Fabrication and characterization of silicon oxycarbide fibre-mats via electrospinning for high temperature applications

C60 Fullerene-Reinforced Silicon Oxycarbide Composite Fiber Mats: Performance as Li-Ion Battery Electrodes

Precursor-derived silicon oxycarbide (SiOC) has emerged as a potential high-capacity anode material for rechargeable Li-ion batteries. The polymer processing and pyrolysis route, a hallmark of polymer-derived ceramics, allows chemical interfacing with a variety of nanoprecursors and nanofiller phases to produce composites with low-dimensional structures such as fibers and coatings not readily attained in traditional sintered ceramics. Here, buckminsterfullerene or C60 was introduced as a filler phase in a hybrid precursor of 1,3,5,7-tetramethyl-1,3,5,7-tetravinyl-cyclotetrasiloxane (TTCS) along with polyvinylpyrrolidone or PVP as a spinning agent to fabricate electrospun fiber mats, which upon a high-heat treatment transformed to a C60-reinforced SiOC ceramic composite. Tested as the self-supporting working electrode in a Li-ion half-cell, C60-reinforced fiber mats show a much-improved reversible capacity (825 mA h g-1), nearly 100% Coulombic efficiency, and superior rate capability with low-capacity decay at high currents (only 25.5% decay at 800 mA g-1) compared to neat C60 and neat carbonized fiber electrodes.

Novel multifibrillar carbon and oxidation-stable carbon/ceramic hybrid fibers consisting of thousands of individual nanofibers with high tensile strength

In this study, multifibrillar carbon and carbon/ceramic (C/SiCON) fibers consisting of thousands of single nanofibers are continuously manufactured. The process starts with electrospinning of polyacrylonitrile (PAN) and PAN/oligosilazane precursors resulting in poorly aligned polymer fibers. Subsequent stretching leads to parallel aligned multifibrillar fibers, which are continuously stabilized and pyrolyzed to C or C/SiCON hybrid fibers. The multifibrillar carbon fibers show a high tensile strength of 911 MPa and Young's modulus of 154 GPa, whereas the multifibrillar C/SiCON fibers initially have only tensile strengths of 407 MPa and Young's modulus of 77 GPa, due to sticking of the nanofibers during the stabilization in air. Additional curing with electron beam radiation, results in a remarkable increase in tensile strength of 707 MPa and Young's modulus of 98 GPa. The good mechanical properties are highlighted by the low linear density of the multifibrillar C/SiCON fibers (~ 1 tex) compared to conventional C and SiC fiber bundles (~ 200 tex). In combination with the large surface area of the fibers better mechanical properties of respective composites with a reduced fiber content can be achieved. In addition, the developed approach offers high potential to produce advanced endless multifibrillar carbon and C/SiCON nanofibers in an industrial scale.

Development of hybrid electrospun alginate-pulverized moringa composites

The consideration of biopolymers with natural products offers promising and effective materials with intrinsic and extrinsic properties that are utilized in several applications. Electrospinning is a method known for its unique and efficient performance in developing polymer-based nanofibers with tunable and diverse properties presented as good surface area, morphology, porosity, and fiber diameters during fabrication. In this work, we have developed an electrospun sodium alginate (SA) incorporated with pulverized Moringa oleifera seed powder (PMO) as a potential natural biosorbent material for water treatment applications. The developed fibers when observed using a scanning electron microscope (SEM), presented pure sodium alginate with smooth fiber (SAF) characteristics of an average diameter of about 515.09 nm (±114.33). Addition of pulverized Moringa oleifera at 0.5%, 2%, 4%, 6%, and 8% (w/w) reduces the fiber diameter to an average of about 240 nm with a few spindle-like pulverized Moringa oleifera particles beads of 300 nm (±77.97) 0.5% particle size and 110 nm (±32.19) with the clear observation of rougher spindle-like pulverized Moringa oleifera particle beads of 680 nm (±131.77) at 8% of alginate/Moringa oleifera fiber (AMF). The results from the rheology presented characteristic shear-thinning or pseudoplastic behaviour with a decline in viscosity, with characteristic behaviour as the shear rate increases, indicative of an ideal polymer solution suitable for the spinning process. Fourier transform infrared spectroscopy (FT-IR) shows the presence of amine and amide functional groups are prevalent on the alginate-impregnated moringa with water stability nanofibers and thermogravimetric analysis (TGA) with change in degradation properties in a clear indication and successful incorporation of the Moringa oleifera in the electrospun fiber. The key findings from this study position nanofibers as sustainable composites fiber for potential applications in water treatment, especifically heavy metal adsorption.

New insights into the electrochemical performance of precursor derived Si(Nb)OC composites as anode materials for batteries

This work represents a first attempt to synthesize Si(Nb)OC ceramic composites through the polymer pyrolysis or the precursor-derived ceramics (PDC) route for use as a hybrid anode material for lithium-ion batteries (LIB). Electron microscopy, X-ray diffraction, and various spectroscopy techniques were used to examine the micro/nano structural features and phase evolution during cross-linking, pyrolysis, and annealing stages. During the polymer-to-ceramic transformation process, in situ formation of carbon (so-called "free carbon"), and crystallization of t-NbO2, NbC phases in the amorphous Si(Nb)OC ceramic matrix are identified. The first-cycle reversible capacities of 431 mA h g-1 and 256 mA h g-1 for the as-pyrolyzed and annealed Si(Nb)OC electrodes, respectively, exceeded the theoretical Li capacity of niobium pentaoxide or m-Nb2O5 (at approximately 220 mA h g-1). With an average reversible capacity of 200 mA h g-1 and close to 100% cycling efficiency, as-pyrolyzed Si(Nb)OC demonstrates good rate capability. X-ray amorphous SiOC with uniformly distributed nanosized Nb2O5 and graphitic carbon structure likely provides stability during repeated Li+ cycling and the formation of a stable secondary electrolyte interphase (SEI) layer, leading to high efficiency.

High Toughness Combined with High Strength in Oxide Ceramic Nanofibers

Traditional oxide ceramics are inherently brittle and highly sensitive to defects, making them vulnerable to failure under external stress. As such, endowing these materials with high strength and high toughness simultaneously is crucial to improve their performance in most safety-critical applications. Fibrillation of the ceramic materials and further refinement of the fiber diameter, as realized by electrospinning, are expected to achieve the transformation from brittleness to flexibility owing to the structural uniqueness. Currently, the synthesis of electrospun oxide ceramic nanofibers must rely on an organic polymer template to regulate the spinnability of the inorganic sol, whose thermal decomposition during ceramization will inevitably lead to pore defects, and seriously weaken the mechanical properties of the final nanofibers. Here, a self-templated electrospinning strategy is proposed for the formation of oxide ceramic nanofibers without adding any organic polymer template. An example is given to show that individual silica nanofibers have an ideally homogeneous, dense, and defect-free structure, with tensile strength as high as 1.41 GPa and toughness up to 34.29 MJ m-3 , both of which are far superior to the counterparts prepared by polymer-templated electrospinning. This work provides a new strategy to develop oxide ceramic materials that are strong and tough.

WS2 Nanotube-Embedded SiOC Fibermat Electrodes for Sodium-Ion Batteries

Layered transition metal dichalcogenides (TMDs) such as tungsten disulfide (WS₂) are promising materials for a wide range of applications, including charge storage in batteries and supercapacitors. Nevertheless, TMD-based electrodes suffer from bottlenecks such as capacity fading at high current densities, voltage hysteresis during the conversion reaction, and polysulfide dissolution. To tame such adverse phenomena, we fabricate composites with WS₂ nanotubes. Herein, we report on the superior electrochemical performance of ceramic composite fibers comprising WS₂ nanotubes (WS₂NTs) embedded in a chemically robust molecular polymer-derived ceramic matrix of silicon-oxycarbide (SiOC). Such a heterogeneous fiber structure was obtained via electrospinning of WS₂NT/preceramic polymer solution followed by pyrolysis at elevated temperatures. The electrode capacity fading in WS₂NTs was curbed by the synergistic effect between WS₂NT and SiOC. As a result, the composite electrode exhibits high initial capacity of 454 mAh g^-1 and the capacity retention approximately 2-3 times higher than that of the neat WS₂NT electrode.

Approaches to Preceramic Polymer Fiber Fabrication and On-Demand Applications

The demand for lightweight, high-modulus, and temperature-resistant materials for aerospace and other high-temperature applications has contributed to the development of ceramic fibers that exhibit most of the favorable properties of monolithic ceramics. This review demonstrates preceramic-based polymer fiber spinning and fiber classifications. We discuss different types of fiber spinning and the advantages of each. Tuning the preceramic polymer chemical properties, molar mass, functional chemistry influences, and incorporation with fillers are thoroughly investigated. Further, we present the applications of preceramic-based polymer fibers in different fields including aerospace, biomedical, and sensor applications. This concise review summarizes recent developments in preceramic fiber chemistry and essential applications.

Enhanced Li-Ion Rate Capability and Stable Efficiency Enabled by MoSe2 Nanosheets in Polymer-Derived Silicon Oxycarbide Fiber Electrodes

Transition metal dichalcogenides (TMDs) such as MoSe2 have continued to generate interest in the engineering community because of their unique layered morphology-the strong in-plane chemical bonding between transition metal atoms sandwiched between two chalcogen atoms and the weak physical attraction between adjacent TMD layers provides them with not only chemical versatility but also a range of electronic, optical, and chemical properties that can be unlocked upon exfoliation into individual TMD layers. Such a layered morphology is particularly suitable for ion intercalation as well as for conversion chemistry with alkali metal ions for electrochemical energy storage applications. Nonetheless, host of issues including fast capacity decay arising due to volume changes and from TMD's degradation reaction with electrolyte at low discharge potentials have restricted use in commercial batteries. One approach to overcome barriers associated with TMDs' chemical stability functionalization of TMD surfaces by chemically robust precursor-derived ceramics or PDC materials, such as silicon oxycarbide (SiOC). SiOC-functionalized TMDs have shown to curb capacity degradation in TMD and improve long term cycling as Li-ion battery (LIBs) electrodes. Herein, we report synthesis of such a composite in which MoSe2 nanosheets are in SiOC matrix in a self-standing fiber mat configuration. This was achieved via electrospinning of TMD nanosheets suspended in pre-ceramic polymer followed by high temperature pyrolysis. Morphology and chemical composition of synthesized material was established by use of electron microscopy and spectroscopic technique. When tested as LIB electrode, the SiOC/MoSe2 fiber mats showed improved cycling stability over neat MoSe2 and neat SiOC electrodes. The freestanding composite electrode delivered a high charge capacity of 586 mAh g-1electrode with an initial coulombic efficiency of 58%. The composite electrode also showed good cycling stability over SiOC fiber mat electrode for over 100 cycles.

Self-supporting carbon-rich SiOC ceramic electrodes for lithium-ion batteries and aqueous supercapacitors

Fabrication of precursor-derived ceramic fibers as electrodes for energy storage applications remains largely unexplored. Within this work, three little known polymer-derived ceramic (PDC)-based fibers are being studied systemically as potential high-capacity electrode materials for electrochemical energy devices. We report fabrication of precursor-derived SiOC fibermats via one-step spinning from various compositions of siloxane oligomers followed by stabilization and pyrolysis at 800 °C. Electron microscopy, Raman, FTIR, XPS, and NMR spectroscopies reveal transformation from polymer to ceramic stages of the various SiOC ceramic fibers. The ceramic samples are a few microns in diameter with a free carbon phase embedded in the amorphous Si–O–C structure. The free carbon phase improves the electronic conductivity and provides major sites for ion storage, whereas the Si–O–C structure contributes to high efficiency. The self-standing electrodes in lithium-ion battery half-cells deliver a charge capacity of 866 mA h g_electrode⁻¹ with a high initial coulombic efficiency of 72%. As supercapacitor electrode, SiOC fibers maintain 100% capacitance over 5000 cycles at a current density of 3 A g⁻¹.

Fabrication of precursor-derived ceramic fibers as electrodes for energy storage applications remains largely unexplored.