Flower-like Co3O4 Research Articles

Imidazolate-mediated synthesis of hierarchical flower-like Co3O4 for the oxidation of toluene

Abstract Cobalt oxide (Co3O4) materials with specific structure have shown great potential as highly efficient catalysts in the oxidation reactions. In this work, a novel hierarchical flower-like Co3O4 was synthesized by the imidazolate-induced hydrothermal and subsequent thermolysis method. The effect of reaction parameters as well as the phase evolution of the flower-like structure was investigated in detail. For comparison, a rod-like Co3O4 was also prepared with urea under similar conditions. The morphology-dependent effect of Co3O4 towards toluene oxidation was studied. Moreover, the physicochemical properties of Co3O4 were analyzed by various characterization techniques. The flower-like Co3O4 catalyst presented a higher catalytic activity for toluene oxidation than the rod-like Co3O4, which was associated with hierarchical flower-like morphology, reactive exposed planes, abundant adsorbed oxygen species at surface and better low-temperature reducibility.

Gas sensor towards n-butanol at low temperature detection: Hierarchical flower-like Ni-doped Co3O4 based on solvent-dependent synthesis

In this work, hierarchical flower-like Ni-doped Co3O4 was synthesized via a facile one-step coprecipitation method. In the synthesis process, a series of solvent-dependent experiments were carried out to investigate the effect of ethanol/water ratio (R-E/W) on samples. With the increasing ethanol/water ratio, the doping concentration of Ni2+ increased and the microstructure evolved from micro-leaves to micro-flowers. Additionally, gas sensors based on prepared materials were fabricated to evaluate their gas sensing properties. The comparative analysis illustrated that the sensor based on 5.3 mol% Ni-doped Co3O4 microflowers (R-E/W = 3/30) presented the highest response (8.34) to 100 ppm n-butanol at low optimum temperature (165 °C), with a response/recovery time of 59/63 s, and it also exhibited excellent anti-humidity properties and long-term stability. The unique hierarchical flower-like microstructure and the optimized parameters (catalytic sites, carrier concentration, ratio of Co2+, oxygen component) caused by the doping of Ni were responsible for the improved gas sensing performance. Therefore, this work presented a simple solvent-dependent route to controllably synthesize Ni-doped Co3O4 sensing material, and the excellent gas sensing properties of the sensor based on 5.3 mol% Ni-doped Co3O4 microflowers revealed a great application prospect in detecting n-butanol.

Structural, electrochemical and optical properties of hydrothermally synthesized transition metal oxide (Co3O4, NiO, CuO) nanoflowers

In this work, structural, electrochemical and optical properties of the flower-like Co3O4, NiO and CuO nanostructures were investigated. Co3O4, NiO and CuO nanoflowers were prepared using hydrothermal method. Fourier transform infrared spectroscopy was used in the confirmation of the chemical composition of the nanostructures. X-ray diffraction (XRD) was used in the analysis of crystal structures that peaks observed in the XRD analysis confirms good crystallinity of the nanoflowers. Scanning electron microscopy analysis was used to illustrate the flower-like structure of the nanostructures. Cyclic voltammetry (CV) was used in the assessment of the electrochemical properties. It was seen that flower-like Co3O4, NiO and CuO nanostructures have enhanced electrochemical properties. Using CV results, redox reaction processes of the Co3O4, NiO and CuO nanoflowers were determined. Diffusion constants were determined and NiO nanoflowers found to have the highest diffusion constant among those. Nyquist and Bode diagrams were evaluated. Energy band gaps of Co3O4, NiO, CuO nanoflowers were calculated which were found to be 2.10 eV, 2.25 eV and 3.71 eV, respectively.

Facile synthesis of magnetic hierarchical flower-like Co3O4 spheres: Mechanism, excellent tetra-enzyme mimics and their colorimetric biosensing applications

Magnetic hierarchical flower-like Co3O4 spheres (Co3O4 nanoflowers) were facilely prepared via one-step surfactant-free and template-free wet chemical route at room temperature. The formation mechanism of Co3O4 nanoflowers was explored. The as-prepared Co3O4 nanoflowers exhibited excellent tetra-enzyme mimetic activities, including oxidase-like, peroxidase-like, catalase-like and superoxide dismutase (SOD)-like activity. The catalytic mechanism of the Co3O4 nanoflowers was studied in detail. The oxidase-like catalytic activity of Co3O4 nanoflowers was derived from the inherent oxygen vacancies of Co3O4, while the peroxidase-like catalytic activity originated from the •OH radical generated by hydrogen peroxide (H2O2). Only one specific enzyme mimics reaction with Co3O4 nanoflowers can be obtained by inhibiting specifically other nanozymes via varying pH, adding appropriate scavengers or selecting its specific substrate. Further, the steady-state kinetic and catalytic performance of the oxidase-, peroxidase- and catalase mimics of Co3O4 nanoflowers were studied. Based on the oxidase-like and peroxidase-like activities of Co3O4 nanoflowers, bifunctional colorimetric sensing platforms were constructed for the sensitive detection of acid phosphatase (ACP) with the linear range of 0.1–25 U L-1 and H2O2 with the linear range of 4–400 μM. Further, it is capable of detecting ACP in serum samples and H2O2 in water samples, respectively. Thus, the tetra-enzyme mimetic Co3O4 nanoflowers show broad prospects in the fields of biosensors, tumor therapy, environmental monitoring and biocatalysis.

Hierarchical 3D micro flower-like Co3O4 structures for NO2 detection at room temperature

Micro flowers-like Co3O4 structures have been synthesized by a low-cost single-step hydrothermal route. The XRD pattern and Raman spectra confirmed the cubic crystal structure of Co3O4 and FESEM images displayed that the synthesized Co3O4 attained a flower-like morphology. The higher sensor response ∼22% was recorded for hierarchical 3D flower-like Co3O4 structures at room temperature for 60 ppm NO2 exposure with response (recovery) time of the order of ∼25 (70) s respectively. The flower-like Co3O4 structures attained a reversible, highly stable and selective response towards NO2 at room temperature.

Three-Dimensional Precursor-Derived Synthesis of Co3O4 Towards High Electrochemical Performance

Three-dimensional (3D) cobalt oxide (Co3O4) flowers with different shapes were prepared by a facile hydrothermal synthesis. The morphology of Co3O4 precursors has adjusted obviously from acicular shapes to acicular-sheet-like flowers and then to sheet-like flowers by changing reaction temperature and solution concentration. After annealing, as-prepared precursors were converted into 3D flower-like Co3O4 samples and their morphology and sizes were well preserved. The effect of experimental conditions on growth of Co3O4 precursors was explored and the growth mechanism was proposed. Moreover, the electrochemical properties of various Co3O4 with different shapes were tested. The result of electrochemical investigation indicates that 3D flower-like Co3O4 assembled by sheets exhibited high capacitance and excellent cycling performance.

Aggregation-Morphology-Dependent Electrochemical Performance of Co3O4 Anode Materials for Lithium-Ion Batteries.

The aggregation morphology of anode materials plays a vital role in achieving high performance lithium-ion batteries. Herein, Co3O4 anode materials with different aggregation morphologies were successfully prepared by modulating the morphology of precursors with different cobalt sources by the mild coprecipitation method. The fabricated Co3O4 can be flower-like, spherical, irregular, and urchin-like. Detailed investigation on the electrochemical performance demonstrated that flower-like Co3O4 consisting of nanorods exhibited superior performance. The reversible capacity maintained 910.7 mAh·g−1 at 500 mA·g−1 and 717 mAh·g−1 at 1000 mA·g−1 after 500 cycles. The cyclic stability was greatly enhanced, with a capacity retention rate of 92.7% at 500 mA·g−1 and 78.27% at 1000 mA·g−1 after 500 cycles. Electrochemical performance in long-term storage and high temperature conditions was still excellent. The unique aggregation morphology of flower-like Co3O4 yielded a reduction of charge-transfer resistance and stabilization of electrode structure compared with other aggregation morphologies.

Flower-like Co3O4 microstrips embedded in Co foam as a binder-free electrocatalyst for oxygen evolution reaction

Designing appropriate oxygen evolution reaction (OER) electrocatalysts to meet the requirements of high efficiency, long-term durability, and low cost remains the challenge for scientific community. Cobalt oxide (Co3O4) has been proven as a promising candidate for OER with attractive activity and stability in alkaline media. In this study, flower-like Co3O4 microstrips have been successfully prepared and directly embedded in Co foam (denoted as Co3O4@Co foam) by a green and facile two-step strategy including hydrothermal treatment and subsequent annealing process under relatively low temperatures. It demonstrates that the OER performance of the Co3O4@Co foam electrode can rival to the commercial RuO2 on glassy carbon electrode. The Co3O4@Co foam electrode displays high OER activity with a low overpotential of 273 mV at a current density of 10 mA cm−2, and a low Tafel slope of 61.8 mV dec−1. The flower-like Co3O4 microstrips greatly increase the active surface area to expose more active sites, and the directly growth of Co3O4 microstrips on Co foam with intimate contact improves the electron transport and ensures the stability of the Co3O4@Co foam electrode.

Glucose-assisted synthesis of hierarchical flower-like Co3O4 nanostructures assembled by porous nanosheets for enhanced acetone sensing

Ultrathin Co3O4 nanosheets are excellent candidate materials for high performance chemiresistive gas sensors. However, the restacking and aggregation of nanosheets during sensor fabrication greatly impact the sensing response. In this work, by adding the structure-directing agent of glucose, hierarchical flower-like Co3O4 nanostructures assembled by porous nanosheets were synthesized through hydrothermal method with subsequent calcination treatment to further improve the sensing performance. The fabricated hierarchical flower-like Co3O4 sensor exhibited the highest response of 48.1 toward 100 ppm acetone at 130 °C, which was 7.2 times higher than the Co3O4 microplates synthesized without glucose. The excellent long-term stability and selectivity of gas sensors were further validated and the theoretical limit of detection was experimentally calculated to be as low as 200 ppb. Flower-like Co3O4 nanostructures for acetone gas sensor with good performance provide a promising candidate to fabricate high performance gas sensor for safety monitoring and health care.

Synthesis and characterization of LiFe0.5Mn0.3Co0.2PO4/C composite material for high-voltage Li-ion battery application

A LiFe0.5Mn0.3Co0.2PO4/C composite cathode material was prepared using a solid-state ball-milling method. The flower-like Co3O4 precursor was prepared by hydrothermal method and used to improve the electrochemical properties of composite material. The galvanostatic charge–discharge profile is performed in the potential range of 2–5 V by using different electrolyte compositions with/without 1 wt% trimethyl boroxane (TMB) additive at various C rates. The highest discharge capacities of the composite material were 150.42 mAh g−1 at 0.1C and 120 mAh g−1 at 1C in LiPF6+1 wt%TMB in EC:EMC (1:2, v/v). In addition, the excellent cycle-life was observed at 0.1C and 1C rate for 30 and 100 cycles with the charge retention of 97.7% and 73%, respectively. These appreciable results were obtained due to the carbon coating layer and highly active composite material. The thickness of cathode electrolyte interphase layer on composite electrode is ca. 3 nm which was measured by secondary ion mass spectroscopy. And also, we found that the B element on interphase layer that acts as F-scavenger to reduce the amount of LiF formation over cathode interphase layer. As a result, it can markedly reduce the charge transfer resistance and improve the electrochemical performance for long-term cycling.

ZIF-67-derived Co3O4 micro/nano composite structures for efficient photocatalytic degradation

Flowerlike ZIF-67 micro/nano composite structures were developed by the evolution of ZIF-67 rhombododecahedrons ZIF-67(r) via facile ion-assistant solvothermal treatment. The morphology evolution of ZIF-67 with time-on-stream was studied. The flowerlike Co3O4 micro/nano composite were formed under calcination at relatively low temperature. The flowerlike Co3O4 micro/nano composite structures showed good catalytic properties for photocatalytic degradation of RhB (83.2%), higher than that of Co3O4(p) (69.7%) and Co3O4(r) (75.7%) after 90 min irradiation.

Synthesis of hierarchical flower-like Co3O4 superstructure and its excellent catalytic property for ammonium perchlorate decomposition

Hierarchical flower-like cobalt tetroxide (Co3O4) was successfully synthesized via a facile precipitation method in combination with heat treatment of the cobalt oxalate precursor. The samples were systematically characterized by thermo gravimetric analysis and derivative thermo gravimetric analysis (TGA-DTG), X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and N2 adsorption-desorption measurements. The results indicate that the as-fabricated Co3O4 exhibits uniform flower-like morphologies with diameters of 8–12 μm, which are constructed by one-dimensional nanowires. Furthermore, catalytic effect of this hierarchical porous Co3O4 on ammonium perchlorate (AP) pyrolysis was investigated using differential scanning calorimetry (DSC) techniques. It is found that the pyrolysis temperature of AP shifts 142 °C downward with a 2 wt% addition content of Co3O4. Meanwhile, the addition of Co3O4 results in a dramatic reduction of the apparent activation energy of AP pyrolysis from 216 kJ mol−1 to 152 kJ mol−1, determined by the Kissinger correlation. The results endorse this material as a potential catalyst in AP decomposition.

Advanced flower-like Co3O4 with ultrathin nanosheets and 3D rGO aerogels as double ion-buffering reservoirs for asymmetric supercapacitors

An advanced flower-like DBS-Co3O4 hierarchical microspheres with specific surface as electrochemical active sites have been synthesized from a novel DBS-intercalated Co(OH)2 (DBS-Co(OH)2) flower spheres with atomically ultrathin Co(OH)2 nanosheets. The hierarchical DBS-Co3O4 flower microspheres exhibit specific capacitance value of 1104.4 F g-1 at a current density of 0.5 A g−1 in 6 M KOH solution. Meanwhile, the 3D rGO aerogels are prepared by a facile method as negative electrode materials, and the specific capacitance of 213.3 F g−1 can be achieved at a current density of 2 A g−1. Therefore, both the DBS-Co3O4 microspheres with opened hierarchical honeycomb-like structures and 3D rGO aerogels with an interconnected pore network structures can be filled with electrolyte ions as double “ion-buffering reservoirs” in the charge-discharge process. Hence, the asymmetric supercapacitors of the double “ion-buffering reservoirs” are fabricated with the DBS-Co3O4 as positive electrode of promising Faradaic pseudocapacitors materials and the 3D rGO aerogels as the negative electrode of electrical double-layer capacitors materials, exhibiting a high energy density of 25.5 Wh kg−1 at the power density of 400 kW kg−1 with excellent cycling performance.

Hierarchical three-dimensional flower-like Co3O4 architectures with a mesocrystal structure as high capacity anode materials for long-lived lithium-ion batteries

In this work, we rationally design a high-capacity electrode based on three-dimensional (3D) hierarchical Co3O4 flower-like architectures with a mesocrystal nanostructure. The specific combination of the micro-sized 3D hierarchical architecture and the mesocrystal structure with a high porosity and single crystal-like nature can address the capacity fading and cycling stability as presented in many conversion electrodes for lithium-ion batteries. The hierarchical 3D flower-like Co3O4 architecture accommodates the volume change and mitigates mechanical stress during the lithiation–delithiation processes, and the mesocrystal structure provides extra lithium-ion storage and electron/ion transport paths. The achieved hierarchical 3D Co3O4 flower-like architectures with a mesocrystal nanostructure exhibit a high reversible capacity of 920 mA·h·g−1 after 800 cycles at 1.12 C (1 C = 890 mA·h·g−1), improved rate performance, and cycling stability. The finding in this work offers a new perspective for designing advanced and long-lived lithium-ion batteries.

Facile synthesis of mesoporous Co3O4 nanoflowers for catalytic combustion of ventilation air methane

Flower-like Co3O4 hierarchical microspheres composed of self-assembled porous nanoplates were prepared by employing Pluronic F127 block-copolymer as template. The samples were characterized by powder X-ray diffraction(PXRD), scanning/transmission electron microscopy(SEM/TEM), and nitrogen adsorption-desorption at 77 K. The results show that the catalytic activity of Co3O4 nanoflowers for the combustion of ventilation air methane is higher than that of commercial Co3O4. The superior catalytic performance of this material can be related to its dominantly exposed {112} crystal planes and higher content of surface Co3+.

Asymmetric supercapacitors utilizing highly porous metal-organic framework derived Co3O4 nanosheets grown on Ni foam and polyaniline hydrogel derived N-doped nanocarbon electrode materials

In the present work, asymmetric supercapacitors (ASCs) are assembled using a highly conductive N-doped nanocarbon (NDC) material derived from a polyaniline hydrogel as a cathode, and Ni foam covered with flower-like Co3O4 nanosheets (Co3O4-Ni) prepared from a zeolitic imidazolate metal-organic framework as a single precursor serves as a high gravimetric capacitance anode. At a current of 0.2 A g−1, the Co3O4-Ni electrode provides a gravimetric capacitance of 637.7 F g−1, and the NDC electrode provides a gravimetric capacitance of 359.6 F g−1. The ASC assembled with an optimal active material loading operates within a wide potential window of 0–1.1 V, and provides a high areal capacitance of 25.7 mF cm−2. The proposed ASC represents a promising strategy for designing high-performance supercapacitors.

Porous layer assembled hierarchical Co3O4 as anode materials for lithium-ion batteries

The flower-like Co3O4 particles with three-dimensional structure have been achieved by inheriting the flower-like framework of β-Co(OH)2 particles fabricated by a facile solvothermal method without any surfactant. The obtained Co3O4 microflower, which was composed of large amounts of self-assembled porous ultrathin nanosheets, exhibited excellent electrochemical performances in terms of high specific capacity and good cycle stability when being evaluated as anode materials for lithium-ion battery. Specifically, a high reversible capacity of above 1100 mA h g−1 was achieved after 50 cycles at the current density of 296 mA g−1. Hierarchical flower-like structure with mesoporous was considered as providing more active sites for Li+ insertion and paths for transport of Li+, which led to faster lithium-ion diffusion. Co3O4 porous flower-like nanostructures possessed significant potential application in energy storage systems.

Enhanced oxygen reduction reaction in air-cathode microbial fuel cells using flower-like Co3O4 as an efficient cathode catalyst

In this study, the potential of mesoporous flower-like Co3O4 is investigated for the application of oxygen reduction reaction (ORR) in aqueous air-cathode microbial fuel cell (MFC). The flower-like Co3O4 was prepared by a hydrothermal route. The X-ray photoelectron spectroscopy results suggested that flower-like Co3O4 contained positively charged ions i.e., Co2+/Co3+ on its surface that probably acted as ORR active sites. The electrochemical tests demonstrated that flower-like Co3O4 enhanced the electrocatalytic activity of the cathode significantly as the onset potentials obtained in cyclic voltammetry and linear sweep voltammetry were more positive than the bare cathode. Besides, Tafel plots showed that Co3O4 increased the electron transfer kinetics and achieved an exchange current density of 2.46 A/m2, which was ∼30% higher than bare cathode. Subsequently, this improved ORR activity increased the power output in the MFC and a maximum power density of 248 mW/m2 was achieved, which was 6.3 times higher than the bare cathode. The higher ORR activity and improved electric output in the MFC could be attributed to the excellent electrocatalytic activity of Co2+/Co3+ and mesoporous nature of flower-like Co3O4 that exposed extra active sites for oxygen molecules on the cathode surface.

Flower-like binary cobalt-nickel oxide with high performance for supercapacitor electrode via cathodic electrodeposition

Flower-like cobalt-nickel binary oxide was prepared as electrode materials for supercapacitors via cathodic electrodeposition. The deposition experiments were performed at the constant potential of −1 V on Ni foam substrate without any surfactant and template. Scanning electron microscopy (SEM) images indicate that the flower-like Co3O4 nano-sheet layers are homogeneously distributed on NiO layer with length of about 200 nm. The as-prepared Co3O4-NiO exhibits a specific capacitance of 687.5 F g−1 at the current density of 0.5 A g−1 (vs. Ag/AgCl). Meanwhile, they show excellent rate performance (94% retained from 0.5 A g−1 to 10 A g−1) and outstanding cycle life (92% retained after 2500 cycles). These results indicate that the flower-like cobalt-nickel binary oxide electrode deposited on Ni foam can be considered as a promising candidate for the supercapacitor electrode materials.

Facile synthesis of three dimensional flower-like Co3O4@MnO2 core-shell microspheres as high-performance electrode materials for supercapacitors

In this work, we reported the synthesis of three dimensional flower-like Co3O4@MnO2 core-shell microspheres by a controllable two-step reaction. Flower-like Co3O4 microspheres cores were firstly built from the self-assembly of Co3O4 nanosheets, on which MnO2 nanosheets shells were subsequently grown through the hydrothermal decomposition of KMnO4. The MnO2 nanosheets shells were found to increase the electrochemical active sites and allow faster redox reaction kinetics. Based on these advantages, when used as an electrode for supercapacitors, the prepared flower-like Co3O4@MnO2 core-shell composite electrode demonstrated a significantly enhanced specific capacitance (671Fg−1 at 1Ag−1) as well as improved rate capability (84% retention at 10Ag−1) compared with the pristine flower-like Co3O4 electrode. Moreover, the optimized asymmetric supercapacitor device based on the flower-like Co3O4@MnO2//active carbon exhibited a high energy density of 34.1Whkg−1 at a power density of 750Wkg−1, meaning its great potential application for energy storage devices.