High-performance proton exchange membrane fuel cell with ultra-low loading Pt on vertically aligned carbon nanotubes as integrated catalyst layer

Reducing a Pt loading with improved power output and durability is essential to promote the large-scale application of proton exchange membrane fuel cells(PEMFCs).To achieve this goal,constructing optimized structure of catalyst layers with efficient mass transportation channels plays a vital role.Herein,PEMFCs with order-structured cathodic electrodes were fabricated by depositing Pt nanoparticles by Ebeam onto vertically aligned carbon nanotubes(VACNTs)growth on Al foil via plasma-enhanced chemical vapor deposition.Results demonstrate that the proportion of hydrophilic Pt-deposited region along VACNTs and residual hydrophobic region of VANCTs without Pt strongly influences the cell performance,in particular at high current densities.When Pt nanoparticles deposit on the top depth of around 600 nm on VACNTs with a length of 4.6μm,the cell shows the highest performance,compared with others with various lengths of VACNTs.It delivers a maximum power output of 1.61 W cm^(-2)(H_(2)/O_(2),150 k Pa)and 0.79 W cm^(-2)(H_(2)/Air,150 k Pa)at Pt loading of 50μg cm^(-2),exceeding most of previously reported PEMFCs with Pt loading of<100μg cm^(-2).Even though the Pt loading is down to 30μg cm^(-2)(1.36 W cm^(-2)),the performance is also better than 100μg cm^(-2)(1.24 W cm^(-2))of commercial Pt/C,and presents better stability.This excellent performance is critical attributed to the ordered hydrophobic region providing sufficient mass passages to facilitate the fast water drainage at high current densities.This work gives a new understanding for oxygen reduction reaction occurred in VACNTs-based ordered electrodes,demonstrating the most possibility to achieve a substantial reduction in Pt loading<100μg cm^(-2) without sacrificing in performance.

Aligned single-walled carbon nanotubes array electrode:Fabrication,characterization and application

In the presence of 1-（3-dimethylaminopropyl）-3-ethylcarbodiimide hydrochloride （EDC） and N-hydroxysuccinimide （NHS）, carboxylic group-functionalized single-walled carbon nanotubes （SWNTs） were assembled vertically on the glassy carbon electrode using ethylenediamine as linking agent to fabricate an aligned electrode （SWNTE）. The morphological characteristic was studied with atomic force microscope （AFM） and its electrochemical property was investigated using K3[Fe（CN）6] as probe. ssDNA had a sensitive voltammetric response at the SWNTE and the oxidative peak potentials of guanine base and adenine base were 0.608 Vand 0.896 V, respectively. Under the optimal conditions, the DPV peak current of guanine base vs. the concentration of ssDNA was linear in the range of 5.4 μg/L-10.8 mg/L with a detection limit of 1 μg/L （S/N = 3）.

Growth of Aligned Carbon Nanotubes on Large Scale by Methane Decomposition with Deactivation Inhibitor

The effects of additives containing iron or nickel during chemical vapor deposition （CVD） on the growth of carbon nanotubes （CNTs） by methane decomposition on Mo/MgO catalyst were investigated. Ferrocene and nickel nitrate were introduced as deactivation inhibitors by in-situ evaporation during CVD. The precisely controlled in-situ introduction of these inhibitors increased the surface renewal of catalyst, and therefore prevented the catalyst from deactivation. Using this method, aligned multi-walled CNTs with parallel mesopores can be produced on a large scale.

Effect of Particle Density on the Aligned Growth of Carbon Nanotubes

Aligned carbon nanotubes (CNTs) were prepared on Ni-coated Ni substrate by microwave plasma chemical vapor deposition (MWPCVD) with a mixture of methane and hydrogen gases at temperature of 550℃.The experimental results show a direct correlation between the alignment of CNTs and the density of the catalyst particles at low temperature.When the particle density is high enough,among CNTs there are strong interactions that can inhibit CNTs from growing randomly.The crowding effect among dense CNTs results in the aligned growth of CNTs at low temperature.

Controlled Growth of Well-Aligned Carbon Nanotubes, Electrochemical Modification and Electrodeposition of Multiple Shapes of Gold Nanostructures

An efficient method has been developed to synthesize well-aligned multi-walled carbon nanotubes (MWCNTs) on a conductive Ta substrate by chemical vapour deposition (CVD). Free-standing MWCNTs arrays were functionalized through electrochemical oxidation with the formation of hydroxyl and carboxyl functional groups. Using a new oven drying technique, we demonstrate that the unidirectionally aligned and laterally spaced geometry of the CNT arrays can be retained after being subjected to each step of electrochemical modification. Samples were analyzed by using a field emission scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier transformed infrared (FTIR) and Raman spectroscopy. Useful electrochemical methods for the synthesis of various gold nanostructures onto the aligned MWCNTs were then presented for the first time. The results demonstrated that flowerlike nanoparticle arrays, nanosheets and nanoflowers were obtained on the aligned CNTs under different experimental conditions. These kinds of aligned-CNT/Au nanostructures hybrid materials introduced by these efficient and simple electrochemical methods could lead to development of a new generation device for ultrasensitive catalytic and biological application.

Novel aerosol method for aligned carbon nanotubes synthesis

A novel aerosol method for the production of alighed carbon nanotubes was presented. Multi-walled carbon nanotubes(MWNTs) with fairly uniform diameters and aligned MWNT bundles were obtained by using solutions of organometallics such as ferrocene in hydrocarbon solvents. A hollow and multi-walled structure was observed with diameter ranging from 15 to 50 nm,leading aspect ratio to be over 200. The quality of the product is dependent on the pyrolysis temperature,carrier gas flow rate and the catalyst precursor concentration. For the sample synthesized at 900 ℃,G/D is 1.81. G/D of samples obtained at 850 ℃ and 800 ℃ are 1.18 and 0.77,respectively. The inclusion of acetylene to an atomized spray of ferrocene in hexane yield aligned MWNT bundles with a narrow diameter distribution.

Printable Aligned Single-Walled Carbon Nanotube Film with Outstanding Thermal Conductivity and Electromagnetic Interference Shielding Performance

Ultrathin,lightweight,and flexible aligned single-walled carbon nanotube(SWCNT)films are fabricated by a facile,environmentally friendly,and scalable printing methodology.The aligned pattern and outstanding intrinsic properties render“metal-like”thermal conductivity of the SWCNT films,as well as excellent mechanical strength,flexibility,and hydrophobicity.Further,the aligned cellular microstructure promotes the electromagnetic interference(EMI)shielding ability of the SWCNTs,leading to excellent shielding effectiveness(SE)of~39 to 90 dB despite a density of only~0.6 g cm^(−3) at thicknesses of merely 1.5-24μm,respectively.An ultrahigh thickness-specific SE of 25693 dB mm^(−1) and an unprecedented normalized specific SE of 428222 dB cm^(2)g^(−1) are accomplished by the freestanding SWCNT films,significantly surpassing previously reported shielding materials.In addition to an EMI SE greater than 54 dB in an ultra-broadband frequency range of around 400 GHz,the films demonstrate excellent EMI shielding stability and reliability when subjected to mechanical deformation,chemical(acid/alkali/organic solvent)corrosion,and high-/low-temperature environments.The novel printed SWCNT films offer significant potential for practical applications in the aerospace,defense,precision components,and smart wearable electronics industries.

A general surface-treatment-free approach to fabrication of alignment layers using a super-aligned carbon nanotube film template

We develop a general approach to the fabrication of films with unidirectional grooves, such as silicon nitride, silicon dioxide and aluminium oxide, in which the surface is not required to be treated. Super-aligned carbon nanotube （SACNT） film may be used as a template and as sacrificial layer, which is subsequently removed by heating in an atmosphere of air. The unidirectional morphology of the SACNT film turns into a desired film, which is found to possess the ability to align liquid crystal molecules. This approach also features high efficiency, low cost and easy scaling-up for mass production.

Preparation of super-aligned carbon nanotube-reinforced nickel-matrix laminar composites with excellent mechanical properties

A homogeneous and compact super-aligned carbon nanotube(SACNT)-reinforced nickel-matrix composite was successfully prepared by electrodeposition. The mechanical properties of the laminar SACNT/Ni composites were substantially improved compared with those of pure nickel. With increasing content of SACNTs, the tensile strength of the composite increased and the elongation decreased because of the high-strength SACNTs bearing part of an applied load and the fine-grained strengthening mechanism. The nanohardness of the SACNT/Ni composites was improved from 3.92 GPa(pure nickel) to 4.62 GPa(Ni-4 vol%SACNTs). The uniform distribution of SACNTs in the composites and strong interfacial bonding between the SACNTs and the nickel matrix resulted in an improvement of the mechanical properties of the SACNT/Ni composites. The introduced SACNTs refined the nickel grains, increased the amount of crystal twins, and changed the preferred orientation of grain growth.

A Study on the Effects of Carrier Gases on the Structure and Morphology of Carbon Nanotubes Prepared by Pyrolysis of Ferrocene and C_2H_2 Mixture

Carbon nanotubes （CNTs） were prepared using different carrier gases, with ferrocene as the catalyst precusor and acetylene as the carbon source. The effects of ammonia and nitrogen as carrier gases on the structure and morphology of CNTs were investigated. Transmission electron microscope （TEM）, high-resolution electron microscope （HRTEM）, scanning electron microscope （SEM） and X-ray diffraction （XRD） were employed to characterize the products and the catalyst. Experiment results show that the CNTs grown in N2 gas exhibited cylindrical and tubular structure, while a bamboo-like structure was observed for the CNTs grown in NH3 gas. Moreover, vertically aligned CNTs were obtained on an A12O3 disk when NH3 was used as the carrier gas. The carrier gas also exerted influence on the shape of the catalyst. Based on the theory of active centers of catalysis and combined with the particle shape of the catalyst, a growth model for the vertically aligned CNTs on the substrate is given.

Flow Field Induced Steady Alignment of Oxidized Multi-walled Carbon Nanotubes

The steady ordered micro-ribbons of oxidized multi-walled carbon nanotubes (MWNTs) were obtained through micro-aperture PTFE membrane by vacuum filtration. After treatment by mixture of concentrated nitric acid and sulfuric acid, the surface functional groups modified MWNTs can be easily dispersed to form a homogeneous suspension. It is found that the steady micro-ribbons existed in the films obtained by vacuum filtration of the suspension. The filtration formed steady flow field and induced steady alignment of oxidized MWNTs. The chemical treatment of MWNTs forming strong interaction between MWNTs is necessity to keep steady of the micro-ribbons microstructure.

Investigation on the Formation Mechanism of Double-Layer Vertically Aligned Carbon Nanotube Arrays via Single-Step Chemical Vapour Deposition

The mechanism for the formation of double-layer vertically aligned carbon nanotube arrays(VACNTs) through single-step CVD growth is investigated. The evolution of the structures and defect concentration of the VACNTs are tracked by scanning electron microscopy(SEM) and Raman spectroscopy. During the growth, the catalyst particles are stayed constantly on the substrate. The precipitation of the second CNT layer happens at around 30 min as proved by SEM.During the growth of the first layer, catalyst nanoparticles are deactivated with the accumulation of amorphous carbon coatings on their surfaces, which leads to the termination of the growth of the first layer CNTs. Then, the catalyst particles are reactivated by the hydrogen in the gas flow, leading to the precipitation of the second CNT layer. The growth of the second CNT layer lifts the amorphous carbon coatings on catalyst particles and substrates. The release of mechanical energy by CNTs provides big enough energy to lift up amorphous carbon flakes on catalyst particles and substrates which finally stay at the interfaces of the two layers simulated by finite element analysis. This study sheds light on the termination mechanism of CNTs during CVD process.

Alignment of Multi-walled Carbon Nanotubes in Polyacrylonitrile Fibers by Mechanical Drawing

Polyacrylonitrile(PAN)/multi-walled carbon nanotubes(MWNTs)nanocomposites were prepared by an in-situ polymerization method and the fibers from these composites were obtained by a wet-spinning process.The orientation behavior of MWNTs in the PAN fibers was investigated by X-ray diffraction and sound velocity methods.The dispersion and the alignment of the nanotubes were also studied by scanning electron microscopy.

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.

定向碳纳米管/丁苯橡胶复合材料的摩擦学各向异性行为研究

应用机械剪切诱导法制备定向碳纳米管/丁苯橡胶(CNTs/SBR)复合材料,研究碳管含量、定向性对复合橡胶材料力学特性和摩擦学特性的影响规律,分析这些结果产生的机理。结果表明:CNTs取向对SBR复合材料的摩擦学性能有显著影响。当CNTs-z垂直于摩擦界面和滑动方向,CNTs-z/SBR的力学、摩擦学性能均优于CNTs-x/SBR和CNTs-y/SBR。当CNTs平行于摩擦界面时,与滑动方向一致的CNTs-x/SBR力学性能优于与滑动方向垂直时的CNTs-y/SBR。CNTs-z可以提升橡胶复合材料的抗剪切性能,降低温升幅度和表面黏附作用,有效提升橡胶材料的摩擦学性能。载荷和速度工况下,摩擦因数与磨损量为负相关关系,即摩擦因数减小而磨损量增大,速度对摩擦学性能的影响大于载荷。研究结果可以为CNTs复合轮胎橡胶材料的摩擦学性能改善以及产业化应用提供科学参考。

Aligned carbon nanotubes for lithium-ion batteries:A review

Nanoscale materials are gaining massive attention in recent years due to their potential to alleviate the present electrochemical electrode constraints.Possessing high conductivity(both thermally and electrically),high chemical and electrochemical stability,exceptional mechanical strength and flexibility,high specific surface area,large charge storage capacity,and excellent ionadsorption,carbon nanotubes(CNTs)remain one of the most researched of other nanoscale materials for electrochemical energy storage.Rather than having them packed at random,CNTs perform better when packed/grown to order,vertically or horizontally aligned to a substrate.This study presents an overview of the impact of CNT alignment on the electrochemical performance of lithium-ion batteries(LIBs).The unique properties of vertically aligned CNTs(VACNTs)for LIB application were discussed.Furthermore,the mechanisms of charge storage and electrochemical performances in VACNT-based(pristine and composites)anodes and cathodes of LIBs were succinctly reviewed.In the end,the existing challenges and future directions in the field were also briefly discussed.

文献挖掘和高通量方法优化碳纳米管垂直阵列生长

具有良好力学性能和高导热性的碳纳米管垂直阵列(VACNT)可用作热管理中的有效热界面材料。为了利用沿碳纳米管轴向的高导热性,需要优化碳纳米管垂直阵列的结晶度和高度。然而,碳纳米管垂直阵列的生长参数空间(如退火时间、催化剂种类、生长温度、载气、碳源等)复杂,结构特征之间相互影响,同时提高碳纳米管垂直阵列的高度和质量仍是一个巨大的挑战。与此同时,缺乏对参数调控方向的指导进一步增加了实验结果的不确定性,并限制了产物结构优化的效率。本研究开发了一种文献挖掘-机器学习-高通量制备策略,有效优化了碳纳米管垂直阵列的高度和质量。为了揭示碳纳米管垂直阵列结构与关键生长参数之间的潜在关系,采用随机森林回归算法对一组已发布的样本数据(864个样本)进行建模,并利用机器学习模型解释包SHAP(SHapley Additive exPlanations)分析获得影响垂直阵列高度和结晶度的主要生长参数。经分析确定,高通量实验旨在调节4个关键参数:生长温度、生长时间、催化剂组分和碳源浓度。结果发现,经筛选的Fe/Gd/Al_(2)O_(3)催化剂能够生长出具有毫米级高度和更高结晶度的碳纳米管垂直阵列。结果表明,文献挖掘、高通量实验和基于数据的机器学习可以有效地处理碳纳米管生长等多参数过程,提高对结构的控制。

Aligned Graphene Nanoribbons and Crossbars from Unzipped Carbon Nanotubes

Aligned graphene nanoribbon (GNR) arrays have been made by unzipping of aligned single-walled and few-walled carbon nanotube (CNT) arrays. Nanotube unzipping was achieved by a polymer-protected Ar plasma etching method, and the resulting nanoribbon array can be transferred onto any chosen substrate. Atomic force microscope (AFM) imaging and Raman mapping on the same CNTs before and after unzipping confirmed that ~80% of CNTs were opened up to form single layer sub-10 nm GNRs. Electrical devices made from the GNRs (after annealing in H2 at high temperature) showed on/off current (Ion/Ioff) ratios up to 103 at room temperature, suggesting the semiconducting nature of the narrow GNRs. Novel GNR-GNR and GNR-CNT crossbars were fabricated by transferring GNR arrays across GNR and CNT arrays, respectively. The production of such ordered graphene nanoribbon architectures may allow for large scale integration of GNRs into nanoelectronics or optoelectronics.

Length-dependent alignment of large-area semiconducting carbon nanotubes self-assembly on a liquid–liquid interface

Aligned arrays of semiconducting carbon nanotubes(s-CNTs)with high homogenous density and orientation are urgently needed for high-performance carbon-based electronics.Herein,a length-controlled approach using combined technologies was developed to regulate the s-CNT length and reduce the length distribution.The impact of different lengths and length distributions was studied during aligned self-assembly on a liquid–liquid confined interface was investigated.The results show that short s-CNTs with a narrow distribution have the best alignment uniformity over the large scale.The optimized and aligned s-CNT array can reach a density as high as 100 CNTs·μm−1 on a 4-inch wafer.The field-effect transistor(FET)performance of these optimized s-CNT arrays was 64%higher than arrays without length-control.This study clarified that rational control of s-CNTs with desired length and length distribution on the aligned self-assembly process within the liquid–liquid confined interface.The results illustrate a solid foundation for the application of emerging carbon-based electronics.

Nonpolar cross-stacked super-aligned carbon nanotube membrane for efficient wastewater treatment

Membrane separation technology has made great progress in various practical applications,but the unsatisfactory separation performance of prevailing membrane materials hampers its further sustainable growth.This study proposed a novel nonpolar super-aligned carbon nanotube(SACNT)membrane,which was prepared with a layer-by-layer cross-stacking method.Through controlling the number of stacked SACNT layers,three kinds of SACNT membranes(SACNT_200,SACNT 300,and SACNT_400)were prepared.Systematic characterizations and filtration tests were performed to investigate their physico-chemical properties,surface wetting behavior,and filtration performance.Compared with two commercial membranes(Com_0.22 and Com_0.45),all the SACNT membranes achieved smoother and more uniform structures.Due to the hexagonal graphene structure of CNTs,the surface chemistry of the SACNT membranes is simple and inert,thereby potentially eliminating the covalent-bonding-induced membrane fouling.Besides,the SACNT membranes exhibited a typical nonpolar wetting behavior,with high contact angles for polar liquids(water:~124.9°-126.5°;formamide:~80.0°-83.99)but low contact angles for nonpolar diodomethane(~18.8°-20.99).This unique nonpolar feature potentially leads to weak interactions with polar substances.Furthermore,compared with the commercial membranes,the SACNT membranes obtained a significantly higher selectivity while achieving a comparable or higher permeability(depending on the number of stacked layers).Moreover,the SACNT membranes exhibited superior separation performance in various application scenarios,including municipal wastewater treatment(2.3 times higher cleaning efficiency),electro-assistant fouling inhibition(or even self-cleaning),and oil/water separation(>99.2%of separation efficiency),suggesting promising application prospects in various fields.