High‐Efficiency Encapsulation of Pt Nanoparticles into the Channel of Carbon Nanotubes as an Enhanced Electrocatalyst for Methanol Oxidation

Pt‐based nanostructures serving as anode catalysts for the methanol oxidation reaction (MOR) have been widely studied for many years. Nevertheless, challenging issues such as poor reaction kinetics and the short‐term stability of the MOR are the main drawbacks of such catalysts and limit their applications. Herein, we have developed a facile approach to encapsulate Pt nanoparticles (NPs) inside the nanochannels of porous carbon nanotubes (CNTs; Pt‐in‐CNTs) as a new enhanced electrocatalytic material. The as‐prepared CNTs offer simultaneously ordered diffusion channels for ions and a confinement effect for the NPs, which both facilitate the promotion of catalytic kinetics and avoid the Ostwald ripening of Pt NPs, thus leading to high activity and durable cycle life as an anode catalyst for MOR. This work provides a new approach for enhancing the stability and activity by optimizing the structure of the catalyst, and the Pt‐in‐CNTs represent the most durable catalysts ever reported for MOR.     

高分散在氮掺杂碳纳米管表面铂纳米粒子的高效甲醇电氧化性能

以氮掺杂碳纳米管（NCNT）为载体,利用掺杂氮原子的锚定作用,通过微波辅助乙二醇还原法方便地将Pt纳米粒子高分散地固载于NCNT表面,制得了Pt/NCNT系列催化剂,对催化剂制备规律、电催化甲醇氧化反应（MOR）性能及构效关系开展了系统深入的研究。结果表明,随Pt负载量在18.2%~58.7%（w/w,下同）范围增加,Pt纳米粒子的粒径在2.2~3.7 nm范围相应地逐渐增大。单位质量催化剂的MOR催化活性先增加后急剧减小,在负载量为47.8%时达到最大。Pt的质量比活性在中等负载量（27.6%~47.8%）区间出现高值平台。该变化规律源于Pt纳米粒子的MOR催化活性在3 nm前后的明显差异,即<3 nm时活性差,>3 nm时活性优异。高负载量（58.7%）时活性的急剧下降源于Pt纳米粒子因团聚引起的Pt利用率的降低。     

高分散在氮掺杂碳纳米管表面铂纳米粒子的高效甲醇电氧化性能

以氮掺杂碳纳米管(NCNT)为载体,利用掺杂氮原子的锚定作用,通过微波辅助乙二醇还原法方便地将Pt纳米粒子高分散地固载于NCNT表面,制得了Pt/NCNT系列催化剂,对催化剂制备规律、电催化甲醇氧化反应(MOR)性能及构效关系开展了系统深入的研究。结果表明,随Pt负载量在18.2%~58.7%(w/w,下同)范围增加,Pt纳米粒子的粒径在2.2~3.7 nm范围相应地逐渐增大。单位质量催化剂的MOR催化活性先增加后急剧减小,在负载量为47.8%时达到最大。Pt的质量比活性在中等负载量(27.6%~47.8%)区间出现高值平台。该变化规律源于Pt纳米粒子的MOR催化活性在3 nm前后的明显差异,即3 nm时活性差,3 nm时活性优异。高负载量(58.7%)时活性的急剧下降源于Pt纳米粒子因团聚引起的Pt利用率的降低。     

Platinum‐Decorated Au Porous Nanotubes as Highly Efficient Catalysts for Formic Acid Electro‐Oxidation

Au porous nanotubes (PNTs) were synthesized by a templating technique that involves the chemical synthesis of Ag nanowire precursors, electroless surface modification with Au, and selective etching. A subsequent galvanic replacement reaction between [PtCl₆]^2? and residual Ag generates Pt‐decorated Au porous nanotubes (Pt/Au PNTs), which represents a new type of self‐sustained high surface area electrocatalysts with ultra‐low Pt loading. Structural characterizations with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X‐ray powder diffraction (XRD) reveal a novel nanoarchitecture with multimodal open porosity and excellent structural continuity and integrity. Cyclic voltammetry (CV) demonstrates that these Pt/Au PNTs possess very high electrocatalytic activity toward formic acid oxidation with enhanced tolerance to CO poisoning.     

Small‐Sized and Contacting Pt–WC Nanostructures on Graphene as Highly Efficient Anode Catalysts for Direct Methanol Fuel Cells

The synergistic effect between Pt and WC is beneficial for methanol electro‐oxidation, and makes Pt–WC catalyst a promising anode candidate for the direct methanol fuel cell. This paper reports on the design and synthesis of small‐sized and contacting Pt–WC nanostructures on graphene that bring the synergistic effect into full play. Firstly, DFT calculations show the existence of a strong covalent interaction between WC and graphene, which suggests great potential for anchoring WC on graphene with formation of small‐sized, well‐dispersed WC particles. The calculations also reveal that, when Pt attaches to the pre‐existing WC/graphene hybrid, Pt particles preferentially grow on WC rather than graphene. Our experiments confirmed that highly disperse WC nanoparticles (ca. 5 nm) can indeed be anchored on graphene. Also, Pt particles 2–3 nm in size are well dispersed on WC/graphene hybrid and preferentially grow on WC grains, forming contacting Pt–WC nanostructures. These results are consistent with the theoretical findings. X‐ray absorption fine structure spectroscopy further confirms the intimate contact between Pt and WC, and demonstrates that the presence of WC can facilitate the crystallinity of Pt particles. This new Pt–WC/graphene catalyst exhibits a high catalytic efficiency toward methanol oxidation, with a mass activity 1.98 and 4.52 times those of commercial PtRu/C and Pt/C catalysts, respectively.     

Chitosan‐Functionalized Carbon Nanotubes as Support for the High Dispersion of PtRu Nanoparticles and their Electrocatalytic Oxidation of Methanol

Carbon nanotubes (CNTs) were non‐covalently functionalized with chitosan (Chit) and then employed as the support for PtRu nanoparticles. The functionalization was carried out at room temperature without the use of corrosive acids, thereby preserving the integrity and the electronic conductivity of the CNTs. Transmission electron microscopy reveals that PtRu nanoparticles were highly dispersed on the surface of Chit‐functionalized CNTs (CNT‐Chit) with small particle‐size. Cyclic voltammetry studies indicated that the PtRu nanoparticle/CNT‐Chit nanohybrids have a higher electrochemical surface area, electrocatalytic performance, and stability towards methanol oxidation compared to PtRu nanoparticles supported on the pristine CNTs.     

Functionalization of Carbon Nanotubes by an Ionic‐Liquid Polymer: Dispersion of Pt and PtRu Nanoparticles on Carbon Nanotubes and Their Electrocatalytic Oxidation of Methanol

Small beginnings : Metal nanoparticle/CNT nanohybrids are synthesized from carbon nanotubes (CNTs) functionalized with an ionic‐liquid polymer. The Pt and PtRu nanoparticles with narrow size distribution (average diameter: (1.3±0.4) nm for PtRu, (1.9±0.5) nm for Pt) are dispersed uniformly on the CNTs (see images) and show good performance in methanol electrooxidation.

     

Magnetic Bistability of Individual Single‐Molecule Magnets Grafted on Single‐Wall Carbon Nanotubes

A POM to remember : Hexanuclear Fe^III polyoxometalate (POM) single‐molecule magnets (see structure) can be noncovalently assembled on the surface of single‐wall carbon nanotubes. Complementary characterization techniques (see TEM image and magnetic hysteresis loops) demonstrate the integrity and bistability of the individual molecules, which could be used to construct single‐molecule memory devices.

     

Tungsten Nitride‐Cobalt Anchored in N‐Doped Ordered Porous Carbon as an Efficient Oxygen Reduction Reaction Electrocatalyst

We prepared a non‐precious‐metal tungsten nitride‐cobalt (WN‐Co) electrocatalyst anchored in nitrogen‐doped ordered porous carbon (NOPC) through an in situ method. The WN‐Co/NOPC electrocatalyst possesses good oxygen reduction reaction (ORR) capability in alkaline media, including a high onset potential of −132 mV, a dominant four‐electron process, and a superior stability (onset potential and limiting current density were almost unchanged after 5000 cycles in 0.1 m KOH). The improved ORR performance was comparable to that of WN/NOPC and Co/NOPC with regard to three aspects: the even dispersion and uniform size of electrocatalyst particles provide more reactive sites; the nitrogen doping, high specific surface area and highly ordered mesoporous channel of catalyst support (NOPC) are conducive to the infiltration of the electrolyte; the existence of WN reinvests the catalyst with good stability, and the anchored configuration of WN and Co in the NOPC will prevent the particles from agglomerating after a long‐term cycle, thereby improving the stability of the catalyst particles.     

Surfactant‐Dependent Charge Transfer between Polyoxometalates and Single‐Walled Carbon Nanotubes: A Fluorescence Spectroscopic Study

Hybridizations of redox‐active polyoxometalates (POMs) with single‐walled carbon nanotubes (SWNTs) have been widely investigated for their diverse applications. For the purpose of constructing high‐quality electronic devices, controlling charge transfer within POM/SWNT hybrids is an inevitable issue. As determined by means of fluorescence spectroscopy, electron transfer between SWNTs and a common POM dopant, phosphomolybdic acid (PMo₁₂), can be tuned simply by an alteration of nanotube surfactant type from anionic to nonionic. The mechanism is attributed to the influence of surfactant type on the stabilization of the electron donor–acceptor hybrid and effect of surfactant–nanotube interactions. These results will be important to control charge‐transport behavior in nanohybrids consisting of carbon nanotubes.     

Electro‐oxidation of Methanol and Ethanol Catalyzed by Pt/ZSM‐5/C

Direct alcohol fuel cells are a promising source of future energy generation for small and portable devices. Platinum is considered the best catalyst for electro‐oxidation of alcohols in fuel cells but the major hurdles with platinum catalysts are high cost of platinum as well as low selectivity, slow reaction kinetics and carbonaceous poisoning associated with platinum. This particular research reports electro‐oxidation of methanol and ethanol over platinum electrodeposited on ZSM‐5 without any carbon additive. From the cyclic voltammetry and chronoamperometry, linear sweep voltammetry, tafel plot and multiple scan analyses, it is found that Pt/ZSM‐5/C electrodes can catalyze electro‐oxidation of methanol and ethanol with higher efficiency. ZSM‐5 supports the formation of smaller sized platinum nanoparticles in a dispersed manner on the zeolite support and thus increases the active surface area of the metal for catalytic activity. It favors adsorption of alcohol molecules on the modified electrode surface and thus increases the diffusion process. It also stabilizes the modified electrodes.     

以切短多壁碳纳米管为载体制备高活性Pt/SCNT及PtRu/SCNT燃料电池催化剂

采用乙醇为助磨剂,利用球磨的方法将5-15μm长的多壁碳纳米管切短成长度约为200nm,并且分布较为均匀的短碳纳米管(SCNT).以SCNT为载体,采用有机溶胶法制得了含铂20%(w)的Pt/SCNT及PtRu/SCNT催化剂.实验发现:对于甲醇的阳极电氧化过程,以切短碳纳米管为载体的Pt/SCNT催化剂具有比相同条件制得的Pt/CNT催化剂高得多的催化活性,前者甲醇氧化峰电流密度是后者的1.4倍,并且远远高于商品的Pt/C催化剂.同时我们发现添加了钌的PtRu/SCNT具有比不含钌的催化剂更好的活性.采用X射线衍射(XRD)、透射电镜(TEM)、比表面积分析(BET)等方法对催化剂进行表征,结果表明,切短碳纳米管的晶相结构并未改变,但Pt/SCNT和PtRu/SCNT催化剂的比表面积和电化学活性得到了显著的提高.     

Investigation of Platinum Dispersed on Reduced Graphene Oxide‐supported Tungsten Carbide via Sacrificial Cu Adlayers for Methanol Oxidation

Reduced graphene oxide‐supported tungsten carbide composite (WC/RGO) was prepared by program‐controlled reduction‐carburization technique. Scanning electron microscope (SEM) and transmission electron microscope (TEM) show that WC nanoparticles with a narrow distribution (10–20 nm) are highly dispersed both on the edge and between the layers of RGO. And then it was used as a support to load different low contents (no more than 0.4 wt%) of Pt via sacrificial Cu adlayers. The morphology and the electrocatalytic activity of the prepared catalysts were characterized by TEM and cyclic voltammograms (CV), respectively. The results indicate that a small amount of isolated Pt atoms show low or even no activity for methanol oxidation. With the increasing deposition cycles, the content of Pt and the ensembles of neighboring Pt atoms are increased, which makes the onset potential shift negatively and mass current density increase. The results demonstrate that controllable amount of Pt can be deposited on WC/RGO by galvanic displacement with Cu, and the extent and domain of Pt loading affect the electrochemical performance. Meanwhile, this research also provides another route to prepare a catalyst with ultra low noble metal on WC/RGO for solving the problem of high cost of the catalyst.     

Electrostatic‐Assembly of Carbon Nanotubes (CNTs) and Polymer Particles in Water: a Facile Approach to Improve the Dispersion of CNTs in Thermoplastics

Summary: A facile and organic‐solvent‐free method for preparing thermoprocessable multiwalled carbon nanotube (MWCNT)‐filled thermoplastics is presented. MWCNTs are oxidized, neutralized, and then assembled with cationic soap‐free poly(methyl methacrylate) (PMMA) particles directly in water. The spontaneous electrostatic coupling between the negatively charged MWCNTs and positively charged PMMA particles, and the viscoelastic and thermomechanical behavior of the nanocomposites, are investigated. The electrostatic coupling interactions improve the dispersion of nanotubes and facilitate the formation of filler networks in the polymer matrix.

Preparation of nanocomposites of oxidized MWCNTs and positively charged PMMA particles through electrostatic assembly.     

Advanced Catalytic Performance of Au–Pt Double‐Walled Nanotubes and Their Fabrication through Galvanic Replacement Reaction

Bimetallic tubular nanostructures have been the focus of intensive research as they have very interesting potential applications in various fields including catalysis and electronics. In this paper, we demonstrate a facile method for the fabrication of Au–Pt double‐walled nanotubes (Au–Pt DWNTs). The DWNTs are fabricated through the galvanic displacement reaction between Ag nanowires and various metal ions, and the Au–Pt DWNT catalysts exhibit high active catalytic performances toward both methanol electro‐oxidation and 4‐nitrophenol (4‐NP) reduction. First, they have a high electrochemically active surface area of 61.66 m² g^?1, which is close to the value of commercial Pt/C catalysts (64.76 m² g^?1), and the peak current density of Au–Pt DWNTs in methanol oxidation is recorded as 138.25 mA mg^?1, whereas those of Pt nanotubes, Au/Pt nanotubes (simple mixture), and commercial Pt/C are 24.12, 40.95, and120.65 mA mg^?1, respectively. The Au–Pt DWNTs show a markedly enhanced electrocatalytic activity for methanol oxidation compared with the other three catalysts. They also show an excellent catalytic performance in comparison with common Au nanotubes for 4‐nitrophenol (4‐NP) reduction. The attractive performance exhibited by these prepared Au–Pt DWNTs can be attributed to their unique structures, which make them promising candidates as high‐performance catalysts.     

Electrocatalytic Oxidation of Methanol and Related Chemical Species on Ultrafine Pt and PtRu Particles Supported on Carbon

Well-homogenized PtRu/C electrocatalysts possessing high specific activity for methanol electro-oxidation were prepared by a co-impregnation method from carbon black and ethanolic solutions of Pt(NH₃)₂(NO₂)₂ and RuNO(NO₃) _x . The specific activity for methanol electro-oxidation increased with an increase in the PtRu particle size. A similar size effect was observed for Pt/C electrocatalysts. The size effect was discussed by considering a model catalyst method.     

A Two‐Step Method for Transferring Single‐Walled Carbon Nanotubes onto a Hydrogel Substrate

Carbon nanotube (CNT)‐hydrogel nanocomposites are beneficial for various biomedical applications, such as nerve regeneration, tissue engineering, sensing, or implant coatings. Still, there are impediments to developing nanocomposites, including attaining a homogeneous CNT‐polymer dispersion or patterning CNTs on hydrogels. While few approaches have been reported for patterning CNTs on polymeric substrates, these methods include high temperature, high vacuum or utilize a sacrificial layer and, hence, are incompatible with hydrogels as they lead to irreversible collapse in hydrogel structure. In this study, a novel two‐step method is designed to transfer CNTs onto hydrogels. First, dense CNTs are grown on quartz substrates. Subsequently, hydrogel solutions are deposited on the quartz‐grown CNTs. Upon gelation, the hydrogel with transferred CNTs is peeled from the quartz. Successful transfer is confirmed by scanning electron microscopy and indirectly by cell attachment. The efficient transfer is attributed to π‐interactions pregelation between the polymers in solution and the CNTs.

     

Covalent Attachment of Anderson‐Type Polyoxometalates to Single‐Walled Carbon Nanotubes Gives Enhanced Performance Electrodes for Lithium Ion Batteries

Single‐walled carbon nanotubes (SWNTs) covalently functionalized with redox‐active organo‐modified polyoxometalate (POM) clusters have been synthesized and employed as electrode materials in lithium ion batteries. The Anderson cluster [MnMo₆O₂₄]^9? is functionalized with Tris (NH₂C(CH₂OH)₃) moieties, giving the new organic–inorganic hybrid [N(nC₄H₉)₄]₃[MnMo₆O₁₈{(OCH₂)₃CNH₂}₂]. The compound is then covalently attached to carboxylic acid‐functionalized SWNTs by amide bond formation and the stability of this nanocomposite is confirmed by various spectroscopic methods. Electrochemical analyses show that the nanocomposite displays improved performance as an anode material in lithium ion batteries compared with the individual components, that is, SWNTs and/or Anderson clusters. High discharge capacities of up to 932 mAh g^?1 at a current density of 0.5 mA cm^?2 can be observed, together with high long‐term cycling stability and decreased electrochemical impedance. Chemisorption of the POM cluster on the SWNTs is shown to give better electrode performance than the purely physisorbed analogues.