Carbon fibers (CFs) are considered promising composite materials for various applications. However, the high cost of CFs (as much as $26 per kg) limits their practical use in the automobile and energy industries. In this study, we developed a continuous stabilization process for manufacturing low-cost CFs. We employed a textile-grade polyacrylonitrile (PAN) fiber as a low-cost precursor and UV irradiation technique to shorten the thermal stabilization time. We confirmed that UV irradiation on the textile-grade PAN fibers could lower the initial thermal stabilization temperature and also lead to a higher reaction. These resulted in a shorter overall stabilization time and enhancement of the tensile properties of textilegrade PAN-based CFs. Our study found that only 70 min of stabilization time with UV irradiation was required to prepare textile-grade PAN-based low-cost CFs with a tensile strength of 2.37 ± 0.22GPa and tensile modulus of 249 ± 5 GPa.

Energy storage systems should address issues such as power fluctuations and rapid charge-discharge; to meet this requirement, CoFe₂O₄ (CFO) spinel nanoparticles with a suitable electrical conductivity and various redox states are synthesized and used as electrode materials for supercapacitors. In particular, CFO electrodes combined with carbon nanofibers (CNFs) can provide long-term cycling stability by fabricating binder-free three-dimensional electrodes. In this study, CFO-decorated CNFs are prepared by electrospinning and a low-cost hydrothermal method. The effects of heat treatment, such as the activation of CNFs (ACNFs) and calcination of CFO-decorated CNFs (C-CFO/ACNFs), are investigated. The C-CFO/ACNF electrode exhibits a high specific capacitance of 142.9 F/g at a scan rate of 5 mV/s and superior rate capability of 77.6% capacitance retention at a high scan rate of 500 mV/s. This electrode also achieves the lowest charge transfer resistance of 0.0063 Ω and excellent cycling stability (93.5% retention after 5,000 cycles) because of the improved ion conductivity by pathway formation and structural stability. The results of our work are expected to open a new route for manufacturing hybrid capacitor electrodes containing the C-CFO/ACNF electrode that can be easily prepared with a low-cost and simple process with enhanced electrochemical performance.

The (Ga_1-xZn_x)(N_1-xO_x) solid solution is attracting extensive attention for photocatalytic water splitting and wastewater treatment owing to its narrow and controllable band gap. To optimize the photocatalytic performance of the solid solution, the key points are to decrease its band gap and recombination rate. In this study, (Ga_1-xZn_x)(N_1-xO_x) nanofibers with various Zn fractions are prepared by electrospinning followed by calcination and nitridation. The effect of the composition and crystallinity of electrospun oxide nanofibers on the morphology and optical properties of the obtained solid-solution nanofibers are systematically investigated. The results show that the final shape of the (Ga_1-xZn_x) (N_1-xO_x) material is greatly affected by the crystallinity of the oxide nanofibers before nitridation. The photocatalytic properties of (Ga_1-xZn_x)(N_1-xO_x) with different Ga:Zn atomic ratios are investigated by studying the degradation of rhodamine B under visible light irradiation.

Citations

Citations to this article as recorded by  

• Fabrication of Nanowire by Electrospinning Process Using Nickel Oxide Particle Recovered from MLCC
  Haein Shin, Jongwon Bae, Minsu Kang, Kun-Jae Lee
  journal of Korean Powder Metallurgy Institute.2023; 30(6): 502.     CrossRef

Magnetic 0-D Nd₂Fe₁₄B powders are successfully fabricated using 1-D Nd₂Fe₁₄B nanowire formed by an efficient and facile electrospinning process approach. The synthesized Nd-Fe-B fibers and powders are investigated for their microstructural, crystallographic, and magnetic properties according to a series of subsequent heat treatments. Each heat-treatment process leads to the removal of organic impurities and the formation of the respective oxides/composites of Nd, Fe, and B, resulting in the formation of Nd₂Fe₁₄B powders. Nd-Fe-B fibers exhibit the following magnetic properties: The coercivity (H_ci) of 3260 Oe, a maximum magnetization at 3T of 109.44 emu/g, and a magnetization remanence (M_r) of 44.11 emu/g. This process easily mass produces hard magnetic Nd₂Fe₁₄B powders using a 1-D synthesis process and can be extended to the experimental design of other magnetic materials.

Citations

Citations to this article as recorded by  

• Nd2Fe14B/FeCo Core–Shell Nanoparticle Synthesis Using Galvanic Substitution Based Electroless Plating
  Muhammad Aneeq Haq, Han-Saem Lee, Mi Hye Lee, Da-Woon Jeong, Eom Nu Si A, Bin Lee, Yoseb Song, Bum Sung Kim
  Coatings.2022; 12(3): 389.     CrossRef

To meet the current demand in the fields of permanent magnets for achieving a high energy density, it is imperative to prepare nano-to-microscale rare-earth-based magnets with well-defined microstructures, controlled homogeneity, and magnetic characteristics via a bottom-up approach. Here, on the basis of a microstructural study and qualitative magnetic measurements, optimized reduction conditions for the preparation of nanostructured Sm-Co magnets are proposed, and the elucidation of the reduction-diffusion behavior in the binary phase system is clearly manifested. In addition, we have investigated the microstructural, crystallographic, and magnetic properties of the Sm-Co magnets prepared under different reduction conditions, that is, H₂ gas, calcium, and calcium hydride. This work provides a potential approach to prepare high-quality Sm-Co-based nanofibers, and moreover, it can be extended to the experimental design of other magnetic alloys.

To meet the current demand in the fields of permanent magnets for achieving a high energy density, it is imperative to prepare nano-to-microscale rare-earth-based magnets with well-defined microstructures, controlled homogeneity, and magnetic characteristics via a bottom-up approach. Here, on the basis of a microstructural study and qualitative magnetic measurements, optimized reduction conditions for the preparation of nanostructured Sm-Co magnets are proposed, and the elucidation of the reduction-diffusion behavior in the binary phase system is clearly manifested. In addition, we have investigated the microstructural, crystallographic, and magnetic properties of the Sm-Co magnets prepared under different reduction conditions, that is, H₂ gas, calcium, and calcium hydride. This work provides a potential approach to prepare high-quality Sm-Co-based nanofibers, and moreover, it can be extended to the experimental design of other magnetic alloys.

Whisker-type magnesium hydroxide sulfate hydrate (5Mg(OH)₂·MgSO₄·3H₂O, abbreviated 513 MHSH), is used in filler and flame-retardant composites based on its hydrate phase and its ability to undergo endothermic dehydration in fire conditions, respectively. In general, the length of whiskers is determined according to various synthetic conditions in a hydrothermal reaction with high temperature (~180°C). In this work, high-quality 513 MHSH whiskers are synthesized by controlling the concentration of the raw material in ambient conditions without high pressure. Particularly, the concentration of the starting material is closely related to the length, width, and purity of MHSH. In addition, a ceramic-coating system is adopted to enhance the mechanical properties and thermal stability of the MHSH whiskers. The physical properties of the silica-coated MHSH are characterized by an abrasion test, thermogravimetric analysis, and transmission electron microscopy.

Citations

Citations to this article as recorded by  

• Effect of sulfate ion on synthesis of 5 Mg(OH)2·MgSO4·3H2O whiskers using non-hydrothermal method with acid catalyst
  Areum Choi, Nuri Oh, YooJin Kim
  Journal of the Korean Ceramic Society.2022; 59(2): 224.     CrossRef
• Study of SiO2 coating and carboxylic surface-modification on Mg-based inorganic fiber by one-step reflux reaction
  Minsol Park, Areum Choi, Seiki Kim, Wooyoung Shim, YooJin Kim
  Journal of the Korean Ceramic Society.2022; 59(6): 869.     CrossRef
• Effect of H₂SO₄ and Reaction Time on Synthesis of 5Mg(OH)₂∙MgSO₄∙3H₂O Whiskers using Hydrothermal Reaction
  Areum Choi, Nuri Oh, YooJin Kim
  Journal of Korean Powder Metallurgy Institute.2020; 27(5): 401.     CrossRef

Conductive and dielectric SiC are fabricated using electroless plating of Ni–Fe films on SiC chopped fibers to obtain lightweight and high-strength microwave absorbers. The electroless plating of Ni–Fe films is achieved using a two-step process of surface sensitizing and metal plating. The complex permeability and permittivity are measured for the composite specimens with the metalized SiC chopped fibers dispersed in a silicone rubber matrix. The original noncoated SiC fibers exhibit considerable dielectric losses. The complex permeability spectrum does not change significantly with the Ni–Fe coating. Moreover, dielectric constant is sensitively increased with Ni–Fe coating, owing to the increase of the space charge polarization. The improvements in absorption capability (lower reflection loss and small matching thickness) are evident with Ni–Fe coating on SiC fibers. For the composite SiC fibers coated with Ni–Fe thin films, a -35 dB reflection loss is predicted at 7.6 GHz with a matching thickness of 4 mm.

Citations

Citations to this article as recorded by  

• Magnetic sputtering of FeNi/C bilayer film on SiC fibers for effective microwave absorption in the low-frequency region
  Tong Guo, Ben Huang, Changgeng Li, Yumin Lou, Xiu-Zhi Tang, Xiaozhong Huang, Jianling Yue
  Ceramics International.2021; 47(4): 5221.     CrossRef

The friction characteristics of Al-Fe alloy powders are investigated in order to develop an eco-friendly friction material to replace Cu fiber, a constituent of brake-pad friction materials. Irregularly shaped Al-Fe alloy powders, prepared by gas atomization, are more uniformly dispersed than conventional Cu fiber on the brake pad matrix. The wear rate of the friction material using Al-8Fe alloy powder is lower than that of the Cu fiber material. The change in friction coefficient according to the friction lap times is 7.2% for the Cu fiber, but within 3.8% for the Al-Fe alloy material, which also shows excellent judder characteristics. The Al-Fe alloy powders are uniformly distributed in the brake pad matrix and oxide films of Al and Fe are homogeneously formed at the friction interface between the disc and pad, thus exhibiting excellent friction and lubrication characteristics. The brake pad containing Al-Fe powders avoids contamination by Cu dust, which is generated during braking, by replacing the Cu fiber while maintaining the friction and lubrication performance.

Well-dispersed platinum catalysts on ruthenium oxide nanofiber supports are fabricated using electrospinning, post-calcination, and reduction methods. To obtain the well-dispersed platinum catalysts, the surface of the nanofiber supports is modified using post-calcination. The structures, morphologies, crystal structures, chemical bonding energies, and electrochemical performance of the catalysts are investigated. The optimized catalysts show well-dispersed platinum nanoparticles (1-2 nm) on the nanofiber supports as well as a uniform network structure. In particular, the well-dispersed platinum catalysts on the ruthenium oxide nanofiber supports display excellent catalytic activity for oxygen reduction reactions with a half-wave potential (E_1/2) of 0.57 V and outstanding long-term stability after 2000 cycles, resulting in a lower E_1/2 potential degradation of 19 mV. The enhanced electrochemical performance for oxygen reduction reactions results from the well-dispersed platinum catalysts and unique nanofiber supports.

Citations

Citations to this article as recorded by  

• Fabrication of Porous Electrodes for Zinc-Ion Supercapacitors with Improved Energy Storage Performance
  Geon-Hyoung An
  Korean Journal of Materials Research.2019; 29(8): 505.     CrossRef
• Surface tailoring of zinc electrodes for energy storage devices with high-energy densities and long cycle life
  Geon-Hyoung An, SeungNam Cha, Jung Inn Sohn
  Applied Surface Science.2019; 467-468: 1157.     CrossRef
• Synthesis of Nitrogen Doped Protein Based Carbon as Pt Catalysts Supports for Oxygen Reduction Reaction
  Young-geun Lee, Geon-hyeong An, Hyo-Jin Ahn
  Korean Journal of Materials Research.2018; 28(3): 182.     CrossRef

N-doped carbon nanofibers as catalysts for oxygen-reduction reactions are synthesized using electrospinning and carbonization. Their morphologies, structures, chemical bonding states, and electrochemical performance are characterized. The optimized N-doped carbon nanofibers exhibit graphitization of carbon nanofibers and an increased nitrogen doping as well as a uniform network structure. In particular, the optimized N-doped carbon nanofibers show outstanding catalytic activity for oxygen-reduction reactions, such as a half-wave potential (E1/2) of 0.43 V, kinetic limiting current density of 6.2 mA cm^-2, electron reduction pathways (n = 3.1), and excellent long-term stability after 2000 cycles, resulting in a lower E_1/2 potential degradation of 13 mV. The improvement in the electrochemical performance results from the synergistic effect of the graphitization of carbon nanofibers and the increased amount of nitrogen doping.

Carbon nanofiber (CNF) composites coated with spindle-shaped Fe₂O₃ nanoparticles (NPs) are fabricated by a combination of an electrospinning method and a hydrothermal method, and their morphological, structural, and chemical properties are measured by field-emission scanning electron microscopy, transmission electron microscopy, Xray diffraction, and X-ray photoelectron spectroscopy. For comparison, CNFs and spindle-shaped Fe₂O₃ NPs are prepared by either an electrospinning method or a hydrothermal method, respectively. Dye-sensitized solar cells (DSSCs) fabricated with the composites exhibit enhanced open circuit voltage (0.70 V), short-circuit current density (12.82 mA/cm2), fill factor (61.30%), and power conversion efficiency (5.52%) compared to those of the CNFs (0.66 V, 11.61 mA/cm2, 51.96%, and 3.97%) and spindle-shaped Fe₂O₃ NPs (0.67 V, 11.45 mA/cm2, 50.17%, and 3.86%). This performance improvement can be attributed to a synergistic effect of a superb catalytic reaction of spindle-shaped Fe₂O₃ NPs and efficient charge transfer relative to the one-dimensional nanostructure of the CNFs. Therefore, spindle-shaped Fe₂O₃-NPcoated CNF composites may be proposed as a potential alternative material for low-cost counter electrodes in DSSCs.

Citations

Citations to this article as recorded by  

• Ni Nanoparticles-Graphitic Carbon Nanofiber Composites for Pt-Free Counter Electrode in Dye-Sensitized Solar Cells
  Dong-Hyeun Oh, Bon-Ryul Koo, Yu-Jin Lee, HyeLan An, Hyo-Jin Ahn
  Korean Journal of Materials Research.2016; 26(11): 649.     CrossRef