Additive-assisted oriented growth of cobalt oxide: controlled morphology and enhanced supercapacitor performance

This research investigates the supercapacitor properties of cobalt oxide (Co3O4) thin films enhanced by five different additives: urea, ammonium chloride (NH4Cl), ammonium hydroxide (NH4OH), ammonium fluoride (NH4F), and hexamethylenetetramine (HMT). The thin films are synthesized using a double hydrothermal approach on stainless steel substrates. Morphological and XRD analyses reveal well-separated Co3O4 nanowires stacked together, with diameters ranging from 10 to 34 nm and an average crystallite size between 19 and 23 nm. The additives serve as complexing agents, influencing the pH of the solution and facilitating the formation of cobalt-containing complexes, thereby promoting the uniform growth of Co3O4. Notably, the C-HMT nanowires exhibit superior supercapacitive performance, achieving a specific capacitance of 468.68 F g-1 at a scan rate of 5 mV s-1 and an impressive retention rate of 98.31% after 10 000 cycles at a scan rate of 100 mV s-1. Additionally, a symmetric device composed of two C-HMT electrodes is developed, demonstrating practical application by effectively illuminating five parallel-connected LEDs for approximately 20 seconds. In conclusion, this study presents a pioneering application of C-HMT as a symmetric supercapacitor, showcasing significant advancements in performance for future flexible energy storage devices.

Effect of cobalt doping on the electrochemical performance of trimanganese tetraoxide

Nanostructured transition metal oxides (TMO) are potential materials widely explored by researchers for energy storage applications. In this study, spinel trimanganese tetraoxide (Mn₃O₄) and cobalt doped trimanganese tetraoxide (Co-Mn₃O₄) was synthesized by using a simple solvent assisted hydrothermal route. Pure Mn₃O₄ and Co-Mn₃O₄ nanomaterials were characterized by an x-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), UV-diffuse reflectance spectroscopy (UV-DRS), field emission scanning electron microscope (FESEM), and high resolution transmission electron microscope (HRTEM). XRD analysis revealed the body centered tetragonal spinel structure of Mn₃O₄ and Co-Mn₃O₄ with a space group as l4₁/amd (141) and an approximate crystallite size of 45-33 nm. The presence of an Mn-O bond vibration was confirmed using FTIR and the band gap properties were analyzed through UV-DRS. Surface morphology and average grain size were examined using FESEM and HRTEM micrographs as nanosquares and nanospheres with diameter 126 nm and 118 nm, respectively. Electrochemical properties of Mn₃O₄ and Co-Mn₃O₄ were evaluated using cyclic voltammograms, charge-discharge curves, and electrochemical impedance spectra (EIS). Pure Mn₃O₄ showed a specific capacitance of 971 F g^-1 at 0.1 A g^-1 current density while Co-Mn₃O₄ achieved relatively higher specific capacitance of 1852 F g^-1 at the same current density. It is observed that the increased specific capacitance of Co-Mn₃O₄ mainly arises from the doping effect. Electrochemical analysis shows that the Co doped Mn₃O₄ nanomaterials can be a promising electrode material for supercapacitor.

Facile Synthesis of Bio-Template Tubular MCo2O4 (M = Cr, Mn, Ni) Microstructure and Its Electrochemical Performance in Aqueous Electrolyte

In this project, we present a comparative study of the electrochemical performance for tubular MCo2O4 (M = Cr, Mn, Ni) microstructures prepared using cotton fiber as a bio-template. Crystal structure, surface properties, morphology, and electrochemical properties of MCo2O4 are characterized using X-ray diffraction (XRD), gas adsorption, scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FTIR), cyclic voltammetry (CV), and galvanostatic charge-discharge cycling (GCD). The electrochemical performance of the electrode made up of tubular MCo2O4 structures was evaluated in aqueous 3M KOH electrolytes. The as-obtained templated MCo2O4 microstructures inherit the tubular morphology. The large-surface-area of tubular microstructures leads to a noticeable pseudocapacitive property with the excellent electrochemical performance of NiCo2O4 with specific capacitance value exceeding 407.2 F/g at 2 mV/s scan rate. In addition, a Coulombic efficiency ~100%, and excellent cycling stability with 100% capacitance retention for MCo2O4 was noted even after 5000 cycles. These tubular MCo2O4 microstructure display peak power density is exceeding 7000 W/Kg. The superior performance of the tubular MCo2O4 microstructure electrode is attributed to their high surface area, adequate pore volume distribution, and active carbon matrix, which allows effective redox reaction and diffusion of hydrated ions.

Co3O4 Nanowires on Flexible Carbon Fabric as a Binder-Free Electrode for All Solid-State Symmetric Supercapacitor

Developing portable, lightweight, and flexible energy storage systems has become a necessity with the advent of wearable electronic devices in our modern society. This work focuses on the fabrication of Co₃O₄ nanowires on a flexible carbon fabric (CoNW/CF) substrate by a simple cost-effective hydrothermal route. The merits of the high surface area of the prepared Co₃O₄ nanostructures result in an exceptionally high specific capacitance of 3290 F/g at a scan rate of 5 mV/s, which is close to their theoretical specific capacitance. Furthermore, a solid-state symmetric supercapacitor (SSC) based on CoNW/CF (CoNW/CF//CoNW/CF) was fabricated successfully. The device attains high energy and power densities of 6.7 Wh/kg and 5000 W/kg. It also demonstrates excellent rate capability and retains 95.3% of its initial capacitance after 5000 cycles. Further, the SSC holds its excellent performance at severe bending conditions. When a series assembly of four such devices is charged, it can store sufficient energy to power a series combination of five light-emitting diodes. Thus, this SSC device based on a three-dimensional coaxial architecture opens up new strategies for the design of next-generation flexible supercapacitors.

Carbon-Coated Honeycomb Ni-Mn-Co-O Inverse Opal: A High Capacity Ternary Transition Metal Oxide Anode for Li-ion Batteries

We present the formation of a carbon-coated honeycomb ternary Ni-Mn-Co-O inverse opal as a conversion mode anode material for Li-ion battery applications. In order to obtain high capacity via conversion mode reactions, a single phase crystalline honeycombed IO structure of Ni-Mn-Co-O material was first formed. This Ni-Mn-Co-O IO converts via reversible redox reactions and Li2O formation to a 3D structured matrix assembly of nanoparticles of three (MnO, CoO and NiO) oxides, that facilitates efficient reactions with Li. A carbon coating maintains the structure without clogging the open-worked IO pore morphology for electrolyte penetration and mass transport of products during cycling. The highly porous IO was compared in a Li-ion half-cell to nanoparticles of the same material and showed significant improvement in specific capacity and capacity retention. Further optimization of the system was investigated by incorporating a vinylene carbonate additive into the electrolyte solution which boosted performance, offering promising high-rate performance and good capacity retention over extended cycling. The analysis confirms the possibility of creating a ternary transition metal oxide material with binder free accessible open-worked structure to allow three conversion mode oxides to efficiently cycle as an anode material for Li-ion battery applications.

Fabrication of a snail shell-like structured MnO2@CoNiO2 composite electrode for high performance supercapacitors

MnO₂@CoNiO₂ snail shell-like structures exhibits superior specific capacitance and cyclic stability than the MnO₂ and CoNiO₂ electrodes.

Electrochemical properties of NiCoO2 synthesized by hydrothermal method

NiCoO₂ microspheres were successfully synthesized via an easy hydrothermal method, followed by an annealing process at 350 °C under a nitrogen atmosphere.

Pseudocapacitive materials for electrochemical capacitors: from rational synthesis to capacitance optimization

Among various energy-storage devices, electrochemical capacitors (ECs) are prominent power provision but show relatively low energy density. One way to increase the energy density of ECs is to move from carbon-based electric double-layer capacitors to pseudocapacitors, which manifest much higher capacitance. However, compared with carbon materials, the pseudocapacitive electrodes suffer from high resistance for electron and/or ion transfer, significantly restricting their capacity, rate capability and cyclability. Rational design of electrode materials offers opportunities to optimize their electrochemical performance, leading to devices with high energy density while maintaining high power density. This paper reviews the different approaches of electrodes striving to advance the energy and power density of ECs.

Controllable synthesis of self-assembly Co3O4 nanoflake microspheres for electrochemical performance

Tuning the ratios of ethanol to water, self-assembling microspheres composed of Co3O4 nanoflakes are synthesized by the hydrothermal method. The scanning electron microscopy (SEM) images of as-grown samples obviously show that the dispersive multilayered structures gradually change into micro/nanobelts and cubic blocks structures, and then into the desired self-assembled microspheres with increasing ratios of ethanol to water. Also, all the x-ray diffraction (XRD) patterns evidently demonstrate that all obtained Co3O4 has cubic crystal structure. The corresponding synthesis mechanism is discussed in detail. More importantly, the unique self-assembling Co3O4 nanoflake microspheres have excellent electrochemical performance with large specific capacitance, good rate capability and excellent cycling performance, evidently presenting a potential capability of Co3O4 nanoflake microspheres to act as electrode materials for supercapacitors in sustainable power sources.

Controllable fabrication of urchin-like Co3O4 hollow spheres for high-performance supercapacitors and lithium-ion batteries

Urchin-like cobalt oxide (Co₃O₄) hollow spheres can be successfully prepared by thermal decomposition of cobalt carbonate hydroxide hydrate (Co(CO₃)_0.5(OH)·0.11H₂O) obtained by template-assisted hydrothermal synthesis.

Mesoporous Co3O4@carbon composites derived from microporous cobalt-based porous coordination polymers for enhanced electrochemical properties in supercapacitors

In this work, mesoporous Co₃O₄@carbon composites were prepared through a simple, one-step, carbonization of microporous cobalt-based porous coordination polymer ZSA-1.

Facile synthesis of mesoporous cobalt oxide rugby balls for electrochemical energy storage

Mesoporous Co₃O₄ rugby balls for the asymmetric supercapacitor manifest high energy/power density and no decay after 10 000 cycles.

A novel 3D oxide nanosheet array catalyst derived from hierarchical structured array-like CoMgAl-LDH/graphene nanohybrid for highly efficient NOx capture and catalytic soot combustion

A novel 3D oxide nanosheet array catalyst was fabricated using a graphene template induced strategy for highly efficient NO_x capture and catalytic soot combustion.

Biomorphic synthesis of mesoporous Co₃O₄ microtubules and their pseudocapacitive performance

A novel meosoporous tubular Co3O4 has been fabricated by a simple and cost-effective biomorphic synthesis route, which consists of infiltration of cotton fiber with cobalt nitrate solution and postcalcination at 673 K for 1 h. Its electrochemical performance as a supercapacitor electrode material is investigated by means of cyclic voltammetry and chronopotentiometry tests. Compared with bulk Co3O4 prepared without using cotton template, biomorphic Co3O4 displays 2.8 fold enhancement of pseudocapacitive performance because of the unique tubular morphology, relative high specific surface area (3 and 0.8 m(2)/g for biomorphic Co3O4 and bulk Co3O4, respectively), and mesoporous nature.

Solution synthesis of metal oxides for electrochemical energy storage applications

This article provides an overview of solution-based methods for the controllable synthesis of metal oxides and their applications for electrochemical energy storage. Typical solution synthesis strategies are summarized and the detailed chemical reactions are elaborated for several common nanostructured transition metal oxides and their composites. The merits and demerits of these synthesis methods and some important considerations are discussed in association with their electrochemical performance. We also propose the basic guideline for designing advanced nanostructure electrode materials, and the future research trend in the development of high power and energy density electrochemical energy storage devices.

Scalable one-pot bacteria-templating synthesis route toward hierarchical, porous-Co3O4 superstructures for supercapacitor electrodes

Template-driven strategy has been widely used to synthesize inorganic nano/micro materials. Here, we used a bottom-up controlled synthesis route to develop a powerful solution-based method of fabricating three-dimensional (3D), hierarchical, porous-Co₃O₄ superstructures that exhibit the morphology of flower-like microspheres (hereafter, RT-Co₃O₄). The gram-scale RT-Co₃O₄ was facilely prepared using one-pot synthesis with bacterial templating at room temperature. Large-surface-area RT-Co₃O₄ also has a noticeable pseudocapacitive performance because of its high mass loading per area (~10 mg cm⁻²), indicating a high capacitance of 214 F g⁻¹ (2.04 F cm⁻²) at 2 A g⁻¹ (19.02 mA cm⁻²), a Coulombic efficiency averaging over 95%, and an excellent cycling stability that shows a capacitance retention of about 95% after 4,000 cycles.

One-step hydrothermal fabrication of strongly coupled Co3O4 nanosheets–reduced graphene oxide for electrochemical capacitors

A one-step alkaline hydrothermal strategy was developed to fabricate a strongly coupled Co₃O₄ NSs–rGO hybrid with large specific capacitance and high electrochemical utilization at high rates for advanced supercapacitors.

A hybrid of CoOOH nanorods with carbon nanotubes as a superior positive electrode material for supercapacitors

A hybrid of CoOOH nanorods with MWCNTs has been synthesized by hydrothermal method, exhibiting high reversible capacitance, good high-rate capability and excellent cycling performance.