New baths for the deposition of manganese and cobalt oxides

New methods have been adopted for the anodic deposition of the different manganese and cobalt oxides. The deposition of the diferent oxides is usually carried out from their metal salt solutions in presence of a reducing agent. The oxides deposited are as follows: Mn₂O₃ from manganous sulphate in presence of boric, acid and formaldehyde at pH=5.5, Mn₃O₄ from manganous sulphate in presence of formic acid at pH=5.0 MnO from manganous sulphate-ammonium chloride solution in presence of telluric acid, Co₂O₃ from cobalt chloride in presence of telluric acid and sodium fluoride, Co₃O₄ from cobaltite in presence of formaldehyde and potassium chloride and finally CoO from cobalt chloride in presence of alcohol. The results of chemical analysis revealed that the purity of the oxides is 99.99% and their molecular formulae are MnO_1.5, MnO_1.33, MnO, CoO_1.5, CoO_1.33 and CoO respectively.     

Structural characterization and electrochemical intercalation of Li+ in layered Na0.65Ni0.5Mn0.5O2 obtained by freeze-drying method

New data on the structure and reversible lithium intercalation properties of sodium-deficient nickel–manganese oxides are provided. Novel properties of oxides determine their potential for direct use as cathode materials in lithium-ion batteries. The studies are focused on Na _x Ni_0.5Mn_0.5O₂ with x?=?2/3. Between 500 and 700 °C, new layered oxides Na_0.65Ni_0.5Mn_0.5O₂ with P3-type structure are obtained by a simple precursor method that consists in thermal decomposition of mixed sodium–nickel–manganese acetate salts obtained by freeze-drying. The structure, morphology, and oxidation state of nickel and manganese ions of Na_0.65Ni_0.5Mn_0.5O₂ are determined by powder X-ray diffraction, SEM and TEM analysis, and X-ray photoelectron spectroscopy (XPS). The lithium intercalation in Na_0.65Ni_0.5Mn_0.5O₂ is carried out in model two-electrode lithium cells of the type Li|LiPF₆(EC:DMC)|Na_0.65Ni_0.5Mn_0.5O₂. A new structural feature of Na_0.65Ni_0.5Mn_0.5O₂ as compared with well-known O3–NaNi_0.5Mn_0.5O₂ and P2–Na_2/3Ni_1/3Mn_2/3O₂ is the development of layer stacking ensuring prismatic site occupancy for Na⁺ ions with shared face on one side and shared edges on the other side with surrounding Ni/MnO₆ octahedra. The reversible lithium intercalation in Na_0.65Ni_0.5Mn_0.5O₂ is demonstrated and discussed.     

Mechanistic studies on the pyrolysis and combustion of polystyrene/ammonium perchlorate propellants in the presence of transition metal oxides

The effect of transition metal oxides (Fe₂O₃, MnO₂, Ni₂O₃ and Co₂O₃) on polystyrene/ammonium perchlorate propellant systems has been examined. The mechanism of action of the oxides in increasing the burning rate was examined by studying the effect of the oxides on the thermal decomposition and combustion of the oxidizer and the propellant. It has been concluded that one of the mechanisms by which the oxides act is by promoting the charge-transfer process, which is indicated by the enhancement of the electron-transfer process in ammonium perchlorate and by the correlation between the redox potential of the metal ions and the corresponding burning rates of the propellant.     

Effect of charge state and stoichiometry on the structure and reactivity of nickel oxide clusters with CO

The collision induced fragmentation and reactivity of cationic and anionic nickel oxide clusters with carbon monoxide were studied experimentally using guided-ion-beam mass spectrometry. Anionic clusters with a stoichiometry containing one more oxygen atom than nickel atom (NiO₂⁻, Ni₂O₃⁻, Ni₃O₄⁻ and Ni₄O₅⁻) were found to exhibit dominant products resulting from the transfer of a single oxygen atom to CO, suggesting the formation of CO₂. Of these four species, Ni₂O₃⁻ and Ni₄O₅⁻ were observed to be the most reactive having oxygen transfer products accounting for approximately 5% and 10% of the total ion intensity at a maximum pressure of 15 mTorr of CO. Our findings, therefore, indicate that anionic nickel oxide clusters containing an even number of nickel atoms and an odd number of oxygen atoms are more reactive than those with an odd number of nickel atoms and an even number of oxygen atoms. The majority of cationic nickel oxides, in contrast to anionic species, reacted preferentially through the adsorption of CO onto the cluster accompanied by the loss of either molecular O₂ or nickel oxide units. The adsorption of CO onto positively charged nickel oxides, therefore, is exothermic enough to break apart the gas-phase clusters. Collision induced dissociation experiments, employing inert xenon gas, were also conducted to gain insight into the structural properties of nickel oxide clusters. The fragmentation products were found to vary considerably with size and stoichiometry as well as ionic charge state. In general, cationic clusters favored the collisional loss of molecular O₂ while anionic clusters fragmented through the loss of both atomic oxygen and nickel oxide units. Our results provide insight into the effect of ionic charge state on the structure of nickel oxide clusters. Furthermore, we establish how the size and stoichiometry of nickel oxide clusters influences their ability to oxidize CO, an important reaction for environmental pollution abatement.     

Porous microtubes of nickel-cobalt double oxides as non-enzymatic hydrogen peroxide sensors

Non-enzymatic electrochemical sensors for the determination of hydrogen peroxide(H_2 O_2) have attracted more and more concerns.A series of nickel and cobalt double oxides(Ni_xCo_y-DO) with the different ratios of Ni/Co have been prepared by a polyol-mediated solvothermal method for H_2 O_2 detection.The obtained products exhibit honeycomb-like open porous microtubes constituted with the low-dimensional nanostructured Ni_xCo_y-DO blocks after the calcination treatment.Compared with nickel oxides,the introduced Co ions in Ni_xCo_y-DO can induce the production of surficial oxygen vacancies,and further enhance the electrode surface activity.In particular,the NiCo-DO sample(with an atomic ratio of Ni/Co=4:3) shows the richest surficial oxygen vacancies and presents the highest H_2 O_2 detection activity among all the as-prepared samples,demonstrating an excellent sensitivity of698.60 μAL mmol ~1 cm~(-2)(0～0.4 mmol/L),low detection limit(0.28 μmol/L,S/N=3),as well as long stability,high selectivity and good reproducibility.This work lends a new impetus to the potential application of double metal oxides for the next generation of non-enzymatic sensors.     

Metal complexes of mercaptoamines—I. Synthesis and crystal and molecular structure of tetrakis (3-amino-1-propanethiolato) trinickel(II)chloride

The reaction of nickel(II)chloride with γ-mercapto-propylamine in ethanolic solution gives the complex [Ni₃(MPA)₄]Cl₂(MPA=NH₂-(CH₂)₃-S). The complexes [Ni₃(MPA)₄]X₂(X=Br, I, ClO₄) can be synthesized from the chloride complex by addition of the sodium salt in aqueous solution. The crystal structure consists of discrete divalent trinuclear cations and chloride anions. Each sulphur atom of the ligand acts as a bridge between two nickel atoms, and the nitrogen atoms complete the coordination around the terminal nickel atoms. The geometry around the metal atoms is square-planar. The electronic and IR spectra of the complexes [Ni₃(MPA)₄]X₂(X=Br, I, ClO₄) indicate that all these compounds are composed of the [Ni₃(MPA)₄]²⁺ and X^? ions.     

Ammonia synthesis by means of plasma over MgO catalyst

Ammonia synthesis from H₂-N₂ mixed gas was studied at room temperature in a glow-discharge plasma in the presence of metals or metal oxides. Magnesia (MgO) and calcia (CaO), which are oxides with solid basicity, revealed catalytic activity in the plasma synthesis of ammonia, although they are catalytically inactive in industrial ammonia synthesis. The acidic oxides (Al₂O₃, WO₃, and SiO₂-Al₂O₃) lead to the consumption of the reactant, i.e., the H₂-N₂ mixed gas. No ammonia was isolated. Metal catalysts showed higher activity than the above basic oxides. They have, however, different activities. The reaction was faster over the active materials than over sodium chloride (NaCl) or glass wool or in a blank reactor without any catalyst.     

Synthesis of nanosize particles of cobalt and nickel oxides from solutions

Rounded nanosize particles of Co₃O₄ and NiO were prepared by precipitation with ammonium carbonate from cobalt and nickel nitrate solutions. Cobalt and nickel oxides and their precursors were characterized by thermal and X-ray phase analyses, electron microscopy, and IR spectroscopy.     

Enhanced Electrochemical Capacitive Properties of Nickel‐Cobalt Oxide Nano‐flakes Materials

Nickel‐cobalt oxide nano‐flakes materials are successfully synthesized by a facile chemical co‐precipitation method followed by a simple calcination process. The studies show that the as‐prepared nickel‐cobalt oxides with different Ni/Co ratio are composed of NiO and Co₃O₄ compounds. The Co_0.56Ni_0.44 oxide material, which exhibits a mesoporous structure with a narrow distribution of pore size from 2 to 7 nm, possesses markedly enhanced charge‐discharge properties at high current density compared with the pure NiO and pure Co₃O₄. The Co_0.56Ni_0.44 oxide electrode shows a specific capacitance value of 1227 F/g at 5 mA/cm², which is nearly three times greater than that of the pure NiO electrode at the same current density.     

A mixed cation nickel diphosphate with a layered intergrowth structure: synthesis, structural and magnetic characterization of Na(NH4)[Ni3(P2O7)2(H2O)2]

A nickel diphosphate with mixed cations, Na(NH₄)[Ni₃(P₂O₇)₂(H₂O)₂] with a layered structure has been synthesized under hydrothermal conditions for the first time and characterized by single crystal X-ray diffraction, IR spectroscope and magnetization measurements. The structure consists of cis- and trans-edge sharing NiO₆ octahedral chains linked via P₂O₇ units to [Ni₃P₄O₁₆]²⁻ layers. The ammonium and sodium cations are alternately located in the interlayer spaces. The mixed cations play an important role in the structural formation of this layered compound, leading to a new layer-stacking variant. The magnetic susceptibility obeys a Curie–Weiss law with μ_eff of 3.32 μ_B, showing the Ni²⁺ character and weak antiferromagnetic interactions.     

Synthesis, crystal structure and magnetic property of a new nickel selenite chloride: Ni5(SeO3)4Cl2

The new nickel selenite chloride, Ni₅(SeO₃)₄Cl₂, was obtained by high-temperature solid state reaction of NiCl₂, Ni₂O₃ and SeO₂ in a 1:2:4 molar ratio at 700 °C in an evacuated quartz tube. Its structure was established by single-crystal X-ray diffraction. Ni₅(SeO₃)₄Cl₂ crystallizes in the triclinic system, space group P-1 (No. 2) with cell parameters of a=8.076(2), b=9.288(2), c=9.376(2) Å, α=101.97(3), β=105.60(3), γ=91.83(3)° and Z=2. All nickel(II) ions in Ni₅(SeO₃)₄Cl₂ are octahedrally coordinated by selenite oxygens or/and chloride anions (([Ni(1)O₅Cl], [Ni(2)O₄Cl₂], [Ni(3)O₅Cl], [Ni(4)O₆] and [Ni(5)O₄Cl]). The structure of the title compound features a condensed three-dimensional (3D) network built by Ni(II) ions interconnected by SeO₃²⁻ anions as well as Cl⁻ anions. Magnetic property measurements show strong antiferromagnetic interaction between nickel(II) ions.     

Effect of Different Treatments on the Reducibility of NiO—Y2O3 Mixed Oxides by Hydrogen

Some physico-chemical properties and reactivity in their reduction with hydrogen of NiO—Y₂O₃ mixed oxides prepared in a dry way have been studied using isothermal thermogravimetry in the range of 320–410°C and temperature-programmed reduction. It was found that addition of small amounts of chloride and acetate anions retarded the reduction of nickel oxide and accelerated the reduction of mixed oxides. The presence of oxalate and formate ions manifests itself by a small positive effect. Introduction of platinum activator or heat treatment of the samples in various atmospheres led to a pronounced increase in the reduction rate. The efficiency of the spill-over effect increases with increasing proportion of non-reducible Y₂O₃. The pre-irradiation of the samples by accelerated electrons and gamma rays at a dose of 1 MGy results in a negative kinetic effect only with the samples containing an excess of nickel oxide.This revised version was published online in November 2005 with corrections to the Cover Date.     

Iron- and nickel-containing oxide-phosphate layers on aluminum and titanium

Oxide-phosphate surface structures with thicknesses of 5 to 50 μm containing iron and nickel compounds have been synthesized by plasma electrolysis (PE) in aqueous electrolytes with polyphosphate nickel(II) and iron(III) complexes. The elemental and phase compositions have been studied as affected by polarization parameters, electrolytes, and annealing parameters. Simple and complex oxides and phosphates crystallize in layers: on aluminum, AlPO₄, NiAl₂O₄, and Fe₂O₃ crystallize; on titanium, Ni₂P₂O₇, Ni_0.5TiOPO₄, NaTi₂(PO₄)₃, M^(II)M^(III)Ti(PO₄)₃, FePO₄, and Fe₂Fe(P₂O₇)₂ crystallize.     

Physicochemical properties and desulfurization activities of metal oxide/biomass-based activated carbons prepared by blending method

Column activated carbons were prepared from walnut shell chars and transition metal oxide powders (i.e. Co₂O₃, Ni₂O₃, CuO and V₂O₅) with blending method. Samples were characterized by N₂ adsorption–desorption, X-ray diffraction, X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. The texture properties of all modified activated carbons with metal oxides dosage of <5 wt% did not change evidently. The basic functionalities of these activated carbons increased relative to blank carbon. Moreover, metal species with different oxidation states coexisted on the modified activated carbons. The optimal dosage of all metal oxides was 2 wt%. The sulfur capacities of these modified activated carbons were 7.7–46.0 % higher than that of blank activated carbon and the highest occurred for V₂O₅ modified activated carbon. The improved desulfurization performance was mainly attributed to the higher catalytic activity of the active metal oxides formed in the presence of O₂ during the desulfurization process.     

Thermodynamic possibilities and constraints of pure hydrogen production by a chromium,nickel, and manganese-based chemical looping process at lower temperatures

The reduction of chromium, nickel, and manganese oxides by hydrogen, CO, CH₄, and model syngas (mixtures of CO + H₂ or H₂ + CO + CO₂) and oxidation by water vapor has been studied from the thermodynamic and chemical equilibrium point of view. Attention was concentrated not only on the convenient conditions for reduction of the relevant oxides to metals or lower oxides at temperatures in the range 400–1000 K, but also on the possible formation of soot, carbides, and carbonates as precursors for the carbon monoxide and carbon dioxide formation in the steam oxidation step. Reduction of very stable Cr₂O₃ to metallic Cr by hydrogen or CO at temperatures of 400–1000 K is thermodynamically excluded. Reduction of nickel oxide (NiO) and manganese oxide (Mn₃O₄) by hydrogen or CO at such temperatures is feasible. The oxidation of MnO and Ni by steam and simultaneous production of hydrogen at temperatures between 400 and 1000 K is a difficult step from the thermodynamics viewpoint. Assuming the Ni—NiO system, the formation of nickel aluminum spinel could be used to increase the equilibrium hydrogen yield, thus, enabling the hydrogen production via looping redox process. The equilibrium hydrogen yield under the conditions of steam oxidation of the Ni—NiO system is, however, substantially lower than that for the Fe—Fe₃O₄ system. The system comprising nickel ferrite seems to be unsuitable for cyclic redox processes. Under strongly reducing conditions, at high CO concentrations/partial pressures, formation of nickel carbide (Ni₃C) is thermodynamically favored. Pressurized conditions during the reduction step with CO/CO₂ containing gases enhance the formation of soot and carbon-containing compounds such as carbides and/or carbonates.     

Aqueous solutions of colloidal nickel: Radiation-chemical preparation, absorption spectra, and properties

Radiation-chemical reduction of Ni²⁺ ions in aqueous solutions of Ni(ClO₄)₂ containing sodium formate or isopropyl alcohol was studied, γ-Irradiation of deaerated solutions in the presence of polyethyleneimine, polyacrylate, or polyvinyl sulfate gives stable metal sols containing spherical particles 2–4 nm in diameter. The optical absorption spectra of nickel nanoparticles exhibit a band with a maximum at 215±5 nm (ε₂₁₅=4.7·10³ L mol⁻¹ cm⁻¹) and a shoulder at 350 nm. A mechanism for the radiation-chemical reduction of Ni²⁺ ions by hydrated electrons and organic radicals (CO₂- radical anions in the case of HCOONa and Me₂C·OH radicals in the case of PrⁱOH). The redox potentials of the Ni²⁺/Ni⁰ and Ni⁺/Ni⁰ pairs (Ni⁰ is a nickel atom) are approximately −2.2 and −1.7 V, respectively. The nanoparticles are readily oxidized by O₂, H₂O₂, and other oxidants. The reactions of these species with silver ions yield relatively stable nanoaggregates containing both nickel and silver in addition to silver nanoparticles. Published inIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 1733–1739, October, 2000.     

Impedance measurements for nickel deposition in sulfate and chloride electrolytes

From the analysis of the impedance of nickel deposition, the electrode kinetics is shown to be dependent on the type of anion. In chloride electrolytes a slow electrode activation with cathodic polarization is predominant. In sulfate solutions a low-frequency capacitive feature, favored by a pH decrease, appears to result from interactions between the nickel and hydrogen discharges. An interpretation is proposed where the ad-ion Ni_ads^I acts as both a reaction intermediate and a catalyst associated with a propagating kink site, and where the adsorbed species H_ads^*, generated by the presence of Ni_ads^I, inhibit the hydrogen evolution. It is concluded that the active area is closely connected to the coverages by adsorbates.     

Rose‐like Nanocomposite of Fe‐Ni Phosphides/Iron Oxide as Efficient Catalyst for Oxygen Evolution Reaction

In order to accelerate the reaction rate of water splitting, it is of immense importance to develop low‐cost, stable and efficient catalysts. In this study, the facile synthesis of a novel rose‐like nanocomposite catalyst (Ni₂P/Fe₂P/Fe₃O₄) is reported. The synthesis process includes a solvothermal step and a phosphatization step to combine iron oxides and iron‐nickel phosphides. Ni₂P/Fe₂P/Fe₃O₄ performs well in catalyzing oxygen evolution reaction, with a very low overpotential of 365 mV to reach 10 mA cm^?2 current density. The Tafel slope is as low as 59 mV dec^?1. Ni₂P/Fe₂P/Fe₃O₄ has a large double‐layer capacitance that contributes to a high electrochemically active area. Moreover, this catalyst is very stable for long‐term use. Therefore, the Ni₂P/Fe₂P/Fe₃O₄ catalyst has a high potential for use in oxygen evolution reactions.     

Electrolytic Synthesis of Complex Oxide Systems by Cathodic Deposition of Molybdenum Oxide from Aqueous Solutions in the Presence of Nickel(II) and Thiosulfate Ions

Cathodic processes occurring in electrolytic deposition of molybdenum oxide from aqueous solutions of sodium molybdate in the presence of nickel(II) and thiosulfate ions were studied. Conditions for formation of cathodic deposits in the form of complex oxide systems Mo-Ni and Mo₄O_{1 1}-MoS₂ were determined.     

Water photoelectrolysis using nickel titanate and niobate as photoanodes

Nickel titanate (NiTiO₃) and nickel niobate (NiNb₂O₆), both with a cationic valence and conduction band, were examined for their photoelectrochemical properties. Applied as photoanode in a photoelectrochemical cell for water electrolysis, reduced pellets of these oxides show a photoresponse when irradiated in the optical band gap. The corresponding absorption is due to Ni²⁺ → Ti⁴⁺ and Ni²⁺ → Nb⁵⁺ charge-transfer transitions, respectively. These are situated at lower energy than the O^2? → Ti⁴⁺ and O^2? → Nb⁵⁺ charge-transfer transitions. The flatband potentials of both compounds were determined from photocurrent versus applied potential measurements. During reduction both compounds showed superficial decomposition. The effect of this decomposition on the photocurrents is discussed.