Co3O4 Nanostructures Research Articles

Hydrothermal-assisted defect engineering in spinel Co3O4 nanostructures as bifunctional catalysts for oxygen electrode

Developing efficient non-precious materials as bifunctional catalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is very urgent for the practical application of the regenerative fuel cells. Herein, a hydrothermal-assisted defect engineering is introduced as an efficient strategy to enhance the electro-catalytic performance of spinel Co3O4 nanostructures without complex chemical treatments. By simply tuning the hydrothermal time, we fabricate a typical cubic Co3O4 nanostructure with high density of oxygen vacancy defects. The formation of the surface oxygen vacancies is measured by XPS, Raman spectroscopy, and TG/DTA measurements. The relative concentration of oxygen vacancies could reach 8.5 at% for the cubic oxide fabricated at a hydrothermal time of 3 h. In 1 M NaOH electrolyte, the cubic Co3O4 displays improved both ORR and OER activity with a total overpotential of 783 mV, which is close to that obtained by commercial Pt/C or RuO2 catalysts. The enhanced performance should be attributed to the increased oxygen vacancy defects as well as the desired Co2+/Co3+ ratio for the cubic oxide. This work may offer a possibility for developing other spinel oxides with high performance through hydrothermal-assisted defect engineering.

Facile morphology-controlled synthesis of Co3O4 nanostructure on carbon cloth and their morphology-dependent pseudocapacitive performances

Tailoring the morphology and size of metal oxide by a facile synthetic method is challenging. In this paper, we in situ synthesized Co3O4 with different morphologies and sizes (nanosheets, nanowires, nanowire-clusters, rhombus-like thick round nanosheets) on carbon cloth by a facile hydrothermal reaction. The morphologies of Co3O4 were controlled by simply varying the mole ratio of NH4F to cobalt salt in the reaction solution. The effects of the morphologies of Co3O4 on its electrochemical performances were compared, and the results reveal that the nanowire-clusters Co3O4 exhibits the best electrochemical performance among all types of Co3O4, including a high specific capacitance of 621.8 F g−1 at 1 A g−1, outstanding rate capability and superior cycling stability of 90.6% retention over 3000 cycles. Also, its asymmetric supercapacitor (activated carbon as negative electrode) could deliver a high energy density of 17.92 Wh kg−1 at 1499.91 W kg−1, demonstrating a great potential for supercapacitor applications. This work provides a novel morphology-controllable synthesis approach to better understand the morphology effect on the electrochemical properties of Co3O4.

Graphene/Co3O4 composites in application of electrochemical energy conversion and storage

This work summarizes the use of graphene/Co3O4 composites in electrochemical energy conversion and storage applications. Graphene is considered the most promising carbon material for accommodating multifarious nanoparticles and achieving excellent electrochemical performance, such as a high electrolyte contact area, electron transport rate and structural stability. This work presents different nanostructures of Co3O4 that consist of nanowires, nanotubes and ordered mesoporous structures, many of which have been poorly synthesized by facile strategies. Graphene can effectively house Co3O4 nanoparticles inside its 3D structure and greatly enhance the electrochemical performance of these nanoparticles. The synergistic effects of graphene and Co3O4 lead to a variety of attractive properties, such as excellent reversible capacity and good cycling stability. In addition, these unique properties are due to the many short diffusion pathways and active sites of nanosized Co3O4 and the elastic buffer space and conductive pathways provided by graphene. This comprehensive review outlines the excellent electrochemical performance of graphene/Co3O4 composites in electrocatalysis, supercapacitors, lithium-ion batteries and other batteries.

Synthesis of morphology controllable free-standing Co3O4 nanostructures and their catalytic activity for Li[sbnd]O2 cells

Free-standing Co3O4 on nickel foam is synthesized by a simple hydrothermal route, using cobalt nitrate hexahydrate as the cobalt source, and urea as the precipitator. The effects of urea on the structural and electrochemical characteristics are investigated in detail. As the urea increased, the morphology of the free-standing Co3O4 turns from hexagonal nanosheets to nanoflakes, and finally turns to nanoflakes/nanowires hybrid structure. This hybrid structure is made up of ultrathin porous nanoflakes, and short nanowires anchored at the edge of the nanoflakes, which may enhance the diffusion rate of the electrolyte and O2 and provide more active sites for both O2 reduction and evolution reactions. When applied as a free-standing cathode for the LiO2 cells, it shows better performance for the nanoflakes/nanowires hybrid structure than the others. It exhibits a high specific capacity of 5958 mA h g−1 at 0.1 mA cm−2, a long cycle life of 108 cycles with a limited capacity of 500 mA h g−1, and unique morphology of the discharge products.

Cobalt Oxide Porous Nanocubes-Based Electrochemical Immunobiosensing of Hepatitis B Virus DNA in Blood Serum and Urine Samples.

In this work, we report a new biosensing platform for hepatitis B virus (HBV) DNA genosensing using cobalt oxide (Co3O4) nanostructures. The tunable morphologies of Co3O4 nanostructures such as porous nanocubes (PNCs), nanooctahedra (NOHs), and nanosticks (NSKs) are synthesized, and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) patterns, nitrogen adsorption/desorption isotherms (BET), and electrochemical impedance spectral (EIS) methods. The HBV probe DNA (ssDNA) is immobilized on the Co3O4 nanostructures through coordinate bond formation between nucleic acid of ssDNA and Co metal, which results in highly stable nanostructured biosensing platform. To the best of our knowledge, first time the target cDNA of HBV is detected using ssDNA/Co3O4PNCs/GCE electrode by EIS method with a limit of detection (LOD) of 0.38 pM (signal-to-noise ratio (S/N) = 3). Moreover, the ssDNA/Co3O4PNCs/GCE has shown excellent specificity to HBV target cDNA, compared with noncomplementary DNA, and 1- and 3-mismatch DNAs. Finally, we explore ssDNA/Co3O4PNCs/GCE as potential electrode to test HBV DNA in blood serum and urine samples for practical applications.

Facile precursor conversion synthesis of hollow coral-shaped Co3O4 nanostructures for high-performance supercapacitors

In this work, novel hollow coral-shaped Co3O4 nanostructures are synthesized via a precursor conversion method for the first time, and the detailed process of precursor conversion is revealed. l-ascorbic acid as the structure-directing agent and the origin of oxalate (C2O42−) contributes to the formation of the precursors, providing a low-cost and facile method for preparing Co3O4. Hollow coral-shaped Co3O4 nanostructures are obtained by calcining cobalt oxalate precursors in air. The special Co3O4 nanostructures exhibit noticeable pseudocapacitive properties with a capacitance of 626.5 F g-1 at 5 mV s-1 and show superior stability (capacity retention of 99%) and outstanding Coulombic efficiency (˜100%) within 5000 charge–discharge cycles at 10 A g-1. Furthermore, the asymmetric supercapacitor Co3O4//G fabricated by Co3O4 cathode and graphene hydrogel anode delivers a specific capacitance of 115 F g-1 (47.9 mA h g-1) at 1 A g-1 and attains the maximum energy density of 35.93 Wh kg-1 at the power density of 801.6 W kg-1. The excellent durability of Co3O4//G is demonstrated by the retention of 85.1% of initial capacitance after 5000 cycles at 5 A g-1. The novel and feasible route proposed in the work is expected to be applied prospectively and widely in preparing Co3O4 pseudo-capacitance material, which owns great application value in supercapacitors, as well as in batteries.

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.

Synthesized pure cobalt oxide nanostructure and doped with yttrium by hydrothermal method for photodetector applications

In this study, pure Co3O4 nano structure and doping with 4 %, and6 % of Yttrium is successfully synthesized by hydrothermal method.The XRD examination, optical, electrical and photo sensingproperties have been studied for pure and doped Co3O4 thin films.The X-ray diffraction (XRD) analysis shows that all films arepolycrystalline in nature, having cubic structure.The optical properties indication that the optical energy gap followsallowed direct electronic transition calculated using Tauc equationand it increases for doped Co3O4. The photo sensing properties ofthin films are studied as a function of time at different wavelengths tofind the sensitivity for these lights.High photo sensitivity doped Co3O4 with 6% of Yttrium, is a118.774% at wavelength 620 nm, while for pure Co3O4 films nosensitivity at the same wavelength. So, higher sensitivity is found fordoping Co3O4 with fast rise and fall times less than 1s.

A cobalt oxide nanocubes interleaved reduced graphene oxide nanocomposite modified glassy carbon electrode for amperometric detection of serotonin

Cobalt oxide nanocubes incorporated with reduced graphene oxide (rGO-Co3O4) was prepared by using simple one-step hydrothermal route. Crystallinity and structural characteristics of the nanocomposite were analyzed and confirmed using X-ray diffraction (XRD) and Raman analysis, respectively. The cubical shape of the Co3O4 nanostructures and the distribution of Co3O4 nanocubes on the surface of rGO sheets were identified through field emission scanning electron microscopy (FESEM) and energy dispersive X-ray (EDX) mapping analysis, respectively. Raman spectra depicted the presence of D and G bands for GO and rGO with different ID/IG values and thus confirmed the reduction of GO into rGO. The electrochemical study reflects that the rGO-Co3O4 nanocomposite shows good electrocatalytic activity in oxidation of depression biomarker serotonin (5-HT) in phosphate buffer (pH 7.2). The detection of 5-HT was carried out by using rGO-Co3O4 nanocomposite modified glassy carbon electrode under dynamic condition using amperometry technique with a linear range of 1–10 μM. The limit of detection and limit of quantification were calculated and found to be 1.128 and 3.760 μM, respectively with a sensitivity value of 0.133 μΑ·μM−1. The sensor showed selectivity in the presence of different interferent species such as ascorbic acid, dopamine and uric acid.

Morphology-controlled synthesis of Co3O4 composites with bio-inspired carbons as high-performance supercapacitor electrode materials

Herein, we developed a nanostructured Co3O4 and bio-inspired carbon (BIC) composite by a facile hydrothermal reaction as a supercapacitor electrode material. Microstructural analysis revealed that the BIC-Co3O4 composites possessed the hierarchical structure with a microflower shape consisting of thin nano-petals. Due to its characteristic nanostructure, the BIC-Co3O4 electrode exhibited a high specific capacitance of 473 F/g at a current density of 1 A/g. Moreover, the all-solid-state symmetric device with this electrode delivered the energy density of 17 Wh/kg at a power density of 184 W/kg with remarkable cycling stability over 10,000 cycles.

Investigation of structural, optical and magnetic characteristics of Co3O4 thin films

Nano-structured Co3O4 thin film are synthesized by dip coating and their structural, surface, optical and magnetic properties have been studied. The X-ray diffraction of film shows that the crystalline Co3O4 has cubic structure with preferrd orientation along the (400) plane which makes them advantageous for optoelectronic devices. The scanning electron microscopy micrograph reveals that the film has a porous structure. The transmission of the films gradually decreases with the decrease of the wavelength in the 900–300 nm region. Upon enhancing the withdrawal speed of the substrate, the transmission shows decrement due to increase in film thickness. From the investigation of the transmission spectra of Co3O4 films, the band-gap is found to lie between 2.12 and 2.30 eV. Magnetic characteristic of thin films relies on the withdrawal speed and thickness of thin films. With the increase of withdrawal speed saturation magnetization increases while coercivity of thin films decreases.

Production of Methanol from Aqueous CO2 by Using Co3O4 Nanostructures as Photocatalysts

In this work, we report for the first time the photocatalytic activity of Co3O4 nanostructures for the reduction of aqueous CO2 to methanol (MeOH). This could be considered a simple example of artificial photosynthesis. The photocatalysis experiments were developed under simulated solar light of 100 mW/cm2 and without using any sacrificial agent. To carry out this study, nanostructured mixed valence cobalt oxide (Co3O4) powders, with porous nanoparticle aggregates of different morphologies, have been prepared by two synthesis methods. The characterization of structural (PXRD, XPS, SEM, and TEM) and optical (UV-vis-NIR, Raman, and FT-IR) properties, magnetization curves, and surface area (BET) was accomplished.

Morphology-dependent charge storage performance of Co3O4 nanostructures in an all-solid-state flexible supercapacitor

A microwave-assisted hydrothermal method is demonstrated to synthesize Co3O4 nanostructures as the positive electrode and a graphene hydrogel as the negative electrode for a supercapacitor.

Fabrication of hollow pompon-like Co3O4 nanostructures with rich defects and high-index facet exposure for enhanced oxygen evolution catalysis

A hollow pompon-like Co3O4 nanostructure with rich defects and high-index facets exhibits enhanced electrocatalytic performance for the oxygen evolution reaction (OER).

Development of an acetone sensor using nanostructured Co3O4 thin films for exhaled breath analysis.

In recent times, the development of breath sensors for the detection of Diabetic Keto-Acidosis (DKA) has been gaining prominent importance in the field of health care and advanced diagnostics. Acetone is one of the prominent biomarkers in the exhaled breath of persons affected by DKA. In this background, nanostructured cobalt oxide sensing elements were fabricated using a spray pyrolysis technique at different deposition temperatures (473 to 773 K in steps of 100 K) towards the fabrication of an acetone sensor. The influence of deposition temperature on the various properties of the nanostructured cobalt oxide thin films was investigated. Formation of cubic spinel phase cobalt oxide was confirmed from the structural analysis. The shifting of plane orientation from (3 1 1) to (2 2 0) at 773 K deposition temperature revealed the migration of cobalt atoms to the highly favorable energy positions. Further, the downshifted peak absorption wavelength and upshifted PL profile at higher deposition temperature confirmed the migration of cobalt ions. The sensor fabricated at higher deposition temperature (773 K) showed a sensing response of 235 at room temperature towards 50 ppm of acetone. Also, the fabricated sensor showed a lower detection limit (LOD) of 1 ppm with the response–recovery times of 6 and 4 s, respectively. The LOD reported here is lower than the minimum threshold level (1.71 ppm) signifying the presence of DKA.

Electrospun nanostructured Co3O4/BiVO4 composite films for photoelectrochemical applications

Co3O4/BiVO4 (Co/BiV) based nanostructured photoanode films were fabricated by simple facile electrospinning method and were characterized by a variety of techniques. It was found that the films have web-linked structure, composed of BiVO4 and Co3O4 nanostructures. The photoanode was used for the photoelectrochemical (PEC) degradation of bisphenol-A (BPA) by illumination at 0.25 V vs. SCE assisted by 1 mM peroxymonosulfate (PMS). The removal percentage of BPA was enhanced to 96% for the Co/BiV film that was much better than that of BiVO4 film, which was 48%. The pseudo-first kinetic constants were raised from 0.1126 min−1 to 0.4714 min−1, respectively. The enhanced PEC performance of Co/BiV films can be attributed its p-n heterojunction setup and synergetic contribution of PMS, which efficiently inhibits the recombination of photogenerated electron-hole pairs. The free radicals quenching experiment and electron spin resonance suggested that the major reactive oxygen species were photogenerated holes, superoxide radicals and sulfate radicals. These findings demonstrate that PMS assisted Co/BiV films, are good candidates for PEC application in environmental purification.

Advanced three-dimensional hierarchical Pr6O11@Ni-Co oxides-based core-shell electrodes for supercapacitance application

A facile solvothermal method is used to fabricate hierarchical core-shell nanostructures based on praseodymium, nickel and cobalt oxides supported on nickel foam. The Pr6O11 nanoparticles were first grown on the nickel foam and then utilized as a backbone for anchoring NiO, Co3O4 and NiCo2O4 nanostructures to form a core-shell structure. The core-shell electrodes exhibit superior electrochemical performance than single Pr6O11 nanoparticles electrodes. A superior specific capacitance of 1635 F/g at a current density of 0.5 mA/cm2 with good cycling stability was obtained for the Pr6O11@NiCo2O4 electrode. Moreover, a solid-state supercapacitor was fabricated by assembling Pr6O11@NiCo2O4 electrodes using KOH/PVA as the solid electrolyte. The as-prepared solid-state device demonstrated impressive energy density of 6.6 W h/kg and a power density of 150 W/kg. This optimal performance could be attributed to the high conductive nickel foam current collector and synergistic effects generated from the core-shell architecture of NiCo2O4 and the Pr6O11 nanoparticles.

A direct route to activated two-dimensional cobalt oxide nanosheets for electrochemical energy storage, catalytic and environmental applications

Two-dimensional Co3O4 nanosheets have emerged as attractive materials for use in a number of relevant technological applications. To exhibit a competitive performance in such uses, however, their structure needs to be activated, which is frequently accomplished via post-synthesis reduction strategies that introduce oxygen vacancies and increase the number of active Co(II) sites. Here, we investigate a direct route for the synthesis of activated Co3O4 nanosheets that avoids reduction post-treatments, yielding materials with a high potential towards energy- and environment-related applications. The synthesis relied on an interim amorphous cobalt oxide material with nanosheet morphology, which upon calcination afforded Co3O4 nanosheets having Co(II) sites in quantities similar to those usually found for Co3O4 nanostructures activated by reduction post-treatments. When tested as electrodes for charge storage, the nanosheets demonstrated a competitive behavior in terms of both capacity and rate capability, e.g., a gravimetric capacity of ∼293 mAh g−1 at 1 A g−1 with 57% retention at 60 A g−1 was measured for nanosheets calcined at 350 °C. The materials were shown to be efficient catalysts for the reduction of nitroarenes (4-nitrophenol and 4-nitroaniline), outperforming other Co3O4 nanostructures, as well as effective adsorbents for the removal of organic dyes (methyl orange, methylene blue) from water.

Finely tunable morphology controlled synthesis of spinel-cobalt oxide nanostructures and their electrocatalytic applications

Herein, we synthesize four morphologies of spinel-Co3O4 nanostructures, including rice-, dumbbell sheet-, nanoboxes-, and nanosheets spheres using a hydrothermal strategy. The surface morphology and size of the Co3O4 nanostructures are characterized by field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction(XRD), and electrochemical methods. Among the other Co3O4 nanostructures, nanosheets spheres- like morphology display a significantly enhanced electrochemical oxidation of sulfite (SO32−) in terms of higher anodic current density (1.50 mA cm−2) and low onset oxidation potential (∼1.10 V vs RHE). The Co3O4 nanosheets spheres offer a large surface area, and numerous active sites for accessing numerous sulfite molecules for efficient and enhanced electrocatalytic responses. Further, the Co3O4 nanosheets spheres based electrode display a low Rp value, and high durability when compared to other nanostructured electrodes. Thus, the Co3O4 nanostructured materials are versatile candidates, and offer a new optimism for use in various electrochemical technological applications.

Structural, magnetic and dielectric properties of pure and Dy-doped Co3O4 nanostructures for the electrochemical evolution of oxygen in alkaline media

In this study, spinel-type cobalt oxide (Co3O4) and Co3-xDyxO4 (x = 0.04 and 0.05 molar ratio) nanoparticles were synthesized via combustion method at 700 °C. Crystallite nature, phase purity and thermal analysis of the prepared compounds were investigated by PXRD, FT-IR and TGA techniques. Structural analyses were performed by the FullProf program employing profile matching with constant scale factors. The results showed that the patterns had a main cubic structure with space group of Fd3m. The cell parameter data calculated by rietveld analysis showed that the cell parameters were nearly constant. The morphological and structural properties of the obtained materials were examined by FESEM and TEM images. Besides, the magnetic measurements of Co3O4 and Co3-xDyxO4 nanoparticles were performed by vibration sampling magnetometer (VSM). Coercivity (Hc) and remanent magnetization (Mr) were found to be reduced in Dy3+ doped Co3O4 while saturation magnetization (Ms) was increased moderately. The effect of dysprosium ion addition was also studied using cyclic voltammetry (CV) for the oxygen evolution reaction in an alkaline environment. The obtained data showed that the presence of Dy3+ exhibited a much higher oxygen evolution activity and lower over potential compared to Co3O4.