Co3O4 Nanostructures Research Articles

Highly sensitive determination of atropine using cobalt oxide nanostructures: Influence of functional groups on the signal sensitivity

This study describes sensitive determination of atropine using glassy carbon electrodes (GCE) modified with Co3O4 nanostructures. The as-synthesised nanostructures were grown using cysteine (CYS), glutathione (GSH) and histidine (HYS) as effective templates under hydrothermal action. The obtained morphologies revealed interesting structural features, including both cavity-based and flower-shaped structures. The as-synthesised morphologies were noted to actively participate in electro-catalysis of atropine (AT) drug where GSH-assisted structures exhibited the best signal response in terms of current density and over-potential value. The study also discusses the influence of functional groups on the signal sensitivity of atropine electro-oxidation. The functionalisation was carried with the amino acids originally used as effective templates for the growth of Co3O4 nanostructures. The highest increment was obtained when GSH was used as the surface functionalising agent. The GSH-functionalised Co3O4-modified electrode was utilised for the electro-chemical sensing of AT in a concentration range of 0.01–0.46 μM. The developed sensor exhibited excellent working linearity (R2 = 0.999) and signal sensitivity up to 0.001 μM of AT. The noted high sensitivity of the sensor is associated with the synergy of superb surface architectures and favourable interaction facilitating the electron transfer kinetics for the electro-catalytic oxidation of AT. Significantly, the developed sensor demonstrated excellent working capability when used for AT detection in human urine samples with strong anti-interference potential against common co-existing species, such as glucose, fructose, cysteine, uric acid, dopamine and ascorbic acid.

Graphene-like holey Co3O4 nanosheets as a highly efficient catalyst for oxygen evolution reaction

Co3O4 nanosheets with a graphene-like holey structure are successfully synthesized through a bottom-up self-assembly approach and utilized as a catalyst for the oxygen evolution reaction (OER). This unique nanostructure possesses a large fraction of low-coordinated surface atoms and highly accessible surface areas due to its atomic thickness and mesoporosity, which could provide abundant active sites and facilitate the electrode/electrolyte contact for OER catalysis. In addition, density functional theory (DFT) calculations reveal that the loss of the neighboring layers gives the ultrathin nanostructure remarkable lattice distortion, which leads to decreased energy barriers for facile mass conversion and transfer on the surface of the catalyst. As a result, the graphene-like holey Co3O4 nanosheets exhibit excellent OER catalytic performance with low onset potential of 0.617 V vs. Hg/HgO, high current density of 12.26 mA cm-2 at 0.8 V vs. Hg/HgO, and long-term stability with negligible fading in current density after 2000 cycles, significantly outperforming the performances of conventional Co3O4 nanostructures and commercial IrO2. This unique graphene-like holey structure should be of great benefit for applications ranging from electronic devices to energy conversion and storage systems.

Charge storage, electrocatalytic and sensing activities of nest-like nanostructured Co3O4

We synthesized nanostructured Co3O4 samples using anionic (SDS), cationic (CTAB) and nonionic (Triton X-100) surfactant molecules in hydrothermal conditions and subsequent calcination. This approach facilitates the synthesis of porous Co3O4 material with bundle-like-sheet, nest-like and flake-like morphologies with specific surface areas in the range of 50–77m2g−1. Among these materials, the nest-like nanostructured Co3O4 material has unique pore architecture, larger pore volume, low solution and charge transfer resistance, and found to be an active material for charge storage, electrocatalytic and sensing applications. The specific capacitance value of the nest-like Co3O4 is 404Fg−1 at a current density of 2Ag−1 with 80% specific capacitance retention. The electrocatalytic oxidation of methanol occurs at lower onset potential on this material with good electrochemical stability. It has good sensing ability for glucose with high sensitivity of 929μAcm−2mM−1, fast response time of ∼0.5s and detection limit as low as ∼1μM. These results show that the nest-like nanostructured Co3O4 material is a versatile candidate for various applications.

Facile template-free hydrothermal synthesis of Co3O4 hollow microspheres constructed by nanoparticles using [Co(NH3)4CO3]NO3 and their photocatalytic activity

Co3O4 hollow microspheres were successfully prepared by a template-free facile hydrothermal route at 180 °C for 6 h, employing the [Co(NH3)4CO3]NO3 complex as a new precursor. Techniques of X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), UV–visible spectroscopy, Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), and magnetic measurements were used to characterize the structure and morphology of the product. The FT-IR, XRD, Raman and EDX analyses confirmed that the obtained product is highly pure spinel-type Co3O4 phase. The SEM and TEM results showed that the obtained Co3O4 are hollow microspheres with diameter size of about 0.5–3.5 μm and an average shell thickness of approximately 50–100 nm which are composed of about 20–30 nm nanoparticles. The optical absorption spectrum of the Co3O4 hollow spheres showed two direct band gaps of 2.20 and 3.60 eV with a blue shift in comparison with previous reported values. The as-prepared Co3O4 nanostructure showed a weak ferromagnetic behaviour that could be attributed to uncompensated surface spins and/or finite-size effects. The results show that temperature and precursor play key roles on the final morphologies of Co3O4 crystals. A possible formation mechanism of Co3O4 hollow microspheres was proposed. Also, the as-prepared Co3O4 hollow microspheres show high photocatalytic activity for the degradation of methylene blue (MB) by H2O2.

Soft-template-synthesis of hollow CuO/Co3O4 composites for pseudo-capacitive electrode: A synergetic effect on electrochemical performance

Hollow CuO/Co3O4 hybrids, which inherited from its coordination polymer precursor consisting of sheets layer and nanoparticles layer composites, were synthesized and characterized by SEM, EDX, XRD and XPS. To assess its electrochemical capacitive performances, cyclic voltammetry, galvanostatic charging-discharging measurements and A.C. impedance tests were performed successively. The CuO/Co3O4 hybrids had higher capacitance and lower charge transfer resistance than bare Co3O4 nanostructures, revealing that it provided a protection layer and produced a synergistic effect due to the existence of CuO layer. The distinct synergistic effect could be further confirmed by endurance cycling tests. The capacitance of the CuO/Co3O4 hybrids was 111% retained after 500 cycles at a charging rate of 1.0Ag−1 and remained an intense growth trend after 2000 cycles at scan rate of 200mVs−1.

Morphology Engineering of Co3O4 Nanoarrays as Free-Standing Catalysts for Lithium-Oxygen Batteries.

The effective shape-controlled synthesis of Co3O4 nanoarrays on nickel foam substrates has been achieved through a simple hydrothermal strategy. When they served as the binder- and conductive-agent-free porous cathodes for nonaqueous Li-O2 batteries, they sufficiently reflect the favorable catalytic characteristic of Co3O4 and alleviate the problems of serious pore blocking and surface passivation caused by insoluble and insulating discharge products. In particular, Co3O4 rectangular nanosheets exhibit superior electrocatalytic performance comparing with Co3O4 nanowires and hexagonal nanosheets, leading to higher specific capacity and better cycling stability over 54 cycles at 100 mA g(-1), which relate to their good pore structure, large specific surface area, and highly active {112} exposed plane, effectively promoting the mass transport and reversible formation and decomposition of discharge products in the cathode. These comparisons further indicate the morphology effect of nanostructured Co3O4 on their performances as free-standing catalysts for Li-O2 batteries, which also have been proved through the further analysis of discharge products on different shapes of Co3O4 nanoarrays electrodes.

Facile Synthesis of Nanostructured Co3O4 thin Films at Low Temperature for High-Performance Pseudocapacitors

Co3O4 as a low cost, environmental friendly and nice corrosion resistant electrode material for pseudocapacitors, owns a high theoretical specific capacitance up to 3650 F g-1. However, the actual specific capacitance of Co3O4 is much lower than its theoretical value according to the present literatures. In order to improve the electrochemical performance of Co3O4 electrodes, various binder-free and self-supported Co3O4 thin films with distinct nanostructures were prepared by facile chemical bath deposition at low temperature (Figure.1). The diverse morphologies of Co3O4 thin films (3D thorn-like structure, porous nanoplates, nanoparticles and ultrathin nanosheets) were controlled by the different anions (SO4 2-, NO3 -, Cl- and CH3COO-) of cobalt sources used in synthesis procedure. Among them, the cobalt acetate derived Co3O4 thin film electrodes (A-Co3O4) exhibit the best electrochemical performances in 2 M KOH electrolyte (Figure. 2), such as a high specific capacitance (1545 F g-1) and nice cycling stability (84.6 % retention after 1000 charge-discharges at a high current density of 4 A g-1). Figure 1

Metal-Organic Frameworks (MOFs) Derived Porous Co3O4/Carbon Composites for Lithium-Air Batteries

Commercial Li-ion batteries (LIBs) cannot meet the requirements in high performance energy storage systems because of its low specific capacity (372 mAh g-1) and limited rate capability [1]. For this reason, lithium-air batteries (LABs) have been researched due to their highest theoretical energy density (11,140 Wh kg-1) [2]. Metal oxides such as MnO2, Co3O4, RuO2 and LaFeO3 have attracted as a cathode catalyst for LABs since they have efficient ORR/OER catalytic effect in LAB batteries. Among them, Cobalt oxides (Co3O4) is considered as a promising candidate of cathode catalyst due to its excellent catalytic performance properties, including their initial capacity, capacity retention, and low charging voltages (4 V) [3]. However, low electrical conductivity and agglomeration of its particles will bring about negative effect such as electrode pulverization, capacity loss and poor cycling performance. To alleviate these problems, there are many strategies have been studied. One of the major methods is fabrication of Co3O4 with nanostuctures, such as nanoparticles, nanosheets, nanowires, nanoflowers which permitting the high surface area, small dimension of these nanostructured Co3O4 [4-7]. But, the aggregation of these nanostructured Co3O4 particles and the collapse of their structure during charge-discharge test or fabrication steps still hinder LAB performances. Another competitive strategy is to synthesis hybrid materials consist of nanostructured Co3O4and carbon-based materials, such as graphene, carbon nanotubes, carbon nanofibers [8-10]. This strategy helps to release the volumetric change and improve the electrical conductivity. Recently, metal-organic frameworks (MOFs) have been investigated as a nanoporous materials because of their diverse structural topologies and tunable functionalities [11]. They have used a wide range of application in catalyst, gas separation, and energy storage with no further process. More recently, MOFs can be employed for the synthesis of porous carbon materials as the self-sacrificial templates. Herein, we synthesize mesoporous Co3O4/carbon hybrid composites for LABs using aliphatic ligand-based MOFs as the precursor. Lower thermal stability of aliphatic ligand results in interconnected porous structures and uniform distribution of Co3O4 in carbonaceous matrix. When we apply this Co3O4/carbon hybrid composite to cathode catalyst for LABs, it exhibit high capacity, good rate capability, and improved cycle performance. Reference [1] L.Z. Bai, D.L. Zhao, T.M. Zhang, W.G. Xie, J.M. Zhang, Z.M. Shen, Electrochimica Acta 107 (2013) 555–561. [2] N. Imanishi, O. Yamamoto, Materials Today. 17 (2014) 24–30 [3] C. Sun, R. Li, C. Ma, Y. Wang, Y. Ren, W. Yang, Z. Ma, J. Li, Y. Chen, Y. Kim, L. Chen, J. Mater. Chem. A 2 (2014) 7188–7196. [4] Y.N. Huang, C.C. Chen, C.H. An, C.C. Xu, Y.N. Xu, Y.J. Wang, L.F. Jiao, H.T. Yuan, Electrochimica Acta 145 (2014) 34–39. [5] L. Tian, H.L. Zou, J.X. Fu, X.F. Yang, Y. Wang, H.L. Guo, X.H. Fu, C.L. Liang, M.M. Wu, P.K. Shen, Q.M. Gao, Advanced Functional Materials 20 (2010) 617–623. [6] K. Feng, H.W. Park, X.L. Wang, D.U. Lee, Z.W. Chen, Electrochimica Acta 139 (2014) 145–151. [7] X.X. Qing, S.Q. Liu, K.L. Huang, K.Z. Lv, Y.P. Yang, Z.G. Lu, D. Fang, X.X. Liang, Electrochimica Acta 56 (2011) 4985–4991. [8] Y.B. Lou, J. Liang, Y.L. Peng, J.X. Chen, Physical Chemistry Chemical Physics 17 (2015) 8885–8893. [9] G. Huang, F.F. Zhang, X.C. Du, Y.L. Qin, D.M. Yin, L.M. Wang, ACS Nano 9 (2015) 1592–1599. [10] B.W. Huang, L. Li, Y.J. Hea, X.Z. Liao, Y.S. H, W. Zhang, Z.F. Ma, Electrochimica Acta 137 (2014) 183–189. [11] D. Zhu, F. Zheng, S. Xu, Y. Zhang and Q. Chen, Dalton Trans 44 (2015) 16946-16952 Acknowledgements “This research was supported by the MSIP(Ministry of Science, ICT and Future Planning), Korea, under the “IT Consilience Creative Program” (IITP-2015-R0346-15-1008) supervised by the IITP(Institute for Information & Communications Technology Promotion)

Cobalt Alloyed Catalyst Combined with Carbide and Carbon As Efficient Oxygen Evolution Reaction Catalysts for Alkaline Water Electrolysis

Increasing demand for clean energy have triggered researches on alternative energy sources and devices to reduce use of fossil fuel. Hydrogen has been considered as one of the most promising energy source for future due to its high energy density and no air pollutant emission. Splitting water into hydrogen and oxygen is an environmentally friendly method for producing hydrogen gas. This technology can store excess electric energy in the form of chemical bonds of hydrogen, which can resolve an issue about surplus electric power of present renewable energy systems caused by irregular energy source such as airflow and sunlight. Water electrolysis reaction is divided into two half reactions; hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). High overpotential of both HER and OER is the most significant problems to hamper reaction rate and overall efficiency of water electrolysis, especially OER has much higher overpotential than HER. Therefore, recently major efforts have been devoted to exploring active catalysts for the OER in water electrolysis cell. Among many kinds of candidate materials for OER catalyst, cobalt (Co) and various Co based materials, including nanostructured Co3O4, CoSe2, Co based perovskites, CoP, CoB and Co/N-doped carbon, have drawn much attention for use in the alkaline water electrolysis system. These Co based catalysts have high OER activity in alkaline media comparable with precious metal based catalysts, such as IrO2 and RuO2. However, previous studies has focused mainly on the exploring desirable composites for low OER overpotential without careful mechanistic study. OER mechanism on Co based catalysts and descriptors for designing more efficient catalysts have been unclear yet. Herein, we tried to modify the electronic structure of Co through the strain effect. The strain effect modifies the adsorption energy of gaseous or ionic species for OER on Co surface that can be an effective way to design an active electrocatalyst. For making a strain in the Co lattice, we alloyed Co with other transition metals, such as iron (Fe), manganese (Mn), nickel (Ni), and combined with carbide and carbon through a facile solution based process. Graphitic carbon-nitride (g-C3N4) was used as a carbon source. Synthesized alloyed catalyst exhibited higher activity and durability for OER compared with Co and ruthenium dioxide (RuO2) catalysts in alkaline media (0.1 and 1 M KOH). And, the catalysts with tensile strain have much enhanced OER activity than compressive strained one.

Amine ligand-based hydrothermal synthesis of Co3O4 nanoparticles, characterization and magnetic study

Cobalt(II,III) oxid (Co3O4) nanostructures have been successfully synthesized using [Co(NH3)6]Cl3 and [Co(en)3]Cl3 (en: ethylenediamine) as the single precursors via hydrothermal method, and CoCl2·6H2O through a facile ammonia-assisted approach. Indeed, ammine and en ligands, as well as ammonia vapor, act as the sources of hydroxide ion in the preparation of Co3O4 nanoparticles. The structure of products was confirmed by X-ray diffraction (XRD) technique and Fourier-transform infrared (FT-IR) spectroscopy and their morphologies were examined by scanning electron microscopy (SEM). The optical study of the as-prepared Co3O4 nanostructures using UV–Vis diffused reflectance spectroscopy (DRS) exhibited their semiconducting property by revealing one optical band gap in 3.3 eV. Moreover, the vibrating sample magnetometry (VSM) measurements showed a weak ferromagnetic behavior that could be attributed to uncompensated surface spins and/or finite-size effects. Further, the effects of the nature of the precursor, its concentration, temperature and reaction time on the size and morphology of the samples were studied in detail.

Morphology-dependent performance of Co3O4 via facile and controllable synthesis for methane combustion

Spinel type cobalt oxide (Co3O4) nanocrystals were controllably synthesized with different morphologies (cubical, hexagonal and flower-like) via a facile hydrothermal method. The properties of the nanostructured Co3O4 were characterized by XRD, SEM, TEM, HRTEM and XPS techniques. The performance of the catalysts in methane combustion was evaluated under lean methane atmosphere. Superior catalytic activities for methane combustion were observed over these oxides. The performances seemed to depend on their morphologies. The catalytic activities of flower-like Co3O4 and hexagonal plate-like Co3O4 were comparable to those of noble metal catalysts due to the preferred exposure of more active {111} crystal plane. In case of cubical Co3O4 the {001} plane is the dominantly exposed crystal plane. The results may provide significant insights for the development of nanostructured metal oxide catalysts for the catalytic combustion of methane.

A DFT study on adsorption behaviour of CO on Co3O4 nanostructures

The adsorption characteristics of CO on Co3O4 nanostructure on various sites are studied using density functional theory and reported. The structural stability of Co3O4 base material is studied using formation energy and vibrational analysis. The most significant parameters such as adsorption energy, energy gap, average energy gap variation and Mulliken charge transfer are taken into count to study the favourable adsorption site of CO on Co3O4 base material. Moreover, the incorporation of In atoms in Co3O4 nanostructures enhances the adsorption characteristics of CO on Co3O4 base material. The findings of the present work infer that pristine and In substituted Co3O4 nanostructures can be used to detect low concentrations of CO in the atmosphere.

Morphology-controlled fabrication of Co3O4 nanostructures and their comparative catalytic activity for oxygen evolution reaction

Rod-like, mixed rod-like and sheet-like, and sheet-like cobalt oxide (Co3O4) nanostructures were synthesized by a two-step process of microwave-hydrothermal and calcination using cobalt hydroxide carbonate as precursor, whose morphology could be controlled by adjusting the urea concentration in microwave-hydrothermal. With the increasing urea concentration, the cobalt hydroxide carbonate precursors transformed from rods to sheets, and their crystal structures changed from orthorhombic to monoclinic. After the calcination process, the cobalt hydroxide carbonate converted to Co3O4 without obvious change of their morphology. Meanwhile, a large number of mesopores appeared in the Co3O4 nanostructures. Of the three morphologies, analysis of catalytic activity for oxygen evolution reaction (OER) demonstrated that the Co3O4 nanosheets exhibited highest current density and lowest overpotential. The superior electrochemical performance of Co3O4 nanosheets might be attributed to their high surface areas and porous structure, which could efficiently accelerate electron transport and improve the catalytic activity for OER in alkaline solution.

Cobalt-Molybdenum Carbide Hybrids As Efficient Oxygen Evolution Reaction Catalysts for Alkaline Water Electrolysis

Increasing demand for clean energy have triggered researches on alternative energy sources and devices to reduce use of fossil fuel. Hydrogen has been considered as one of the most promising energy source for future due to its high energy density and no air pollutant emission. Splitting water into hydrogen and oxygen is an environmentally friendly method for producing hydrogen gas. This technology can store excess electric energy in the form of chemical bonds of hydrogen, which can resolve an issue about surplus electric power of present renewable energy systems caused by irregular energy source such as airflow and sunlight. Water electrolysis reaction is divided into two half reactions; hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). High overpotential of both HER and OER is the most significant problems to hamper reaction rate and overall efficiency of water electrolysis, especially OER has much higher overpotential than HER. Therefore, recently major efforts have been devoted to exploring active catalysts for the OER in water electrolysis cell. Among many kinds of candidate materials for OER catalyst, cobalt (Co) and various Co based materials, including nanostructured Co3O4, CoSe2, Co based perovskites, CoP, CoB and Co/N-doped carbon, have drawn much attention for use in the alkaline water electrolysis system. These Co based catalysts have low OER ovepotential in alkaline media comparable with precious metal based catalysts, such as IrO2 and RuO2. However, previous studies has focused mainly on the exploring desirable composites for high OER activity without careful mechanistic study. OER mechanism on Co based catalysts and descriptors for designing more efficient catalysts have been unclear yet. Herein, we report novel hybrid type catalysts, which composed of Co and molybdenum carbide (Mo2C), as efficient OER catalysts for alkaline water electrolysis, and evaluate the OER mechanism by investigating the effects of surface acidity of the catalysts on the OER activity in alkaline media. Mo2C has very similar electronic structure with platinum (Pt) group metal. So, it can be promising candidate as an efficient electrocatalyst for water electrolysis system. We synthesized Co-Mo2C hybrids using facile solution based process. Synthesized Co-Mo2C hybrids exhibit enhanced activity and durability compared with Co and ruthenium dioxide (RuO2) catalysts in alkaline media (0.1 and 1 M KOH). This result is ascribed to increase in surface acidity by formation of Co-Mo bimetallic surface on the Co-Mo2C hybrids. Increase in surface acidity leads to increase in hydroxide ion (OH-) adsorption on the catalyst surface, which can promote the OER kinetics in alkaline media. Fig. 1. XRD patterns of Co-Mo2C hybrids. Fig. 2. OER activities of Co-Mo2C hybrids, Co, RuO2 and Mo2C in 0.1 M KOH solution. Figure 1

Glucose-assisted synthesis of Co3O4 nanostructure with controllable morphologies from nanosheets to nanowires

Here, we develop a convenient route to obtain shape-controllable porous Co3O4 nanostructure from nanosheets to nanowires, which is realized with the assistance of additive glucose by a hydrothermal synthesis. Hydrothermal temperature, calcination temperature and additive glucose dosage significantly determine the morphologies of the final products. Upon the enhancement of additive glucose dosage, the shape of Co3O4 evolves from nanosheets in high aspect-ratio to dendritic nanowires. Meanwhile, a probable growth mechanism is proposed to explain the generation of various morphologies. Acting as electrode materials for pseudocapacitor application in 3 M KOH, the electrochemical performance of as-prepared Co3O4 nanomaterials are evaluated by cyclic voltammetry and chronopotentiometry tests. Compared with the resultant Co3O4 nanosheets materials, the obtained Co3O4 nanowires exhibit preferable pseudo-capacitive property with a higher specific capacitance and more satisfactory cycle stability. The optimal porous Co3O4 nanowire sample is prepared by heat-treatment at 300 °C with a cobalt salt/glucose mass ratio of 1:2, which exhibits a highest capacitance value of 471.8 F g−1 at 0.5 A g−1 and an excellent cycling stability with a ca. 94.8% capacitance retention after 1000 cycles at 2 A g−1.

Preparation of Co3O4 Nanostructures via a Hydrothermal- Assisted Thermal Treatment Method by Using of New Precursors

Abstract Co3O4 nanostructures have been synthesized via a hydrothermal-assisted thermal treatment process. A new complex formulated as [Co(py)2(H2O)2(NO3)2] was synthesized, and then used to prepare Co3O4 nanostructures. Cubic phase of spinel Co3O4 nanostructures with particle size of about 39 nm could be produced after calcination of the Co(OH)2 materials prepared with hydrothermal method at 160 °C for 15 h. Using of inorganic precursors decreased the time and temperature of Co3O4 preparation. The effect of pH on the morphology of the product s synthesized by hydrothermal reactions was investigated. It was found that the best morphology was achieved on pH=8, where was not prepared any precipitation. In this method, we could decrease the reaction temperature in synthetic rout to fabricate Co3O4 nanostructures. Nanostructures were characterized by SEM, TEM, X-ray diffraction (XRD), UV–visible, Fourier transformed infrared (FT-IR) spectroscopy and Nuclear magnetic resonance (1H-NMR).

Magnetic evolution in transition metal-doped Co3−x M x O4 (M = Ni, Fe, Mg and Zn) nanostructures

In this study, M (Ni, Fe, Mg, and Zn)-doped Co3O4 nanoparticles were controllably synthesized by microwave reaction method. The growth of the Co3O4 nanoparticles was induced by the transition metal ions without the addition of any surfactants. The phase and morphology of nanoparticles were analyzed through XRD and SEM analyses. The vibrational modes of metal oxides were confirmed from FTIR and Raman spectroscopic studies. Optical properties were carried out from PL study, and it confirms the presence of defect-level emissions. Vibrating sample magnetometer study revealed small ferromagnetic nature of Co3O4 nanoparticles. The results manifest that TM-doped Co3O4 nanostructures are promising materials for magnetic applications.

Nanoparticle Decorated Ultrathin Porous Nanosheets as Hierarchical Co3O4 Nanostructures for Lithium Ion Battery Anode Materials.

We report a facile synthesis of a novel cobalt oxide (Co3O4) hierarchical nanostructure, in which crystalline core-amorphous shell Co3O4 nanoparticles with a bimodal size distribution are uniformly dispersed on ultrathin Co3O4 nanosheets. When tested as anode materials for lithium ion batteries, the as-prepared Co3O4 hierarchical electrodes delivered high lithium storage properties comparing to the other Co3O4 nanostructures, including a high reversible capacity of 1053.1 mAhg−1 after 50 cycles at a current density of 0.2 C (1 C = 890 mAg−1), good cycling stability and rate capability.

Coralloid and hierarchical Co3O4 nanostructures used as supercapacitors with good cycling stability

Coralloid and hierarchical Co3O4 nanostructures were synthesized by a facile two-step approach composed of room temperature solution-phase synthesis without any surfactant and calcination of precursor. Owing to the unique structural features, the capacitance of Co3O4 could reach up to 591 F g−1 at a current density of 0.5 A g−1. Especially the cycling stability remained about 97 % after 2000 cycles at a current density of 1 A g−1. These results demonstrated that the coralloid and hierarchical Co3O4 were excellent candidates for electrochemical supercapacitor devices.

A precursor-derived morphology-controlled synthesis method for mesoporous Co3O4nanostructures towards supercapacitor application

The controlled synthesis of multifarious nanostructures is valuable for understanding the properties associated with the surface structure and for exploring potential applications. Herein, various morphological Co3O4 precursors were synthesized hydrothermally for fabricating mesoporous Co3O4 nanostructures. Importantly, the morphology, size, and crystalline phase of precursors were independently tuned by controlling the components in solution (e.g. anions, cations, and hydrolysis agents). The microstructure of Co3O4 precursors has obviously changed from porous hexagons to nanoneedles by changing the anions in solution. After calcination, as-prepared precursors were converted into mesoporous Co3O4 nanostructures, and their morphology and size were well preserved. The effect of experimental conditions on the growth of Co3O4 precursors was explored, and the corresponding growth mechanism was proposed. Moreover, the electrochemical properties of Co3O4 with different morphologies were tested. The results showed that the 3D hierarchical flower-like Co3O4 assembled by hexagonal nanosheets exhibited higher specific capacitance (327.3 F g−1 at 0.5 A g−1) with excellent retention (96.07% at 5 A g−1) after 10 000 cycles. It is believed that this anion-assisted synthetic approach can be extended to the preparation of other transition metal oxides.