Transition Metal Carbon Research Articles

Ultrathin supercapacitor electrodes with high volumetric capacitance and stability using direct covalent-bonding between pseudocapacitive nanoparticles and conducting materials

We introduce high-performance ultrathin supercapacitor electrodes obtained through the direct covalent-bonding layer-by-layer (LbL) assembly (or ligand-exchange LbL assembly) of amine-functionalized multiwalled carbon nanotubes (CNTs) and transition metal oxide nanoparticles (TMO NPs). The main characteristic of our approach is that the internal interfacial resistance of the electrodes can be minimized through the direct covalent-bonding adsorption of densely packed, high-quality TMO NPs onto CNTs without the aid of nonactive binders or insulating NP ligands, and the resulting volumetric capacitance and cycling stability of the electrodes can be significantly enhanced. For this study, well-defined oleic acid-stabilized pseudocapacitive metal oxide nanoparticles (i.e., OA–Fe3O4 and OA–MnO NPs) prepared in toluene were densely adsorbed onto the CNT layer due to the high affinity between the surface of the TMO NPs and the NH2 moieties of the CNTs. The (CNT/OA–Fe3O4 NP)20 multilayer electrode exhibited a high volumetric capacitance of 248±15Fcm−3 (128±7Fg−1) at 5mVs−1 despite the intrinsically low specific capacitance of the Fe3O4 NPs. Additionally, these film electrodes exhibited high performance stability, maintaining 99.2% of their initial capacitance after 1000 cycles. Furthermore, upon the insertion of OA–MnO NPs with high crystallinity and a high theoretical pseudocapacitance value within multilayers instead of OA–Fe3O4 NPs, the formed electrodes (i.e., (CNT/OA–MnO NP)20 multilayers) exhibited a higher volumetric capacitance of 305±10Fcm−3 (183±5Fg−1) (at a scan rate of 5mVs−1) than other conventional ultrathin supercapacitor electrodes, including manganese oxide or iron oxide NPs.

An experimental survey of additives for improving dehydrogenation properties of magnesium hydride

The use of a wide range of additives has been known as an important method for improving hydrogen storage properties of MgH2. There is a lack of a standard methodology, however, that can be used to select or compare the effectiveness of different additives. A systematic experimental survey was carried out in this study to compare a wide range of additives including transitions metals, transition metal oxides, hydrides, intermetallic compounds, and carbon materials, with respect to their effects on dehydrogenation properties of MgH2. MgH2 with various additives were prepared by using a high-energy-high-pressure planetary ball milling method and characterized by using thermogravimetric analysis (TGA) techniques. The results showed that additives such as Ti and V-based metals, hydride, and certain intermetallic compounds have strong catalytic effects. Additives such as Al, In, Sn, Si showed minor effects on the kinetics of the dehydrogenation of MgH2, while exhibiting moderate thermodynamic destabilizing effects. In combination, MgH2 with both kinetic and thermodynamic additives, such as the MgH2–In–TiMn2 system, exhibited a drastically decreased dehydrogenation temperature.

Formation, characterization, structure and bonding analysis of the metal–carbon bond OM-(η6-C6H6) (M = Sc, Ti) complexes in solid matrix: Infrared spectroscopic and theoretical study

The reactions of ScO and TiO molecules with benzene have been studied in solid argon with infrared absorption spectroscopy combining with theoretical calculations. Laser-evaporation of bulk higher oxide targets prepared the scandium and titanium monoxide molecules. The scandium and titanium monoxide molecules reacted with benzene to form the typical transition metal–carbon bond (MCB) complexes, OM-(η6-C6H6) (M = Sc, Ti), which have been identified on the basis of isotopic infrared studies and density functional calculations. The theoretical calculation results illustrate the deformation of the planar carbon skeleton of benzene takes place and the bond lengths of M–O are largely elongated upon OM-(η6-C6H6) (M = Sc, Ti) complexes. The population results illustrate the OM-(η6-C6H6) are determined to have 2A1 and 1A1 electronic ground state both with C2v symmetry arising from 2Δ and 1∑− of excited-state ScO and TiO reaction with benzene, respectively. The OSc-(η6-C6H6) and OTi-(η6-C6H6) are both stable d–pπ coordination compounds and can also not be photoisomerized by UV irradiation under low temperature in solid argon matrix. Natural bond orbital analyses conclude that the OTi-(η6-C6H6) system includes two equivalent Ti–C single bonds with strong binding bond energies.

Controlled growth of nanostructured MnO2 on carbon nanotubes for high-performance electrochemical capacitors

The rational combination of transition metal oxides and carbon materials has been regarded as an efficient way of accessing the next-generation electrode materials for electrochemical capacitors. Here we demonstrate a facile synthesis of nanostructured MnO2 supported on carbon nanotubes (CNTs) via a direct redox route. By varying the reaction time, it can be convenient to control the growth density of MnO2 as well as the structural integrity of CNTs, which endow the novel hybrids with adjustable electrochemical performance. As a consequence, the resulting MnO2-CNT electrodes exhibit a maximum specific capacitance of 247.9Fg-1, with good rate capability and extraordinary cycling life stability (92.8% retention of initial capacitance after 5000 cycles), suggesting such materials have great potential in constructing high-performance energy-storage systems.

Contact-induced spin polarization in BNNT(CNT)/TM (TM=Co, Ni) nanocomposites

The interaction between carbon and BN nanotubes (NT) and transition metal Co and Ni supports was studied using electronic structure calculations. Several configurations of interfaces were considered, and the most stable ones were used for electronic structure analysis. All NT/Co interfaces were found to be more energetically favorable than NT/Ni, and conductive carbon nanotubes demonstrate slightly stronger bonding than semiconducting ones. The presence of contact-induced spin polarization was established for all nanocomposites. It was found that the contact-induced polarization of BNNT leads to the appearance of local conductivity in the vicinity of the interface while the rest of the nanotube lattice remains to be insulating.

Design and synthesis of ternary Ferrite/Graphene/polyaniline hierarchical nanocomposites for high-performance supercapacitors

As typical active electrode materials for pseudocapacitor, transition metal oxides, hydroxides, and conductive polymers possess multiple oxidation states/structures that enable rich redox reactions for pseudocapacitance generation. Spinel ferrite oxides (MFe2O4, M=Fe, Co, Ni, Cu, Mn) has been conceived as a promising cost-effective and scalable alternative for supercapacitor. It is expected that ferrite oxides (MFe2O4) may offer richer redox reactions, including contributions from both M and Fe ions, than those of the monometallic oxide. However, it is noted that the pure ferrite oxides cannot be conductive to satisfactory performance. A promising approach to enhance the performance is designing novel ferrite-based hybrids.Conducting polymer, such as polyaniline (PANI) is usually used to hybrid with metal oxides to enhance the electronic conductivity and achieve higher capacitance, owing to its low cost, environmental compatibility, excellent electrical conductivity, large pseudo-capacitance, and fast doping/dedoping rate. However, the poor cycling stability is a noticeable shortcoming. Graphene is a rising star in supercapacitor owning to its extremely high specific surface area, superior mechanical properties, good electrochemical stability and high intrinsic electrical conductivity. Recently, a hierarchically ternary composites composed of carbon nanomaterials, conducting polymers and transition metal oxides have been explored. This novel ternary hybrids provide a new direction for the fabrication of the next generation high-performance electrochemical electrodes. Based on the above, it is of great interest to fabricate the ternary ferrite-based composites as an capacitor material. To the best of our knowledge, very few studies on the synthesis of ferrite-based hybrids have been reported so far, especially this intriguing ternary nanostructure.Herein, we first reported ternary ferrite/graphene/PANI hybrid by a facile two-step method. This ternary nanostructures show enhanced electrochemical capacitance and improved cycling stability than those of the three separated components and their corresponding binary hybrids.

ChemInform Abstract: Recent Advances in Transition‐Metal‐Catalyzed C‐S Activation: From Thioester to (Hetero)aryl Thioether

AbstractReview: 103 refs.

Vapour deposition technologies for the fabrication of hot-forming tools: a review

This paper reports recent developments of vacuum coatings technologies for hot-forming tooling applications. Whilst well implanted in the machining and cutting industry, vacuum coatings face important challenges for the fabrication of forming tools, and more specifically in hot forming, due to the extreme operation conditions to be met, such as high loading forces, impact/thermal cycling, working material adhesion, etc. Present and future coatings adapted to hot work tooling are discussed in this paper: transition metal nitrides, carbon nitrides, borides and mixed oxides are among the currently postulated coating formulations for high temperature forming. The study is complemented with current strategies of characterizing the properties of the coatings in the adequate environment of high temperatures and contact loadings. To this aspect, a number of examples, from using standard laboratory equipment to the use of in-house developed tribological set-ups, are given, together with recent findings obtained from the authors’ research groups. The data available is, however, quite limited from the scientific literatures on the field trials with reliable, statistical relevance, which is, probably, attributed to the high costs normally incurred for carrying out experiments in real industrial environment. Nevertheless, we could still draw a conclusion of that vacuum coating for tooling applications is at a front edge of knowledge generation and technology transfer to industry, and while being already mature, there is still a needed effort for significant industrial up-take from the novel coatings developed or being under the development.

Recent Advances in Transition-Metal-Catalyzed C–S Activation: From Thioester to (Hetero)aryl Thioether

Carbon–sulfur bonds widely exist in natural products, pesticides, and drugs, and their activation, cleavage, and transformation via transition metal catalysis have become more and more important in organic chemistry. During the past several decades, great progress on transition-metal catalyzed carbon–sulfur activation of thioesters and their transformations has been achieved. Carbon–sulfur bonds linking to both heteroaryl and aryl groups can be cleaved to construct carbon–carbon bonds by coupling reactions or to construct carbon–hydrogen bonds by reductions. This perspective is focused on recent advances in cleavage and transformations of transition-metal-catalyzed carbon–sulfur bonds.

New insights into designing metallacarborane based room temperature hydrogen storage media

Metallacarboranes are promising towards realizing room temperature hydrogen storage media because of the presence of both transition metal and carbon atoms. In metallacarborane clusters, the transition metal adsorbs hydrogen molecules and carbon can link these clusters to form metal organic framework, which can serve as a complete storage medium. Using first principles density functional calculations, we chalk out the underlying principles of designing an efficient metallacarborane based hydrogen storage media. The storage capacity of hydrogen depends upon the number of available transition metal d-orbitals, number of carbons, and dopant atoms in the cluster. These factors control the amount of charge transfer from metal to the cluster, thereby affecting the number of adsorbed hydrogen molecules. This correlation between the charge transfer and storage capacity is general in nature, and can be applied to designing efficient hydrogen storage systems. Following this strategy, a search for the best metallacarborane was carried out in which Sc based monocarborane was found to be the most promising H2 sorbent material with a 9 wt.% of reversible storage at ambient pressure and temperature.

ChemInform Abstract: Catalytic Synthesis of Silanols from Hydrosilanes and Applications

AbstractReview: 117 refs.

Impact of Thermal Annealing under Nitrogen Ambient on Structural, Micro-Raman, and Thermogravimetric Analyses of Camphoric-CNT

A systematical study of the effects on thermal annealing treatment under nitrogen ambient on the structural, micro-Raman, and thermogravimetric analyses of camphoric-carbon nanotubes (CNT) has been undertaken. Heat treatment of camphoric-CNT under nitrogen ambient was found to be an efficient technique of removing noncrystalline carbon and residual transition metal. Based on structural analysis, the heat-treated samples showed a clear view of overall camphoric-CNT structure.

Quantum chemical studies on a series of transition metal carbon dioxide complexes: Metal–carbon bonding and electronic structures

The bonding features and electronic structures of a series of transition metal carbon dioxide complexes have been studied by density functional theory (DFT) calculations combined with natural bond orbital (NBO) analysis and energy-decomposition analysis (EDA). NBO analysis shows that the interaction between the metal center and the carbon atom of the carbon dioxide ligand (M–C) is stronger than the other interaction between the metal center and the carbon dioxide ligand. Natural hybrid orbital (NHO) analysis gives the detailed bonding features of the M–C bond for each complex. The NBO charge distribution on the carbon dioxide unit in all studied complexes is negative, which indicates charge transfer from the metal center to the carbon dioxide ligand for all studied complexes. The hyperconjugation effect of the metal center and the two C–O bonds of the carbon dioxide ligand has been estimated using the NBO second-order perturbation stabilization energy. It was found that the NBO second-order stabilization energy of C–O → nM* is sensitive to the coordinated sphere and the metal center. Frontier molecular orbital (FMO) analysis shows that complexes 1 and 4 may be good nucleophilic reagents for activation of the carbon dioxide molecule. However, the EDAs show that the M–CO2 bond interaction energy of complex 4 is about two times as large as that of complex 1. The high M–CO2 bond interaction energy of complex 4 may limit its practical application.

Insights into the ultrahigh glass-forming ability of the Fe-Co-Cr-Mo-C-B-Y alloy system from the electronic-structure perspective

The effect of cobalt on the glass-forming ability (GFA) of Fe-Co-Cr-Mo-C-B-Y bulk metallic glasses has been investigated by using ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy. The alloy containing 7% Co (Co7 alloy) exhibits the highest binding energy and the minimum electronic density of states at the Fermi energy in the valence band spectrum and possesses the largest carbide and metal boride peak intensity in the C 1s and B 1s core-level spectrum. The origin of the ultrahigh GFA for the Co7 alloy has been discussed in terms of the unique electronic structures, which are closely related to the densest atomic packing, the smallest atomic clusters, the minimum electronic density of states at the Fermi energy, and the most numerous transition-metal–carbon and transition-metal–boron bonds.

Catalytic Synthesis of Silanols from Hydrosilanes and Applications

In recent years reusable and highly active metal-nanoparticle catalysts were developed for the selective transformation of hydrosilanes into the corresponding silanols using water as the oxidant. The catalysts are much more active than conventional homogeneous ones under ambient conditions. In this perspective, we summarize known catalyst systems as well as stoichiometric methods for the synthesis of silanols from hydrosilanes. Plausible pathways for the hydrolytic oxidation of hydrosilanes on metal nanoparticles are described on the basis of the observations of mechanistic studies, including Si–H bond activation, nucleophilic attack of water (or silanol) at the silicon bonded to metal, and the liberation of silanol (or disiloxane) products. The applications of silanols are classified into usages in organic synthesis and silicon-based materials. Silanols were employed as nucleophilic partners in transition-metal catalyzed carbon–carbon cross-coupling reactions, organocatalysts for activating carbonyl compounds, intramolecular guiding groups for C–H bond activation reactions, inhibitors of enzymes, and isosteres of bioactive compounds. Various polymeric silicon-based materials were synthesized by the activation of Si–H bonds in bis-trihydrosilanes, bis-hydrosilanes, and polyhedral oligomeric silsesquioxanes (POSS).

Preparation of Tourmaline and Carbon Nanotubes Based Composite Materials and its Heat Emission Performance

The tourmaline-based composite materials as an effective thermal coating of heat exchanger unit were prepared from natural mineral tourmaline, transition metal oxides and carbon nanotubes. The far infrared emission properties and heat emission performance were studied. The results indicated that thermal performance of materials can be adjusted with the chemical composition of materials, and when the mass percentage of carbon nanotubes is 10%, the fractional of 26.77% of energy saving efficiency can be achieved.

Preparation of TiO2Photocatalyst Dual-modified by Transition Metal Doping and Carbon Nanotube (CNT) Grafting

提出了一种过渡金属掺杂和碳纳米管(CNT)双重改性TiO2的新方法:首先采用溶胶-凝胶法合成掺杂镍和铁的二氧化钛基催化剂,然后采用流化床化学气相沉积方法(FBCVD)在二氧化钛基催化剂表面接枝生长CNT,得到CNT/Fe-Ni/TiO2复合光催化剂.通过X射线衍射、扫描电子显微镜、比表面分析、拉曼光谱、紫外-可见吸收光谱、荧光光谱等方法考察了双重改性复合光催化剂CNT/Fe-Ni/TiO2的结构和性能,通过降解亚甲基蓝溶液评价了双重改性复合光催化剂的活性.结果表明,在TiO2表面接枝的CNT具有较好的石墨化结构,CNT生长过程中小部分TiO2由锐钛矿向金红石晶型转变.过渡金属和CNT双重改性有效地克服了TiO2的比表面积小、量子效率低等缺点,明显提高了TiO2的光催化活性.

ChemInform Abstract: Carbene Insertion into Transition Metal—Carbon Bonds: A New Tool for Catalytic C—C Bond Formation.

AbstractReview: 92 refs.

Preparation and electrochemical studies of metal–carbon composite catalysts for small-scale electrosynthesis of H 2O 2

Numerous transition metal–carbon composite catalysts (M = V, Zn, Ni, Sn, Ce, Ba, Fe, Cu) have been synthesized and tested for electroreduction of O 2 to H 2O 2, The activity and selectivity of all synthesized catalysts for electrosynthesis of H 2O 2 were determined by the rotating ring-disk electrode method in acidic and neutral electrolytes. The Co-based catalysts in general showed the highest activity towards H 2O 2 formation. Experiments with different loading contents of Co showed that the activation overpotential losses of oxygen reduction to H 2O 2 reduces as loading increases to about 4 wt% Co. Addition of Co beyond this level did not seem to impact the overpotential losses. The cobalt-based catalysts, were spray-coated onto 120 μm thick Toray ® graphite substrates, and were studied in bulk electrolysis cells for up to 100 h at potentiostatic conditions (0.25 V vs. RHE) in pH 0, 3, and 7 electrolytes. At (25 °C and 1 bar) with a catalysts loading of about 1 mg c m geometric − 2 and using dissolved O 2 in 0.5 M H 2SO 4, typical H 2O 2 electrosynthesis rates of about 5 μ mol h − 1 c m geometric − 2 were reached with current efficiencies of about 85 ± 5% at 0.25 V (vs. RHE).

9-Fluorenyl radical: Electrochemical generation and cathodic immobilization at solid interfaces

9-Bromofluorene (FluHBr) is electrochemically reduced at solid electrodes such as glassy carbon (GC) and smooth transition metal surfaces (gold, palladium, and platinum). At smooth palladium or gold, two well-separated steps are obtained and are assigned (i) to the electro-catalytic formation of the radical and then (ii) to its reduction. Additionally, galvanostatic depositions of different transition metals (Pd, Au, Ni, Co, and Rh) onto solid substrates like glassy carbon, platinum and gold lead to comparable results. It is worth noting that the potential of the second reduction step remains the same whatever the metal. Fixed potential electrolyses at the level of the first step permitted to obtain (especially at Au and GC surfaces) cathodic signals assigned to the grafting of 9-fluorenyl radical FluH ●. The transient formation of this radical has been established by means of electron spin resonance (electrolysis at low temperature or trapping by a nitrone).