Co3O4 Nanospheres Research Articles

Low temperature CO oxidation and CH4 combustion over Co3O4 nanosheets

Co3O4 nanomaterials were synthesized by hydrothermal method and were applied for low temperature CO oxidation and methane combustion. The addition of ethylene glycol and its concentration significantly influenced the size and shape of the Co3O4 oxides. Nanosheets of Co3O4 were synthesized in ethylene glycol solution and nanospheres were formed in water. The activity of oxygen species in the nanosheets and nanospheres were characterized by hydrogen/methane programmed reduction, oxygen programmed desorption and XPS. The results showed that the Co3O4 nanosheets exhibited more active oxygen species than the Co3O4 nanospheres, leading to the higher activity in the oxidative reactions. The study demonstrated the importance of active oxygen species in Co3O4 catalysts to achieve high catalytic performance towards the carbon monoxide and methane elimination at low temperatures.

Morphology-controlled synthesis of porous Co3O4 nanostructures by in-situ dealloying and oxidation route for application in supercapacitors

Synthesis of electrode materials with desirable morphology and size for supercapacitor applications is an important and challenging research topic. In this work, four types of Co3O4 nanostructures, namely hexagonal-shaped nanosheets, nanoflake arrays, nanoflowers and oval-shaped nanospheres were synthesized via a facile in-situ dealloying method. Applied as electrode material for supercapacitiors, the Co3O4 nanospheres achieves highest areal capacitance of 16.58 F cm−2 at current density of 10 mA cm−2. The Co3O4 nanoflowers exhibited promising capacitive properties and excellent retention. Its areal capacitance can reach 9.27 F cm−2 at the current density of 10 mA cm−2 and retain 98.5% of its initial capacitance at the current density of mA cm−2 after 1000 charge–discharge cycles. This work could provide a deeper understanding of the morphology effect on the supercapacitive performance, and also suggests the importance of rational design and synthesis of electrode materials with desirable morphology and size for high performance supercapacitor applications.

One‐Step Synthesis of Co3O4/Graphene Aerogels and Their All‐Solid‐State Asymmetric Supercapacitor

A facile one‐step hydrothermal strategy has been developed to prepare 3D porous Co3O4/graphene aerogel (Co3O4/GA). Due to the combination of a highly interconnected 3D network of GA and porous Co3O4 nanospheres, the resulting Co3O4/GA electrode exhibits exceptional electrical conductivity and pseudocapacitance, making it an excellent material for energy‐storage devices. The Co3O4/GA composites possess a high specific surface area of 127 m2 g–1 and a broad pore‐size distribution of 1–110 nm. The presence of porous Co3O4 is found to be remarkably effective in enhancing the specific capacitance of the composite aerogel, up to 1512.7 F g–1 at 1 A g–1. Furthermore, the combination of the two aerogel electrodes with a LiOH/PVA‐gel electrolyte endows our all‐solid‐state asymmetric supercapacitor (SASC) of Co3O4/GA//GA with a stable cycling performance in the high‐voltage region of 0–1.6 V (capacitance retention of 81.5 % after 5000 continuous charge/discharge cycles), and superior electrochemical performance, with an energy density of 68.1 W h kg–1 at a power density of 982.9 W kg–1, which is even higher than the maximum energy density of 58.7 W h kg–1 at a power density of 1209.4 W kg–1 of this ASC in a liquid‐state electrolyte. These results indicate that Co3O4/GA could be a potential candidate in the field of supercapacitors.

P-type Co3O4 nanomaterials-based gas sensor: Preparation and acetone sensing performance

Uniform Co3O4 nanocubes have been prepared via an effective one-pot hydrothermal method. Sphere-shape Co3O4 nanomaterials can be synthesized by varying the concentration of Co(NO3)2·6H2O and NaOH without the utilization of surfactants. Co3O4 nanocubes and Co3O4 nanospheres show regular geometry structure with diameters of 250nm and 300nm, respectively. Gas sensors based on different Co3O4 nanostructured are fabricated and used for investigating acetone sensing performances. The response of Co3O4 nanocubes based sensor to 500ppm acetone is 4.88 at 240°C, which is higher than that of Co3O4 nanospheres. In addition, sensors based on Co3O4 nanocubes not only exhibit a high response but also have a rapid response time (2s) and recovery process (5s) to acetone. The enhanced sensing performances to acetone can be attributed to the effective catalytic activity of Co2+ at special low-index crystal facets. This finding demonstrates the shape-related synthesis of nanomaterials can be an effective way of designing high performance gas sensor, and also provides a new insight into gas-sensing mechanism.

Synthesis of 3D Flower‐like Nanocomposites of Nitrogen‐Doped Carbon Nanosheets Embedded with Hollow Cobalt(II,III) Oxide Nanospheres for Lithium Storage

AbstractDespite a high theoretical specific capacity (890 mA h g−1) as an anode material for Li‐ion batteries, Co3O4 has not been used in practice due to its inferior mechanical stability and poor electrical conductivity. Herein, we synthesized three‐dimensional (3D) flower‐like nanocomposites consisting of nitrogen‐doped carbon nanosheets decorated with hollow Co3O4 nanospheres (H‐Co3O4@N‐CNSs) with an ultrahigh loading mass (83 wt %) of Co3O4. The H‐Co3O4@N‐CNSs exhibited excellent performance of 750 mA h g−1 at 500 mA g−1 and 700 mA h g−1 at 1000 mA g−1 after 400 cycles and a high capacity retention rate of 93.75 % at 500 mA g−1. This excellent electrochemical performance was attributed to a synergistic effect between the hollow Co3O4 nanospheres, the N‐doped carbon nanosheets, and the pores between adjacent carbon nanosheets. Our suggested fabrication strategy for creating a hierarchical structure has great potential for the design of high‐performance anode materials.

Superior electrochemical properties of SiO2-doped Co3O4 hollow nanospheres obtained through nanoscale Kirkendall diffusion for lithium-ion batteries

Hollow SiO2-doped Co3O4 (SiCo3O4) nanospheres with excellent Li-ion storage properties were synthesized via flame spray pyrolysis by applying a nanoscale Kirkendall diffusion process. A solid SiO2-doped CoO (filled SiCoO) nanopowder was prepared through this process, and then it was transformed into hollow SiCo3O4 nanopowder by way of a core-shell-structured CoSiO2 (filled Co@SiCoO) composite nanopowder. In addition, the direct oxidation of the filled SiCoO nanopowder at 300 °C under an air atmosphere resulted in the formation of a solid SiO2-doped Co3O4 (filled SiCo3O4) nanopowder. At a high current density of 2 A g−1, the hollow SiCo3O4 nanospheres exhibited a 150th-cycle discharge capacity of 971 mA h g−1 and capacity retention of 99.5%, which was measured relative to the second cycle. However, the corresponding capacity retentions of the filled SiCoO and SiCo3O4 nanopowders were only 82.2% and 71.5%, respectively. The high structural stability during cycling and high Li-ion conductivity, which are caused by the hollow structure, are responsible for the excellent Li-ion storage properties of the hollow SiCo3O4 nanospheres obtained through nanoscale Kirkendall diffusion.

Comprehensive Study of an Earth-Abundant Bifunctional 3D Electrode for Efficient Water Electrolysis in Alkaline Medium.

We report efficient electrolysis of both water-splitting half reactions in the same medium by a bifunctional 3D electrode comprising Co3O4 nanospheres nucleated on the surface of nitrogen-doped carbon nanotubes (NCNTs) that in turn are grown on conductive carbon paper (CP). The resulting electrode exhibits high stability and large electrochemical activity for both oxygen and hydrogen evolution reactions (OER and HER). We obtain a current density of 10 mA/cm(2) in 0.1 M KOH solution at overpotentials of only 0.47 and 0.38 V for OER and HER, respectively. Additionally, the experimental observations are understood and supported by analyzing the Co3O4:NCNT and NCNT:CP interfaces by ab initio calculations. Both the experimental and the theoretical studies indicate that firm and well-established interfaces along the electrode play a crucial role on the stability and electrochemical activity for both OER and HER.

Hybrid of porous cobalt oxide nanospheres and nitrogen-doped graphene for applications in lithium-ion batteries and oxygen reduction reaction

A new single-source precursor has been developed from the hydrothermal reaction of graphite oxide (GO), melamine resin (MR) monomers, and CoCl2 to prepare a sandwich-like hybrid of ultrathin nitrogen-doped graphene (NG) sheets and porous Co3O4 nanospheres (Co3O4/NG). This unique structure endows the Co3O4/NG hybrid with large surface area and enhanced electrochemical performances as both anode material for Li-ion batteries and electrocatalyst for oxygen reduction reaction (ORR). As an anode material, it exhibits high reversible capacity, excellent cycling stability and rate performance (1236 and 489 mAh g−1 over 200 cycles at 0.1C and 2C, respectively; 371 mAh g−1 at 5C). As an ORR electrocatalyst, it shows superior catalytic activity and high selectivity for the four-electron reduction pathway compared to the bare Co3O4 and NG alone. Moreover, the Co3O4/NG hybrid is insensitive to methanol, and is much more stable than Pt/C catalyst over long term operation.

Cu2+ ions inducing the growth of porous Co3O4 nanospheres as high-capacity supercapacitors

Porous Co3O4 nanospheres were successfully synthesized using Cu2+ ions as structure-inducing agents, which exhibit good capacitive properties.

Hollow Co3O4 nanospheres for the direct electrochemistry and electrocatalysis of hemoglobin with an ionic liquid as an enhancer

Hollow Co3O4 nanospheres were synthesized via a hydrothermal process and applied to fabricate a redox protein-based sensing platform.

Synthesis and calcinations effects on size analysis of Co3O4 nanospheres and their superparamagnetic behaviors

Co 3 O 4 nanoparticles were synthesized by microwave process using citric acid as a capping agent. Interestingly, when calcination temperature is increased to 600 °C, nanoparticles were formed into nanospheres of about less than 20 nm observed from SEM images. The particles were aggregated into bigger size of about 65 nm when the calcination temperature was increased to 800 °C. The samples calcined at 400 °C and 800 °C show superparamagnetism above the blocking temperature and the existence of small ferromagnetism is observed when T < T b . At 600 °C, sphere like Co 3 O 4 particles exhibit complete super paramagnetism from 5 K to 300 K. These results indicated that the structural, optical and magnetic properties may be tuned by choosing appropriate calcination temperature of the sample. • Spinel Co 3 O 4 nanoparticles are synthesized by fast and effective microwave route. • Tuning of size and morphology of Co 3 O 4 was investigated by calcination temperatures. • Well defined sphere morphology was achieved for the calcinations of 600 °C. • The prepared Co 3 O 4 was modified into moderate size of less than 20 nm for 600 °C. • The 600 °C calcined sample completely obeys superparamagnetism nature from 5K–300K.

Porous nano-structured Co3O4 anode materials generated from coordination-driven self-assembled aggregates for advanced lithium ion batteries.

A simple and scalable coordination-derived method for the synthesis of porous Co3O4 hollow nanospheres is described here. The initially formed coordination-driven self-assembled aggregates (CDSAAs) could act as the precursor followed by calcination treatment. Then the porous hollow Co3O4 nanospheres are obtained, in which the primary Co3O4 nanoparticles are inter-dispersed. When the nanospheres are used as anode materials for lithium storage, they show excellent coulombic efficiency, high lithium storage capacity and superior cycling performance. In view of the facile synthesis and excellent electrochemical performance obtained, this protocol to fabricate special porous hollow frameworks could be further extended to other metal oxides and is expected to improve the practicality of superior cycle life anode materials with large volume excursions for the development of the next generation of LIBs.

Precursor-directed formation of hollow Co3O4 nanospheres exhibiting superior lithium storage properties

Hollow Co3O4 nanospheres, assembled by nanoplatelets, have been obtained by annealing urchin-like hollow Co(CO3)0.5(OH)·0.11H2O nanospheres synthesized at room temperature. The as-obtained hollow Co3O4 nanospheres exhibit greatly enhanced lithium storage properties as anode materials for lithium-ion batteries.

Controllable synthesis of core–shell Co@CoO nanocomposites with a superior performance as an anode material for lithium-ion batteries

The present study reports a straightforward template-free route for the synthesis of core–shell Co@CoO nanocomposites by the controlled reduction of Co3O4 nanospheres. The target Co@CoO nanoparticles consist of an unsealed hollow porous CoO shell with a metal Co core, in which the outer porous CoO shell as the active anode material can be fully in contact with the electrolyte. The void within the particles provides a remarkable buffer to tolerate volume changes of the electrode materials during the insertion and extraction of lithium. Most importantly, the inner nanosized metal Co core gives a new impetus to the reversible decomposition of Li2O due to its catalytic activity. Furthermore, the exposed metal Co portion outside the nanoshells provides a favorable electrical contact between adjacent particles and greatly improves the efficiency of the electronic connection between the active material and the current collector. The Co@CoO nanocomposite maintains an excellent reversible capacity over 800 mA h g−1 after 50 cycles with an initial coulombic efficiency of 74.2%, which is much higher than that of pure CoO (67.8%). This superior electrochemical performance is closely related to the unique composition and nanostructure of the electrode material. Notably, it is the first case of a hybrid-structured Co@CoO anode material derived from the reduction process from oxide precursors. Such a conclusion may be advantageously used to guide the design of a wide range of nanostructured metal oxides.