Preparation of electrospun Co3O4 nanofibers as electrode material for high performance asymmetric supercapacitors

Conversion of cobalt from spent LIBs to Co3O4 electrode material for application in supercapacitors

The cathode material of lithium-ion batteries (LIBs) is endowed with valuable metals, such as cobalt. The improper treatment of these batteries pollutes the environment and causes enormous resource waste. Therefore, the recovery of valuable metals from spent LIBs has attracted widespread attention. In this study, Co3O4 electrode materials were prepared by a simple homogeneous precipitation method and heat treatment using a leaching solution of spent LIBs-positive electrode material as the cobalt source. The crystal structure and morphology of the products were examined at different annealing temperatures, and their electrochemical performance was analyzed. The results show that low-temperature annealing contributes to grain refinement. The Co3O4 material prepared at 300°C annealing temperature has a rod-like structure with distinct pores and a specific surface area of 58.98 m2 g-1. Furthermore, electrochemical performance testing reveals that Co3O4 prepared at 300°C displays the best electrochemical performance as an electrode material, with a specific capacitance of 97.93 F g-1 and a cycle retention rate of 79.12% after 500 charge-discharge cycles. These findings demonstrate the feasibility of recycling valuable metal cobalt from spent LIBs cathode materials to produce Co3O4 materials for use as supercapacitor electrode materials, opening up new avenues for the recycling and utilisation of spent LIBs.

Structure and Morphological Properties of Cobalt-Oxide-Based (Co3O4) Materials as Electrodes for Supercapacitors: A Brief Review

Over the past 15 years, there has been a significant increase in the search for environmentally friendly energy sources, and transition-metal-based energy storage devices are leading the way in these new technologies. Supercapacitors are attractive in this regard due to their superior energy storage capabilities. Electrode materials, which are crucial components of supercapacitors, such as cobalt-oxide-based electrodes, have great qualities for achieving high supercapacitor performance. This brief review presents some basic concepts and recent findings on cobalt-based materials used to fabricate electrodes for supercapacitors. The text also clarifies how morphological characteristics typically influence certain properties. The inner surface of the electrode exhibits several properties that change to provide it a great boost in specific capacitance and charge storage. Porous structures with defined pore sizes and shapes and high surface areas are important features for improving electrochemical properties. Finally, we present some perspectives for the development of cobalt-oxide-based supercapacitors, focusing on their structure and properties.

A Review on the Application of Cobalt-Based Nanomaterials in Supercapacitors

Among many electrode materials, cobalt-based nanomaterials are widely used in supercapacitors because of their high natural abundance, good electrical conductivity, and high specific capacitance. However, there are still some difficulties to overcome, including poor structural stability and low power density. This paper summarizes the research progress of cobalt-based nanomaterials (cobalt oxide, cobalt hydroxide, cobalt-containing ternary metal oxides, etc.) as electrode materials for supercapacitors in recent years and discusses the preparation methods and properties of the materials. Notably, the focus of this paper is on the strategies to improve the electrochemical properties of these materials. We show that the performance of cobalt-based nanomaterials can be improved by designing their morphologies and, among the many morphologies, the mesoporous structure plays a major role. This is because mesoporous structures can mitigate volume changes and improve the performance of pseudo capacitance. This review is dedicated to the study of several cobalt-based nanomaterials in supercapacitors, and we hope that future scholars will make new breakthroughs in morphology design.

Synthesis of Needle-like Nanostructure Composite Electrode of Co3O4/rGO/NF for High-Performance Symmetric Supercapacitor

In this work, a hierarchical electrode structure of cobaltosic oxide (Co3O4) growing on a reduced graphene oxide (rGO)-covered nickel foam (NF) substrate (named Co3O4/rGO/NF) is fabricated by a facile hydrothermal and subsequent annealing process. Thousands of nanoneedle units uniformly arranged on the surface of the rGO sheet stimulate the evident increase in the specific surface area and thus produce more active sites. Because of the special hierarchical structure, the Co3O4/rGO/NF electrode shows a high specific capacitance of 1400 F g−1 at 1 A g−1 and retains 58% capacitance even when the current density increases to 30 A g−1. In addition, a symmetric supercapacitor based on the Co3O4/rGO/NF electrode is assembled, exhibiting high specific capacitance of 311 F g−1 at 1 A g−1, as well as remarkable power density and energy density (40.67 Wh kg−1 at 12 kW kg−1). The device also demonstrates a great cycling performance after 10,000 cycles under the current density of 10 A g−1, acquiring 89.69% capacitance retention of the initial state. The accessible synthetic method and superior electrochemical performance of the Co3O4/rGO/NF composite electrode implicate its extensive application prospects in terms of new energy storage.

Application of Electrospun Nanofibers for Fabrication of Versatile and Highly Efficient Electrochemical Devices: A Review

Electrochemical devices convert chemical reactions into electrical energy or, vice versa, electricity into a chemical reaction. While batteries, fuel cells, supercapacitors, solar cells, and sensors belong to the galvanic cells based on the first reaction, electrolytic cells are based on the reversed process and used to decompose chemical compounds by electrolysis. Especially fuel cells, using an electrochemical reaction of hydrogen with an oxidizing agent to produce electricity, and electrolytic cells, e.g., used to split water into hydrogen and oxygen, are of high interest in the ongoing search for production and storage of renewable energies. This review sheds light on recent developments in the area of electrospun electrochemical devices, new materials, techniques, and applications. Starting with a brief introduction into electrospinning, recent research dealing with electrolytic cells, batteries, fuel cells, supercapacitors, electrochemical solar cells, and electrochemical sensors is presented. The paper concentrates on the advantages of electrospun nanofiber mats for these applications which are mostly based on their high specific surface area and the possibility to tailor morphology and material properties during the spinning and post-treatment processes. It is shown that several research areas dealing with electrospun parts of electrochemical devices have already reached a broad state-of-the-art, while other research areas have large space for future investigations.

Preparation and Electrochemical Properties of Co3O4 Supercapacitor Electrode Materials

A special gas-phase diffusion precipitation method with ammonia as the gas-phase diffusion precipitant was adopted. After fully reacting with different cobalt sources in a sealed space, the liquid funnel was separated and dried, and calcined at different temperatures for 2 h. The prepared Co3O4 powder was used as a supercapacitor (SCs) electrode to measure the electrochemical properties of the prepared material. The influences of different cobalt sources and sodium phosphate monobasic dehydrate on the preparation of Co3O4 SCs electrodes were investigated. The optimal performance of Co3O4 was 640 F·g−1 before modification, and this reached 1140 F·g−1 after modification, which was an improvement of 78.1%.

Cobalt-tungsten diselenide-supported nickel foam as a battery-type positive electrode for an asymmetric supercapacitor device: comparison with various MWSe2 (M = Ni, Cu, Zn, and Mn) on the structural and capacitance characteristics

New exploration in nanomaterial research has been greatly encouraged so as to discover active electrode materials with extraordinary properties and performances. In this report, we demonstrated the synthesis of different transition metal-incorporated MWSe2 (M = Co, Ni, Cu, Zn, and Mn) and studied them using various characterization techniques. Subsequently, the proposed bimetallic chalcogenides were successfully applied as the active electrode materials for pseudocapacitor applications. The results of the electrochemical studies showed that CoWSe2 exhibited a higher specific capacitance of 3309.58 F g-1 at a constant applied current density of 1.35 A g-1, which is 1.07, 1.76, 2.04, 8.7, and 12.28-fold higher than that of NiWSe2, CuWSe2, ZnWSe2, MnWSe2, and pristine WSe2, respectively. The interconnected nanosheet structure with voids facilitates rich active sites for efficient electrolyte uptake and superior charge transfer during the faradaic redox reaction. In addition, the cycle stability of CoWSe2/NF was studied and the retention capacitance of about 82.1% was recorded, which is higher than that of NiWSe2 (60.4%), CuWSe2 (50.12%), ZnWSe2 (46.44%), MnWSe2 (40.12%), and pristine WSe2 (31.2%). Owing to the higher specific capacitance and cycle stability, CoWSe2 was proposed as a battery-type electrode material for the fabrication of an asymmetric device. The fabricated CoWSe2//AC device provided excellent energy density and power density of 182.54 W h kg-1 and 2810.81 W kg-1, respectively, at 3.51 A g-1. Based on these properties, the proposed research and studies can provide a way for the profound development of 2D-layered metal chalcogenides for energy storage applications.

Zeolitic imidazolate framework derived ZnCo2O4 hollow tubular nanofibers for long-life supercapacitors

Uniform one-dimensional metal oxide hollow tubular nanofibers (HTNs) have been controllably prepared using a calcination strategy using electrospun polymer nanofibers as soft templates and zeolitic imidazolate framework nanoparticles as precursors. Utilizing the general synthesis method, the ZnO HTNs, Co3O4 HTNs and ZnCo2O4 HTNs have been successfully prepared. The optimal ZnCo2O4 HTNs, as a representative substance applied in supercapacitors as the positive electrode, delivers a high specific capacity of 181 C g-1 at a current density of 0.5 A g-1, an excellent rate performance of 75.14% and a superior capacity retention of 97.42% after 10 000 cycles. Furthermore, an asymmetric supercapacitor assembled from ZnCo2O4 HTNs and active carbon also shows a stable and ultrahigh cycling stability with 95.38% of its original capacity after 20 000 cycle tests.

Progress of electrospray and electrospinning in energy applications

In the promotion of energy strategies to address the global energy crisis, nanotechnology has been successfully used to generate novel energy materials with excellent characteristics, such as high specific surface area, good flexibility and large porosity. Among the various methods for fabricating nanoscale materials, electrospray and electrospinning technologies have unlocked low-cost, facile and industrial routes to nanotechnology over the past ten years. This review highlights research into the key parts and primary theory of these techniques and their application in preparing energy-related materials and devices: especially fuel cells, solar cells, lithium ion batteries, supercapacitors as well as hydrogen storage systems. The challenges and future prospects of the manufacturing technologies are also covered in this paper.

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.

Recent Advance in Co3O4 and Co3O4-Containing Electrode Materials for High-Performance Supercapacitors

Among the popular electrochemical energy storage devices, supercapacitors (SCs) have attracted much attention due to their long cycle life, fast charge and discharge, safety, and reliability. Transition metal oxides are one of the most widely used electrode materials in SCs because of the high specific capacitance. Among various transition metal oxides, Co3O4 and related composites are widely reported in SCs electrodes. In this review, we introduce the synthetic methods of Co3O4, including the hydrothermal/solvothermal method, sol-gel method, thermal decomposition, chemical precipitation, electrodeposition, chemical bath deposition, and the template method. The recent progress of Co3O4-containing electrode materials is summarized in detail, involving Co3O4/carbon, Co3O4/conducting polymer, and Co3O4/metal compound composites. Finally, the current challenges and outlook of Co3O4 and Co3O4-containing composites are put forward.

Nano spinel cobaltites and their catalytic and electrochemical properties: facile synthesis of metal (Co, Ni, and Zn) and mixed metal (Co–Ni and Co–Zn) complexes of Schiff bases prepared from α-ketoglutaric acid and ethyl carbazate

Nanocobaltites synthesized from solid solution precursors showed strong photocatalytic activity and enhanced electrochemical properties.

Facile Electrodeposition of Poly(3,4-ethylenedioxythiophene) on Poly(vinyl alcohol) Nanofibers as the Positive Electrode for High-Performance Asymmetric Supercapacitor

Poly(vinyl alcohol)/poly(3,4-ethylenedioxythiophene) (PVA/PEDOT) nanofibers were synthesized as a positive electrode for high-performance asymmetric supercapacitor (ASC). PVA/PEDOT nanofibers were prepared through electrospinning and electrodeposition meanwhile reduced graphene oxide (rGO) was obtained by electrochemical reduction. The PVA/PEDOT nanofibers demonstrated cauliflower-like morphology showing that PEDOT was uniformly coated on the smooth cross-linking structure of PVA nanofibers. In addition, the ASC showed a remarkable energy output efficiency by delivering specific energy of 21.45 Wh·kg−1 at a specific power of 335.50 W·kg−1 with good cyclability performance (83% capacitance retained) after 5000 CV cycles. The outstanding supercapacitive performance is contributed from the synergistic effects of both PVA/PEDOT//rGO, which gives promising materials for designing high-performance supercapacitor applications.

Synthesis, Characterization and Photocatalytic Activity of Nanocrystalline First Transition-Metal (Ti, Mn, Co, Ni and Zn) Oxisde Nanofibers by Electrospinning

In this work, five nanocrystalline first transition-metal (Ti, Mn, Co, Ni and Zn) oxide nanofibers were prepared by electrospinning and controlled calcination. The morphology, crystal structure, pore size distribution and specific surface area were systematically studied by scanning electron microscope (SEM), transmission electron microscope (TEM), surface and pore analysis, and thermo gravimetric analyzer (TGA). The results reveal that the obtained nanofibers have a continuously twisted three-dimensional scaffold structure and are composed of neat nanocrystals with a necklace-like arrangement. All the samples possess high specific surface areas, which follow the order of NiO nanofiber (393.645 m2/g) > TiO2 nanofiber (121.445 m2/g) > ZnO nanofiber (57.219 m2/g) > Co3O4 nanofiber (52.717 m2/g) > Mn2O3 nanofiber (18.600 m2/g). Moreover, the photocatalytic degradation of methylene blue (MB) in aqueous solution was investigated in detail by employing the five kinds of metal oxide nanofibers as photocatalysts under ultraviolet (UV) irradiation separately. The results show that ZnO, TiO2 and NiO nanofibers exhibit excellent photocatalytic efficiency and high cycling ability to MB, which may be ascribed to unique porous structures and the highly efficient separation of photogenerated electron-hole pairs. In brief, this paper aims to provide a feasible approach to achieve five first transition-metal oxide nanofibers with excellent performance, which is important for practical applications.

In situ grown nickel selenide on graphene nanohybrid electrodes for high energy density asymmetric supercapacitors

Nickel selenide (NiSe) nanoparticles uniformly supported on graphene nanosheets (G) to form NiSe-G nanohybrids were prepared by an in situ hydrothermal process. The uniform distribution of NiSe on graphene bestowed the NiSe-G nanohybrid with faster charge transport and diffusion along with abundant accessible electrochemical active sites. The synergistic effect between NiSe nanoparticles and graphene nanosheets for supercapacitor applications was systematically investigated for the first time. The freestanding NiSe-G nanohybrid electrode exhibited better electrochemical performance with a high specific capacitance of 1280 F g-1 at a current density of 1 A g-1 and a capacitance retention of 98% after 2500 cycles relative to that of NiSe nanoparticles. Furthermore, an asymmetric supercapacitor device assembled using the NiSe-G nanohybrid as the positive electrode, activated carbon as the negative electrode and an electrospun PVdF membrane containing 6 M KOH as both the separator and the electrolyte delivered a high energy density of 50.1 W h kg-1 and a power density of 816 W kg-1 at an extended operating voltage of 1.6 V. Thus, the NiSe-G nanohybrid can be used as a potential electrode material for high-performance supercapacitors.

Core-Shell Nitrogen-Doped Carbon Hollow Spheres/Co3 O4 Nanosheets as Advanced Electrode for High-Performance Supercapacitor

Co₃ O₄ /nitrogen-doped carbon hollow spheres (Co₃ O₄ /NHCSs) with hierarchical structures are synthesized by virtue of a hydrothermal method and subsequent calcination treatment. NHCSs, as a hard template, can aid the generation of Co₃ O₄ nanosheets on its surface; while SiO₂ spheres, as a sacrificed-template, can be dissolved in the process. The prepared Co₃ O₄ /NHCS composites are investigated as the electrode active material. This composite exhibits an enhanced performance than Co₃ O₄ itself. A higher specific capacitance of 581 F g^-1 at 1 A g^-1 and a higher rate performance of 91.6% retention at 20 A g^-1 are achieved, better than Co₃ O₄ nanorods (318 F g^-1 at 1 A g^-1 and 67.1% retention at 20 A g^-1 ). In addition, the composite is employed as a positive electrode to fabricate an asymmetric supercapacitor. The device can deliver a high energy density of 34.5 Wh kg^-1 at the power density of 753 W kg^-1 and display a desirable cycling stability. All of these attractive results make the unique hierarchical Co₃ O₄ /NHCS core-shell structure a promising electrode material for high-performance supercapacitors.

Facile synthesis of electrostatically anchored Nd(OH)3 nanorods onto graphene nanosheets as a high capacitance electrode material for supercapacitors

Nd(OH)₃/G hybrid is prepared by a solvothermal reduction process and used as an electrode material for asymmetric supercapacitors.

Hydrothermal assisted in situ growth of CoSe onto graphene nanosheets as a nanohybrid positive electrode for asymmetric supercapacitors

Cobalt selenide–graphene (CoSe–G) nanohybrid was successfully synthesised by a one-pot hydrothermal method and used as a positive electrode for asymmetric supercapacitor, which provides an energy density of 45.5 W h kg⁻¹ and a power density of 1.1 kW kg⁻¹.

Solid-state supercapacitors with rationally designed heterogeneous electrodes fabricated by large area spray processing for wearable energy storage applications

Supercapacitors are in demand for short-term electrical charge and discharge applications. Unlike conventional supercapacitors, solid-state versions have no liquid electrolyte and do not require robust, rigid packaging for containment. Consequently they can be thinner, lighter and more flexible. However, solid-state supercapacitors suffer from lower power density and where new materials have been developed to improve performance, there remains a gap between promising laboratory results that usually require nano-structured materials and fine-scale processing approaches, and current manufacturing technology that operates at large scale. We demonstrate a new, scalable capability to produce discrete, multi-layered electrodes with a different material and/or morphology in each layer, and where each layer plays a different, critical role in enhancing the dynamics of charge/discharge. This layered structure allows efficient utilisation of each material and enables conservative use of hard-to-obtain materials. The layered electrode shows amongst the highest combinations of energy and power densities for solid-state supercapacitors. Our functional design and spray manufacturing approach to heterogeneous electrodes provide a new way forward for improved energy storage devices.

Mesoporous NiCo2O4 nanospheres with a high specific surface area as electrode materials for high-performance supercapacitors

Ternary nickel cobaltite has attracted more and more attention as a promising electrode material for high performance supercapacitors (SCs) due to its high theoretical capacity, unique crystal structure and excellent electronic conductivity.

Electrochemical properties of PVA–GO/PEDOT nanofibers prepared using electrospinning and electropolymerization techniques

Conducting nanofibers composed of poly(vinyl alcohol) (PVA), graphene oxide (GO) and poly(3,4-ethylenedioxythiophene) (PEDOT) were fabricated via a combined method using electrospinning and electropolymerization techniques.

CoOx nanoparticles embedded in porous graphite carbon nanofibers derived from electrospun polyacrylonitrile@polypyrrole core–shell nanostructures for high-performance supercapacitors

A novel composite nanostructure of C–CoO_x–C with CoO_x nanoparticles embedded in N-containing porous graphite carbon nanofibers exhibited a more acceptable specific capacitance, higher rate capability and better cycling stability.