximum specific capacitance is obtained in 0.5 M H₂SO₄ as 204 F g^?1. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45723.     

The production of porosity in carbon nanofibers by the catalytic action of Ni nanoparticles in low temperature activation

Carbon nanofibers (CNFs) containing Ni nanoparticles were synthesized by carbonization of electrospun polyacrylonitrile nanofibers containing NiCl₂ followed by low-temperature activation (∼325 °C) in an oxygen atmosphere. The surface area of activated CNFs with 0.11 wt.% of the Ni oxide nanoparticles was 654 m²/g with increasing nanopores, which is significantly higher than the value for pure CNFs (30 m²/g). It was confirmed that the addition of trace amounts of Ni nanoparticles effectively produces a porous structure due to their catalytic role, which can increase the specific adsorption capacity of the activated CNFs without structural deformation.     

Electrospun mesoporous carbon nanofibers produced from phenolic resin and their use in the adsorption of large dye molecules

Mesoporous carbon nanofibers (CNFs) were prepared by a sol–gel/electrospinning process using phenolic resin precursor as carbon source and triblock copolymer Pluronic F127 as template. The final CNFs were obtained after carbonization of as-spun nanofibers and removal of SiO₂. Three samples (C-1, C-2, and C-3) with different pore textures were synthesized. The CNF structures were characterized by scanning and transmission electron microscopy, and N₂ adsorption–desorption measurements, demonstrating that the samples consisted of nanofibers with mesopores and the mesopore volumes depended on the amount of tetraethyl orthosilicate in the spinnable sols. According to thermogravimetric analysis, the CNF yields of 2.57%, 2.78%, and 2.13% from the spinnable sols for sample C-1, C-2, and C-3 were obtained, respectively. The mesoporous CNFs were used as highly efficient adsorbents for large dye molecules. The relationship between the pore textures and adsorption properties was studied. It is suggested that the adsorption of different dyes depend on an appropriate pore size distribution in addition to surface area. However, the adsorption capacity of the regenerated adsorbents gradually decreased with the number of regeneration cycles. The adsorption of acid red 1 could reach 186 mg g^?1 for C-3 after seven regeneration cycles. Furthermore, the mechanical strength of CNFs needs improvement.     

Robust growth of herringbone carbon nanofibers on layered double hydroxide derived catalysts and their applications as anodes for Li-ion batteries

Herringbone carbon nanofibers (CNFs) were efficiently produced by chemical vapor deposition on Ni nanoparticles derived from layered double hydroxide (LDH) precursors. The as-obtained CNFs with a diameter ranging from 40 to 60 nm demonstrated herringbone morphologies when they grew on Ni/Al LDH derived catalysts both in the fixed-bed and fluidized-bed reactor. The Ni/Mg/Al, Ni/Cu/Al, as well as Ni/Mo/Mg/Al catalysts were also effective to grow herringbone CNFs. The diameter and specific surface area of the as-obtained CNFs highly depended on the catalyst composition and the growth temperature. When CNFs were grown at 550 °C on Ni/Al catalyst, the as-obtained products had an outer diameter of ca. 50 nm and a specific surface area of 242 m² g⁻¹, possessed a discharge capacity of 330 mAh g⁻¹ as the electrode in a two-electrode coin-type cell. With the increase of the surface area, the discharge capacity increased at a rate of 0.90 mAh cm⁻², while the initial coulombic efficiency decreased gradually on nanocarbon anodes. This is attributed to the fact that CNFs with higher surface area afford smaller sp² carbon layer that facilitated more Li ions to extract from the anodes.     

Effect of cellulose nanofibers and acetylated cellulose nanofibers on the properties of low‐density polyethylene/thermoplastic starch blends

The aim of this study was to evaluate the effect of cellulose nanofibers (CNFs) and acetylated cellulose nanofibers (ACNFs) on the properties of low‐density polyethylene/thermoplastic starch/polyethylene‐grafted maleic anhydride (LDPE/TPS/PE‐g‐MA) blends. For this purpose, CNFs, isolated from wheat straw fibers, were first acetylated using acetic anhydride in order to modify their hydrophilicity. Afterwards, LDPE/TPS/PE‐g‐MA blends were reinforced using either CNFs or ACNFs at various concentrations (1–5 wt%) with a twin‐screw extruder. The mechanical results demonstrated that addition of ACNFs more significantly improved the ultimate tensile strength and Young's modulus of blends than addition of CNFs, albeit elongation at break of both reinforced blends decreased compared with the neat sample. Additionally, biodegradability and water absorption capacity of blends improved due to the incorporation of both nanofibers, these effects being more pronounced for CNF‐assisted blends than ACNF‐reinforced counterparts. © 2018 Society of Chemical Industry     

Preparation of porous carbon nanofibers derived from graphene oxide/polyacrylonitrile composites as electrochemical electrode materials

Porous carbon nanofibers (CNFs) derived from graphene oxide (GO) were prepared from the carbonization of electrospun polyacrylonitrile nanofibers with up to 15 wt.% GO at 1200 °C, followed by a low-temperature activation. The activated CNFs with reduced GOs (r-GO) revealed a specific surface area and adsorption capacity of 631 m²/g and 191.2 F/g, respectively, which are significantly higher than those of pure CNFs (16 m²/g and 3.1 F/g). It is believed that rough interfaces between r-GO and CNFs introduce oxygen pathways during activation, help to produce large amounts of all types of pores compared to pure activated CNFs.     

Porous carbon nanosheet with high surface area derived from waste poly(ethylene terephthalate) for supercapacitor applications

Converting waste plastics into valuable carbon materials has obtained increasing attention. In addition, carbon materials have shown to be the ideal electrode materials for double-layer supercapacitors owing to their large specific surface area, high electrical conductivity, and stable physicochemical properties. Herein, an easily operated approach is established to efficiently convert waste poly(ethylene terephthalate) beverage bottles into porous carbon nanosheet (PCNS) through the combined processes of catalytic carbonization and KOH activation. PCNS features an ultrahigh specific surface area (2236 m² g⁻¹), hierarchically porous architecture, and a large pore volume (3.0 cm³ g⁻¹). Such excellent physicochemical properties conjointly contribute to the outstanding supercapacitive performance: 169 F g⁻¹ (6 M KOH) and 135 F g⁻¹ (1 M Na₂SO₄). Furthermore, PCNS shows a high capacitance of 121 F g⁻¹ and a corresponding energy density of 30.6 Wh kg⁻¹ at 0.2 A g⁻¹ in the electrolyte of 1 M TEATFB/PC. When the current density increases to 10 A g⁻¹, the capacitance remains at 95 F g⁻¹, indicating the extraordinary rate capability. This work not only proposes a facile approach to synthesize PCNS for supercapacitors, but also puts forward a potential sustainable way to recycle waste plastics and further hopefully mitigates the waste plastics-related environmental issues. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48338.     

Reinforcement effect of poly (methyl methacrylate)-<Emphasis Type="Italic">g</Emphasis>-cellulose nanofibers on LDPE/thermoplastic starch composites: preparation and characterization

The effect of cellulose nanofibers (CNFs) and poly [methyl methacrylate (MMA)]-grafted cellulose nanofibers (CNF-g-PMMA) on mechanical properties and degradability of a 75/25 low density polyethylene/thermoplastic starch (LDPE/TPS) blend was investigated. Graft copolymerization on CNFs was performed in an aqueous suspension by free radical polymerization using MMA as an acrylic monomer. In addition, a LDPE/TPS blend was reinforced by different amounts of CNFs (1–5 wt%) and CNF-g-PMMA (1–7 wt%) using a twin-screw extruder. A 61% grafting of PMMA on the surface of CNFs was demonstrated by gravimetric analysis. Moreover, after modification the X-ray photoelectron spectroscopy analysis showed a 20% increase of carbon atoms on the surface of CNFs and a 22.6% decrease in the oxygen content of its surface. The mechanical properties of the CNFs-modified composites were significantly improved compared to the unmodified nanocomposites. The highest tensile strength and Young’s modulus were obtained for the composites reinforced by 3 and 7 wt% CNF-g-PMMA, respectively. The degradability of cellulose nanocomposites was studied by water absorption and soil burial tests. Surface modification of CNFs lowered water absorption, and soil burial test of the LDPE/TPS blend showed improvement in biodegradability by addition of CNF-g-PMMA.     

Enhancement of superhydrophobicity and conductivity of carbon nanofibers-coated glass fabrics

This paper explores the role of carbon nanofibers (CNFs) on its potential to produce surperhydrophobic and conductive surfaces of glass fiber (GF) fabrics when processed by the catalytic chemical vapor deposition. Large-area helical CNFs were prepared over GF surfaces by the pyrolysis of acetylene. CNFs/GFs composites were characterized by XPS, SEM, and contact angle measurements. The results indicate the CNFs/GF fabrics surface exhibited excellent superhydrophocity and electroconductivity due to the grown CNFs The contact angle and volume resistivity of CNFs decorating the GF fabrics was equal to 152° and 1.13 × 10⁻³ Ω cm, respectively.     

Effects of carbon nanofibers on the fracture,mechanical, and thermal properties of PP/SEBS‐g‐MA blends

Polypropylene/maleated (styrene‐ethylene‐butadiene‐styrene) (PP/SEBS‐g‐MA) blends reinforced with 0.2–2.5 wt% carbon nanofibers (CNFs) were prepared by injection molding. The structure, thermal, mechanical, and fracture behaviors of PP/SEBS‐g‐MA blends and their nanocomposites were studied. Wide‐angle X‐ray diffraction (WAXD) results showed that the SEBS‐g‐MA and/or CNF additions do not induce a structural change of PP. Tensile measurements showed that the Young's modulus and tensile yield strength increase with the increasing filler content. Izod impact and essential work of fracture test results demonstrated that CNFs are beneficial to improve the impact strength and specific essential work of fracture of PP/SEBS‐g‐MA blends. Therefore, tough PP‐nanocomposites can be achieved by melt‐blending low fractions of CNFs and appropriate elastomer contents. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Electrospun melamine-blended activated carbon nanofibers for enhanced control of indoor CO2

Electrospun carbon nanofibers were activated with melamine–polyacrylonitrile [melamine-blended carbon nanofibers (MACNFs)] for use as a fibrous adsorbent for indoor CO₂ removal. Although, melamine doping was intended solely to incorporate basic nitrogen functionalities on the nanofibers, it also shortened fabrication time, conserving time, and energy cost. The specific surface area and microporosity of the fibers were enhanced from 412 m² g⁻¹ and 0.1646 cm³ g⁻¹ to 547 m² g⁻¹ and 0.220 cm³ g⁻¹, respectively, upon final CO₂ activation of the nanofibers. With the chemical properties, we observed significant tethering of pyridine functionality. The sample, MACNF-7 (10 mL of polymer solution doped with 0.7 g of melamine), provided the optimum melamine doping condition to achieve the highest CO₂ adsorption capacity of 3.15 mmol g⁻¹. The adsorption performance was based on simultaneous improvement in microporosity (physical) and surface basicity (chemical) properties of the adsorbent. However, in a binary mixture with nitrogen, the selective adsorption of CO₂ showed the predominance of the improved surface basicity over microporosity. The highest CO₂ selective capture (1.22 mmol g⁻¹) was occurred for a CO₂:N₂ ratio of 0.15:0.85, with a selectivity of 58.19 at 273 K. In a regeneration test, stable and robust performance was achieved more than five cycles. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47747.     

Preparation of Iron Oxide Particle-Decorated Lignin-Based Carbon Nanofibers as Electrode Material for Pseudocapacitor

Iron oxide particle-decorated lignin-based carbon nanofibers (IO-LCNFs) were fabricated from organic mixtures containing acetic acid lignin (AAL) together with ferric acetylacetonate (Fe(acac)₃) via electrospinning followed by stabilization in air and carbonization in nitrogen. After the addition of Fe(acac)₃, IO-LCNFs showed different morphologies: Non-fused IO-LCNFs were obtained with diameters of 400–500 nm; iron oxide nanoparticles with diameters of 30–60 nm were exposed outside and well-distributed when sufficient amounts of Fe(acac)₃ were added. These carbon nanofibers were then used as electrode material for pseudocapacitor. It was found that the iron oxide particles enhanced the resulting electrochemical properties via reversible redox reactions. IO-LCNFs made from the composite nanofibers with mass ratio of AAL/Fe(acac)₃ of 80/20 [i.e., IO-LCNFs (80/20)] exhibited the highest specific capacitance, 72.1 F g^?1, at current density of 500 mA g^?1.     

Pitch carbon and LiF co-modified Si-based anode material for lithium ion batteries

To improve the electrochemical performance of silicon-based anode material, lithium fluoride (LiF) and pitch carbon were introduced to co-modify a silicon/graphite composite (SG), in which the graphite acts as a dispersion matrix. The pitch carbon helps to improve the electronic conductivity and lithium ion transport of the material. LiF is one of the main components of the solid electrolyte interphase (SEI) formed on the silicon surface, helping to tolerate the large volume changes of Si during lithiation/delithiation. The modified SG sample delivered a capacity of over 500 mA h g⁻¹, whereas unmodified SG delivered a capacity of lower than 50 mAh g⁻¹ after 100 cycles at 100 mA g⁻¹. When performed at 4 A g⁻¹, the reversible capacity of the modified SG was 346 mAh g⁻¹, much higher than that of SG (only 37 mA h g⁻¹). The enhanced cycling and rate properties of the modified SG can be attributed to the synergetic contribution of the pitch carbon and LiF which help accommodate the volume change, reduce the side reaction, and form a stable solid electrolyte interface layer.     

Biomimetic synthesis and characterization of carbon nanofiber/hydroxyapatite composite scaffolds

Three dimensional electrospun carbon nanofiber (CNF)/hydroxyapatite (HAp) composites were biomimetically synthesized in simulated body fluid (SBF). The CNFs with diameter of ∼250 nm were first fabricated from electrospun polyacrylonitrile precursor nanofibers by stabilization at 280 °C for 2 h, followed by carbonization at 1200 °C. The morphology, structure and water contact angle (WCA) of the CNFs and CNF/HAp composites were characterized. The pristine CNFs were hydrophobic with a WCA of 139.6°, resulting in the HAp growth only on the very outer layer fibers of the CNF mat. Treatment in NaOH aq. solutions introduced carboxylic groups onto the CNFs surfaces, and hence making the CNFs hydrophilic. In the SBF, the surface activated CNFs bonded with Ca²⁺ to form nuclei, which then easily induced the growth of HAp crystals on the CNFs throughout the CNF mat. The fracture strength of the CNF/HAp composite with a CNF content of 41.3% reached 67.3 MPa. Such CNF/HAp composites with strong interfacial bondings and high mechanical strength can be potentially useful in the field of bone tissue engineering.     

Improving water desalination performance of electrospun carbon nanofibers by supporting with binary metallic carbide nanoparticles

Capacitive deionization (CDI) technology is proposed as an environmentally friendly way to desalinate brackish water samples with outstanding efficiency. Since the nanomaterial composition is the controlling factor in the measured activity of fabricated CDI cells, much efforts are directed to explore highly effective nanocomposites with increased electrosorptive capacity and enhanced regeneration behavior during operation for longer periods. Here, the electrospinning process was devoted to synthesize mixed cobalt and titanium carbides nanoparticles onto carbon nanofibers [Co–TiC@CNFs] using cobalt acetate tetrahydrate (CoAc) and titanium (IV) isopropoxide (TIP) as precursor salts and polyvinylpyrrolidone (PVP) as a carbon source. Electrospun mats were then calcined at 950 °C for 6 h using a tube furnace with passing argon gas. This formed nanoporous material could provide numerous pathways for increased ions adsorption with extraordinary electrical conductivity. This could explain its enhanced electrochemical properties as evidenced by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy (EIS) methods. A specific capacitance value of 979.40 F g^?1 was estimated for Co–TiC@CNFs as 7.42 times higher than that for bare CNFs. Furthermore, this nanohybrid material had a salt adsorption capacity of 33.10 mg g^?1 in 1.0 M NaCl solution at 1.2 V that highly exceeded the obtained ones for TiC [2.20 mg g^?1] and CNFs [8.20 mg g^?1]. Accordingly, modifying carbon nanofibers with metallic carbides can create suitable nano-constituents for promising CDI cell output.     

Fabrication and electrochemical characterization of polyimide-derived carbon nanofibers for self-standing supercapacitor electrode materials

We report the electrochemical performance of aromatic polyimide (PI)-based carbon nanofibers (CNFs), which were fabricated by electrospinning, imidization, and carbonization process of poly(amic acid) (PAA) as an aromatic PI precursor. For the purpose, PAA solution was electrospun into nanofibers, which were then converted into CNFs via one-step (PAA-CNFs) or two-step heat treatment (PI-CNFs) of imidization and carbonization. The FTIR and Raman spectra demonstrated a successful structural evolution from PAA nanofibers to PI nanofibers to CNFs at the molecular level. The SEM images revealed that the average diameter of the nanofibers decreased noticeably via imidization and carbonization, while it decreased slightly with increasing the carbonization temperature from 800 °C to 1000 °C. In case of PI-CNF carbonized at 1000 °C, a porous structure was developed on the surface of nanofibers. The electrical conductivity of PI-CNFs, which was even higher than that of PAA-CNFs, increased significantly from 0.41 to 2.50 S/cm with increasing the carbonization temperature. From cyclic voltammetry and galvanostatic charge/discharge tests, PI-CNF carbonized at 1000 °C was evaluated to have a maximum electrochemical performance of specific capacitance of ~126.3 F/g, energy density of ~12.2 Wh/kg, and power density of ~160 W/kg, in addition to an excellent operational stability. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47846.     

Si/CNTs@melamine-formaldehyde resin-based carbon composites and its improved energy storage performances

In this paper, Si/carbon nanotubes@melamine-formaldehyde resin (MFR)-based carbon (Si/CNTs@C) composites have been fabricated by surface modification, electrostatic self-assembly, cross-linking of MFR under hydrothermal treatment and further carbonization. The microstructure of the Si/CNTs@C composites was characterized, and the effects of CNTs content in Si/CNTs@C composites on their electrochemical performances were also investigated in detail. The results indicate Si/CNTs@C composites as anode materials of Li-ion batteries exhibit better high-rate and cycling performances compared to Si and Si@MFR-based carbon composites. Notably, Si/CNTs@C composites with 10.4 wt% CNTs show specific capacities of 1900, 1879, 1,688, 1,394, 1,189 mAh·g⁻¹ at 0.2, 0.5, 1, 2, and 3 A·g⁻¹, respectively. Even at 4 and 5 A·g⁻¹, their capacities still reach 970 and 752 mAh·g⁻¹, respectively. Moreover, they deliver a reversible capacity of 1,184 mAh·g⁻¹ at 0.5 A·g⁻¹ after 100 cycles. Therefore, the reasonable structure is of great significance for enhancing the electrochemical performances of Si-based composites.     

Influence of wet oxidation of herringbone carbon nanofibers on the pseudocapacitance effect

Herringbone carbon nanofibers (CNFs) were treated with concentrated HNO₃ and a mixture of diluted HNO₃/H₂SO₄ to obtain a series of oxygen enriched CNF with different oxygen group distribution, but with a similar porous texture. Oxygen functional groups were determined by X-ray photoelectron spectroscopy. CNFs with a very high relative concentration of carbonyl and/or quinone groups and hydroxyl groups were obtained by adjusting the suitable temperature and time of oxidation with HNO₃ and HNO₃/H₂SO₄, respectively. The electrochemical behavior of the samples was studied in three- and two-electrode cells. The performance of oxidized CNFs-based supercapacitors working in 1 mol L⁻¹ H₂SO₄ and 6 mol L⁻¹ KOH was analyzed using cyclic voltammetry and galvanostatic charging/discharging. The specific capacitance of the oxidized CNFs was more than twice enhanced in acidic and alkaline media compared to the pristine CNFs due to the pseudocapacitance effect. It was revealed that not only quinone groups but also hydroxyl groups contribute into the overall capacitance through the pseudocapacitance effect. With increasing surface concentration of the CO and C–OH groups, the capacitance values increase for the capacitors operating in both media.     

Preparation of electrospun magnetic polyvinyl butyral/Fe2O3 nanofibrous membranes for effective removal of iron ions from groundwater

Removing iron ions from groundwater to purify, it is a challenge faced by countries across the globe, which is why developing polymeric microfiltration membranes has garnered much attention. The authors of this study set out to develop nanofibrous membranes by embedding magnetic Fe₂O₃ nanoparticles (MNPs) into polyvinylbutyral (PVB) nanofibers via the electrospinning process. Investigation was made into the effects of the concentration of the PVB and MNPs on the morphology of the nanofibers, their magnetic properties, and capacity for filtration to remove iron ions. The fabrication and presence of well-incorporated MNPs in the PVB nanofibers were confirmed by scanning electron microscopy and transmission electron microscopy. Depending on the concentration of the MNPs, the membranes exhibited magnetization to the extent of 45.5 emu g⁻¹; hence, they exceeded the performance of related nanofibrous membranes in the literature. The magnetic membranes possessed significantly higher efficiency for filtration compared to their nonmagnetic analogues, revealing their potential for groundwater treatment applications.     

Hollow C/Co9S8 hybrid polyhedra-modified carbon nanofibers as sulfur hosts for promising Li–S batteries

Lithium-sulfur (Li–S) batteries hold great expectations as next-generation advanced capacity storage devices due to their higher theoretical energy density and low cost. Even so, polysulfide shuttles, insulation, and volume expansion of sulfur impede its commercial progress. To suppress these problems, we used electrospinning and self-templating to construct C/Co₉S₈ hybrid polyhedra-modified carbon nanofibers (denoted as C/Co₉S₈–C@S fibers) as sulfur hosts. The quasi-metallic polar Co₉S₈ strongly bonds and locks polysulfides, and the hollow polyhedra provide sulfur storage space. Moreover, the overall nanofiber forms an interconnected conductive network to assist the transmission of Li⁺/e⁻ and restrain the escape of the sulfur phase to a certain extent. Compared with C/Co₉S₈ polyhedra and carbon nanofibers, the C/Co₉S₈–C@S fiber delivers excellent adsorption characteristics for polysulfides. As a Li–S battery cathode, the C/Co₉S₈–C@S fiber (sulfur content: 87.20 wt%) exhibits an initial specific capacity of 1013.7 mAh g⁻¹ at 0.1 C, displaying a stable capacity of 694.9 mAh g⁻¹ after 150 cycles. Additionally, it shows a high specific capacity of 894.7 mAh g⁻¹ at 1C with a capacity decay of ~0.116% per cycle over 500 cycles.