Synthesis of LiNi1/3Mn1/3Co1/3O2@graphene for lithium-ion batteries via self-assembled polyelectrolyte layers

LiNi_1/3Co_1/3Mn_1/3O₂ cathode coated with a thin layer of graphene (~8 nm) is successfully synthesized by self-assembly and pyrolysis of polyelectrolyte layers on the surface of NMC particles. The graphene coated NMCs still possess a layered structure with good crystallinity and demonstrate a superior electrochemical performance (e.g., rate capability and cycling stability). The best graphene coated NMC cathode is prepared at a calcination temperature of 800 °C, exhibiting a capacity retention of ~90% vs. 78% for pristine NMC @ cycle 100 and 1 C rate. The improvement in cycling performance is further enlarged after 500 cycles (74% vs. 51%). This can be attributed to the dual functions of graphene coating in enhancing electronic conductivity and protecting NMC surface from the contact with electrolyte during the electrochemical reaction.     

Design of a ductile carbon nanofiber/ZrB2 nanohybrid film with entanglement structure fabricated by electrostatic spinning

Polyacrylonitrile (PAN), a kind of multi-purpose man-made polymer material, has been widely used in various products, including carbon fiber precursor fiber manufacturing. Organic/inorganic nanocomposites can provide precursor material with unique properties due to optimal structural design. Herein, PAN based carbon nanofiber (CNF) coated zirconium borate (ZrB₂) particles fiber film was prepared via electrostatic spinning strategy. Crosslinking network between carbon atoms formed at 280 °C due to long chain PAN molecules, which underwent pyrolysis at 800–1200 °C. Scanning electron microscope analysis showed that ductile CNF/ZrB₂ hybrid material with entanglement structure was successfully fabricated. Phase composition of the materials was analyzed by X-ray diffractometer, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy, which confirmed the presence of carbon atoms in the materials. Entanglement structure between CNFs and ZrB₂ enhanced tensile performance of nanohybrid film, in which CNF film with 25% ZrB₂ content exhibited optimal mechanical properties. The design of nanohybrid structure provides facile and universal approach for exploration of organic/inorganic nanocomposites with controlled structures and excellent mechanical properties.     

Fabrication of Ni/ZnO/C hollow microspheres decorated graphene composites towards high-efficiency electromagnetic wave absorption in the Ku-band

Developing light-weight, thin thickness and high-efficiency electromagnetic wave (EMW) absorbers is an effective strategy for dealing with the increasingly serious problem of electromagnetic radiation pollution. Herein, nickel/zinc oxide/carbon (Ni/ZnO/C) hollow microspheres decorated graphene composites were facilely prepared through the high-temperature pyrolysis of bimetallic NiZn metal-organic frameworks (MOFs) precursors. Morphological characterization results manifested that the Ni/ZnO/C microspheres with unique hollow structure were almost evenly anchored on the wrinkled surfaces of flake-like graphene. Moreover, the influences of additive amounts of graphene oxide (GO) in the MOFs precursors on the crystal structure, graphitization degree, micromorphology, magnetic properties, electromagnetic parameters and EMW absorption performance were investigated in detail. It was found that the superior EMW absorption performance could be achieved through facilely adjusting the additive amounts of GO in the precursors. As the additive amount of GO was equal to 60 mg, the obtained composite showed the comprehensive excellent EMW absorption performance. Notably, the optimal minimum reflection loss reached ?57.5 dB at 16.5 GHz in the Ku-band under an ultrathin matching thickness of merely 1.34 mm, and the broadest effective absorption bandwidth achieved 5.6 GHz (from 12.4 to 18 GHz) when the thickness was 1.5 mm. Furthermore, the underlying EMW absorption mechanisms of as-prepared composites were revealed. It was believed that our results could be valuable for the structural design and EMW absorption performance modulation for MOFs derived magnetic carbon composites.     

Direct laser fabrication of large-area and patterned graphene at room temperature

Direct fabrication of graphene on solid carbon coated nickel surface was realized by laser irradiation at room temperature. High-quality graphene was obtained rapidly, e.g. 28.8 cm²/min. Arbitrary patterns designed by computer aided design (CAD) software were fabricated directly on Ni substrates without additional mask or setup. Raman mapping results showed that monolayer/bilayer graphene regions accounted for 64% of the film area. Graphene films exhibited excellent resistance to corrosion. The extremely low corrosion current density and high free corrosion potential in 3.5% NaCl aqueous (aq) solutions showed that the as-produced graphene had a superior anti-corrosion performance. The penetration and precipitation mechanism of carbon into Ni substrate during the fabrication process were also discussed. This approach may reach the scale large enough for practical applications.     

An all-graphene based transparent and flexible field emission device

All-graphene based cathode and anode structures were fabricated and their application as a flexible and transparent field emission device is presented. The graphene film was grown on a Cu foil by thermal chemical vapor deposition and later transferred to a polymer substrate through a hot press lamination technique. Multiwall carbon nanotubes (MWCNTs) were spin-coated onto a graphene film on a transparent, flexible substrate to form the cathode of the field emission device. A green-phosphor coated graphene-PET film was used as the anode. The device showed good transparency and flexibility as well as giving an appreciable emission current. The simple processing techniques used can easily be upgraded to a larger scale and be tailored for any transparent and flexible substrate. The device offers exciting applications of carbon nanostructures in foldable electronics.     

Optical reflectance measurement of large-scale graphene layers synthesized on nickel thin film by carbon segregation

The change of surface roughness during graphene synthesis on evaporated Ni thin films was monitored. It was found that Ni is highly agglomerated during high temperature annealing but the surface roughness is made smoother by the coverage of graphene. It is demonstrated that diffuse reflectance is a fast and convenient technique for evaluating surface roughness over a large area of graphene on a metal film, and specular reflectance is a good indicator of the coverage of graphene on the metal film.     

The additive-free electrode based on the layered MnO2 nanoflowers/reduced,graphene oxide film for high performance supercapacitor

The MnO₂ nanoflowers/reduced graphene oxide composite is coated on a nickel foam substrate (denoted as MnO₂ NF/RGO @ Ni foam) via the layer by layer (LBL) self-assembly technology without any polymer additive, following the soft chemical reduction. The layered MnO₂ NF/RGO composite is uniformly anchored on the Ni foam skeleton to form the 3D porous framework, and the interlayers have access to lots of ions channels to improve the electron transfer and diffusion. This special construction of 3D porous structure is beneficial to the enhancement of electrochemical property. The specific capacitance is up to 246 F g⁻¹ under the current density of 0.5 A g⁻¹. After 1000 cycles, it can retain about 93%, exhibiting excellent cycle stability. The electrochemical impedance spectroscopy measurements confirm that MnO₂ NF/RGO @ Ni foam electrode has lower R_ESR and R_CT values when compared to MnO₂ @ Ni foam and RGO @ Ni foam. This study opens a new door to the preparation of composite electrodes for high performance supercapacitor.     

Graphene wrapped copper–nickel nanospheres on highly conductive graphene film for use as counter electrodes of dye-sensitized solar cells

A novel architecture of graphene wrapped copper–nickel (Cu–Ni) nanospheres (NSs)/graphene film was proposed to be TCO- and Pt-free counter electrode (CE) with high electrocatalytic activity for dye-sensitized solar cells (DSSCs). The novel architecture CE is composed of highly conductive graphene film, Cu–Ni alloy NSs and the wrapping graphene on the surface of alloy NSs. The graphene film as an electrically conductive layer was synthesized by chemical vapor deposition (CVD) on the insulating SiO₂ substrate, and graphene wrapped Cu–Ni alloy catalyst NSs on the graphene film were in situ formed by the reduction of Cu–Ni acetate and graphene growth using CVD. The graphene wrapped Cu–Ni NSs/graphene film CE shows much superior electrocatalytic activity, compared with graphene film, and the power conversion efficiency of 5.46% was achieved in DSSC devices, which is close to that of Pt/FTO electrode (6.19%). Therefore, the novel architecture of graphene wrapped Cu–Ni NSs/graphene film CE may be used as Pt- and TCO-free CEs for low-cost, high performance DSSCs.     

Thermomechanical and corrosion inhibition properties of graphene/epoxy ester–siloxane–urea hybrid polymer nanocomposites

The effect of graphene on the corrosion inhibition properties of a hybrid epoxy–ester–siloxane–urea polymer was investigated. The weight fraction of graphene was varied from 1 to 2 wt%. Direct current polarization (DCP) and electrochemical impedance spectroscopic (EIS) techniques were used to measure the polarization and coating resistance of the coated aluminum alloy substrate. The grapheme/hybrid polymer composite coatings showed much higher corrosion inhibition property when compared to the neat hybrid polymer coating. An increase in glass transition temperature and rubbery region modulus was also observed for composites containing 1–2 wt.% of graphene. A direct correlation between the rubbery plateau modulus of free standing composite thin films and corrosion resistance of the composite coatings was made, indicating that the corrosion protection mechanism is due to restriction of the polymer chain motion by graphene which causes a decrease in coating permeability.     

Laser direct synthesis of graphene on quartz

We demonstrate a laser-based technique to directly synthesize few layer graphene on quartz substrates without using any metal catalyst. In our approach, a photoresist S-1805 (from Shipley Comp.) film coated on quartz wafers was heated, and then decomposed, by irradiation of a continuous-wave laser. The carbon atoms from the photoresist were dissolved in the molten quartz, and then extracted to form graphene when the temperature of the quartz was decreased. Raman spectroscopy shows the as-produced graphene is two to three layers thick. This laser-based method will provide a new approach and platform for applications of graphene-based devices.     

Preparation and performance of braid‐reinforced poly(vinyl chloride) hollow fiber membranes

A novel braid‐reinforced (BR) poly(vinyl chloride) (PVC) hollow fiber membrane was fabricated via dry‐wet spinning process. The mixtures of PVC polymer solutions were uniformly coated on the tubular braid which contained polyester (PET) and polyacrylonitrile (PAN) fibers. The influences of braid composition on structure and performance of BR PVC hollow fiber membranes were investigated. The results showed that the prepared BR PVC hollow fiber membranes were composed of two layers which contained separation layer and tubular braid supported layer when the PET and PET/PAN hybrid tubular braids were used as the reinforcement. But the sandwich structure appeared when the PAN tubular braid was used as the reinforcement, which revealed outer separation layer, tubular braid supported layer and the inner polymer layer. The BR PVC hollow fiber membranes that prepared by PET/PAN hybrid tubular braid had favorable interfacial bonding state compared with the membrane prepared by pure PET or PAN tubular braid. The pure water flux of the BR PVC hollow fiber membranes that prepared by the PET/PAN hybrid tubular braid were lower than that prepared by pure PET or PAN tubular braid, but the rejection of Bovine serum albumin was opposite. The tensile strength of prepared BR PVC hollow fiber membrane was higher than 50 MPa. Both of the tensile strength and elongation at break decreased with the increase of the PAN filaments in the PET/PAN hybrid tubular braid. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45068.     

Allyl-Functionalization enhanced thermally stable graphene/fluoroelastomer nanocomposites

Development of new elastomers with novel functionality has continued since their discovery in order to meet industrial and defense needs in harsh environments. The recent advance of carbon nanomaterials inspired innovative material design strategies and enable more effective production of high-performance elastomers. In this paper, the free radical initiated crosslinking reaction in graphene/fluoroelastomer nanocomposites was studied and the effects of chemical functionalization of graphene nanosheets were analyzed. It indicated that graphene oxide (GO) enhanced fluoroelastomer nanocomposites demonstrated poor high-temperature stability due to the pyrolysis at around 200 °C. In contrast, reduced graphene oxide (RGO) enhanced fluoroelastomer exhibited good thermal stability, but RGO didn't participate in the crosslinking, resulting in very limited improvement in mechanical properties. In this paper, reduced allyl functionalized graphene was studied for the first time to enhance free radical initiated elastomers. The reduced allyl functionalization of graphene was demonstrated to impart superior thermal stability and enhanced mechanical properties to the elastomer matrices. The study of vulcanization kinetics provided insights that the allyl functional groups participated in and accelerated the crosslinking. These results indicated a scalable method to incorporate the advantages of graphene into polymer matrices through free radical reaction. The discovery is very promising to be used in the industry to fabricate gaskets, o-rings, and membranes for high temperature applications.     

Graphene as initiator/catalyst in polymerization chemistry

One of the most important applications of graphene-based materials is the formation of nanocomposite materials, where graphene in the bulk-polymer matrix transfers its properties onto the polymeric material. Control of the polymer/graphene interface by attached polymeric interlayers is essential to generate nanocomposites, thus avoiding the aggregation of graphene nanoparticles. Among all graphene materials graphene oxide (GO) and reduced graphene oxide (r-GO) can be prepared on large scales useful for mass production graphene/polymer composites. The direct use of graphene materials as both, the polymerization initiator or catalyst and additive not only diminishes the agglomeration of particles in composites but also reduces the process of composite production to one facile step, which in turn avoids further purification regarding to strong acid initiators and metal particles catalysts. Here, literature activities within the past ∼10 years using graphene-based materials either as initiator or catalyst in different polymerization reactions are reviewed.     

Enhancement in photovoltaic properties of bismuth ferrite/zinc oxide heterostructure solar cell device with graphene/indium tin oxide hybrid electrodes

Integrating of ferroelectric thin films with two-dimensional materials may provide a novel and unique characteristics in the field of optoelectronics due to the coupling of their distinctive intrinsic features. A heterostructure (bismuth ferrite/zinc oxide) device is fabricated with different types of the electrode to enhance the power conversion efficiency (PCE). A single-phase multiferroic BFO thin film is grown by atomic layer deposition (ALD) method and annealed in different environments such as helium, nitrogen, and oxygen. We investigated the effect of annealing parameters and different types of electrodes on solar cell applications. We observed that the leakage current 10 orders of magnitude was reduced by decreasing in the dielectric loss. Further, the power conversion efficiency (PCE) is improved from 4.1% to 7.4% with a hybrid transparent electrode (graphene/indium tin oxide). The value of PCE is further increased at a low temperature. So, the improvement in the key parameter of bismuth ferrite thin-film evidently highlights the importance of annealing atmosphere and graphene as an electrode in BFO thin film applications in optoelectronics.     

Solvent assisted capillary force lithography

Capillary force lithography (CFL) utilizes the capillary-filling phenomenon of a polymeric melt into a cavity to pattern the polymer film coated on a substrate. Most CFL approaches are realized at high temperatures. The solvent-assisted CFL method proposed here realizes patterning at ambient temperature. A swollen PDMS (poly(dimethysilane)) stamp by solvent is placed in contact with a polymer thin film. As the solvent reserved in the PDMS stamp diffuses into the polymer film, the polymer can be dissolved or swollen. Then the capillary force drives the pattern formation. By carefully choosing the experimental conditions, it is possible to produce highly regular and reproducible nano- to micrometer scale polymer patterns using the same microscopic patterned mold. Complex polymer patterns can also be fabricated through the multiple printing.     

On the mechanism of the anodic protection of aluminium alloy AA5182 by emeraldine base coatings: Evidences of a galvanic coupling

Aluminium AA5182 coupons covered by a polyaniline film in the emeraldine base (EB) form showed increasing corrosion potential and decreasing corrosion current as a function of the thickness of the polymer layer. The cathodic reaction was proved not limited by diffusion of species inside the electrolyte solution and oxygen had no effect on the electrochemical behaviour of the coated samples. An EB coating on indium tin oxide conducting layer appeared slightly electroactive in neutral media. The IR spectra of aluminium coated samples, before and after heating in argon atmosphere, confirmed a redox reaction between the polymer film and the metal. This galvanic coupling can explain the good protective behaviour of emeraldine base against corrosion of aluminium.     

On the oxidation kinetics and mechanisms of various SiC-coated carbon-carbon composites

SiC coatings on the surface of C-C were produced by either silicone resin impregnation/ pyrolysis or reaction sintering. Cycles of resin impregnation/pyrolysis produced an SiC coating, on the walls of fine open pores, which was effective in reducing the oxidation rate of C-C and in shifting the transition temperature to a higher value. Unless it is pre-coated with a pyrocarbon layer before sintering, plain reaction sintered SiC has oxidation behaviors similar to those of the above-mentioned SiC. The dense pyrocarbon film deposition on the surface of C-C could form a better SiC film than others. The carbon film homogenized the surface of C-C and a dense SiC film was established. The oxidation of the coated C-C can be modelled by a set of “oxidation resistors” in series and/or in parallel, with each resistor corresponding to an oxidation element. The controlling mechanism can be resolved from the activation energy. A combined resistant layer, consisting of resin impregnation, pyrocarbon film and reaction sintering SiC, showed the best oxidation resistance of any single-layer coated C-C composite.     

Binder-free multilayered SnO2/graphene on Ni foam as a high-performance lithium ion batteries anode

The reasonable structure construction of electrode materials with superior performance is desired for the new generation lithium ion batteries (LIBs). Herein, binder-free multilayered SnO₂/graphene (GN) on Ni foam was fabricated via a dip coating method. SnO₂ nanoparticles and GN were alternatively coated on Ni foam to form a sandwich-like structure. The wrapping of GN can raise the conductivity and keep the structural integrality of the binder-free material, preventing structure collapse arised from the volume expansion of SnO₂. Benefiting from the porous Ni foam framework and sandwich-like structure, the SnO₂/GN composite exhibited good rate performance and excellent cycle stability. High capacities of 708 and 609?mAh?g^?1 were achieved at rates of 1 and 2?A?g^?1. Besides, the SnO₂/GN electrode delivered a high capacity of 757?mAh?g^?1 after 500 cycles at 1?A?g^?1.     

Fabrication of palladium/graphene oxide composite by plasma reduction at room temperature

ABSTRACT: Pd nanoparticles were fabricated on graphene oxide (GO) using a deposition-precipitation method with a glow discharge plasma reduction at room temperature. Argon was employed as the plasma-generating gas. The novel plasma method selectively reduces the metal ions. The graphene oxide has no change with this plasma reduction according to the Fourier transform infrared analysis. The Pd nanoparticles on the GO were uniformly distributed with an average diameter of 1.6 nm. The functional groups on the GO not only prevent Pd nanoparticles from further aggregation but also provide a strong hydrophilic property to the Pd/GO composite, which can form stable colloidal dispersions in water.     

Hydrogen production by catalysed pyrolysis of polymer blends

Differently composed mixtures of HDPE and PMMA were pyrolysed at 700 °C and 815 °C in pyrolysis reactor. It was directly coupled with gas chromatography/mass spectrometry (GC/MS). On line pyrolysis GC/MS was applied in analysis of hydrogen, methane and carbon monoxide yielding in polymer blends pyrolyzate with/without metal (Ni,Co) coated particles, tested as a methane to hydrogen conversion catalysts supporting additives. They were prepared by electrochemical deposition of Ni and Co on the small iron particles surface. Maximum hydrogen production was confirmed at the highest pyrolysis temperature (815 °C), and the highest HDPE contents in the blends mixture. Higher content of the PMMA in the mixture led to higher production of CO and lower hydrogen contents in pyrolyzate. Nickel and cobalt containing additives affected production of hydrogen and other components at both 700 °C and 815 °C pyrolysis temperatures. An effect of different heat distribution between metal particles and polyblends occurred and affected hydrogen production. Application of pyrolysis gas chromatography in hydrogen production from polyblends represents an important tool to model future technological outputs as well simultaneous hydrogen production and CO, CO₂ elimination. Moreover, catalysis assisted conversion of methane to hydrogen can improve final hydrogen content in pyrolyzate. Effectivity of pyrolysis hydrogen production was determined by its quantification based on analytical calibration.