As-synthesized Co3O4 Research Articles

O22-/O- functionalized oxygen-deficient Co3O4 nanorods as high performance supercapacitor electrodes and electrocatalysts towards water splitting

Owing to high theoretical specific capacitance of 3560Fg−1 and intrinsic activity towards oxygen evolution reaction (OER), inexpensive Co3O4 is drawing much attention as either a promising pseudocapacitive electrode or OER catalyst. However, restricted to poor conductivity and lack of active sites, Co3O4 usually exhibits limited experimental capacitance and OER activity, barely satisfying high energy density delivering of supercapacitors and low energy input of water-splitting systems. Herein, we report O22-/O- functionalized oxygen-deficient Co3O4 nanorods for supercapacitor and water splitting dual applications. The CoC2O4·2H2O converted oxygen-deficient Co3O4 nanorods show enhanced electrical conductivity as confirmed by the increased carrier density. The increased number of Co2+ sites (oxygen vacancies) and CoOOH are believed to contribute to the improvement in faradaic reactions and OER activity. Additionally, surface functionalization by O22-/O- is realized in oxygen-deficient Co3O4 nanorods. On the basis of these merits, the as-synthesized Co3O4 nanorods demonstrate a significantly high specific capacitance of 739Fg−1 and an ultralow overpotential of 275mV at 10mAcm−2 for OER with ultralong stability of over 300h (@ 100mAcm−2). Specifically, an electrolyzer for overall water splitting can be driven by asymmetric supercapacitors with the optimized cobalt oxide as both electrocatalyst and electrode material.

Single-crystalline porous nanosheets assembled hierarchical Co3O4 microspheres for enhanced gas-sensing properties to trace xylene

Hierarchical porous (HP) nanostructures of p-type metal oxide have attracted great attention in gas-sensing application due to their less agglomerated configurations and the advantages for gas diffusion. However, the contacts between grain boundaries around pores of HP nanostructures are usually too fragile to resist the shear force caused by ultrasonic treatment during sensor fabrication processes and the thermal stress produced from high operating temperature. To solve this problem, uniform Co3O4 microspheres assembled by single-crystalline porous nanosheets were synthesized by an ethylene glycol (EG) mediated solvothermal method with the co-assistant of water and polyvinyl pyrrolidone (PVP). Due to the structural stability of single-crystalline nanosheets, the as-synthesized HP Co3O4 is well kept during the sensor fabrication processes. Moreover, the Co3O4 shows a high response (Rg/Ra=74.5–100ppm) to xylene at the optimized temperature (150°C), which is almost 4 times larger than that of commercial Co3O4 (19.1). It also exhibits excellent long-term stability with small deviations (less than 6%) for two months, which can be ascribed to the structural stability of single-crystalline nanosheets. Combined with their high selectivity and low detection limit, the as-prepared HP Co3O4 microspheres assembled by single-crystalline porous nanosheets are highly promising gas-sensing materials for xylene detection.

Self-supported porous Cobalt Oxide Nanowires with enhanced Electrocatalytic performance toward Oxygen evolution reaction

Development of hybrid electrocatalysts with high activity and good stability is crucial for oxygen evolution reaction (OER) of water electrocatalysis. In this work, cobalt oxide (Co3O4) nanowires loaded on carbon fiber paper (CFP) were synthesized via hydrothermal method and annealing. The as-synthesized Co3O4 nanowires exhibit an enhanced catalytic activity with low onset overpotential (1.52 V vs. RHE) and a small overpotential of 330 mV for a current density of 10 mA cm−2 with a Tafel slope of 60 mV ⋅ dec−1. In addition, the Co3O4 nanowires maintain its electrocatalytic activity for at least 24 h in basic media. The enhanced performance of Co3O4 nanowires/CFP can be attributed to the high conductivity of CFP, the synergistic effect of Co3O4 and carbon, and high porosity of the nanowire. This study will open new possibilities for exploring water electrocatalysis. The porous Co3O4 nanowires grown on carbon fiber paper act as efficient and stable electrocatalyst for oxygen evolution reaction.

Facile Synthesis of Co3O4 with Different Morphologies via Oxidation Kinetic Control and Its Application in Hydrogen Peroxide Decomposition

Co3O4 nanoparticles (NPs) with tubular and hollow structures were successfully synthesized by the formation of CoOOH and subsequent high-temperature calcination in air. The as-synthesized Co3O4 retained the morphologies of CoOOH. Therefore, the key step for the synthesis of Co3O4 was the controllable preparation of CoOOH NPs with tubular and hollow structures, which were prepared through a facile strategy involving the oxidation of β-Co(OH)2 under strong basic conditions (template-free, aqueous solution, and mild temperature). The morphology of CoOOH was tuned by employing air and H2O2 as the oxidizing agents which possessed different oxidation abilities and thus resulted in different oxidation kinetics. The plausible formation mechanism of CoOOH NPs with tubular and hollow structures was both related to the Kirkendall effect. In contrast to the commercial Co3O4, the as-prepared Co3O4 NPs with tubular and hollow structures showed superior catalytic activities for the decomposition of H2O2. The reaction ra...

Structure and magnetic properties of Co3O4/SiO2 nanocomposite synthesized using combustion assisted sol-gel method

This paper reports on novel cobalt oxide nanoparticles (NPs) embedded in an amorphous silica (SiO2) matrix, synthesized using a modified sol-gel method. SEM and TEM images show as-synthesized particles to aggregate in the shape of spheres and less than 5nm in size, while XRD and SAED analysis both point to well crystallized cubic spinel cobalt oxide phase with an average crystallite size of about 4.6nm. Raman analysis confirms the formation of cobalt (III) oxide (Co3O4) NPs. As-synthesized Co3O4 single-nanocrystallite has magnetic properties that correlate with finite size effects and uncompensated surface spins. Temperature dependence of ZFC-FC magnetization curves reveals a sharp peak around 10K which corresponds to the blocking temperature. A Curie-Weiss behavior of magnetization above 25K shows lower Néel temperature of the sample compared with its bulk counterpart TN=40K (possibly due to crystal defects and nano-dimensionality of the particles). The magnetic measurements exhibit high magnetization at low temperatures (MS=54.3emu/g) which can be associated with random canting of the particles’ surface spins and uncompensated spins in the core which tends to interact ferromagnetically at low temperatures. The initial magnetization curve falls out from the hysteresis loop at 5K, which could be also the effect of surface spins.

Electrochemical Partial Reforming of Ethanol into Ethyl Acetate Using Ultrathin Co3O4 Nanosheets as a Highly Selective Anode Catalyst

Electrochemical partial reforming of organics provides an alternative strategy to produce valuable organic compounds while generating H2 under mild conditions. In this work, highly selective electrochemical reforming of ethanol into ethyl acetate is successfully achieved by using ultrathin Co3O4 nanosheets with exposed (111) facets as an anode catalyst. Those nanosheets were synthesized by a one-pot, templateless hydrothermal method with the use of ammonia. NH3 was demonstrated critical to the overall formation of ultrathin Co3O4 nanosheets. With abundant active sites on Co3O4 (111), the as-synthesized ultrathin Co3O4 nanosheets exhibited enhanced electrocatalytic activities toward water and ethanol oxidations in alkaline media. More importantly, over the Co3O4 nanosheets, the electrooxidation from ethanol to ethyl acetate was so selective that no other oxidation products were yielded. With such a high selectivity, an electrolyzer cell using Co3O4 nanosheets as the anode electrocatalyst and Ni–Mo nanopowders as the cathode electrocatalyst has been successfully built for ethanol reforming. The electrolyzer cell was readily driven by a 1.5 V battery to achieve the effective production of both H2 and ethyl acetate. After the bulk electrolysis, about 95% of ethanol was electrochemically reformed into ethyl acetate. This work opens up new opportunities in designing a material system for building unique devices to generate both hydrogen and high-value organics at room temperature by utilizing electric energy from renewable sources.

Synthesis of nanoparticles-assembled Co3O4 microspheres as anodes for Li-ion batteries by spray pyrolysis of CoCl2 solution

Nanoparticles-assembled Co3O4 microspheres with different primary particle size are synthesized via a facile one-step ultrasonic spray pyrolysis process, using CoCl2·6H2O as precursor. The as-synthesized Co3O4 powders are directly used as anode material for Li-ion batteries without further calcinations. The primary particle size is tuned by controlling the spray pyrolysis temperature and its effects on the electrochemical performance of the prepared samples are systemically investigated. The results reveal that primary particles size exerts significant effect on the initial coulombic efficiency, specific capacity and rate performance. In addition, we find that the temperature of powder collector strongly influences the chlorine content in the products, which is resulted from the chloridization of Co3O4 by gaseous HCl from the off-gas. A simple and effective strategy is proposed to prevent the chloridization reaction. The sample with the smallest primary particle size and low Cl content shows the highest initial coulombic efficiency of 73% and a high reversible capacity of 1340mAhg−1 after 50 cycles at a current density of 200mAg−1.

Hierarchical macro- and mesoporous assembly of metal oxide nanoparticles derived from metal-organic complex

The hierarchical porous metal oxide combines the advantages of each class of hierarchical pores and has potential applications in different fields. Here we proposed an emulsion-calcination route for producing porous metal oxide. The porous metal-organic complex was first synthesized in CO2-in-water emulsion, then the metal-organic complex was calcined to remove the organic linker and form porous metal oxide. The hierarchical macro- and mesoporous assemblies of Co3O4 nanoparticles were produced. The hierarchical macro- and mesoporous assemblies of Co3O4 nanoparticles were produced, with the macropores in size of hundreds of nanometers and the mesopores in 9–15 nm. The porosity properties and nanoparticle size of Co3O4 can be modulated by controlling CO2 pressure. The as-synthesized Co3O4 is an excellent candidate catalyst for the methylene blue degradation. By taking advantages of the high porosity and small particle size, the Co3O4 have potential applications in catalysis, gas separation, and controlled drug release. The strategy proposed in this work can be applied to the synthesis of different kinds of porous metal oxides.

Hierarchical Co3O4 nanoflowers assembled from nanosheets: facile synthesis and their application in supercapacitors

In this paper, three-dimensional hierarchical Co3O4 nanoflowers have been synthesized through a redox precipitation approach followed by calcination in air. The as-synthesized hierarchical Co3O4 nanoflowers are 250 nm in size, and composed of numerous self-assembled porous ultrathin nanosheets with a thickness of 10 nm. According to the experimental results, a possible formation mechanism for hierarchical Co3O4 nanoflowers is proposed. When evaluated as an electrode material for supercapacitors, hierarchical Co3O4 nanoflowers exhibit a high specific capacitance of 198 F g−1 at a current density of 1 A g−1 and cycling stability (94.6 % capacity retention after 1500 cycles) in 2 M KOH electrolyte. This remarkable electrochemical performance can be ascribed to their unique structural characteristics such as open flower-like architectures and ultrathin porous nanosheets.

Co3O4nanostructures with a high rate performance as anode materials for lithium-ion batteries, prepared via book-like cobalt–organic frameworks

The self-assembly of cobalt coordination frameworks (Co-CPs) with a two-dimensional morphology is demonstrated by a solvothermal method. The morphology of the Co-CPs has been controlled by various solvothermal conditions. The two-dimensional nanostructures agglomerated by Co3O4 nanoparticles remained after the pyrolysis of the Co-CPs. The as-synthesized Co3O4 anode material is characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge measurements. The morphology of Co3O4 plays a crucial role in the high performance anode materials for lithium batteries. The Co3O4 nanoparticles with opened-book morphology deliver a high capacity of 597 mA h g-1 after 50 cycles at a current rate of 800 mA g-1. The opened-book morphology of Co3O4 provides efficient lithium ion diffusion tunnels and increases the electrolyte/Co3O4 contact/interfacial area. At a relatively high current rate of 1200 mA g-1, Co3O4 with opened-book morphology delivers an excellent rate capability of 574 mA h g-1.

MOF-Templated Synthesis of Porous Co3O4Concave Nanocubes with High Specific Surface Area and Their Gas Sensing Properties

Porous metal oxides nanomaterials with controlled morphology have received great attention because of their promising applications in catalysis, energy storage and conversion, gas sensing, etc. In this paper, porous Co3O4 concave nanocubes with extremely high specific surface area (120.9 m(2)·g(-1)) were synthesized simply by calcining Co-based metal-organic framework (Co-MOF, ZIF-67) templates at the optimized temperature (300 °C), and the formation mechanism of such highly porous structures as well as the influence of the calcination temperature are well explained by taking into account thermal behavior and intrinsic structural features of the Co-MOF precursors. The gas-sensing properties of the as-synthesized porous Co3O4 concave nanocubes were systematically tested towards volatile organic compounds including ethanol, acetone, toluene, and benzene. Experimental results reveal that the porous Co3O4 concave nanocubes present the highest sensitivity to ethanol with fast response/recovery time (< 10 s) and a low detection limit (at least 10 ppm). Such outstanding gas sensing performance of the porous Co3O4 concave nanocubes benefits from their high porosity, large specific surface area, and remarkable capabilities of surface-adsorbed oxygen.

Fast response/recovery performance of comb-like Co3O4 nanostructure

A new type of comb-like architecture with a hierarchical structure was prepared via a simple and effective hydrothermal strategy in the case of Co3O4. FESEM and TEM confirm the comb-like architecture of the hierarchical structure, and that the Co3O4 nanorods with secondary nanostructures are the building units. The studies of the sensing performance demonstrate that the as-synthesized comb-like Co3O4 nanostructures show excellent catalytic activity upon exposure to CO gases in comparison with rod-like Co3O4. Importantly, the comb-like Co3O4 nanostructure-based sensor shows a fast response and recovery speed for CO gas. It is believed that the strategy of combining the hierarchical nanostructure and catalytic activity of Co3O4 nanomaterials can further provide potential for applications as real-time monitoring gas sensors.

Morphology-Controlled Synthesis of Co&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; Nanocubes and Their Catalytic Performance in CO Oxidation

Co3O4 nanocubes that were exclusively terminated with {100} facets of edge size 10 nm were solvothermally fabricated in a mixed solution of ethanol and triethylamine. Analyses of the structural evolution of the intermediates at different intervals during the synthesis, together with an examination of the influences of the cobalt precursor and solvent on the product structure, showed that the formation of Co3O4 nanocubes followed a dissolution-recrystallization mechanism. After calcination at 200 degrees C, the as-synthesized Co3O4 material retained a cubic morphology with the same edge size, but calcination at 400 degrees C resulted in the formation of spherical Co3O4 particles of diameter about 13 nm. The Co3O4 nanocubes exhibited inferior activity in room-temperature CO oxidation compared with Co3O4 nanoparticles ({111} facets), primarily as a result of the exposure of the less-reactive {100} facets, demonstrating the morphology effect of Co3O4 nanomaterials.

Synthesis of Small-Sized Freestanding Co3O4 Nanosheets with Improved Activity for H2O2 Sensing and Oxygen Evolution

Small-sized freestanding Co3O4 nanosheets have been successfully synthesized on conductive substrate via a novel and simple electrochemical-based strategy. The as-synthesized sheets have a small size of 30 ± 10 nm in edge length and about 10 ± 5 nm in thickness with most sheets lying perpendicular to the substrate. The combined properties of products such as small size, two-dimension shape and freestanding pose could lead to integrative advantages of high surface-to-volume ratio, the maximized exposed surfaces without particles aggregation, strong affinity and good conductivity. As for electrochemical tests, the as-synthesized Co3O4 nanosheets show an improved sensitivity of ∼0.56 A M−1 cm−2 with lower detection limit of 1 μM at concentration range of 0–1.8 mM for H2O2 sensing, and also exhibit good performance for oxygen evolution with low evolution over-potential, high catalytic efficiency and durable stability.

Co3O4–carbon nanotube heterostructures with bead-on-string architecture for enhanced lithium storage performance

In this report, alkylcarboxyl group-decorated carbon nanotubes (CNTs) with clustered functionalization patterns are achieved based on a modified Birch reduction in liquid ammonia. By using these functional CNTs (f-CNTs), a new type of Co3O4-CNT heterostructure is prepared via a simple hydrothermal method. SEM and TEM analyses reveal that the as-synthesized Co3O4-CNT heterostructures exhibit bead-on-string architecture, in which the Co3O4 spheres are threaded with CNTs. A possible growth mechanism is proposed to explain the formation of these Co3O4-CNT heterostructures. The electrochemical properties of the Co3O4-CNT heterostructures as anode materials for lithium ion batteries are investigated. The Co3O4-CNT heterostructures display high electrochemical activity, good cycle stability and improved rate performance. Such a large improvement of the electrochemical performance can be related to the robust necklace-like architectures which possess properties such as high mechanical stability, excellent electric conductivity and good strain accommodation.

Surfactant-free thermal decomposition route to phase pure tricobalt tetraoxide nanoparticles from cobalt(II)-tartrate complex

Tricobalt tetraoxide nanoparticles have been successfully synthesized following a ‘bottom-up’ approach by surfactant-free thermal decomposition of cobalt(II)-tartrate complex obtained by a modified sol–gel route. The synthesized complex was characterized by Fourier transform infrared (FT-IR) spectroscopy, elemental and thermogravimetric-differential thermal analysis (TG–DTA). The nanoparticles were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and Raman studies. The powder XRD pattern furnished evidence for a face-centered cubic structure of Co3O4. With the rise in calcination temperature from 400 through 500 to 600 °C, the average crystallite sizes of Co3O4 were found to increase from 28 through 36 to 46 nm. The TEM image revealed a faceted morphology of the as-synthesized Co3O4 nanoparticles. The high-resolution TEM image indicated the interplanar separation to be 0.28 nm which corresponds to the (220) plane in face-centered cubic Co3O4. The electron diffraction (ED) pattern showed single-crystalline nature of the synthesized nanoparticles. Raman spectrum showed four characteristic peaks of Co3O4 which further confirmed the phasic purity of the material.

Facile synthesis of hierarchically porous Co3O4 nanowire arrays with enhanced electrochemical catalysis

We report a facile template-free procedure to synthesize freestanding Co3O4 nanowire arrays on nickel substrate. Cobalt oxalate nanowire arrays are formed by immersing the electrodeposited Co film in an oxalic acid solution, and their morphologies can be conveniently tuned by changing the composition of precursor solution. The thermal treatment of the cobalt oxalate nanowire arrays at 250°C results in the formation of Co3O4 nanowire arrays. The as-synthesized Co3O4 nanowires exhibit a hierarchically porous structure inside their architectures. The Co3O4 nanowire array shows a much high sensitivity and a relatively wide linear range for the electrochemical detection of H2O2, resulting from the unique hierarchical nanostructure.

Generation of Co3O4 microparticles by solution combustion method and its Zn–Co3O4 composite thin films for corrosion protection

Microcrystalline cobalt oxide (Co3O4) powder was successfully synthesized by a simple, fast, economical and eco-friendly solution-combustion method. The as-synthesized powder was calcined for an hour at temperatures ranging from 100 to 900°C. The crystallite size, morphology, and chemical state of synthesized powders were characterized by powder XRD, TG-DTA, XPS, SEM/EDAX, TEM and FT-IR spectral methods. The as-synthesized Co3O4 powder was single-crystalline and Rietveld refinement of calcined samples exhibited cubic structure with space group of Fm3m (No. 227). The effect of calcination temperature on crystallite size and morphology was assessed. Scanning electron micrographs show a uniform, randomly oriented pseudo-cubic particle with porous like morphology and EDAX measurement showed its chemical composition. Thermal behavior of as-synthesized compound was examined. The TEM result revealed that, the particles are pseudo-cubic in nature with diameter of 0.2–0.6μm and a length of 0.9–1.2μm. The crystallite size increased with increase of calcination temperature. The synthesized Co3O4 powder was used to fabricate Zn–Co3O4 composite thin films and its corrosion behavior was analyzed by anodic polarization, tafel extrapolation and electrochemical impedance spectroscopy. The results indicate that the Zn–Co3O4 composite thin films have potential applications to corrosion protection.

Nanostructure cobalt oxide reinforced conductive and magnetic polyaniline nanocomposites

Nanocrystalline cobalt oxide (Co3O4) was synthesized by sol–gel method using cobalt chloride as precursor. Conducting polyaniline-cobalt oxide (PANI/Co3O4) nanocomposites were synthesized by in situ polymerization of aniline (monomer) in the presence of as-synthesized nanocrystalline Co3O4. The synthesized nanocomposites were characterized by XRD, FTIR, UV-VIS and TEM analysis. TEM images show that PANI has been coated on nanocrystalline Co3O4, which confirms the formation of nanocomposites. XRD pattern show that nanocrystalline Co3O4 embedded into polycrystalline PANI to form crystalline nanocomposites. Fourier transform infrared and ultraviolet visible spectroscopy show that cobalt oxide nanoparticles get electrostatically bound to the specific sites of polyaniline. PANI/Co3O4 nanocomposites show semiconducting behavior as that of conducting polyaniline. In this article, the influence of filler concentration on the transport parameters and magnetic properties of polyaniline nanocomposites has been investigated.

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.