Co3O4 Films Research Articles

Introducing p-n junction interface into enzyme loading matrix for enhanced glucose biosensing performance

Eggshell membranes were used as biotemplate to fabricate a 3D hierarchical porous Co3O4/ZnO p-n junction film. Multiple catalysis and accelerated electron transfer were achieved on the Co3O4/ZnO-GOx electrode by introducing the p-n junction interface into enzyme loading matrix. A stable and well-defined oxidation peak of glucose was obtained with a largely decreased detection potential of 0.25V. Furthermore, an enhanced sensitivity (116.64μA·mM−1·cm−2) was also achieved comparing with the simple biotemplate-synthesized Co3O4 and ZnO film. The results demonstrated it is a novel strategy to improve the biosensing performance by introducing p-n junction interface into enzyme loading matrix.

Synthesis of porous nickel networks supported metal oxide nanowire arrays as binder-free anode for lithium-ion batteries

Directional design/preparation of porous metal/metal oxides composite arrays is critical for construction of advanced optical-electrochemical devices. Herein we report three-dimensional (3D) porous Ni networks supported cobalt oxide nanowire arrays (Ni-Co3O4 NWs) by combining electro-deposition and hydrothermal process. 3D Ni networks with porous branches and interconnected pores are well formed and used as the skeleton for the growth of cobalt oxide nanowire arrays. High porosity and integrated growth are combined in the composite electrode. Due to the unique composite architecture, the Ni-Co3O4 NWs electrode exhibits higher discharge capacities, better cycling stability (714 mAh g−1 at 0.5 A g−1 after 100 cycles), and enhanced rate capability, as compared to the Ni networks supported dense Co3O4 film (Ni-Co3O4 dense film). The proposed method is useful for construction of other porous metal/metal oxide composite films for application in electrochemical catalysis, energy storage and sensing.

Synthesis of 3D hierarchical porous Co3O4 film by eggshell membrane for non-enzymatic glucose detection

We provide a facile, cost-effective and environmentally friendly method to prepare 3D hierarchical porous Co3O4 film by employing eggshell membrane as bio-templates. The Co3O4 nanofibers interconnected with each other to construct a 3D hierarchical porous film with macropores and mesopores, which is more effective in facilitating reactants diffusion and the electron transfer. The developed sensor was applied for direct electrochemical non-enzymatic detection of glucose. High sensitivity (366.03μAmM−1cm−2), fast response (3s), anti-interference performance and excellent stability were achieved. The results demonstrate that the 3D hierarchical porous Co3O4 film have great potential applications in developing direct electrochemical non-enzymatic glucose biosensors.

Fast electrochromic response of porous-structured cobalt oxide (Co3O4) thin films by novel nebulizer spray pyrolysis technique

Electrochromic effect of cobalt oxide thin films was studied as a function of substrate temperature (573–673 K). Tricobalt tetraoxide (Co3O4) thin films were deposited on glass and fluorine-doped tin oxide (FTO) substrates by nebulized spray technique using cobalt nitrate as precursor material. The XRD patterns indicated (311) plane was dominant for all the films irrespective of the deposition temperature. Williamson-Hall (W-H) analysis was made to understand the strain variation in the prepared Co3O4 films under different deposition temperature by employing uniform deformation model (UDM). Scanning electron microscopy images revealed porous morphology for the film prepared at 623 K. The optical parameters such as refractive index (n), extinction coefficient (k), and band gap were derived from UV-visible spectra of Co3O4 films. The electrochromic performance of the deposited Co3O4 films was analyzed through cyclic voltammetry, chronocoulometry, chronoamperometry, and iono-optical studies.

Thin (111) oriented CoFe2O4 and Co3O4 films prepared by decomposition of layered cobaltates

The formation and structural characterization of highly (111)-oriented Co3O4 and CoFe2O4 films prepared by a novel procedure from 00l-oriented NaCoO2 and Na(CoFe)O2 is reported. The Na(CoFe)O2 films were deposited on MgO, SrTiO3, LaAlO3, and Zr(Y)O2 single crystals with (100) and (111) orientations by chemical solution deposition method and crystallized at 700°C. Subsequently they were transformed into (111)-oriented spinel phase during post-growth annealing at 800–1000°C. Morphology and structure of the films was investigated by means of scanning electron microscopy and X-ray diffraction. While all spinel films exhibit pronounced out-of-plane orientation irrespective of substrate, the rate of in-plane orientation strongly depend on lattice misfit values. Different epitaxial phenomena ranging from true one-to-one epitaxy to the existence of many-to-one epitaxy involving two or more orientations were determined by full 3D texture analysis.

Stainless steel grid mesh-supported CVD made Co3O4 thin films for catalytic oxidation of VOCs of olefins type at low temperature

The effective evaluation of the catalytic performance of Co3O4 supported on an inert carrier was investigated toward the deep oxidation of light olefins. Thin Co3O4 films were deposited on grid mesh of stainless steel using one-step chemical vapor deposition method. The as-deposited materials were characterized in terms of structure, morphology and composition. Co3O4 crystals with cubic spinel structures composed of Co2+, Co3+ and nucleophilic oxygen species (O2−) were obtained. The catalytic results indicated that Co3O4 supported on steel mesh was highly active to enable the complete conversion of C3H6 and n-C4H8 with a Mars-van Krevelen type mechanism.

Functionalized Porphyrins on an Atomically Defined Oxide Surface: Anchoring and Coverage-Dependent Reorientation of MCTPP on Co3O4(111)

We have studied the adsorption of tetraphenylporphyrin (2HTPP) and its carboxylated counterpart mono-para-carboxyphenyltriphenylporphyrin (MCTPP) on an atomically defined Co3O4(111) film under ultrahigh vacuum (UHV) conditions. Using time-resolved infrared reflection absorption spectroscopy (TR-IRAS), we show that 2HTPP adsorbs molecularly in a flat-lying orientation, whereas MCTPP binds to the surface via formation of a chelating bidentate carboxylate upon deposition at 400 K. Combining TR-IRAS and density-functional theory (DFT), we determine the molecular tilting angle as a function of coverage. We show that the MCTPP adsorption geometry changes from a nearly flat-lying orientation (tilting angle <30°) at low coverage to a nearly perfectly upright-standing orientation (tilting angle of approximately 80°) in the full monolayer.

Thermite synthesis and characterization of Co–ZrO2ferromagnetic nanocomposite thin films

Co–ZrO2 ferromagnetic nanocomposite thin films were successfully synthesized using a new thermite reaction between Zr and Co3O4 in layer geometry. The initial Zr/Co3O4 bilayers were obtained by the deposition of Zr layers onto Co3O4 films at room temperature. The process of mixing at the Zr/Co3O4 interface and synthesis of fine-crystalline Co and amorphous ZrO2 phases started at a temperature above the initiation temperature Tin ∼250 °С which did not depend on the bilayer thickness. For the bilayer thickness more than 300 nm high-temperature fcc-Co and cubic c-ZrO2 (or tetragonal t-ZrO2) phases were formed. For the bilayer thickness less than ∼50 nm stable low-temperature hexagonal hcp-Co and monoclinic m-ZrO2 phases were also present in the reaction product. A partial transformation from Co3O4 to CoO occurred after annealing at 300 °С. The secondary reaction between CoO and Zr started soon after Co3O4 had been converted to the CoO phase. After annealing at 500 °С more than 80% of Co was reduced and the final product contained Co nanoparticles above and below the superparamagnetic critical size embedded into a dielectric ZrO2 matrix. The synthesized Co–ZrO2 nanocomposite films possessed soft magnetic behavior, high magnetization and good chemical stability.

Self-organized nano-structuring of CoO islands on Fe(001)

The realization of nanometer-scale structures through bottom-up strategies can be accomplished by exploiting a buried network of dislocations. We show that, by following appropriate growth steps in ultra-high vacuum molecular beam epitaxy, it is possible to grow nano-structured films of CoO coupled to Fe(001) substrates, with tunable sizes (both the lateral size and the maximum height scale linearly with coverage). The growth mode is discussed in terms of the evolution of surface morphology and chemical interactions as a function of the CoO thickness. Scanning tunneling microscopy measurements reveal that square mounds of CoO with lateral dimensions of less than 25nm and heights below 10 atomic layers are obtained by growing few-nanometers-thick CoO films on a pre-oxidized Fe(001) surface covered by an ultra-thin Co buffer layer. In the early stages of growth, a network of misfit dislocations develops, which works as a template for the CoO nano-structuring. From a chemical point of view, at variance with typical CoO/Fe interfaces, neither Fe segregation at the surface nor Fe oxidation at the buried interface are observed, as seen by Auger electron spectroscopy and X-ray Photoemission Spectroscopy, respectively.

Magnetic-field-assisted synthesis of Co3O4 nanoneedles with superior electrochemical capacitance

Nanostructured Co3O4 films have been deposited on nickel foam in a magnetic-field-assisted hydrothermal process followed by annealing in air. The magnetic field strength is varied to study its relationship with nanostructures, morphology, and electrochemical properties of the Co3O4 electrodes. The Co3O4 films synthesized in the weak magnetic fields consist of dispersed nanoneedles, which are different from clustered nanoneedles when the magnetic field is absent. Moreover, the magnetic fields (of several millitesla) induced substantial changes in the nanostructures and electrochemical properties of the Co3O4 films. A possible formation mechanism of Co3O4 nanoneedles is proposed by comparing the morphologies and nanostructures of the films synthesized with and without the magnetic fields. Among these electrodes, the optimal one has a high specific capacitance (970.8 F g−1 at 0.5 A g−1), good power capability (847.5 F g−1 at 6.0 A g−1), and an excellent retention ratio (93.7 % over 1000 cycles). All these impressive results demonstrate that magnetic fields may be an economic and effective tool in hydrothermal synthesis of Co3O4 electrodes for high-performance supercapacitors.

Strain-Induced High Coercivity in La&lt;sub&gt;0.7&lt;/sub&gt;Sr&lt;sub&gt;0.3&lt;/sub&gt;CoO&lt;sub&gt;3&lt;/sub&gt; Films

Here, we report strain-induced high coercivity in La0.7Sr0.3CoO3 (LSCO) films, which suffer in-plane tensile strains due to the positive lattice mismatch between the substrate and the LSCO bulk. The films on (011)-0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 exhibit large uniaxial anisotropy, large coercivity, and high saturation magnetization at low temperature in contrast to the well soft magnetic behaviors in LSCO bulk. It is found that the coercivity of the 40 nm (001)-LSCO/SrTiO3 film can be as high as 1.45 T at 10 K and the observed coercivity decreases rapidly as the thickness increases, though the Curie temperature is below room temperature. The large coercivity and anisotropy should be closely related to the strain-induced structural changes and the different orbital ordering of Co3+ and Co4+ ions. Meanwhile, the enhanced domain wall pinning by the tensile strain may also contribute to the observed high coercivity.

Synthesis, characterization and ellipsometric study of ultrasonically sprayed Co3O4 films

In the present study, cobalt oxide (Co3O4) films were produced using ultrasonic spray pyrolysis technique onto the glass substrate at different temperatures (200–250–300–350 °C). The effect of substrate temperature on the structural, optical, surface and electrical properties of Co3O4 films was reported. Thickness, refractive index and extinction coefficient of the films were determined by spectroscopic ellipsometry, and X-ray diffraction analyses revealed that Co3O4 films were polycrystalline fcc structure and the substrate temperature significantly improved the crystal structure of Co3O4 films. The films deposited at 350 °C substrate temperature showed the best structural quality. Transmittance, absorbance and reflectance spectra were taken by means of UV–Vis spectrophotometer, and optical band gap values were calculated using optical method. Surface images and roughness values of the films were taken by atomic force microscopy to see the effect of deposition temperature on surface properties. The resistivity of the films slightly decreases with increase in the substrate temperature from 1.08 × 104 to 1.46 × 102 Ω cm. Finally, ultrasonic spray pyrolysis technique allowed production of Co3O4 films, which are alternative metal oxide film for technological applications, at low substrate temperature.

Influence of Substrate Temperature on the Properties of Cobalt Oxide Thin Films Prepared by Nebulizer Spray Pyrolysis (NSP) Technique

Cobalt oxide thin films are prepared by the nebulizer spray pyrolysis technique using cobalt chloride as the precursor material. The structural, optical, morphological and electrical properties are investigated as a function of substrate temperature (300–450 °C). The X-ray diffraction (XRD) analysis reveals that all the films are polycrystalline in nature, having cubic structure with preferential orientation along the (111) plane. The optical spectra show that the films are transparent (68 %) in the IR region. The optical band gap values are calculated for different substrate temperature. Photoluminescence (PL) spectra of the films indicate the presence of indigo, blue and green emission peaks with an ultraviolet emission peak centered around 368nm. SEM images reveals small sphere-like structures for the prepared Co3O4 films. The maximum conductivity obtained is 1.48 x 10−3 S/cm at 350 °C. The activation energy varies between 0.039 and 0.138 eV for the substrate temperature variation from 300-450 Q°C.

Methyl salicylate detection via electrochemical transients using nano spinel Co3O4 films

The mixed nano spinel Co3O4 films were fabricated through electrochemical deposition followed by peroxide oxidation and heat treatment. Electrochemical characteristics of the deposition and textural as well as morphological characteristics of the films were analyzed. Both 400 plane for Co3O4 and the 200 plane for CoO were noted. Based on IR studies, hydroxides decomposed into oxides on annealing. Oxide films are having the stoichiometric atomic weight ratio, O:Co as 1:2.7. Chronopotentiometric and chronoamperometric transients were recorded for the anodic oxidation of methyl salicylate using cobalt oxide films. Based on the electrochemical kinetic data, oxidation mechanism scheme is proposed and the net oxidation rate depends on sluggish charge-transfer limitations. Salicylate di-ion to 1, 2 benzoquinone is more favorable than 1, 4 benzoquinone derivative with four-electron transfer, whereas methoxide to formaldehyde involves two-electron transfer.

An insight in the structural, morphological, electrical and optical properties of spray pyrolysed Co3O4 thin films

The spray pyrolysis deposition of stable and single phase cobalt oxide (Co3O4) thin films at three different deposition temperatures viz. 350 °C, 420 °C and 470 °C was undertaken in the present work. It was found that substrate temperature played a pivotal role in obtaining pure thin layers. X-ray diffraction analysis confirmed the cubic spinel type structure (a = 8.094 Å) of polycrystalline Co3O4 with predominant orientation along (311) plane. The average crystallite size was found to be around 49 nm. Fourier transform IR spectra revealed the presence of an OB3 vibration at 540 cm−1 and an ABO3 vibration at 640 cm−1 where, B denotes Co3+ ions in an octahedral hole and A denotes Co2+ ions in a tetrahedral hole. The Raman spectra recorded in the wave number range 200–800 cm−1 indicated five Raman peaks and the strong characteristic peak at 694 cm−1 was assigned to the A1g mode which corresponds to Co–O breathing vibration of Co2+ ions in tetrahedral coordination. Surface analysis was carried out with the aid of SEM and AFM. The formation of Co3O4 was confirmed by analyzing the binding energies and intensities of Co 3s, Co 2p and O 1s obtained from XPS. Temperature dependent resistivity was realized from the two probe electrical measurements validating the semiconducting behaviour of the prepared films. Co3O4 films had low transmittance values in the order of 23%–43% in the UV–Vis-NIR region. Estimation through Tauc plots revealed direct optical band gap energies around 2–2.24 eV due to charge transfer transition between p states of O2− and t2 states of Co2+. Related optical parameters like extinction coefficient (k) and refractive index (μ) were calculated using Swanepoel method.

Electrochemical behavior of Co3C carbide

The electrochemical properties of the Co3C carbide have been studied. In contrast to metallic cobalt, its carbide is characterized by higher electrocatalytic activity in the hydrogen evolution reaction and low rate of anodic oxidation in acidic sulfate solutions. The oxidation in borate solutions (pH = 6.3–9.0) results in the formation of oxide films different in phase composition. In the case of metallic cobalt, a passive film consisting of CoO and Co(OH)2 forms, while the cobalt carbide oxidation results in the formation of the Co3O4 film. The oxidation of cobalt carbide is an irreversible process accompanied by the accumulation of carbon on the surface.

Room-temperature selective epitaxial growth of CoO (1 1 1) and Co3O4 (1 1 1) thin films with atomic steps by pulsed laser deposition

Cobalt oxide epitaxial thin films of both rock-salt CoO and spinel Co3O4 were selectively synthesized on atomically stepped α-Al2O3 (0001) substrates at room temperature under well-controlled oxygen pressures by pulsed laser deposition. X-ray diffraction and reflection high-energy electron diffraction analyses demonstrated that the CoO and Co3O4 films were grown with phase control and good epitaxial quality at room temperature (20°C). The CoO (111) film was obtained in ultra-high vacuum of 1×10−8Torr, while the Co3O4 (111) film was grown in 1×10−2Torr of O2. X-ray reciprocal space mapping results indicated that the in-plane mismatches of the {1=10} planes of CoO (111) and Co3O4 (111) films with the substrate were 4.5% and 2.5%, respectively. The films were almost entirely relaxed with ratios of expansion less than ±2%; the films underwent slight elongation along the [111] axis and shrinkage in the (111) plane. The surfaces of the as-grown CoO and Co3O4 thin films revealed atomic steps reflective of those on the substrates. Their root-mean-square roughness values were about 0.1nm indicating suppressed grain growth on the substrates at room temperature. The optical bandgap of the epitaxial CoO (111) film was estimated to be 2.72eV accompanied with a broad absorption attributable to non-stoichiometry or d-d transition. The bandgap of the Co3O4 (111) film was evaluated as 1.42eV, and also absorption at 1.86eV was observed. The obtained room-temperature epitaxial growth of CoO and Co3O4 thin films contributes to enhance their catalytic ability and quality of layer-stacking devices in terms of improving surface/interface flatness and specific surface area.

Cobalt Oxide Electrodes-Problem and a Solution Through a Novel Approach using Cetyltrimethylammonium Bromide (CTAB)

In this article, we present a critical review of the literature on cobalt oxide modified electrodes, focusing on their cyclic voltammetric behavior. This article provides a broad survey of the field of electrochemical preparation of cobalt oxide films and their application in elecrocatalysis and electroanalysis. We discuss and analyze the complexity associated with the electrochemical behavior of cobalt oxide films, formed either through electrochemical methods or other methods. A solution is offered to the problem of complex redox couples of CoO film by introducing a novel cobalt oxide film. This is the first review paper on cobalt oxide modified electrodes. Focusing on this topic, all articles from 1922 to April 2014 are verified and the relevant articles are cited.

Multiple in-plane spin reorientation transitions inFe/CoObilayers grown on vicinalMgO(001)

Step-induced antiferromagnetic (AFM) uniaxial anisotropy and its effects on the exchange coupling have been systematically investigated in the epitaxial $\mathrm{Fe}/\mathrm{CoO}$ bilayers on a $\mathrm{MgO}(001)$ vicinal surface. X-ray magnetic linear dichroism measurements proved that the atomic steps induced a strong in-plane AFM uniaxial anisotropy in the CoO film. We found that the thermal activation induced in-plane 90\ifmmode^\circ\else\textdegree\fi{} switching of CoO AFM in-plane spins. The competition among the step-induced AFM anisotropy, the interface exchange coupling, and thermal activation generate a novel multiple in-plane spin reorientation transition of the Fe magnetization, which can further provide new insights on the exchange coupling in FM/AFM systems.

Growth and characterization of thin oriented Co3O4 (111) films obtained by decomposition of layered cobaltates NaxCoO2

The formation and structural characterization of highly (111)-oriented Co3O4 films prepared by a novel procedure from weakly (001)-oriented NaxCoO2 is reported. The NaxCoO2 films were deposited on both single crystal and amorphous substrates by chemical solution deposition (CSD) method and crystallized at 700°C. Subsequently they were transformed into (111)-oriented Co3O4 phase during post-growth annealing at 900°C. The degree of preferred orientation in Co3O4, which was determined by phi-scan and pole figure measurements, depends on the content of Na in the starting NaxCoO2 phase. Surface morphology of the films was investigated using electron microscopy and atomic force microscopy.