Porous graphene/carbon nanotube composite cathode for proton exchange membrane fuel cell

Porous Pt-graphene/multiwalled carbon nanotube (MWCNT) composite cathodes were fabricated for proton exchange membrane fuel cells and their electro-chemical performances were examined. Rod-like MWCNTs with a high aspect ratio induced a porous network structure and Pt-graphene was bound homogeneously to the porous network structure of MWCNTs in the form of a very rough surface, which facilitated simultaneous access between the Pt electro-catalyst and reactant. In addition, the porous MWCNT network enabled the Pt-graphene electrode to overcome the deficiency induced by high electrical resistance by providing an electrical pathway for the oxygen reduction reaction (ORR). Therefore, the ORR charge transfer resistance of the Pt-graphene/MWCNT composite cathode was much smaller than that of the Pt-graphene cathode, and the maximum power density of the Pt-graphene/MWCNT composite cathode was four times higher than that of the Pt-graphene cathode.     

Plain carbon steel bipolar plates for PEMFC

Bipolar plates are a multifunctional component of PEMFC. Comparing with the machined graphite and stainless steels, the plain carbon steel is a very cheap commercial metal material. In this paper, the possibility of applying the plain carbon steels in the bipolar plate for PEMFC was exploited. In order to improve the corrosion resistance of the low carbon steel in the PEMFCs' environments,two surface modification processes was developed and then the electrochemical performances and interfacial contact resistance (ICR) of the surface modified plate of plain carbon steel were investigated. The results show that the surface modified steel plates have good corrosion resistance and relatively low contact resistance, and it may be a candidate material as bipolar plate of PEMFC.     

Non-isothermal effects induced by natural illumination and infrared irradiation on cathodically polarized carbon steel electrodes

Experimental–theoretical approach was developed to analyse the heating behavior of carbon steel electrodes cathodically protected in quiescent NaCl 3.5 wt.% solution and exposed to irradiation. Natural and infrared wavelengths induced an increase of electrode surface temperature, enabling to determine oxygen limiting current enhancement. Numerical simulations of laboratory tests performed with infrared wavelength indicated that the Nusselt number ranges between 3.5 and 6, revealing the convective nature of the irradiation depolarization effect. The results obtained in NaCl 3.5 wt.% solution permit us to state that in seawater environment the sunlight depolarizing effect does not affect the current demand for cathodic protection.     

Magnetite nanoparticles by organic-phase synthetic route for carbon nanotube growth

In the present study, monodisperse Fe₃O₄ nanoparticles with diameters ranging from 10 nm to 25 nm were synthesized using a simple organic-phase synthetic route and these monodispersed nanoparticles were then used as catalyst for seed growth of carbon nanotube. Fe₃O₄ nanoparticles were reduced to iron nanoparticles assembly by Argon mixed with 5% Hydrogen gas at 400 °C and then it was examined by atomic force microscopy (AFM), thermomechanical analysis (TMA) and powder diffraction X-ray spectroscopic techniques. XRD indicates that iron clusters are bcc in nature and AFM image shows that the iron nanoparticles assemblies are 50–65 nm in size. To control the agglomeration of iron nanoparticles, nanoporous hybrid support material of Al₂O₃ and SiO₂ was used. However, this matrix also fails to stop the agglomeration of iron nanoparticles mainly due to the inhomogeneous distribution of pore diameters. TMA analysis of iron clusters shows a temperature-dependent morphology, therefore, the CNTs growth temperature critically ascertain the nature and structure of CNTs.     

Microwave absorption by polyaniline–carbon nanotube composites

Conductive thermoplastic composites containing both multi-walled carbon nanotubes and polyaniline doped with para-toluene sulfonic acid were formulated using two different methods. In the first method, PAni-pTsA-coated MWNTs were synthesized and processed into an insulating matrix. The second method involved mechanical mixing of separate synthetic PAni-pTsA and non-coated MWNT solids into an insulating matrix. Microwave absorption measurements at X-band frequencies (8–12 GHz) indicated that the former composites are poor absorbers, while the latter are good absorbers and showed stronger absorption than composites containing only PAni-pTsA or MWNTs.     

Welding method for fabricating carbon nanotube probe

A simple and reliable welding method was developed to fabricate carbon nanotube probe used in atomic force microscopy here. First, apply less than 20 V voltage between silicon probe and carbon nanotube when they were in close proximity under direct view of optical microscope. Then, let carbon nanotube contact with silicon probe and increase the external voltage to 30–60 V until carbon nanotube was divided and attached to the end of silicon probe. The fabricated carbon nanotube probe could be shortened to appropriate length by electron bombard. The weld strength of carbon nanotube probe was calculated by drawing the ordinary AFM probe and measuring the probe's deflections. For one carbon nanotube probe with 75 nm diameter, the weld strength was calculated more than 268 nN. Carbon nanotube probe showed higher aspect ratio and could more accurately reflect the true topography of sample than silicon probe.     

一种碳纳米管增强的铜基块体非晶合金复合材料(英文)

采用热压成型法制备碳纳米管增强的Cu50Zr40Ti10非晶合金复合材料,并研究碳纳米管添加量对其密度、热导率和力学性能的影响。结果发现,随着碳纳米管含量的增加,块体非晶合金复合材料的密度和抗压强度都降低;当碳纳米管的含量少于0.1%或超过0.6%时,块体非晶合金复合材料的热导率随着碳纳米管含量的增加而降低,然而,当碳纳米管的含量介于0.1%和0.6%之间时,块体非晶合金复合材料的热导率随着碳纳米管含量的增多而增大;当碳纳米管的含量少于1.0%时,块体非晶合金复合材料的应变量与模量明显得到提高,并随着碳纳米管含量的进一步增加块体非晶合金复合材料的应变量与模量明显下降。综合各种性能得出,碳纳米管的添加量少于0.2%为宜。     

Strengthening of copper matrix composites by nickel-coated single-walled carbon nanotube reinforcements

Mechanical, electrical and thermal properties of nickel-coated single-walled carbon nanotube (SWNT) reinforced copper matrix composites were investigated. The composites were fabricated by means of a powder metallurgy process, which consists of mixing nickel-coated carbon nanotubes with copper powders followed by hot-pressing. A homogeneous mixture could be obtained by the mechanical mixing process due to the similar density of nickel and copper. A high temperature displacement rate tester and a ball-on-disk device were employed to evaluate mechanical and tribological properties. Also, a four-point probe technique and a laser flash method were used to obtain electrical resistance and thermal conductivity. The mechanical and tribological properties of the copper matrix composites significantly improved by the incorporation of nickel-coated SWNT reinforcements. However, electrical resistance and thermal conductivity of the nickel-coated SWNT reinforced copper matrix composites were similar to those of the sintered nickel–copper specimens with the equivalent composition.     

Synthesis of aligned carbon nanotube with straight-chained alkanes by nebulization method

Aligned carbon nanotubes (CNTs) were synthesized by nebulized spray pyrolysis of solutions of organometallics in carbon precursor solvents. Four types of straight-chained alkanes including n-pentane, n-hexane, n-heptane and n-octane were used as precursor solvents for synthesis of aligned CNTs. The results from scanning electron microscopy, transmission electron microscopy and Raman spectroscopy show that the CNTs obtained from them have different diameters and degrees of graphitization. It is found that the n-heptane is the most suitable for the growth of aligned CNTs with high quality and yield. The thermodynamic properties of precursory carbon sources such as boiling point and formation enthalpy are considered to play a decisive role in the synthesis of CNTs. It will be very helpful for the controllable preparation of aligned CNTs at relatively low cost.     

Preparation of carbon nanotube composite material with metal matrix by electroplating

It is demonstrated that the nickel can be deposited directly on the surface of carbon nanotubes without pre-sensitization by Sn^2＋ and Pd^2＋ in a watt bath containing suspended nanotubes by electroplating. The nickel is deposited as spherical nanoparticle on the nanotubes. By increasing reaction time, the carbon nanotube is fully coated with nickel. A probable model, which represents the formation process of carbon nanotube-nickel composites by electroplating, is presented. The results show that this method is efficient and simple for preparing carbon nanotube-metal composite.     

Optical absorption spectroscopy for determining carbon nanotube concentration in solution

A simple method of determining concentration of carbon nanotubes in solution was provided by using optical absorption spectroscopy. The extinction coefficient of single-walled carbon nanotubes in Beer's law was determined after subtraction of the plasmon background. We found that the extinction coefficient was strongly dependent on the wavelength in the resonant region, whereas this was independent of wavelength in the non-resonant region after plasmon subtraction. This work demonstrates that the concentration of unknown carbon nanotubes dispersed in aqueous solution can be easily determined by simply measuring absorbance, once the extinction coefficient of the material is determined in advance.     

Polyaniline and multi-walled carbon nanotube composite electrode for rechargeable battery

The multi-walled carbon nanotube was introduced into the polymer matrix (PANI) to improve the electric conductivity as well as mechanical properties of the original polymer matrix.PANI/multi-walled carbon nanotube (MWCNT) composites were synthesized via ex-situ and in-situ polymerization to improve their electrical property.And the DC conductivities of PANI/MWCNT according to content and diameter of MWCNT were measured by four-point probe.The highest electric conductivity of PANI/MWCNT composite is 20 S/cm when 0.3% (mass fraction) MWCNTs with 10 nm in diameter and 15 μm in length are added in composite.     

采用循环伏安法研究微孔型多孔炭电极的电容特性

以酚醛树脂为原料,KOH为活化剂,制备出3种不同孔径分布的微孔型多孔炭(孔径≤2 nm)。在低温氮气吸附法测定BET比表面积和孔结构的基础上,采用循环伏安法考察了这3种微孔型多孔炭作电极的双电层电容器(EDLC)的电容特性。实验结果表明,微孔型多孔炭作电极的EDLC的电容特性是:在低扫描速率下,其循环伏安曲线达到电容平台后在高电压(±1.0 V)附近出现峰电容;延长在电解液中的浸渍时间,电极的比电容增大,高电位附近的峰电容减小。3种不同孔径分布的微孔型多孔炭作电极的EDLC的循环伏安特性受浸渍时间影响的程度也不同。     

Thickness limitations in carbon nanotube reinforced silicon nitride coatings synthesized by vapor infiltration

Chemical vapor infiltration is a convenient method for synthesizing carbon nanotube (CNT)-reinforced ceramic coatings. The thickness over which infiltration is relatively uniform is limited by gas phase diffusion in the pore structure. These effects were investigated in two types of silicon nitride matrix composites. With CNTs that were distributed uniformly on the substrate surface dense coatings were limited to thicknesses of several microns. With dual structured CNT arrays produced by photolithography coatings up to 400 μm thick were obtained with minimal residual porosity. Gas transport into these dual structured materials was facilitated by creating micron sized channels between “CNT pillars” (i.e. each pillar consisted of a large number of individual CNTs). The experimental results are consistent with basic comparisons between the rates of gas diffusion and silicon nitride growth in porous structures. This analysis also provides a general insight into optimizing infiltration conditions during the fabrication of thick CNT-reinforced composite coatings.     

Drilling delamination and thermal damage of carbon nanotube/carbon fiber reinforced epoxy composites processed by microwave curing

The drilling-induced delamination and thermal damage of carbon fiber reinforced epoxy composite materials are serious problems especially for high value components of the aviation industry. To suppress the delamination and drilling ablation, an innovative approach was employed in this study. The multiwalled carbon nanotubes (MWCNTs) were introduced to the matrix resin to improve the interlaminar strength and thermal conductivity. The as-prepared composite was processed by microwave curing to enhance the interface strength between carbon fiber and the carbon nanotubes modified matrix. During the drilling processes, optical fiber Bragg grating sensors were utilized to precisely measure the drilling temperature. Experimental results indicated that the interlaminar fracture toughness was increased by more than 66% compared to that of the traditional thermal cured samples without MWCNTs. And the delamination factor was decreased by 16% according to the computerized tomography scanning results. The maximum drilling temperature of the MWCNTs reinforced composite was below the glass transition temperature of the matrix resin and declined by 23 °C compared to traditional composites. With this novel method of carbon nanotube modification and microwave curing, we provide the capability of reducing the drilling delamination and thermal damage of carbon fiber composites simultaneously, and explored the possibility of manufacturing and machining integration.     

Freestanding strontium vanadate/carbon nanotube films for long-life aqueous zinc-ion batteries

Aqueous rechargeable zinc-ion battery(ZIB)is considered to be a potential energy storage system for large-scale applications due to its environmental friendliness,high safety,and low cost.However,it remains challenging to develop suitable cathode materials with high specific capacity and long-term cyclic stability.Herein,we have fabricated freestanding Sr0.19V2O51.3H2O/carbon nanotubes(SrVO/CNTs)composite films with different mass ratios by incorporating SrVO into CNTs network.The synthesized SrVO possesses a large interlayer spacing of 1.31 nm,which facilitates Zn(2+)diffusion.Furthermore,the SrVO/CNTs composite film with conductive network structure promotes electron transfer and ensures good contact between SrVO and CNTs during the long-term cycling process.As a result,the battery based on the SrVO/CNTs composite cathode with a mass ratio of 7:3 delivers a specific capacity of 326 mAh·g^-1at 0.1 A·g^-1and 145 mAh·g^-1at 5 A·g^-1,demonstrating a high capacity and excellent rate capability.Remarkably,the assembled ZIB shows good capacity retention of 91%even after ultra-long cycling for 7500 cycles at a high current rate of 5 Ag^-1.More importantly,the battery also delivers a high energy density and power density,as 290 Wh·kg^-1at 125 W·kg^-1(0.1 A·g^-1),or 115 Wh·kg^-1at 6078 W·kg^-1(5 Ag^-1).The results demonstrate that the SrVO/CNTs composite is a promising cathode toward large-scale energy storage applications.     

Densification of in situ prepared mesocarbon microbead/carbon nanotube composites by hot-press sintering

In situ prepared mesocarbon microbead/carbon nanotube(MCMB/CNT) composites are potential precursors of high density carbon materials for various applications. Integrated MCMB/CNT composites were successfully fabricated by hot-press sintering at 550 ℃ under 30 MPa. After further calcination at 900 ℃, the hot-press sintering fabricated MCMB block has an apparent density of 1.77 g/cm3 and the open porosity 5.1%. With the addition of 5%(mass fraction) CNTs, the density of the composite block is elevated to 1.84 g/cm3, and its open porosity is reduced to 3.5%. The flexural strength of composite block with 5% CNTs is elevated to 116 MPa. Through the hot-press sintering, pores of 10-50 nm in the calcinated bulks are remarkably eliminated. The interstice between microbeads in the composite blocks is filled up by CNTs together with β-resin and quinoline-insoluble spheres, which can further contribute to the densification.     

Enhanced thermal conductivity by the magnetic field in heat transfer nanofluids containing carbon nanotube

In this paper, we report for the first time that the thermal conductivity (TC) of the heat transfer nanofluids could be enhanced by the external magnetic field. The heat transfer nanofluids contain carbon nanotubes (CNTs) and magnetic-field-sensitive nanoparticles of Fe₂O₃. The reasonable explanation for these interesting results is that the Fe₂O₃ particles form aligned chains under applied magnetic field and help to connect the nanotubes, which results in improved thermal conductivity. On longer holding in magnetic field, the particles gradually move and form large clumps of particles, causing clumping of CNTs, then decreasing the TC. We also found that the time to reach the maximum peak value of TC is increased as the applied magnetic field is reduced by increasing the gap between two magnets. Scanning electron microscopy (SEM) pictures show that the nanotubes and nanoparticle are aligned well under the influence of magnetic field.