Carbon Protective Layer Research Articles

Application of a novel plasma-based method of introducing maleic acid and pentaerythritol phosphate urea salt onto polyester fabrics for durable flame-retardant treatment

In this work, a novel anti-flame poly(ethylene terephthalate) (PET) fabric was successfully fabricated by plasma-based technology combined with pad-dry-cure treatment finishing. Low-temperature plasma can graft maleic acid (MA) onto a PET polymer backbone, which can activate the PET fiber and provide the opportunity of reaction with pentaerythritol phosphate urea salt (PEPAS) to achieve an excellent and durable anti-flame ability. Furthermore, the chemical reaction between PET-MA and PEPAS can form a complex and compact net structure that can effectively improve the anti-dripping property of PET. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy analysis showed that MA and PEPAS were successfully introduced onto the surface of the PET fabric, and a compact protective carbon layer was formed during the combustion process due to the synergistic effect of phosphorus and nitrogen. The flame-retardant and anti-dripping properties were evaluated by thermogravimetric analysis, the limiting oxygen index (LOI) and a vertical burning test. The treated samples showed the maximum LOI value of 29.3, possessing excellent thermal stability and self-extinguishing ability and inhibiting melt-dripping ability. Moreover, tensile strength at break of the treated PET fabric was slightly greater than that of the original PET fabric, indicating that this type of treatment had little negative impact on the bulk of the PET fabric. After 20 laundering cycles, the LOI value of the treated sample still remained at 26.8, which indicated durability in the flame-retarding effect.

Rational synthesis of two-dimensional G@porous FeS2@C composite as high-rate anode materials for sodium/potassium ion batteries

Pyrite (FeS2) with the advantages of high capacity, low cost and environmental benign has been considered as a promising anode material for alkali metal (Li, Na, K) ion batteries. However, the large volume expansion and its semiconductor nature result in poor battery performance and hamper its practical applications. To overcome these drawbacks, we rationally construct a two-dimensional FeS2-carbon architecture, from which porous FeS2 nanoparticles are distributed within reduced graphene oxide matrix and carbon coating shell with abundant interior void space. Benefiting from its structure properties with conductive carbon network, protective carbon layer, and interior void room, as-prepared rGO@p-FeS2@C composite displays superior electrochemical performance as anode materials for sodium/potassium ion batteries. For sodium storage, it exhibits good cyclic performance with a high capacity 598 mA h g−1 sustained after 100 cycles at 0.1 A g−1, and excellent rate capability (428 mA h g−1 at 10 A g−1). For potassium storage, it also maintains a superior rate capacity of 298 mA h g−1 at 2 A g−1. Moreover, pseudocapacity has been proved to be dominated in charge/discharge process, accounting for the excellent rate performance.

Nitrogen-doped carbon-coated Fe3O4/rGO nanocomposite anode material for enhanced initial coulombic efficiency of lithium-ion batteries

Nitrogen-doped carbon-coated Fe3O4/reduced graphite oxide (NC@Fe3O4/rGO) nanocomposites with in situ polymerized melamine-formaldehyde resin (MFR) as the carbon sources were synthesized via the decomposition of MFR/Fe3O4/rGO nanocomposites. Fe3O4 NPs were embedded in the integrated carbon matrix composed of protective carbon layer and conductive rGO sheets offering excellent buffer effect. The NC@Fe3O4/rGO nanocomposites were tested as anode materials for lithium-ion batteries (LIBs) and displayed a large reversible specific capacity of above 900 mA h g−1 after 100 cycles at a current density of 50 mA g−1, high coulombic efficiency (~ 98%) with an initial coulombic efficiency of 86%. The high initial coulombic efficiency is critical for the practical application of the transition metal oxide–based anode materials.

Bi-functional nitrogen-doped carbon protective layer on three-dimensional RGO/SnO2 composites with enhanced electron transport and structural stability for high-performance lithium-ion batteries

Three-dimensional reduced graphene oxide@SnO2@nitrogen-doped carbon (3DG@SnO2@N-C) composites are designed as high efficiency anode materials for lithium-ion batteries. The SnO2 particle size, surface area and pore size distribution of the 3DG@SnO2@N-C could be simply controlled by altering the GO dosages. The optimized 3DG@SnO2@N-C electrode demonstrates a reversible capacity of 1349.5 mAh g−1 after 100 cycles at the current density of 100 mA g−1. Based on the structural and electrochemical dynamic tests, the bi-functional N-doped carbon coating layer could serve as both conductive channel for electron transport and as buffer layer to alleviate the volume change of embedded SnO2 NPs. In addition, the cross-linked conducting 3DG with porous structure attributes to the reduced electron transport and Li ion diffusion resistances, which finally leads to the enhanced cycling stability and rate performances.

Stabilizing Pt Nanocrystals Encapsulated in N-Doped Carbon as Double-Active Sites for Catalyzing Oxygen Reduction Reaction.

Polypropylene fiber, a cheap source of nitrogen-doped carbon, is introduced to design robust nitrogen-doped carbon-encapsulated small Pt nanocrystals with Pt and nitrogen-carbon double-active centers toward oxygen reduction reaction (ORR). Ascribed to the separation effect of the polypropylene fiber, even suffering from a high-temperature carbonization treatment at 720 °C for 90 min, the polypropylene fiber-derived carbon-encapsulated Pt nanocrystal maintains a small particle size (3 nm diameter on average). As expected, its ORR mass activity is up to 116.5 mA/mg at 0.9 V. After 8000 cycles, the half-wave potential of the prepared catalyst declines only by 14 mV compared with 43 mV for the commercial Pt/C catalyst. The significantly improved electrochemical properties of the as-prepared catalyst areresulted from the nitrogen-doped carbon-encapsulated Pt nanocrystal structure,whichis benefited to adsorption and activation of oxygen due to the presence of nitrogen-doped carbon asthe important active site for ORR besides Pt metal. In addition, the migration, aggregation, and growth of Pt nanoparticles are prohibited in terms of the outer nitrogen-doped carbon protection layer, greatly enhancing the stability of the catalyst.

Designing of hierarchical mesoporous/macroporous silicon-based composite anode material for low-cost high-performance lithium-ion batteries

A mass-produced and low-cost hierarchical mesoporous/macroporous silicon-based composite material with an ample porous structure and dual carbon protective layers has been rationally designed and constructed. The Si/SiO2@C composite anode materials for LIBs show enhanced electrochemical properties.

Nitrogen-doped carbon sheets coated on CoNiO2@textile carbon as bifunctional electrodes for asymmetric supercapacitors

Oxidative polymerization of dopamine and the subsequent thermal conversion generate N-doped carbon protective layers which could significantly improve the cycling stability of CoNiO2 electrodes.

Study of nanocarbon black as synergist on improving flame retardancy of ethylene-vinyl acetate/brucite composites

Nanocarbon black (CB) was introduced into ethylene-vinyl acetate/brucite (EM) composites to investigate the synergistic effect of CB and metal hydroxide on improving the flame retardancy of EVA. Flammability properties of the as-prepared EVA composites were investigated by thermogravimetric analysis, limiting oxygen index (LOI), UL-94 test and cone calorimetry test. The results indicated that the optimum mass ratio of CB/brucite was 1/54, at which the EVA composites displayed dramatic improvement on thermal stability and flame retardancy. The LOI value was as high as 35.3%, the UL-94 passed the V-0 rating, and the peak heat release rate reduced 79% in comparison with pure EVA. Based on the morphology and structure analysis for residue chars, the flame-retardant mechanism was attributed mainly to the positive synergistic effect of CB and brucite on promoting the formation of better carbon protective layer during combustion.

Mechanical properties of individual core-shell-structured SnO2@C nanofibers investigated by atomic force microscopy and finite element method

Although SnO2-based nanomaterials used to be considered as being extraordinarily versatile for application to nanosensors, microelectronic devices, lithium-ion batteries, supercapacitors and other devices, the functionalities of SnO2-based nanomaterials are severely limited by their intrinsic vulnerabilities. Facile electrospinning was used to prepare SnO2 nanofibers coated with a protective carbon layer. The mechanical properties of individual core-shell-structured SnO2@C nanofibers were investigated by atomic force microscopy and the finite element method. The elastic moduli of the carbon-coated SnO2 nanofibers remarkably increased, suggesting that coating SnO2 nanofibers with carbon could be an effective method of improving their mechanical properties.

Application of self-templated PHMA sub-microtubes in enhancing flame-retardance and anti-dripping of PET

Tubular one-dimensional poly (cyclotriphosphazene-melamine) (PHMA) sub-microtubes were conveniently synthesized from co-polymerization of hexachloro -cyclotriphosphazene and melamine. The SEM and TEM results showed PHMA sub-microtubes were opened at one end with diameters of 100–300 nm and lengths of 1–10 μm. The inner diameters of closed and open end were 10–30 nm and 50–100 nm, respectively. The PHMA sub-microtubes were melt blended with PET (PET/PHMA) to be used as an effective flame retardant. The flame-retardant and anti-dripping properties of PET/PHMA composites were evaluated by TGA, LOI, vertical burning, MCC and rheological test. The results confirmed the efficiency of PHMA in enhancing the self-extinguishing ability and inhibiting melt-dripping of PET. The morphological characteristics and graphitic structure of the charred residues were evaluated by SEM, Raman spectroscopy. Results demonstrated the formation of a compact protective carbon layer and a carbonaceous micro-structures, which acted as insulator against oxygen and heat.

Z-scheme Photocatalytic CO2 Conversion on Three-Dimensional BiVO4/Carbon-Coated Cu2O Nanowire Arrays under Visible Light

Cuprous oxide (Cu2O) is one of the most promising materials for photoreduction of CO2 because of its high conduction band and small band gap, which enable the production of high-potential electrons under visible-light irradiation. However, it is difficult to reduce the CO2 using a Cu2O-based photocatalyst due to fast charge recombination and low photostability. In this work, we enhanced the photocatalytic CO2 conversion activity of Cu2O by hybridization of Cu2O NWAs, carbon layers, and BiVO4 nanoparticles. By construction of a Z-scheme charge flow on a 3-D NWA structure, the BiVO4/carbon-coated Cu2O (BVO/C/Cu2O) NWAs show significantly enhanced charge separation and light harvesting property. As a result, CO formation rate of BVO/C/Cu2O was 9.4 and 4.7 times those of Cu2O mesh and Cu2O NWAs, respectively, under visible light irradiation. In addition, the material retained 98% of its initial photocatalytic CO2 conversion performance after five reaction cycles (20 h) because of the protective carbon layer a...

Mesoporous Hollow Sb/ZnS@C Core–Shell Heterostructures as Anodes for High‐Performance Sodium‐Ion Batteries

Combining the advantage of metal, metal sulfide, and carbon, mesoporous hollow core-shell Sb/ZnS@C hybrid heterostructures composed of Sb/ZnS inner core and carbon outer shell are rationally designed based on a robust template of ZnS nanosphere, as anodes for high-performance sodium-ion batteries (SIBs). A partial cation exchange reaction based on the solubility difference between Sb2 S3 and ZnS can transform mesoporous ZnS to Sb2 S3 /ZnS heterostructure. To get a stable structure, a thin contiguous resorcinol-formaldehyde (RF) layer is introduced on the surface of Sb2 S3 /ZnS heterostructure. The effectively protective carbon layer from RF can be designed as the reducing agent to convert Sb2 S3 to metallic Sb to obtain core-shell Sb/ZnS@C hybrid heterostructures. Simultaneously, the carbon outer shell is beneficial to the charge transfer kinetics, and can maintain the structure stability during the repeated sodiation/desodiation process. Owing to its unique stable architecture and synergistic effects between the components, the core-shell porous Sb/ZnS@C hybrid heterostructure SIB anode shows a high reversible capacity, good rate capability, and excellent cycling stability by turning the optimized voltage range. This novel strategy to prepare carbon-layer-protected metal/metal sulfide core-shell heterostructure can be further extended to design other novel nanostructured systems for high-performance energy storage devices.

Rational design and fabrication of multifunctional catalyzer Co2SnO4-SnO2/GC for catalysis applications: Photocatalytic degradation/catalytic reduction of organic pollutants

Hollow porous Co2SnO4-SnO2/graphite carbon (Co2SnO4-SnO2/GC) nanocube heterojunction was designed and constructed as advanced catalytic material by calcining CoSn(OH)6 precursors followed an immersion carbon coating (using the recyclable napkin as graphite carbon source) and calcinations treatment. The design methods focus on forming intimate interfacial contacts among Co2SnO4, SnO2 and GC (in situ hybridization of the composite). The obtained Co2SnO4-SnO2/GC exhibits remarkable dual catalytic behavior including the high catalytic efficiency for photocatalytic (under visible light) degradation of chlorotetracycline (CTC)/tetracycline (TC) and catalytic reduction of p-nitrophenol (p-NP). Co2SnO4-SnO2/GC could be recycled more than four times, preserving its activity and stability based on graphite carbon protective layer on the surface of catalysts. Owing to multiple heterojunctions structure features and the synergistic effects of different junctions, greatly enhance the charge carrier generation and suppress the charge recombination of electron-hole pairs, which would be beneficial to improve its catalytic activity. The possible mechanisms for the dual-functional catalytic reactions for organic contaminants over Co2SnO4-SnO2/GC were made a thorough inquiry. This study not only shows a possibility for the utilization of low cost the recyclable napkin as a substitute for graphene but also provides a new insight into the design and construction of new heterojunction catalysts for enhancing catalytic activity.

Polyaniline-encapsulated silicon on three-dimensional carbon nanotubes foam with enhanced electrochemical performance for lithium-ion batteries

Seeking free volume around nanostructures for silicon-based anodes has been a crucial strategy to improve cycling and rate performance in the next generation Li-ion batteries. Herein, through a simple pyrolysis and in-situ polymerization approach, the low cost commercially available melamine foam as a soft template converts carbon nanotubes into highly dispersed and three-dimensionally interconnected framework with encapsulated silicon/polyaniline hierarchical nanoarchitecture. This unique core-sheath structure based on carbon nanotubes foam integrates a large number of mesoporous, thus providing well-accessible space for electrolyte wetting, whereas the carbon nanotubes matrix serves as conductive thoroughfares for electron transport. Meanwhile, the outer polyaniline coated on silicon nanoparticles provides effective space for volume expansion of silicon, further inhibiting the active material escape from the current collector. As expected, the PANI-Si@CNTs foam exhibits a high initial specific capacity of 1954 mAh g−1 and retains 727 mAh g−1 after 100 cycles at 100 mA g−1, which can be attributed to highly electrical conductivity of carbon nanotubes and protective layer of polyaniline sheath, together with three-dimensionally interconnected porous skeleton. This facile structure can pave a way for large scale synthesis of high durable silicon-based anodes or other electrode materials with huge volume expansion.

A Synthetic Route for the Preparation of Core-Shell Nanoparticles Using a Protective Carbon Layer and Ozone Treatment

A novel synthetic process was developed to synthesize nano-sized core-shell catalysts through atomic rearrangement by heat-treatment. Agglomeration of nanoparticles caused by the high-temperature heat-treatment was alleviated by using a modified protective coating method. In this method, the carbon layer formed by the carbonization of polydopamine serves as a protective coating layer, which suppresses the sintering of the catalyst particles continuously until the high-temperature heat-treatment is completed. Later, the carbonized carbon layer is removed by ozone treatment because it blocks the active site of the catalyst. Since ozone is a highly oxidative gas, it can selectively remove the carbon layer at room temperature in just 7 minutes without affecting the physical properties of the catalyst itself, which makes this method suitable for mass production. The Pt-based alloy catalyst was prepared by this unique process was proved to have a Pt-rich shell structure, and the particles can remain small (∼5 nm) even after high-temperature heat-treatment, thus exhibiting high oxygen reduction reaction (ORR) activity in fuel cells.

Rod-like hierarchical Sn/SnOx@C nanostructures with enhanced lithium storage properties

Rod-like hierarchical Sn/SnOx@C nanostructures have been designed and synthesized via calcining resorcinol-formaldehyde (RF) resin coated Sn-based metal-organic frameworks. The rod-like hierarchical Sn/SnOx@C nanostructures are made of a great number of carbon-wrapped primary Sn/SnOx nanospheres of 100–200nm in diameter. The as-prepared hierarchical Sn/SnOx@C nanocomposite manifests a high initial reversible capacity of 1177mAhg−1 and remains 1001mAhg−1 after 240 cycles at a current density of 200mAg−1. It delivers outstanding high-rate performance with a reversible capacity of 823mAhg−1 even at a high current density of 1000mAg−1. The enhanced electrochemical performances of the Sn/SnOx@C electrode are mainly attributed to the synergistic effect of the unique hierarchical micro/nanostructures and the protective carbon layer.

Li2S nano spheres anchored to single-layered graphene as a high-performance cathode material for lithium/sulfur cells

Fully lithiated lithium sulfide (Li2S) has become a promising cathode material for Li/S cells due to its high theoretic capacity (1166mAhg−1) and specific energy (2600Whkg−1). However, low utilization of sulfur and poor rate capability still hinder the practical application of Li/S cells. In this paper, a carbon coated Li2S/graphene composite (Li2S/G@C) was developed by incorporating Li2S nano spheres with single-layered graphene and further forming a durable protective carbon layer on the surface of the Li2S particles using a facile CVD method. The high rate capability and remarkable cycle life of the Li2S/G@C cathode were demonstrated, which was mainly attributed to the unique structure of the Li2S/G@C that can significantly improve not only the electrical conductivity, but also the mechanical stability of the sulfur cathode.

Tribological performance of few layer graphene on textured M2 steel surfaces

In this study, we propose an easy and effective way to enhance the tribological performance of few layer graphene on M2 steel surfaces. Microgrooves with different area ratios were fabricated on M2 steel surfaces by laser surface texturing method. Subsequently, few layer graphene flakes were dripped on the textured surfaces with graphene-containing ethanol solution. The macro-scale tribological performance of graphene was investigated by ball-on-disk tribometer. The results showed that graphene lubrication with appropriate groove area ratios (35% and 56%) were effective in enhancing the wear resistance compared with that of the bare M2 steel, the improvement was attributed to the effectiveness of wear debris entrapment and the formation of protective carbon layer. Especially with 35% groove area, there was sufficient graphene to reduce the friction, meanwhile, enough support to the high contact stress can be provided as well, demonstrating an obvious improvement in the friction behavior. As a result, low coefficient of friction (COF) around 0.22 can be sustained for 870 sliding cycles.

Performance of Li-Air Battery Cell with Folded Structure

The Li-Air batteries which convert the electrochemical reactions of lithium and O2 into electrical energy have high theoretical gravimetric capacity (3861 mAh/gLi) that is ten times higher than that of lithium ion batteries (372 mAh/gc). Its potential to generate high energy density makes it a promising candidate to replace the lithium ion batteries which practically reached the gravimetric energy density limit in the electric vehicle applications. To meet the requirements of the electric vehicle applications, the Li-Air batteries need to overcome the technical barriers that limit the cycle life such as electrolyte and cathode instability. Although recent developments have been focused on improving the cycle life (1) and safety (2) of Li-Air battery in efforts to extend its application into the electric vehicle, it is also important to design a cell structure that can achieve the highest possible energy density. The Li-Air battery uses lithium metal, porous carbon layer, protective layer and gas diffusion layer (GDL). The properties of lithium metal anode and porous carbon cathode layer are well known, and the cell design will mainly be affected by the mechanical property of the electrolyte, protective layer and GDL. Figure 1 shows the schematic of a Li-Air fold cell where the Li metal anode, protective layer, and cathode are folded. The oxygen can be distributed to the cathode through the GDL which is inserted between the two cathode layers that are formed from folding. The cell design enables the two layers of the cathode to share one common GDL layer and thus increasing energy density of the cell. The capacity of the Li-Air fold cell can be controlled by changing the length (L) and the number of folds of the cell. The width (W) of the cell affects the O2 distribution in cathode, thus the choice of W is limited. Figure 2 shows the areal capacity of three Li-Air fold cells which contained polyethylene oxide with LiTFSI as electrolyte in the cathode and protective layer. The cells were tested in 1 atm O2 at 60 C. The capacities of the cells were adjusted by changing the number of folds. For the cells in Figure 2, the three cells had WxL dimension of 1x5 cm and were folded 1, 10 and 50 times which resulted in the cells with capacity values of 0.02, 0.2 and 1 Ah, respectively. Figure 2 indicates that the performance of the Li-Air fold cell is reproducible as the number of folds increase. In the presentation, the effects of cell dimension on cell performance, the technical difficulties of manufacturing Li-Air cells with high energy density as well as the issues that need to be overcome to improve the cycle life will be discussed.

Facile fabrication of integrated three-dimensional C-MoSe2/reduced graphene oxide composite with enhanced performance for sodium storage

Scrupulous design and fabrication of advanced electrode materials are vital for developing high-performance sodium ion batteries. Herein, we report a facile one-step hydrothermal strategy for construction of a C-MoSe2/rGO composite with both high porosity and large surface area. Double modification of MoSe2 nanosheets is realized in this composite by introducing a reduced graphene oxide (rGO) skeleton and outer carbon protective layer. The MoSe2 nanosheets are well wrapped by a carbon layer and also strongly anchored on the interconnected rGO network. As an anode in sodium ion batteries, the designed C-MoSe2/rGO composite delivers noticeably enhanced sodium ion storage, with a high specific capacity of 445 mAh·g-1 at 200 mA·g-1 after 350 cycles, and 228 mAh·g-1 even at 4 A·g-1; these values are much better than those of C-MoSe2 nanosheets (258 mAh·g-1 at 200 mA·g-1 and 75 mAh·g-1 at 4 A·g-1). Additionally, the sodium ion storage mechanism is investigated well using ex situ X-ray diffraction and transmission electron microscopy methods. Our proposed electrode design protocol and sodium storage mechanism may pave the way for the fabrication of other high-performance metal diselenide anodes for electrochemical energy storage. Open image in new window