Unique Network Structure Research Articles

A nanofibrous polypyrrole/silicon composite derived from cellulose substance as the anode material for lithium-ion batteries.

A bio-inspired nanofibrous polypyrrole/silicon composite derived from natural cellulose substance was synthesized. Due to its unique porous network structure and PPy coating on the silicon fibres, it showed improved reversible capacity, cyclability and rate capability upon long-term charge/discharge cycling when employed as an anode material for lithium-ion batteries.

Bacterial cellulose nanofibrous membrane as thermal stable separator for lithium-ion batteries

Thermal shrinkage is a severe problem for the conventional polyolefin separators. In this work, we report the excellent performance of bacterial cellulose (BC) nanofibrous membranes as separators for lithium (Li) ion batteries. Properties of BC separator including morphology, ionic conductivity, electrochemical stability, thermal stability, mechanical strength and battery charge–discharge performance are characterized and compared to a commercial separator membrane (Celgard® 2325). Because of the unique fibrous and cross-linked three-dimensional network structure, BC separator shows excellent dimensional stability up to 180 °C, good ionic conductivity and competitive battery performance.

Two-dimensional V2O5 sheet network as electrode for lithium-ion batteries.

Two-dimensional V2O5 and manganese-doped V2O5 sheet network were synthesized by a one-step polymer-assisted chemical solution method and characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermal-gravimetric analysis, and galvanostatic discharge-charge analysis. The V2O5 particles were covered with thin carbon layers, which remained after decomposition of the polymer, forming a network-like sheet structure. This V2O5 network exhibits a high capacity of about 300 and 600 mA·h/g at a current density of 100 mA/g when it was used as a cathode and anode, respectively. After doping with 5% molar ratio of manganese, the capacity of the cathode increases from 99 to 165 mA·h/g at a current density of 1 A/g (∼3 C). This unique network structure provides an interconnected transportation pathway for lithium ions. Improvement of electrochemical performance after doping manganese could be attributed to the enhancement of electronic conductivity.

Conductive network structure formed by laser sintering of silver nanoparticles

The sintering of a silver (Ag) nanoparticle film by laser beam irradiation was studied using a CW DPSS laser. The laser sintering of the Ag nanoparticle thin film gave a transparent conductive film with a thickness of ca. 10 nm, whereas a thin film sintered by conventional heat treatment using an electronic furnace was an insulator because of the formation of isolated silver grains during the slow heating process. The laser sintering of the Ag nanoparticle thin film gave a unique conductive network structure due to the rapid heating and quenching process caused by laser beam scanning. The influences of the laser sintering conditions such as laser scan speed on the conductivity and the transparency were studied. With the increase of scan speed from 0.50 to 5.00 mm/s, the surface resistivity remarkably decreased from 4.45 × 108 to 6.30 Ω/sq. The addition of copper (Cu) nanoparticles to silver thin film was also studied to improve the homogeneity of the film and the conductivity due to the interaction between the oxidized surface of Cu nanoparticle and a glass substrate. By adding 5 wt% Cu nanoparticles to the Ag thin film, the surface resistivity improved to 2.40 Ω/sq.

Free-standing nitrogen-doped carbon nanotubes at electrospun carbon nanofibers composite as an efficient electrocatalyst for oxygen reduction

Efficient and non-Pt catalysts are highly desirable for many kinds of electrochemical applications. Herein, we have investigated the free-standing nitrogen-doped carbon nanotubes/carbon nanofibers composite (NCNT/CNFs) as an efficient cathode catalyst for the oxygen reduction reaction (ORR). The composite with a hierarchical structure is prepared by the pyrolysis of pyridine over flexible electrospun carbon nanofibers film (CNFs) supported with the nano-Fe catalyst. Scanning electron microscopy and transmission electron microscopy characterizations indicated that the curved NCNTs are sparsely, but tightly distributed on CNF surface. The as-prepared composite displayed good catalytic activity for ORR in an alkaline medium, with a favorable four-electron pathway, better long-term stability (94.6% retention after 10000 s), selectivity and resistance to the methanol crossover compared to the powder-form NCNTs and commercial Pt/C catalyst. The improved electrochemical performance of the NCNT/CNFs can be mainly attributed to the pyridinic-N doping and unique three-dimensional network structure. The results indicate that this novel composite can be used as a promising Pt-free ORR electrocatalyst.

Facile fabrication of a three-dimensional cross-linking TiO2 nanowire network and its long-term cycling life for lithium storage.

We describe a simple preparation of amorphous TiO2 nanomaterial through a simple dealloying method with high throughput at room temperature. The as-made TiO2 sample has a unique three-dimensional network structure built by cross-linking nanowires with the diameter of ∼5 nm. As an anode material for Li-ion batteries, the TiO2 product exhibits high capacities and a long cycling life at high rates of 500 and 1000 mA g(-1). In addition, it has a good rate capability. The as-made TiO2 nanowire network shows great application potential as an anode material with the advantages of unique performance and easy preparation.

Hierarchicality of trade flow networks reveals complexity of products.

With globalization, countries are more connected than before by trading flows, which amounts to at least trillion dollars today. Interestingly, around percents of exports consist of intermediate products in global. Therefore, the trade flow network of particular product with high added values can be regarded as value chains. The problem is weather we can discriminate between these products from their unique flow network structure? This paper applies the flow analysis method developed in ecology to 638 trading flow networks of different products. We claim that the allometric scaling exponent can be used to characterize the degree of hierarchicality of a flow network, i.e., whether the trading products flow on long hierarchical chains. Then, it is pointed out that the flow networks of products with higher added values and complexity like machinary, transport equipment etc. have larger exponents, meaning that their trade flow networks are more hierarchical. As a result, without the extra data like global input-output table, we can identify the product categories with higher complexity, and the relative importance of a country in the global value chain by the trading network solely.

The effects of highly structured low density carbon nanotube networks on the thermal degradation behaviour of polysiloxanes

Abstract Carbon nanotube-carbon aerogel (CNT-CA) networks are a member of a novel class of ultra-low density, high surface area, hierarchically structured, carbon-based materials possessing unique mechanical and physical properties. Through the secondary incorporation of a polymer matrix into these aerogel systems it is now possible to form intercalated polymeric hybrid CNT-CA composite materials with polymer to carbon surface internal surface contact areas in the order of ∼600 m2 g−1 at carbon loadings as low as ∼1.5 wt %. Reported here is the synthesis of a series of well-defined poly(dimethylsiloxane) (PDMS)/CNT-CA composite systems, their characterization and the in-depth analysis of the effects of the carbon architecture on the thermal stability and degradation behaviour of the of the PDMS matrix. The results of degradative thermal analysis using both pyrolysis gas-chromatography/mass spectrometry (py-GC/MS) and thermogravimetric analysis (TGA), clearly demonstrate that the presence of the CNT-CA scaffold within the PDMS matrix greatly increases the thermal stability of the system and drives the matrix towards calcination at temperatures above 600 °C. Subsequent characterization of the residual materials using a combination of fast magic angle spinning solid-state nuclear magnetic resonance (Fast-MAS NMR), energy dispersive X-ray spectroscopy (EDAX) and electron microscopy have demonstrated that the improvements in thermal stability are concurrent with the relative loading of carbon nanotubes within the aerogel matrix, that the PDMS matrix is being driven towards the formation of increased levels of SiO2 on degradation and that the preferential calcination effect is a function of the unique high surface area fibular network structure of the CNT-CA monoliths.

V2O5/functionalized MWCNT hybrid nanocomposite: the fabrication and its enhanced supercapacitive performance

The unique network structure of V2O5/f-MWCNT hybrid nanocomposite provides facile pathways for ion transport and enhances the electrochemical performance.

Grid-Connected Photovoltaic System Based on QZSI

Quasi-Z-source inverter (QZSI) is a new topology, which has been proposed to be simple and realize the single stage energy conversion in recent years. Due to the unique impedance network structure, it has the characteristic of shoot-through. In this paper the voltage-source QZSI is applied to grid-connected photovoltaic system. Firstly the operating principle of QZSI is deep analyzed, and then a grid-connected photovoltaic system using a QZSI is proposed. In order to conform to the requirement of grid-connection, the decoupling control thought of active current and reactive current by d-q rotating coordinate system and the modified PWM strategy of this system are studied. The rationality and feasibility of the proposed control strategy is verified through MATLAB/Simulink.

Personalized Recommendation Based on Co-Ranking and Query-Based Collaborative Diffusion

In this paper, we present an adaptive graph-based personalized recommendation method based on co-ranking and query-based collaborative diffusion. By utilizing the unique network structure of n-partite heterogeneous graph, we attempt to address the problem of personalized recommendation in a two-layer ranking process with the help of reasonable measure of high and low order relationships and analyzing the representation of user’s preference in the graph. The experiments show that this algorithm can outperform the traditional CF methods and achieve competitive performance compared with many model-based and graph-based recommendation methods, and have better scalability and flexibility.

Ultrahigh Durable PtPd/C Nanowire Networks Catalyst Synthesized by Modified Phase Transfer Method for Methanol Oxidation

AbstractA novel PtPd/C nanowire catalyst with interconnected network and fewer great grain boundaries has been successfully prepared by templateless and modified phase‐transfer method using cetyltrimethylammonium bromide as a capping in ethylene glycol solution by microwave‐assisted process. Its structure, composition, and morphology are characterized by X‐ray diffraction, energy dispersive analysis of X‐ray, and transmission electron microscopy, respectively. The electrochemical measurements demonstrate that the highly dispersed and uniform PtPd/C nanowire networks catalyst has a significantly higher electrocatalytic activity and durability for the methanol oxidation as compared to solid solution PtPd/C. The greatly improved durability of PtPd/C nanowire networks catalyst is mainly a consequence of the unique interconnected network structure with fewer grain boundaries, which provide more facile pathway for the electron transfer, and inhibit the particle growth and agglomeration, as well as prevent the particles embedded in the microporous of carbon support to enhance the Pt utilization.

Three-dimensional polypyrrole/MnO2 composite networks deposited on graphite felt as free-standing electrode for supercapacitors

Polypyrrole/MnO2 composites with unique three-dimensional network structure were successfully deposited on graphite felt (GF) fibers at the temperature of 50°C to fabricate PYMG-HT composite, which can be used as a free-standing electrode for supercapacitors. For comparison, PYMG-LT electrode was also prepared in ice bath, and the polypyrrole/MnO2 deposits on GF prepared at 0°C exhibit nano-flower shape, which is different from PYMG-HT. The PYMG-HT electrode displays specific capacitance as high as 821.3Fg−1 at the current density of 0.5Ag−1, which is much higher than that of PPy/MnO2 reported previously. Moreover, the PYMG-HT exhibits enhanced capacitive performance compared to PYMG-LT electrode.

Carbon microfibers with hierarchical porous structure from electrospun fiber-like natural biopolymer.

Electrospinning offers a powerful route for building one-dimensional (1D) micro/nanostructures, but a common requirement for toxic or corrosive organic solvents during the preparation of precursor solution has limited their large scale synthesis and broad applications. Here we report a facile and low-cost way to prepare 1D porous carbon microfibers by using an electrospun fiber-like natural product, i.e., silk cocoon, as precursor. We surprisingly found that by utilizing a simple carbonization treatment, the cocoon microfiber can be directly transformed into 1D carbon microfiber of ca. 6 μm diameter with a unique three-dimensional porous network structure composed of interconnected carbon nanoparticles of 10~40 nm diameter. We further showed that the as-prepared carbon product presents superior electrochemical performance as binder-free electrodes of supercapacitors and good adsorption property toward organic vapor.

High performance carbon molecular sieve membranes derived from hyperbranched polyimide precursors for improved gas separation applications

A series of hyperbranched polyimides (HBPI) were selected as precursors for the production of carbon molecular sieve membranes (CMSMs) and the gas separation performance of the resultant CMSMs was explored. By varying the monomer compositions of HBPI precursor polymers, the influences of degree of branching on pore size and distribution of the CMSMs are investigated and examined. A CO2 permeability of 1085Barrer with CO2/CH4 selectivity of 52 is attained. Thermal analyses reveal that the chain rigidity of the precursors increases with the degree of branching, while the density of the CMSMs shows an opposite trend. In view of the unique network structure offered by the HBPI precursors, it is speculated that the rigid network of the HBPI with the highest degree of branching has facilitated the formation of ultra-micropores, giving rise to the more constrained structure and improved diffusivity selectivity. The unique hyperbranched network structure found in HBPI possesses great potential to producing CMSMs with superior performance.

One template approach to synthesize C-doped titania hollow spheres with high visible-light photocatalytic activity

Carbon-doped titania hollow spheres (THS) with unique hollow three-dimensional network structure were synthesized by a facile method using carbon spheres as template. The resultant samples, such as carbon spheres, carbon spheres coated with titania precursor, and final THS were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectra (FTIR), Brunauer–Emmett–Teller (BET) and UV–vis absorption spectrum. Based on the results of these characterizations, a reasonable formation mechanism of the hollow three-dimensional network structure was proposed. The photocatalytic activity of as-prepared THS was evaluated by decoloration of methylene blue solution under visible light irradiation. Results indicated that THS possessed higher visible light-induced photocatalytic activity than commercial P25, which could be attributed to its visible light absorption characteristic created by C-doping and the unique hollow three-dimensional network structure.

An Indium Tin Oxide Conductive Network for Flexible Electronics Produced Using a Cotton Template

A regular indium tin oxide (ITO) conductive network is fabricated by a simple “dipping and drying” process using cotton as a template. The flexible composite consists of an interconnected conductive network of ITO, which acts as a transport channel for charge carriers, and a poly(dimethyl siloxane) substrate. The composite shows a very high electrical conductivity of ∼5 S m–1, which is ∼12 times of magnitude higher than those of other ordinary ITO-based composites. Moreover, it exhibits superior electrical/mechanical performance when bent or twisted compared to other ITO-based composites. The unique network structure and outstanding electrical, mechanical, and optical properties of the composite possess great potential for use in flexible, foldable, and stretchable electronics and other devices.

Composites of chemically-reduced graphene oxide sheets and carbon nanospheres with three-dimensional network structure as anode materials for lithium ion batteries

It is challenging to develop lithium ion batteries (LIBs) possessing simultaneously large reversible capacity, high rate capability, and good cycling stability, which are in turn determined mainly by the component materials of batteries. We designed and synthesized a series of composites of chemically-reduced graphene oxide (CRG) sheets and carbon nanospheres (CNS). It was illustrated that within the as-obtained composites the CNSs were fully cladded and bridged with CRG sheets forming a three-dimensional (3D) network with cavities and pores. Coin cells using the anodes made of the as-obtained composites with appropriate composition exhibit large reversible capacity, high rate capability, and good cycling stability. The highest reversible specific capacity could reach up to 925 mA h g−1 and 604 mA h g−1 at charge–discharge current densities of 5 A g−1 and 10 A g−1, respectively, and faint capacity and rate capability fades were detected even after 200 charge–discharge cycles. The excellent electrochemical performance of the anodes made of the as-obtained composites in the LIBs originates from the unique 3D network structure and the intrinsic properties of CRG and CNS that provide plenty of transportation pathways for electron and Li+, and sufficient tolerant sites for Li/Li+.

LiFePO4/CA cathode nanocomposite with 3D conductive network structure for Li-ion battery

A novel LiFePO4/Carbon aerogel (LFP/CA) nanocomposite with 3D conductive network structure was synthesized by using carbon aerogels as both template and conductive framework, and subsequently wet impregnating LiFePO4 precursor inside. The LFP/CA nanocomposite was characterized by X-ray diffraction (XRD), TG, SEM, TEM, nitrogen sorption, electrochemical impedance spectra and charge/discharge test. It was found that the LFP/CA featured a 3D conductive network structure with LiFePO4 nanoparticles ca. 10–30 nm coated on the inside wall of the pore of CA. The LFP/CA electrodes delivered discharge capacity for LiFePO4 of 157.4, 147.2, 139.7, 116.3 and 91.8 mA h g−1 at 1 °C, 5 °C, 10 °C, 20 °C and 40 °C, respectively. In addition, the LFP/CA electrode exhibited good cycling performance, which lost less than 1% of discharge capacity over 100 cycles at a rate of 10 °C. The good high rate performances of LiFePO4 were attributed to the unique 3D conductive network structure of the nanocomposite.

Ultrahigh Tensibility and Stimuli‐Response of Polymer‐Hectorite Nanocomposite Hydrogels

AbstractSummary: In the field of hydrogels with high mechanical performance, the nanocomposite hydrogel (NC gel) is widely interested due to its unique network structure with extraordinary mechanical, optical, and swelling/deswelling properties. Over the past few years, our group has investigated the fabrication and mechanical properties of a variety of the NC gels with different monomers. The effective network chain density and relaxation were well characterized by dynamic mechanical measurements. From these efforts, we found that the high tensibility of the NC gels came from the low effective network chain density with moderate relaxation. Besides, transparent and ultratensible NC gels with pH response and dual response of pH and temperature have successfully fabricated and characterized. This review will give a brief introduction of our achievements on the understanding of the preparation and properties of NC gels.