Microporous Carbon Nanofibers Research Articles

Synergistic effect of pore generation and nitrogen doping on the enhanced CO2 capture and selectivity of carbon nanofibers

The porosity and heteroatom doping of carbon materials are crucial for their adsorption capacity and selectivity toward CO2. Herein, nitrogen-doped microporous carbon nanofibers (CNFs) were prepared by carbonizing electrospun polyacrylonitrile (PAN) nanofibers, using nitrogen-rich polyvinylpyrrolidone (PVP) as porogen and nitrogen source simultaneously. The synergistic effect of pore generation and nitrogen doping improved the porosity and preserved a substantial nitrogen content in the CNFs. Compared to the nitrogen-free polyethylene glycol (PEG) porogen, the incorporation of PVP can facilitate nitrogen doping during the carbonization process. With an increasing amount of PVP addition, the specific surface area of the CNFs significantly expanded to 410 m2/g, maintaining a high nitrogen content of 10.32 wt%. The porosity and nitrogen functionalities (Pyridinic N and pyrrolic N) collaborated synergistically in determining CO2 adsorption capacity, with elevated nitrogen content resulted in improved selectivity. The CNFs exhibited remarkable IAST CO2/N2 (10:90) selectivity of 38 and cycling stability, demonstrating their potential for long-term practical applications. This work provides unique inspiration for the design of porous nanofibers with exceptional CO2 adsorption capacity and selectivity.

Incorporating Gadolinium Oxide (Gd2O3) as a Rare Earth Metal Oxide in Carbon Nanofiber Skeleton for Supercapacitor Application

AbstractIn this study, we synthesized gadolinium oxide nanoparticles (Gd2O3 NPs) incorporated heteroatom‐doped microporous carbon nanofibers (CNF) to serve as electrode materials for enhancing supercapacitive energy storage. Our primary focus is on elucidating the impact of these hybrid electrode materials on key supercapacitor performance properties such as specific capacitance, specific energy, and specific power. To comprehensively assess the structural and chemical attributes of Gd2O3 NPs‐incorporated heteroatom‐doped microporous CNFs (CNF/Gd2O3) we employed an array of advanced characterization techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy (RAMAN), X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS). Our research has yielded impressive results, demonstrating a significant increase in supercapacitive performance. Specifically, the CNF/Gd2O3‐1 symmetric supercapacitor cell (SSC) has demonstrated a good specific capacitance of 162.3 F/g and a high specific energy of 8.12 Wh/kg at a specific power of 300 W/kg. These findings could be a new pathway to prepare composite electrodes for use in energy storage applications and promote further development for other rare‐earth nanostructures.

Electrospun polyacrylonitrile fibers incorporated with microporous carbon for improved airborne PM2.5 filtration

Particulate matter 2.5 (PM2.5) pollutant particles have been identified as significant participants in air pollution, thus, special attention is paid to air filtration as a method of their efficient removal. A novel and simple method of producing nanofiber-based filters for efficient PM2.5 capture with multiple active components are proposed. Electrospun polyacrylonitrile (PAN) polymer was used both as a base filter material and as a precursor for producing microporous carbon nanofibers (MCNFs), which incorporated into the nanofibrous structure of the filter media. The fabricated PAN/MCNFs filters could reach removal efficiency of PM2.5 pollutant particles of up to 99% for with polluted air airflow velocity of 500 ml min−1, showing greater pollutant particle binding affinity with incorporated MCNFs. Experiments also show enhanced mechanical and thermal properties of studied air filters, with the addition of MCNFs – more than 4% and 6% increase in storage modulus and cyclization temperature in comparison to the base PAN filter, respectively. While using a facemask with inserted PAN/MCNFs filter, a reduced temperature variation in the facial region of the user was recorded – several degrees less when compared to a commonly used 3 M Aura 9320+ mask. This opens a possibility of their application in both industrial air filtering and as filters in facemask production.

Flexible and freestanding manganese/iron oxide carbon nanofibers for supercapacitor electrodes

In this study, freestanding carbon nanofibers embedded with bimetallic manganese-iron oxide are fabricated for flexible supercapacitor applications via electrospinning. A polyacrylonitrile solution is used as the carbon source, and poly(methyl methacrylate) functions as a sacrificial template to produce microporous carbon nanofibers. The concentrations of manganese acetate and iron acetylacetonate are varied to determine the fabrication conditions for maximal electrochemical performance. The optimized supercapacitor cell exhibits a capacitance of 467 F g−1 at a current density of 1 A g−1 and a capacitance retention of 94% at the end of N = 10,000 cycles. The higher mechanical durability of the electrode is confirmed by the absence of electrochemical deterioration at the end of performing 500 bending cycles. Overall, the sample comprising carbon nanofibers, in which the optimal amount of manganese-iron oxide is embedded, has the required pseudocapacitive characteristics and is an interesting choice for high-energy-storage supercapacitor electrodes.

Rational design of meso-/micro-pores for enhancing ion transportation in highly-porous carbon nanofibers used as electrode for supercapacitors

Carbon nanofiber has been one of the promising electrode materials for supercapacitors. It is desirable but still challenging to optimize meso-/micro-pore ratio and configuration while achieving a high specific surface area in carbon nanofibers. Here, we present the design and preparation of carbon nanofiber mats with both high specific surface area and rational meso-/micropore configuration by electrospinning tetraethyl orthosilicate (TEOS)/phenolic resin (PR)/polyvinylpyrrolidone (PVP)/F127 blend solution, followed by carbothermal reduction, removal of carbon and chlorination. Silicon carbide nanofibers constructed by regulatable secondary nanostructure were achieved by adjusting TEOS content in the spinning solution, derived from which microporous carbon nanofibers with considerable mesopores (60–70% in mesoporosity), diverse secondary nanostructure (24–44 nm), and high specific surface area (1765–1890 m2 g−1) were prepared. The formation mechanism of the diverse secondary nanostructure in carbon nanofiber was proposed. The carbide-derived carbon nanofibers showed an excellent specific capacitance (316 F g−1 at 0.1 A g−1) and high-rate capability (186 F g−1 at 100 A g−1) due to the enhanced ion transportation, which was achieved by shortening micropore channels and offering convenient mesoporous channel towards microporous domains.

ZnO-assisted synthesis of lignin-based ultra-fine microporous carbon nanofibers for supercapacitors

Reducing the material size could be an effective approach to enhance the electrochemical performance of porous carbons for supercapacitors. In this work, ultra-fine porous carbon nanofibers are prepared by electrospinning using lignin/ polyvinylpyrrolidone as carbon precursor and zinc nitrate hexahydrate (ZNH) as an additive, followed by pre-oxidation, carbonization, and pickling processes. Assisted by the ZnO template, the pyrolytic product of ZNH, abundant micropores are yielded, leading to the formation of microporous carbon nanofibers with specific surface area (SSA) up to 1363 m2 g−1. The average diameter of the lignin-based ultra-fine porous carbon nanofibers (LUPCFs) is effectively controlled from 209 to 83 nm through adjusting the ZNH content. With good flexibility and self-standing nature, the LUPCFs could be directly cut into electrodes for use in supercapacitors. High accessible surface, enriched surface N/O groups, and reduced fiber diameters endow the LUPCFs-based electrodes with an excellent specific capacitance of 289 F g−1. The reduction of fiber diameters remarkably improves the rate performance of the LUPCFs and leads to a low relaxation time constant of 0.37 s. The high specific capacitance of 162 F g−1 is maintained when the current density is increased from 0.1 to 20 A g−1. Besides, the fabricated LUPCFs show exceptional cycling stability in symmetrical supercapacitors, manifesting a promising application prospect in the next generation of supercapacitors.

The Effect of the Stabilization and Carbonization Temperatures on the Properties of Microporous Carbon Nanofiber Cathodes for Fuel Cells on Polybenzimidazole Membrane

Materials based on pyrolyzed electrospun nanofiber polyacrylonitrile were studied by the method of standard contact porosimetry. An influence of oxidation and pyrolysis temperatures on specific surface area. It was shown that an increase of oxidation temperature from 300 to 350°C and of pyrolysis temperature from 900 to 1000°C leads to a decrease of pore specific surface area and to a decrease of a part of micropore specific surface area. Platinated samples showed sufficient values of electrochemically active platinum surface area (12‒35 m2 g $$_{{{\text{Pt}}}}^{{ - 1}}$$ ) and were tested as cathodes for high temperature polymer electrolyte membrane fuel cell. An increase in power density was found when a part of electrode micropore specific surface area was decreasing.

Targeted Synthesis of Polymer and Microporous Carbon Nanofibers via Temperature‐Dependent and Molecularly‐Triggered Interfacial Assembly

AbstractMicroporous carbon nanofibers (CNFs) derived from polymer nanofibers (PNFs), featured with short radial diffusion length of ions, have been proposed as ideal electrode materials for energy storage devices. However, lacking precise control of selective formation of fibrous micelle templates, the targeted synthesis of microporous CNFs is still a challenge. To address this issue, PNFs are first fabricated by using triblock copolymer F127 as the structure directing agent via the temperature‐dependent and molecularly‐triggered interfacial assembly process. Two crucial factors are figured that determine the fibrous morphology of the assembled polymer. At suitable temperatures, F127 starts to form fibrous micelles, and molecular trigger hexamethylenetetramine generates formaldehyde and ammonia in situ. Then, phenolic polymer assemble around the fibrous micelles, following with the formation of PNFs. This feasible synthesis method can grow PNFs and precisely control the PNFs' diameters ranging from 30 to 80 nm. Microporous CNFs with high specific surface area of 1175 m2 g−1, and an average diameter of 40 nm can be prepared through carbonization of PNFs and an activation step. Taking such microporous CNFs as electrode materials for a supercapacitor, they exhibit an excellent specific capacitance 295 F g−1 at a high current density 50 A g−1.

Electrospun Nb2O5 nanorods/microporous multichannel carbon nanofiber film anode for Na+ ion capacitors with good performance

For the disadvantages of both the slow reaction kinetics and the poor conductivity for Nb2O5 electrode materials as sodium-ion capacitors (SICs), Nb2O5 NRs/NMMCNF film electrode with good flexibility and high electrochemical property has been fabricated by electrospinning PAN/PMMA/H2Nb2O6·H2O homogeneous viscous suspension and followed by an annealing treatment, in which the precursor H2Nb2O6·H2O nanorods are obtained by grinding H2Nb2O6·H2O nanowires, and Nb2O5 nanorods are uniformly embedded in nitrogen doped microporous multichannel carbon nanofiber. Benefiting from the multichannel network structure, Nb2O5 NRs/NMMCNF film electrode delivers the fast kinetics of Na+-storage and the superior Na-ion storage performance, it delivers outstanding rate capability (101 mAh g−1 at 4 A g−1) and ultralong lifespan (91% capacity retention after 10,000 cycles at 2 A g−1). A Nb2O5 NRs/NMMCNF//AC SIC based on the Nb2O5 NRs@NMMCNF fiber film anode and the AC cathode is assembled. The energy density of the as-assembled device is as high as 91 Wh kg−1 and its maximum power density is 7499 W kg−1. This work offers a new structure design strategy toward intercalation-type metal oxide electrodes for application in SICs.

Sulfur doping induced anionic oxidation of niobium-pentoxide-based anode for ultralong-life and high energy-density Na-ion capacitors

Sodium-ion supercapacitors (SICs) have attracted increasing scientific attention for mid-to-large-scale energy storage applications due to their high energy and power densities. Herein, an ultra-flexible and free-standing hybrid anode material consisting of sulfur-doped Nb2O5 quantum dots (~3 nm) uniformly embedded within nitrogen and sulfur co-doped microporous carbon nanofiber (S–Nb2O5@NS-PCNF) is successfully fabricated by electrospinning followed by a sulfidation treatment. The designed 3D microporous network not only offers a continuous conducting framework for electron-transport, but also provides more accessible channels for rapid Na-ions migration. Furthermore, the S-doping induced anionic oxidation of Nb2O5 (O2-2−→O−) and S-doping in microporous carbon nanofibers result in the formation of numerous oxygen vacancies and defects for enhanced electrical conductivity and surface pseudocapacitance. In particular, the oxygen vacancies induced by the S-doping on Nb2O5 have been firstly demonstrated. This S–Nb2O5@NS-PCNF film electrode exhibits superior rate capability (124 mAh g−1 at 4 A g−1) and ultralong cycling life (173 mAh g−1 after 10000 cycles at 2 A g−1). The SIC full-cell comprising a S–Nb2O5@NS-PCNF anode and an activated carbon cathode delivers a maximum energy density of 112 Wh kg−1 at 80 W kg−1 and a ultralong-term cycling stability. This strategy provides a promising application for highly efficient energy storage systems.

Effects of activation on the properties of electrospun carbon nanofibers and their adsorption performance for carbon dioxide

Microporous carbon nanofibers were prepared by stabilization, carbonization, and activation of electrospun polyacrylonitrile-based nanofibers. The average fiber diameters of activated electrospun carbon nanofibers (AECNF) samples, ranging from 280 to 500 nm, generally decreased with increasing activation degree. The evolution of nitrogen was observed during the fabricated processes, and the predominant nitrogen functionalities were shifted to those at higher binding energies when the activation degree increased. The N/C ratios on the surface of the samples were affected significantly by the activation temperature and activation time. The AECNF samples were featured with microporosity and the ultramicropores were also newly formed with increasing activation degree. It was expected that the activation process involved a three-step predominant reaction: the transformation from ultramicropores to submicropores, the micropore enlargement reaction followed by the micropore formation reaction. The equilibrium CO2 adsorption capacities could achieve 1.2 mmole/g (0.15 atm) and 3.2 mmole/g (1 atm) at 298 K. The CO2 uptake at low partial pressure and ultramicroporosity of the adsorbents were related to the isosteric heat of adsorption. The AECNF samples for CO2 adsorption had an energetically heterogeneous surface and Freundlich equation provided a satisfactory fit. Synergetic effects of microporosity and nitrogen content of AECNF on CO2 uptakes at low pressure were observed.

N, F-Codoped Microporous Carbon Nanofibers as Efficient Metal-Free Electrocatalysts for ORR

HighlightsA new and facile method to synthesize N, F-codoped microporous carbon nanofiber (N, F-MCF) electrocatalysts via electrospinning, hydrothermal process, and thermal treatment.Polyvinylidene fluoride is applied as a fluorine source in oxygen reduction reaction (ORR) catalysis for the first time in literature.N, F-MCFs exhibit distinguished electrocatalytic activity, stability, and methanol tolerance for ORR in alkaline media.

Iron oxide and phosphide encapsulated within N,P-doped microporous carbon nanofibers as advanced tri-functional electrocatalyst toward oxygen reduction/evolution and hydrogen evolution reactions and zinc-air batteries

Developing cheap, efficient and stable tri-functional catalysts can reduce the producing process of catalysts for different electrochemical energy conversion devices, therefore being important to their commercialization. In light of this, we firstly report an advanced catalyst with both FeP and Fe3O4 nanoparticles embedded in N,P-doped microporous carbon nanofibers obtained by electrospinning. The resultant catalyst exhibits robust catalytic activities towards oxygen reduction reaction, hydrogen evolution reaction and oxygen evolution reaction, all of which surpass or are comparable to previously reported tri-functional catalysts. The Fe3O4 nanoparticles and N-doped carbon are the main active species toward oxygen reduction reaction and oxygen evolution reaction, while FeP nanoparticles remarkably promote the hydrogen evolution reaction. The catalyst also shows excellent oxygen reduction stability due to the unique nanoparticle-embedded microporous carbon nanofibers structure. Furthermore, the obtained tri-functional catalyst is also applied in a disposable zinc-air battery, showing good performance. This work offers an effective method to construct a tri-functional catalyst in electrochemical energy devices.

Optimization of the pore structure of PAN-based carbon fibers for enhanced supercapacitor performances via electrospinning

Activated microporous polyacrylonitrile-based carbon nanofibers (APCFs) were synthesized by a sequential process of electrospinning, carbonization, and KOH activation. The porosity and surface chemistry of the APCFs strongly depended on the activation temperature. The specific surface area and pore volume varied from 15 to 1886 m2 g−1 and 0.021–1.196 cm3 g−1, respectively, as the activation temperature increased; this was accompanied by morphology changes at high temperature. The dominant microstructure and minor mesostructure improved the capacitance of carbon. Compared to the other samples, APCFs activated at an optimum temperature of 1000 °C showed the highest specific capacitance of 103.01 F g−1 at 1 A g−1 in 1 mol L−1 Na2SO4 aqueous electrolyte, and an excellent cycling durability up to 3000 cycles. The improved electrochemical efficiency could be explained by the high specific surface area, suitable pore size, and influence of heteroatoms relative to the increased electrical double-layers. The change in the pore size distribution with activation temperature is also discussed in detail.

Preparation and Comparative Study of Microporous and Mesoporous Carbon Nanofibers as Supercapacitor Electrodes.

Microporous carbon nanofibers (Mi-CNFs) and mesoporous carbon nanofibers (Me-CNFs) with high surface area were prepared by electrospinning resol resin/PVP/TEOS/F127 ethanol solution, followed by curing, carbonization and pickling process. TEOS was responsible for structural stability and producing micropores, while F127 for forming mesopores. Mi-CNFs showed high specific surface area of 1841 m2 g-1, while Me-CNFs possessed both high specific surface area of 1674 m2 g-1 and mesoporosity of 64%. The electrochemical test revealed that Mi-CNFs had higher capacitance (276 F g-1 at 0.5 A g-1) and Me-CNFs possessed higher capacitance retention (71%, 150 F g-1 at 30 A g-1).

Flexible polypyrrolone-based microporous carbon nanofibers for high-performance supercapacitors.

Flexible materials have drawn considerable attention due to the demand for wearable and flexible electronic products. Seeking new kinds of precursors for preparing carbon nanofibers with good flexibility for high-performance supercapacitors is a hot issue. In this work, a flexible polypyrrolone (BBB)/polyimide (PI) composite-based carbon nanofiber membrane (PBPICF) is prepared by a facile electrospinning and carbonization process. The PBPICF membranes exhibit a three-dimensional (3D) porous, fluffy and self-standing structure with good mechanical performance and flexibility, and can be arbitrarily bent and folded. PBPICF-65-35 (consisting of BBB (65 wt%) and PI (35 wt%)) exhibits a high specific capacitance of 172.44 F g−1 in 6 M KOH aqueous solution, which is two-fold more than that of commercial polyacrylonitrile-based carbon nanofibers. In addition, PBPICF-65-35 also displays good power density (90 W kg−1) and energy density (19.4 W h kg−1), and the capacitance remains at 96% even after 10 000 cycles at 1.0 A g−1. Therefore, the simple preparation and good capacitance performance of PBPICFs make them a promising binder-free electrode for wearable supercapacitors.

A Freestanding and Long-Life Sodium-Selenium Cathode by Encapsulation of Selenium into Microporous Multichannel Carbon Nanofibers.

Selenium cathode has attracted more and more attention because of its comparable volumetric capacity but much higher electrical conductivity than sulfur cathode. Compared to Li-Se batteries, Na-Se batteries show many advantages, including the low cost of sodium resources and high volumetric capacity. However, Na-Se batteries still suffer from the shuttle effect of polyselenides and high volumetric expansion, resulting in the poor electrochemical performance. Herein, Se is impregnated into microporous multichannel carbon nanofibers (Se@MCNFs) thin film with high flexibility as a binder-free cathode material for Na-Se batteries. The fibrous unique structure of the Se@MCNFs is beneficial to alleviate the volume change of Se during cycling, improve the utilization of active material, and suppress the dissolution of polyselenides into electrolyte. The freestanding Se@MCNF thin-film electrode exhibits high discharge capacity (596 mA h g-1 at the 100th cycle at 0.1 A g-1 ) and excellent rate capability (379 mA h g-1 at 2 A g-1 ) for Na-Se batteries. In addition, it also shows long cycle life with a negligible capacity decay of 0.067% per cycle over 300 cycles at 0.5 A g-1 . This work demonstrates the possibility to develop high performance Na-Se batteries and flexible energy storage devices.

Enhanced hydrogen storage in graphitic carbon micro-nanofibers at moderate temperature and pressure: Synergistic interaction of asymmetrically-dispersed nickel-ceria nanoparticles

Nickel (Ni) and ceria (CeO2) nanoparticles (NPs) containing microporous and graphitic carbon nanofiber (CNF)-activated carbon microfiber (ACF)-based adsorbent was prepared as an efficient hydrogen (H2) storage material at 200 °C and 1 bar. The prepared NiCeO2-ACF/CNF was tested for the H2 storage capacity under batch (static) as well as dynamic (flow) conditions, and the amounts of H2 adsorbed were measured to be approximately the same. In its multiple roles, Ni NP served as the chemical vapor deposition catalyst to grow the CNFs on ACF, besides enhancing H2 adsorption via the spillover mechanism, and decreasing the reduction temperature of CeO2. The experimental data corroborated the positive effects of the synergistic interaction between the Ni and CeO2 NPs and the graphitic characteristics of the CNFs on H2 adsorption. Although CeO2 induced irreversibility in H2 adsorption on NiCeO2-ACF/CNF, the adsorbent was completely regenerated at 300 °C and 1 bar, indicating the developed H2 storage-regeneration process in this study to be effective, practical, and energy efficient.

High‐Stability Electrodes for High‐Temperature Proton Exchange Membrane Fuel Cells by Using Advanced Nanocarbonaceous Materials

AbstractThis work studies the stability and performance of a cathodic electrode for high‐temperature proton exchange membrane (HT‐PEMFC) systems prepared with a carbon nanosphere (CNS) based microporous layer and carbon nanofibers (CNFp) used as a catalyst support. The obtained results are compared with a standard Vulcan carbon XC72 based electrode. With this purpose, two membrane−electrode assemblies (MEAs) were prepared using the cathodic electrodes and tested in a 25 cm2 HT‐PEMFC system. Preliminary short‐life tests around 330 h were carried out with both MEAs. During the tests, different characterization procedures, consisting of polarization curves, spectroscopy impedance analysis, cyclic voltammetry and linear sweep voltammetry were performed in order to evaluate the evolution of the main stability and performance parameters of the MEAs. Results showed that the application of these new materials increases positively the stability of the MEA in comparison with the standard Vulcan carbon XC72 material, with a negligible decrease in the performance of the advanced MEA during all tests, making these results very promising to overcome the service lifetime limitations of these systems.

Flexible, ultrafine and abundant microporous carbon nanofibers prepared by electrospinning from resole-type liquefied biomass-based resin

In the present work, flexible porous carbon nanofibers (PCNFs) of 175 nm diameter were prepared by electrospinning process using resole-type liquefied biomass-based resin (RLBR) as precursor. The addition of defined amount of polyvinyl alcohol (PVA) is essential for the bead-free fibers forming. The final PCNFs were obtained after one-step carbonization of as-spun nanofibers, which presented abundant micropores (0.9 and 1.8 nm) and high specific surface area of 956 m2/g without any activation process. This indicates that the flexible RLBR-based PCNFs will be promising not only in adsorbent and catalyst support materials but also as materials in electrode capacitance application.