Conventional Transition Metal Research Articles

Substituent Effects on Redox Potential of Organic Electrode Materials in Li/Na Rechargeable Batteries: Electronic Effects Vs. Cation-Substituents Interaction

1. Introduction Conventional Li rechargeable battery system contains transition metal based electrodes. These conventional transition metal based electrodes have severe problems such as scarcity of resources, potentially high cost, and toxicity. With respect to the high sustainability for the next-generation energy storage system, another candidate of electrode materials is needed. Due to high sustainability and chemical tunability, organic battery system holds a great potential in next generation energy storage system. In order to develop these new battery system, understanding factors affecting a performance should have priority than others. It is well-known that the LUMO level of organic compounds has a linear correlation with redox voltage in rechargeable batteries (Figure 2). 6 However, it has been recently reported additional factors affecting redox voltage of organic electrode materials. 4,5 This research is focusing on categorization of factors affecting a voltage, especially, on cation-substituents interaction. With many references and our experiment results, it is convinced that voltage of organic materials is determined by several factors. Additional substituent effect and cation species effect should be considered for predicting an exact voltage behavior with molecular tuning. 2. Results and Discussion The target species based on terephthalate are shown in Figure 3. Terephthalate is one of the simplest form in organic electrode materials. Therefore, another effect can be reduced to study cation-substituent effect. The plot of LUMO level vs. discharge voltage of target species is shown in Figure 4. Four types of cathode materials have same redox center based on terephthalate already reported by J.-M. Tarascon group.7 Tendency of almost species follows conventional rules which of correlation between LUMO level and discharge voltage, but some species having special substituent shows different behavior. Table 1. LUMO level vs. Experimental voltage Species Na2H2TP Na2TP Na2DMTP Na2MeO2TP Li cell (vs. Li/Li+) 0.93 0.84 0.81 0.9 Na cell (vs. Na/Na+) 0.55 0.59 0.54 0.38 LUMO (eV) -1.58 -1.41 -1.4 -1.34 3. Concluding remarks Firstly, some special substituent gives a big effect to determine a voltage. Methoxy group (-OCH3) is an electron-donating substituent. With LUMO level, voltage should be lower than others. But, in Li cell system, it does not follow. Interaction between lithium and oxygen from methoxy group make a stable discharge form. On the other hand, in Na cell system, sodium ion has a bigger size than lithium ion. So, interaction between oxygen cannot be occurred because of steric strain. Secondly, with LUMO level, voltage of Na2H­2TP should be higher than Na2TP. But, in Na cell system, it is not. Steric strain affect to the voltage of Na2H2TP. In our conclusion, lithium ion size is negligible affecting to the voltage but sodium ion size starts to affect the lowering of voltage in Na2H2TP electrode material. It is expected that competition between factors affecting a voltage of organic electrode materials. In summary, cation-substituent interaction should be considered to predict an exact voltage. It is important for tuning an organic electrode material to make an appropriate voltage in our use. More additional factors may exist and it is needed to categorize them. The more understanding of factors affecting to a voltage gathered, then more accurate prediction and molecular tuning can be possible. 4.

Experimental Study and CFD Model for Partial Oxidation of Methane over Self-Sustained Electrochemical Promotion Catalyst

The so-called self-sustained electrochemical promotion catalyst or SSEP catalyst is a micro-particulate material with solid-solid interfaces between the active catalyst phase, the oxygen ion conductor, and oxygen reduction phase forming multiple micro-electrochemical cells. We have demonstrated that electrochemical promotion can make the catalyst more effective than conventional transition metal (Ni, Co) based catalysts and precious metal based catalyst for partial oxidation (POX) reforming of hydrocarbons. A computational fluid dynamics (CFD) model will help quantify the effects of the components in the microscopic electrochemical cells and of detailed thermal-chemical processes on electrochemical promotion thereby allowing better understanding and further optimization of the catalyst system. A multi-physical multi-scale CFD was developed for analyzing POX of methane (CH4) over a SSEP catalyst in a fixed-bed reformer. The model incorporates a conventional transport processes, heat transfer, and kinetics for POX of CH4 over the active components and the electrochemical processes occurring in the unique microstructure. The simulation results show that the temperature in the first reactor with the Ni based conventional catalyst is generally about 30 K lower than that in the second reactor with the Ni-based SSEP catalyst. This temperature difference is impossible to explain the huge difference in the conversion in these two reactors. The simulation results are compared with the experimental results. The good agreement can only be achieved by correctly describing the electrochemical processes and electrochemical promotion in the theoretical system. The validated model was used to predict the performance of the SSEP catalysts as a function of flow rate, O/C ratio, and the microstructure of the catalysts providing guidance for further optimization the SSEP catalyst.

Unveiling the Dynamic Capacitive Storage Mechanism of Co3O4 @NiCo2O4 Hybrid Nanoelectrodes for Supercapacitor Applications

For pseudocapacitors, the electrode material plays a vital role in the electrochemical properties. Among various electrode materials, spinel nickel cobaltite (NiCo2O4) has been widely investigated as an advanced electrode material owing to its better electronic conductivity (two orders of magnitude higher than conventional transition metal oxides), low cost, and high availability. With all the excitement about new electrode materials, less attention has been paid to their dynamic storage mechanism that commonly exhibit intriguing capacitive activation during charge/discharge cycling. Here, we report a simple and cost-effective approach to the synthesis of hierarchical mesporous Co3O4@NiCo2O4 nanoforests on Ni foam for supercapacitor (SC) electrode applications by a coupled one-step solution and annealing process. The synthesized electrode exhibits capacitive activation during charge-discharge cycling (from 0.73 F/cm2 of the pristine state to the peak value of 1.12 F/cm2 after 2000 cycles with only 1.8% loss compared to the peak capacitance after another 2000 cycles). Using ex situ TEM characterization and electrical test, We attribute such dynamic capacitive activation to (1) enlarged electroactive surface area through the formation of Co3O4@NiCo2O4 core-shell structure and (2) enhanced electrical conductivity by forming oxygen vacancies and hydroxyl groups during charge-discharge cycling. Our findings provide a scientific explanation for the capacitive activation in cobalt oxide-binary nickel cobaltite compounds, and a new design guideline for the development of capacitive activation enabled, high performance transitional oxide electrodes. Figure 1

Flexible Integrated Electrical Cables Based on Biocomposites for Synchronous Energy Transmission and Storage

It becomes increasingly important to develop integrated systems with the aim of achieving maximum functionality for the state‐of‐the‐art electronic devices. Here, a flexible integrated electrical cable is reported by incorporating biomaterials based fiber supercapacitors into a resistor–capacitor circuit. In this unique integrated configuration, the fiber electrodes are alternately winded along the twisted electric wires, which worked not only as scaffolding to support and strengthen the slight electrodes but also as separators to spatially confine them to avoid short circuit. It exhibits excellent electrochemical performance comparable to conventional transition metal compounds based cells, and can especially realize sophisticated applications in synchronous energy transmission and storage, presenting a new member for the integrated energy storage system family.

Understanding the Low-Overpotential Production of CH4 from CO2 on Mo2C Catalysts

While Cu is the only electrocatalyst that converts CO2 into meaningful quantities of CH4 fuel, it requires significant overpotentials (onset potential of ∼−0.80 V vs RHE), decreasing energy conversion efficiencies. We report that Mo2C is capable of catalyzing CO2 into CH4 at low potentials (onset potential of ∼−0.55 V vs RHE), where Cu electrocatalysts do not convert CO2. This low-overpotential catalyst was first identified as a candidate by electronic structure calculations, which indicated the free energetics of CO hydrogenation to be more favorable than that on conventional transition metals such as Cu. Despite the low onset potential for CH4, the CH4 has a steep Tafel slope (∼−280 mV/dec), resulting in most of the current passing through the Mo2C electrocatalysts being utilized for the competitive hydrogen evolution reaction. We conducted a detailed theoretical analysis on the basis of density functional theory calculations, microkinetic analysis, and simulated Pourbaix diagrams to suggest the reasons...

(Invited) Li Intercalation into Multi-Layers Transition Metal Carbides and Carbonitrides "Mxenes" in Li-Ion Batteries

Two-dimensional, 2D, transition metal carbides and carbonitrides, so called MXenes, consist of nearly closed packed layers of early transition metals “M” with “X” atoms (X stands for carbon or nitrogen) filling the octahedral sites with a nominal composition of Mn +1 Xn where n = 1, 2, or 3. Depending on the value of n, the thickness of the Mn +1 Xn change; if n = 1 the MXene layer consists of a single block of octahedra (3 atoms thick). If n = 2 the MXene layer consists of 2 octahedra blocks; if n = 3, consists of 3 blocks of octahedra. The surface of as-synthesized MXenes is terminated by a mixture of moieties viz. O, OH, and F (this mixture is referred hence after by Tx). To date, the following MXenes were successfully synthesized: Ti2CTx, Nb2CTx, V2CTx, (Ti0.5,Nb0.5)2CTx, Ti3C2Tx, (V0.5,Cr0.5)3C2Tx, Ti3CNTx, Ta4C3Tx, and Nb4C3Tx. Unlike conventional 3D transition metal carbides and nitrides which are known to be inert for Li, MXenes were found to be electrochemically active as host materials for Li-ions. The latter intercalate/de-intercalate reversibly between the MXenes layers during the electrochemical cycling in Li batteries. This was confirmed by in situ XRD studies during electrochemical lithiation and de-lithiation. When they were tested as electrode materials for Li-ion batteries (LIBs), each MXene showed its own electrochemical voltage window. In principle, some MXenes could function as cathodes and some as anodes for LIBs. MXenes electrodes exhibited an excellent capability to handle high cycling rates with good capacity. This was explained by a low Li diffusion barrier in case of MXene compared to other electrode materials such as graphite. MXenes powders can be cold pressed into freestanding thick discs resulting in electrodes with high areal capacities exceeding 5 mAh/cm2. Most of the research conducted –experimentally- on MXenes as electrodes for LIBs was limited to the as-synthesized MXene without further control of the surface termination. However, ab initio calculations predict that controlling the surface termination could enhance the performance. Herein the progress in the synthesis of MXenes and controlling their surface termination, in addition to their performance as electrode materials in LIBs will be discussed.

Activity of transition metal sulfides supported on Al2O3, TiO2 and ZrO2 in the parallel hydrodesulfurization of 1-benzothiophene and hydrogenation of 1-methyl-cyclohex-1-ene

Sulfided conventional transition metals Co, Ni, Mo, and W and noble metals Rh, Pd, Ir, Pt, and Re deposited over conventional support γ-Al2O3 (SBET = 262 m2g−1), and unconventional supports TiO2 (anatase, SBET = 140 m2g−1) and ZrO2 (baddeleyite, SBET = 108 m2g−1) were studied in the parallel hydrodesulfurization of 1-benzothiophene (HDS) and hydrogenation of 1-methyl-cyclohex-1-ene (o-HYD) at 360 °C and 1.6 MPa. Mo, W, Co, and Ni sulfided catalysts exhibited relatively low activity in both HDS and o-HYD. For these sulfides, the TiO2 and ZrO2 support effect relative to γ-Al2O3 varied by the factor 0.4–9.3. In contrast, the supported sulfides of Rh, Re, Pd, Pt, and Ir were highly active in HDS with low TiO2 and ZrO2 support effect relative to γ-Al2O3 (Rh/ZrO2 being an exception). Rh, Re, and Pd sulfided species exhibited relatively low activities in o-HYD reaction while Ir and Pt species exhibited high activities in o-HYD. The reference industrial bimetallic CoMo and NiMo Al2O3 supported catalysts exhibited desirable high HDS but low o-HYD activities.

A facile synthesis of 2H-indazoles under neat conditions and further transformation into aza-γ-carboline alkaloid analogues in a tandem one-pot fashion

We have described a facile, microwave-assisted, catalyst-free and solvent-free approach to 2H-indazoles and further developed a robust tandem one-pot metal-free strategy for C–C bond formation at the C-3 position of 2H-indazoles leading to a unique class of aza-γ-carboline alkaloid analogues. This straightforward expedient synthesis constitutes an interesting alternative to the existing conventional transition metal catalyzed reactions.

Exploring the limits: A low-pressure, low-temperature Haber–Bosch process

The Haber–Bosch process for ammonia synthesis has been suggested to be the most important invention of the 20th century, and called the ‘Bellwether reaction in heterogeneous catalysis’. We examine the catalyst requirements for a new low-pressure, low-temperature synthesis process. We show that the absence of such a process for conventional transition metal catalysts can be understood as a consequence of a scaling relation between the activation energy for N2 dissociation and N adsorption energy found at the surface of these materials. A better catalyst cannot obey this scaling relation. We define the ideal scaling relation characterizing the most active catalyst possible, and show that it is theoretically possible to have a low pressure, low-temperature Haber–Bosch process. The challenge is to find new classes of catalyst materials with properties approaching the ideal, and we discuss the possibility that transition metal compounds have such properties.

ChemInform Abstract: The Development of Gold Catalysts for Use in Hydrogenation Reactions

AbstractReview: 333 refs.

Bimetallic gold–palladium alloy nanoclusters: an effective catalyst for Ullmann coupling of chloropyridines under ambient conditions

An efficient method for the Ullmann coupling of chloropyridines catalyzed by poly(N-vinylpyrrolidone) (PVP)-stabilized bimetallic Au–Pd alloy nanoclusters (NCs) under ambient conditions is demonstrated. The reaction does not occur with either gold or palladium single-metal clusters alone, nor with a physical mixture of the two metals. The experimental results indicate that the inclusion of Au as a nearest heteroatom is crucial to initiate the coupling and its composition up to 50% is essential to accelerate the reaction. Unlike the conventional transition metal catalysis, 2-chloropyridine was found to be highly reactive as compared to 2-bromopyridine. From the UV-vis and ICP-AES measurements, a significant amount of leached Pd(II) was observed in the coupling with 2-bromopyridine as compared with 2-chloropyridine, indicating that the leaching process might be a crucial factor in diminishing the reactivity.

Half-metallic ferromagnetism in the hypothetical RbN and CsN compounds: First-principles calculations

We report a first-principles study of the hypothetical RbN and CsN compounds. The spin-polarized calculations indicate that these materials are half-metallic ferromagnets and exhibit an integer magnetic moment of 2μB. The most important property in these alkaline metal nitrides is that the half-metallicity is originated from the polarization of the p-N orbitals not present in the conventional transition metal or rare earth nitrides. We find also that the half-metallicity is maintained in the zinc-blende structure on a wide range of lattice constant. This offers the possibility to growth such materials on various semiconductor substrates.

The development of gold catalysts for use in hydrogenation reactions

With increasing emphasis placed on cleaner chemical synthesis, energy efficiency and waste minimisation, the manufacture of pharmaceuticals and fine chemicals is undergoing a progressive shift from conventional stoichiometric organic processes to a harnessing of catalytic selectivity. In hydrogenation processes, gold catalysts have untapped potential in terms of selectivity in the reduction of a target functionality in multifunctional reactants. This Review provides a comprehensive evaluation of the catalytic applications of Au in hydrogenation, assessing the benefits relative to conventional transition metal (e.g. Pt, Pd and Ni) catalytic systems. Hydrogenation activity requires the formation of nanoscale Au particles that are (typically) anchored to oxide supports. The crucial catalyst structural and surface properties required to achieve enhanced hydrogenation performance in terms of rate, selectivity and stability are discussed. The synthesis procedures and characterisation methodologies directed at catalyst optimisation are evaluated. The practical application of Au catalysts is illustrated taking, as a case study, the hydrogenation of nitroaromatics, where critical features such as hydrogen adsorption/activation, structure sensitivity, metal–support interactions and active site characteristics are discussed. Commonality with the catalytic action of supported Ag is flagged with a consideration of the future outlook and direction for selective hydrogenation using Au catalysts.

Single-walled carbon nanotube synthesis on SiO2/Si substrates at very low pressures by the alcohol gas source method using a Pt catalyst

A platinum catalyst was used for single-walled carbon nanotube (SWCNT) growth on SiO2/Si substrates using an alcohol gas source method, a type of cold-wall chemical vapor deposition. Compared to Co, a conventional transition metal catalyst, the optimal ethanol pressure was considerably reduced in the growth at 700°C, and SWCNTs could be grown even at an ambient ethanol pressure of 1×10−5Pa. Raman spectroscopy measurements showed that the G/Si ratios of SWCNTs grown at 700°C with the Pt catalyst under an ethanol pressure between 1×10−4 and 1×10−1Pa was larger than that grown with Co catalyst under optimal conditions (700°C, 1×10−1Pa), indicating that the Pt catalyst is suitable for SWCNT growth under a low ethanol pressure. In addition, the diameter distributions of SWCNTs grown with the Pt catalyst were narrower than those grown with the Co catalyst. Taking into account the results by transmission electron microscopy observation, the diameter reduction was caused by the smaller migration distance of Pt on the substrate. Based on these results, we discuss the growth mechanism of SWCNTs from the Pt catalyst.

Metal-free diamination of alkenes employing bromide catalysis

A unique metal-free intramolecular diamination of alkenes based on bromide catalysis is reported that uses only potassium bromide and sodium chlorite avoiding any use of transition metal. This unprecedented halide catalysis is of general applicability, uses economic reagents, can be conveniently up-scaled and proceeds under mild and selective conditions that surpass all conventional transition metals in scope.

Detailed Studies of a High-Capacity Electrode Material for Rechargeable Batteries, Li2MnO3−LiCo1/3Ni1/3Mn1/3O2

Lithium-excess manganese layered oxides, which are commonly described by the chemical formula zLi(2)MnO(3)-(1-z)LiMeO(2) (Me = Co, Ni, Mn, etc.), are of great importance as positive electrode materials for rechargeable lithium batteries. In this Article, Li(x)Co(0.13)Ni(0.13)Mn(0.54)O(2-δ) samples are prepared from Li(1.2)Ni(0.13)Co(0.13)Mn(0.54)O(2) (or 0.5Li(2)MnO(3)-0.5LiCo(1/3)Ni(1/3)Mn(1/3)O(2)) by an electrochemical oxidation/reduction process in an electrochemical cell to study a reaction mechanism in detail before and after charging across a voltage plateau at 4.5 V vs Li/Li(+). Changes of the bulk and surface structures are examined by synchrotron X-ray diffraction (SXRD), X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectroscopy (SIMS). SXRD data show that simultaneous oxygen and lithium removal at the voltage plateau upon initial charge causes the structural rearrangement, including a cation migration process from metal to lithium layers, which is also supported by XAS. This is consistent with the mechanism proposed in the literature related to the Li-excess manganese layered oxides. Oxygen removal associated with the initial charge on the high voltage plateau causes oxygen molecule generation in the electrochemical cells. The oxygen molecules in the cell are electrochemically reduced in the subsequent discharge below 3.0 V, leading to the extra capacity. Surface analysis confirms the formation of the oxygen containing species, such as lithium carbonate, which accumulates on the electrode surface. The oxygen containing species are electrochemically decomposed upon second charge above 4.0 V. The results suggest that, in addition to the conventional transition metal redox reactions, at least some of the reversible capacity for the Li-excess manganese layered oxides originates from the electrochemical redox reaction of the oxygen molecules at the electrode surface.

Negative permeability due to exchange spin-wave resonances in thin magnetic films with surface pinning

We report a theory of the effective permeability of multilayered metamaterials containing thin ferromagnetic layers with magnetization pinned on either one or both surfaces. Because of the pinning and small film thickness, the lowest frequency magnetic resonances are due to nonuniform exchange spin waves with frequencies far above those expected for uniform ferromagnetic resonance in known magnetic materials. Yet, the coupling of the nonuniform spin-wave modes to the electromagnetic field is shown to be strong enough to lead, for magnetic parameters characteristic for conventional transition metal alloys, to negative values of the effective permeability at frequencies of several hundred gigahertzs. The permittivity of metals is already negative in this frequency range. Hence, this system represents a negative refractive index metamaterial at subterahertz frequencies. The ways by which to maximize the frequency and the strength of the negative magnetic response are analyzed.

Lanthanide‐Catalyst‐Mediated Tandem Double Intramolecular Hydroalkoxylation/Cyclization of Dialkynyl Dialcohols: Scope and Mechanism

Lanthanide-organic complexes of the general type [Ln{N(SiMe(3))(2)}(3)] (Ln=La, Sm, Y, Lu) serve as effective precatalysts for the rapid, exo-selective, and highly regioselective tandem double intramolecular hydroalkoxylation/cyclization of primary and secondary dialkynyl dialcohols to yield the corresponding bi-exocyclic enol ethers. Conversions are highly selective with products distinctly different from those generally produced by conventional transition metal or other catalysts, and the turnover frequencies with some substrates are too large to determine accurately. The rates of terminal alkynl alcohol hydroalkoxylation/cyclization are significantly more rapid than those of internal alkynyl alcohols, arguing that steric demands dominate the cyclization transition state. The hydroalkoxylation/cyclizations of internal dialkynyl dialcohols afford excellent E selectivity. The rate law for dialkynyl dialcohol hydroalkoxylation/cyclization is first-order in [catalyst] and zero-order in [alkynyl alcohol], as is observed for the organolanthanide-catalyzed hydroamination/cyclization of aminoalkenes, aminoalkynes, and aminoallenes, and the intramolecular single-step hydroalkoxylation/cyclization of alkynyl alcohols. An ROH/ROD kinetic isotope effect of 0.82(0.02) is observed for the tandem double hydroalkoxylation/cyclization. These mechanistic data implicate turnover-limiting insertion of C-C unsaturation into the Ln-O bond, involving a highly organized transition state, with subsequent, rapid Ln-C protonolysis.

Reaction of Imidazoline-2-Selone with Acids and Its Use for Selective Coordination of Platinum Ions on Silica Surface

A new and efficient system for the selective recovery of platinum ions from conventional cheap transition metal mixtures was developed. We found that the selone is reactive toward the conventional acids. Mesoporous silica functionalized by reaction of selone showed excellent selectivity to platinum ions among various transition metal ions.

Intramolecular Hydroalkoxylation/Cyclization of Alkynyl Alcohols Mediated by Lanthanide Catalysts. Scope and Reaction Mechanism

Lanthanide-organic complexes of the general type Ln[N(SiMe(3))(2)](3) (Ln = La, Sm, Y, Lu) serve as effective precatalysts for the rapid, exoselective, and highly regioselective intramolecular hydroalkoxylation/cyclization of primary and secondary alkynyl alcohols to yield the corresponding exocyclic enol ethers. Conversions are highly selective with products distinctly different from those generally produced by conventional transition metal catalysts, and turnover frequencies as high as 52.8 h(-1) at 25 degrees C are observed. The rates of terminal alkynl alcohol hydroalkoxylation/cyclization are significantly more rapid than those of internal alkynyl alcohols, arguing that steric demands dominate the cyclization transition state. The hydroalkoxylation/cyclization of internal alkynyl alcohols affords excellent E-selectivity. The hydroalkoxylation/cyclization of the SiMe(3)-terminated internal alkynyl alcohols reveals interesting product profiles which include the desired exocyclic ether, a SiMe(3)-eliminated exocyclic ether, and the SiMe(3)-O-functionalized substrate. The rate law for alkynyl alcohol hydroalkoxylation/cyclization is first-order in [catalyst] and zero-order in [alkynyl alcohol], as observed in the intramolecular hydroamination/cyclization of aminoalkenes, aminoalkynes, and aminoallenes. An ROH/ROD kinetic isotope effect of 0.95(0.03) is observed for hydroalkoxylation/cyclization. These mechanistic data implicate turnover-limiting insertion of C-C unsaturation into the Ln-O bond, involving a highly organized transition state, with subsequent, rapid Ln-C protonolysis.