Three-dimensional graphene combined with hierarchical CuS for the design of flexible solid-state supercapacitors

Application of Copper-Sulfur Compound Electrode Materials in Supercapacitors

Supercapacitors (SCs) are a novel type of energy storage device that exhibit features such as a short charging time, a long service life, excellent temperature characteristics, energy saving, and environmental protection. The capacitance of SCs depends on the electrode materials. Currently, carbon-based materials, transition metal oxides/hydroxides, and conductive polymers are widely used as electrode materials. However, the low specific capacitance of carbon-based materials, high cost of transition metal oxides/hydroxides, and poor cycling performance of conductive polymers as electrodes limit their applications. Copper-sulfur compounds used as electrode materials exhibit excellent electrical conductivity, a wide voltage range, high specific capacitance, diverse structures, and abundant copper reserves, and have been widely studied in catalysis, sensors, supercapacitors, solar cells, and other fields. This review summarizes the application of copper-sulfur compounds in SCs, details the research directions and development strategies of copper-sulfur compounds in SCs, and analyses and summarizes the research hotspots and outlook, so as to provide a reference and guidance for the use of copper-sulfur compounds.

Facile and Controllable Synthesis of CuS@Ni-Co Layered Double Hydroxide Nanocages for Hybrid Supercapacitors

The synthesis of battery-type electrode materials with hollow nanostructures for high-performance hybrid supercapacitors (HSCs) remains challenging. In this study, hollow CuS@Ni-Co layered double hydroxide (CuS-LDH) composites with distinguished compositions and structures are successfully synthesized by co-precipitation and the subsequent etching/ion-exchange reaction. CuS-LDH-10 with uniformly dispersed CuS prepared with the addition of 10 mg of CuS shows a unique hollow polyhedral structure constituted by loose nanosphere units, and these nanospheres are composed of interlaced fine nanosheets. The composite prepared with 30 mg of CuS addition (CuS-LDH-30) is composed of a hollow cubic morphology with vertically aligned nanosheets on the CuS shell. The CuS-LDH-10 and CuS-LDH-30 electrodes exhibit high specific capacity (765.1 and 659.6 C g^-1 at 1 A g^-1, respectively) and superior cycling performance. Additionally, the fabricated HSC delivers a prominent energy density of 52.7 Wh kg^-1 at 804.5 W kg^-1 and superior cycling performance of 87.9% capacity retention after 5000 cycles. Such work offers a practical and effortless route for synthesizing unique metal sulfide/hydroxide composite electrode materials with hollow structures for high-performance HSCs.

Facile decoration of two-dimensional Ti3C2Txnanoplates with CuS nanoparticles via a facilein situsynthesis strategy at room temperature for superhigh specific capacitance of supercapacitors

Although supercapacitors have attracted more and more attention owing to their fast charging speed and high power density, their wide applications have still been limited by their low energy density. In this study, a new CuS-nanoparticle-decorated Ti₃C₂T_xelectrode material is fabricated via a facilein situsynthesis strategy at room temperature. CuS nanoparticles, generated from thein situreaction of Cu (NO₃)₂·3H₂O with Na₂S·9H₂O, are anchored between the Ti₃C₂T_xinterlayers through electrostatic interaction. This type of structural construction is found capable of not only reducing the surface oxidation of Ti₃C₂T_x, but also preventing the accumulation of CuS nanoparticles by the template effect of Ti₃C₂T_xnanoplates. As a result, the CuS/Ti₃C₂T_xnanohybrid delivers a maximum specific capacitance of 911 F g^-1at 1 A g^-1and a good cycling stability. A symmetric supercapacitor fabricated using the CuS/Ti₃C₂T_xnanohybrid as the electrode material exhibits an energy density of 43.56 W h kg^-1with a power density of 475 W kg^-1. Consequently, this work provides a new perspective of microstructural design for the preparation of electrode materials with superhigh specific capacitance through an easy and low-costin situ-reaction method at room temperature.

Preparation and Properties of an Ultrahigh-Energy-Density Aqueous Supercapacitor with a Superconcentrated Electrolyte and a Sr-Modified Lanthanum Zirconate Flexible Electrode

Although supercapacitors are considered to play a vital role in flexible electronic devices, there are still some problems that need to be overcome, such as low energy density and narrow electrochemical stability windows in aqueous electrolytes. Herein, we have successfully synthesized a series of Sr-modified La₂Zr₂O₇ (LZO-x) nanofibers as a new electrode material by a facile electrospinning technique. To determine the best doping sample, the changes in structures and electrochemical performances of La₂Zr₂O₇ (LZO-x) nanofibers with various Sr contents are investigated carefully. Then, the LZO-0.2 sample shows the highest capacitance (1445 mF·cm^-2). Furthermore, we also develop a low-cost superconcentrated electrolyte, which achieves a wide electrochemical stability window of 2.7 V using a working electrode (LZO-0.2). Finally, we use the LZO-0.2 electrode and the superconcentrated electrolyte to fabricate a flexible supercapacitor device, which shows an excellent capacitance of 175 F·g^-1 at a current density of 1.15 A·g^-1. Moreover, the aqueous device has excellent cycle stability and outstanding flexibility, and the energy density of this device is 177.2 Wh·kg^-1 and the corresponding power density is 1557.7 W·kg^-1.

Copper sulfide nanoparticles with potential bifunctional properties: supercapacitor and photocatalysis

Pure hexagonal CuS nanoparticles with stable high capacitance and photocatalytic activity were obtained by a mild solvothermal method.

Marigold flower like structured Cu2NiSnS4 electrode for high energy asymmetric solid state supercapacitors

The growth in energy devices and the role of supercapacitors are increasingly important in today’s world. Designing an electrode material for supercapacitors using metals that have high performance, superior structure, are eco-friendly, inexpensive and highly abundant is essentially required for commercialization. In this point of view, quaternary chalcogenide Cu₂NiSnS₄ with fascinating marigold flower like microstructured electrodes are synthesized using different concentrations of citric acid (0, 0.05 M, 0.1 M and 0.2 M) by employing solvothermal method. The electrode materials physicochemical characteristics are deliberated in detail using the basic characterization techniques. The electrochemical studies revealed better electrochemical performances, in particular, Cu₂NiSnS₄@0.1 M-CA electrode revealed high 1029 F/g specific capacitance at 0.5 A/g current density. Further, it retained 78.65% capacity over 5000 cycles. To prove the practical applicability, a full-cell asymmetric solid-state device is fabricated, and it delivered 41.25 Wh/Kg and 750 Wh/Kg energy and power density at 0.5 A/g. The optimum citric acid added Cu₂NiSnS₄ electrode is shown to be a promising candidate for supercapacitor applications.

CuCo2 S4 -rGO Microflowers: First-Principle Calculation and Application in Energy Storage

This paper demonstrates the ability of a CuCo₂ S₄ -reduced graphene oxide (rGO) composite to perform robust electrochemical performances applying to supercapacitors (SCs) and lithium ion batteries (LIBs). The first-principle calculation based on density functional theory is conducted to study the electronic property of CuCo₂ O₄ and CuCo₂ S₄ and provide a theoretical basis for this work. Then, the 3D spinel-structured CuCo₂ O₄ and CuCo₂ S₄ microflowers are synthesized and compared as electrodes for both SCs and LIBs. The CuCo₂ S₄ microflowers can provide a larger specific surface area, which enlarges the contact area between the electrode material and the electrolyte and contributes to high-efficiency electrochemical reactions. The reduced graphene oxides are coated on the CuCo₂ S₄ microflowers, therefore effectively increasing the conductivity, and further absorbing the stress produced in the reaction process. As an electrode of a symmetric supercapacitor, the optimized CuCo₂ S₄ -rGO composite exhibits an energy density of 16.07 Wh kg^-1 and a maximum power density of 3600 W kg^-1 . Moreover, the CuCo₂ S₄ -rGO composite can also be used as an anode for lithium ion batteries, exhibiting a reversible capacity of 1050 mAh g^-1 after 140 cycles at the current density of 200 mA g^-1 . The galvanostatic intermittence titration techniques also reveal superior Li-ion diffusion behavior of the CuCo₂ S₄ -rGO composite during redox reactions.

Synthesis and Electrochemical Study of Three-Dimensional Graphene-Based Nanomaterials for Energy Applications

Graphene is an attractive soft material for various applications due to its unique and exclusive properties. The processing and preservation of 2D graphene at large scales is challenging due to its inherent propensity for layer restacking. Three-dimensional graphene-based nanomaterials (3D-GNMs) preserve their structures while improving processability along with providing enhanced characteristics, which exhibit some notable advantages over 2D graphene. This feature article presents recent trends in the fabrication and characterization of 3D-GNMs toward the study of their morphologies, structures, functional groups, and chemical compositions using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Owing to the attractive properties of 3D-GNMs, which include high surface areas, porous structures, improved electrical conductivity, high mechanical strength, and robust structures, they have generated tremendous interest for various applications such as energy storage, sensors, and energy conversion. This article summarizes the most recent advances in electrochemical applications of 3D-GNMs, pertaining to energy storage, where they can serve as supercapacitor electrode materials and energy conversion as oxygen reduction reaction catalysts, along with an outlook.

Synthesis of zinc sulfide/copper sulfide/porous carbonized cotton nanocomposites for flexible supercapacitor and recyclable photocatalysis with high performance

The composite material composed of zinc sulfide, copper sulfide and porous carbon is prepared in this study, exhibiting excellent performances in the field of supercapacitor electrode and photocatalysts. In the degradation process of organic pollutants, zinc sulfide/copper sulfide with heterostructure effectively reduce the recombination rate of photo-generated electron-hole pairs. And the porous carbon substrate can not only accelerate the separation of photo-carriers but also provide numerous active sites. Furthermore, the sample can be easily separated after decomposing the organic pollutants. As a supercapacitor electrode, the combination of zinc sulfide/copper sulfide with large pseudo-capacitance and porous carbon material with excellent double-layercapacitance results in superior electrochemical performances. The composite electrode shows a high specific capacitance of 1925 mF cm^-2/0.53 mAh cm^-2 at 4 mA cm^-2. And the symmetric flexible supercapacitor based on the composite electrode achieves an outstanding energy density (0.39 Wh cm^-2 at the power density of 4.32 W cm^-2). Therefore, the zinc sulfide/copper sulfide/porous carbonized cotton nanocomposites (pCZCS) prepared herein exhibit dual functions of photocatalysts with high efficiency as well as energy storage materials with high energy density, which is interesting and important for expanding the practical applications in cross fields.

Design of Double-Shelled CuS Nanocages to Optimize Electrocatalytic Dynamic for Sensitive Detection of Ascorbic Acid

Although transition metal sulfides have presented prospect in electrochemical sensing, their electrocatalytic performance still cannot meet the demands for practical applications due to the difficulties in mass transport and electron transfer. In this work, double-shelled CuS nanocages (2-CuS NCs) were prepared for enzyme-free ascorbic (AA) sensor through a Cu2O- templated method. The unique double-shelled hollow structure displayed large specific surface areas, ordered diffusion channels, increased volume occupying rate, and accelerated electron transfer rate, resulting in enhanced electrochemical dynamic. As a sensing electrode for AA, 2-CuS NCs modified glassy carbon electrode (2-CuS NCs/GCE) exhibited eminent electrocatalytic activity in terms of satisfying sensitivity (523.7 μA mM-1 cm-2), short response time (0.31 s), and low limit of detection (LOD, 0.15 μM). 2-CuS NCs look promising for analytical sensing of AA in electrochemical sensors thanks to its prominent electrocatalytic kinetics issued from double-shelled hollow porous structure.

The ultralong cycle life of solid flexible asymmetric supercapacitors based on nickel vanadium sulfide nanospheres

The nickel vanadium sulfide electrodes shows an capacitance of 697.4 C g⁻¹ at current density of 1A g⁻¹. The flexible ACS Ni–V–S–2//rGO gives rise to a remarkable cyclic stability with 100% capacitance retention over 7000 charge–discharge cycles.

Novel chemical route for CeO2/MWCNTs composite towards highly bendable solid-state supercapacitor device

Electrode materials having high capacitance with outstanding stability are the critical issues for the development of flexible supercapacitors (SCs), which have recently received increasing attention. To meet these demands, coating of CeO₂ nanoparticles have been performed onto MWCNTs by using facile chemical bath deposition (CBD) method. The formed CeO₂/MWCNTs nanocomposite exhibits excellent electrochemical specific capacitance of 1215.7 F/g with 92.3% remarkable cyclic stability at 10000 cycles. Light-weight flexible symmetric solid-state supercapacitor (FSSC) device have been engineered by sandwiching PVA-LiClO₄ gel between two CeO₂/MWCNTs electrodes which exhibit an excellent supercapacitive performance owing to the integration of pseudocapacitive CeO₂ nanoparticles onto electrochemical double layer capacitance (EDLC) behaved MWCNTs complex web-like structure. Remarkable specific capacitance of 486.5 F/g with much higher energy density of 85.7 Wh/kg shows the inherent potential of the fabricated device. Moreover, the low internal resistance adds exceptional stability along with unperturbed behavior even under high mechanical stress which can explore its applicability towards high-performance flexible supercapacitor for advanced portable electronic devices.

One-pot synthesis of ZnS nanowires/Cu7S4 nanoparticles/reduced graphene oxide nanocomposites for supercapacitor and photocatalysis applications

ZnS nanowires/Cu₇S₄ nanoparticles/rGO nanocomposites were fabricated as photocatalysts and supercapacitor electrodes for the first time.

Electrodeposited Ni(OH)2-modified CuS core–shell-like hybrids as binder-free electrodes for high-performance supercapacitors

In this work, binder-free electrodes of CuS@Ni(OH)₂ were fabricated by hydrothermal and electrodeposition methods.

Facile preparation of partially reduced graphite oxide nanosheets as a binder-free electrode for supercapacitors

Preparation of graphene (GR) based electrode materials with excellent capacitive properties is of great importance to supercapacitors. Herein, we report a facile approach to prepare partially reduced graphite oxide (PRG) nanosheets by reducing graphite oxide (GO) using commercial Cu2O powder as a reduction agent, moreover, we demonstrate that the PRG nanosheets can act as building blocks for assembling hydrogels (PRGH) and flexible film (PRGF). The obtained PRGH and PRGF can be directly used as binder-free electrodes for supercapacitors and give high specific capacitance (292 and 273 F g-1 at a current density of 0.5 A g-1 in a three-electrode system, respectively) due to the existence of oxygen-containing functional groups in PRG nanosheets. PRG also gives excellent rate ability and cycle stability. This study suggests a facile pathway to produce GR-based materials with excellent capacitive properties and is meaningful for flexible supercapacitors.

Towards flexible solid-state supercapacitors for smart and wearable electronics

Flexible solid-state supercapacitors (FSSCs) are frontrunners in energy storage device technology and have attracted extensive attention owing to recent significant breakthroughs in modern wearable electronics. In this study, we review the state-of-the-art advancements in FSSCs to provide new insights on mechanisms, emerging electrode materials, flexible gel electrolytes and novel cell designs. The review begins with a brief introduction on the fundamental understanding of charge storage mechanisms based on the structural properties of electrode materials. The next sections briefly summarise the latest progress in flexible electrodes (i.e., freestanding and substrate-supported, including textile, paper, metal foil/wire and polymer-based substrates) and flexible gel electrolytes (i.e., aqueous, organic, ionic liquids and redox-active gels). Subsequently, a comprehensive summary of FSSC cell designs introduces some emerging electrode materials, including MXenes, metal nitrides, metal-organic frameworks (MOFs), polyoxometalates (POMs) and black phosphorus. Some potential practical applications, such as the development of piezoelectric, photo-, shape-memory, self-healing, electrochromic and integrated sensor-supercapacitors are also discussed. The final section highlights current challenges and future perspectives on research in this thriving field.

Nanostructure selenium compounds as pseudocapacitive electrodes for high-performance asymmetric supercapacitor

The electrochemical performance of an energy conversion and storage device like the supercapacitor mainly depends on the microstructure and morphology of the electrodes. In this paper, to improve the capacitance performance of the supercapacitor, the all-pseudocapacitive electrodes of lamella-like Bi₁₈SeO₂₉/BiSe as the negative electrode and flower-like Co_0.85Se nanosheets as the positive electrode are synthesized by using a facile low-temperature one-step hydrothermal method. The microstructures and morphology of the electrode materials are carefully characterized, and the capacitance performances are also tested. The Bi₁₈SeO₂₉/BiSe and Co_0.85Se have high specific capacitance (471.3 F g^-1 and 255 F g^-1 at 0.5 A g^-1), high conductivity, outstanding cycling stability, as well as good rate capability. The assembled asymmetric supercapacitor completely based on the pseudocapacitive electrodes exhibits outstanding cycling stability (about 93% capacitance retention after 5000 cycles). Moreover, the devices exhibit high energy density of 24.2 Wh kg^-1 at a power density of 871.2 W kg^-1 in the voltage window of 0-1.6 V with 2 M KOH solution.