Controllable Synthesis of Mesoporous Peapod‐like Co3O4@Carbon Nanotube Arrays for High‐Performance Lithium‐Ion Batteries

Transition metal oxides are regarded as promising anode materials for lithium‐ion batteries because of their high theoretical capacities compared with commercial graphite. Unfortunately, the implementation of such novel anodes is hampered by their large volume changes during the Li⁺ insertion and extraction process and their low electric conductivities. Herein, we report a specifically designed anode architecture to overcome such problems, that is, mesoporous peapod‐like Co₃O₄@carbon nanotube arrays, which are constructed through a controllable nanocasting process. Co₃O₄ nanoparticles are confined exclusively in the intratubular pores of the nanotube arrays. The pores between the nanotubes are open, and thus render the Co₃O₄ nanoparticles accessible for effective electrolyte diffusion. Moreover, the carbon nanotubes act as a conductive network. As a result, the peapod‐like Co₃O₄@carbon nanotube electrode shows a high specific capacity, excellent rate capacity, and very good cycling performance.     

General Self‐Template Synthesis of Transition‐Metal Oxide and Chalcogenide Mesoporous Nanotubes with Enhanced Electrochemical Performances

The development of a general strategy for synthesizing hierarchical porous transition‐metal oxide and chalcogenide mesoporous nanotubes, is still highly challenging. Herein we present a facile self‐template strategy to synthesize Co₃O₄ mesoporous nanotubes with outstanding performances in both the electrocatalytic oxygen‐evolution reaction (OER) and Li‐ion battery via the thermal‐oxidation‐induced transformation of cheap and easily‐prepared Co‐Asp(cobalt–aspartic acid) nanowires. The initially formed thin layers on the precursor surfaces, oxygen‐induced outward diffusion of interior precursors, the gas release of organic oxidation, and subsequent Kirkendall effect are important for the appearance of the mesoporous nanotubes. This self‐template strategy of low‐cost precursors is found to be a versatile method to prepare other functional mesoporous nanotubes of transition‐metal oxides and chalcogenides, such as NiO, NiCo₂O₄, Mn₅O₈, CoS₂ and CoSe₂.     

Enhanced Electrochemical Capacitive Properties of Nickel‐Cobalt Oxide Nano‐flakes Materials

Nickel‐cobalt oxide nano‐flakes materials are successfully synthesized by a facile chemical co‐precipitation method followed by a simple calcination process. The studies show that the as‐prepared nickel‐cobalt oxides with different Ni/Co ratio are composed of NiO and Co₃O₄ compounds. The Co_0.56Ni_0.44 oxide material, which exhibits a mesoporous structure with a narrow distribution of pore size from 2 to 7 nm, possesses markedly enhanced charge‐discharge properties at high current density compared with the pure NiO and pure Co₃O₄. The Co_0.56Ni_0.44 oxide electrode shows a specific capacitance value of 1227 F/g at 5 mA/cm², which is nearly three times greater than that of the pure NiO electrode at the same current density.     

Highly Ordered Mesoporous Cobalt Oxide Nanostructures: Synthesis,Characterisation, Magnetic Properties,and Applications for Electrochemical Energy Devices

Highly ordered mesoporous Co₃O₄ nanostructures were prepared using KIT‐6 and SBA‐15 silica as hard templates. The structures were confirmed by small angle X‐ray diffraction, high resolution transmission electron microscopy, and N₂ adsorption–desorption isotherm analysis. Both KIT‐6 cubic and SBA‐15 hexagonal mesoporous Co₃O₄ samples exhibited a low Néel temperature and bulk antiferromagnetic coupling due to geometric confinement of antiferromagnetic order within the nanoparticles. Mesoporous Co₃O₄ electrode materials have demonstrated the high lithium storage capacity of more than 1200 mAh g^?1 with an excellent cycle life. They also exhibited a high specific capacitance of 370 F g^?1 as electrodes in supercapacitors.     

Meso-macroporous Co3O4 electrode prepared by polystyrene spheres and carbowax templates for supercapacitors

Meso-macroporous Co₃O₄ electrode is synthesized by drop coating with a mixed solution containing Co(OH)₂ colloid, polystyrene spheres, and carbowax (namely polyethylene glycol), followed by calcining at 400?°C to remove polystyrene spheres and carbowax. For comparison, nonporous Co₃O₄ and mesoporous Co₃O₄ electrodes are prepared by drop coating with Co(OH)₂ colloid and with a mixed solution containing Co(OH)₂ colloid and carbowax under the same condition, respectively. Capacitive property of these electrodes is measured by cyclic voltammetry, potentiometry and electrochemical impedance spectroscopy. The results show that meso-macroporous Co₃O₄ electrode exhibits larger specific capacitance than those of nonporous Co₃O₄ electrode and mesoporous Co₃O₄ electrode at various current densities. The specific capacitance of meso-macroporous Co₃O₄ electrode at the current density of 0.2?A?g^?1 is 453?F?g^?1. Meanwhile, meso-macroporous Co₃O₄ electrode possesses the highest specific capacitance retention ratio at the current density ranging from 0.2 to 1.0?A?g^?1, indicating that meso-macroporous Co₃O₄ electrode suits to high-rate charge?Cdischarge.     

Mesoporous Semimetallic Conductors: Structural and Electronic Properties of Cobalt Phosphide Systems

Mesoporous cobalt phosphide (meso‐CoP) was prepared by the phosphorization of ordered mesoporous cobalt oxide (meso‐Co₃O₄). The electrical conductivity of meso‐CoP is 37 times higher than that of nonporous CoP, and it displays semimetallic behavior with a negligibly small activation energy of 26 meV at temperatures below 296 K. Above this temperature, only materials with mesopores underwent a change in conductivity from semimetallic to semiconducting behavior. These properties were attributed to the coexistence of nanocrystalline Co₂P phases. The poor crystallinity of mesoporous materials has often been considered to be a problem but this example clearly shows its positive aspects. The concept introduced here should thus lead to new routes for the synthesis of materials with high electronic conductivity.     

Mass‐Production of Mesoporous MnCo2O4 Spinels with Manganese(IV)‐ and Cobalt(II)‐Rich Surfaces for Superior Bifunctional Oxygen Electrocatalysis

A mesoporous MnCo₂O₄ electrode material is made for bifunctional oxygen electrocatalysis. The MnCo₂O₄ exhibits both Co₃O₄‐like activity for oxygen evolution reaction (OER) and Mn₂O₃‐like performance for oxygen reduction reaction (ORR). The potential difference between the ORR and OER of MnCo₂O₄ is as low as 0.83 V. By XANES and XPS investigation, the notable activity results from the preferred Mn^IV‐ and Co^II‐rich surface. The electrode material can be obtained on large‐scale with the precise chemical control of the components at relatively low temperature. The surface state engineering may open a new avenue to optimize the electrocatalysis performance of electrode materials. The prominent bifunctional activity shows that MnCo₂O₄ could be used in metal–air batteries and/or other energy devices.     

Facile Microstructure Control of Mesoporous Co1.29Ni1.71O4 and the Effect of the Microstructure on Lithium‐Storage Performance

A simple and efficient pathway has been designed and developed to synthesize mesoporous Co_1.29Ni_1.71O₄ nanostructures without the use of any templates. By adjusting the volume ratio of water to ethanol, the Co_1.29Ni_1.71O₄ microstructure can be facilely controlled, and different nanostructures such as microflowers, nanorods, and nanoparticles were obtained. All three as‐synthesized samples have a mesoporous structure, but with different pore‐size distributions, in which the nanorod sample exhibits the highest capacity, good rate capability, and cycle stability as an anode material in lithium‐ion batteries (LIBs). The possible reason might be that the one‐dimensional structure of the nanorods accounts for their higher conductivity relative to microflowers and nanoparticles, and their high conductivity coupled with their mesoporous structure might contribute to their excellent electrochemical performance.     

Redox‐Inert Fe3+ Ions in Octahedral Sites of Co‐Fe Spinel Oxides with Enhanced Oxygen Catalytic Activity for Rechargeable Zinc–Air Batteries

Bimetallic cobalt‐based spinel is sparking much interest, most notably for its excellent bifunctional performance. However, the effect of Fe³⁺ doping in Co₃O₄ spinel remains poorly understood, mainly because the surface state of a catalyst is difficult to characterize. Herein, a bifunctional oxygen electrode composed of spinel Co₂FeO₄/(Co_0.72Fe_0.28)_Td(Co_1.28Fe_0.72)_OctO₄ nanoparticles grown on N‐doped carbon nanotubes (NCNTs) is designed, which exhibits superior performance to state‐of‐the‐art noble metal catalysts. Theoretical calculations and magnetic measurements reveal that the introduction of Fe³⁺ ions into the Co₃O₄ network causes delocalization of the Co 3d electrons and spin‐state transition. Fe³⁺ ions can effectively activate adjacent Co³⁺ ions under the action of both spin and charge effect, resulting in the enhanced intrinsic oxygen catalytic activity of the hybrid spinel Co₂FeO₄. This work provides not only a promising bifunctional electrode for zinc–air batteries, but also offers a new insight to understand the Co‐Fe spinel oxides for oxygen electrocatalysis.     

Synthesis of 2D/2D Structured Mesoporous Co3O4 Nanosheet/N‐Doped Reduced Graphene Oxide Composites as a Highly Stable Negative Electrode for Lithium Battery Applications

Mesoporous Co₃O₄ nanosheets (Co₃O₄‐NS) and nitrogen‐doped reduced graphene oxide (N‐rGO) are synthesized by a facile hydrothermal approach, and the N‐rGO/Co₃O₄‐NS composite is formulated through an infiltration procedure. Eventually, the obtained composites are subjected to various characterization techniques, such as XRD, Raman spectroscopy, surface area analysis, X‐ray photoelectron spectroscopy (XPS), and TEM. The lithium‐storage properties of N‐rGO/Co₃O₄‐NS composites are evaluated in a half‐cell assembly to ascertain their suitability as a negative electrode for lithium‐ion battery applications. The 2D/2D nanostructured mesoporous N‐rGO/Co₃O₄‐NS composite delivered a reversible capacity of about 1305 and 1501 mAh g^?1 at a current density of 80 mA g^?1 for the 1st and 50th cycles, respectively. Furthermore, excellent cyclability, rate capability, and capacity retention characteristics are noted for the N‐rGO/Co₃O₄‐NS composite. This improved performance is mainly related to the existence of mesoporosity and a sheet‐like 2D hierarchical morphology, which translates into extra space for lithium storage and a reduced electron pathway. Also, the presence of N‐rGO and carbon shells in Co₃O₄‐NS should not be excluded from such exceptional performance, which serves as a reliable conductive channel for electrons and act as synergistically to accommodate volume expansion upon redox reactions. Ex‐situ TEM, impedance spectroscopy, and XPS, are also conducted to corroborate the significance of the 2D morphology towards sustained lithium storage.     

Supercapacitive performance of homogeneous Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/TiO<Subscript>2</Subscript> nanotube arrays enhanced by carbon layer and oxygen vacancies

Self-supported and binder-free electrodes based on homogeneous Co₃O₄/TiO₂ nanotube arrays enhanced by carbon layer and oxygen vacancies (Co₃O₄/co-modified TiO₂ nanotube arrays (m-TNAs)) are prepared via a simple and cost-effective method in this paper. The highly ordered TNAs offer direct pathways for electron and ion transport and can be used as 3D substrate for the decoration of electroactive materials without any binders. Then, by a facile one-step calcination process, the electrochemical performance of the as-obtained carbon layer and oxygen vacancy m-TNAs is approximately 83 times higher than that of pristine TNAs. In addition, Co₃O₄ nanoparticles are uniformly deposited onto the m-TNAs by a universal chemical bath deposition (CBD) process to further improve the supercapacitive performance. Due to the synergistic effect of m-TNAs and Co₃O₄ nanoparticles, a maximum specific capacitance of 662.7 F g^?1 can be achieved, which is much higher than that of Co₃O₄ decorated on pristine TNAs (Co₃O₄/TNAs; 166.2 F g^?1). Furthermore, the specific capacitance retains 86.0 % of the initial capacitance after 4000 cycles under a high current density of 10 A g^?1, revealing the excellent long-term electrochemical cycling stability of Co₃O₄/m-TNAs. Thus, this kind of heterostructured Co₃O₄/m-TNAs could be considered as promising candidates for high-performance supercapacitor electrodes.     

Mesoporous Co3O4 Nanobundle Electrocatalysts

Tailoring metal oxide nanostructures with mesoporous architectures is vital to improve their electrocatalytic performance. Herein, we demonstrate the synthesis of 2D mesoporous Co₃O₄ (meso‐Co₃O₄) nanobundles with uniform shape and size by employing a hard‐template method. In this study, the incipient wetness impregnation technique has been chosen for loading metal precursor into the silica hard template (SBA‐15). The results reveal that the concentration of a saturated precursor solution plays a vital role in mesostructured ordering, as well as the size and shape of the final meso‐Co₃O₄ product. The optimized precursor concentration allows us to synthesize ordered meso‐Co₃O₄ with four to seven nanowires in each particle. The meso‐Co₃O₄ structure exhibits excellent electrocatalytic activity for both glucose and water oxidation reactions.     

Facile Synthesis of Graphene/Cobalt Oxide Nanohexagons for the Selective Detection of Dopamine

This work presents a simple green approach for the chemical synthesis of cobalt oxide nano hexagons (Co₃O₄ NHs) with an average size of 160±40 nm incorporated graphene nanosheets (GR). The techniques used to confirm the formation of GR−Co₃O₄ NHs are transmission electron microscopy (TEM), energy‐dispersive X‐ray spectroscopy (EDX), and X‐ray diffraction spectroscopy (XRD). The dopamine (DA) sensor was fabricated by drop casting GR−Co₃O₄ NHs on the pre‐cleaned glassy carbon electrode (GCE). GR−Co₃O₄ modified GCE displayed a sensitive and selective electrochemical determination of DA compared to only GR and Co₃O₄ NHs modified GCE. Our fabricated sensor showed a wide linear range from 0.2 to 3443 μM with low limit of detection (84 nM) towards the determination of DA. The sensitivity of our fabricated sensor was calculated to be 108 μA mM⁻¹ cm⁻². As well, a significant storage stability, repeatability and reproducibility were attained by GR−Co₃O₄ NHs modified GCE. Human urine samples were targeted for the demonstration of practicality of our sensor.     

A Facile Chemical Synthesis of Cu2O Nanocubes Covered with Co3O4 Nanohexagons for the Sensitive Detection of Glucose

Copper (I) oxide nanocubes (Cu₂O NCs) covered with cobalt oxide nanohexagons (Co₃O₄ NHs) were prepared through simple chemical method. Here, ascorbic acid is used as reducing and capping agent for the synthesis of nanocubes and nanohexagons. Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Energy‐dispersive X‐ray spectroscopy (EDX) and X‐ray diffraction spectroscopy (XRD) were employed to confirm the prepared nanocomposite. Cu₂O NCs?Co₃O₄ NHs nanocomposite is drop cast on the glassy carbon electrode (GCE) for the fabrication of glucose sensor. The fabricated Cu₂O NCs?Co₃O₄ NHs/GCE exhibited a better electrocatalytic activity towards the determination of glucose than that of individually fabricated Cu₂O NCs and Co₃O₄ NHs modified GCE. Our finding exhibited a wide linear range from 1 μM to 5330 μM with LOD of 0.63 towards glucose. In addition, the sensor attained appreciable stability, repeatability and reproducibility. Practicality of the sensor was demonstrated in human serum samples. The main advantages of the fabricated sensor are simple, biocompatible, cost effective, fast response and highly stable electrode surface.     

Cobalt Hydroxide Nanosheets and Their Thermal Decomposition to Cobalt Oxide Nanorings

We demonstrate herein that single‐crystalline β‐cobalt hydroxide (β‐Co(OH)₂) nanosheets can be successfully synthesized in large quantities by a facile hydrothermal synthetic method with aqueous cobalt nitrate as the cobalt source and triethylamine as both an alkaline and a complexing reagent. This synthetic method has good prospects for the future large‐scale production of single‐crystalline β‐Co(OH)₂ nanosheets owing to its high yield, low cost, and simple reaction apparatus. Single‐crystalline porous nanosheets and nanorings of cobalt oxide (Co₃O₄) were obtained by a thermal‐decomposition method with single‐crystalline β‐Co(OH)₂ nanosheets as the precursor. A probable mechanism of formation of β‐Co(OH)₂ nanosheets, porous Co₃O₄ nanosheets, and Co₃O₄ nanorings was proposed on the basis of the experimental results.     

Cobalt Functionalization of Mesoporous Silica by Organosilane Grafting

MCM‐41, MCM‐48, and SBA‐15 have been functionalized with cobalt by grafting of different organosilane molecules and then calcined to remove the organic moieties. The materials have been characterized by N₂‐sorption, UV‐vis spectroscopy, TPR, ICP‐AES, XRD, and TGA. The nature of the formed cobalt species is dependent upon the number of amine groups in the organosilane molecules, due to the strength of the complexation. Only one amine group in the silane molecule leads to precipitation of Co₃O₄ particles during calcination, while two or more amine groups lead to the formation of cobalt silica at the surface. The obtained amount of precipitated cobalt in the samples is also dependent upon the number of amine groups and on the chain length of the silane molecules and the pore structure on the mesoporous material.     

Metallic Co4N Porous Nanowire Arrays Activated by Surface Oxidation as Electrocatalysts for the Oxygen Evolution Reaction

Designing highly efficient electrocatalysts for oxygen evolution reaction (OER) plays a key role in the development of various renewable energy storage and conversion devices. In this work, we developed metallic Co₄N porous nanowire arrays directly grown on flexible substrates as highly active OER electrocatalysts for the first time. Benefiting from the collaborative advantages of metallic character, 1D porous nanowire arrays, and unique 3D electrode configuration, surface oxidation activated Co₄N porous nanowire arrays/carbon cloth achieved an extremely small overpotential of 257 mV at a current density of 10 mA cm⁻², and a low Tafel slope of 44 mV dec⁻¹ in an alkaline medium, which is the best OER performance among reported Co‐based electrocatalysts to date. Moreover, in‐depth mechanistic investigations demonstrate the active phases are the metallic Co₄N core inside with a thin cobalt oxides/hydroxides shell during the OER process. Our finding introduces a new concept to explore the design of high‐efficiency OER electrocatalysts.     

Fabrication of Hierarchically Structured MOF‐Co3O4 on Well‐aligned CuO Nanowire with an Enhanced Electrocatalytic Property

Engineering appropriate shape and size of three‐dimensional inorganic nanostructures materials is of one the main critical problems in pursuing high‐performance electrode materials. Herein, we fabricate a metal‐organic framework derived cobalt oxide (Co₃O₄) are grown on copper oxide nanowire (CuO NWs) supported on the surface of 3D copper foam substrate. The highly aligned CuO NWs were prepared by using electrochemical anodization of copper foam in ambient temperature and followed by MOF Co₃O₄ was grown via a simple in situ solution deposition then consequent calcination process. The obtained binder‐free 3D CuO NWs@Co₃O₄ nanostructures were further characterized by using X‐ray diffraction, X‐ray photoelectron spectroscopy, field‐emission scanning electron microscopy, and transmission electron microscopy. Furthermore, electrochemical sensing of glucose was studied by using Cyclic Voltammetry, and chronoamperometry techniques. Interestingly, 3D CuO NWs@Co₃O₄ electrode exhibits excellent performance for the oxidation of glucose compared with individual entities. The proposed sensor shows wide linear ranges from 0.5 μM to 0.1 mM with the sensitivity of 6082 μA/μM and the lowest detection limit (LOD) of 0.23 μM was observed with the signal to noise ratio, (S/N) of 3. The superior catalytic oxidation of glucose mainly is endorsed by the excellent electrical conductivity and synergistic effect of the Co₃O₄ and CuO NWs.     

Nanoreactors derived from silica-protection-assisted metal-organic framework

The construction of highly stable and regular nanoreactors is a major challenge. In this work, we use a facile template protection method to obtain ZIF-67@SiO₂ (JS) and to encapsulate metal oxide nanoparticles (Co₃O₄) into nanoreactors (SiO₂). ZIF-67 crystals provide a cobalt species; SiO₂ was first used as a protective layer of ZIF-67 and then as a nanoreactor for metastable metal oxide nanoparticles. On this basis, Co₃O₄@SiO₂ with dodecahedron morphology were synthesized by calcining JS at different temperatures, followed by a hydrothermal reaction to obtain Co₃(OH)₄Si₂O₅. Subsequently, CoS_x and CoP-SiO₂ were fabricated through sulfuration and phosphorization. The results in this work show that nanoreactors derived from metal-organic frameworks (MOFs) with a rational structure have broad development prospects.     

Biomimetic Synthesis of Metal Ion‐Doped Hierarchical Crystals Using a Gel Matrix: Formation of Cobalt‐Doped LiMn2O4 with Improved Electrochemical Properties through a Cobalt‐Doped MnCO3 Precursor

We have synthesized spinel type cobalt‐doped LiMn₂O₄ (LiMn_2?yCo_yO₄, 0≤y≤0.367), a cathode material for a lithium‐ion battery, with hierarchical sponge structures via the cobalt‐doped MnCO₃ (Mn_1‐xCo_xCO₃, 0≤x≤0.204) formed in an agar gel matrix. Biomimetic crystal growth in the gel matrix facilitates the generation of both an homogeneous solid solution and the hierarchical structures under ambient condition. The controlled composition and the hierarchical structure of the cobalt‐doped MnCO₃ precursor played an important role in the formation of the cobalt‐doped LiMn₂O₄. The charge–discharge reversible stability of the resultant LiMn_1.947Co_0.053O₄ was improved to ca. 12 % loss of the discharge capacity after 100 cycles, while pure LiMn₂O₄ showed 24 % loss of the discharge capacity after 100 cycles. The parallel control of the hierarchical structure and the composition in the precursor material through a biomimetic approach, promises the development of functional materials under mild conditions.