Commercial Co3O4 Research Articles

Anisotropy of the thermoelectric figure of merit (ZT) in textured Ca3Co4O9 ceramics prepared by using a spark plasma sintering process

Textured Ca3Co4O9 ceramics were prepared by spark plasma sintering (SPS) from commercial CaCO3 and Co3O4 powders to investigate the thermoelectric anisotropy of Ca3Co4O9. The degree of orientation of the textured specimens was evaluated by using the Lotgering factor method, and the SPS process was confirmed to be an effective technology to prepare textured Ca3Co4O9 ceramics. Both the power factors and the thermal conductivities were measured in two different directions, parallel (out-of-plane) and perpendicular (in-plane) to the SPS press axis. The difference in anisotropy between the electrical conductivity and the thermal conductivity was investigated for the textured Ca3Co4O9 ceramics. The maximum figure of merit (ZT) value along the direction perpendicular to the SPS press axis was more than 20% higher than it was along the direction parallel to the SPS press axis. It is noted that the strong thermoelectric anisotropy can give rise to an overestimates of ZT when preparing samples in different directions for power factor and thermal conductivity measurements.

Synthesis of hierarchical worm-like SnO2@C aggregates and their enhanced lithium storage properties

The present paper reports a synthetic strategy of hierarchical worm-like SnO2@C aggregates with enhanced electrochemical performances. Specifically, a glucose-assisted hydrothermal treatment of the intermediate Co–Sn alloy nanoparticles, which were formed by carbothermal reduction of mixed commercial SnO2 and Co3O4 nanoparticles. The SnO2@C sample exhibits enhanced cycling performance in comparison with raw commercial SnO2 nanoparticles and intermediate Co–Sn alloy nanoparticles when used as anode of lithium ion battery. A stable capacity of 533.6mAhg−1 at 100mAg−1 and 477.0mAhg−1 at 400mAg−1 remains after 60 cycles. When the current density increases to 1600mAg−1, the SnO2@C sample still deliver a high capacity of 384.2mAhg−1. The superior electrochemical performances could be attributed to the synergistic effect of unique worm-like aggregates structure and carbon surface-layer, which facilitate the electron transportation and buffer the large volume change.

Enhanced lithium storage capacity of Co3O4hexagonal nanorings derived from Co-based metal organic frameworks

Co3O4 with high capacities and energy density has potential applications to be electrode materials for lithium ion batteries, one of the most important power sources. For improving the cycling stability, the Co3O4 nanostructures are required. Herein, we report successful construction of Co3O4 hexagonal nanorings and nanoplates/nanoparticles via treating Co-based metal organic frameworks (MOFs) with organic amine. The studies show that the release rate of Co(II) to the reaction system and the spatial hindrance of the organic linkers of MOFs determine the final morphology of Co3O4. As an anode for lithium ion batteries, Co3O4 hexagonal nanorings with 1370 mA h g−1 specific capacity after 30 cycles displayed higher reversible capacity and better stability than commercial Co3O4 particles with only 117 mA h g−1 specific capacity after 30 cycles. The improved performance of Co3O4 hexagonal nanorings could be attributed to the shortened transfer path for Li+ afforded by the special morphology. It is expected that plentiful metal oxide nanostructures could be constructed from MOFs due to the available versatile categories of MOFs.

Mesoporous Co3O4 with Controlled Porosity: Inverse Micelle Synthesis and High-Performance Catalytic CO Oxidation at −60 °C

Crystalline mesoporous cobalt oxides with improved catalytic activity in CO oxidation were synthesized using an inverse surfactant micelle method. The prepared materials are monodispersed nanoparticle aggregates, and the mesopores are formed by connected intraparticle voids. Powder X-ray diffraction (PXRD), N2 sorption, field emission scanning electron microscope (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) revealed that both pore and nanoparticle sizes are enlarged with increasing thermal treatment temperatures (150–450 °C). Mesoporous cobalt oxide calcined at 350 °C exhibited the best oxidation activity and can achieve complete oxidization (100% conversion) of CO to CO2 at −60 °C under normal conditions (∼3–10 ppm of H2O) and at 80 °C under moisture rich conditions (∼3% H2O). The commercial Co3O4 reached 100% conversion at 220 °C under normal conditions. X-ray photoelectron spectroscopy (XPS), O2-temperature-programmed desorption (O2-TPD), H2-temperature-programmed reduction (H...

Synthesis of one-dimensional porous Co3O4 nanobelts and their ethanol gas sensing properties

In this paper, one-dimensional porous Co3O4 nanobelts were synthesized via a facile template-free hydrothermal method and subsequent the thermal decomposition. Their microstructures and morphologies were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and N2 adsorption–desorption techniques. The results indicate that the reaction parameters such as the molar ratio of Co(NO3)2·6H2O to C2H4N4, the amount of Co(NO3)2·6H2O, the hydrothermal temperature and time play crucial rules in controlling the microstructures and morphologies of the as-prepared cobalt precursors. A possible formation mechanism was proposed. Moreover, the obtained porous Co3O4 nanobelts exhibit ethanol gas sensing properties superior to the commercial Co3O4 powders at a working temperature of 200°C, suggesting their potential applications as nanosensors.

Nanoparticles-assembled Co3O4 nanorods p-type nanomaterials: One-pot synthesis and toluene-sensing properties

One dimensional (1D) Co3O4 nanorods have been synthesized by a simple one-pot solvothermal method. Field emission scanning electron microscopic and transmission electron microscopic results revealed that the Co3O4 samples were rod-like structure with a diameter of 50nm, where the subunits were irregular-shaped nanoparticles. The response to 10ppm toluene of the rod-like Co3O4-based sensor was 6.0 at 200°C, which was about 6 times higher than that of the commercial Co3O4 powder. Interestingly, the rod-like Co3O4-based sensor exhibited not only a high response but also faster response and recovery speeds to toluene gases. The good sensing performance suggests that this unique rod-like Co3O4 nanostructure could be a promising candidate as a sensing material for gas sensor.

Buckypaper electrode containing carbon nanofiber/Co3O4 composite for enhanced lithium air batteries

In general, air electrodes are fabricated by mixing an oxide catalyst, carbon, and a binder. However, a nanosized oxide catalyst may not disperse homogeneously; instead, it easily aggregates, thus limiting its full catalytic activity. In order to solve this problem, a carbon nanofiber (CNF)/Co3O4 composite was prepared and characterized in this work. A polydopamine layer was used as a binding agent for the CNFs and Co3O4. The polydopamine-assisted CNF/Co3O4 composite was characterized by homogeneously dispersed nanosized Co3O4 particles, resulting in a wide catalytic active area. The electrode containing the CNF/Co3O4 composite was prepared via the buckypaper method and exhibited superior capacity, lower overpotential, and better cyclic performance than an electrode containing commercial Co3O4 nanoparticles and CNFs. This result indicates that the CNF/Co3O4 composite is an effective catalyst for air electrodes of lithium-air cells.

Redox preparation of mixed-valence cobalt manganese oxide nanostructured materials: highly efficient noble metal-free electrocatalysts for sensing hydrogen peroxide

High-performance hydrogen peroxide sensors provide valuable signals of biological interactions, disorders, and developing of diseases. Low-cost metal oxides are promising alternatives but suffer from low conductivity and sensing activity. Multi-component metal oxides are excellent candidates to accomplish these challenges, but the composition inhomogeneity is difficult to manage with conventional material preparation. We demonstrated redox preparation strategies to successfully synthesize highly homogeneous, noble metal-free H2O2 sensors of spinel nanostructured cobalt manganese oxides with enhanced conductivity, multiple mixed-valence features, and efficient H2O2 sensing activities. The designed redox reactions accompanied with material nucleation/formation are the key factors for compositional homogeneity. High conductivity (1.5 × 10(-2) S cm(-1)) and H2O2 sensing activity (12 times higher than commercial Co3O4) were achieved due to the homogeneous multiple mixed-valence systems of Co(ii)/(iii) and Mn(iii)/(iv). A wide linear detection range (from 0.1 to 25 mM) with a detection limit of 15 μM was observed. Manganese species assist the formation of large surface area nanostructures, enhancing the H2O2 reduction activities, and inhibit the sensing interference. The material controls of hierarchical nanostructures, elemental compositions, porosity, and electrochemical performances are highly associated with the reaction temperatures. The temperature-dependent properties and nanostructure formation mechanisms based on a reaction rate competition are proposed.

Exotemplated copper, cobalt, iron, lanthanum and nickel oxides for catalytic oxidation of ethyl acetate

Oxides of cobalt, copper, iron, lanthanum and nickel were prepared by an exotemplating method using two carbon materials as templates: carbon xerogel (CX) and a commercial activated carbon (AC). Samples were characterized by thermogravimetry and differential scanning calorimetry, N2 adsorption at −196°C, temperature programmed reduction, scanning electron microscopy and X-ray diffraction. All exotemplated samples showed improvements in surface area, compared with analogue commercial samples. The materials obtained were tested for ethyl acetate oxidation. CX was found to be a better templating material than AC, producing more active oxide materials. CX exotemplated NiO and Fe2O3 showed a large improvement in performance for the catalytic oxidation of ethyl acetate, compared to the commercial samples and AC analogues; nevertheless, CX exotemplated Co3O4 was the best catalyst. The commercial Co3O4 material showed also a good catalytic performance, being the most active of the commercial samples. However, some deactivation was observed with time. On the other hand, deactivation did not occur with the exotemplated material, which showed no decrease in performance up to 5 cycles and up to 72h of continuous operation (the maximum studied). The enhanced reducibility of exotemplated samples explains their better catalytic activities relatively to the commercial oxides.

Solution combustion synthesized cobalt oxide catalyst precursor for NaBH4 hydrolysis

In this paper we report the solution combustion synthesis of cobalt oxide nanofoam from solutions of cobalt nitrate and glycine and subsequent use as an effective catalyst precursor for NaBH4 hydrolysis. The catalytic activity results show that the hydrogen generation rate (HGR) at room temperature was much higher for the solution combustion synthesized material than for commercial Co3O4 nanopowder, though their specific surface areas were comparable (∼26–32 m2/g). Using a 0.6 wt.% aqueous solution of NaBH4 at 20 °C and a 5 wt.% catalyst precursor loading, a HGR of 1.93 L min−1 gcat−1 was achieved for solution combustion synthesized Co3O4. In contrast, at the same conditions, for commercial Co3O4 and elemental Co powders HGRs of 0.98 and 0.49 L min−1 gcat−1 were achieved respectively. This type of synthesis is amenable to many complex metal oxide catalysts as well, such as LiCoO2, which have also been shown to be good catalyst precursors for hydrolysis of NaBH4.

Highly selective liquid-phase aerobic oxidation of vanillyl alcohol to vanillin on cobalt oxide (Co3O4) nanoparticles

Spinel Co3O4 nanoparticles prepared by solution phase method having particle size in the range of 12–20 nm exhibited excellent activity for the liquid-phase aerobic oxidation of vanillyl alcohol with 80% conversion and 98% selectivity to vanillin. Our catalyst could be reused three times without appreciable loss in activity. The catalytic activity of the Co3O4 nanoparticles was found to be similar to its homogenous precursor (cobalt acetate) and greater than the commercial Co3O4 oxide. The detailed characterization results of morphology, size and structure of the prepared Co3O4 nanoparticles obtained by XRD, FT-IR, H2-TPR, HR-TEM and cyclic voltammetry technique were used to understand the roles of various Co species in directing the selectivity towards vanillin.

Hierarchical structure of Co3O4 nanoparticles on Si nanowires array films for lithium-ion battery applications

The Co3O4@Si nanowires configuration was successfully fabricated by employing the electroless metal deposition (EMD) technology and the following annealing in air. The nanostructure exhibits a uniform Co3O4 nanoparticles grafting on the solution-etched aligned Si nanowires. What is more important, the cost-effective and uncomplicated fabrication strategy as well as the obtained unique architecture will lead to perfect performance in many applications. When functioned as anode electrodes in lithium-ions battery, the Co3O4@Si nanowires configuration displays an excellent Lithium-ion battery performance with larger reversible capacity, more comforting cyclic performance and better rate capability compared with the commercial Co3O4 powders.

Co3O4/ZnO nanocomposites for gas-sensing applications

Co3O4/ZnO nanocomposites were prepared by an easy wet-chemistry route without any organic additive or surfactant used. The nanocomposites were systematically characterized by X-ray powder diffraction, scanning electron microscopy, (high-resolution) transmission electron microscopy, selected area electron diffraction, and energy-dispersive X-ray spectroscopy. The results show that ZnO is loaded on the surface of Co3O4 nanoparticles with a compact and clean hetero-interface. The obtained nanocomposites were tested for gas-sensing applications with ethanol and formaldehyde as model gases. It was revealed that the nanocomposites exhibit enhanced gas-sensing performance such as high stability and high sensing response. The sensing responses to 100ppm ethanol or formaldehyde (46 to ethanol and 20 to formaldehyde) are much higher than those of pristine Co3O4 nanoparticles (6.2 to ethanol and 4.4 to formaldehyde), commercial Co3O4 powder (1.6 to ethanol and 1.5 to formaldehyde), and pure ZnO sample (7.5 to ethanol and 4.1 to formaldehyde). These results suggest that the integration of Co3O4 with ZnO is a promising route to the development of effective sensing materials. The excellent gas-sensing properties and the easily up-scalable preparation route make the prepared nanocomposites be promising for real applications.

Amperometric determination of NADH with Co3O4 nanosheet modifiedelectrode

In this work, we have developed a simple and reliable cobalt oxide (Co3O4) based amperometric sensor for the determination of NADH. A sheet shape Co3O4 nanooxide was synthesized by the CTAB assisted hydrothermal technique and was characterized by SEM and XPS. Owing to the redox property of Co3O4, the operating potential of NADH can be significantly reduced from 0.7down to 0.1V. Compared to a commercial Co3O4 nanoparticle modified electrode, this nanosheet form cobalt oxide possesses a rapid background subsiding characteristic and a low residual current. This scheme was conducted on a flow injection system with a constant operating potential of 0.1V (vs. Ag/AgCl, 3M) in a 0.2M phosphate buffer at pH 6.0. A suitable linear range from 10 to 100μM (R=0.999) with a detection limit of 4.25μM (S/N=3) was obtained. The RSD for 20 successive measurements of 75μM NADH is only 1.4%, which indicates a high stability and no contamination during NADH oxidation. This scheme did not suffer from conventional antioxidants, including dopamine, uric acid, epinephrine, serotonin, histamine, and 4-acetaminophen, except ascorbic acid. Thus, an ascorbate oxidase was introduced to remove the ascorbic acid before the sample was injected into the flow injection analysis system. After this simple pretreatment, the influence of ascorbic acid was eliminated, successfully.

Synthesis of single- and double-walled carbon nanotubes using the calcined MgO supported commercial metal oxide as catalysts

Simple, low-cost and environment-friendly catalysts for synthesizing carbon nanotubes were prepared by simply calcining the mixture of commercial transition metal oxide powders and porous or crystalline MgO at 950°C. The commercial metal oxide powders, including Fe2O3, Co2O3, Ni2O3, Fe3O4 and Co3O4, were directly used without any pretreatment. Calcination of the MgO supported Fe2O3 catalysts results in the formation of MgFe2O4/MgO solid solution or the dissolution of metal into MgO lattices. High quality single- and double-walled carbon nanotubes were synthesized by thermal decomposition of methane, and were characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy. The results bring forward an effective way to prepare the catalyst for synthesizing single- and double-walled carbon nanotubes.

Synthesis of flower-like Co3O4–CeO2 composite oxide and its application to catalytic degradation of 1,2,4-trichlorobenzene

A micrometer-sized, nanostructured, flower-like Co3O4–CeO2 composite oxide was synthesized by an ethylene-glycol-mediated process. The composite oxide was an assembly of polycrystalline nanoparticles, with a typical mesoporous structure. The composite's catalytic activity in 1,2,4-trichlorobenzene degradation was evaluated using a pulsed-flow microreactor–gas chromatography system, and compared with that of quartz sand, commercial CeO2, commercial Co3O4, and a Co3O4/CeO2 equimass mixture. The composite oxide was a promising catalyst for 1,2,4-trichlorobenzene degradation. This is attributed to the structural features of the composite oxide with a high specific surface area and a high total pore volume, and the synergistic effect between the two composite phases. The easy creation of high-mobility active oxygen on CeO2 and the easy cleavage of CoO bonds at the interface of the two components promote reactivity of Co3O4 in 1,2,4-trichlorobenzene degradation. Pulsed catalytic theory suggests a first-order reaction between the composite oxide and 1,2,4-trichlorobenzene, with an apparent activation energy of about 27kJ/mol, and degradation on the Co3O4–CeO2 composite oxide would occur easily.

Co3O4 nanowires as high capacity anode materials for lithium ion batteries

Co3O4 nanowires were synthesized from the decomposition of CoC2O4·2H2O nanowires which were obtained through a polyvinyl alcohol (PVA)-assisted solution-based precipitation process. And the formation mechanism of CoC2O4·2H2O nanowires was discussed. The Co3O4 nanowires had diameters in the range of 30–60nm and lengths of several micrometers, inheriting the morphology of the CoC2O4·2H2O nanowires. The Co3O4 nanowires as an anode material in lithium-ion batteries exhibited a stable specific discharge/charge capacity of 611mAh/g and 598mAh/g after fifty cycles at a current density of 0.11A/g, which were much higher than that of commercial Co3O4 nanoparticles. In addition, the charge capacity of the as-synthesized Co3O4 nanowires was more than two times higher than that of the commercial Co3O4 nanoparticles at a current density of 1.1A/g. These results indicate that the as-prepared Co3O4 nanowires have potential to be a promising candidate as high capacity anode material in the next generation lithium-ion batteries.

Oxygen evolution on Ti/Co3O4-coated electrodes in alkaline solution

AbstractThe electrochemical performances of Co3O4 nanopowders, obtained by the sol-gel method, were investigated and compared with those of commercial Co3O4 powders, for oxygen evolution reaction in alkaline solution. The active oxide powder was mixed with teflon and assembled on Ti substrate to form thin catalyst film. Cyclic voltammetry, polarization curves, and electrochemical impedance spectroscopy were used to assess the mechanism of oxygen evolution reaction, chemical structure, and morphology of the catalyst.