Supercapacitor electrode with a homogeneously Co3O4-coated multiwalled carbon nanotube for a high capacitance

Sonication-supported synthesis of cobalt oxide assembled on an N-MWCNT composite for electrochemical supercapacitors via three-electrode configuration

The Co₃O₄@N-MWCNT composite was synthesized by a sonication-supported thermal reduction process for supercapacitor applications. The structural and morphological properties of the materials were characterized via Raman, XRD, XPS, SEM-EDX, and FE-TEM analysis. The composite electrode was constructed into a three-electrode configuration and examined by using CV, GCD and EIS analysis. The demonstrated electrochemical value of ~ 225 F/g at 0.5 A/g by the electrode made it appropriate for potential use in supercapacitor applications.

Preparation of Cobalt Oxide-Reduced Graphitic Oxide Supercapacitor Electrode by Photothermal Processing

We report a photonic technique to instantaneously synthesize cobalt oxide reduced graphitic oxide (CoOx-rGO) supercapacitor electrodes. The electrode processing is achieved through rapidly heating the precursor material by irradiation of high-energy pulsed mostly visible light from a xenon lamp. Due to the short duration of the light pulse, we prepared the electrodes at room temperature instantaneously (ms), thus eliminating the several hours of processing times of the conventional techniques. The as-prepared electrodes exhibited a highly porous morphology, allowing for enhanced ionic transport during electrochemical interactions. The electrochemical properties of the CoOx-rGO electrodes were studied in 1 M KOH aqueous electrolyte. The non-rectangular cyclic voltammetry (CV) curves with characteristic redox peaks indicated the pseudocapacitive charge storage mechanism of the electrodes. From the discharge curves at 0.4 mA/cm2 and 1.6 A/g constant current densities, the electrode showed areal specific capacitance of 17 mF/cm2 and specific capacitance of 69 F/g, respectively. Cyclic stability was tested by performing 30,000 galvanostatic charge-discharge (GCD) cycles and the electrode exhibited 65% capacitance retention, showing its excellent electrochemical performance and ultra-long cycle life. The excellent electrochemical electrode properties are attributed to the unique processing technique, optimum processing parameters, improved conductivity due to the presence of rGO, and highly porous morphology which offers a high specific surface area. The novel photonic processing we report allows for high-temperature heating of the precursor films achieved via non-radiative recombination of photogenerated electron holes pairs during irradiation. Such extremely quick (ms) heating followed by instantaneous cooling results in the formation of a dense and robust bottom layer of the electrode, resulting in a long cycle life.

Co-Effect Flame Retardation of Co3O4-Loaded Titania Nanotubes and α-Zirconium Phosphate in the Epoxy Matrix

Like most macromolecule polymers, epoxy resin (EP) is easy to burn, and there are great fire safety hazards in the process of use. Therefore, how to improve the fire safety of EP becomes one of the problems to be considered in the application of EP. In this study, tricobalt tetraoxide (Co₃O₄)-loaded TiO₂ nanotube (TNT) (Co₃O₄-TNT) hybrid material was prepared by the co-precipitation method, and organophilic α-ZrP (OZrP) was obtained by hexadecyl trimethyl ammonium bromide-intercalated α-zirconium phosphate (α-ZrP) which was prepared by the hydrothermal synthesis method. Then, a series of nanocomposites were obtained by adding the synthesized nanomaterials to the EP at a certain ratio. The structure and morphology characterization indicated that Co₃O₄-TNTs and OZrP were synthesized successfully. The results of thermogravimetric analysis showed that the co-addition of Co₃O₄-TNTs and OZrP could further enhance the thermal stability of EP. The results of a cone calorimeter showed that EP/OZrP/Co₃O₄-TNTs had the lowest peak heat release rate and total heat release, which decreased by 36.2 and 35.4%, respectively, compared with the pure EP. This indicates that Co₃O₄-TNTs and OZrP had a good synergetic flame retardant effect and could effectively enhance the flame retardancy of EP.

Improvement of the Pseudocapacitive Performance of Cobalt Oxide-Based Electrodes for Electrochemical Capacitors

Cobalt oxide nanopowders are synthesized by the pyrolysis of aerosol particles of water solution of cobalt acetate. Cobalt nanopowder is obtained by subsequent reduction of obtained cobalt oxide by annealing under a hydrogen atmosphere. The average crystallite size of the synthesized porous particles ranged from 7 to 30 nm, depending on the synthesis temperature. The electrochemical characteristics of electrodes based on synthesized cobalt oxide and reduced cobalt oxide are investigated in an electrochemical cell using a 3.5 M KOH solution as the electrolyte. The results of electrochemical measurements show that the electrode based on reduced cobalt oxide (Re-Co3O4) exhibits significantly higher capacity, and lower Faradaic charge–transfer and ion diffusion resistances when compared to the electrodes based on the initial cobalt oxide Co3O4. This observed effect is mainly due to a wide range of reversible redox transitions such as Co(II) ↔ Co(III) and Co(III) ↔ Co(IV) associated with different cobalt oxide/hydroxide species formed on the surface of metal particles during the cell operation; the small thickness of the oxide/hydroxide layer providing a high reaction rate, and also the presence of a metal skeleton leading to a low series resistance of the electrode.

In situ encapsulation of Co3O4 polyhedra in graphene sheets for high-capacitance supercapacitors

Co3O4 polyhedra were well encapsulated in reduced graphene oxide (rGO) sheets by in situ growth of Co-based zeolitic imidazolate framework (ZIF-67) polyhedra in the presence of graphene oxide followed by thermal annealing. The resultant rGO/Co3O4 composites consist of a continuously-conductive double-network constructed from graphene sheets and the derived N-doped carbons from ZIF-67, showing a large specific surface area of 523 m2 g-1. The as-fabricated symmetrical supercapacitor based on rGO/Co3O4 exhibits a high specific capacitance of 277.5 F g-1 at 25 A g-1 and an energy density of 24.7 W h kg-1 at a power density of up to 40 kW kg-1. The supercapacitor also retains 87.5% of the initial capacitance over 5000 cycles at 5 A g-1. Such large capacitance, high energy density, and excellent cycling stability for rGO/Co3O4 are attributable to the 3D double conductive network from 2D graphene sheets and porous channels of pseudo-capacitive Co3O4 polyhedra.

Hierarchical Flowerlike 3D nanostructure of Co3O4@MnO2/N-doped Graphene oxide (NGO) hybrid composite for a high-performance supercapacitor

The present study investigates the fabrication of hierarchical 3D nanostructures with multi-component metal oxides in the presence of highly-porous graphene and characterized for its applications in high-performance supercapacitors. A hierarchical flowers like 3D nanostructure of Co₃O₄ @MnO₂ on nitrogen-doped graphene oxide (NGO) hybrid composite was synthesized by thermal reduction process at 650 °C in the presence of ammonia and urea. The synthesized Co₃O₄@MnO₂/NGO hybrid composites were studied via Raman, XRD, X-ray XPS, FE-SEM, FE-SEM with EDX, FE-TEM and BET analyses. The electrochemical analysis of Co₃O₄@MnO₂/NGO hybrid composite electrode was investigated using cyclic voltammetry, chronopotentiometry and electrochemical impedance measurements. The hybrid composite electrode showed significant specific capacitance results of up to 347 F/g at 0.5 A/g and a corresponding energy density of 34.83 Wh kg⁻¹ with better rate performance and excellent long-term cycling stability were achieved for 10,000 cycles. The obtained electrochemical results paved a way to utilize Co₃O₄@MnO₂/NGO composite electrode as a promising electrode material in high performance supercapacitors.

Reducing and Uniforming the Co3 O 4 Particle Size by Sulfonated Graphenal Polymers for Electrochemical Applications

A novel two-dimensional (2D) nanomaterial, namely sulfonated graphenal polymer (SGP), is used to tune the hydrothermal growth of Co₃O₄ nanoparticles. SGP provides abundant nucleation sites to grow Co₃O₄ nanoparticles and effectively reduces the particle size and dimension. As a result, with considering the improved size uniformity of Co₃O₄ and the tight wrapping of SGP around Co₃O₄ as well, the Co₃O₄/SGP hybrid electrode exhibits a high specific electrochemical capacitance of 234.28 F/g at a current density of 0.2 A/g, 237% higher than that of the pure Co₃O₄ electrode. By using the hybrid as the anode of an all-solid-state asymmetric supercapacitor, the capacitance can be well maintained up to 93% after 5000 cycles even at 2 A/g.

Nanostructured (Co, Mn)3O4 for High Capacitive Supercapacitor Applications

Nanostructured Co doped Mn₃O₄ spinel structure ((Co, Mn)₃O₄) were prepared by co-precipitation under O₃ oxidizing conditions and post-heat treatment. The product was composed of nanogranules with a diameter of 20-60 nm. The electrochemical performance of (Co, Mn)₃O₄ electrode was tested by cyclic voltammetry, impedance, and galvanostatic charge-discharge measurements. A maximum specific capacitance value of 2701.0 F g^-1 at a current density of 5 A g^-1 could be obtained within the potential range from 0.01 to 0.55 V versus Hg/HgO electrode in 6 mol L^-1 KOH electrolyte. When at high current density of 30 A g^-1, the capacitance is 1537.2 F g^-1 or 56.9% of the specific capacitance at 5 A g^-1, indicating its good rate capability. After 500 cycles at 20 A g^-1, the specific capacitance remains 1324 F g^-1 with a capacitance retention of 76.4%.

A nanocrystalline Co3O4@polypyrrole/MWCNT hybrid nanocomposite for high performance electrochemical supercapacitors

In this study, a ternary hybrid nanocomposite of Co₃O₄@polypyrrole/MWCNT was prepared via oxidative polymerization of pyrrole monomer and a hybrid composite by a hydrothermal process.

Fabrication and performance evaluation of hybrid supercapacitor electrodes based on carbon nanotubes and sputtered TiO2

We report a simple and eco-friendly method for the fabrication of a titanium dioxide/functionalized multiwalled carbon nanotube (TiO2/FMWCNT) composite electrode for use in supercapacitors. The nanocomposite electrodes were formed by depositing titanium dioxide onto FMWCNTs using reactive magnetron sputtering, thus providing a green roue for the formation of the binder-free composite electrode. It is shown that the electrochemical performance of the fabricated electrodes can be altered by tuning the thickness of the titanium dioxide overlayer. The integrated nanocomposite electrode showed an improved specific capacitance of 90 Fg(-1) in two-electrode configuration.

Carbon and Binder-Free Air Electrodes Composed of Co3O 4 Nanofibers for Li-Air Batteries with Enhanced Cyclic Performance

In this study, to fabricate a carbon free (C-free) air electrode, Co3O4 nanofibers were grown directly on a Ni mesh to obtain Co3O4 with a high surface area and good contact with the current collector (the Ni mesh). In Li-air cells, any C present in the air electrode promotes unwanted side reactions. Therefore, the air electrode composed of only Co3O4 nanofibers (i.e., C-free) was expected to suppress these side reactions, such as the decomposition of the electrolyte and formation of Li2CO3, which would in turn enhance the cyclic performance of the cell. As predicted, the Co3O4-nanofiber electrode successfully reduced the accumulation of reaction products during cycling, which was achieved through the suppression of unwanted side reactions. In addition, the cyclic performance of the Li-air cell was superior to that of a standard electrode composed of carbonaceous material.