Molybdenum disulfide (MoS2) along with graphene nanoplatelets (GNPs) utilized to enhance the capacitance of conducting polymers (PANI and PPy)

Hybrid composites of molybdenum disulfide (MoS2), graphene nanoplatelets (GNPs) and polyaniline (PANI)/polypyrrole (PPy) have been synthesized as cost-effective electrode materials for supercapacitors. We have produced MoS2 from molybdenum dithiocarbamate by a melt method in an inert environment and then used a liquid exfoliation method to form its composite with graphene nanoplatelets (GNPs) and polymers (PANI and PPy). The MoS2 melt/GNP ratio in the resultant composites was 1 : 3 and the polymer was 10% by wt. of the original composite. XRD (X-ray diffraction analysis) confirmed the formation of MoS2 and SEM (scanning electron microscopy) revealed the morphology of the synthesized materials. The electrochemical charge storage performance of the synthesized composite materials was assessed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge (GCCD) measurements. Resultant composites showed enhanced electrochemical performances (specific capacitance = 236.23 F g-1, energy density = 64.31 W h kg-1 and power density = 3858.42 W kg-1 for MoS2 melt 5 mPP at a current density of 0.57 A g-1 and had 91.87% capacitance retention after 10 000 charge-discharge cycles) as compared to the produced MoS2; thus, they can be utilized as electrode materials for supercapacitors.

Recent Advances of Transition Metal Chalcogenides as Cathode Materials for Aqueous Zinc-Ion Batteries

In recent years, advances in lithium-ion batteries (LIBs) have pushed the research of other metal-ion batteries to the forefront. Aqueous zinc ion batteries (AZIBs) have attracted much attention owing to their low cost, high capacity and non-toxic characteristics. Among various cathodes, transition metal chalcogenides (TMCs) with a layered structure are considered as suitable electrode materials. The large layer spacing facilitates the intercalation/de-intercalation of Zn²⁺ between the layers. In this mini-review, we summarize a variety of design strategies for the modification of TMCs. Then, we specifically emphasize the zinc storage capacity of the optimized electrodes. Finally, we propose the challenges and future prospects of cathode materials for high-energy AZIBs.

High performance aqueous zinc battery enabled by potassium ion stabilization

Aqueous zinc ion batteries (AZIBs) are highly competitive in the energy storage systems due to their feature with operation safety and environmental friendliness. However, the sluggish diffusion kinetics of Zn²⁺ and inferior cathode circulation hinder their widespread application. Herein, we assemble a highly durable zinc ion battery by intercalating K⁺ into V₂O₅ nanolayers. The K⁺ pre-intercalation can buffer the lattice expansion of the electrode materials and reduce the internal stress. In addition, the stable K⁺ acts as a "pillar" to protect the layered structure of V₂O₅ materials from collapse during operation cycling. It delivers a reversible capacity of 479.8 mAh g^-1 at 0.2 A g^-1 and achieves excellent cyclic stability with a retention rate of 91.3% (10 A g^-1) after 3000 cycles. The cell still maintains excellent specific capacity at high work temperature.

Synthesis of NiCo2S4@NiMoO4 Nanosheets with Excellent Electrochemical Performance for Supercapacitor

Currently, the research of energy storage devices mainly focuses on enhancing their electrochemical performance. Core-shell structured NiCo2S4@NiMoO4 is thought to be one of the most promising electrode materials for supercapacitors due to its high specific capacitance and excellent cycle performance. In this work, we report NiCo2S4@NiMoO4 nanosheets on Ni foam by a two-step fabricated method. The as-obtained product has a high capacitance of 1035 F g−1 at 1 A g−1. The as-assembled supercapacitor has a high energy density of 32.4 W h kg−1 at a power density of 3230 W kg−1 and a superior cycle performance, with 70.1% capacitance retention. The electrode materials reported here might exhibit potential applications in future energy storage devices.

Hierarchical Co3O4@Ni3S2 electrode materials for energy storage and conversion

Transition metal oxides are considered to be one of the most potential electrode materials. However, poor conductivity and insufficient active sites limit their actual applications. Rationally designed electrode materials with unique structural features can be ascribed to the efficient route for enhancing electrochemical performance. Here, we report hybrid Co₃O₄@Ni₃S₂ nanostructures obtained via a hydrothermal strategy and subsequent electrodeposition process. The obtained products can be used as electrodes for a hybrid supercapacitor with a specific capacity of 1071 C g^-1 at 1 A g^-1 and excellent rate capability. The as-assembled device delivers an energy density of 77.92 W h kg^-1 at 2880 W kg^-1. As an electrocatalyst, the above electrode possesses an overpotential of 237.6 mV at 50 mA cm^-2 for oxygen evolution reaction.

Hydrazine Hydrate Induced Three-Dimensional Interconnected Porous Flower-like 3D-NiCo-SDBS-LDH Microspheres for High-Performance Supercapacitor

Porous structure and surface defects are important to improve the performance of supercapacitors. In this study, a facile pathway was developed for high-performance supercapacitors, which can produce transition metal hydroxides (LDHs) with abundant porous structure and surface defects. The NiCo-SDBS-LDH was prepared by one-step hydrothermal reaction using sodium dodecylbenzene sulfonate (SDBS) as anionic surfactant. And then, three dimensional (3D) interconnected porous flower-like 3D-NiCo-SDBS-LDH microspheres were designed and synthesized using the gas-phase hydrazine hydrate reduction method. Results showed that the hydrazine hydrate reduction not only introduces a large number of pores into 3D-NiCo-SDBS-LDH microspheres and causes the formation of oxygen vacancies, but it also roughens the surface of the microspheres. All these changes contribute to the enhancement of electrochemical activity of 3D-NiCo-SDBS-LDH; the NiCo-SDBS-LDH electrode after hydrazine hydrate treatment (3D-NiCo-SDBS-LDH) exhibits a higher specific capacitance of 1148 F·g^-1 at 1 A·g^-1 (about 1.46 times larger than that of NiCo-SDBS-LDH) and excellent long cycle life with 94% retention after 4000 cycles. Moreover, the assembled 3D-NiCo-SDBS-LDH//AC (active carbon) asymmetric supercapacitor (ASC) achieves remarkable energy density of 73.14 W h·kg^-1 at 800 W·kg^-1 and long-term cycling stability of 95.5% retention for up to 10,000 cycles. The outstanding electrochemical performance can be attributed to the synergy between the rich porous structure and the roughened surface that has been created by the hydrazine hydrate treatment.

Integrated Conductive Hybrid Electrode Materials Based on PPy@ZIF-67-Derived Oxyhydroxide@CFs Composites for Energy Storage

Due to excellent flexibility and hydrophilicity, cellulose fibers (CFs) have become one of the most potential substrate materials in flexible and wearable electronics. In previous work, we prepared cobalt oxyhydroxide with crystal defects modified polypyrrole (PPy)@CFs composites with good electrochemical performance. In this work, we redesigned the crystalline and nanoscale cobalt oxyhydroxide with zeolitic imidazolate frameworks-67 (ZIF-67) as precursor. The results showed that the PPy@ZIF-67 derived cobalt oxyhydroxide@CFs (PZCC) hybrid electrode materials possess far better capacitance of 696.65 F·g⁻¹ than those of PPy@CFs (308.75 F·g⁻¹) and previous PPy@cobalt oxyhydroxide@CFs (571.3 F·g⁻¹) at a current density of 0.2 A·g⁻¹. The PZCC delivers an excellent cyclic stability (capacitance retention of 92.56%). Moreover, the PZCC-supercapacitors (SCs) can provide an energy density of 45.51 mWh cm⁻³ at a power density of 174.67 mWh·cm⁻³, suggesting the potential application in energy storage area.

A flexible hybrid capacitor based an NiCo2S4 nanowire electrode with an ultrahigh capacitance

It is well-known that the excellent cycling stability and high energy density of electrode materials is very important for supercapacitors. However, their actual performance falls far behind and does not satisfy the practical demand. In this study, we synthesized NiCo₂S₄ nanowire bundles on a nickel foam via facile hydrothermal routes. The as-obtained product as an electrode material possesses excellent specific surface area, which suggests that numerous active sites on the electrode surface can shorten the diffusion channel of ions. The assembled asymmetric supercapacitor delivers an energy density of 57.36 W h kg^-1 at 1412.92 W kg^-1. Also, it exhibits excellent mechanical stability even at different bending angles.

A facile synthetic protocol of α-Fe2O3@FeS2 nanocrystals for advanced electrochemical capacitors

In this work, we report granular α-Fe₂O₃@FeS₂ nanocrystals by a one-pot hydrothermal route. The as-obtained product as an electrode material shows excellent charge transfer ability and cyclic stability.

Rapid photocatalytic degradation of cationic organic dyes using Li-doped Ni/NiO nanocomposites and their electrochemical performance

This work reports novel bi-functional Li-doped Ni/NiO nanocomposites as potential candidates for energy storage and water treatment applications.

Vertically Aligned and Ordered Arrays of 2D MCo2S4@Metal with Ultrafast Ion/Electron Transport for Thickness-Independent Pseudocapacitive Energy Storage

Pseudocapacitance holds great promise for energy density improvement of supercapacitors, but electrode materials show practical capacity far below theoretical values due to limited ion diffusion accessibility and/or low electron transferability. Herein, inducing two kinds of straight ion-movement channels and fast charge storage/delivery for enhanced reaction kinetics is proposed. Very thick electrodes consisting of vertically aligned and ordered arrays of NiCo₂S₄-nanoflake-covered slender nickel columns (NCs) are achieved via a scalable route. The vertical standing ∼5 nm ultrathin NiCo₂S₄ flakes build a porous covering with straight ion channels without the "dead volume", leading to thickness-independent capacity. Benefiting from the architecture acting as a "superhighway" for ultrafast ion/electron transport and providing a large surface area, high electrical conductivity, and abundant availability of electrochemical active sites, the NiCo₂S₄@NC-array electrode achieves a specific capacity up to 486.9 mAh g^-1. The electrode even can work with a high specific capacity of 150 mAh g^-1 at a very high current density of 100 A g^-1. In particular, due to the advanced structure features, the electrode exhibits excellent flexibility with a unexpected improvement of capacity when being largely bent and excellent cycling stability with an obvious resistance decrease after the cycles. An asymmetric pseudocapacitor applying the NiCo₂S₄@NC-array as a positive electrode achieves an energy density of 66.5 Wh kg^-1 at a power density of 400 W kg^-1, superior to the most reported values for asymmetric devices with NiCo₂S₄ electrodes. This work provides a scalable approach with mold-replication-like simplicity toward achieving thickness-independent electrodes with ultrafast ion/electron transport for energy storage.

Transition metal oxide@hydroxide assemblies as electrode materials for asymmetric hybrid capacitors with excellent cycling stabilities

In this work, three-dimensional cactus-like Co₃O₄@Ni(OH)₂ electrode materials are grown directly on Ni foam via a two-step hydrothermal method. The as-prepared products possess a specific capacitance of 464.5 C g⁻¹ at 0.5 A g⁻¹ and 91.67% capacitance retention after 20 000 cycles. The as-assembled device using the as-synthesized samples as positive electrodes delivers an energy density of 112.5 W h kg⁻¹ at a power density of 1350 W h kg⁻¹. The superior electrochemical performance of the electrode materials can be attributed to their unique structure, the synergistic effect between Co₃O₄ and Ni(OH)₂ materials and reversible reaction kinetics. It suggests that the products are potential alternatives in future energy storage devices.

In this work, three-dimensional cactus-like Co₃O₄@Ni(OH)₂ electrode materials are grown directly on Ni foam via a two-step hydrothermal method.