Synthesis of novel Co3O4 nanocubes-NiO octahedral hybrids for electrochemical energy storage supercapacitors

Fabrication of novel metal oxide nanostructured composites is a proficient approach to develop efficient energy storage devices and development of cost-free and eco-friendly metal oxide nanostructures for supercapacitor applications received considerable attention in recent years. The Co₃O₄ nanocubes-NiO octahedral structured composite was constructed using facile and one-step calcination process. Cyclic voltammetry, charge-discharge, and electrochemical impedance spectral techniques have been employed to analyze the specific capacitance of the synthesized nanostructures and the composites. Specific capacitance and cycling stability of the composites were evaluated with the pristine Co₃O₄ and NiO nanostructures. The composite showed a specific capacitance of 832 F g^-1 at a current density of 0.25 A g^-1, which was ~1.5 and ~1.9-times higher than pristine Co₃O₄ nanocubes and NiO octahedral structure, respectively. On the other hand, electrode showed approximately 50 % capacity retention at a higher current density (5 Ag^-1) because of the uniform morphology of Co₃O₄ and NiO. The charge-discharge stability measurements of the composite showed an admirable specific capacitance retention capability, which was 94.5 % after 2000 continuous charge-discharge cycles at a current density of 5 A g^-1. The superior electrochemical performance of the nano-composite was ascribed to synergistic effects and uniform morphology. Efficient nanostructure development using facile and one-step calcination process and electrochemical performance make the synthesized composite a promising device for supercapacitor applications.

Tunable Synthesis of Hollow Co3O4 Nanoboxes and Their Application in Supercapacitors

Hollow Co3O4 nanoboxes constructed by numerous nanoparticles were prepared by using a facile method consisting of precipitation, solvothermal and annealing reactions. The desirable hollow structure as well as a highly porous morphology led to synergistically determined and enhanced supercapacitor performances. In particular, the hollow Co3O4 nanoboxes were comprehensively investigated to achieve further optimization by tuning the sizes of the nanoboxes, which were well controlled by initial precipitation reaction. The systematical electrochemical measurements show that the optimized Co3O4 electrode delivers large specific capacitances of 1832.7 and 1324.5 F/g at current densities of 1 and 20 A/g, and only 14.1% capacitance decay after 5000 cycles. The tunable synthesis paves a new pathway to get the utmost out of Co3O4 with a hollow architecture for supercapacitors application.

3D heterostructured cobalt oxide@layered double hydroxide core–shell networks on nickel foam for high-performance hybrid supercapacitor

3D heterostructured Co₃O₄@LDH networks were grown directly on nickel foam for the positive electrode of a high-performance hybrid supercapacitor.

Hierarchical MnCo2O4@NiMoO4 as free-standing core–shell nanowire arrays with synergistic effect for enhanced supercapacitor performance

A core–shell MnCo₂O₄@NiMoO₄ nanowire array prepared using a facile hydrothermal method showed extraordinary rate capability as a cathode for supercapacitors.

Synthesis of urchin-like Co3O4 spheres for application in oxygen evolution reaction

For oxygen evolution electrocatalysis of water splitting, unique urchin-shaped Co₃O₄ spheres were successfully grown on nickel foam by hydrothermal synthesis of Co(OH)F precursor and subsequent annealing method. The formation process was investigated by the evolution of phase structure and morphology with hydrothermal reaction time. And it can be explained by a 'disks-flowers-urchins' mechanism. Moreover, the Co₃O₄ urchins/NF exhibits considerable catalytic properties. It shows a low overpotential of 308 mV at a current density of 20 mA cm^-2 in alkaline solution. In the meantime, such material has a small Tafel slope of 82.1 mV dec^-1, large electrochemical active surface area and good long-term stability. The obvious promotion of oxygen evolution reaction performance can be attributed to the special morphology and the direct attachment to the substrate, which improve the exposed active sites, lower the internal resistance and accelerate the charge transport. Thus, the Co₃O₄ urchins/NF not only has a great potential promising behavior, but also provides the basis for subsequent performance improvement.

Hierarchically Nanostructured Transition Metal Oxides for Lithium-Ion Batteries

Lithium-ion batteries (LIBs) have been widely used in the field of portable electric devices because of their high energy density and long cycling life. To further improve the performance of LIBs, it is of great importance to develop new electrode materials. Various transition metal oxides (TMOs) have been extensively investigated as electrode materials for LIBs. According to the reaction mechanism, there are mainly two kinds of TMOs, one is based on conversion reaction and the other is based on intercalation/deintercalation reaction. Recently, hierarchically nanostructured TMOs have become a hot research area in the field of LIBs. Hierarchical architecture can provide numerous accessible electroactive sites for redox reactions, shorten the diffusion distance of Li-ion during the reaction, and accommodate volume expansion during cycling. With rapid research progress in this field, a timely account of this advanced technology is highly necessary. Here, the research progress on the synthesis methods, morphological characteristics, and electrochemical performances of hierarchically nanostructured TMOs for LIBs is summarized and discussed. Some relevant prospects are also proposed.

Three-dimensional conductive porous organic polymers based on tetrahedral polythiophene for high-performance supercapacitors

Three dimensional porous organic polymers with excellent electrochemical performance and good cyclic stability were constructed by introducing conductive polythiophene units into the frameworks with diamond topology.

MOF-templated syntheses of porous Co3O4 hollow spheres and micro-flowers for enhanced performance in supercapacitors

In this work, two kinds of MOF micro-precursors (Co-BTB-I, micro-spheres; Co-BTB-II, micro-flowers) have been synthesized with/without surfactant. After the direct pyrolysis, the hollow spherical Co-BTB-I-450 exhibits a better supercapacitor performance.

Morphology-Conserved Transformations of Metal-Based Precursors to Hierarchically Porous Micro-/Nanostructures for Electrochemical Energy Conversion and Storage

To meet future market demand, developing new structured materials for electrochemical energy conversion and storage systems is essential. Hierarchically porous micro-/nanostructures are favorable for designing such high-performance materials because of their unique features, including: i) the prevention of nanosized particle agglomeration and minimization of interfacial contact resistance, ii) more active sites and shorter ionic diffusion lengths because of their size compared with their large-size counterparts, iii) convenient electrolyte ingress and accommodation of large volume changes, and iv) enhanced light-scattering capability. Here, hierarchically porous micro-/nanostructures produced by morphology-conserved transformations of metal-based precursors are summarized, and their applications as electrodes and/or catalysts in rechargeable batteries, supercapacitors, and solar cells are discussed. Finally, research and development challenges relating to hierarchically porous micro-/nanostructures that must be overcome to increase their utilization in renewable energy applications are outlined.

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.

Graphene-Embedded Co3O4 Rose-Spheres for Enhanced Performance in Lithium Ion Batteries

Co₃O₄ has been widely studied as a promising candidate as an anode material for lithium ion batteries. However, the huge volume change and structural strain associated with the Li⁺ insertion and extraction process leads to the pulverization and deterioration of the electrode, resulting in a poor performance in lithium ion batteries. In this paper, Co₃O₄ rose-spheres obtained via hydrothermal technique are successfully embedded in graphene through an electrostatic self-assembly process. Graphene-embedded Co₃O₄ rose-spheres (G-Co₃O₄) show a high reversible capacity, a good cyclic performance, and an excellent rate capability, e.g., a stable capacity of 1110.8 mAh g^-1 at 90 mA g^-1 (0.1 C), and a reversible capacity of 462.3 mAh g^-1 at 1800 mA g^-1 (2 C), benefitted from the novel architecture of graphene-embedded Co₃O₄ rose-spheres. This work has demonstrated a feasible strategy to improve the performance of Co₃O₄ for lithium-ion battery application.