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• A urea-treated CoO x /CNF freestanding electrode, capable of subduing faradaic currents, was proposed. • Urea treatment enhanced the electrical and ionic conductivities of the CoO x /CNF freestanding electrode. • The urea-treated CoO x /CNF electrode retained 91 % of capacitance after 10,000 GCD cycles. • Urea-induced heteroatoms promoted charge redistribution, achieving an energy density of 61 µWh cm–2. Supercapacitors (SCs) play a crucial role in flexible electronics, necessitating innovative approaches to enhance surface faradaic reactions and minimize faradaic diffusion while using aqueous electrolytes. Thus, the urea treatment of cobalt oxide (CoO x)-decorated carbon nanofibers (CNFs) is proposed in this study to decrease the contribution of faradaic diffusion-limited current. Flexible CoO x /CNF electrodes were obtained by annealing ZIF-67-grafted polyacrylonitrile (PAN) fibers via a wet chemical method. The urea treatment of CoO x /CNFs increased the content of sp2-hybridized carbon and pyridinic nitrogen, as confirmed by X-ray photoelectron spectroscopy, effectively enhancing conductivity and pseudocapacitive charge storage capability via nitrogen doping. Notably, urea-treated CoO x /CNF electrode samples exhibited a capacitance of 750 mF cm−2 at a scan rate of 10 mV s−1, while retaining more than 81 % capacitance at a higher scan rate of 100 mV s-1. The cyclic voltammetry curves during variable bending angle testing (0°, 45°, and 90°) exhibited negligible changes, indicating the excellent flexibility of the SCs. The CoO x /CNFs and urea-treated CoO x /CNFs exhibited 80 % and 91 % capacitance retentions, respectively, after 10,000 galvanostatic charge and discharge cycles. Furthermore, the attained energy densities of 76 and 61 µWh cm−2 at the respective power densities of 2 and 20 mW cm−2 indicated the excellent electrochemical performance of the optimal urea-treated CoO x /CNF electrode. [Display omitted] [ABSTRACT FROM AUTHOR]

• Vertical graphene sheets on carbon nanofibers (VG@CNF) were synthesized as anchors. • VG@CNF was combined with reduced graphene oxide (rGO) to form robust networks. • Fiber-based strain sensors were fabricated by coating the hybrids on spandex fibers. • The enhanced interaction facilitates highly reversible behaviors of the sensor. • The high-performance composite sensor was used for human motion detection. Stretchable strain sensors have great potential for diverse applications including human motion detection, soft robotics, and health monitoring. However, their practical implementation requires improved repeatability and stability along with high sensing performances. Here, we utilized spiky vertical graphene (VG) sheets decorated on carbon nanofibers (VG@CNFs) to establish reliable conductive networks for resistive strain sensing. Three-dimensional (3D) VG@CNFs combined with reduced graphene oxide (rGO) sheets were simply coated on stretchable spandex fibers by ultrasonication. Because of the spiky geometry of the VG sheets, VG@CNF and rGO exhibited enhanced interactions, which was confirmed by mode I fracture tests. Due to the robust conductive networks formed by the VG@CNF and rGO hybrid, the fiber strain sensor exhibited a significantly improved strain range of up to 522% (with a high gauge factor of 1358) and stable resistance changes with minimal variation even after 5000 stretching–releasing cycles under a strain of 50%. In addition, the textile strain sensor based on the VG@CNF/rGO hybrid showed even improved repeatability for various strain levels of 10% to 200%, enabling its implementation on leggings for monitoring of squat posture. This study demonstrates the high potential of the 3D VG@CNF for high-performance and reliable stretchable strain sensors. [Display omitted] [ABSTRACT FROM AUTHOR]

• The FeNi/C nanofibers exhibited excellent microwave absorption performance with a minimum reflection loss of -57.15 dB and an effective absorption bandwidth of 4.0 GHz at 1.6 mm. • The FeNi/C nanofibers showed better electromagnetic microwave absorption performance than the single-component nanofibers and pure carbon fibers. • The superior performance of FeNi/C nanofibers can be attributed to the formation of abundant heterojunction interfaces, a cross-linking conductive network, and multidimensional magnetic components. The advantages of Fe, Ni metals and one-dimensional (1D) carbon materials are combined in this study using a simple method to prepare FeNi/C nanofibers for electromagnetic microwave (EM) absorption. The prepared FeNi/C nanofibers exhibit excellent EM absorption performance under dielectric/magnetic synergistic effect. At a frequency of 13.3 GHz, the minimum reflection loss (RL min) reaches -57.15 dB, and effective absorption bandwidth (EAB) is as high as 4.0 GHz (12.5–16.5 GHz), with a thickness and filling rate of only 1.6 mm and 30 wt.%, respectively. Analysis shows that the EM absorption performance of FeNi/C nanofibers far exceeds that of single-component nanofibers and pure carbon fibers, and the excellent EM absorption performance is due to its unique microstructure and excellent electromagnetic properties. The FeNi alloy loaded on carbon nanofibers forms rich heterogeneous interfaces, and the three-dimensional (3D) conductive network composed of 1D carbon fibers increases the migration path of electrons. In addition, FeNi alloy, as an impedance regulation factor, strengthens the dielectricity of the carbon matrix while providing multidimensional magnetism, achieving impedance matching. This work is thought to contribute to the promotion of emerging absorbers by providing a novel strategy for the development of new 1D magnetic carbon-based high-performance EM absorbing materials. [Display omitted] [ABSTRACT FROM AUTHOR]

• A porous elastic Co@CNF-PDMS composite was prepared by freeze-drying and confined catalysis. • The Co@CNF-PDMS composite with 4.5 mm achieves the minimum reflection loss (RL) of −81.0 dB at 9.9 GHz and RL no higher than −12.1 dB in the whole of X-band. • With the increase of compression strain, the distribution density of the absorbent increases, and the CNF sheet layer extrusion contact forms a conductive path, which leads to the conductive loss increase, finally the absorption band moves to high frequency. • The absorption band can be bi-directionality regulated by loading and strain with good stability. The dielectric loss of carbon materials is closely related to the microstructure and the degree of crystallization, and the microstructure modulation of electromagnetic wave absorbing carbon materials is the key to enhancing absorption properties. In this work, a porous elastic Co@CNF-PDMS composite was prepared by freeze-drying and confined catalysis. The graphitization degree and conductivity loss of carbon nanofibers (CNFs) were regulated by heat treatment temperature and Co catalyst content. The construction of a heterointerface between Co and C enhances the interfacial polarization loss. The Co@CNF-PDMS composite with 4.5 mm achieves the minimum reflection loss (RL min) of –81.0 dB at 9.9 GHz and RL no higher than –12.1 dB in the whole of the X-band. After applying a load of up to 40 % strain and 100 cycles to Co@CNF-PDMS, the dielectric properties of the composite remain stable. With the increase of compression strain, the distribution density of the absorbent increases, and the CNF sheet layer extrusion contact forms a conductive path, which leads to the conductive loss increase, finally, the absorption band moves to a high frequency. The absorption band can be bi-directionally regulated by loading and strain with good stability, which provides a new strategy for the development of intelligent electromagnetic wave absorbing materials. [Display omitted] [ABSTRACT FROM AUTHOR]

• A mechanically strong 3D BN-CNF scaffold was constructed by salt template method. • The prepared 3D networks can provide effective heat transfer pathways. • A hetero-structure was in situ formed between the 1D CNF and 2D BN within the 3D networks after the carbonization. • 3D networks filled EP composites demonstrate strong heat dissipation performance. With the increasing power density and integration of electronic devices, polymeric composites with high thermal conductivity (TC) are in urgent demand for solving heat accumulation issues. However, the direct introduction of inorganic fillers into a polymer matrix at low filler content usually leads to low TC enhancement. In this work, an interconnected three-dimensional (3D) polysulfone/hexagonal boron nitride-carbon nanofiber (PSF/BN-CNF) skeleton was prepared via the salt templated method to address this issue. After embedding into the epoxy (EP), the EP/PSF/BN-CNF composite presents a high TC of 2.18 W m−1 K−1 at a low filler loading of 28.61 wt%, corresponding to a TC enhancement of 990% compared to the neat epoxy. The enhanced TC is mainly attributed to the fabricated 3D interconnected structure and the efficient synergistic effect of BN and CNF. In addition, the TC of the epoxy composites can be further increased to 2.85 W m−1 K−1 at the same filler loading through a post-heat treatment of the PSF/BN-CNF skeletons. After carbonization at 1500°C, the adhesive PSF was converted into carbonaceous layers, which could serve as a thermally conductive glue to connect the filler network, further decreasing the interfacial thermal resistance and promoting phonon transport. Besides, the good heat dissipation performance of the EP/C/BN-CNF composites was directly confirmed by thermal infrared imaging, indicating a bright and broad application in the thermal management of modern electronics and energy fields. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Heterojunctions between carbon nanofiber (CNF) and Ag nanowire (Ag NW) have been successfully achieved by femtosecond laser irradiation. • Two types of nano-junction dependent on joint geometry are studied based on TEM observations and FDTD simulations. • The resistance of single CNF-Ag NW nano-junction is reduced by six orders of magnitude after femtosecond laser joining, from ∼1011 Ω to ∼105 Ω. • A strain sensor has been fabricated based on CNF-Ag NW heterojunctions with an enhanced sensitivity after femtosecond laser irradiation. We report the direct joining of carbon nanofibers (CNFs) to silver nanowire (Ag NWs) by controlled irradiation with femtosecond (fs) laser pulses. Two separate types of nano-junction dependent on joint geometry, laser fluence and irradiation time are identified in irradiated mixtures. In one type of junction, the tip of an Ag NW is melted and flows to form a bond with an adjacent CNF. The second type of junction occurs without significant heating of the Ag NW and involves the softening and flow of carbon in the CNF in response to the transfer of plasmonic energy from the Ag NW into the CNF. Bonding in a T-type joint configuration can be of either kind depending on the relative orientation of the incident optical field and the long axis of the Ag NW. FDTD simulations were used to explore this effect for different joint geometries and laser polarization. The electrical properties of a heterojunction involving a single Ag NW-CNF structure have been measured, and it is found that the junction resistance can be reduced by six orders of magnitude after laser joining. Finally, we have investigated the properties of a strain sensor based on an Ag NW-CNF hybrid nanowire network and find that this device can exhibit high sensitivity. This sensitivity occurs as nano-junctions induced by fs laser irradiation greatly reduces the initial resistance. This laser-based technique for direct nanojoining of CNF and Ag NWs may enable the design of robust nanowire structures for application in a variety of new devices. [ABSTRACT FROM AUTHOR]

Freestanding carbon nanofibers loaded with bimetallic hollow nanocage structures were synthesized. The nanocages inherited the rhombic dodecahedral morphology of the zeolitic imidazolate framework (ZIF) precursors, ZIF-8 and ZIF-67. As anode materials for lithium-ion batteries (LIBs), the bimetallic nanocage-loaded freestanding carbon nanofibers effectively buffered volume expansions and alleviated pulverization through their different reduction and oxidation potentials. The higher capacities of the composite anodes arose via the formation of the Li x Zn alloy and Li 2 O by Zn and Co ions, respectively, and the enhanced conductivity conferred by the carbon nanofibers. A synergistic effect of the composite components toward the strong electrochemical performance (688 mA h·g−1 at 1200 mA·g−1) of the bimetallic nanocage-loaded fibers was demonstrated through the superior long-term stability of the anode (1048 mA h·g−1 after 300 cycles at 100 mA·g−1), suggesting that the fabricated anode can be a promising material for use in portable LIBs. [ABSTRACT FROM AUTHOR]