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.
more »
« less
Fabrication and characterization of silicon oxycarbide fibre-mats via electrospinning for high temperature applications
Electrospinning is an emerging technique for synthesizing micron to submicron-sized polymer fibre supports for applications in energy storage, catalysis, filtration, drug delivery and so on. However, fabrication of electrospun ceramic fibre mats for use as a reinforcement phase in ceramic matrix composites or CMCs for aerospace applications remains largely unexplored. This is mainly due to stringent operating requirements that require a combination of properties such as low mass density, high strength, and ultrahigh temperature resistance. Herein we report fabrication of molecular precursor-derived silicon oxycarbide or SiOC fibre mats via electrospinning and pyrolysis of cyclic polysiloxanes-based precursors at significantly lower weight loadings of organic co-spin agent. Ceramic fibre mats, which were free of wrapping, were prepared by a one-step spinning (in air) and post heat-treatment for crosslinking and pyrolysis (in argon at 800 °C). The pyrolyzed fibre mats were revealed to be amorphous and a few microns in diameter. Four siloxane-based pre-ceramic polymers were used to study the influence of precursor molecular structure on the compositional and morphological differences of cross-linked and pyrolyzed products. Further thermal characterization suggested the potential of electrospun ceramic mats in high temperature applications.
more »
« less
- Award ID(s):
- 1743701
- NSF-PAR ID:
- 10214008
- Date Published:
- Journal Name:
- RSC Advances
- Volume:
- 10
- Issue:
- 63
- ISSN:
- 2046-2069
- Page Range / eLocation ID:
- 38446 to 38455
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
Abstract A liquid‐phase polymer‐to‐ceramic approach is reported for the synthesis of hafnium carbide (HfC)/hafnium oxide (HfO2) composite particles from a commercial precursor. Typically, HfC ceramics have been obtained by sintering of fine powders, which usually results in large particle size and high porosity during densification. In this study a single‐source liquid precursor was first cured at low temperature and then pyrolyzed at varying conditions to achieve HfC ceramics. The chemical structure of the liquid and cured precursors, and the resulting HfC ceramics was studied using various analytical techniques. The nuclear magnetic resonance and Fourier transform infrared spectroscopy indicated the presence of partially hydrated hafnium oxychloride (Hf–O–Cl·
n H2O) in the precursor. Scanning electron microscopy of the resulting HfC crystals showed a size distribution in the range of approx. 600–700 nm. The X‐ray diffraction of the pyrolyzed samples confirmed the formation of crystalline HfC along with monoclinic‐HfO2and free carbon phase. The formation of HfO2in the ceramics was significantly reduced by controlling the low‐temperature curing temperature. Pyrolysis at various temperatures showed that HfC formation occurred even at 1000°C. These results show that the reported precursor could be promising for the direct synthesis of ultrahigh temperature HfC ceramics and for precursor infiltration pyrolysis of reinforced ceramic matrix composites. -
In an effort to develop and design next generation high power target materials for particle physics research, the possibility of fabricating nonwoven metallic or ceramic nanofibers by electrospinning process is explored. A low-cost electrospinning unit is set up for in-house production of various ceramic nanofibers. Yttria-stabilized zirconia nanofibers are successfully fabricated by electrospinning a mixture of zirconium carbonate with high-molecular weight polyvinylpyrrolidone polymer solution. Some of the inherent weaknesses of electrospinning process like thickness of nanofiber mat and slow production rate are overcome by modifying certain parts of electrospinning system and their arrangements to get thicker nanofiber mats of millimeter order at a faster rate. Continuous long nanofibers of about hundred nanometers in diameter are produced and subsequently heat treated to get rid of polymer and allow crystallize zirconia. Specimens were prepared to meet certain minimum physical properties such as thickness, structural integrity, thermal stability, and flexibility. An easy innovative technique based on atomic force microscopy was employed for evaluating mechanical properties of single nanofiber, which were found to be comparable to bulk zirconia. Nanofibers were tested for their high-temperature resistance using an electron beam. It showed resistance to radiation damage when irradiated with 1 MeV Kr2+ ion. Some zirconia nanofibers were also tested under high-intensity pulsed proton beam and maintained their structural integrity. This study shows for the first time that a ceramic nanofiber has been tested under different beams and irradiation condition to qualify their physical properties for practical use as accelerator targets. Advantages and challenges of such nanofibers as potential future targets over bulk material targets are discussed.more » « less
-
more » « less
This review is focused on an attractive class of polymer‐derived high‐temperature ceramics, namely, polymer‐derived nonoxide materials. With a brief introduction of high‐temperature nonoxides, the origin of using polycarbosilane (PCS) polymer melt spinning to synthesize silicon carbide (SiC) fibers is traced back. For SiC formation, the four stages for the conversion from polymer precursors to microcrystalline ceramics are examined first: crosslinking, polymer decomposition, ceramic formation, and crystallization. Also, the important parameters related to PCS pyrolysis are explained, and polymer‐derived SiC microstructures and compositions are evaluated. Solid‐solution carbides and transition metal carbides are further reviewed. For boride materials, the discussion is focused on transition metal borides and boride composites. Similar to PCS conversion to SiC, nitride materials mostly start with polycarbosilazane (PSZ) precursors and form into the final materials through pyrolysis. With different carbide and nitride precursors mixed and pyrolyzed together, high‐temperature nonoxide composites are formed. Such molecular‐level intermixing and versatile capability of forming different shapes enable many exciting properties. Among these are mechanical and thermal properties, along with electrical conductivity, electromagnetic shielding, and charge storage capability. An overview of applications of polymer‐derived nonoxides is provided, followed by a summary and outlook.
-
Electrospinning is a versatile approach to generate nanofibers in situ. Yet, recently, wet electrospinning has been introduced as a more efficient way to deposit isolated fibers inside bulk materials. In wet electrospinning, a liquid bath is adopted, instead of a solid collector, for fiber collection. However, despite several studies focused on wet electrospinning to yield polymer composites, few studies have investigated wet electrospinning to yield ceramic composites. In this paper, we propose a novel in-situ fabrication approach for nanofiber-reinforced ceramic composites based on an enhanced wet-electrospinning method. Our method uses electrospinning to draw polymer nanofibers directly into a reactive pre-ceramic gel, which is later activated to yield advanced nanofiber-reinforced ceramic composites. We demonstrate our method by investigating wet electrospun Polyacrylonitrile and Poly(ethylene oxide) fiber-reinforced geopolymer composites, with fiber weight fractions in the range 0.1–1.0 wt%. Wet electrospinning preserves the amorphous structure of geopolymer while changing the molecular arrangement. Wet electrospinning leads to an increase in both the fraction of mesopores and the overall porosity of geopolymer composites. The indentation modulus is in the range 6.76–8.90 GPa and the fracture toughness is in the range 0.49–0.76 MPam with a clear stiffening and toughening effect observed for Poly(ethylene oxide)-reinforced geopolymer composites. This work demonstrates the viability of wet electrospinning to fabricate multifunctional nanofiber-reinforced composites.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d0ra04060f
