Biomimetic Synthesis of Metal Ion‐Doped Hierarchical Crystals Using a Gel Matrix: Formation of Cobalt‐Doped LiMn2O4 with Improved Electrochemical Properties through a Cobalt‐Doped MnCO3 Precursor

We have synthesized spinel type cobalt‐doped LiMn₂O₄ (LiMn_2?yCo_yO₄, 0≤y≤0.367), a cathode material for a lithium‐ion battery, with hierarchical sponge structures via the cobalt‐doped MnCO₃ (Mn_1‐xCo_xCO₃, 0≤x≤0.204) formed in an agar gel matrix. Biomimetic crystal growth in the gel matrix facilitates the generation of both an homogeneous solid solution and the hierarchical structures under ambient condition. The controlled composition and the hierarchical structure of the cobalt‐doped MnCO₃ precursor played an important role in the formation of the cobalt‐doped LiMn₂O₄. The charge–discharge reversible stability of the resultant LiMn_1.947Co_0.053O₄ was improved to ca. 12 % loss of the discharge capacity after 100 cycles, while pure LiMn₂O₄ showed 24 % loss of the discharge capacity after 100 cycles. The parallel control of the hierarchical structure and the composition in the precursor material through a biomimetic approach, promises the development of functional materials under mild conditions.     

Effect of epitaxial growth on the formation of the cobalt catalysts of the Fischer-Tropsch synthesis

Mixed oxides Co_xAl_yO₄ with different Al/Co ratios applied as supports for the catalysts of the Fischer-Tropsch synthesis were prepared using the solid-state chemical reaction. The Co_xAl_yO₄ supports were prepared by modifying gibbsite with various cobalt salts (acetate, nitrate, and basic carbonate). The use of basic cobalt carbonate gives the Co(20%)/Co_xAl_yO₄ catalyst, which provides an increased yield of hydrocarbons C₅₊ and a decreased methane content compared to the impregnation catalyst Co(30%)/Al₂O₃. The introduction of small amounts of rhenium additives makes it possible to enhance the yield of hydrocarbons C₅₊ (179 g m⁻³) and also to increase the selectivity with respect to the C₅–C₁₈ fraction. The introduction of basic cobalt carbonate into the support, most likely, creates favorable conditions for the epitaxial growth of the precursor of the active phase. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1856–1860, September, 2007.     

A Flame‐Reaction Method for the Large‐Scale Synthesis of High‐Performance SmxCoy Nanomagnets

We report a flame‐reaction method to synthesize high‐performance Sm_xCo_y (x=1, y=5; x=2, y=17) particles on a multigram scale. This flame reaction allows the controlled decomposition of Sm(NO₃)₃ and Co(NO₃)₂ to 320 nm SmCo‐O (SmCoO₃ + Co₃O₄) particles. A 5.8 g sample of SmCo_3.8‐O particles was coated with CaO and then reduced at 900 °C by Ca to give 4.2 g of 260 nm SmCo₅ particles. The SmCo₅ particles are strongly ferromagnetic and the aligned particles in epoxy resin exhibit a large room‐temperature coercivity (H_c) of 41.8 kOe and giant (BH)_max (maximum magnetic energy product) of 19.6 MGOe, the highest value ever reported for SmCo₅ made by chemical methods. This synthesis can be extended to synthesize Sm₂Co₁₇ particles, providing a general approach to scaling up the synthesis of high‐performance Sm_xCo_y nanomagnets for permanent magnet applications.     

Recent advances in layered LiNi x CoyMn1−x−y O2 cathode materials for lithium ion batteries

Lithium cobalt oxide, LiCoO₂, has been the most widely used cathode material in commercial lithium ion batteries. Nevertheless, cobalt has economic and environmental problems that leave the door open to exploit alternative cathode materials, among which LiNi _x Co_yMn_{1 − x − y} O₂ may have improved performances, such as thermal stability, due to the synergistic effect of the three ions. Recently, intensive effort has been directed towards the development of LiNi _x Co _y Mn_{1 − x − y} O₂ as a possible replacement for LiCoO₂. Recent advances in layered LiNi _x Co_yMn_{1 − x − y} O₂ cathode materials are summarized in this paper. The preparation and the performance are reviewed, and the future promising cathode materials are also prospected.     

Cobalt‐Doped Perovskite‐Type Oxide LaMnO3 as Bifunctional Oxygen Catalysts for Hybrid Lithium–Oxygen Batteries

Perovskite‐type oxides based on rare‐earth metals containing lanthanum manganate are promising catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline electrolyte. Perovskite‐type LaMnO₃ shows excellent ORR performance, but poor OER activity. To improve the OER performance of LaMnO₃, the element cobalt is doped into perovskite‐type LaMnO₃ through a sol–gel method followed by a calcination process. To assess electrocatalytic activities for the ORR and OER, a series of LaMn_1?xCo_xO₃ (x=0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5) perovskite oxides were synthesized. The results indicate that the amount of doped cobalt has a significant effect on the catalytic performance of LaMn_1?xCo_xO₃. If x=0.3, LaMn_0.7Co_0.3O₃ not only shows a tolerable electrocatalytic activity for the ORR, but also exhibits a great improvement (>200 mV) on the catalytic activity for the OER; this indicates that the doping of cobalt is an effective approach to improve the OER performance of LaMnO₃. Furthermore, the results demonstrate that LaMn_0.7Co_0.3O₃ is a promising cost‐effective bifunctional catalyst with high performance in the ORR and OER for application in hybrid Li?O₂ batteries.     

A Molecular Approach to Self‐Supported Cobalt‐Substituted ZnO Materials as Remarkably Stable Electrocatalysts for Water Oxidation

In regard to earth‐abundant cobalt water oxidation catalysts, very recent findings show the reorganization of the materials to amorphous active phases under catalytic conditions. To further understand this concept, a unique cobalt‐substituted crystalline zinc oxide (Co:ZnO) precatalyst has been synthesized by low‐temperature solvolysis of molecular heterobimetallic Co_4?xZn_xO₄ (x=1–3) precursors in benzylamine. Its electrophoretic deposition onto fluorinated tin oxide electrodes leads after oxidative conditioning to an amorphous self‐supported water‐oxidation electrocatalyst, which was observed by HR‐TEM on FIB lamellas of the EPD layers. The Co‐rich hydroxide‐oxidic electrocatalyst performs at very low overpotentials (512 mV at pH 7; 330 mV at pH 12), while chronoamperometry shows a stable catalytic current over several hours.     

Model Studies on the Ozone-Mediated Synthesis of Cobalt Oxide Nanoparticles from Dicobalt Octacarbonyl in Ionic Liquids

Low-temperature synthesis in ionic liquids (ILs) offers an efficient route for the preparation of metal oxide nanomaterials with tailor-made properties in a water-free environment. In this work, we investigated the role of 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [C₄C₁Pyr][NTf₂] in the synthesis of cobalt oxide nanoparticles from the molecular precursor Co₂(CO)₈ with ozone. We performed a model study in ultra-clean, ultrahigh vacuum (UHV) conditions by infrared reflection absorption spectroscopy (IRAS) using Au(111) as a substrate. Exposure of the pure precursor to ozone at low temperatures results in the oxidation of the first layers, leading to the formation of a disordered Co_xO_y passivation layer. Similar protection to ozone is also achieved by deposition of an IL layer onto a precursor film prior to ozone exposure. With increasing temperature, the IL gets permeable for ozone and a cobalt oxide film forms at the IL/precursor interface. We show that the interaction with the IL mediates the oxidation and leads to a more densely packed Co_xO_y film compared to a direct oxidation of the precursor.     

Photoelectrochemical Study of Anodic Oxide Films on Titanium–Cobalt Alloys

Properties of anodic oxide films as a function of the composition of Ti _x –Co (x= 0, 10, 20, 30, 50, 67, 75 at. %) alloys in solutions of a borate buffer and sodium sulfate are studied by the voltammetric technique combined with photocurrent measurements. The oxide film on the alloys is shown to contain TiO₂and Co₂O₃. In a borate buffer, the oxide film presumably comprises two layers: an outer layer of cobalt oxides and an inner layer of a mixture of cobalt and titanium oxides.     

Preparation of hierarchical LiNixCoyMnzO2 from solvothermal [NixCoyMnz](OH)2 via regulating the ratio of Ni,Co, and Mn and its excellent properties for lithium-ion battery cathode

The ternary-layered oxide (LiNi_xCo_yMn_zO₂) has become the most promising cathode material for lithium-ion batteries due to the advantages of higher discharge platform, better conductivity, and higher theoretical capacity. The [Ni_xCo_yMn_z](OH)₂ with different ratios of nickel, cobalt, and manganese (NCM) was prepared by solvothermal method, and then ternary cathode material LiNi_xCo_yMn_zO₂ was obtained by mixing lithium and calcining. In this paper, ternary cathode materials with different ratios of NCM were prepared by the solvothermal method. The structure and morphology of the materials were analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The effects of the ratio on the electrochemical properties of the materials were investigated by constant current charge and discharge test and electrochemical impedance spectroscopy test. The synthesized lithium-nickel-cobalt-manganese oxide belongs to the hexagonal system and has an α-NaFeO₂ layered structure, which is an R-3m space group. The NCM ternary cathode materials with different morphologies were obtained by changing the ratio of NCM. The sample with NCM ratio of 5:3:2 has a unique sheet-like spherical shape and has the best rate performance.     

Nickel‐substituted cobalt ferrite nanoparticles supported on arginine‐modified graphene oxide nanosheets: Synthesis and catalytic activity

The amino acid arginine was used to modify the surface of graphene oxide nanosheets and then nickel‐substituted cobalt ferrite nanoparticles were supported on those arginine‐grafted graphene oxide nanosheets (Ni_0.5Co_0.5Fe₂O₄@Arg–GO). The prepared Ni_0.5Co_0.5Fe₂O₄@Arg–GO was characterized using flame atomic absorption spectroscopy, inductively coupled plasma optical emission spectrometry, energy‐dispersive spectroscopy, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, Raman spectroscopy, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy. The application of Ni_0.5Co_0.5Fe₂O₄@Arg–GO as a catalyst was examined in a one‐pot tandem oxidative cyclization of primary alcohols with o ‐phenylenediamine to benzimidazoles under aerobic oxidation conditions. The results showed that 2‐phenylbenzimidazole derivatives were successfully achieved using Ni_0.5Co_0.5Fe₂O₄@Arg–GO nanocomposite catalyst via the one‐pot tandem oxidative cyclization strategy.     

水热合成Co3O4的制备参数调变及其催化分解N2O性能

以十六烷基三甲基溴化胺（CTAB）为模板剂,通过调变CTAB浓度水热合成了氧化钴前驱体,焙烧制得棒状形貌的Co₃O₄,在其表面浸渍K₂CO₃溶液制得K改性的Co₃O₄催化剂,用于N₂O分解。用X射线衍射（XRD）、N₂物理吸附（BET）、扫描电镜（SEM）、X射线光电子能谱（XPS）、H₂程序升温还原（H₂-TPR）和O₂程序升温脱附（O₂-TPD）等技术对催化剂进行了表征,考察了CTAB/钴及尿素/钴物质的量比等制备参数对Co₃O₄催化分解N₂O活性的影响。结果表明,CTAB浓度为0.05 mol/L、CTAB/钴离子物质的量比为1、尿素/钴离子物质的量比为4时,所制备的Co₃O₄催化剂具有较高的N₂O分解活性,而K改性可以进一步提升其催化性能。K改性的Co₃O₄在有氧有水气氛中400℃下进行N₂O分解反应,50 h后N₂O转化率仍保持在91%以上。     

Effect of Substitution of Cobalt for Iron in Sr4Fe6O13-δon the Catalytic Activity for Methane Combustion

A series of mixed oxides Sr₄Fe_6?xCo_xO_13?δ (x=0, 1, 2, 3, or 4) were prepared by sol‐gel method and used for catalytic combustion of methane. The structural properties of oxides were characterized by XRD, TGA, and XPS. The layered intergrowth perovskite‐like oxide Sr₄Fe₅CoO_13?δ exhibits the highest catalytic activity for methane combustion under the experimental conditions. The enhanced catalytic activity of Sr₄Fe₅CoO_13?δ for methane combustion could be attributed to the increased amount of oxygen vacancy caused by the partial substitution of cobalt for iron in the Sr₄Fe₆O₁₃, which was confirmed by TGA and XPS.     

Kinetics of Oxidation Processes in the System Co/Ga studied by in situ X‐Ray Diffraction

Oxidation processes in the system Co/Ga were studied by in situ X‐ray diffraction at temperatures between 800 and 1000 °C. Experiments were performed with metal powders and planar substrates. Oxidation of cobalt‐rich alloys, Co_1‐xGa_x, results in the formation of mixtures of cobalt‐ and gallium‐containing oxides. During oxidation of the intermetallic compounds CoGa and CoGa₃ only gallium is oxidized, and dense tarnishing layers of β‐Ga₂O₃ are formed. In all cases the oxide products are only intermediate products on the way to thermodynamic equilibrium, i.e. total oxidation of both metals. The kinetics during oxidation of the intermetallic compound CoGa was studied in detail by time resolved in situ X‐ray diffraction. After an induction time the kinetics can be described by a parabolic rate law with an activation energy of 312 kJ mol^—1. From the decrease of the parabolic rate constant with decreasing oxygen partial pressure and the observation of pore formation at the metal‐oxide interface it can be concluded that (i) outward diffusion of Ga‐ions through β‐Ga₂O₃ is the rate determining step during this solid state reaction, and (ii) Ga‐ions are mobile by means of gallium vacancies.     

Ultrahigh‐Content Nitrogen‐doped Carbon Encapsulating Cobalt NPs as Catalyst for Oxidative Esterification of Furfural

It is an attractive and challenging topic to endow non‐noble metal catalysts with high efficiency via a nitrogen‐doping approach. In this study, a nitrogen‐doped carbon catalyst with high nitrogen content encapsulating cobalt NPs (CoO_x@N‐C(g)) was synthesized, and characterized in detail by XRD, HRTEM, N₂‐physisorption, ICP, CO₂‐TPD, and XPS techniques. g‐C₃N₄ nanosheets act as nitrogen source and self‐sacrificing templates, giving rise to an ultrahigh nitrogen content of 14.0 %, much higher than those using bulk g‐C₃N₄ (4.4 %) via the same synthesis procedures. As a result, CoO_x@N‐C(g) exhibited the highest performance in the oxidative esterification of biomass‐derived platform furfural to methylfuroate under base‐free conditions, achieving 95.0 % conversion and 97.1 % selectivity toward methylfuroate under 0.5 MPa O₂ at 100 °C for 6 h, far exceeding those of other cobalt‐based catalysts. The high efficiency of CoO_x@N‐C(g) was closely related to its high ratio of pyridinic nitrogen species that may act as Lewis basic sites as well as its capacity for the activation of dioxygen to superoxide radical O₂^.?.     

Cobalt-zeolite catalysts for the synthesis of hydrocarbons from CO and H2

Catalysts prepared by mechanical mixing of high-silica zeolite ZSM-5 with cobalt oxide Co₃O₄, basic cobaltous carbonate, and cobaltous carbonate were studied. The nature of the cobalt compound introduced into the mixture affects the catalytic and physicochemical properties of the catalyst. The presence of Co₃O₄ in the sample (introduced as oxide or obtained by thermal decomposition of the carbonate) is favorable to the formation of aromatic compounds from CO and H₂. The use of cobaltous carbonates for the preparation of catalysts results in development of the porous structure of the catalyst. During preparation of samples, the mechanical treatment partially destroys the zeolite framework of the support.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1070–1073, June, 1995.     

Synthesis, Characterization and Thermal Decomposition of M1[M2(C2O4)2]xH2O (x=5 for M1=Co and x=4 for M1=Cd; M2=Ni)

Cobalt bis(oxalato)nickelate pentahydrate, Co[Ni(C₂O₄)₂]5H₂O and cadmium bis(oxalato)nickelate tetrahydrate, Cd[Ni(C₂O₄)2]4H₂O have been synthesized and characterized by elemental analysis, reflectance and IR spectral studies. Thermal decomposition studies (TG, DTG and DTA ) in air showed that both the compound of cobalt and cadmium produced the oxide, MNiO_x (x=3 for M=Co; x=2 for M=Cd ) at 325 and 360°C respectively. DSC studies in nitrogen attributed only the mixture of both the metal at the end. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nitrogen‐doped Hollow Co3O4 Nanofibers for both Solid‐state pH Sensing and Improved Non‐enzymatic Glucose Sensing

Nitrogen‐doped hollow cobalt oxide nanofibers (Co₃O₄ NFs) with both glucose catalytic activity and pH sensitivity were fabricated through core‐sheath electrospinning technique, followed by calcination. The as‐developed nitrogen‐doped hollow Co₃O₄ NFs were thoroughly characterized using various techniques, and then employed to fabricate a dual electrochemical sensor for both pH sensing and glucose sensing. The pH sensitivity of the developed nitrogen‐doped hollow Co₃O₄ NFs demonstrated a Nernst constant of 12.9–15.9 mV/pH in the pH range of 3.0～9.0 and 6.8–10.7 mV/pH in the pH range of 9.0～13.0, respectively. The developed hollow cobalt oxides nanofibers sensor also possesses glucose sensitivity of 87.67 μA mM^?1 cm^?2, the limit of detection of 0.38 μM (S/N=3), and an acceptable selectivity against several common interferents in non‐enzymatic glucose determination. High accuracy for monitoring glucose in human serum sample was also demonstrated. These features indicate that the as‐synthesized nitrogen‐doped hollow cobalt oxides nanofibers hold great potential in the development of a unique dual sensor for both solid‐state pH sensing and superior non‐enzymatic glucose sensing.     

Emf Measurements on Nanocrystalline Copper-Doped Ceria

Mixed oxide samples of nanostructured Cu_xCe_1−xO_2−yof various composition were generated by (i) chemical precipitation and ball milling and (ii) inert gas condensation. X-ray diffraction measurements suggested that copper oxide was dissolved in nanostructured cerium oxide up to concentrations ofx=0.15. Solid electrolyte cells of the typeA, Cu₂O/CuBr/Cu_xCe_1−xO_2−y(A=Cu or CuO) showed reversible cell voltages. The ratio of the formal chemical activities of CuO and Cu₂O dissolved in nanostructured cerium oxide were calculated from the cell voltages. The results are discussed in terms of an apparent macroscopic solubility, due to interfacial segregation of copper oxide on nanostructured cerium oxide.     

Monolithically Integrated Spinel MxCo3−xO4 (M=Co,Ni, Zn) Nanoarray Catalysts: Scalable Synthesis and Cation Manipulation for Tunable Low‐Temperature CH4 and CO Oxidation

A series of large scale M_xCo_3−xO₄ (M=Co, Ni, Zn) nanoarray catalysts have been cost‐effectively integrated onto large commercial cordierite monolithic substrates to greatly enhance the catalyst utilization efficiency. The monolithically integrated spinel nanoarrays exhibit tunable catalytic performance (as revealed by spectroscopy characterization and parallel first‐principles calculations) toward low‐temperature CO and CH₄ oxidation by selective cation occupancy and concentration, which lead to controlled adsorption–desorption behavior and surface defect population. This provides a feasible approach for scalable fabrication and rational manipulation of metal oxide nanoarray catalysts applicable at low temperatures for various catalytic reactions.     

富氧条件下Co/ZSM-5催化剂对C_3H_8选择还原NO_x的性能

采用多种物理化学手段研究了在模拟的轻型柴油车尾气中不同Co担载量及Cu掺杂的Co/ZSM-5催化剂的Co组分分散状态、可还原性、NO吸附脱附性质对C3H8选择性催化还原NOx性能的影响。结果表明,浸渍法制备的Co/ZSM-5催化剂上既有外表面上的Co3+和Co2+物种,也有孔内的Co2+离子。富氧条件下Co/ZSM-5催化剂上C3H8选择性催化还原NOx的活性主要与ZSM-5载体孔外表面分散的CoOx物种中的钴离子可还原能力和NO吸附脱附性能密切相关。Co/ZSM-5催化剂上适宜的Co担载量约为4.0wt%,低担载量时随Co担载量增加,表面CoOx物种中钴离子可还原能力增强,C3H8选择性催化还原NOx的低温转化活性增加;高担载量时,随Co担载量增加,单位Co离子的NO吸附量的减少以及催化剂表面活性中心数的减少,导致了Co/ZSM-5催化剂NOx的转化率和催化剂比速率(k)的下降。孔外表面Co3O4晶体的存在使催化剂表面产生较强的NO吸附,并在高温时有利于C3H8的氧化燃烧,使C3H8选择性催化还原NOx的活性降低。