Conductive Carbon Nanofibers Research Articles

Enhanced photovoltaic properties of dye-sensitized solar cells using three-component CNF/TiO2/Au heterostructure

To further increase the photoelectric efficiency of dye-sensitized solar cell (DSSC), enhancing the light adsorption of photoanode and suppressing the recombination of photo-generated charges are of great importance. Motivated by this, a novel and efficient three-component CNF/TiO2/Au heterostructure was successfully constructed and employed as an alternative photoanode material. The as-prepared CNF/TiO2/Au is characterized by conductive carbon nanofiber (CNF) core, uniform TiO2 outer shell assembled by upright nanorods, and surface modification with well-dispersed Au nanoparticles. To demonstrate the potential application of such material in DSSC, a comparison of photoelectric properties with commercial P25 and binary composite CNF/TiO2 was carried out. By contrast, the ternary composite CNF/TiO2/Au exhibited the highest short-circuit photocurrent density of 15.47 mA cm−2 and photoelectric conversion efficiency of 6.45%, which is about 31% higher than that of the commercial P25-based DSSCs. The great improvement of photoelectric properties for ternary composite CNF/TiO2/Au might be attributed to not only the conspicuous light adsorption ability derived from the sufficient dye loading of CNF/TiO2/Au and the surface plasmon resonance of Au nanoparticles, but also the reduced recombination endowed by the conductive CNF core and the heterojunctions at the interface.

Integrating TiO₂/SiO₂ into Electrospun Carbon Nanofibers towards Superior Lithium Storage Performance.

In order to overcome the poor electrical conductivity of titania (TiO2) and silica (SiO2) anode materials for lithium ion batteries (LIBs), we herein report a facile preparation of integrated titania–silica–carbon (TSC) nanofibers via electrospinning and subsequent heat-treatment. Both titania and silica are successfully embedded into the conductive N-doped carbon nanofibers, and they synergistically reinforce the overall strength of the TSC nanofibers after annealing (Note that titania–carbon or silica–carbon nanofibers cannot be obtained under the same condition). When applied as an anode for LIBs, the TSC nanofiber electrode shows superior cycle stability (502 mAh/g at 100 mA/g after 300 cycles) and high rate capability (572, 518, 421, 334, and 232 mAh/g each after 10 cycles at 100, 200, 500, 1000 and 2000 mA/g, respectively). Our results demonstrate that integration of titania/silica into N-doped carbon nanofibers greatly enhances the electrode conductivity and the overall structural stability of the TSC nanofibers upon repeated lithiation/delithiation cycling.

A Janus nanofiber-based separator for trapping polysulfides and facilitating ion-transport in lithium-sulfur batteries.

Endowing separators with the polysulfide-blocking function is urgently needed for high-performance lithium-sulfur (Li-S) batteries. Thus far, most of the reported research has focused on modifying conventional polyolefin separators but with poor thermal stability and low ionic conductivity. To address these issues, herein we report a Janus separator based on a thermally stable polymeric nanofabric designed with abilities to trap polysulfides and facilitate the transport of Li+ simultaneously. This Janus separator possesses a configuration of a carbon nanofiber (CNF) layer toward the sulfur cathode and the polyimide (PI) nanofabric toward the Li metal anode. It is demonstrated that the conductive CNF layer can effectively anchor and convert the polysulfides; meanwhile, the excellent wettability with liquid electrolytes and the highly porous structure of the PI nanofiber layer significantly promote the Li+-transport. In addition, the Janus separator presents notable advantages in thermal dimensional stability benefiting from the PI nanofabric. As a result, the Li-S battery armed with the Janus separator shows a high initial capacity (1393 mA h g-1 at 0.1 A g-1), stable cycling performance (822 mA h g-1 at 1 A g-1) and high coulombic efficiency of 99.6%.

CoSe2 nanoparticles grown on carbon nanofibers derived from bacterial cellulose as an efficient electrocatalyst for hydrogen evolution reaction

Exploration of high-efficiency and inexpensive Pt-free electrochemical catalysts for hydrogen evolution reaction (HER) is highly significative for carbon dioxide free energy conversion systems. In this work, we described the development of CoSe2 nanoparticles grown on the carbon nanofibers (CNFs) derived from bacterial cellulose (CNFs/CoSe2) through a facile one-step hydrothermal preparation, which not only showed a three-dimensional (3D) porous network structure, but also possessed large surface area. This rationally designed architecture realizes the uniform distribution of CoSe2 nanoparticles to provide with fully exposed active edges and the unique conductive interwoven carbon nanofibers facilitates the charge transportation in HER process, thus leading to remarkable HER activity. As expected, the CNFs/CoSe2 shows a low onset overpotential of −85 mV, low overpotential (η10 = 119 mV) for reaching a current density of −10 mA cm−2 and smaller Tafel slope of 54 mV dec−1 as well as good cycling stability in acidic electrolyte.

Fabrication of Si Nanoparticles@Conductive Carbon Framework@Polymer Composite as High‐Areal‐Capacity Anode of Lithium‐Ion Batteries

AbstractLow‐cost and scalable processes to fabricate Si‐based anodes with high areal capacity and excellent cycling performance remain a challenge, thereby limiting their widespread application. Herein, we report Si nanoparticles@conductive carbon framework@polymer (Si@C@P) composite electrodes, in which Si nanoparticles are homogeneously immobilized within a three‐dimensional network of conductive carbon nanofibers bound by a high‐viscosity polymer. When used as anodes for lithium‐ion batteries, the obtained Si@C@P composite electrodes deliver an initial coulombic efficiency of 83.5 % and an areal capacity of 2.0 mAh cm−2 (1152 mAh ), with a capacity retention about 0.8 mAh cm−2 (466 mAh ) after 150 discharge–charge cycles at 0.1 C. This work provides a low‐cost route for the large‐scale manufacture of Si‐based anodes with high areal capacity, which may be very significant for the development of lithium‐ion batteries with high energy density.

Minimizing the Electrolyte Volume in Li–S Batteries: A Step Forward to High Gravimetric Energy Density

AbstractSulfur electrodes confined in an inert carbon matrix show practical limitations and concerns related to low cathode density. As a result, these electrodes require a large amount of electrolyte, normally three times more than the volume used in commercial Li‐ion batteries. Herein, a high‐energy and high‐performance lithium–sulfur battery concept, designed to achieve high practical capacity with minimum volume of electrolyte is proposed. It is based on deposition of polysulfide species on a self‐standing and highly conductive carbon nanofiber network, thus eliminating the need for a binder and current collector, resulting in high active material loading. The fiber network has a functionalized surface with the presence of polar oxygen groups, with the aim to prevent polysulfide migration to the lithium anode during the electrochemical process, by the formation of S–O species. Owing to the high sulfur loading (6 mg cm−2) and a reduced free volume of the sulfide/fiber electrode, the Li–S cell is designed to work with as little as 10 µL cm−2 of electrolyte. With this design the cell has a high energy density of 450 Wh kg−1, a lifetime of more than 400 cycles, and the possibility of low cost, by use of abundant and eco‐friendly materials.

In Situ Strain and Damage Monitoring of GFRP Laminates Incorporating Carbon Nanofibers under Tension.

In this study, conductive carbon nanofibers (CNFs) were dispersed into epoxy resin and then infused into glass fiber fabric to fabricate CNF/glass fiber-reinforced polymer (GFRP) laminates. The electrical resistance and strain of CNF/GFRP laminates were measured simultaneously during tensile loadings to investigate the in situ strain and damage monitoring capability of CNF/GFRP laminates. The damage evolution and conduction mechanisms of the laminates were also presented. The results indicated that the percolation threshold of CNFs content for CNF/GFRP laminates was 0.86 wt % based on a typical power law. The resistance response during monotonic tensile loading could be classified into three stages corresponding to different damage mechanisms, which demonstrated a good ability of in situ damage monitoring of the CNF/GFRP laminates. In addition, the capacity of in situ strain monitoring of the laminates during small strain stages was also confirmed according to the synchronous and reversible resistance responses to strain under constant cyclic tensile loading. Moreover, the analysis of the resistance responses during incremental amplitude cyclic tensile loading with the maximum strain of 1.5% suggested that in situ strain and damage monitoring of the CNF/GFRP laminates were feasible and stable.

Electro-responsive carbon membranes with reversible superhydrophobicity/superhydrophilicity switch for efficient oil/water separation

Abstract Membrane filtration has shown great potential for the separation of oil-water mixtures. The separation of oil-water mixtures is essentially an interfacial issue, and thus controllable surface wettability of membrane is extremely significant for efficient and cost-effective oil/water separation. Herein, poly-3-methylthiophene (P(3-MTH))/carbon membranes (CMs-P) with switchable surface wettability between superhydrophobicity and superhydrophilicity were designed. The CMs-P, prepared from coating P(3-MTH) on the highly porous and electrically conductive carbon nanofiber membranes, could exhibit the wettability switch by doping or dedoping the P(3-MTH) with ClO4− under electro-stimuli. The switch can be quickly achieved in less than 30 s and shows desired recyclability. Driven by gravity only, the prepared CMs-P are capable of completely separating free oil-water mixture. Furthermore, the separation efficiency reaches to 99.5% for surfactant-stabled emulsions with various oil-water ratios. This work presents new insights into the study for smart gating membranes and the design of novel functional oil/water separation devices.

Hierarchically designed ZIF-8-derived Ni@ZnO/carbon nanofiber freestanding composite for stable Li storage

We present a uniform rhombohedral Ni@ZnO bimetallic oxide host over carbon nanofibers (CNF) as an anode material for Li-ion batteries. Ni@ZnO was produced by annealing a Ni@zeolitic imidazolate framework (ZIF-8) hierarchically decorated over CNFs. The rationally-designed freestanding composite exhibited promising stability in electrochemical performance. A first reversible capacity of 1051 mA·h·g−1 was measured at a current density of 100 mA·g−1, and 88% of this capacity was retained after 100 cycles. We attribute this high capacity retention to the hierarchical structure of the Ni@ZnO-enwrapped carbon framework encapsulating the conductive CNFs, as demonstrated by scanning and transmission electron microscopy. The composite electrode also showed a high specific capacity of ∼497 mA·h·g−1 in high-rate testing at 1000 mA·g−1, because the cage-like framework of the material allowed rapid charge transfer and Li-ion diffusion in the anode.

Carbon nanofiber-filled conductive silicone elastomers as soft, dry bioelectronic interfaces.

Soft and pliable conductive polymer composites hold promise for application as bioelectronic interfaces such as for electroencephalography (EEG). In clinical, laboratory, and real-world EEG there is a desire for dry, soft, and comfortable interfaces to the scalp that are capable of relaying the μV-level scalp potentials to signal processing electronics. A key challenge is that most material approaches are sensitive to deformation-induced shifts in electrical impedance associated with decreased signal-to-noise ratio. This is a particular concern in real-world environments where human motion is present. The entire set of brain information outside of tightly controlled laboratory or clinical settings are currently unobtainable due to this challenge. Here we explore the performance of an elastomeric material solution purposefully designed for dry, soft, comfortable scalp contact electrodes for EEG that is specifically targeted to have flat electrical impedance response to deformation to enable utilization in real world environments. A conductive carbon nanofiber filled polydimethylsiloxane (CNF-PDMS) elastomer was evaluated at three fill ratios (3, 4 and 7 volume percent). Electromechanical testing data is presented showing the influence of large compressive deformations on electrical impedance as well as the impact of filler loading on the elastomer stiffness. To evaluate usability for EEG, pre-recorded human EEG signals were replayed through the contact electrodes subjected to quasi-static compressive strains between zero and 35%. These tests show that conductive filler ratios well above the electrical percolation threshold are desirable in order to maximize signal-to-noise ratio and signal correlation with an ideal baseline. Increasing fill ratios yield increasingly flat electrical impedance response to large applied compressive deformations with a trade in increased material stiffness, and with nominal electrical impedance tunable over greater than 4 orders of magnitude. EEG performance was independent of filler loading above 4 vol % CNF (< 103 ohms).

Fabrication of Pt nanoparticles on nitrogen-doped carbon/Ni nanofibers for improved hydrogen evolution activity

Among various methods for acquiring hydrogen fuel, electrocatalytic water splitting is considered to be as one of the most efficient and promising approaches. Pt is regarded as the best electrocatalyst for the hydrogen evolution reaction (HER) during water splitting process, however, the scarcity and costliness of Pt restrict the large-scale practical application. On the other hand, transition metal Ni is abundant in earth and exhibits favorable HER catalytic activity theoretically. In this work, we have demonstrated a facile electrospinning combined with calcination and chemical reduction processes to fabricate Pt nanoparticles loaded on nitrogen-doped carbon/Ni nanofibers (Ni-NCNFs-Pt) as efficient HER electrocatalysts. The as-prepared Ni-NCNFs-Pt not only reduced the usage of noble metal Pt but also revealed an excellent electrochemical activity at all values of pH, including the smaller overpotentials of 47, 22 and 84 mV (at j = 10 mA cm−2) in 0.5 M H2SO4, 1 M KOH and 0.1 M phosphate buffer solution, respectively. In addition, Ni-NCNFs-Pt nanocatalyst displayed an extraordinary low Tafel slope and long durability over a wide range of pH. The remarkable HER performance could be ascribed to the increased electrochemical active surface area through the introduction of Ni nanoparticles, synergistic interactions between Ni and Pt nanoparticles and the introduction of the conductive nitrogen-doped carbon nanofibers (NCNFs) substrate which facilitated the fast electron transport. This investigation provides a potential route to construct efficient and low cost HER electrocatalysts with promising practical applications in renewable energy conversion and storage devices.

Brush-Like Cobalt Nitride Anchored Carbon Nanofiber Membrane: Current Collector-Catalyst Integrated Cathode for Long Cycle Li-O2 Batteries.

To achieve a high reversibility and long cycle life for lithium-oxygen (Li-O2) batteries, the irreversible formation of Li2O2, inevitable side reactions, and poor charge transport at the cathode interfaces should be overcome. Here, we report a rational design of air cathode using a cobalt nitride (Co4N) functionalized carbon nanofiber (CNF) membrane as current collector-catalyst integrated air cathode. Brush-like Co4N nanorods are uniformly anchored on conductive electrospun CNF papers via hydrothermal growth of Co(OH)F nanorods followed by nitridation step. Co4N-decorated CNF (Co4N/CNF) cathode exhibited excellent electrochemical performance with outstanding stability for over 177 cycles in Li-O2 cells. During cycling, metallic Co4N nanorods provide sufficient accessible reaction sites as well as facile electron transport pathway throughout the continuously networked CNF. Furthermore, thin oxide layer (<10 nm) formed on the surface of Co4N nanorods promote reversible formation/decomposition of film-type Li2O2, leading to significant reduction in overpotential gap (∼1.23 V at 700 mAh g-1). Moreover, pouch-type Li-air cells using Co4N/CNF cathode stably operated in real air atmosphere even under 180° bending. The results demonstrate that the favorable formation/decomposition of reaction products and mediation of side reactions are hugely governed by the suitable surface chemistry and tailored structure of cathode materials, which are essential for real Li-air battery applications.

Highly anisotropic electric conductivity in PAN-based carbon nanofibers

In addition to the chemical and physical properties of nanostructures their successful utilization for applications is strongly triggered by economic aspects. Electrospinning of nanowires from solution followed by subsequent annealing steps is a comparably cheap technique to fabricate conductive carbon nanofibers (CNF) made from polyacrylonitrile (PAN) molecules in large quantities. In this work, we investigated the microscopic properties of the CNFs with diameters of 100–300 nm by means of Raman and x-ray photoelectron spectroscopy and correlated these results with transport measurements done with a 4-tip STM. In particular, we investigated the effect of fiber alignment and knot densities, which can be controlled by applying constant creep due to stress during the stabilization process. The comparison of the conductivity obtained from single CNFs revealed further that the fiber crossings within the ensemble structure act as scattering centers and proofs that the transport is along the surfaces of the CNFs.

In Situ‐Formed Hierarchical Metal–Organic Flexible Cathode for High‐Energy Sodium‐Ion Batteries

Metal-organic compounds are a family of electrode materials with structural diversity and excellent thermal stability for rechargeable batteries. Here, we fabricated a hierarchical nanocomposite with metal-organic cuprous tetracyanoquinodimethane (CuTCNQ) in a 3 D conductive carbon nanofibers (CNFs) network by in situ growth, and evaluated it as flexible cathode for sodium-ion batteries (SIBs). CuTCNQ in such flexible composite electrode is able to exhibit a high capacity of 252 mAh g-1 at 0.1 C and highly reversible stability for 1200 cycles within the voltage range of 2.5-4.1 V (vs. Na+ /Na). A high specific energy of 762 Wh kg-1 was obtained with high average potential of 3.2 V (vs. Na+ /Na). The in situ-formed electroactive metal-organic composites with tailored nanoarchitecture provide a promising alternative choice for high-performance cathode materials in SIBs with high energy.

Flexible transparent electrodes made of core-shell-structured carbon/metal hybrid nanofiber mesh films fabricated via electrospinning and electroplating

The development of practical flexible transparent electrodes is one of the major core technology fields for future nanoscale optoelectronics. Despite the many efforts to replace the indium tin oxide (ITO) electrode, preparing practical alternatives that satisfy the essential requirements of flexible transparent electrodes remains a challenge. In this work, core-shell-structured carbon/metal hybrid mesh (CS-CMHM) films, comprised of a metal layer coated onto conductive carbon nanofiber network structures, were fabricated using electrospinning and electroplating and demonstrated potential for use as flexible transparent electrodes. In contrast to previously described techniques that use conventional polymer fibers as sacrificial structures, the conductive carbon nanofibers used in the current technique that we developed provided bi-functionality: they formed conductive core channels and artificial supports of the metal structures. The CS-CMHM films displayed superior optoelectrical, mechanical, and thermal properties: they transmitted ∼91% of visible light, showed a low sheet resistance of ∼2.7 Ω/sq, and displayed excellent mechanical stability even after 10000 cycles of bending the films to a radius of 5 mm; also, applying a voltage of only 3 V to a transparent heater based on CS-CMHM films resulted in the temperature of the film surface increasing very rapidly in the first 20 s, and soon thereafter reaching ∼280 °C. Based on these results, we believe that the use of CS-CMHM films and the process we developed to fabricate them open up great opportunities for high-performance flexible transparent electronics.

Electrical conductivity and piezo-resistive characteristics of CNT and CNF incorporated cementitious nanocomposites under static and dynamic loading

The present study deals with the conductivity of carbon nano fiber (CNF) or nano tube (CNT) incorporated cement composite under static and dynamic conditions. Since, microstructure of cement matrix changes during hydration process, the influence of the conduction path on the conductive properties of composite is required to be evaluated. Role of the synthesis process using ultrasonication, type of fiber, % of fiber, etc. to develop the piezo sensitive CNT/CNF composite is investigated. The influence of external voltage to overcome the threshold resistance of the nanocomposite matrix is also investigated. Gauge factors of the developed conductive cement based composites are evaluated. Further, dynamic load sensitive CNT cement nanocomposite is developed, using the developed material with consistent piezo-resistive properties, for measuring the acceleration response of the structures. It is found that the cement based nanocomposite sensors as developed in the present study are good candidate for real time health monitoring of structures.

Uniform growth of MoS2 nanosheets on carbon nanofibers with enhanced electrochemical utilization for Li-ion batteries

A facile route for the uniform growth of MoS2 nanosheets on carbon nanofibers (CNFs) via a simple hydrothermal method is reported. The CNF network provides a porous and three-dimensional scaffold for the deposition of ultrathin MoS2 nanosheets. Benefiting from the highly conductive and porous CNFs as well as the nanostructured MoS2, the coaxial MoS2@CNFnanocomposites(*), when served as a binder-free and flexible anode for Li-ion batteries, could generate a synergistic effect to gain a high electrochemical utilization of MoS2. As a result, the nanocomposites exhibit a high reversible capacity of 846mAhg−1 at 100mAg−1, excellent high-rate capability (455mAhg−1 even at 2Ag−1), and good cycling retention with only 7.4% capacity degradation after 100 cycles. The superior Li-ion storage properties enable the nanocomposites to hold great potential application in high-performance Li-ion batteries.

Electrospun polyacrylonitrile/β-cyclodextrin based porous carbon nanofiber self-supporting electrode for capacitive deionization

With β-CD as both pore-forming reagent and carbon precursor, conductive porous carbon nanofibers are fabricated with excellent capacitive deionization performance.

Development of Continuous and Real Time Structural Health Monitoring of Aircraft Primary Structure Through Embedded Carbon Nano Fiber Sensors

In this article, a new approach for structural health monitoring of aircraft primary structure has been dealt with, embedded carbon nano fiber (CNF) sensors. The multi-functional ability of non-conductive Glass Fiber Reinforced Polymers (GFRP) material is enhanced by addition of conductive CNF. An experimental investigation was carried out on bi-directional glass fiber to study the damage sensing capabilities of nano composite through embedded CNF mat-based sensor. In the study, CNF was dispersed in Poly Vinyl Alcohol (PVA) solution, and PVA-CNF sensor mat was developed by using electro-spinning process. This mat was embedded into the GFRP by using vacuum resin transfer moulding process at the design stage. CNF neither increases the weight of the composites nor affects its structural and mechanical properties. CNF sensor mat at various orientation and different wt% was embedded to the GFRP. The fabrications of specimens were done using bi-directional glass fiber with epoxy resin. Incremental tensile loading and unloading were conducted during test, and their corresponding electrical conductivity was monitored. The electrical resistance measurement of the embedded PVA-CNF mat is used to assess the structural weakness during mechanical test. Mechanical loading and the change in electrical resistance were directly correlated. Residual resistance measurements of the CNF mat were monitored during unloading condition for high stress (or strain). Accumulating damage to the composite material was calculated and correlated to the electrical resistance readings. The standard size of the coupons is 250x25x2 mm as per ASTM standard D3039.

In-situ assembly of three-dimensional MoS2 nanoleaves/carbon nanofiber composites derived from bacterial cellulose as flexible and binder-free anodes for enhanced lithium-ion batteries

With the development of flexible and wearable energy devices, it is highly desirable to exploit flexible and cost-effective electrode materials. In this work, we report a facile and in-situ method for preparing a three-dimensional (3D), flexible and binder-free anode material, composing of leaf-like MoS2 nanostructures uniformly anchored on carbon nanofibers derived from carbonized bacterial cellulose (denoted as MoS2-cBC). With merits of high conductivity, good flexibility and high structural stability, the MoS2-cBC composite was directly used as the anode material and current collector for lithium ion batteries without any binder nor conductive additive. Moreover, owing to the synergistic effect of the uniformly deposited MoS2 nanoleaves and the 3D highly conductive carbon nanofibers, the MoS2-cBC anode exhibits impressively superior electrochemical performance. A high reversible charge capacity of 935mAhg−1 is achieved at 0.1Ag−1, while a capacity of 581mAhg−1 is maintained after 1000 cycles at 1Ag−1 with negligible decay, demonstrating much enhanced long-term cycling stability of the composite. The superior electrochemical performance together with the stability and cost-effective merits make the MoS2-cBC composite promising for next-generation energy storage devices.