Nitrogen-doped Porous Carbon Nanofibers Research Articles

Fabricating hierarchically porous and Fe3C-embeded nitrogen-rich carbon nanofibers as exceptional electocatalysts for oxygen reduction

Transition metal and heteroatom doping porous carbon exhibits a promising perspective as non-noble metal electrocatalyst. In this work, we develop a novel and scalable strategy to synthesize hierarchically porous nitrogen-doped carbon nanofibers embedded with abundant Fe3C nanoparticles from continuous electrospun of iron-based metal organic frameworks (MOFs) and polyacrylonitrile nanofibrous precursors. The as-prepared Fe3C/NCNFs (NCNFs for nitrogen-doped carbon nanofibers) exhibit high graphitization degree, high specific surface area, hierarchically meso-microporous structures and well-dispersion of carbon-shielded ultrafine Fe3C nanoparticles. The Fe3C/NCNFs exhibit superior electrocatalytic performance towards oxygen reduction reaction with an onset potential of 1.012 V and a half-wave potential of 0.873 V in alkaline media, exceeding the benchmark commercial Pt/C catalyst by ca. 13 and 46 mV, respectively. Moreover, the onset and half-wave potentials of Fe3C/NCNF are 0.832 and 0.664 V in acid media, respectively, which are also comparable to commercial Pt/C catalyst. The dramatically improved electrocatalytic performance is attributed to the continuous one-dimensional (1D) structure of Fe3C/NCNFs enhancing electro-conductivity compared with simple MOF-derived carbon. Our study demonstrates the Fe3C/NCNF nanofibers a promising candidate for efficient, robust electrocatalyst for economic platinum-free fuel cells.

TiO2 seeded on nitrogen-doped porous carbon nanofibers for superior electrochemical performance as freestanding anodes of lithium-ion batteries

Fibrous mats piled by nitrogen-doped porous carbon nanofibers with seeded TiO2 are fabricated and punched directly into circles as lithium-ion battery anodes. The seeding structure is composed of semi-wrapped TiO2 nanoparticles on carbon nanofibers (CNFs) coated with a thin layer of carbon. Synchronously, pores with various widths are formed on CNFs. As a freestanding anode, an initial discharge capacity of 615 mAh g−1 with a coulombic efficiency of 56% is reached, and 322 mAh g−1 is obtained after 100 cycles at a current density of 100 mA g−1. This is assigned to the increasing number of active sites for the lithium ion from pores with various widths and improved conductivity originating from nitrogen doping. Superior rate performance (179 mAh g−1 at the current density of 2000 mA g−1) under various current densities compared with that of other counterparts is attributed to the structural stability originating from the seeding structure with the help of the C–O–Ti bond. An additional 800 cycles are displayed at the current density of 2000 mA g−1, and superior stability is also exhibited.

Prussian blue analogues derived iron-cobalt alloy embedded in nitrogen-doped porous carbon nanofibers for efficient oxygen reduction reaction in both alkaline and acidic solutions

Exploring highly active, inexpensive and robust electrocatalysts for oxygen reduction reaction (ORR) is of great significance as a competitive alternative to noble metal-based catalysts in energy conversion and storage devices. In the present study, we design a novel ORR electrocatalyst of iron-cobalt (FeCo) alloy nanoparticles embedded on N-doped porous carbon nanofibers (FeCo@PCNF-T) by electrospinning of [Polyacrylonitrile (PAN)/Prussian blue analogues/CaCO3] and post-calcination treatment. The obtained catalysts with bimetallic active sites show unique three-dimensional (3D) hierarchical meso/macropores structures. FeCo alloy nanoparticles are encapsulated into graphitic carbon that can increase stability and provide additional catalytic active sites. Under the optimized condition, FeCo@PCNF-800 displays excellent ORR electrocatalytic activity in alkaline solutions, with a more positive half-wave potential (E1/2 of 0.854 V vs RHE) and larger limited-diffusion current density (j of 6.012 mA cm−2) than those of 20 wt% Pt/C (E1/2 of 0.849 V and j of 5.710 mA cm−2). In addition, FeCo@PCNF-800 also exhibits comparable ORR electrocatalytic activity in acidic solutions to those of 20 wt% Pt/C with onset potential and half-wave potential as more positive as 0.843 V vs RHE and 0.739 V vs RHE, respectively. Moreover, FeCo@PCNF-800 exhibits excellent tolerance towards methanol, stability and a four-electron pathway in both basic and acidic solutions. The excellent ORR electrocatalytic activity performance of FeCo@PCNF-800 is attributed to the synergistic effect of the FeCo alloy nanoparticles and N-doped porous carbon nanofibers. The synergistic effect can improve the mass and charge transport capability and increase active sites of FeCo-N-C. Furthermore, this work offers a new insight for the reasonable design and development of efficient non-noble metal electrocatalysts for challenging electrochemical energy-related technologies.

Enhanced capacitive deionization by nitrogen-doped porous carbon nanofiber aerogel derived from bacterial-cellulose

In this work, nitrogen-doped carbon nanofiber aerogels (N-CNFA) were successfully prepared by freeze-drying and thermal treatment of bacterial cellulose in NH3 atmosphere. Scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy were used to characterize their morphology and structure. Nitrogen adsorption-desorption isotherms show that nitrogen doping can improve the specific surface area of CNFA obviously. The electrochemical measurements show that N-CNFA possesses higher specific capacitance and lower charge transfer resistance than undoped CNFA. The electrosorption capacity of N-CNFA can reach up to 17.29 mg g−1 in 1000 mg L−1 NaCl solution, much higher than that of undoped CNFA (12.81 mg g−1). These results indicate that N-CNFA should be a promising candidate for CDI application.

M-N-Doped Carbon Nanofibers Modified Separators for Lithium-Sulfur Batteries

A novel lightweight, multi-functional layer comprised of 1D porous metal-embedded nitrogen-doped carbon nanofibers (M-N-C) and 2D graphene sheets is introduced to modify a commercial polyolefin separator for using in lithium-sulfur batteries. Benefiting from the high electrical conductivity and strong lithium polysulfides (LiPSs) chemical adsorption ability of M-N-C, the porous intercalation-structured modified layer exhibits excellent ability to suppress LiPSs shuttling while maintaining high lithium-ion transport, and the modified layer functions as a highly conductive upper current collector to reutilize active sulfur species. The cell assembled with the modified multifunctional separator shows a high rate capability and excellent cycling stability. These exciting results indicate that this multifunctional membrane could be a promising separator candidate for Li-S batteries.

Self-evaporating from inside to outside to construct cobalt oxide nanoparticles-embedded nitrogen-doped porous carbon nanofibers for high-performance lithium ion batteries

The nitrogen-doped porous carbon nanofibers decorated with CoxOy nanoparticles (NPCF) have been synthesized by a facile electrospun method followed by calcination at 950 °C in N2. It is interesting that the self-evaporation of zinc precursor from inside to outside can form the stable pore channels frame structure inside the carbon composites, which can be beneficial to the migration of the ion. Moreover, the pore channels density can be controlled by varying the amount of zinc nitrate. When the NPCF applied as anode materials, it exhibits a high reversible capacity of 983.5 mAh g−1 after 400 cycles at 1000 mA g−1. And it also deliveries an outstanding rate performance, which can be stabilized at ∼1488, ∼1172, ∼957.5, and ∼802.4 mAh g−1 when increasing the discharge/charge current density to 100, 300, 600, 1200 mA g−1, respectively.

Electrospun three dimensional Co/CoP@nitrogen-doped carbon nanofibers network for efficient hydrogen evolution

Designing the hydrogen evolution reaction (HER) electrocatalysts by tuning the micro/nano structure and optimizing composition to overcome the sluggish HER kinetics have fueled intensive research interests in recent years. Herein, the Co and CoP nanograins embedded in porous nitrogen-doped carbon nanofibers (Co/CoP@NC) are prepared by a controllable electrospinning method and subsequent thermal treatments as the wide-pH HER electrocatalysts. Owning to the prominent merits of strong synergistic relationships between Co and CoP nanoparticles, N-doped carbon configuration, and the interconnected three dimensional (3D) porous carbon network, the Co/CoP@NC nanofibers exhibit robust HER activity with affording an overpotential of 117mV in acidic and 180mV in alkaline media to deliver the current density of 10mAcm-2. As a practical application, when integrated the Co/CoP@NC/Ni foam cathode with the NiFe layered double hydroxides/Ni foam anode (NiFe-LDH/Ni foam), the electrolyzer can afford the cell voltage of 1.62V to deliver the current density of 10mA cm-2, as well as ultralong lifetime of 60h in alkaline medium, providing a viable alternative to the noble-metal electrocatalysts for water splitting.

Fe-N-doped carbon nanofiber and graphene modified separator for lithium-sulfur batteries

A novel lightweight, multi-functional layer comprised of 1D porous Fe-embedded nitrogen-doped carbon nanofibers (Fe-N-C) and 2D graphene sheets is introduced to modify a commercial polypropylene (PP) separator for use in lithium-sulfur batteries. Benefiting from the high electrical conductivity and strong lithium polysulfide (LiPS) chemical adsorption ability of Fe-N-C, the porous intercalation-structured modified layer exhibits excellent ability to suppress LiPS shuttling while maintaining high lithium-ion transport, and the modified layer functions as a highly conductive upper current collector to reutilize active sulfur species. The cell assembled with the modified multifunctional separator shows a high rate capability and excellent cycling stability, exhibiting a capacity of 847.9 mAh g−1 at 2 C and a low degradation rate of 0.053% per cycle over 500 cycles at 0.5 C.

Red phosphorus nanoparticles embedded in porous N-doped carbon nanofibers as high-performance anode for sodium-ion batteries

In this paper, red phosphorus nanoparticles (~ 97.7nm, 51wt% content) homogeneously embedded in porous nitrogen-doped carbon nanofibers (denoted as P@C) are prepared using a feasible electrospinning technique for the first time. Meanwhile, red P@C with the character of free-standing membrane is directly used as binder- and current collector-free anode for sodium-ion batteries, exhibiting a highly reversible three-electron transfer reaction (3Na+ + P + 3e- ↔ Na3P) with excellent rate capability (1308mAhg-1 at 200mAg-1 in comparison of 343mAhg-1 at 10,000mAg-1) and remarkable cyclic stability (~ 81% capacity retention after 1000 cycles). Furthermore, a soft package Na-ion full battery with red P@C anode and Na3V2(PO4)2F3/C cathode is assembled, displaying a high operation voltage of ~ 3.65V and an outstanding energy density of 161.8Whkg-1 for the whole battery. This is owing to the distinctive structure of very small amorphous phosphorus nanoparticles uniformly confined in porous N-doped carbon nanofibers, which can effectively facilitate the electronic/ionic transportation and retard the active materials pulverization/fracture caused by volume fluctuation upon prolonged cycling. The simple and scalable synthesis route as well as the promising electrochemical performance shed new insights into the quest for high energy and long life phosphorus-based Na-storage anode materials.

Nitrogen-Enriched Porous Carbon Nanofiber Mat as Efficient Flexible Electrode Material for Supercapacitors

Freestanding nitrogen-doped porous carbon nanofiber (NCNF) mats were prepared by electrospinning polyacrylonitrile/poly(m-aminophenol) (PAN/PmAP) precursor blends with different polymeric compositions followed by thermal stabilization and carbonization. The morphology, pore structure, and surface elemental compositions of as-prepared NCNFs were characterized by different techniques such as scanning electron microscopy, transmission electron microscopy, N2 adsorption, Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The charge-storage capability of the fabricated NCNFs was investigated in KOH electrolyte. The electrochemical performances of NCNFs were evaluated by varying the PmAP loading in the blend compositions. The highest specific capacitance of 347.5 F g–1 at 0.5 mA cm–2 together with a capacitance retention of 173.2 F g–1 at 20 mA cm–2 was achieved for the PAN:PmAP (85:15 w/w) NCNFs (NCNF85:15). The volumetric capacitance of 200.8 F cm–3 at 0.5 mA cm–2 was recorded for NC...

Sensitive and Selective Differential Pulse Voltammetry Detection of Cd(II) and Pb(II) Using Nitrogen-Doped Porous Carbon Nanofiber Film Electrode

Carbon matrix materials are regarded as one of the most important electrode materials for heavy metal detection. But even so, optimization procedures of carbon nanofibers (CNFs) for tracing Cd(II) and Pb(II) remains challenging. Here, zeolitic imidazolate framework (ZIF-8)/polyacrylonitrile (PAN)-derived nitrogen-doped porous carbon nanofibers (N-PCNFs) were investigated as a new electrode material for determining the concentration of Cd(II) and Pb(II). By optimizing electrochemical conditions such as deposition potential, deposition time, pH of buffer solution, and quantity of N-PCNFs loaded on a glassy carbon electrode (GCE), the linear response curves of Cd(II) and Pb(II) could be obtained. Due to the unique structural feature and N content, the N-PCNFs possess excellent detection limits of 0.8 μg L−1 for Cd(II) and 0.3 μg L−1 for Pb(II) (S/N = 3). To manifest the practical use of the sensor platform the concentration of Cd(II) and Pb(II) in normal tap and waste water were monitored. According to the ICP-MS results, the calculated recovery (97.0–107%) indicates that N-PCNFs have potential as a candidate material to monitor the concentration of Cd(II) and Pb(II) in practical samples.

Nitrogen-Doped Porous Carbon Nanofiber Supported Platinum as Promising Oxygen Reduction Reaction Electrocatalysts

Heteroatoms doped Carbon materials have been proved as promising catalyst support material for oxygen reduction reaction (ORR) in proton exchange membrane fuel cell (PEMFC). In this paper, nitrogen-doped porous nanofibers (N-PCNF) were fabricated via cost effective electrospinning technique by blending the PI and PAN as precursors, followed by heat treatment procedures. The N-PCNFs were used as support to prepare platinum (Pt) catalyst (Pt/N-PCNFs). SEM figure indicated that the porous structures not only existed on the surface but also in the cross session of the fibers. XPS and TEM displayed that with the help of heteroatoms nitrogen, the fiber had rougher surface and more defective structure, contributing to the dispersion of Pt nanoparticles. The catalytic performance for ORR was evaluated by cyclic voltammetry (CV) and liner sweep voltammetry (LSV) with a rotating disk electrode (RDE). According to the results, Pt/N-PCNF exhibited superior property (more positive onset potential and half-wave potential) than that of JM20. The excellent ORR activity of Pt/N-PCNF was attributed to the enriched nitrogen heteroatoms coordinated within the microstructure which increased the exposure of more active sites and dispersion of Pt nanoparticles.

Molybdenum carbide nanoparticles embedded in nitrogen-doped porous carbon nanofibers as a dual catalyst for hydrogen evolution and oxygen reduction reactions

An efficient dual catalyst of molybdenum carbide nanoparticles embedded nitrogen-doped porous carbon nanofibers (Mo2C/NPCNFs) has been developed for hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). The well-aligned and nanoporous identity of the desirable hybrid Mo2C/NPCNFs by an electrospun approach provides the good conductivity and rich active sites addressing excellent HER catalytic performance with an onset potential of −85 mV, a Tafel slope of 68 mV dec−1, and an exchange current density of 0.178 mA cm−2 in 0.5 M H2SO4. It is noting that the Mo2C/NPCNFs also shows remarkable ORR catalytic activity with an onset potential of ∼0.9 V, a half-potential of ∼0.77 V and a Tafel slope of 60.2 mV dec−1 at 1600 rpm in 0.1 M KOH. In addition, the experimental results demonstrate the core-shell 1D nanostructures boost the Mo2C/NPCNFs' stability of the durable catalytic activity over 10 h for both HER and ORR. This study designs a new structure for carbon-supported Mo2C composites, providing a distinctive course for the development of high-performance non-noble HER and ORR catalysts.

Electrospun N-doped porous carbon nanofiber webs as anodes for lithium-ion batteries

Nitrogen-doped porous carbon nanofiber webs (NPCNFs) were prepared from mixtures of polyacrylonitrile and melamine byelectrospinning, followed by oxidative stabilization, carbonization and steam activation. The NPCNFs are free-standing,exhibit an interconnected non-woven nanofibrous morphology and a well-developed microporous structure, and can be used directly as anodes for lithium ion batteries without adding binder or conductive filler. The NPCNF from the mixture with a melamine/polyacrylonitrile mass ratio of 1:3 has a high specific capacity of 856 mAh·g-1 and a satisfactory rate capability. These intriguing characteristics make the NPCNFs promising anode candidates for high-performance lithium ion batteries.

A Study on Long-Term Cycle Performance of Conventional Tin Anode for Sodium-Ion Batteries

Tin has been regarded as one of the most promising anode materials owing to its high theoretical specific capacity of 847 mAh g−1, based on the full sodiation of Na15Sn4. However, the pure tin anode has a severe problem of poor cycling properties, as it loses its initial capacity within the first 10 cycles. It is believed that the pulverization of tin induced a rapid degradation of capacity during cycling. The tin anode material expands to 520% of its original volume during sodiation and contracts to its original volume during desodiation. Several approaches have been investigated to overcome this problem. One approach involves stress release by utilizing a buffer layer, decreased tin size, or a thin film. Another approach involved the suppression of volume expansion by encapsulating tin nanoparticles into carbon and coating Al2O3 onto the tin nanoparticles. For example, ultra-small (8 nm) tin nanoparticles embedded in carbon showed 415 mAh g−1 of reversible capacity for 500 cycles, and tin nano-dots (1 ~ 2 nm) encapsulated in porous nitrogen-doped carbon nanofibers showed 483 mAh g−1 for 1300 cycles. Although these previous approaches succeed in improving cycle life, most preparation methods are too complex for commercialization as compared to that of the conventional electrode using tin nanopowder, a conducting additive, and a binder. However, a conventional electrode still showed poor cycling properties. Komaba et al. reported that a conventional electrode demonstrates capacity decay from 758 mAh g−1 to 21 mAh g−1 over the course of 10 cycles, even if using tin nanopowder (< 150 nm). The cycling properties of tin anode could be improved using a conductive binder or polyacrylate binder in short-term cycling of 20 cycles, but improved long-term cycle performance of a conventional electrode has not reported yet. Previous studies indicate that the long-term cycling of tin electrode with high capacity could be improved by the release or suppression of accumulated stress in a tin due to volume change. In order to release stress of conventional electrode, the tin electrode should be designed using suitable binder, conductive additive, and its optimized structure. Therefore, we study on the long-term cycling of conventional tin anode for sodium-ion batteries by the control these components.

Highly Porous Nitrogen-Doped Carbon Nanofibers as Efficient Metal-Free Catalysts toward the Electrocatalytic Oxygen Reduction Reaction

Highly Porous Nitrogen-Doped Carbon Nanofibers as Efficient Metal-Free Catalysts toward the Electrocatalytic Oxygen Reduction Reaction

Nitrogen-doped porous carbon nanofiber based oxygen reduction reaction electrocatalysts with high activity and durability

Sluggish oxygen reduction reaction (ORR) is one of the critical challenges in polymer electrolyte membrane fuel cell (PEMFC) technologies. Carbon materials doped with various heteroatoms have been exactly proved as promising alternative catalysts and even the catalyst supports for the ORR in fuel cells. In this work, we have developed nitrogen-doped porous carbon nanofibers (N-PCNF) as novel ORR catalysts. The obtained N-PCNF shows excellent electrocatalytic performance and durability for ORR both in basic and acid solutions. Furthermore, the N-PCNF acted as support to deposited platinum (Pt) nanoparticles, the Pt nanoparticles with uniform size were well dispersed not only on the surface but also the cross-section of N-PCNF. The electrocatalytic activity and stability of the resultant Pt/N-PCNF along with the commercial one (JM20) were investigated. As a result, the Pt/N-PCNF exhibited enhanced ORR activity when compared with Pt supported on PCNF (Pt/PCNF) as well as the state-of-the-art JM20. In addition, enhanced stability of Pt/N-PCNF, coupled with ORR activity and electrochemical surface area (ECSA) retention after accelerated durability test (ADT) in acid media was observed. These results indicated that the N-PCNF can not only work as the non-precious electrocatalysts toward ORR, but also a promising candidate as catalyst supports.

MnFe2O4@C Nanofibers as High-Performance Anode for Sodium-Ion Batteries.

MnFe2O4 nanodots (∼3.3 nm) homogeneously dispersed in porous nitrogen-doped carbon nanofibers (denoted as MFO@C) were prepared by a feasible electrospinning technique. Meanwhile, MFO@C with the character of flexible free-standing membrane was directly used as binder- and current collector-free anode for sodium-ion batteries, exhibiting high electrochemical performance with high-rate capability (305 mA h g(-1) at 10000 mA g(-1) in comparison of 504 mA h g(-1) at 100 mA g(-1)) and ultralong cycling life (ca. 90% capacity retention after 4200 cycles). The Na-storage mechanism was systematically studied, revealing that MnFe2O4 is converted into metallic Mn and Fe after the first discharge (MnFe2O4 + 8Na(+) + 8e(-) → Mn + 2Fe + 4Na2O) and then to MnO and Fe2O3 during the following charge (Mn + 2Fe + 4Na2O → MnO + Fe2O3 + 8Na(+) + 8e(-)). The subsequent cycles occur through reversible redox reactions of MnO + Fe2O3 + 8Na(+) + 8e(-) ↔ Mn + 2Fe + 4Na2O, of which the reduction/oxidation of MnO/Mn takes place at a lower potential than that of Fe2O3/Fe. Furthermore, a soft package sodium-ion full battery with MFO@C anode and Na3V2(PO4)2F3/C cathode was assembled, delivering a stable capacity of ∼400 mA h g(-1) for MFO@C (with 100 cycles at 500 mA g(-1)) and a promising energy density of 77.8 Wh kg(-1) for the whole battery. This is owing to the distinctive structure of very-fine MnFe2O4 nanodots embedded in porous N-doped carbon nanofibers, which effectively improves the utilization rate of active materials, facilitates the transportation of electrons and Na(+) ions, and prevents the particle pulverization/agglomeration upon prolonged cycling.

Electrospun cobalt embedded porous nitrogen doped carbon nanofibers as an efficient catalyst for water splitting

The major challenge in water splitting is to develop low cost electrocatalysts as alternatives for simultaneously generating oxygen and hydrogen.

Flexible solid-state supercapacitors based on freestanding nitrogen-doped porous carbon nanofibers derived from electrospun polyacrylonitrile@polyaniline nanofibers

Freestanding nitrogen-doped porous carbon nanofibers were successfully fabricated and assembled in symmetric flexible solid-state supercapacitors with outstanding electrochemical performance.