Porous Silicon Oxycarbide Research Articles

Hierarchical porous silicon oxycarbide as a stable anode material for lithium-ion batteries

The porous and amorphous silicon oxycarbides (SiOC) derived from polymer precursors are regarded as promising anode materials for lithium-ion batteries due to their high theoretical capacity and minimal volume expansion. Modulations of carbon nanoclusters and reversible species in Si-O-C units have been performed to improve lithium storage properties of SiOC anodes. Herein, we report the effects of pore structure on cycling stability and rate performance of SiOC anode materials, which are prepared by a sol-gel approach using different additions of solvents and a subsequent calcination. The increase in the solvent addition promotes the formation of macropores in the hierarchical porous structure of the SiOC, thereby facilitating rapid Li ion migration and mitigating volume expansion during the lithiation of the SiOC. The as-prepared SiOC anode exhibits competitive reversible capacities of 750.4 mAh g−1 at 0.1 A g−1 after 150 cycles and 437.1 mAh g−1 at 1 A g−1 after 500 cycles, compared to those of previously reported SiOC anodes. This work provides a new strategy for designing of high-capacity and high-stability SiOC anode materials.

Adsorption of CO2 on mechanochemically synthesized silicon oxycarbide composites

The present study explores the mechanochemical synthesis of porous silicon oxycarbide composites using commercial activated carbon and hydrated silica as precursors without additional functionalization, aiming to be used as effective adsorbents for carbon dioxide removal from gas streams. By adjusting the hydrated silica/activated carbon mass ratio, a set of materials were prepared with varying surface areas (256–662 m2/g), pore volumes (0.28–0.45 cm3/g), and surface functional groups concentrations (0.824–0.996 mmol/g). The optimal silicon oxycarbide composite (hydrated silica/activated carbon mass ratio of 1.5) demonstrated the CO2 adsorption capacity of 3.41 mmol/g at 25 °C and 1 bar, which can be attributed to the composite’s well-developed porosity and high surface functionality. In addition, the adsorbent exhibited high CO2/N2 selectivity of 15.2 along with stable cycling performance. These findings indicate that mechanochemically synthesized silicon oxycarbide composites have a considerable potential in the field of CO2 capture.

Heterostructure Design of Anode Materials for High-Performance Sodium-Ion Batteries

The growing global demand for carbon neutrality has led to an increase in the use of electric vehicles and large-scale energy storage systems, which rely heavily on lithium-ion batteries. However, there are concerns about the limited availability of lithium resources, which may result in depletion and price increases in the near future. To solve this issue, researchers are actively exploring alternative next-generation secondary battery systems to replace current lithium-ion batteries. Sodium-ion batteries have received significant attention as one of promising candidates, as sodium is abundant in the earth's crust and economically viable compared to lithium.Although hard carbon has been considered a reversible anode material capable of sodium-ion insertion and extraction, high-capacity anode materials are required to increase the energy density of sodium-ion batteries. Among various candidates, conversion- and alloy-based materials are highly regarded due to their high theoretical capacity. However, challenges such as huge volume changes of active materials, sluggish reaction rates, and interfacial instability that occur during charging and discharging need to be overcome for these materials to be applied in high-performance sodium-ion batteries.To address these challenges, herein, we designed heterostructured anodes with a unique structure by combining conversion- or alloy-based materials with a porous silicon oxycarbide (SiOC) nanocoating layer, which possesses high surface capacitive reactivity and mechanical strength. We controlled the dispersion of the precursors in silicon oil and performed heat treatment to synthesize high-capacity heterostructured composites (MoS2@SiOC and Sn@SiOC). Subsequently, we conducted extensive physicochemical and electrochemical characterization as well as post-mortem analysis to investigate the properties of these composites, with a specific focus on the impact of the heterostructure on their battery performance. We anticipate that this heterostructure approach will pave the way for the development of novel, high-performance anode materials for sodium-ion batteries in the future.

Additive Manufacturing of Silicon Oxycarbide Ceramics with Minimal Surface Structures

The traditional ceramic powder sintering forming method severely limits the performance of the fabricated parts. Many new solutions have been achieved by precursor derived ceramics (PDC). Silicon oxycarbide ceramics as one of them has many performance advantages such as excellent mechanical properties, low density, excellent thermal stability, low thermal conductivity, and resistance to thermal shock and corrosion. In this paper, a photosensitive polysiloxane resin (PPR) with excellent light curing properties was prepared, which has high precision in the process of additive manufacturing. In addition, samples with minimal surface features in different porosity were fabricated. The compressive strength of the structure with 85%, 75%, and 65% porosity was about 9.51 MPa, 13.76 MPa, and 21.69 MPa, respectively. These porous silicon oxycarbide ceramics are likely to have a wide range of potential applications in aerospace, aviation, and other fields.

Biomimetic porous silicon oxycarbide ceramics with improved specific strength and efficient thermal insulation

Considering the challenge of aerodynamic heating, the development of high-performance insulating ceramic materials with lightweight and low thermal conductivity is crucially important for aerospace vehicles to achieve flight at high speed for a long time. In this work, macro-porous silicon oxycarbide (SiOC) ceramics with directional pores (DP-SiOC) (mean pore size of 88.1 μm) were prepared using polysiloxane precursors via freeze casting and photocrosslinking, followed by pyrolysis. The DP-SiOC samples were lightweight (density ∼0.135 g cm–3) with a porosity of 90.4%, which showed good shapability through the molding of polysiloxane precursors. The DP-SiOC samples also exhibited an ultra-low thermal conductivity of 0.048 W(m K)–1 at room temperature, which can also withstand heat treatment at 1200 °C for 1 h. In addition, scaffolds with triply periodic minimal surfaces (TPMS) were fabricated using digital light processing (DLP) printing, which was further filled with polysiloxane precursors for increasing the strength of DP-SiOC. The TPMS scaffolds filled with macro-porous SiOC ceramics (TPMS-DP-SiOC) showed good integration between TPMS and macro-pore structures, which had a porosity ∼75% and high specific strength of 9.73 × 103 N m kg–1. The thermal conductivity of TPMS-DP-SiOC samples was 0.255 W(m K)–1 at room temperature. The biomimetic TPMS-DP-SiOC ceramics developed in this study are likely used for thermal protection systems.

Molecular Aggregation Strategy for Pore Generation in SiOC Ceramics Induced by the Conjugation Force of Phenyl.

Porous silicon oxycarbide (SiOC) ceramics with tailorable microstructure and porosity were fabricated using phenyl-substituted cyclosiloxane (C-Ph) as a molecular-scale porogen are analyzed in this study. A gelated precursor was synthesized via the hydrosilylation of hydrogenated and vinyl-functionalized cyclosiloxanes (CSOs), followed by pyrolysis at 800-1400 °C in flowing N2 gas. Tailored morphologies, such as closed-pore and particle-packing structures, with porosities in the range 20.2-68.2% were achieved by utilizing the high boiling point of C-Ph and the molecular aggregation in the precursor gel induced by the conjugation force of phenyl. Moreover, some of the C-Ph participated in pyrolysis as a carbon source, which was confirmed by the carbon content and thermogravimetric analysis (TGA) data. This was further confirmed by the presence of graphite crystals derived from C-Ph, as determined by high-resolution transmission electron microscopy (HRTEM). In addition, the proportion of C-Ph involved in the ceramic process and its mechanism were investigated. The molecular aggregation strategy for phase separation was demonstrated to be facile and efficient, which may promote further research on porous materials. Moreover, the obtained low thermal conductivity of 27.4 mW m-1 K-1 may contribute to the development of thermal insulation materials.

Synthesis and Characterization of High Surface Area Transparent SiOC Aerogels from Hybrid Silicon Alkoxide: A Comparison between Ambient Pressure and Supercritical Drying.

In this article, highly porous and transparent silicon oxycarbide (SiOC) gels are synthesized from Bis(Triethoxysilyl) methane (BTEM). The gels are synthesized by the sol-gel technique followed by both ambient pressure and supercritical drying. Then, the portion of wet gels have been pyrolyzed in a hydrogen atmosphere at 800 and 1100 °C. The FT-IR spectroscopy analysis and nitrogen sorption results indicate the successful synthesis of Si-O-Si bonds and the formation of mesopores. From a hysteresis loop, the SiOC ceramics showed the H1 type characteristic with well-defined cylindrical pore channels for the aerogel and the H2 type for the ambigel samples, indicating that the pores are distorted due to the capillary stress. The produced gels are mesoporous materials having high surface areas with a maximum of 1140 m2/g and pore volume of 2.522 cm3/g obtained from BTEM aerogels. The pyrolysis of BTEM aerogels at 800 °C results in the production of a bulk and transparent sample with a slightly pale white color, while BTEM xerogels are totally transparent and colorless at the same temperature. At 1100 °C, all the aerogels become opaque brown, confirming the formation of free carbon and crystalline silicon.

Hierarchical porous fluorine-doped silicon oxycarbide derived materials: Physicochemical characterization and electrochemical behaviour

Novel hierarchical micro-meso-macroporous fluorine-doped silicon oxycarbide derived materials have been obtained by HF etching of silicon oxycarbides pyrolyzed at different temperatures. The influence of etching time (1 or 24 h) and pyrolysis temperature (from 1100 to 1400 °C) on the selective removal of the silica nano-domains present in the silicon oxycarbide and the appearance of oxygen and fluorine functionalities have been determined and evaluated in terms of their electrochemical response. The insertion of fluorine in the silicon oxycarbide matrix (Si–O(F) bonds) and free carbon phase (C–F semi-ionic and C–F covalent bonds) was corroborated. The materials pyrolyzed at 1300–1400 °C and etched during 24 h show values of specific capacitance as high as 225-165 Fg-1 (0.1–30 Ag-1) using a symmetrical configuration and H2SO4 1 M as electrolyte. These materials displayed energy density values of 28-19 Whkg−1 (0.1–45 kWkg-1). The hierarchical microstructure in conjunction with the oxygen and fluorine functionalities are essential in order to explain their good electrochemical response. In particular, those materials present the highest amount of meso (3–10 nm) and larger meso-macropores and the highest content of fluorine in their composition. Then, fluorine-doped silicon oxycarbide derived materials can be potentially used as electrodes for supercapacitors in the field of energy storage applications.

Estudio del envejecimiento acelerado bajo radiación solar concentrada de vidrios de oxicarburo como receptores de alta temperatura

Solar energy and especially concentrated solar power systems (CSP) need materials that can tolerate the demanding working conditions. In this sense, the receivers are exposed to large fluxes of solar radiation that produce very high temperatures. In addition, due to the operational conditions of receivers large temperature variations occur during day and night, or on cloudy days being these the main aging factors. However, other factors such as humidity, salines environments or pollutans in industrial zones can not be ruled out. Silicon oxycarbide glasses (SiOC) are composite materials formed by a SiOC glass phase (matrix phase) and a C phase (reinforcing phase) homogeneously dispersed and they can be very promising candidates for this type of applications due to their excellent intrinsic properties like their high resistante against to both oxidation and very aggressive environments, good mechanical properties, etc. In this work we have focused in the evaluation of the composite materials (SiOC porous and dense) against thermal shock produced by Frenel lens that concentrated solar radiation more than 2600 times. In every cycle materials they have been heated (32 oC s-1) an cooled (27 oC s-1) at very high rates from room temperature to 1000 oC. This process has been repeated 100 times or lesser in the case of catastrophic material damage. The evolution of material surface during thermal shock cycles has been followed by several techniques such confocal and electronic microscopies and Raman, Infrarred and UV-Visible spectroscopies. Porous silicon oxycarbide materials experiencied a rapid and severe degradation during the first cycles but dense one tolerates quite well the exposure againts concentrated solar radiation.

Механохимический синтез пористых кремнийоксиуглеродных композитов

The work is devoted to investigation of the process of mechanochemical synthesis of porous silicon oxycarbide composites. The synthesis was carried out by mechanical treatment of several mixtures of activated carbon and white soot with different mass ratios. Samples were investigated using such methods as X-ray diffraction, infrared spectroscopy, low-temperature nitrogen adsorption/desorption and potentiometric titration. Synchronous thermal analysis including thermogravimetric analysis and differential scanning calorimetry was performed. The results of X-ray diffraction analysis showed that no new phases were formed in the process of mechanochemical synthesis, and the structure of composites obtained can be characterized as highly amorphous. The possibility of activated carbon and white soot to be chemically bonded with the formation of silicon oxycarbides, which act as a binder in the composite structure, during intensive supply of mechanical energy to raw materials was proved. Thermal stability of silicon oxycarbides formed and the amount of free carbon that was not bonded with silicon dioxide were estimated by synchronous thermal analysis. It was established that the initial mixture composition significantly affects the surface chemistry of composites synthesized, which is expressed by a change in concentration of different surface functional groups. A possible mechanism of solid phase interaction between activated carbon and white soot resulting in the formation of Si–O–C bonds was proposed. Investigation of porous structure of composite materials obtained showed that the specific surface area and pore volume become lower with an increase in white soot concentration in the initial mixture. It is possible to adjust the porous structure of composites by changing the activated carbon to white soot mass ratio.

Hydrogen storage in porous polymer derived SiliconOxycarbide ceramics: Outcomes and perspectives

The present study explores the possibility of adopting thermally stable porous silicon oxycarbide (Si-O-C) ceramics as a suitable material for hydrogen storage. Experimental studies of hydrogen storage in these ceramics were conducted using Sievert's apparatus. A maximum specific surface area (SSA) of 158.1 m2/g with an average pore size of 14.5 nm was found for the ceramics. The ceramic showed gravimetric storage density (G.D) of 0.35 wt% at 2 bar and 100 K. Mesopore size, 2–5 nm was found critical for hydrogen adsorption in these ceramics. Hence, hydrofluoric acid etching was carried out to increase their count. Etching led to the removal of the SiO2 phase from the ceramic, thereby creating micro and mesoporosity and resulting in SSA of 451.6 m2/g with an average pore diameter of 4.36 nm. Further, the etched sample showed G.D of 1.19 wt% at 2 bar and 100 K, an increase of 240% over the un-etched sample. Additionally, the interaction potential of hydrogen with Si-O-C was calculated using the Clausius equation and was found to be dependent on the pore size in existing in the ceramic.

Porous and ultrahigh surface area SiOC ceramics based on perhydropolysilazane and polysiloxane

Abstract Micro-/meso-porous ceramics with ultrahigh surface areas are highly desired in high-temperature applications. In this work, formation of porous silicon oxycarbide (SiOC) is studied based on perhydropolysilazane (PHPS) and polysiloxane (PSO) precursors. The PHPS can be chemically anchored to the PSO by hydrosilylation reaction, due to the extensive Si–H bonds from the PHPS. The presence of water vapor during pyrolysis not only accelerates the hydrolysis of the PHPS additive, but also facilitates the Si–O–Si bond formation within the SiOC. The resulting SiOC material has the highest specific surface area (SSA) of ~2000 m2/g with an average pore size of 1.72 nm. The effects of the PHPS additive on the phase evolution and the resulting porous SiOC after hydrogen fluoride (HF) etching are investigated. 3D view of pore distributions qualitatively illustrates the PHPS effect on the SiO2 nanocluster formation in the SiOC. The difference between the experimental and calculated SSAs is explained based on the etchability and wall thickness of the SiO2 domains.

Study on effect of structure and surface/ physical characteristics of a silicon oxycarbide by hydrofluoric acid etching

ABSTRACT In this study, polymer-derived porous silicon oxycarbide (SiOC) ceramic was synthesised by considering various polymer precursors such as polymethylhydrosiloxane, polydimethylsiloxane and cyclic 2,4,6,8-tetramethyl-2,4,6,8tetravinlycyclotetrasiloxane in various proportions. The pyrolysis temperature of 1000°C was fixed to obtain the amorphous nature of SiOC, which is considered to be favourable for use in anode material for the Li ion batteries. Further, to enhance surface properties viz porosity, pore volume of these pyrolysed SiOC ceramics, hydro fluoric acid etching was performed. In order to establish effect of etching on the SiOC ceramic, various structural and physical/surface characterisations such as Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, Brunauer–Emmet–Teller and Barrett–Joyner–Halenda analysis were conducted. The results showed that specific surface area improved from 164 to 474 m2 g−1 before and after etching, respectively.

Numerical approach to evaluate performance of porous SiC5/4O3/2 as potential high temperature hydrogen gas sensor

Porous silicon oxycarbide (SiCO) is a novel class of nano-porous material with superior gas sensing performance. In this work, the amorphous porous structure of SiC5/4O3/2 is successfully reproduced by simulating the experimental etching process, and the gas sensing performance of porous SiCO at high temperature is investigated. The calculation results show porous SiC5/4O3/2 exhibits a much higher sensitivity towards H2 than CO, NO2 and acetone at 773 K. Compared with the other three gases, H2 absorbed system show shorter adsorption distance and more obvious increasing in density of states around Fermi level. Therefore, porous SiC5/4O3/2 shows a highly selective sensitivity toward H2 at high temperature. Moreover, our results show the Si–C/O units are the major sensing sites of H2 at high temperature, and the large diffusion coefficient of H2 in SiC5/4O3/2 is related to the fast response of porous SiCO gas sensor.

Temperature-dependent gas sensing properties of porous silicon oxycarbide: Insight from first principles

Porous silicon oxycarbide (SiCO) has unique gas sensing properties at various temperatures. Characterizing the gas sensing mechanism is important for evaluating and designing porous silicon oxycarbide gas sensors. In this work, the temperature-dependent gas sensing properties of porous silicon oxycarbide are investigated. At 300 K, porous SiCO is significantly more sensitive to NO2 than CO, H2 and acetone. However, at 773 K, SiCO is less sensitive to NO2 compared to H2. An OH bond with a length of 1.04 Å forms between H2 and the mixed Si-C/O bond, and the incorporation of H2 results in an obvious increase in the density of states near the Fermi level. Therefore, porous SiCO is highly selective and sensitive towards H2 at high temperatures, and its response to NO2 disappears, which is consistent with the experimental conclusions. Moreover, our results show that the mixed Si-C/O bonds are the primary sensing sites for NO2 (at 300 K) and H2 (at 773 K). The proposed theoretical approach can be used to evaluate and predict the temperature-dependent gas sensing properties of porous SiCO.

Role of polysiloxanes in the synthesis of aligned porous silicon oxycarbide ceramics

The present work focuses on establishing the role of polysiloxane precursors in the synthesis of aligned porous polymer derived silicon oxycarbide ceramics. The precursors used for the synthesis are, polymethylhydrosiloxane, vinyl terminated polydimethylsiloxane and cyclic tetramethyl-tetravinlycyclotetrasiloxane. Hydrotalcite is used for attaining aligned macroporosity during the crosslinking stage itself. Subsequently, pyrolysis of the sample has been carried out to synthesize the ceramics. The evolution of pore structure in these PDCs during the crosslinking and pyrolysis is co-related to the thermal decomposition behaviour. The pore morphology, structure and the size were analyzed using SEM, X-ray computed tomography and BET. Our studies confirm the presence of bimodal porosity in these PDCs. These PDCs have a specific surface area ranging from 77 to 160 m2/g and a total pore volume ranging from 0.18 to 0.29 cm3/g. These results could be significant for achieving a controlled synthesis process of porous materials suitable for various applications like adsorption, filtering and electrochemical storage.

Silicon Oxycarbide-Derived Carbon as Potential NO2 Gas Sensor: A First Principles’ Study

Silicon oxycarbide (SiCO)-derived porous carbon is a novel class of nano-porous material with unique properties including highly sensitive gas detection. In this letter, SiCO-derived porous carbon (porous SiCO) structures are successfully reproduced by simulating the etching process in experiments. Then, the gas sensing performance of SiCO-derived carbon with different porous morphologies is investigated. The calculated adsorption energy, Mulliken charge transfer, bandgap, and adsorption distance indicate that SiCO-derived porous carbon exhibits a higher sensitivity toward NO2 gas than CO, 2, and acetone in accordance with experimental conclusions. Moreover, the porous SiCO with the largest SSA and PV shows the most excellent NO2 sensing performance. The adsorption of NO2 leads to the appearance of a new strong peak at the edge of the conduction band, resulting in obvious changes of the conductivity of the systems, which is necessary for NO2 detection.

Evaluation of thermal shock resistance of silicon oxycarbide materials for high-temperature receiver applications

Materials used as solar receivers in concentrated solar power technology must withstand severe operational conditions caused by concentrated solar radiation. For this solar technology several ceramic material candidates (silicon carbide, porous and dense silicon oxycarbide) have been subjected to thermal shock resistance test by using Fresnel lens, the equipment available, that concentrates the solar radiation more than 2600 times. Fast heating (37 °C s−1) and cooling rates (28 °C s−1) from 100 to 1200 °C and dwelling time of 10 min are employed. The evolution of materials surface has been evaluated during test by spectroscopic methods and both confocal and electronic microscopies. It has been obtained the surface map of each analyzed sample in order to evaluate the effect of the concentrated solar radiation on the surface and the relationship with their durability. The absorptance values were also determined before and after the ageing test using normal direction between 400 and 1100 nm. Concentrated solar radiation facilitates the decomposition of tested materials producing the formation of gaseous species (mainly CO and CO2) and a dense SiO2 layer which is formed over the material surface. SiC and porous silicon oxycarbide materials fail the thermal shock resistance test. SiC experiences a catastrophic break and in the case of porous silicon oxycarbide, gases generated can evolve easily through the pores producing a severe degradation of the material surface. However, dense silicon oxycarbide resists 100 cycles at 1200 °C due to the formation of a protective SiO2 layer over the material surface and its dense microstructure that slow down the diffusion of the gases preventing bulk material from being degraded. The surface studies confirm the formation of a crystalline SiO2 phase all over the surface. Furthermore, the very similar coefficients of thermal expansion of silicon oxycarbide and silica (≈0.4 × 10−6 °C), protects material against catastrophic failure. Finally, the absorptance values remain fairly constant before and after thermal shock test (94.78 to 95.96–96.09%). The high resistance of dense silicon oxycarbide materials to thermal shock under concentrated solar radiation makes these materials suitable candidates of being used as high temperature solar receivers.

Preparation and properties of TaSi2-MoSi2-ZrO2-borosilicate glass coating on porous SiCO ceramic composites for thermal protection

A TaSi2-MoSi2-ZrO2-borosilicate glass (TMZG) coating was prepared by a slurry method on a carbon fibre-reinforced porous silicon oxycarbide (SiCO) ceramic composite for thermal protection. The coating was well adhered to the substrate and showed a uniform thickness of approximately 375 µm. After thermal cycling from 1873 K to room temperature six times (total oxidation time of 180 min), the shape and dimension of the TMZG remain almost unchanged with no cracking or peeling of the coating surface. The TMZG-coated sample exhibits good oxidation resistance because of a molten SiO2 film with ZrSiO4 particles distributed on the outer layer of the coating. After ablation testing under an oxyacetylene flame at 1927 K for 90 s, the linear ablation rate of the TMZG coated sample are 8.33 × 10−4 mm/s. The whole coating retains integrity, preventing substrate ablation during the test. The TMZG coating with excellent temperature resistance shows broad applicability in thermal insulation materials.

Effects of SiO2-forming additive on polysiloxane derived SiOC ceramics

Novel ultrahigh surface area materials are highly desired for demanding applications such as high temperature catalysts, electrodes, and harsh environment sensors. In-situ conversion of tetraethyl orthosilicate (TEOS) into SiO2 and its incorporation into silicon oxycarbide (SiOC) ceramics during polysiloxane ceramization are investigated by crosslinking TEOS within a polysiloxane matrix and introducing water vapor during pyrolysis. The effects of the TEOS-derived SiO2 on the thermophysical properties, phase development, and the resulting porous SiOC are investigated. The SiOC with 10 wt% TEOS within the crosslinked polymer creates the highest specific surface area of ∼2100 m2/g with an average pore size of ∼2 nm. The specific surface area and pore size distribution are correlated with the theoretical results from Voronoi diagram simulation and an idealized model calculation.