Freestanding nitrogen-doped porous carbon nanofibers (NPCNFs) are prepared by carbonizing the nitrogen-enriched porous binary polymer precursors of electrospun polyacrylonitrile/polyaniline core–shell composite nanofibers at an appropriate temperature. The obtained freestanding NPCNFs with the advantages of a suitable nitrogen content, hierarchical porosity, large specific surface areas, and good conductivity are very promising to achieve desirable electrochemical performance. As expected, the NPCNFs as electrode materials demonstrate a high specific capacitance of 335 F g−1 at a current density of 0.5 A g−1 and high rate capability with a capacitance retention of 175 F g−1 at 32 A g−1 in a three-electrode configuration test. Particularly, the as-fabricated flexible solid-state supercapacitor based on the freestanding NPCNFs delivers a maximum energy density of 9.2 W h kg−1 at 0.25 kW kg−1 and also presents good cycling stability with 86% capacitance retention after 10000 cycles at a current density of 5 A g−1. Therefore, the freestanding NPCNFs as electrode materials for flexible solid-state supercapacitors might have potential applications in portable and flexible electronics.

Recently, hierarchically porous carbon materials with advantages of hierarchical porosity and large specific surface areas exhibiting desirable capacitive performance have been widely investigated. Herein, a facile and template-free phase separation methodology has been presented to prepare three-dimensional freestanding hierarchically porous carbon (HPC) materials. Importantly, the as-fabricated HPC with highly uniform and well-interconnected pores can afford plentiful transport channels for rapid diffusion of more ions, and the highly conductive cross-linked backbones ensure fast electron transfer, both of which can greatly reduce the internal resistance and improve the electrochemical properties. As expected, the as-fabricated HPC-based supercapacitor has achieved outstanding electrochemical performance with a high cell capacitance of 51 F g−1 at a current density of 0.5 A g−1, good rate capability with 75% capacitance retention of initial capacitance at 32 A g−1 as well as a maximum energy density of 4.5 W h kg−1 at 200 W kg−1 and a maximum power density of 15100 W kg−1 at 3.4 W h kg−1. More significantly, a remarkable cycling stability almost without capacitance loss after the 50000 charge/discharge test at 5 A g−1 has been achieved for the HPC-based supercapacitors. All these results suggest that the as-synthesized HPC has great potential for application not only as a supercapacitor electrode but also as a substrate for supporting capacitive materials.

•Hierarchically porous carbon can be facilely prepared by a template-free method.•The HPC/PANI composites present high capacitance and rate capability.•The as-assembled HPC/PANI-based device also exhibits good capacitive performance.Freestanding hierarchically porous carbon electrode materials with favorable features of large surface areas, hierarchical porosity and continuous conducting pathways are very attractive for practical applications in electrochemical devices. Herein, three-dimensional freestanding hierarchically porous carbon (HPC) materials have been fabricated successfully mainly by the facile phase separation method. In order to further improve the energy storage ability, polyaniline (PANI) with high pseudocapacitance has been decorated on HPC through in situ chemical polymerization of aniline monomers. Benefiting from the synergistic effects between HPC and PANI, the resulting HPC/PANI composites as electrode materials present dramatic electrochemical performance with high specific capacitance up to 290 F g−1 at 0.5 A g−1 and good rate capability with ∼86% (248 F g−1) capacitance retention at 64 A g−1 of initial capacitance in three-electrode configuration. Moreover, the as-assembled symmetric supercapacitor based on HPC/PANI composites also demonstrates good capacitive properties with high energy density of 9.6 Wh kg−1 at 223 W kg−1 and long-term cycling stability with 78% capacitance retention after 10 000 cycles. Therefore, this work provides a new approach for designing high-performance electrodes with exceptional electrochemical performance, which are very promising for practical application in the energy storage field.

Design and synthesis of hierarchical carbon hybrid based pseudocapacitive electrodes is the next step forward for achieving high-performance supercapacitors. Here, the freestanding electrospun carbon nanofibers/carbon nanotubes/polyaniline (CNFs/CNTs/PANI) ternary composites have been fabricated successfully. Importantly, the hierarchical carbon hybrids by dense CNT forests decorated CNFs serving as supports are crucial for the ternary composites to achieve high electrochemical properties. The hierarchical CNFs/CNTs hybrids serving as inner current collectors can afford plentiful transport channels for more rapidly transporting and collecting electrons, greatly reduce the ion diffusion length, and increase the utilization of pseudocapacitive materials. As expected, the ternary composites as electrodes present high specific capacitance (i.e., 315 F/g at 1 A/g) and dramatic rate capability (i.e., 235 F/g at 32 A/g) in three-electrode configuration. Moreover, the as-fabricated flexible solid-state supercapacitor based on the ternary composites also achieves desired electrochemical properties with high capacitance, high-rate capability, high energy/power density (i.e., 5.1 Wh/kg at 10.1 kW/kg), and remarkable cycling stability (i.e., 92% capacitance retention after 10 000 cycles at 2 A/g). These extraordinary electrochemical properties can be attributed to the well-designed structural advantages and synergistic effects.Keywords: Carbon nanofibers; Carbon nanotubes; Flexibility; Polyaniline; Solid-state supercapacitors;

•3D MoS2 nanosheet/TiO2 nanofiber heterostructures were successfully prepared.•The 3D heterostructures show enhanced photocatalytic performance.•A possible photocatalytic mechanism under UV light irradiation was proposed.•The 3D heterostructures could be reclaimed easily.We employed electrospun TiO2 nanofibers (NFs) as a synthetic template to develop three-dimensional (3D) MoS2 nanosheet/TiO2 nanofiber (MoS2/TiO2) heterostructures using a simple hydrothermal method. The prepared 3D MoS2/TiO2 heterostructures exhibited a higher performance in photocatalytic degradation of the dye molecules (rhodamine B and methyl orange) than pure TiO2 NFs under UV light irradiation. The enhanced photocatalytic activity might be attributed to the formation of heterostructures between TiO2 and MoS2, in which MoS2 not only served as electron trapper to improve the separation of photogenerated electron-hole pairs, but also provided a greater number of active adsorption sites for the photodegradation of pollutants. The 3D heterostructure photocatalysts could be easily recycled by sedimentation due to their nanofibrous network structure. The photocatalytic mechanism of 3D MoS2/TiO2 heterostructures was also proposed.

In this work, p-MoO3 nanostructures/n-TiO2 nanofiber heterojunctions (p-MoO3/n-TiO2–NF-HJs) were obtained by a two-step fabrication route. First, MoO2 nanostructures were hydrothermally grown on electrospun TiO2 nanofibers. Second, by thermal treatment of the obtained MoO2 nanostructures/TiO2 nanofibers, p-MoO3/n-TiO2–NF-HJs were obtained due to the phase transition of MoO2 to MoO3. With increasing the concentration of molybdenum precursor in hydrothermal process, the morphologies of MoO2 changed from nanoparticles to nanosheets, and then fully covered shells with an increased loading on TiO2 nanofibers. After calcination, the obtained p-MoO3/n-TiO2–NF-HJs possessed similar morphology to that without thermal treatment. X-ray photoelectron spectra showed that both Ti 2p and OTi–O 1s peaks of p-MoO3/n-TiO2–NF-HJs shifted to higher binding energies than that of TiO2 nanofibers, suggesting electron transfer from TiO2 to MoO3 in the formation of p–n nanoheterojunctions. The p–n nanoheterojunctions decreased photoluminescence intensity, suppressed photogenerated electrons and holes recombinations, and enhanced charge separation and photocatalytic efficiencies. The apparent first-order rate constant for the degradation of RB by p-MoO3/n-TiO2–NF-HJs with nanosheets surface morphology was two times that of TiO2 nanofibers. For the core/shell structure of p-MoO3/n-TiO2–NF-HJs, the internal electric field of p–n junction forced the photogenerated electrons transferring to TiO2 cores, then decreased the surface photocatalytic reactions and led to the lowest photocatalytic activity among the p-MoO3/n-TiO2–NF-HJs.Keywords: electrospinning; heterojunction; MoO3; nanofibers; photocatalysis; TiO2;

CuO nanofibers (NFs) were fabricated via the traditional electrospinning technique and subsequent thermal treatment processes. Using CuO NFs as precursors and glucose as a reducing agent, CuO/Cu2O NFs, with high surface areas and ultralong one dimensional (1D) nanostructures, were obtained by a partial reduction of CuO NFs. Comparing with pure CuO NFs, CuO/Cu2O NFs, as non-enzymatic electrode materials, showed a much higher sensitivity of 830 μA mM−1 cm−2 and a much wider detection range from 0.5 mM to 10 mM for the amperometric detection of glucose. The excellent electrocatalytic performances could be ascribed to the following advantages: (1) the CuO/Cu2O NFs with Cu(II)/Cu(I) multiple oxidation states system could promote the redox reactions between electrode materials and glucose, and the reactive sites became more active due to the synergic effect; (2) the surface of CuO/Cu2O NFs became smoother after partial reduction, resulting in less adsorption of the intermediates during the oxidation of glucose, generating the enlarged detection range. Therefore, the CuO/Cu2O composite NFs electrode materials, with a multiple oxidation states system, would be promising candidates for the development of non-enzymatic glucose sensors.

Bi2WO6–carbon nanofibers (Bi2WO6–CNFs) heteroarchitectures were fabricated by two steps consisting of the preparation of CNFs by electrospinning and growth of Bi2WO6 on the CNFs through ethylene glycol solvothermal processing. The results showed that the loading amounts of Bi2WO6 on the surface of CNFs could be controlled by adjusting the precursor concentration for the fabrication of Bi2WO6–CNFs heteroarchitectures during the solvothermal process. The photocatalytic tests revealed that the obtained Bi2WO6–CNFs heteroarchitectures showed higher photocatalytic property under visible light to degrade Rhodamine B than pure Bi2WO6 synthesized by solvothermal process in the absence of CNFs owing to improved separation efficiency of photogenerated electrons and holes. Moreover, the Bi2WO6–CNFs heteroarchitectures could be separated easily by sedimentation due to their one-dimensional nanostructural property. Meanwhile, the photocatalytic activity of Bi2WO6–CNFs heteroarchitectures was stable during the recycling due to the strong interactions between Bi2WO6 nanosheets and CNFs. Trapping experiment suggested that \({\text{O}}_{ 2}^{ \cdot - }\), instead of OH·, was the main active species during the photocatalytic process of the Bi2WO–CNFs heteroarchitectures.

A three-dimensional (3D) free-standing network composed of cross-linked carbon@Au core–shell nanofibers was fabricated by combining the electrospinning technique and an in situ reduction approach. The results showed that a uniform Au layer of approximately 5 nm thickness was formed around the electrospun carbon nanofiber. What's more, it's interesting to note that the Au layer was composed of small Au nanoparticles. And, the as-prepared CNFs@Au network exhibited excellent catalytic activity for the reduction of 4-nitrophenol (4-NP) based on the electron-rich catalytic platform arising from the synergistic effect between carbon and Au. Notably, the free-standing 3D nanofibrous cross-linked network structure could improve the catalyst's performance in separation and reuse.

Carbon-modified BiVO4 microtubes embedded with Ag nanoparticles (BVO@C/Ag MTs) were obtained by a two-step fabrication route. First, the BiVO4@carbon core–shell microtubes (BVO@C MTs) were fabricated by using BiVO4 microtubes (BiVO4 MTs) as a hard-template through a hydrothermal approach. Next, small Ag nanoparticles (Ag NPs) with well-dispersed distribution were assembled inside the carbon layer of the BVO@C MTs via an in situ reduction method. The results showed that small Ag NPs were well dispersed inside the carbon layer of approximately 8 nm in thickness around the BiVO4 microtubes. The photocatalytic studies revealed that the BVO@C/Ag MTs exhibited the highest photocatalytic activity for photodegradation of rhodamine B (RB) compared to the pure BVO-MTs, BVO@C MTs under visible light irradiation. The high separation efficiency of photogenerated electron–hole pairs based on the photosynergistic effect among the three components of BiVO4, carbon, and Ag and the improved visible light utilization from the sensitizing effects of carbon layers both contribute to the enhanced photocatalytic activity. The BVO@C/Ag MTs did not exhibit any significant loss of activity after three cycles of RB photodegradation, which results from the fact that the presence of the carbon layer could inhibit loss and oxidation of Ag NPs during repeated applications. The BVO@C/Ag MTs could be easily recovered by sedimentation due to their one-dimensional nanostructural property.

•BiOCl nanosheets exposing {001} facets were uniformly grown on TiO2 nanofibers.•The p–n heterostructures exhibited enhanced UV-light photocatalytic activity.•The composites could be recycled easily due to nonwoven nanofibrous structures.Hierarchical heterostructures of p-type BiOCl nanosheets/n-type TiO2 nanofibers (p-BiOCl/n-TiO2 HHs) were prepared by combining the electrospinning technique and solvothermal method. BiOCl nanosheets with exposed {001} facets were densely and uniformly grown on the electrospun TiO2 nanofibers. The obtained p-BiOCl/n-TiO2 HHs exhibited enhanced UV-light photocatalytic activity due to the effects of p-n heterojunctions and high surface areas. Experiments proved that the generation rate of hydroxyl radicals for p-BiOCl/n-TiO2 HHs was much larger than that of TiO2 nanofibers. Moreover, the p-BiOCl/n-TiO2 HHs could be recycled easily by sedimentation because of their nanofibrous nonwoven web structure.p-BiOCl/n-TiO2 HHs exhibit enhanced photocatalytic activity due to the p-n heterojunction effects, large surface areas, and more active surface reaction sites.Download full-size image

•Synthesis of In2S3/CNFs/Au ternary synergetic system.•Enhanced visible-light photocatalytic activity.•Easy photocatalyst separation and reuse.In this paper, carbon nanofibers (CNFs) were successfully synthesized by electrospinning technique. Next, Au nanoparticles (NPs) were assembled on the electrospun CNFs through in situ reduction method. By using the obtained Au NPs modified CNFs (CNFs/Au) as hard template, the In2S3/CNFs/Au composites were synthesized through hydrothermal technique. The results showed that the super long one-dimensional (1D) CNFs (about 306 nm in average diameter) were well connected to form a nanofibrous network; and, the Au NPs with 18 nm in average diameter and In2S3 nanosheets with 5–10 nm in thickness were uniformly grown onto the surface of CNFs. Photocatalytic studies revealed that the In2S3/CNFs/Au composites exhibited highest visible-light photocatalytic activities for the degradation of Rhodamine B (RB) compared with pure In2S3 and In2S3/CNFs. The enhanced photocatalytic activity might arise from the high separation efficiency of photogenerated electron–hole pairs based on the positive synergetic effect between In2S3, CNFs and Au components in this ternary photocatalytic system. Meanwhile, the In2S3/CNFs/Au composites with hierarchical structure possess a strong adsorption ability towards organic dyes, which also contributed to the enhancement of photocatalytic activity. Moreover, the In2S3/CNFs/Au composites could be recycled easily by sedimentation due to their nanofibrous network structure.We describe a route to synthesize In2S3/CNFs/Au ternary synergetic system with high efficiency visible-light photocatalytic activity.Download full-size image

Freestanding nitrogen-doped porous carbon nanofibers (NPCNFs) are prepared by carbonizing the nitrogen-enriched porous binary polymer precursors of electrospun polyacrylonitrile/polyaniline core–shell composite nanofibers at an appropriate temperature. The obtained freestanding NPCNFs with the advantages of a suitable nitrogen content, hierarchical porosity, large specific surface areas, and good conductivity are very promising to achieve desirable electrochemical performance. As expected, the NPCNFs as electrode materials demonstrate a high specific capacitance of 335 F g−1 at a current density of 0.5 A g−1 and high rate capability with a capacitance retention of 175 F g−1 at 32 A g−1 in a three-electrode configuration test. Particularly, the as-fabricated flexible solid-state supercapacitor based on the freestanding NPCNFs delivers a maximum energy density of 9.2 W h kg−1 at 0.25 kW kg−1 and also presents good cycling stability with 86% capacitance retention after 10000 cycles at a current density of 5 A g−1. Therefore, the freestanding NPCNFs as electrode materials for flexible solid-state supercapacitors might have potential applications in portable and flexible electronics.

Recently, hierarchically porous carbon materials with advantages of hierarchical porosity and large specific surface areas exhibiting desirable capacitive performance have been widely investigated. Herein, a facile and template-free phase separation methodology has been presented to prepare three-dimensional freestanding hierarchically porous carbon (HPC) materials. Importantly, the as-fabricated HPC with highly uniform and well-interconnected pores can afford plentiful transport channels for rapid diffusion of more ions, and the highly conductive cross-linked backbones ensure fast electron transfer, both of which can greatly reduce the internal resistance and improve the electrochemical properties. As expected, the as-fabricated HPC-based supercapacitor has achieved outstanding electrochemical performance with a high cell capacitance of 51 F g−1 at a current density of 0.5 A g−1, good rate capability with 75% capacitance retention of initial capacitance at 32 A g−1 as well as a maximum energy density of 4.5 W h kg−1 at 200 W kg−1 and a maximum power density of 15100 W kg−1 at 3.4 W h kg−1. More significantly, a remarkable cycling stability almost without capacitance loss after the 50000 charge/discharge test at 5 A g−1 has been achieved for the HPC-based supercapacitors. All these results suggest that the as-synthesized HPC has great potential for application not only as a supercapacitor electrode but also as a substrate for supporting capacitive materials.

A three-dimensional (3D) free-standing network composed of cross-linked carbon@Au core–shell nanofibers was fabricated by combining the electrospinning technique and an in situ reduction approach. The results showed that a uniform Au layer of approximately 5 nm thickness was formed around the electrospun carbon nanofiber. What's more, it's interesting to note that the Au layer was composed of small Au nanoparticles. And, the as-prepared CNFs@Au network exhibited excellent catalytic activity for the reduction of 4-nitrophenol (4-NP) based on the electron-rich catalytic platform arising from the synergistic effect between carbon and Au. Notably, the free-standing 3D nanofibrous cross-linked network structure could improve the catalyst's performance in separation and reuse.