Free-standing Fiber Research Articles

A one-pot strategy for modifying the surface of Ti3C2Tx MXene

Surface modification of MXenes significantly expands their potential for a wide range of applications. Here, we demonstrate a one-pot spontaneous polymerization of acrylic acid onto MXene sheet surfaces using an aryl diazonium coupling agent (nitrobenzene diazonium salt) as an approach to tune MXene interfacial properties. We use this formation of polymer coatings as a coagulation strategy for spinning fibers from liquid crystal MXene dispersions, obtaining densified free-standing fibers with tensile strength and breaking energy of ~155 MPa and ~4.5 MJ m−3. This simple method potentially offers a scalable approach for fabricating functional MXene macroarchitectures.

Roller-like Spore Carbon Sphere-Orientated Graphene Fibers Prepared via Rheological Engineering for Lithium Sulfur Batteries.

Flexible batteries with large energy densities, lightweight nature, and high mechanical strength are considered as an eager goal for portable electronics. Herein, we first propose free-standing graphene fiber electrodes containing roller-like orientated spore carbon spheres via rheological engineering. With the help of the orientated microfluidic cospinning technology and the plasma reduction method, spore carbon spheres are self-assembled and orientedly dispersed into numerous graphene flakes, forming graphene fiber electrodes enriched with internal rolling woven structures, which cannot only enhance the electrical contact between active materials but also effectively improve the mechanical strength and structure stability of graphene fiber electrodes. When the designed graphene fibers are combined with the active sulfur cathode and lithium metal anode, the assembled flexible lithium sulfur batteries possess superior electrochemical performance with high capacity (>1000 mA h g-1) and excellent cycling life as well as good mechanical properties. According to density functional theory and COMSOL simulations, the roller-like spore carbon sphere-orientated graphene fiber hosts provide reinforced trapping-catalytic-conversion behavior to soluble polysulfides and nucleation active sites to lithium metal, thus synergistically suppressing the shuttle effect of polysulfides at the cathode side and lithium dendrite growth at the anode side, thereby boosting the whole electrochemical properties of lithium sulfur batteries.

SWCNT fibers decorated with Au nanoparticles as voltammetric sensors for arsenic (III) determination

We developed a new method to produce fiber electrodes from single-walled carbon nanotube (SWCNT) films, which can be employed as a novel sensing platform for electrochemical investigations and analysis. By assembling SWCNT bundles in the form of a strong free-standing fiber with almost entire surface accessible to an analyte, we are able to avoid the interference of substrate and improve detection efficiency. We examined the influence of physical, chemical and electrochemical pretreatments of the new electrode SWCNT material on its properties. Transmission and scanning electron microscopy, Raman spectroscopy and cyclic voltammetry were used to characterize the SWCNT fibers. The modification of the SWCNT fiber electrode with gold nanoparticles provides the necessary analytical characteristics including high repeatability and sensitivity and low detection limit (1.3 – 2.1 μg L-1) for arsenic determination by anodic stripping voltammetry. Arsenic detection parameters such as deposition potential, deposition time and scan rate were optimized. Linear responses were found in concentration ranges from 3 to 210 μg L-1 and 7 to 125 μg L-1 for gold modified SWCNT fiber sensors (the SWCNTs were synthesized using CO or ethanol as precursors) at a relatively low deposition time of 60 s. The developed Au-SWCNT sensors allow rapid As determination in real samples and exhibit high durability and long service life.

Soft, Multifunctional MXene-Coated Fiber Microelectrodes for Biointerfacing.

Flexible fiber-based microelectrodes allow safe and chronic investigation and modulation of electrically active cells and tissues. Compared to planar electrodes, they enhance targeting precision while minimizing side effects from the device-tissue mechanical mismatch. However, the current manufacturing methods face scalability, reproducibility, and handling challenges, hindering large-scale deployment. Furthermore, only a few designs can record electrical and biochemical signals necessary for understanding and interacting with complex biological systems. In this study, we present a method that utilizes the electrical conductivity and easy processability of MXenes, a diverse family of two-dimensional nanomaterials, to apply a thin layer of MXene coating continuously to commercial nylon filaments (30-300 μm in diameter) at a rapid speed (up to 15 mm/s), achieving a linear resistance below 10 Ω/cm. The MXene-coated filaments are then batch-processed into free-standing fiber microelectrodes with excellent flexibility, durability, and consistent performance even when knotted. We demonstrate the electrochemical properties of these fiber electrodes and their hydrogen peroxide (H2O2) sensing capability and showcase their applications in vivo (rodent) and ex vivo (bladder tissue). This scalable process fabricates high-performance microfiber electrodes that can be easily customized and deployed in diverse bioelectronic monitoring and stimulation studies, contributing to a deeper understanding of health and disease.

Enhancing reaction kinetics in aprotic magnesium-air batteries using a freestanding flexible metal-free carbon fiber cathode

Metal-air batteries hold great promises for future energy storage, driven by their impressive energy density. However, practical applications encounter challenges due to the sluggish kinetics of oxygen reduction and evolution reactions taking place at cathode interface, particularly in demanding conditions such as high-current density and open-air scenarios. Addressing these challenges requires cathodes with high reactivity and optimized structure to efficiently facilitate electrochemical reactions. This necessitates the development of self-supporting cathodes that eliminate the current electrode fabrication process, which can lead to binder-induced blockage of reactive sites and reduce energy density due to heavy current collectors. Here, we propose an effective strategy to design freestanding cathodes with high reactivity and a well-designed hierarchical pore structure. This cathode significantly enhances battery reaction kinetics while accommodating insoluble discharge products and preserving air and electrolyte transport pathways for high-performance Mg-air batteries. The freestanding flexible metal-free carbon fiber cathode (E-CNFs) enables a Mg-air battery operating in an open-air condition to exhibit an ultralow overvoltage of 0.4 V as well as delivered a long-term lifetime of 280 h. As a result, an impressive full discharge capacity of 5772 mAh/g under a current density of 800 mA g−1 is achieved, surpassing those in all previously reported Mg-O2/air batteries.

Encapsulation hierarchical bimetallic oxide with flexible electrospinning carbon nanofibers for efficient capacitive deionization

Water scarcity, an intensifying issue, has spurred extensive research into the development of sophisticated freestanding pseudocapacitive electrode materials. Characterized by their precise morphology, intricate mechanics, and superior desalination capabilities, these materials are revolutionizing water treatment technologies. However, their broad adoption is hampered by complex fabrication processes and the necessity for various unique components. Herein, the paper introduces a streamlined method combining electrospinning and carbonization to produce a freestanding nitrogen-doped carbon nanofiber encapsulating manganese cobalt oxide (MCO) nanoparticles for desalination purposes. The approach significantly enhances interfacial interactions, mitigates volume shifts during sodium ion adsorption and desorption, and strengthens interfacial stability. Benefiting from its structural and compositional merits, the optimal MCO-1.0 electrode showcases exceptional electrochemical attributes. It achieves an impressive desalination efficiency (34.68 mg g−1), swift capacitive deionization rate (0.58 mg g−1 min−1), and superior cyclic durability. The study enhances our understanding of freestanding carbon fibers encapsulated with metal oxide nanoparticles, a key step toward developing robust electrodes for industrial applications.

Development of a new class of stable and adaptable free-standing fibre mats with high room-temperature hydroxide-ion conductivity

For alkaline anion-exchange membrane electrolysers and fuel cells to become a technological reality, hydroxide-ion (OH−) conducting membranes that are flexible, robust, affording high OH− conductivity, and synthesised in a low-cost and scalable way must be developed. In this paper, we engineer a stable, self-supporting, and flexible fibre mat using a low-cost ZIF-8 metal–organic framework composited with ionic liquid tetrabutylammonium hydroxide and widely used polyacrylonitrile as polymeric backbone. We obtain mats with a high intrinsic OH− conductivity for a metal–organic framework-based material already at room temperature, without added ion-conductor polymers. This approach will contribute to the development of low-cost and tuneable ion-conducting membranes.

Engineering free-standing electrospun PLLCL fibers on microfluidic platform for cell alignment

Here, a PLLCL-on-chip platform was developed by direct electrospinning of poly (L-lactide-co-ε-caprolactone) (PLLCL) on polymethyl methacrylate (PMMA) microfluidic chips. Designed microchip provides the electrospinning of free-standing aligned PLLCL fibers which eliminates limitations of conventional electrospinning. Besides, aligned fiber structure favors cell alignment through contactless manipulation. Average fiber diameter, and fiber alignment was evaluated by SEM analyses, then, leakage profile of microchip was investigated. 3D cell culture studies were conducted using HeLa and NIH-3T3 cells, and nearly 85% cell viability was observed in PLLCL-on-chip for 15 days, while cell viability of 2D control started to decrease after 7 days based on Live dead and Alamar Blue analyses. These findings emphasize biocompatibility of PLLCL-on-chip platform for 3D cell culture and its ability to mimic extracellular matrix (ECM). Immunostaining results prove that PLLCL-on-chip platform favors the secretion of ECM proteins compared to control groups, and cytoskeletons of cells were in aligned orientation in PLLCL-on-chip, while they were in random orientation in control groups. Overall, these results demonstrate that the developed platform is suitable for the formation of various 3D cell culture models and a potential candidate for cell alignment studies.Graphical

Support effect and confinement effect of porous carbon loaded tin dioxide nanoparticles in high-performance CO2 electroreduction towards formate

Leveraging the interplay between the metal component and the supporting material represents a cornerstone strategy for augmenting electrocatalytic efficiency, e.g., electrocatalytic CO2 reduction reaction (CO2RR). Herein, we employ freestanding porous carbon fibers (PCNF) as an efficacious and stable support for the uniformly distributed SnO2 nanoparticles (SnO2PCNF), thereby capitalizing on the synergistic support effect that arises from their strong interaction. On one hand, the interaction between the SnO2 nanoparticles and the carbon support optimizes the electronic configuration of the active centers. This interaction leads to a noteworthy shift of the d-band center toward stronger intermediate adsorption energy, consequently lowering the energy barrier associated with CO2 reduction. As a result, the SnO2PCNF realizes a remarkable CO2RR performance with excellent selectivity towards formate (98.1 %). On the other hand, the porous carbon fibers enable the uniform and stable dispersion of SnO2 nanoparticles, and this superior porous structure of carbon supports can also facilitate the exposure of the SnO2 nanoparticles on the reaction interface to a great extent. Consequently, adequate contact between active sites, reactants, and electrolytes can significantly increase the metal utilization, eventually bringing forth a remarkable 7.09 A/mg mass activity. This work might provide a useful idea for improving the utilization rate of metals in numerous electrocatalytic reactions.

Rutile titanium dioxide and graphene-like OCN tailoring free-standing carbon fiber aerogel as polysulfide anchoring materials for lithium–sulfur batteries

The rational design of a host material with strong adsorption and excellent electrical conductivity function for sulfur cathode to suppress the shuttle effects of soluble lithium polysulfide (LiPS) is crucial to advance the lithium–sulfur (Li–S) battery for future commercial applications. In this work, we designed a three-dimensional (3D) carbon fiber aerogel with graphene-like oxygenated carbon nitrogen (OCN) and TiO2 (OCNF–TiO2) as a sulfur anchoring material for Li–S battery and explored the regulating effects of TiO2 on the electrochemical performances. The OCNF–TiO2/S cathode presents an initial discharge-specific capacity of 1039 mAh/g (0.1C), a rate capacity of 690 mAh/g at 1C, a cycling performance with a capacitance retention of 72.1%, and the decay of 0.13% per cycle after 200 cycles at 0.5C.

Free-standing cross-linked hollow carbonaceous nanovesicle fibers with atomically dispersed CoN4 electrocatalytic centers driving high-performance Li-S battery

Atomically distributed CoN4 moieties within free-standing cross-linked hollow carbonaceous nanovesicle fibers (CoNCNF) are fabricated by electrostatic spinning following with thermal treatment. The conductive hollow carbonaceous nanovesicles are favorable for storage of electrolytes and fast transmission of electrons. The CoN4 sites of CoNCNF film provide high-efficiency electrocatalytic sites for approving lithium polysulfides capture and fast kinetic transformation suppressing the shuttle effect. Using as cathode-separator interlayer, the CoNCNF-based Li-S battery presents a high initial capacity of 1023.9 mAh g−1 and an ideal capacity of 746.2 mAh g−1 maintains after 1000 cycles at 1 C. Interestingly, it easily performs 5000 cycles at a low decay rate of 0.016% at 2 C. Even at a high current density of 5 C, it provides an excellent capacity of 812.6 mAh g−1. Surprisingly, it has a very high areal capacity of 10.7 mAh cm−2 when the cathode S mass loading is up to 12.5 mg cm−2.

Additively manufactured characteristics of carbon fibers deposited from alkane precursors

Laser Chemical Vapor Deposition (LCVD) is an additive processing technique in which freestanding fibers are deposited. This is accomplished by the thermal dissociation of a precursor gas under a translating laser focal point. In this study the relationships between deposited carbon fiber growth regimes based on precursor chemistry, microstructure, mechanical properties, and processing conditions are compared. The precursor gases include gases from the alkane family, i.e., methane (CH4), ethane (C2H6), and propane (C3H8) and the alkene family, i.e., ethylene (C2H4). Each of these gases offer differences in molecular geometry, the amount of carbon and hydrogen present per molecule, and molecular weight. In the hyperbaric growth condition, these variances reveal different abilities to access either the surface-reaction kinetic limited or mass transport limited growth regimes. The deposited fibers morphology revealed either a core shell or nodular structure with each of these morphologies a function of the accessible growth regime. The fracture stress for the different fibers, in each of the accessible growth regimes, are compared revealing a strength dependence that is linked to the extent of graphitization (via Raman spectroscopy characterization). Collectively, these outcomes fundamentally address how precursor chemistry is a critical variable in the manipulation of the processing-structure-property space in LCVD carbon fibers.

Freestanding fibers assembled by CoPSe@N-doped carbon heterostructures as an anode for fast potassium storage in hybrid capacitors

Although the fast development of potassium-ion hybrid capacitors (PIHC) recently, the issues such as the slow kinetics and poor durability of potassium ion hosts greatly restric their applications. Herein, a freestanding fiber (NHF fiber) with necklace-like configuration and CoPSe@N-doped carbon (CoPSe@NCNT) heterostructured units is introduced as the anode in PIHC. The highly porous network of NHF fiber facilitates the fast ion transports and promises the good high-rate property. Additionally, the nanoscle crystallites inside in-situ grown NCNT favor the high adaption to volume expansion/shrinkage and endow good structure stability during ion insertion/deinsertion. Density function theoretical (DFT) calculations disclose the CoPSe@NCNT heterostructure has improved intrinsic conductivity, fast potassium migration, and decreased energy barrier. Meanwhile, the finite element simulation analysis (FEA) reveals the decreased stress inside the NHF architecture during charge/discharge processes. Moreover, the electrochemical tests confirm the fast and durable properties of the CoPSe@NCNT NHF fibers for potassium storage. Furthermore, the PIHC full cell with the anode of CoPSe@NCNT NHF fiber is assembled, which obtains the superior energy/power densities and high capacity retention (89%) after 2000 cycles at 2 A g−1. When the polymer electrolyte is incooperated, the flexible PIHC device achieves the good pliability and good adaptation during wide temperature changes from −20 to 25 °C. Therefore, this work introduces a novel anode for fast potassium ion storage, and opens a new approach to assemble the power sources for flexible electronics in diverse conditions.

Biomimetic Spun Silk Ionotronic Fibers for Intelligent Discrimination of Motions and Tactile Stimuli.

Innovation in the ionotronics field has significantly accelerated the development of ultraflexible devices and machines. However, it is still challenging to develop efficient ionotronic-based fibers with necessary stretchability, resilience, and conductivity due to inherent conflict in producing spinning dopes with both high polymer and ion concentrations and low viscosities. Inspired by the liquid crystalline spinning of animal silk, this study circumvents the inherent tradeoff in other spinning methods by dry spinning a nematic silk microfibril dope solution. The liquid crystalline texture allows the spinning dope to flow through the spinneret and form free-standing fibers under minimal external forces. The resultant silk-sourced ionotronic fibers (SSIFs) are highly stretchable, tough, resilient, and fatigue-resistant. These mechanical advantages ensure a rapid and recoverable electromechanical response of SSIFs to kinematic deformations. Further, the incorporation of SSIFs into core-shell triboelectric nanogenerator fibers provides outstanding stable and sensitive triboelectric response to precisely and sensitively perceive small pressures. Moreover, by implementing a combination of machine learning and Internet of Things techniques, the SSIFs can sort objects made of different materials. With these structural, processing, performance, and functional merits, the SSIFs prepared herein are expected to be applied in human-machine interfaces.

Photonic hydrogel for continuous glucose monitoring using smartphone readout

Diabetes has become one of the leading deaths causes worldwide. Developing low-cost, rapid, and reusable sensors can provide a solution for continuous glucose monitoring to reduce the diabetic complications that could be fatal. Here, Phenylboronic acid (PBA)-based hydrogel sensors with embedded photonic nanostructures were developed for rapid and continuous glucose quantification within the physiological range. The photonic nanostructures were imprinted on the PBA-based hydrogel using simple and rapid process. Three different sensors: free-standing (FS), stand-alone (SA), and optical fiber (OF) were fabricated and tested in the glucose concentration range of 0–50 mM. A sensitivity of 6, 3, and 1.2 µW/mM was documented for FS, SA, and OF sensors, respectively. A rapid response time of 20 s and saturation time of 3 min were recorded along with a limit of detection of 1 mM. The sensing capabilities of these sensors were examined in both transmission and reflection configurations. Practicality of the sensors was tested using smartphone readout. The optical power was measured using a smartphone exploiting its photodiode and the power changes were correlated with glucose concentrations. These developed sensors may have applications in remote, continuous, and real-time glucose monitoring systems.

Free-standing N-doped hollow carbon fiber encapsulate P/GeP hybrid anode for rechargeable Li-ion battery

Red phosphorus (RP) with appropriate working voltage and high lithium storage specific capacity has been considered as high-performance anode for Li-ion battery (LiB). However, the volume expansion of the RP anode reached 350 % during the intercalation/deintercalation of Li-ion processes, resulting in the detachment of active material and poor specific capacity. Herein, flexible hollow nanochannel carbon nanofiber was prepared through simple electrospinning, then P/GeP nano powder were encapsulated in the N-rich carbon nanofiber using a facile in situ synthesis method, where the introduction of GeP not only innovatively served as the high conductive dispersant for P, but simultaneously acted as the active component in reacting with Li-ion. The unique designed nanoarchitecture not only boosted the structural stability and electronic conductivity of the hybrid composite, but also facilitated the transport of electrons and Li-ion. Upon served as free-standing LiB anode, the N-doped hollow carbon fiber encapsulate P/GeP (P/GeP/C) anode displayed remarkably reversible capacities, superior rate performances, and long-term cycle stability for lithium storage. For instance, P/GeP/C of only 10.6 wt% GeP and 28.5 wt% P delivered 290.2 mA h g−1 under a high current density of 5 A g−1 and showed a high capacity of 575.6 and 436.9 mA h g−1 at a current density of 0.1 A g−1 and 1.0 A g−1 after 50 cycles, respectively.

Electrochemical performance of SiCN embedded carbon (SiCN–C) fiber mat electrodes for lithium-ion battery: Electrospinning polysilazane in air or protective atmosphere

Here polysilazane/polyacrylonitrile fiber mats were manufactured by electrospinning in air or protective atmosphere. After pyrolysis, SiCN embedded carbon (SiCN–C) was tested as lithium-ion battery (LIB) electrode. Fibers electrospun in nitrogen are found to be thinner due to the slower solidification of the flying jet. XPS analysis confirmed that fibers electrospun in air incorporated a great oxygen content during shaping. The highest charge capacity of 773 mA h g−1 at 50 mA g−1 was recovered for SiCN–C electrospun in air. Oxygen increased the capacity due to its high character to attract Li+ ions, but SiCN–C electrospun in air suffered voltage hysteresis. Contrariwise, the SiCN–C electrospun in nitrogen demonstrated stable cycling with a charge capacity of 299 mA h g−1 and 98% recovery of the initial capacity due to enhanced free carbon content. These findings make electrospinning very promising for the highly controlled production of freestanding SiCN fiber mat electrodes.

Fabrication and application of free-standing fiber based on blue phase liquid crystal.

The application of blue phase liquid crystals (BPLCs) in optical control devices has been widely studied due to their fast response characteristics. However, the fabrication of free-standing BPLC fiber with emerging functionalities is challenging. Here, we demonstrate a free-standing fiber based on BPLC with excellent stability, flexibility, and multifunction. The multi-mode fiber (MMF) end face is etched by the etching agent of buffered oxide etch (BOE), which can be fixedly connected with the free-standing BPLC fiber after polymerization in order to overcome the problems of optical signals transmission and reception. Three types of free-standing BPLC fiber-based devices, including Volatile Organic Compound (VOC) vapor sensors, vector position sensors, and color fibers, are fabricated and investigated, to the best of our knowledge, for the first time. The free-standing BPLC fiber as a multifunctional material will provide broad application prospects in VOC sensors without power supply, smart fabrics, flexible displays, decorations fields with no dyes, as well as vector displacement sensors for robotic arm positioning.

Design of free-standing porous carbon fibers anode with high-efficiency potassium-ion storage

Designing porous structures is emerging as a promising approach to prominently improve the potassium storage performance of carbonaceous materials. In this work, we design free-standing porous carbon fibers (PCF) by electrospinning for highly potassium-ion storage. With the introduction of Zn in the electrospinning precursor, the PCF was obtained after the evaporation of Zn during the heat treatment. After bending and folding, the free-standing PCF also presents excellent flexibility. As the free-standing anode for potassium-ion battery (KIB), it is found that the PCF presents an enhanced potassium-ion storage performance with a reversible specific capacity of 256 mAh/g after 80 cycles at 50 mA g−1. Even at the current density of 1 A/g, our PCF still remains a high reversible specific capacity of 149 mAh/g after 3300 cycles for KIBs. According to the density functional theory calculation and finite element analysis, we find that K-ions can also inset into the carbon layer during the fully potassiation state for the porous structure of PCF. In addition, due to the strong adsorption characteristics of K-ions, the porous structure of porous carbon fibers also can accommodate K-clusters in the pore defects. The common effects of the K-intercalation and K cluster contribute to the improvement of the K-ion storage performance of porous carbon fibers.

Orientation of the microstructure of free-standing carbon hollow fiber membranes modulated by carbonization condition triggers aging-resistant properties

The aim of this study is to determine the optimal carbonization conditions for carbon hollow fiber membranes for hydrogen purification. To this end, it is a prerequisite to obtain the best permselectivity of the resultant membrane. Three different carbonization atmospheres (vacuum, helium flow, and argon flow) were examined, while their effects on the changes in the microstructure and gas permeation properties of the as-synthesized carbon membranes were elucidated using a pure gas permeation test, coupled with an array of characterizations, including Raman spectroscopy and XPS. Moreover, the issue of vacuum degree was addressed to maintain the best reproducibility of the carbon membrane. The results revealed that CHFM-HV exhibited the best separation capability for H2/CH4 of 516.90, thereby indicating distinct hydrogen purification characteristics. Such good performance was driven by the attractive synergism of the ordered microstructure and larger pore volume. Notably, the recovery of permselectivity for CHFM-HV reached 90% after four months, thus suggesting its aging resistance. Hence, the demonstrated approach is efficient for altering the microstructure of the carbon membrane, thereby strengthening the separation performance and long-term stability. Overall, it is suitable for broad applications of diverse polymer precursors and prolonged the lifespan of the as-prepared carbon membrane.