Tailoring Carbon Nanotube Microsphere Architectures with Controlled Porosity

Nanomaterials are at the core of fuel cell electrodes, providing high‐area catalytic, proton, and electron conducting surfaces, traditionally on carbon black supports. Other carbons, e.g., carbon nanotubes (CNTs) and graphene are less prone to oxidation; however, their handling is not trivial due to health risks associated with their size. Assembling them into microscale structures without jeopardizing their performance is ideal, but there are mass transfer limitations as thickness increases. In this work, a soluble acicular calcium carbonate (aragonite) is used as a porogen to create connected porosity in microspheres. Increasing macroporosity has a considerable positive impact on the mass transfer process. The experimental manipulation of porosity of the microspheres is combined with pore network modeling to better understand how pore distribution throughout the whole microsphere can optimize platinum utilization decorated onto the CNTs. Oxygen reduction reaction (ORR) activity is compared with the prepared composite materials and a commercial Pt/C catalyst for 4 weeks. The composite materials exhibit a highly interconnected network resulting in a 3.4 times higher ORR activity (at 0.9 V vs reversible hydrogen electrode) than that of the nanoporous spheres with no macroporosity.     

A General and Efficient Route to Fabricate Carbon Nanotube‐Metal Nanoparticles and Carbon Nanotube‐Inorganic Oxides Hybrids

Novel pyrenyl‐moieties‐decorated hyperbranched polyglycidol (pHBP) is synthesized and utilized for the functionalization of carbon nanotubes (CNTs) via a non‐covalent (non‐destructive) process. Mediated by a pHBP layer on the CNT sidewall, Au, Ag and Pt nanoparticles and uniform SiO₂, GeO₂ and TiO₂ coatings are generated in situ and deposited onto the as‐prepared CNT/pHBP hybrids, forming versatile homogeneous CNT‐based nanohybrid sols. The coverage of metal nanoparticles and oxide coatings is controllable simply by changing the employed amount of precursors. This easy synthetic strategy provides a general and convenient route to efficiently assemble a wide range of metal nanoparticles and inorganic oxide components on the sidewalls of CNTs, and enables the construction of heterogeneous nanostructures with novel functionalities. As a means of demonstrating the versatility of the fabricated hybrid materials, the catalytic function of CNT/pHBP/Pt hybrids towards the reduction of 4‐nitrophenol and the incorporation of dye molecules into the CNT/pHBP/SiO₂ matrix resulting in fluorescent nanofibers are investigated.     

Fabrication and Electrical and Mechanical Properties of Carbon Nanotube Interconnections

Individual carbon nanotubes (CNTs) have been cut, manipulated, and soldered via electron‐beam‐induced deposition of amorphous carbon (a‐C) and using a scanning tunneling microscope inside a transmission electron microscope. All CNT structures, including simple tube–tube connections, crossed junctions, T‐junctions, zigzag structures, and even nanotube networks, have been successfully constructed with a high degree of control, and their electrical and mechanical properties have been measured in situ inside the transmission electron microscope. It is found that multiple CNTs may be readily soldered together with moderate junction resistance and excellent mechanical resilience and strength, and the junction resistance may be further reduced by current‐induced graphitization of the deposited a‐C on the junction.     

Carbon Nanotube‐Encapsulated Noble Metal Nanoparticle Hybrid as a Cathode Material for Li‐Oxygen Batteries

Although Li‐oxygen batteries offer extremely high theoretical specific energy, their practical application still faces critical challenges. One of the main obstacles is the high charge overpotential caused by sluggish kinetics of charge transfer that is closely related to the morphology of discharge products and their distribution on the cathode. Here, a series of noble metal nanoparticles (Pd, Pt, Ru and Au) are encapsulated inside end‐opened carbon nanotubes (CNTs) by wet impregnation followed by thermal annealing. The resultant cathode materials exhibit a dramatic reduction of charge overpotentials compared to their counterparts with nanoparticles supported on CNT surface. Notably, the charge overpotential can be as low as 0.3 V when CNT‐encapsulated Pd nanoparticles are used on the cathode. The cathode also shows good stability during discharge–charge cycling. Density functional theory (DFT) calculations reveal that encapsulation of “guest” noble metal nanoparticles in “host” CNTs is able to strengthen the electron density on CNT surfaces, and to avoid the regional enrichment of electron density caused by the direct exposure of nanoparticles on CNT surface. These unique properties ensure the uniform coverage of Li₂O₂ nanocrystals on CNT surfaces instead of localized distribution of Li₂O₂ aggregation, thus providing efficient charge transfer for the decomposition of Li₂O₂.     

Carbon Electrodes Modified with TiO2/Metal Nanoparticles and Their Application for the Detection of Trinitrotoluene

The preparation of modified, catalytically active, functional carbon electrodes and their application to the electrochemical reduction of trinitrotoluene (TNT) is reported. Modification of the electrodes is performed with composites of nanometer‐sized, mesoporous titanium dioxide, which acts as a support containing inserted/deposited nanoparticles of ruthenium, platinum, or gold. These composites are prepared by a novel sonochemical synthesis using simple and low‐cost precursors. Cyclic voltammetry shows that 2,4,6‐trinitrotoluene can be reduced on thus‐modified carbon‐paper electrodes at potentials of around –0.5 V (vs. Ag/AgCl/Cl^–) in aqueous solutions. Unexpectedly, carbon‐paper electrodes modified with the TiO₂/nano‐Pt composites demonstrate a remarkable electrochemical activity toward the reduction of trinitrotoluene. A significant finding is that the two electrode processes—the reduction of TNT and of oxygen—are quite well separated in potential on the modified carbon‐paper electrodes because of selective electrochemical activity of the TiO₂/nano‐Pt and TiO₂/nano‐Au composites. TiO₂/nano‐Ru composites are found to be much less electrochemically active for the detection of TNT compared to the previous two. It was also established that the titanium dioxide support of TiO₂/nano‐Pt composites plays a specific role for facilitating the TNT‐ and oxygen‐reduction processes.     

Yolk–Shell Structured FeP@C Nanoboxes as Advanced Anode Materials for Rechargeable Lithium‐/Potassium‐Ion Batteries

Maintaining structural stability and alleviating the intrinsic poor conductivity of conversion‐type reaction anode materials are of great importance for practical application. Introducing void space and a highly conductive host to accommodate the volume changes and enhance the conductivity would be a smart design to achieve robust construction; effective electron and ion transportation, thus, lead to prolonged cycling life and excellent rate performance. Herein, uniform yolk–shell FeP@C nanoboxes (FeP@CNBs) with the inner FeP nanoparticles completely protected by a thin and self‐supported carbon shell are synthesized through a phosphidation process with yolk–shell Fe₂O₃@CNBs as a precursor. The volumetric variation of the inner FeP nanoparticles during cycling is alleviated, and the FeP nanoparticles can expand without deforming the carbon shell, thanks to the internal void space of the unique yolk–shell structure, thus preserving the electrode microstructure. Furthermore, the presence of the highly conductive carbon shell enhances the conductivity of the whole electrode. Benefiting from the unique design of the yolk–shell structure, the FeP@CNBs manifests remarkable lithium/potassium storage performance.     

Magnetically Recyclable Catalytic Carbon Nanoreactors

Multifunctional nanoreactors are assembled using hollow graphitized carbon nanofibers (GNFs) combined with nanocatalysts (Pd or Pt) and magnetic nanoparticles. The latter are introduced in the form of carbon‐coated cobalt nanomagnets (Co@C_n) adsorbed on GNF, or formed directly on GNF from ferrocene yielding carbon‐coated iron nanomagnets (Fe@C_n). High‐resolution transmission electron microscopy demonstrates that Co@C_n and Fe@C_n are attached effectively to the GNFs, and the loading of nanomagnets required for separation of the nanoreactors from the solution with an external magnetic field is determined using UV–vis spectroscopy. Magnetically functionalized GNFs combined with palladium or platinum nanoparticles result in catalytically active magnetically separable nanoreactors. Applied to the reduction of nitrobenzene the multifunctional nanoreactors demonstrate high activity and excellent durability, while their magnetic recovery enables significant improvement in the reuse of the nanocatalyst over five reaction cycles (catalyst loss < 0.5 wt%) as compared to the catalyst recovery by filtration (catalyst loss <10 wt%).     

Cover Picture: Fabrication and Electrical and Mechanical Properties of Carbon Nanotube Interconnections (Adv. Funct. Mater. 11/2005)

The fabrication of carbon nanotube (CNT) structures, including simple tube–tube connections, crossed junctions, T‐junctions, zigzag structures, and even nanotube networks, has been achieved by cutting and soldering CNTs using electron‐beam‐induced deposition of amorphous carbon (a‐C), as detailed in the work of Peng and co‐workers on p. 1825. These CNT structures have been constructed with a high degree of control, and it is found that the electric conductance and mechanical strength of the junctions can be improved by the deposition of a‐C and by increasing the contact area of the junctions. Individual carbon nanotubes (CNTs) have been cut, manipulated, and soldered via electron‐beam‐induced deposition of amorphous carbon (a‐C) and using a scanning tunneling microscope inside a transmission electron microscope. All CNT structures, including simple tube–tube connections, crossed junctions, T‐junctions, zigzag structures, and even nanotube networks, have been successfully constructed with a high degree of control, and their electrical and mechanical properties have been measured in situ inside the transmission electron microscope. It is found that multiple CNTs may be readily soldered together with moderate junction resistance and excellent mechanical resilience and strength, and the junction resistance may be further reduced by current‐induced graphitization of the deposited a‐C on the junction.     

Synthesis of Carbon Nanotubes Using Microwave Radiation

We report a method for the synthesis of carbon nanotubes (CNTs) by microwave irradiation. CNTs were successfully synthesized by microwave heating of the catalyst loaded on various supports such as carbon black, silica powder, or organic polymer substrates (Teflon and polycarbonate). Microwave (2.45 GHz, 800 W) irradiation used acetylene as a hydrocarbon source, and 3d transition metals and metal sulfides were used as the catalysts. Different carbon yields and morphologies were obtained depending on the reaction conditions. Fibrous nanocarbons—linear or Y‐branched—were observed as well as carbon nanoparticles and amorphous carbon. High‐resolution transmission electron microscopy (HRTEM) revealed that these fibrous nanocarbons are either multiwalled CNTs or graphitic nanofibers (GNFs). This novel method has the potential to grow CNTs virtually on any substrate provided its absorption of microwave energy is small.     

Ultrafine Amorphous SnOx Embedded in Carbon Nanofiber/Carbon Nanotube Composites for Li‐Ion and Na‐Ion Batteries

Core–shell‐structured, ultrafine SnO_x/carbon nanofiber (CNF)/carbon nanotube composite films are in situ synthesized by electrospinning through a dual nozzle. The carbon shell layer functions as a buffer to prevent the separation of SnO_x particles from the CNF core, allowing full utilization of high‐capacity SnO_x in both Li‐ion and Na‐ion batteries. The composite electrodes reveal an anomalous Li‐ and Na‐ion storage mechanism where all the intermediate phases, like Li_xSn and Na_xSn alloys, maintain amorphous states during the entire charge/discharge process. The uniform dispersion on an atomic scale and the amorphous state of the SnO_x particles remain intact in the carbon matrix without growth or crystallization even after 300 cycles, which is responsible for sustaining excellent capacity retention of the electrodes. These discoveries not only shed new insights into fundamental understanding of the electrochemical behavior of SnO_x electrodes but also offer a potential strategy to improve the cyclic stability of other types of alloy anodes that suffer from rapid capacity decays due to large volume changes.     

2D Dual‐Metal Zeolitic‐Imidazolate‐Framework‐(ZIF)‐Derived Bifunctional Air Electrodes with Ultrahigh Electrochemical Properties for Rechargeable Zinc–Air Batteries

Here first a 2D dual‐metal (Co/Zn) and leaf‐like zeolitic imidazolate framework (ZIF‐L)‐pyrolysis approach is reported for the low‐cost and facile preparation of Co nanoparticles encapsulated into nitrogen‐doped carbon nanotubes (Co‐N‐CNTs). Importantly, the reasonable Co/Zn molar ratio in the ZIF‐L is the key to the emergence of the encapsulated microstructure. Specifically, high‐dispersed cobalt nanoparticles are fully encapsulated in the tips of N‐CNTs, leading to the full formation of highly active Co–N–C moieties for oxygen reduction and evolution reactions (ORR and OER). As a result, the obtained Co‐N‐CNTs present superior electrocatalytic activity and stability toward ORR and OER over the commercial Pt/C and IrO₂ as well as most reported metal‐organic‐framework‐derived catalysts, respectively. Remarkably, as bifunctional air electrodes of the Zn–air battery, it also shows extraordinary charge–discharge performance. The present concept will provide a guideline for screening novel 2D metal‐organic frameworks as precursors to synthesize advanced multifunctional nanomaterials for cross‐cutting applications.     

Real‐Time Imaging of Nanoscale Redox Reactions over Bimetallic Nanoparticles

The catalytic performance of bimetallic nanoparticles (NPs) strongly depends on their structural and compositional changes under reaction conditions. At the fundamental level, these changes are driven by redox reactions that occur on the surface of the NPs. The degree of complexity in the redox reactions is further amplified in bimetallic NPs because both metals can have their own reactions with the reactant molecules, in addition to any synergistic effects between the metal nanocatalysts and their reducible oxides. Here, the gas phase oxidation and reduction reactions, and the oxidation of carbon monoxide (CO) over Pt–Ni rhombic dodecahedron NPs with segregated Pt frames and Pt–Ni alloy NPs are investigated using in situ gas cell transmission electron microscopy. The real‐time observations show that NiO shell formation and Pt segregation are two important features during the oxidation and reduction of Pt–Ni NPs, respectively. Moreover, the two types of NPs evolved in different ways. By combining high‐resolution imaging, mass spectroscopy, and modeling, it is shown that the evolution of NP morphology and composition during redox reactions plays an important role in controlling the catalytic activity of the NPs.     

Solid‐State Pyrolysis of Polyphenylene–Metal Complexes: A Facile Approach Toward Carbon Nanoparticles

Novel polyphenylene–metal complexes with discotic, linear, and dendritic geometries are synthesized by using a facile approach consisting of reactions between Co₂(CO)₈ and ethynyl functionalities in dichloromethane. Various carbon nanoparticles (CNPs), including graphitic carbon nanotubes (CNTs), graphitic carbon rods, and carbon–metal hybrid particles are obtained from the solid‐state pyrolysis of these complexes. The ultimate structures of the CNPs are found to be dependant on the structure and composition of the starting compounds. Precursors containing graphenes always result in graphitic CNTs in high yield, whereas dendritic precursors give rodlike carbon materials. Alternatively, linear oligo(arylethylene) precursors afford mostly carbon–metal hybrids with large amounts of amorphous carbon. Furthermore, the CNP structures could be controlled by adjusting the carbon/metal ratio, the type and position of the metal incorporated into the precursor, and the mode of pyrolysis. These results provide further chances toward understanding the mechanism of CNP formation.     

碳纳米管的大面积合成及磁性(英文)

通过溶胶凝胶法和氢气还原法制备出Co纳米颗粒并以此作为催化剂材料,通过催化裂解苯的方法,实现了较低温度(460℃)下在Co纳米颗粒表面上合成碳纳米管。采用X射线衍射、激光喇曼光谱、场发射扫描电镜、透射电子显微镜和振动样品磁强计对所合成的碳纳米材料进行了表征。通过优化实验参数,可制备出最大产率和纯度分别为约50和98.02%(质量分数)的碳纳米管。由于铁磁性Co纳米颗粒的进入,使得整个复合物表现出比较好的磁性能。和以往以苯作为碳源合成碳纳米材料相比,此合成方案简单、成本低,且对环境无任何危害,非常适用于磁性碳纳米复合物的批量合成。     

Highly Efficient Electrocatalysts for Oxygen Reduction Reaction Based on 1D Ternary Doped Porous Carbons Derived from Carbon Nanotube Directed Conjugated Microporous Polymers

One‐dimensional (1D) porous materials have shown great potential for gas storage and separation, sensing, energy storage, and conversion. However, the controlled approach for preparation of 1D porous materials, especially porous organic materials, still remains a great challenge due to the poor dispersibility and solution processability of the porous materials. Here, carbon nanotube (CNT) templated 1D conjugated microporous polymers (CMPs) are prepared using a layer‐by‐layer method. As‐prepared CMPs possess high specific surface areas of up to 623 m² g^?1 and exhibit strong electronic interactions between p‐type CMPs and n‐type CNTs. The CMPs are used as precursors to produce heteroatom‐doped 1D porous carbons through direct pyrolysis. As‐produced ternary heteroatom‐doped (B/N/S) 1D porous carbons possess high specific surface areas of up to 750 m² g^?1, hierarchical porous structures, and excellent electrochemical‐catalytic performance for oxygen reduction reaction. Both of the diffusion‐limited current density (4.4 mA cm^?2) and electron transfer number (n = 3.8) for three‐layered 1D porous carbons are superior to those for random 1D porous carbon. These results demonstrate that layered and core–shell type 1D CMPs and related heteroatom‐doped 1D porous carbons can be rationally designed and controlled prepared for high performance energy‐related applications.     

Formation Mechanism of Epitaxial Palladium–Platinum Core–Shell Nanocatalysts in a One‐Step Supercritical Synthesis

The scarcity of platinum group metals provides a strong incentive to optimize the catalytic activity and stability, e.g., through nanoalloys or core–shell nanoparticles. Here, time‐resolved X‐ray total scattering and transmission electron microscopy characterization are used to study the formation of palladium–platinum core–shell nanoparticles under solvothermal conditions. It is shown that Pd rapidly forms small (5–10 nm), disordered primary particles, which agglomerate and crystallize when reaching 20–25 nm. The primary Pd particles provide nucleation sites for Pt, and, with extended reaction time, the Pd cores become fully covered with Pt shells. The observed core–shell material is surprising when considering the Pt–Pd phase diagram and relative surface energies, but it can be rationalized through the kinetics of precursor conversion. To bridge the gap between scientific studies and industrial demand for large‐scale production, the synthesis process is successfully transferred to a continuous flow supercritical reactor providing a simple scalable and green process for production of bimetallic nanocatalysts.     

Open‐Ended,N‐Doped Carbon Nanotube–Graphene Hybrid Nanostructures as High‐Performance Catalyst Support

A hierarchical N‐doped carbon nanotube‐graphene hybrid nanostructure (NCNT‐GHN), in which the graphene layers are distributed inside the CNT inner cavities, was designed to efficiently support noble metal (e.g., PtRu) nanoparticles. Well‐dispersed PtRu nanoparticles with diameters of 2–4 nm were immobilized onto these NCNT‐GHN supports by a low‐temperature chemical reduction method without any pretreatment. Compared to conventional CNTs and commercial catalysts. a much better catalytic performance was achieved by a synergistic effect of the hierarchical structure (graphene‐CNT hybrid) and electronic modulation (N‐doping) during the methanol electrooxidation reaction. Improved single‐cell performances with long‐term stability are also demonstrated using NCNT‐GHN as catalyst support.     

Carbon Nanotube Assisted Enhancement of the Magneto-Optical Kerr Signal in Nickel Thin Films

In this paper, the effect of carbon nanotubes (CNTs) acting as a covering layer on the [Glass/Ni] sample was experimentally investigated. To this end, a 48 nm thick Ni thin film was initially deposited on the glass substrate using a thermal evaporation method. Afterward, a spin-coating method was employed to deposit a thin layer of CNTs on the Ni thin film, thereby forming the [Glass/Ni/CNT] structure. Compared to [Glass/Ni] samples, the presence of CNTs led to 100% and 180% enhancement in the longitudinal Kerr signal of spin-coated samples. Field emission scanning electron microscopy, energy-dispersive x-ray spectroscopy, UV–Vis spectra and vibrating-sample magnetometer analyses were employed to characterize and investigate the morphology, elemental analysis, and optical and magnetic characteristics of the resulting structures. As a covering layer, the CNTs enhanced the absorption of light in the UV–visible wavelength range while also amplifying the interaction of light with the Ni layer without seriously changing other magnetic properties of the structure. Accordingly, using a simple approach, the Kerr signal was amplified more than three times compared to that of an uncovered sample, providing useful applications for magnetic sensors.     

Iron–Nitrogen‐Doped Vertically Aligned Carbon Nanotube Electrocatalyst for the Oxygen Reduction Reaction

A highly active iron–nitrogen‐doped carbon nanotube catalyst for the oxygen reduction reaction (ORR) is produced by employing vertically aligned carbon nanotubes (VA‐CNT) with a high specific surface area and iron(II) phthalocyanine (FePc) molecules. Pyrolyzing the composite easily transforms the adsorbed FePc molecules into a large number of iron coordinated nitrogen functionalized nanographene (Fe–N–C) structures, which serve as ORR active sites on the individual VA‐CNT surfaces. The catalyst exhibits a high ORR activity, with onset and half‐wave potentials of 0.97 and 0.79 V, respectively, versus reversible hydrogen electrode, a high selectivity of above 3.92 electron transfer number, and a high electrochemical durability, with a 17 mV negative shift of E _1/2 after 10 000 cycles in an oxygen‐saturated 0.5 m H₂SO₄ solution. The catalyst demonstrates one of the highest ORR performances in previously reported any‐nanotube‐based catalysts in acid media. The excellent ORR performance can be attributed to the formation of a greater number of catalytically active Fe–N–C centers and their dense immobilization on individual tubes, in addition to more efficient mass transport due to the mesoporous nature of the VA‐CNTs.     

Yolk–Shell Hybrid Materials with a Periodic Mesoporous Organosilica Shell: Ideal Nanoreactors for Selective Alcohol Oxidation

This contribution describes the preparation of multifunctional yolk–shell nanoparticles (YSNs) consisting of a core of silica spheres and an outer shell based on periodic mesoporous organosilica (PMO) with perpendicularly aligned mesoporous channels. The new yolk–shell hybrid materials were synthesised through a dual mesophase and vesicle soft templating method. The mesostructure of the shell, the dimension of the hollow space (4～52 nm), and the shell thickness (16～34 nm) could be adjusted by precise tuning of the synthesis parameters, as evidenced by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen sorption investigations. Various metal nanoparticles (e.g., Au, Pt, and Pd) were encapsulated and confined in the void space between the core and the shell using impregnation and reduction of adequate metal precursors. The selective oxidation of various alcohol substrates was then carried out to illustrate the benefits of such an architecture in catalysis. High conversion (～100%) and excellent selectivity (～99%) were obtained over Pd nanoparticles encapsulated in the hybrid PMO yolk–shell structures.