Co3O4 Nanowire Arrays Research Articles

Electrochemical sensing of glucose by carbon cloth-supported Co3O4/PbO2 core-shell nanorod arrays

A novel electrochemical sensor for the detection of glucose was constructed based on the use of Co3O4/PbO2 core-shell nanorod arrays as electrocatalysts. In this paper the Co3O4/PbO2 core-shell nanorod arrays grow directly on a flexible carbon cloth substrate by the combination of hydrothermal synthesis and electrochemical deposition methods. The as-prepared hierarchical nanocomposites show the structural characteristics of nanowire core and nanoparticle shell. The carbon cloth-supported Co3O4/PbO2 nanorod array electrode exhibits higher sensitivity (460.3μAmM−1cm−2 in the range from 5μM to 1.2mM) and lower detection limit (0.31μM (S/N=3)) than the carbon cloth-supported Co3O4 nanowire array electrode. Both the three-dimensional network of carbon cloth substrate and the hierarchical nanostructure of binary Co3O4/PbO2 composites make such an electrode have high electrocatalytic activity towards the glucose oxidation. Due to the excellent sensitivity, repeatability and anti-interference ability, the carbon cloth-supported Co3O4/PbO2 nanorod arrays will be the promising materials for fabricating practical non-enzymatic glucose sensors.

Ternary core/shell structure of Co3O4/NiO/C nanowire arrays as high-performance anode material for Li-ion battery

Self-supported core/shell nanowire arrays are highly desirable for designing high-performance electrochemical energy storage devices. Herein, we report self-supported ternary core/shell nanowire arrays of Co3O4/NiO/C on the nickel foam with the help of hydrothermal synthesis, chemical bath deposition and annealing carbonation methods. As an anode material for lithium ion batteries, the Co3O4/NiO/C core/shell nanowire arrays exhibit excellent electrochemical performances with lower polarization, higher capacity, improved cycle life and better high-rate capability than the pure Co3O4 nanowire arrays and single NiO nanoflake arrays. The enhanced electrochemical properties are mainly ascribed to the core/shell nanowire architecture with potential synergistic contribution such as improved mechanical stability and enhanced conductivity as well as faster ion/electron transfer.

Exploring the local structure of Fe in Co3−xFexO4 electrode by XAFS

Determining the local structure of dopant atoms is critical for understanding the mechanism of enhanced photoelectrochemical activity in doping-modified semiconductor photoelectrodes. Here, we have synthesized Fe-doped Co3O4 nanowire arrays photoanodes on Ti foil and detected the local structure and role of Fe atoms via X-ray absorption fine structure (XAFS) spectra and electrochemical impedance measurements. The XAFS analysis shows that Fe dopants are doped into Co3O4 and occupy the octahedral sites. Coupling with Co atoms at octahedral sites, Fe dopants significantly increases the carrier density by an order of magnitude and results in a five-fold increase of the photoconversion efficiency. These results provide some guidance for optimization of Co3O4 as a practical photoanode material.

Pd doped Co3O4 nanowire array as the H2O2 electroreduction catalyst

Co3O4 nanowire arrays freely standing on Ti foil (Co3O4/Ti) are prepared via a template-free growth method. Pd nanoparticles are electrochemically deposited by cyclic voltammetry method on Co3O4 nanowires to obtain a nanocomposite electrode (Pd@Co3O4/Ti). The morphology and phase structure of the Pd@Co3O4/Ti electrode are characterized by scanning electron microscope and X-ray diffraction spectrometer. The catalytic activity of H2O2 electroreduction on the Pd@Co3O4/Ti electrode in alkaline medium is evaluated by means of linear scan voltammetry and chronoamperometry. The Pd@Co3O4/Ti electrode exhibits high performance and good stability to H2O2 electroreduction with a current density of 145.8 mA cm−2 at −0.4 V in 3.0 mol dm−3 KOH and 0.4 mol dm−3 H2O2 electrolyte, which outperforms the bare Co3O4 nanowire arrays without Pd doping.

Hierarchical Mo-decorated Co3O4 nanowire arrays on Ni foam substrates for advanced electrochemical capacitors

Herein, we report the synthesis of hierarchical small quantity Mo-decorated Co3O4 nanowire arrays on nickel foam substrates by a powerful two-step solution-based method. The “oriented attachment” and “self-assembly” crystal growth mechanisms are proposed to discuss the growth of the Mo-decorated Co3O4 heterostructures. This heterostructure material with a high specific surface areas provides an extraordinarily high area capacitance of 3.5 F cm−2 at a current density of 17 mA cm−2 (∼2000 F g−1 at a current density of 10 A g−1) in the initial cycles, compared with a bare Co3O4 nanowire array electrode with 2.2 F cm−2 at 17 mA cm−2 (∼1257 F g−1 at 10 A g−1), exhibiting a significant increase in the capacitance of around 60%. When the current density of the hybrid array is increased by 20 times (1.7 to 34 mA cm−2), more than 73% of the specific capacitance can be maintained, which shows a good rate performance. Such a growth approach offers a versatile technique for the design and synthesis of metal oxide hierarchical nanoarrays for electrochemical energy storage applications.

Ag Doped Co<sub>3</sub>O<sub>4</sub> Nanowire Arrays as an Electrode Material for Electrochemical Capacitors

Co3O4 nanowire arrays freely standing on nickel foam are prepared via a template-free growth method，and it is doped by Ag via electrodeposition method (denoted as NWA-Ag/Co3O4，NWA represents Nanowire Arrays). The morphology of NWA-Ag/Co3O4 is examined by scanning electron microscopy. The phase structure of the NWA-Ag/Co3O4 electrode is characterized by X-ray diffraction spectroscopy. The supercapacitance behavior of the NWA-Ag/Co3O4 electrodes is investigated by cyclic voltammetry, galvanostatic charge/discharge test and electrochemical impedance spectroscopy. The results show that the nanowire arrays densely cover the nickel foam substrate and have diameters around 250 nm. The NWA-Ag/Co3O4 electrodes exhibit a specific capacitance of 1009 F g−1 at a current density of 5 mA cm-2 in 6.0 mol dm-3 KOH electrolyte. The capacitance loss is less than 6.5% after 500 charge/discharge cycles at 10 mA cm-2 and with columbic efficiency higher than 97.5%.

Porous Co3O4/NiO core/shell nanowire array with enhanced catalytic activity for methanol electro-oxidation

A self-supported Co3O4/NiO core/shell nanowire array is prepared by the combination of hydrothermal synthesis and electro-deposition methods. The Co3O4/NiO core/shell nanowire array shows a combined structure of mesoporous nanowire core and branch nanoflakes shell as well as hierarchically porous structure. The electro-oxidation properties of methanol of the Co3O4/NiO core/shell nanowire array are elucidated by cyclic voltammetry (CV) and chronoamperometry tests. Impressively, the Co3O4/NiO core/shell nanowire array exhibits much higher electro-catalytic activity, lower over-potential and much more stability for methanol electro-oxidation compared to the single Co3O4 nanowire array in alkaline medium. The enhancement of the electro-catalytic reactivity is due to the synergistic effect and unique porous core/shell nanowire architecture, which provides fast ion/electron transfer, sufficient contact between active materials and electrolyte, leading to faster kinetics, lower over-potential and higher electro-catalytic reactivity.

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.

Synthesis of Co<SUB>3</SUB>O<SUB>4</SUB> Nanowire Arrays Supported on Ni Foam for Removal of Volatile Organic Compounds

Crystalline Co3O4 nanowire arrays freely supported on Ni foam are successfully synthesized using a template-free method. The effects of reaction time, concentration of reactants, and temperature on the morphology of the nanowires are studied. The results indicate that uniform Co3O4 nanowires could be synthesized at 90 degrees C, and a transformation of the samples' morphology from nanoparticles to nanowires to microrods is observed by controlling the concentration of the reactants. The well-ordered nanowires synthesized under the selected reaction conditions are composed of spinel Co3O4 with diameters of 500-580 nm and lengths of 6-8 microm. These nanowires show good catalytic activity for the ozone catalytic oxidation of toluene.

CuO nanosheets grown on cupper foil as the catalyst for H2O2 electroreduction in alkaline medium

The growth of CuO nanosheet arrays on Cu foil was demonstrated. The morphology and structure of the CuO were examined by scanning electron microscopy and X-ray diffraction spectroscopy. The catalytic performance of the obtained CuO/Cu electrode for hydrogen peroxide electroreduction in 3.0moldm−3 KOH was evaluated by means of cyclic voltammetry and chronoamperometry. The CuO/Cu electrode shows an onset potential for H2O2 electroreduction comparable to Co3O4 nanowire arrays grown on Ni foam and around 100mV more negative than precious metal catalysts, such as Pt and Pd, demonstrating its good catalytic activity for H2O2 electroreduction. The stabilized mass current density for H2O2 electroreduction on the CuO/Cu electrode at −0.3V reached about 57% of that on Co3O4 nanowire arrays grown on nickel foam. Compared to conventional fuel cell electrodes fabricated by mixing active materials with conducting agents and polymer binders, this electrode of CuO nanosheet arrays directly grown on Cu has superior mass transport property, which combining with its low-cost and facile preparation, make it a promising electrode for fuel cell using H2O2 as the oxidant.

Co3O4–C core–shell nanowire array as an advanced anode material for lithium ion batteries

We report on the synthesis of a Co3O4–C core–shell nanowire array and its application as an anode material for lithium ion batteries. The core–shell nanowire array is prepared by combining a facial hydrothermal synthesis and direct current magnetron sputtering. The amorphous carbon layer with a thickness of 18 nm is homogeneously coated on the surface of the porous Co3O4 nanowire. The Co3O4–C core–shell nanowire array delivers an initial discharge capacity of 1330.8 mA h g−1 at 0.5 C and maintains a high reversible capacity of 989.0 mA h g−1 after 50 cycles, much higher than the unmodified Co3O4 nanowire array (490.5 mA h g−1). The improved electrochemical performance can be attributed to the introduction of a thin carbon layer, which improves the electrical conductivity and structure stability of the Co3O4 nanowire array.

Freestanding Co3O4 nanowire array for high performance supercapacitors

We report a single-crystalline Co3O4 nanowire array grown on a nickel foam prepared by a hydrothermal synthesis method for supercapacitor application. The Co3O4 nanowires show sharp tips and have an average diameter of 70 nm, and a length up to 25 μm. Impressively, the as-prepared single-crystalline Co3O4 nanowire array exhibits noticeable pseudocapacitive performance with a high capacitance of 754 F g−1 at 2 A g−1 and 610 F g−1 at 40 A g−1 as well as excellent cycling stability. The enhanced supercapacitor performance is due to the unique one-dimensional (1D) architecture, which provides fast diffusion paths for ions and facilitates the electron and ion transfer on the Co3O4/electrolyte interfaces. Moreover, the 1D nanowire array can accommodate the volume expansion and restrain the pulverization and deterioration of Co3O4 during the repeated cycling process, resulting in enhanced cycling stability.

Mesoporous Co3O4 and CoO@C Topotactically Transformed from Chrysanthemum‐like Co(CO3)0.5(OH)·0.11H2O and Their Lithium‐Storage Properties

AbstractIn this work, a novel hydrothermal route is developed to synthesize cobalt carbonate hydroxide, Co(CO3)0.5(OH)·0.11H2O. In this method, sodium chloride salt is utilized to organize single‐crystalline nanowires into a chrysanthemum‐like hierarchical assembly. The morphological evolution process of this organized product is investigated by examining different reaction intermediates during the synthesis. The growth and thus the final assembly of the Co(CO3)0.5(OH)·0.11H2O can be finely tuned by selecting preparative parameters, such as the molar ratio of the starting chemicals, the additives, the reaction time and the temperature. Using the flower‐like Co(CO3)0.5(OH)·0.11H2O as a solid precursor, quasi‐single‐crystalline mesoporous Co3O4 nanowire arrays are prepared via thermal decomposition in air. Furthermore, carbon can be added onto the spinel oxide by a chemical‐vapor‐deposition method using acetylene, which leads to the generation of carbon‐sheathed CoO nanowire arrays (CoO@C). Through comparing and analyzing the crystal structures, the resultant products and their high crystallinity can be explained by a sequential topotactic transformation of the respective precursors. The electrochemical performances of the typical cobalt oxide products are also evaluated. It is demonstrated that tuning of the surface texture and the pore size of the Co3O4 products is very important in lithium‐ion‐battery applications. The carbon‐decorated CoO nanowire arrays exhibit an excellent cyclic performance with nearly 100% capacity retention in a testing range of 70 cycles. Therefore, this CoO@C nanocomposite can be considered to be an attractive candidate as an anode material for further investigation.

An Alkaline Al–H2O2 Semi‐Fuel Cell Based on a Nickel Foam Supported Co3O4 Nanowire Arrays Cathode

AbstractThe electrode of Co3O4 nanowire arrays directly grown on nickel foam is prepared via a facile one‐step method. The electrode is characterised by scanning and transmission electron microscopy and tested as the cathode of an Al–H2O2 semi‐fuel cell. We found that Co3O4 forms clusters of nanowires with length up to around 15 μm and diameter around 250 nm. The nanowire is composed of interconnected nanoparticles. Effects of H2O2 concentrations, catholyte KOH concentration, catholyte flow rate and operation temperature on the cell performance are investigated. The cell exhibited an open circuit voltage of 1.4 V, and peak power densities of 85 and 137 mW cm–2 at 25 and 65 °C, respectively, while running on 0.4 mol L–1 H2O2 at a flow rate of 80 mL min–1.

Self-supported hydrothermal synthesized hollow Co3O4 nanowire arrays with high supercapacitor capacitance

We report a facile hydrothermal synthesis method for the large-area growth of self-supported hollow Co3O4 nanowire arrays. The Co3O4 nanowires have an average diameter of 200 nm and grow vertically to the substrates forming aligned nanowire arrays. Interestingly, the as-prepared Co3O4 nanowire arrays combine properties of hollow structure and quasi-single crystallinity. A plausible formation mechanism of hollow Co3O4 nanowire arrays is proposed here. The Co3O4 nanowire arrays grown on the nickel foam are tested as a cathode electrode material for supercapacitor by cyclic voltammograms (CVs) and galvanostatic charge–discharge tests in 1 M KOH. The self-supported hollow Co3O4 nanowire arrays exhibit superior supercapacitor performances with high specific capacitances (599 F g−1 at 2 A g−1 and 439 F g−1 at 40 A g−1) as well as excellent cycle life, making them suitable for high-rate supercapacitor application. The enhanced supercapacitor performances are due to its unique porous structure providing fast ion and electron transfer, large reaction surface area and good strain accommodation.

A facile method to improve the high rate capability of Co3O4 nanowire array electrodes

The capability of fast charge and fast discharge is highly desirable for the electrode materials used in supercapacitors and lithium ion batteries. In this article, we report a simple strategy to considerably improve the high rate capability of Co3O4 nanowire array electrodes by uniformly loading Ag nanoparticles onto the surfaces of the Co3O4 nanowires via the silver-mirror reaction. The highly electrically conductive silver nanoparticles function as a network for the facile transport of electrons between the current collectors (Ti substrates) and the Co3O4 active materials. High capacity as well as remarkable rate capability has been achieved through this simple approach. Such novel Co3O4-Ag composite nanowire array electrodes have great potential for practical applications in pseudo-type supercapacitors as well as in lithium ion batteries.

Critical Role of Screw Dislocation in the Growth of Co(OH)2 Nanowires as Intermediates for Co3O4 Nanowire Growth

In our prior studies, we reported the growth of Co3O4 nanowire arrays via the ammonia-evaporation-induced growth in solution and their promising applications in a Li-ion battery and oxygen evolution. Although we had identified that the growth of Co3O4 nanowire went through the β-Co(OH)2 intermediate, the growth mechanism of Co(OH)2 nanowire was still elusive. The problem seemed to be rooted in its layered brucite crystal structure, which was not previously known to grow one-dimensionally (1D) perpendicular to the layers. In this paper, we present our recent discovery that axial screw dislocation is responsible for such longitudinal growth. Through bright-field transmission electron microscope (TEM) characterizations, the screw dislocation was directly observed as a dark-contrasted line along Co(OH)2 nanowires. Emergent spiral growth steps provide active sites for immediate adsorption of incoming molecules, resulting in a fast spiral advance rate along the c-axis of the brucite crystal. This study shows a new example of the screw-dislocation driven growth of 1D nanostructures.

Nickel Foam Supported-Co3O4 Nanowire Arrays for H2O2 Electroreduction

Ni foam supported-Co3O4 nanowire arrays are prepared by a template-free growth method, followed by a thermal treatment in air, and are characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, infrared spectroscopy, and thermogravimetric and differential thermal analysis. The Co3O4 nanowires have a diameter of about 250 nm, a length up to 15 μm, and a Brunauer-Emmett-Teller surface area of 78.4 m2 g−1. They grow almost vertically from the surface of Ni foam skeleton, pack densely, and uniformly cover the entire surface of Ni foam skeleton. Electroreduction of H2O2 on Co3O4 nanowire arrays in alkaline medium is investigated by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. The Co3O4 nanowire electrode exhibits superior activity, stability, and mass transport property for H2O2 electroreduction. A current density of 90 mA cm−2 is achieved at −0.4 V in 0.4 mol dm−3 H2O2 and 3.0 mol dm−3 NaOH at room temperature. The per gram current density measured at −0.4 V on Co3O4 nanowires is about 1.5 times of that on Co3O4 nanoparticles.

FABRICATION AND CHARACTERIZATION OF CoxGd1-x NANOWIRE ARRAYS AND CORE-SHELL-LIKE CoxGd1-x/CoO NANOWIRE ARRAYS

Amorphous Co x Gd 1-x nanowire arrays and core-shell-like Co x Gd 1-x/ CoO nanowire arrays with composite amorphous and crystalline structures, where 0.75 < x < 0.99, are fabricated successfully by employing electrochemical deposition with the assistance of AAO templates. Based on the experiments, dissolving of the organic salt of Gd in dimethylsulfoxide and the deposition potentials are the critical factors for formation of amorphous structures and different morphologies. Investigation of the magnetic properties shows that Co x Gd 1-x nanowire arrays have superparamagnetic characteristics, and core-shell-like Co x Gd 1-x/ CoO nanowire arrays possess better soft ferromagnetic properties. Moreover, these magnetic behaviors are attributed to spin disorder of amorphous structures and shape anisotropy, which arise from the large aspect ratio of one-dimensional nanoscale materials.

Mesoporous Co3O4Nanowire Arrays for Lithium Ion Batteries with High Capacity and Rate Capability

We report the high capacity and rate capability of mesoporous Co3O4 nanowire (NW) arrays as anodes in Li ion batteries. At a current of 1C, the NW arrays maintain a capacity of 700 mAh/g after 20 discharge/charge cycles. When the current is increased to 50C, 50% of the capacity can be retained. With their ease of large area synthesis and superior electrochemical properties, these Co3O4 NW arrays will be interesting for practical Li ion batteries.