Co oxide films were prepared on glass substrates at 150–400°C by plasma-enhanced metalorganic chemical vapour deposition using cobalt (II) acetylacetonate as a source material. NaCl-type CoO films were formed at low O2 flow rate of 7cm3 min–1 and at a substrate temperature of 150–400°C. The CoO films possessed (100) orientation, independent of substrate temperature. Deposition rates of the CoO films were 40–47 nm min–1. The CoO film deposited at 400 °C was composed of closely packed columnar grains and average diameter size at film surface was 60 nm. At high O2 flow rate of 20–50 cm3 min–1, high crystalline spinel-type Co3O4 films were formed at a substrate temperature of 150–400°C. The Co3O4 film deposited at 400°C possessed (100) preferred orientation and the film deposited at 150°C possessed (111) preferred orientation. Deposition rates of the Co3O4 films were 20–41 nm min–1. Both Co3O4 films with (100) and (111) orientation had columnar structure. The shape and average size of the columnar grains at the film surface were different; a square shape and 35 nm for (100)-oriented Co3O4 film and a hexagonal shape and 60 nm for (111)-oriented film, respectively. 相似文献
We present results of the studies of structural and chemical transformations in Co/CoO nanoparticles prepared by inert gas condensation. The effect of the morphology and agglomeration on the phase transformation reaction path in self-oxidation and in controlled reduction processes are discussed in detail. As-prepared samples show self-oxidation related to the non-core/shell morphology of the particles. Annealing of particles at 250 °C in reducing atmosphere leads to the oxidation of the particles showing coexistence of CoO and Co3O4 structures. This is explained by the diffusion of oxygen from the amorphous oxide surface to the bulk of the nanoparticles. Upon increasing the reaction temperature beyond 250 °C, reductive transformation of the samples occurs systematically, from CoO/Co3O4 to CoO to Co (HCP + FCC) and eventually to Co (FCC). We have presented X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and magnetic data to track the structural and chemical transformation paths. We found strong correlation between structural and magnetic properties. Thermodynamic stability as a function of reaction temperature on the phase/chemical transformation is also discussed. 相似文献
In this work, Al2O3/Co nanocomposite was successfully prepared by mechanochemical reaction between Co3O4 and Al powders in a planetary high energy ball mill. The mechanism of the reaction was dealt using X-ray diffraction (XRD), differential thermal analysis (DTA), and thermodynamics calculations. It was found that Co3O4 reacts with Al through a self-sustaining combustion reaction after an incubation period of 50 min and the reaction between Co3O4 and Al involves two steps. First, Co3O4 reacts with Al to form CoO and Al2O3 at the temperature around melting point of Al, and at higher temperature, CoO reacts with remaining Al to form Co and Al2O3. Mechanical activation process decreases the reaction temperature from 1041 °C for as-received Co3O4 and Al powder mixture to 869 °C for 45 min milled powders. After annealing of powder milled for 12 h, no phase transformation has been detected. The crystallite sizes of both α-Al2O3 and Co remained in nanometeric scale after annealing at 1000 °C for 1 h. 相似文献
Microporous tricobalt tetraoxide, Co3O4, nanoparticles (NPs) clusters have been successfully fabricated using a simple but efficient controlled solution combustion route. Such a synthesis involves combustion reaction of cobalt nitrate with cetyl trimethylammonium bromide (CTAB). The combustion process has been analyzed by simultaneous thermal analysis. The resultant powders were characterized by means of X-ray diffraction technique (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and nitrogen adsorption at −196 °C. The morphology and specific surface area of the obtained Co3O4 nanoparticles clusters have proved to be strongly dependent on the fuel (F)/oxidizer (O) molar ratio and the calcination temperature. It was found that both the crystallite size and the lattice parameter nanocrystalline Co3O4 increase with increasing the F/O molar ratio as well as the calcination temperature. X-ray diffraction confirmed the formation of CoO phase together with spinel Co3O4 using F/O ratio of 1. The concentration of such phase increases with increasing the F/O ratio. Moreover, when the calcination is applied at 900–1000 °C traces of CoO was obtained together with Co3O4 as a major phase. 相似文献
In this work, synthesis of nanocrystalline Co||Co|||xAl2–xO4 (where x = 0, 0.5, 0.8, 1, 1.18 and 2) spinels by the thermal decomposition of complex precursors derived from metal nitrate salts and ethylenediaminetetraacetic acid (EDTA) has been systematically studied. Based on XRD, FTIR, DTA, TGA, SEM and TEM analyses, it has been found that the as-prepared metal organic precursors with different Co and Al contents display different thermal behavior and crystal development and particle morphology. Increment of Co content in precursors improves the degree of crystallinity of the powder. Treated at 400°C, in contrast to the well formed Co3O4 or Co3O4-like spinel structure for the powder precursors containing higher Co content, most of the powders from precursors containing lower Co content are still amorphous. Higher Co content in the precursors slightly decreases the unit cell parameters of the resulting Co||Co|||xAl2–xO4 spinels. Prepared at 900°C, the unit cell parameters of Co||Al2O4, Co||Co|||0.5Al1.5O4, Co||Co|||AlO4, Co||Co|||2O4 are 8.1038, 8.1007, 8.0867, and 8.0834 Å, respectively. Based on this work, preparation of a series of the Co||Co|||xAl2–xO4 spinels including black or bright blue Co||Al2O4, Co||Co|||0.5Al1.5O4, Co||Co|||AlO4, Co||Co|||2O4 from EDTA-Co(Al) complexing precursor has been established. 相似文献
Three CoFe-bimetallic oxides with different compositions (termed as CoFeOx-A/N/H) are prepared by thermally treating metal-organic-framework (MOF) precursors under different atmospheres (air, N2, and NaBH4/N2), respectively. With the aid of vast oxygen vacancies (Ov), cobalt at tetrahedral sites (Co2+(Th)) in spinel Co3O4 is diffused into interstitial octahedral sites (Oh) to form rocksalt CoO and ternary oxide CoFe2O4 has been induced to give the unique defective CoO/CoFe2O4 heterostructure. The resultant CoFeOx-H exhibits superb electrocatalytic activity toward water oxidation: overpotential at 10 mA cm−2 is 192 mV, which is 122 mV smaller than that of CoFeOx-A. The smaller Tafel slope (42.53 mV dec−1) and higher turnover frequency (785.5 h−1) suggest fast reaction kinetics. X-ray absorption spectroscopy, ex situ characterizations, and theoretical calculations reveal that defect engineering effectively tunes the electronic configuration to a more active state, resulting in the greatly decreased binding energy of oxo intermediates, and consequently much lower catalytic overpotential. Moreover, the construction of hetero-interface in CoFeOx-H can provide rich active sites and promote efficient electron transfer. This work may shed light on a comprehensive understanding of the modulation of electron configuration of bimetallic oxides and inspire the smart design of high-performance electrocatalysts. 相似文献
Nanocrystallites of tricobalt tetraoxide (Co3O4) have been synthesized by sol–gel process using cobalt acetate tetrahydrate, oxalic acid as precursors and ethanol as a solvent. The process comprises of gel formation, drying at 80 °C for 24 h to obtain cobalt oxalate dihydrate (α-CoC2O4·2H2O) followed by calcination at or above 400 °C for 2 h in air. These results combined with thermal analysis have been used to determine the scheme of oxide formation. The room temperature optical absorption spectra exhibits blue shift in both (i) ligand to metal (p(O2−) → eg(Co3+), 3.12 eV), and (ii) metal to metal charge transfer transitions (a) t2g(Co3+) → t2(Co2+), 1.77 eV, (b) t2(Co2+) → eg(Co3+), 0.95 eV together with the d–d transitions (0.853 and 0.56 eV) within the Co2+ tetrahedra. The temperature dependent ac electrical and dielectric properties of these nanocrystals have been studied in the frequency range 100 Hz to 15 MHz. There are two regimes distinguishing different temperature dependences of the conductivity (70–100 K and 200–300 K). The ac conductivity in both the temperature regions is explained in terms of nearest neighbor hopping (NNH) mechanism of electrons. The carrier concentration measured from the capacitance (C)–voltage (V) measurements is found to be 1.05 × 1016 m−3. The temperature dependent dc magnetic susceptibility curves under zero field cooled (ZFC) and field cooled (FC) conditions exhibit irreversibilities whose blocking temperature (TB) is centered at 35 K. The observed Néel temperature (TN 25 K) is significantly lower than the bulk Co3O4 value (TN = 40 K) possibly due to the associate finite size effects. 相似文献
The reactive d.c. sputtering of a Co target in argon-oxygen mixtures has been studied. The chemical structure of the thin films formed (Co-β, CoO and Co3O4) has been studied by X-ray diffraction, and particles ionized in the plasma have been detected with a quadrupole mass filter. The mechanisms suggested are: CoO formation on the surface of the target and sputtering of CoO; CoO production in the plasma and Co3O4 production on the substrate. 相似文献
Cobalt, nickel and mixed cobalt–nickel nanostructured oxides have been obtained by thermal treatments in oxygen of Co, Ni and Co50Ni50/silica nanocomposites produced by ion implantation technique. The thermal treatment produces the total or partial oxidation of the original metallic species, which diffuse towards the surface and in the depth of the substrate. This process gives rise to the growth of different oxides in both regions depending on the kind of metal. In the Co sample, mainly Co3O4 is formed; in the Ni sample, Ni and NiO nanoparticles are present, while in the Co–Ni sample Co3O4, Ni2SiO4 and mainly (CoxNi1−x)O nanostructures are formed. The optical features of cobalt and nickel samples are determined by the optical properties of the Co3O4 and NiO p-type semiconductor phases, respectively, with energy gaps littler than the corresponding bulk ones. The Co–Ni mixed nanostructured oxide is characterized by a direct absorption gap at 3.4 eV that is smaller than the band gaps of CoO and NiO oxides. 相似文献
Hierarchical structure and surface properties of selective support afford some special effects on the catalytic activity, which could be tuned to achieve improved performance. Herein, using a combination of hydrothermal coprecipitation and thermal processing, we integrated highly-distributed Co3O4 spinel nanospecies on laminated hierarchically structured Al2O3 which could be used as a highly efficient VOCs treatment catalyst. Impressively, compared to Co-free Al2O3 counterpart (SBET = 188.2 m2·g?1), these obtained Co3O4 spinel functionalized catalysts are endowed with adjustable Co loading, optimized Co activity state, and obviously improved hierarchically structural properties (SBET = 274.7 m2·g?1). The microporous and mesoporous structures both existed in the obtained Al2O3, which is beneficial to the heterogeneous catalytic reaction process. The results reveal that the proper Co loading in the hierarchically structured Al2O3 could enable the rational modulation of catalytic activity in the combustion of toluene and exceeds the commercial 5 wt% Pd/C catalyst in the light of total catalytic oxidation ability. This developed heterogeneous Co3O4 compositing hierarchically structured Al2O3 provides a significant potential value for practical VOCs treatment. 相似文献
Co3O4/CoO nanoparticles have been synthesized by a simple method which is based on the ball-milling and calcination of cobalt acetate
and citric acid. The samples were characterized using X-ray diffraction, transmission electron microscope, and Fourier transform
infrared spectroscopy. The results show that Co3O4 nanoparticles with an average particle size of ∼40 nm can be obtained by calcination of ball-milled precursors at relatively
low temperature (350 °C) for 3 hours. It should be noted that it is possible to control the size of Co3O4 particles by calcination temperature, calcination time and also by ball-milling duration using this method. Meanwhile, the
pure CoO nanoparticles were obtained successfully by thermal decomposition of Co3O4 at 950 °C and quickly quenching to liquid nitrogen. 相似文献
The oxidation behavior of Co80Ni20 thin films used for magnetic recording was studied using Auger and X-ray photoelectron spectroscopy. At 500 °C and under an oxygen pressure of 1 × 10−5 Torr cobalt oxidized to CoO but nickel remained in the metallic state. The growth of CoO followed a parabolic dependence on the oxygen exposure time, suggesting diffusion-controlled kinetics for oxidation. The [Co]/[Ni] ratio at the surface increased with oxidation indicating an oxygen-induced segregation of cobalt in the alloy. 相似文献
Cobalt oxides as efficient oxygen evolution reaction (OER) electrocatalysts have received much attention because of their rich reserves and cheap cost. There are two common cobalt oxides, Co3O4 (spinel phase, stable but poor intrinsic activity) and CoO (rocksalt phase, active but easily be oxidatized). Constructing Co3O4/CoO heterophase can inherit both characteristic features of each component and form a heterophase interface facilitating charge transfer, which is believed to be an effective strategy in designing excellent electrocatalysts. Herein, an atomic arrangement engineering strategy is applied to improve electrocatalytic activity of Co3O4 for the OER. With the presence of oxygen vacancies, cobalt atoms at tetrahedral sites in Co3O4 can more easily diffuse into interstitial octahedral sites to form CoO phase structure as revealed by periodic density functional theory computations. The Co3O4/CoO spinel/rocksalt heterophase can be in situ fabricated at the atomic scale in plane. The overpotential to reach 10 mA cm?2 of Co3O4/CoO is 1.532 V, which is 92 mV smaller than that of Co3O4. Theoretical calculations confirm that the excellent electrochemical activity is corresponding to a decline in average p‐state energy of adsorbed‐O on the Co3O4/CoO heterophase interface. The reaction Gibbs energy barrier has been significantly decreased with the construction of the heterophase interface. 相似文献
Co3O4 with high theoretical capacitance is a promising electrode material for high-end energy applications, yet the unexcited bulk electrochemical activity, low conductivity, and poor kinetics of Co3O4 lead to unsatisfactory charge storage capacity. For boosting its energy storage capability, rare earth (RE)-doped Co3O4 nanostructures with abundant oxygen vacancies are constructed by simple, economical, and universal chemical precipitation. By changing different types of RE (RE = La, Yb, Y, Ce, Er, Ho, Nd, Eu) as dopants, the RE-doped Co3O4 nanostructures can be well transformed from large nanosheets to coiled tiny nanosheets and finally to ultrafine nanoparticles, meanwhile, their specific surface area, pore distribution, the ratio of Co2+/Co3+, oxygen vacancy content, crystalline phase, microstrain parameter, and the capacitance performance are regularly affected. Notably, Eu-doped Co3O4 nanoparticles with good cycle stability show a maximum specific capacitance of 1021.3 F g−1 (90.78 mAh g-1) at 2 A g-1, higher than 388 F g-1 (34.49 mAh g-1) of pristine Co3O4 nanosheets. The assembling asymmetric supercapacitor delivers a high energy density of 48.23 Wh kg-1 at high power density of 1.2 kW kg-1. These findings denote the significance and great potential of RE-doped Co3O4 in the development of high-efficiency energy storage. 相似文献
Structural perfection of gadolinium gallium garnet (GGG; Gd3Ga5O12) epitaxial layers with incorporated divalent Co ions has been studied by means of high resolution X-ray diffraction, X-ray topography, transmission electron microscopy and optical spectroscopy. Epitaxial layers were grown by liquid phase epitaxy from super-cooled high temperature solution with different concentration of Co3O4 and GeO2 on both sides of the polished < 111> oriented GGG substrates. In order to facilitate incorporation of Co2+ ions into the garnet lattice optically inert Ge4+ ions have to be introduced first. High structural perfection is a prerequisite to obtain absorption spectra required for the use GGG epitaxial layers as tunable infrared absorbers. 相似文献
Hexagonal plate-like Co3O4 was prepared by the thermal oxidation of a Co(OH)2 precursor with a hexagonal plate morphology at 600 °C in air. The Co(OH)2 precursor was obtained by hydrothermal synthesis from CoCl2, KCN and hydrazine at 180 °C. The hexagonal plates had a side length of approximately 3.5 μm and 1 μm in thickness. Octahedral Co3O4 was prepared by a hydrothermal method with CoCl2, KCN, and H2O2 at 180 °C. H2O2 played an important role in the formation of Co3O4 with an octahedral morphology. A hierarchical hexagonal skeleton-like morphology assembled with small octahedral Co3O4 particles was also prepared using a hydrothermal method with CoCl2 and KCN. The mechanism of the morphology-controlled synthesis of Co3O4 is discussed. 相似文献
A facile hydrothermal synthetic method, followed by in situ reduction and galvanic replacement processes, is used to prepare PtCo-modified Co3O4 nanosheets (PtCo/Co3O4 NSs) supported on Ni foam. The prepared nanomaterial is used as an electrocatalyst for NaBH4 oxidation in alkaline solution. The morphology and phase composition of PtCo/Co3O4 NSs are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The catalytic performance of PtCo/Co3O4 NSs is investigated by cyclic voltammetry (CV) and chronoamperometry (CA) in a standard three-electrode system. Current densities of 70 and 850 mA·cm–2 were obtained at–0.4 V for Co/Co3O4 and PtCo/Co3O4 NSs, respectively, in a solution containing 2 mol·L–1 NaOH and 0.2 mol·L–1 NaBH4. The use of a noble metal (Pt) greatly enhances the catalytic activity of the transition metal (Co) and Co3O4. Besides, both Co and Co3O4 exhibit good B–H bond breaking ability (in NaBH4), which leads to better electrocatalytic activity and stability of PtCo/Co3O4 NSs in NaBH4 electrooxidation compared to pure Pt. The results demonstrate that the as-prepared PtCo/Co3O4 NSs can be a promising electrocatalyst for borohydride oxidation.
Co3O4 nanorods with average diameter and length of ∼ 50 nm and 1 μm were successfully prepared via a simple surfactant-assisted solvothermal method at 160 °C for 12 h. The formation of Co3O4 nanorods is attributed to alcoholysis of cobalt ions dispersed in ethanol in the presence of a capping agent—CTAB. The composition and purity of the sample were characterized by X-ray diffraction (XRD). Transmission and scanning electron microscopy images show that the particles are homogenous and have the shape of rods. The mechanism of forming Co3O4 nanorods is also discussed. 相似文献
Cobalt oxide nanoparticles (Co3O4 NPs) were successfully synthesized using ethanolic extract of Trigonella foenumgraceum L. (fenugreek) leaves as a green, potentially low cost, and easily biosynthesized method. The organic bioactive compounds present in fenugreek leaves extract acted as both reducing agents and stabilizing agents for synthesizing metal NPs from cobalt chloride hexahydrate as a precursor. As evidence from UV/Visible spectroscopy, energy dispersive spectroscopy (EDS), and X-ray diffraction analysis (XRD) studies, high alkaline pH was found favorable for the preparation of pure and crystallized single-phase Co3O4 NPs. The interaction of biomolecules from fenugreek leaves extract with Co3O4 NPs was defined by Fourier transform infrared spectroscopy (FTIR) analysis and X-ray photoelectron spectroscopy (XPS). The hydrodynamic size and surface charge of the biosynthesized NPs were measured using light-scattering (DLS) and zeta potential analyses; revealed the formation of negative charged Co3O4 NPs with uniform hydrodynamic size distribution. According to transmission electron microscopy (TEM) analysis, quasi-spherical Co3O4 NPs were synthesized with an average size of 13.2 nm under the modified condition of pH 12 and reaction time of 2 h through inexpensive, environmental friendly benign synthesis process without the use of any additional toxic chemical. 相似文献
Battery‐type materials are promising candidates for achieving high specific capacity for supercapacitors. However, their slow reaction kinetics hinders the improvement in electrochemical performance. Herein, a hybrid structure of P‐doped Co3O4 (P‐Co3O4) ultrafine nanoparticles in situ encapsulated into P, N co‐doped carbon (P, N‐C) nanowires by a pyrolysis–oxidation–phosphorization of 1D metal–organic frameworks derived from Co‐layered double hydroxide as self‐template and reactant is reported. This hybrid structure prevents active material agglomeration and maintains a 1D oriented arrangement, which exhibits a large accessible surface area and hierarchically porous feature, enabling sufficient permeation and transfer of electrolyte ions. Theoretical calculations demonstrate that the P dopants in P‐Co3O4@P, N‐C could reduce the adsorption energy of OH? and regulate the electrical properties. Accordingly, the P‐Co3O4@P, N‐C delivers a high specific capacity of 669 mC cm?2 at 1 mA cm?2 and an ultralong cycle life with only 4.8% loss over 5000 cycles at 30 mA cm?2. During the fabrication of P‐Co3O4@P, N‐C, Co@P, N‐C is simultaneously developed, which can be integrated with P‐Co3O4@P, N‐C for the assembly of asymmetric supercapacitors. These devices achieve a high energy density of 47.6 W h kg?1 at 750 W kg?1 and impressive flexibility, exhibiting a great potential in practical applications. 相似文献