Polyacrylonitrile Precursor Research Articles

Using higher rates of stabilization of a wet-spun pan fibre to understand the effect of microstructure on the tensile and compressive properties of carbon fibre

The transformation of a polyacrylonitrile (PAN) precursor fibre into carbon fibre using varying stabilization times during carbon fibre manufacture is presented in this work. The wet-spun precursor fibre is a specifically designed PAN co-polymer made up of acrylonitrile, methyl acrylate and 3 wt% itaconic acid. The residence or stabilization times in the oxidation ovens are varied from 32, 64 and 96 min, enabling investigation of the impact upon microstructure upon tensile and compressive properties. Using a continuous pilot scale carbonization line for faster cyclization and dehydrogenation, the precursor fibres exhibited lower oxygen uptake contributing to the formation of a less dense and more amorphous carbon fibre. Synchrotron based SAXS-WAXS characterisation and Raman spectroscopy of the carbon fibre microstructure displays lower orientation and crystallinity, with higher void concentration. This led to lower electrical conductivity, lower tensile strength (19 %) but higher compressive strength (27 %) when reducing stabilisation times from 96 to 32 min.

Can Two-Dimensional Correlation Spectroscopy (2D-COS) Indicate Biocompatible Material?

Carbon nanofibers are a new type of carbon materials. One of the methods of obtaining them is the carbonization of a polymer precursor. They are attractive in many areas, including medicine, due to the possibility of modifying their properties in a wide range. For example, the conditions of the carbonization process result in the creation of materials with designed structures and surface parameters. In the current work, the nanoprecursor was polyacrylonitrile (PAN) fibers. Two types of carbon fibers obtained by carbonization of the PAN precursor at 1000 °C were tested. The first electrospun carbon nanofibers (ESCNFs) were cytotoxic, while the second ESCNF-f were biocompatible after functionalization. The parameters obtained from Raman tests did not clearly discriminate between the tested materials. Multiwavelength Raman studies, analyzed using the two-dimensional correlation spectroscopy (2D-COS), treating the laser energy as an external disturbance, showed a difference between both fibrous structures. 2D-COS indicates that structures resembling graphite systems, devoid of disordered carbon forms, are nontoxic.

Effect of carbon nanofibers fabricated from electrospun PAN precursors on the characteristics and densification of MgO–CaO ceramic systems

MgO–CaO composites are basic materials with high melting points, high chemical resistance to alkaline environments, clean steel production, environmental friendliness, and abundant sources. In the current work, carbon nanofibers (CNFs) with diameters between 150 and 270 nm were prepared at different temperatures (up to 1200 °C) by carbonization of electrospun polyacrylonitrile (PAN) precursors. Then, the MgO–CaO composites were prepared in two steps. First, 3 wt% CNFs carbonized at different temperatures were added to the composite to determine the optimal carbonization temperature. Subsequently, the physical properties (apparent porosity and bulk density) and mechanical properties (flexural strength (FS) and cold crushing strength (CCS)) of the MgO–CaO-CNF composites were investigated. X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), Energy-Dispersive X-ray spectroscopy (EDS), and thermogravimetric analysis (TGA) were used to analyze the composition, morphology, and structure of the CNFs powders and composite samples. Based on the results obtained, such as the percentage graphitization, length, average diameter, and morphology of the CNFs, 1000 °C was determined as the appropriate carbonization temperature for the next steps of this study. In a second step, the CNFs synthesized at 1000 °C were added to the MgO–CaO with different wt% (0, 0.5, 1, 1.5, 2, 2.5, and 3 wt%). It was found that by adding CNFs (up to 1.5 wt%) into the MgO-CaO composites, the physical properties increased due to the improvement of densification, and mechanical properties improved due to the activation of reinforcing mechanisms, the reduction of surface defects and the creation of a dense body. However, these properties decreased from 1.5 to 3 wt% due to the agglomeration and poor dispersion of the CNFs. Finally, the results illustrated that adding CNFs, even in small amounts, significantly improved the features of MgO-CaO compounds; the ideal content was 1.5 wt% CNFs.

Decreasing the environmental impact of carbon fibre production via microwave carbonisation enabled by self-assembled nanostructured coatings

The use of carbon fibre (CF)-based composites is of growing global importance due to their application in high-end sectors such as aerospace, automotive, construction, sports and leisure amongst others. However, their current high production cost, high carbon footprint and reduced production capability limit their use to high-performance and luxury applications. Approximately 50% of the total cost of CF production is due to the thermal conversion of polyacrylonitrile (PAN) precursor fibre (PF) to CF as it involves the use of high energy consumption and low heating efficiency in large furnaces. Looking at this scenario, this study proposes in the present study to use microwave (MW) heating to convert PF to CF. This is scientifically and technologically challenging since PF does not absorb microwave energy. While MW plasma has been utilised to carbonise fibres, it is the high temperature from the plasma that does the carbonisation and not the MW absorption of the fibres. Therefore, for the first time, this research shows how carbonisation temperatures of >1000 °C can be reached in a matter of seconds through the use of a novel microwave (MW) susceptor nanocoating methodology developed via a layer-by-layer assembly of multiwall carbon nanotubes (MWCNTs) on the PF surface. Remarkably, these CFs can be produced in an inexpensive domestic microwave and exhibit mechanical performance equivalent to CF produced using conventional heating. Additionally, this study provides a life cycle and environmental impact analysis which shows that MW heating reduces the energy demand and environmental impact of lignin-based CF production by up to 66.8% and 69.5%, respectively.Graphical

Microstructural Evolution during Dry-Jet Wet Spinning Postprocessing from Coagulation Bath Fiber to High-Performance Polyacrylonitrile Precursor Fiber

Microstructural Evolution during Dry-Jet Wet Spinning Postprocessing from Coagulation Bath Fiber to High-Performance Polyacrylonitrile Precursor Fiber

Market analysis of carbon fiber production with reference to the oxidation ovens used

AbstractAn important process step in carbon fiber production is the stabilization of the pan precursor fiber, which makes it infusible and incombustible. This article gives a market overview of the carbon fiber producers relating to their used oxidations oven and of market of oxidations oven itself. All six industrially available oxidation oven types are described and an overview of the oven supplier is given. The analysis of the oxidation oven market shows that only three out of six oxidation oven technologies are used for large‐volume production. CtE is currently the most widely used oven technology with approximately 55%. Since 2014, CF demand has been growing faster than the expansion of production capacities. A shortage is predicted within the next 5 years. In addition, the production capacities of existing CF lines have stagnated at an average of 1.5 kt*a−1 since the last 10 years. To meet the increasing CF demand in the coming years, various options are available: (1) Increasing large‐tow production, (2) Increasing process speed (3) Increasing the loading factor (4) Increasing with of oxidation oven.

Confined pyrolysis-driven one-dimensional carbon structure evolution from polyacrylonitrile fiber and its microwave absorption performance

The evolution of one-dimensional carbon structures from polyacrylonitrile (PAN) fiber precursors is investigated based on confined pyrolysis strategy, which is employed to convert electrospun PAN fibers into carbon in a closed system. Carbon tube with ultra-large diameter derived from silica-coated organic PAN precursor fiber is observed and its low-performance of microwave absorption is revealed. To enhance microwave absorption, cobalt acetylacetonate is introduced as a magnetic resource into PAN, facilitating one-dimensional carbon structure evolution and yielding magnetic/carbon nanofibers. The mechanism resulting in such one-dimensional carbon structure evolution is discussed. The microwave absorption performances of the prepared magnetic carbon nanofibers are analyzed based on their complex permittivity and permeability. Remarkably, the magnetic carbon nanofibers exhibit strong microwave absorption intensity of −42 dB at only 20 wt% filler content. Further simulations are conducted based on radar-absorbing structure with prepared magnetic carbon nanofibers-coated laminate and wing models by using CST software. The laminated composite structure appears the maximum RCS reduction value of 18.70 dBsm at 6 GHz with 3.0 mm thickness in the frequency range of 2–18 GHz. In the corresponding wing structure, highly efficient electromagnetic wave absorption is observed and the RCS reduction can achieve −14.12 dBsm at 10 GHz with 3.5 mm thickness.

Investigation of the Microstructure of PAN Precursor Fibers Obtained at Various Processing Stages

The production of high-performance carbon fibers relies heavily on the structural transformations of polyacrylonitrile (PAN) fiber during processing. In this article differential scanning calorimetry (DSC), synchrotron small-angle X-ray scattering (SAXS), and synchrotron wide-angle X-ray diffraction (WAXD) were used to study the changes of the thermal properties, voids and crystal structure of the PAN precursor fibers on industrial lines during the continuous processing stages, i.e., after the treatment in the coagulation bath, after stretching in boiling water and after stretching in high-temperature steam. The findings of this study suggest that after boiling water stretching the molecular chain motion of the PAN precursor fiber weaken, resulting in the expansion of the voids. After high-temperature steam stretching the voids became elliptical and oriented in the stretching direction. Although the boiling water stretching process partially damaged the (100) crystal planes of the PAN precursor fibers, it does not hinder their overall crystalline structure. The high stretching ratio primarily affected the orientation of the molecular chains. This orientation, even in the context of partial crystal plane disruption, further promoted the crystallization of the (100) crystal planes in the fibers. These experiments explored the correlation between the processing technology and fiber structure transformation of PAN-based carbon fibers, resulting in producing a guide for the preparation of high-performance carbon fibers with fewer defects.

High temperature oxidation of additively manufactured silicon carbide/carbon fiber nanocomposites

An additive manufacturing process and subsequent pyrolysis cycle were used to fabricate SiC matrix/carbon fiber hybrid composites. The matrix was fabricated using a mixture of preceramic polymer and acrylate monomers, while polyacrylonitrile (PAN) precursor was used to fabricate fibers via electrospinning. The precursor matrix and reinforcing fibers at 0, 2, 5, or 10 wt% were printed using digital light processing, and both were simultaneously pyrolyzed to yield the final ceramic matrix composite structure. After pyrolysis, XRD and SEAD analysis proved the existence of SiC nanocrystals and turbostratic carbon structure in the matrix, while the reinforcement phase was shown to have a turbostratic carbon structure similar to commercial carbon fibers. Thermogravimetric analysis (TGA) in air up to 1400 °C was used to evaluate the oxidation resistance of this material. TGA results showed some weight loss due to oxidation of SiC and/or carbon up to about 900 °C, followed by weight gain to about 1200 °C due to the formation of a protective SiO2 layer. Although increasing carbon fiber content negatively impacted the total mass loss for the first heating cycle, exposure of the composite to second-run air revealed negligible weight loss. This is explained by SiO2 layer formation which acts as a protective film that prevents oxygen diffusion. Oxidation of SiC and the formation of a glassy layer has been proven to protect the sample from further oxidation, as well as provide healing of surface cracks and defects as revealed by SEM analysis.

Hexagonal crystalline nanofillers reinforced composite carbon nanofibers with optimized crystal structure and improved mechanical properties

The mechanical properties of carbon nanofibers (CNFs) are always restricted by their disorganized crystal structures. Herein, this paper utilizes two typical hexagonal crystalline flake materials, nanoscale flake graphite (NG) and hexagonal nitride boron (BN), as nanofillers to optimize the crystal domains of CNFs and achieves enhancement in fiber strength, modulus and toughness. For this purpose, in situ polymerization technique is developed for the rapid and uniform mixing of nanofillers with polyacrylonitrile (PAN) precursors of CNFs. The nanofillers are exfoliated in this process and wrapped with PAN to prevent potential agglomeration. The obtained core-shell nanocomposites can be produced into composite CNFs via electrospinning, stabilization and carbonization. Based on the attraction effect, the dispersed nanofillers can organize PAN molecular chains into oriented crystalline fibrils in as-spun nanofibers and accelerate their transformation to more ladder structures in stabilized nanofibers. On this basis, NG is shown to act as the templating and nucleating agent to promote the formation, growth and compact stacking of graphitic planes in CNFs. BN also improves fiber crystallinity, while its limited templating effect leads to looser and finer crystal domains. As a result, NG-doped CNFs have significantly improved strength and modulus, and BN-doped CNFs possess simultaneously enhanced strength and toughness.

Fabrication of Internal Electric Field Sns/Sb2S3 with Engineered Porous Structure for Fast Kinetics Sodium Ion Storage

Benefiting from the abundance and low cost of sodium, sodium-ion batteries show great potential as lithium-ion batteries in application of large-scale energy storage. However, anode material graphite with high theoretical capacity 372 mAh g-1, low charge-discharge plateau potential and good cyclability, widely applied in lithium-ion batteries, exhibited poor electrochemical performance. The larger radius of Na-ion compared to Li-ion hinders the mass and ion transfer during charge-discharge cycling. Thus, anode material with large abundance, stability and high conductivity is crucial for the development and further application of sodium-ion batteries.Sodium-ion batteries have the potential to benefit greatly from metallic sulfide anodes, which offer high theoretical capacities. Unfortunately, the practical use of these anodes is limited by poor electrochemical performance, as sulfides tend to expand significantly in volume and Na+ ions exhibit sluggish kinetics during cycling. We have developed a facile and scalable approach to synthesizing a SnS/Sb2S3 heterostructure that is porous and bimetallic, with an additional sulfur and nitrogen co-doped carbon matrix encapsulation (SnS/Sb2S3@SNC). The PAN precursor is mixed homogeneously with SnSbx and S with a ball milling process. The sulfur evaporates from the mixture and reacts with the SnSbx alloy, leading to the formation of bimetallic sulfides SnS/Sb2S3. As a result, voids are generated, which in turn contributes to the development of a porous structure. At the same time, the PAN is carbonized, generating a S, N co-doped carbon matrix. SnS and Sb2S3 are two highly promising anode materials for sodium-ion batteries, with high theoretical specific capacity of 1022 mAh g-1 and 947 mAh g-1, respectively. Moreover, bimetallic sulfides possess different bandgap make them ideal components for generating a strong internal electric field on the hetero-interface, which allows to improve the charge carrier transport and interface reaction kinetics. The porous nature of the structure can contain the volume expansion of sulfides during cycling, thereby ensuring superior structural stability. The distinctive heterostructure, in combination with the S, N co-doped carbon matrix, enables fast-charge transport and accelerate Na-ion storage kinetics.The SnS/Sb2S3@SNC anode demonstrates impressive electrochemical performance, with high capacities of 425 mAh g-1 at 200 mA g-1 after 100 cycles, and 302 mAh g-1 at 500 mA g-1 after 400 cycles. Additionally, the SnS/Sb2S3 @SNC anode exhibits remarkable rate capability, with a capacity of over 200 mAh g-1 at a high current density of 5000 mA g-1. Figure 1

Multistep structure evolution during the coagulation of PAN/DMSO solution studied by in-situ FTIR spectroscopy

Coagulation is the first step in the formation of the aggregation structure during the preparation of polyacrylonitrile (PAN) fiber, which has a significant effect on the mechanical properties of PAN precursor and its based carbon fiber. However, due to the rapid coagulation speed of the PAN/DMSO solution in the coagulation bath, research about the complex matter exchange and structural evolution during this process is still a challenging topic. In the present study, the PAN/DMSO solution was set in an environment with constant humidity to slow down the coagulation rate. In situ FTIR measurements combined with two-dimensional correlation analysis were used for the first time to study the detailed evolution of the intermolecular interaction and PAN chain conformation caused by the change of H2O, DMSO, and PAN content during coagulation. The results indicated that with the diffusion of H2O from the atmosphere to PAN/DMSO solution, hydrogen bonds between H2O and DMSO were gradually generated, which led to a chemical environmental change around PAN chains and promoted the dissociation of PAN and DMSO. After that, the parallel-oriented –CN groups promoted the conformation change of the PAN chains.

Uniform doping of onion-like carbon nanofillers in carbon nanofibers via functionalization and in-situ polymerization for improved fiber graphitic structure and mechanical properties

Carbonaceous nanofillers have been widely used as template additives to strengthen carbon nanofibers (CNFs), while their poor dispersion and insufficient interaction with fiber matrix often limit their optimization roles. Herein, this paper takes functionalized onion-like carbon (fOLC) as an improved nanofiller and provides a bottom-up solution to prepare fOLC-reinforced CNFs. The in-situ polymerization technique is developed to introduce fOLC in polyacrylonitrile (PAN) precursors. Meanwhile, moderate functionalization of the nanofiller is applied to further promote their dispersion and interaction with PAN. On this bases, the nanoscale spherical fOLC can achieve uniform distribution in the fiber matrix without the trouble of shape control, thus having more comprehensive impacts on fiber structures. It is shown that the added fOLC can organize the PAN molecular chains into crystalline nanofibrils in as-spun nanofibers and further promote their graphitization through nucleating and templating effects during annealing. In this case, the dispersed fOLC not only increases nucleation sites to cause grain refinement, but these rigid nanoparticles with well-developed interaction with the fiber matrix can further impede crack propagation through dispersion strengthening. As a result, the tensile strength and elongation at break of CNFs simultaneously increase by up to 65.15 % and 41.25 %, respectively.

A Competitive Study Using Electrospinning and Phase Inversion to Prepare Polymeric Membranes for Oil Removal.

Polyacrylonitrile (PAN) is a popular polymer that can be made into membranes using various techniques, such as electrospinning and phase inversion. Electrospinning is a novel technique that produces nonwoven nanofiber-based membranes with highly tunable properties. In this research, electrospun PAN nanofiber membranes with various concentrations (10, 12, and 14% PAN/dimethylformamide (DMF)) were prepared and compared to PAN cast membranes prepared by the phase inversion technique. All of the prepared membranes were tested for oil removal in a cross-flow filtration system. A comparison between these membranes' surface morphology, topography, wettability, and porosity was presented and analyzed. The results showed that increasing the concentration of the PAN precursor solution increases surface roughness, hydrophilicity, and porosity and, consequently, enhances the membrane performance. However, the PAN cast membranes showed a lower water flux when the precursor solution concentration increased. In general, the electrospun PAN membranes performed better in terms of water flux and oil rejection than the cast PAN membranes. The electrospun 14% PAN/DMF membrane gave a water flux of 250 LMH and a rejection of 97% compared to the cast 14% PAN/DMF membrane, which showed a water flux of 117 LMH and 94% oil rejection. This is mainly because the nanofibrous membrane showed higher porosity, higher hydrophilicity, and higher surface roughness compared to the cast PAN membranes at the same polymer concentration. The porosity of the electrospun PAN membrane was 96%, while it was 58% for the cast 14% PAN/DMF membrane.

Effect of sulfurized polyacrylonitrile-g-rGO composition on the specific capacity and cycling stability of lithium sulfur batteries

Sulfurized polyacrylonitrile (SPAN) is a promising cathode material for the commercialization of lithium-sulfur batteries with extremely stable cycling performance. However, its inherent low sulfur content and poor electrical conductivity severely impairs its electrochemical performance. In this work, we construct a sulfur cathode in the form of a unique bamboo-shaped structured nanofiber, using SPAN as the bamboo stalk and reduced graphene oxide (rGO) as the bamboo joint, thus ensuring that the SPAN has excellent electronic conductivity. Polyacrylonitrile grafted with rGO (PAN-g-rGO) is an effective composite of ultra-high molecular weight PAN (UHMW PAN) and rGO at the molecular level. The UHMW PAN precursor can provide high sulfur loading, and the bamboo joint-like rGO can offer short-range accelerated electron transfer, thus effectively enhancing the electrochemical performance of the battery. Sulfurized PAN-g-rGO fiber (SFPAN-g-rGO) with a sulfur content of approximately 53 wt% is fabricated using PAN-g-rGO with a molecular weight of 3.6 × 105 Da as the precursor. The battery has a high reversible specific capacity (1463 mAh g−1 at 0.2C), excellent C-rate performance (1239 mAh g−1 at 2C), and good cycling stability (guaranteed over 800 cycles). In addition, the electrode offers a high reversible specific capacity of 1383 mAh g−1 at 0.1C and 1280 mAh g−1 at 0.2C when tested under a lean electrolyte (E/S: 10 μL mg−1) and high mass loading (4.8 mg cm−2), thus illustrating its good development potential.

Wet-Spun Porous Carbon Microfibers for Enhanced Electrochemical Detection.

We present a novel copolymer-based, uniform porous carbon microfiber (PCMF) formed via wet-spinning for significantly improved electrochemical detection. Carbon fiber (CF), fabricated from a polyacrylonitrile (PAN) precursor, is commonly used in batteries or for electrochemical detection of neurochemicals due to its biplanar geometry and desirable edge plane sites with high surface free energy and defects for enhanced analyte interactions. Recently, the presence of pores within carbon materials has presented interesting electrochemistry leading to detection improvements; however, there is currently no method to uniformly create pores on a carbon microfiber surface impacting a broad range of electrochemical applications. Here, we synthesized controllable porous carbon fibers from a spinning dope of the copolymers PAN and poly(methyl methacrylate) (PMMA) in dimethylformamide via wet spinning for the first time. PMMA serves as a sacrificial block introducing macropores of increased edge-plane character on the fiber. Methods were optimized to produce porous CFs at similar dimensions to traditional CF. We prove that an increase in porosity enhances the degree of disorder on the surface, resulting in significantly improved detection capabilities with fast-scan cyclic voltammetry. Local trapping of analytes at porous geometries enables electrochemical reversibility with improved sensitivity, linear range of detection, and measurement temporal resolution. Overall, we demonstrate the utility of a copolymer synthetic method for PCMF fabrication, providing a stable, controlled macroporous fiber framework with enhanced edge plane character. This work will significantly advance fundamental investigations of how pores and edge plane sites influence electrochemical detection.

Study on the relationship between ring formation and properties of pre-oxidized polyacrylonitrile-based fibres

The relationship between the degree of ring formation and the overall properties of the pre-oxidized fibre was studied by treating PAN precursor with KClO3/H2SO4 solution and different pre-oxidation techniques. PFs are polar materials and the dielectric constant increases after solution treatment. The bulk density of Cl-MSFs is always higher than that of MSFs and CSFs in the same temperature zone. The bulk density of Cl-MSFs5 is 1.401 g/cm3, which is 1.6% higher than that of MSFs5. The EOR value of Cl-MSFs5 is 0.767, which is 11.97% higher than the value of MSFs5. The modified polyacrylonitrile precursor showed a high degree of cyclization during microwave heat treatment. The temperature can be reduced by about 40 °C by modifying and microwave heat treatment to achieve the same level of cyclization. Cl-MSFs5 has a higher O content than MSFs5. The microscopic morphology shows that the number of "grooves" and fibre diameter of Cl-MSFs5 is significantly smaller than that of MSFs5, indicating that it has a higher degree of stability. There is no Cl element on the surface of Cl-MSFs5, which indicates that the structure of the pre-oxidized fibre is not affected after the pre-oxidation treatment. In addition, the structural transformation of KClO3-modified PFs during microwave pre-oxidation is proposed. The cyclization reaction occurs first, followed by dehydrogenation and oxidation reactions. In the carbon fibre production process, the pre-oxidation stage takes a long time and consumes a lot of energy. The new composite treatment technology used in this study can effectively reduce the treatment temperature and shorten the treatment time in the pre-oxidation stage, which provides a reference for the development of low-cost and efficient pre-oxidation process.

Modification of large tow textile grade polyacrylonitrile fiber by dopamine hydrochloride to prepare low-cost carbon fibers

Owing to high specific strength and modulus, low density, corrosion resistance, etc., polyacrylonitrile (PAN)-based carbon fibers (CFs) have been widely used in aerospace, new energy, sporting goods, and other fields. However, their application in some civil fields is limited due to their high price. Textile grade polyacrylonitrile fiber (TPF) has a structure similar to the PAN precursor of PAN-based CFs and its cost is also comparatively low, which could be expected to replace the PAN precursor in the preparation of low-cost CFs. However, the lack of active groups in the initial copolymer of TPFs leads to rapid cyclization and extremely exothermic reaction in the pre-oxidation process, which further results in the danger of fiber melting and combustion. In the present work, surface impregnation of TPFs in dopamine hydrochloride aqueous solution together with a further ultrasonic treatment were carried out, and successive pre-oxidation and carbonization resulted in the formation of TPF-based CFs. The results showed that the cyclization temperature of modified TPFs decreased significantly and the exothermic peak also widened with the introduction of oxygen anion of dopamine hydrochloride during the pre-oxidation process, and the microstructure characterization detected by FTIR, XRD and Raman confirmed that the functional groups of dopamine hydrochloric were helpful to accelerate the formation of a ladder structure. Owing to the controllable evolution of fiber architectures during the whole heat treatment process, the final tensile strength and tensile modulus of obtained TPF-based CFs were 3.31GPa and 223.80GPa, respectively.

Binder-free Ruthenium Oxide/MXene/Carbon Nanofiber Ternary Composite Electrode for Supercapacitors

Carbon nanofiber-based electrodes are generally embedded with either metal oxides or two-dimensional materials to enhance their specific capacitance and rate performance. For the first time in this study, a flexible carbon nanofiber electrode consisting of metal oxide (RuO2) and two-dimensional MXene was prepared to realize the synergetic effect on the electrochemical performance. This ternary composite electrode was prepared by electrospinning RuO2, and MXene dispersed polyacrylonitrile precursor solution, followed by thermal treatment. The distribution of RuO2 nanoparticles and delaminated MXene sheets within a carbon nanofiber matrix was examined using X-ray diffraction (XRD) and transmission electron microscopy (TEM), while morphological analysis was carried out using scanning electron microscopy (SEM). The electrode with pseudocapacitive RuO2 and layered MXene facilitated charge storage by faradic reactions and intercalation of electrolyte ions. Electrochemical studies demonstrated that the prepared ternary composite electrodes exhibit a specific capacitance of 322 F g−1 with a capacitance retention of 90% after 2500 cycles at 1 A g−1. Additionally, the ternary composite showed an excellent rate capability with a minimal drop in capacitance when the current density was varied from 2 A g−1 to 10 A g−1.

The dispersion of iron nitride among porous carbon fibers to enhance redox conversion for high-performance zinc-iodine batteries

To address the insulating nature and the shuttle effect of iodide species that would deteriorate the battery performance, herein iron nitride is well-dispersed into porous carbon fibers with good flexibility via the facile electrospinning method and subsequent pyrolysis. The polyacrylonitrile precursor introduces the nitrogen doping under thermal treatment while the addition of iron acetylacetonate leads to the in-situ formation of iron nitride among the carbon matrix. The crucial pyrolysis procedure is adjustable to determine the hierarchical porous structure and final composition of the novel carbon fiber composites. As the self-supporting electrode for loading iodine, the zinc-iodine battery exhibits a large specific capacity of 214 mAh/g and good cycling stability over 1600 h. In the combination of in-situ/ex-situ experimental measurements with the theoretical analysis, the in-depth understanding of intrinsic interaction between composited support and iodine species elucidates the essential mechanism to promote the redox kinetics of iodine via the anchoring effect and electrocatalytic conversion, thus improving cycling life and rate performance. Such fundamental principles on the basic redox conversion of iodine species would evoke the rational design of advanced iodine-based electrodes for improving battery performance.