Synthesis of Capsule-like Porous Hollow Nanonickel Cobalt Sulfides via Cation Exchange Based on the Kirkendall Effect for High-Performance Supercapacitors

Morphological control and performance engineering of Co-based materials for supercapacitors

As one of the most promising energy storage devices, supercapacitors exhibit a higher power density than batteries. However, its low energy density usually requires high-performance electrode materials. Although the RuO2 material shows desirable properties, its high cost and toxicity significantly limit its application in supercapacitors. Recent developments demonstrated that Co-based materials have emerged as a promising alternative to RuO2 for supercapacitors due to their low cost, favorable redox reversibility and environmental friendliness. In this paper, the morphological control and performance engineering of Co-based materials are systematically reviewed. Firstly, the principle of supercapacitors is briefly introduced, and the characteristics and advantages of pseudocapacitors are emphasized. The special forms of cobalt-based materials are introduced, including 1D, 2D and 3D nanomaterials. After that, the ways to enhance the properties of cobalt-based materials are discussed, including adding conductive materials, constructing heterostructures and doping heteroatoms. Particularly, the influence of morphological control and modification methods on the electrochemical performances of materials is highlighted. Finally, the application prospect and development direction of Co-based materials are proposed.

Large-Scale Synthesis of High Energy Thermal Battery Cathode Ni0.5Co0.5S2 by a Simple Sintering Technique

With the synergies of multiple elements, bimetallic sulfides exhibit excellent performance as splendid electrode materials and effective catalysts. However, large-scale synthesis of high-performance single-phase multicomponent sulfides has always been a challenge. Based on thermodynamic calculations, the intermediate phases NiS2 and Co3S4 are devoted to the synthesis of single-phase Ni0.5Co0.5S2. Because the reaction from NiS2 and Co3S4 to Ni0.5Co0.5S2 goes through a lower energy, it thermodynamically contributes to achieving a single-phase structure. Thus, single-phase Ni0.5Co0.5S2 can be simply and quickly prepared by two-step sintering and successfully scalable for mass production. This technique can extend to the whole ingredients Ni1-xCoxS2. Ni0.5Co0.5S2 demonstrates excellent thermal stability and good conductivity. It delivers a specific capacity of 671 mAh·g-1 and a specific energy of 1173 Wh·kg-1 when applied to a thermal battery cathode, which are increased by 18.6% and 25.0%, respectively, compared to pristine NiS2 (566 mAh·g-1) and CoS2 (537 mAh·g-1). This work proposes an innovative sintering method, which is applicable for cost-efficient and large-scale synthesis of single-phase multicomponent sulfides.

Construction of thickness-controllable bimetallic sulfides/reduced graphene oxide as a binder-free positive electrode for hybrid supercapacitors

Devices for electrochemical energy storage with exceptional capacitance and rate performance, outstanding energy density, simple fabrication, long-term stability, and remarkable reversibility have always been in high demand. Herein, a high-performance binder-free electrode (3D NiCuS/rGO) was fabricated as a supercapacitor by a simple electrodeposition process on a Ni foam (NF) surface. The thickness of the deposited materials on the NF surface was adjusted by applying a low cycle number of cyclic voltammetry (5 cycles) which produced a thin layer and thus enabled the easier penetration of electrolytes to promote electron and charge transfer. The NiCuS was anchored by graphene layers producing nicely integrated materials leading to a higher electroconductivity and a larger surface area electrode. The as-fabricated electrode displayed a high specific capacitance (2211.029 F g-1 at 5 mV s-1). The NiCuS/rGO/NF//active carbon device can achieve a stable voltage window of 1.5 V with a highly specific capacitance of 84.3 F g-1 at a current density of 1 A g-1. At a power density of 749 W kg-1, a satisfactory energy density of 26.3 W h kg-1 was achieved, with outstanding coulombic efficiency of 100% and an admirable life span of 96.2% after 10 000 GCD cycles suggesting the significant potential of the as-prepared materials for practical supercapacitors.

Ni-Co-Mn hydrotalcite-derived hierarchically porous sulfide for hybrid supercapacitors

Ternary transition metal sulfides have attracted much attention due to their superior electrochemical properties. Nevertheless, it is difficult to commercialize sulfides due to their intrinsic properties such as dull reaction kinetics and an insufficient number of active sites. Herein, a self-supporting porous NiCoMnS sulfide (NiCoMnS/NF) arrayed on nickel foam (NF) with 3D honeycomb-like structure was designed and prepared via a hydrothermal and post-sulfidation process. It was found that the 3D hierarchically network architecture, constructed by nanosheets with abundant cavities, endowed NiCoMnS/NF with a high specific area and rich ion/electron-transport channels, which facilitated ion/electron transfer and Faradaic reaction kinetic. The optimal NiCoMnS/NF exhibited a markedly improved electrochemical performance due to the merits of complementary multi-composition and unique 3D network structure with multi-level "superhighways". Furthermore, the NiCoMnS//AC device fabricated with NiCoMnS/NF cathode and activated carbon (AC) anode delivered an excellent specific charge and exceptional energy density. This work offers a reference for designing the structure of electrode materials.

Facile Synthesis of Battery-Type CuMn2O4 Nanosheet Arrays on Ni Foam as an Efficient Binder-Free Electrode Material for High-Rate Supercapacitors

The development of battery-type electrode materials with hierarchical nanostructures has recently gained considerable attention in high-rate hybrid supercapacitors. For the first time, in the present study novel hierarchical CuMn₂O₄ nanosheet arrays (NSAs) nanostructures are developed using a one-step hydrothermal route on a nickel foam substrate and utilized as an enhanced battery-type electrode material for supercapacitors without the need of binders or conducting polymer additives. X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques are used to study the phase, structural, and morphological characteristics of the CuMn₂O₄ electrode. SEM and TEM studies show that CuMn₂O₄ exhibits a nanosheet array morphology. According to the electrochemical data, CuMn₂O₄ NSAs give a Faradic battery-type redox activity that differs from the behavior of carbon-related materials (such as activated carbon, reduced graphene oxide, graphene, etc.). The battery-type CuMn₂O₄ NSAs electrode showed an excellent specific capacity of 125.56 mA h g^-1 at 1 A g^-1 with a remarkable rate capability of 84.1%, superb cycling stability of 92.15% over 5000 cycles, good mechanical stability and flexibility, and low internal resistance at the interface of electrode and electrolyte. Due to their excellent electrochemical properties, high-performance CuMn₂O₄ NSAs-like structures are prospective battery-type electrodes for high-rate supercapacitors.

Rationally Designed Bimetallic Co-Ni Sulfide Microspheres as High-Performance Battery-Type Electrode for Hybrid Supercapacitors

Rational designing of electrode materials is of great interest for improving the performance of battery-type supercapacitors. The bimetallic NiCo₂S₄ (NCS) and CoNi₂S₄ (CNS) electrode materials have received much attention for supercapacitors due to their rich electrochemical characteristics. However, the comparative electrochemical performances of NCS and CNS electrodes were never studied for supercapacitor application. In this work, microsphere-like bimetallic NCS and CNS structures were synthesized via a facile one-step hydrothermal method by controlling the molar ratio of Ni and Co precursors. The physico-chemical results confirmed that microsphere-like structures with cubic spinel-type NCS and CNS materials were successfully fabricated by this method. When tested as the supercapacitor electrode materials, both NCS and CNS electrodes exhibited battery-type behavior in a three-electrode configuration with outstanding electrochemical performances such as specific capacity, rate performance and cycle stability. Impressively, the CNS electrode delivered a high specific capacity of 430.1 C g^-1 at 1 A g^-1, which is higher than 345.9 C g^-1 of the NCS electrode. Furthermore, the NCS and CNS electrodes showed a decent cycling stability with 75.70 and 84.70% capacity retention after 10,000 cycles. Benefiting from the electrochemical advantage of CNS microspheres, we fabricated a hybrid supercapacitor (HSC) device based on CNS microspheres (positive electrode) and activated carbon (AC, negative electrode), which is named as CNS//AC. The assembled CNS//AC HSC device showed a large energy density of 41.98 Wh kg^-1 at a power density of 800.04 W kg^-1 and displayed a remarkable cycling stability with a capacity retention of 91.79% after 15,000 cycles. These excellent electrochemical performances demonstrate that both bimetallic NCS and CNS microspheres may provide potential electrode materials for high performance battery-type supercapacitors.

A hollow Co9S8 rod-acidified CNT-NiCoLDH composite providing excellent electrochemical performance in asymmetric supercapacitors

Co9S8 and transition metal hydroxides are both potential pseudo-capacitance electrode materials for supercapacitors. Co9S8 has a large specific capacitance and electrochemical activity, and transition metal hydroxides have the advantages of high capacitance and redox activity due to their multiple valence metals and open layered structure. In this study, Co9S8 and NiCoLDH are used to form a Co9S8-aCNT-NiCoLDH composite electrode material by twining acidified carbon nanotubes (aCNTs) around hollow Co9S8 rods and then compounding nickel cobalt hydroxide (NiCoLDH) on the outside. aCNTs provide more electronic channels, which bring more active electrochemical reactions and absorb the volume expansion of Co9S8. The hollow Co9S8 rods and flower-like NiCoLDH structures ensure that the electrode has a highly open structure, which increases the contact area with the electrolyte and is beneficial for ion transport. The outer NiCoLDH can also reduce the volume expansion of Co9S8. These advantages ensure the high specific capacitance and rate performance of the Co9S8-aCNT-NiCoLDH electrode material. Co9S8-aCNT-NiCoLDH was used as the positive material to fabricate asymmetric supercapacitors with attractive energy density and power density, which further proved its excellent electrochemical performance.

Mn3-x Fex O4 Hollow Nanostructures for High-Performance Asymmetric Supercapacitor Applications

Design of hollow nanostructure and controllable phase of mixed metal oxides for improving performance in supercapacitor applications is highly desirable. Here we demonstrate the rational design and synthesis of Mn_3-x Fe_x O₄ hollow nanostructures for supercapacitor applications. Owing to high porosity and the specific surface area that provides more active sites for electrochemical reactions, the electrochemical performance of Mn_3-x Fe_x O₄ hollow nanostructure substantially enhanced comparing with pristine Mn₃ O₄ . Particularly, in 1.0 M KOH electrolyte, Mn_0.16 Fe_2.84 O₄ with a typical diameter of 20 nm exhibits excellent specific capacitance of 2675, 2320, 1662, 987 F g^-1 at current densities of 1, 2, 5, 10 A g^-1 , respectively, which is significantly superior to those of other transition metal oxides. Besides, an asymmetric supercapacitor is assembled by using Mn_0.16 Fe_2.84 O₄ and activated carbon as a positive and a negative electrode, respectively. Electrochemical results indicate a high energy density of 42 Wh kg^-1 at a power density of 0.75 kW kg^-1 , which makes this hollow nanostructure a highly promising electrode for achieving high-performance next-generation supercapacitors.

Site-Selective Transformation for Preparing Tripod-like NiCo-Sulfides@Carbon Boosts Enhanced Areal Capacity and Cycling Reliability

Flexible power supply systems for future wearable electronics desperately require high areal capacity (C_a) and robust cycling reliability due to the limited surface area of the human body. Transition metal sulfides are preferred as cathode materials for their improved conductivity and rich redox centers, yet their practical applications are severely hindered by the sluggish charge transport kinetics and unavoidable capacity decay due to the phase transformation during charge/discharge processes. Herein, we develop a site-selective transformation strategy for preparing tripod-like NiCo-sulfides@carbon (T-NCS@C) arrays on carbon cloth. The mass loading of active materials is balanced with charge (electron and ion) transport efficiency. The optimized T-NCS@C delivers a superior C_a of 494 μA h/cm² (corresponding to 235 mA h/g) at 3 mA/cm². Due to the protection of the carbon layer that is derived from transformed metal-organic framework (MOF) sheath, the T-NCS@C displays excellent stability with 92% retention over 5000 charge/discharge cycles. The flexible full cell adopting Fe₂O₃ as the anode and T-NCS@C as the cathode exhibits an improved E_a (areal energy density) of 389 μW h/cm² at a P_a (areal power density) of 4.22 mW/cm² together with robust cycling reliability.

Enhanced Supercapacitor Performance Using a Co3 O4 @Co3 S4 Nanocomposite on Reduced Graphene Oxide/Ni Foam Electrodes

To avoid an enormous energy crisis in the not-too-distant future, it be emergent to establish high-performance energy storage devices such as supercapacitors. For this purpose, a three-dimensional (3D) heterostructure of Co₃ O₄ and Co₃ S₄ on nickel foam (NF) that is covered by reduced graphene oxide (rGO) has been prepared by following a facile multistep method. At first, rGO nanosheets are deposited on NF under mild hydrothermal conditions to increase the surface area. Subsequently, nanowalls of cobalt oxide are electro-deposited on rGO/Ni foam by applying cyclic-voltammetry (CV) under optimized conditions. Finally, for the synthesis of Co₃ O₄ @Co₃ S₄ nanocomposite, the nanostructure of Co₃ S₄ was fabricated from Co₃ O₄ nanowalls on rGO/NF by following an ordinary hydrothermal process through the sulfurization for the electrochemical application. The samples are characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The obtained sample delivers a high capacitance of 13.34 F cm^-2 (5651.24 F g^-1 ) at a current density of 6 mA cm^-2 compared to the Co₃ O₄ /rGO/NF electrode with a capacitance of 3.06 F cm^-2 (1230.77 F g^-1 ) at the same current density. The proposed electrode illustrates the superior electrochemical performance such as excellent specific energy density of 85.68 W h Kg^-1 , specific power density of 6048.03 W kg^-1 and a superior cycling performance (86% after 1000 charge/discharge cycles at a scan rate of 5 mV s^-1 ). Finally, by using Co₃ O₄ @Co₃ S₄ /rGO/NF and the activated carbon-based electrode as positive and negative electrodes, respectively, an asymmetric supercapacitor (ASC) device was assembled. The fabricated ASC provides an appropriate specific capacitance of 79.15 mF cm^-2 at the applied current density of 1 mA cm^-2 , and delivered an energy density of 0.143 Wh kg^-1 at the power density of 5.42 W kg^-1 .

Novel Conductive Ag-Decorated NiFe Mixed Metal Telluride Hierarchical Nanorods for High-Performance Hybrid Supercapacitors

Mixed metal chalcogenide nanoarchitectures have been attracting enormous attention as battery-type electrodes for hybrid supercapacitors (HSCs) owing to their enhanced electrochemical (EC) performance. Despite having high electrical conductivity and good EC properties, tellurium has not been fully utilized in metal chalcogenide electrodes as much as sulfur and selenium. Herein, a facile strategy for the fabrication of nickel and iron (NiFe) mixed metal telluride hierarchical nanorods (MMT HNRs) on nickel foam (NF) is proposed. Furthermore, conductive silver (Ag) is decorated on MMT HNRs (AMMT HNRs) to improve the conducting channels, thereby EC performance. Benefitting from the combined advantages of electroactive NiFe mixed metal, conductive tellurium and Ag, and hierarchical nanorod-like nanomorphology, the AMMT HNR electrode has delivered high areal capacity (1.1 mAh cm^-2). Finally, the AMMT based HSC with activated carbon coated NF (AC/NF) as a negative electrode exhibited the highest areal capacitance (1176.5 mF cm^-2) with high areal energy density (0.669 mWh cm^-2) and power density (64 mW cm^-2). Moreover, the HSC device has maintained good cycling stability (86% capacity retention) even after 5000 cycles. New findings of this study definitely shed light on the development of telluride-based mixed metal chalcogenide supercapacitors.

Sulfide remediation from wastewater using hydrothermally synthesized δ-MnO2/porous graphitic carbon as adsorbent

A facile hydrothermal assisted in-situ precipitation technique was employed for synthesizing highly efficient porous graphitic carbon/manganese dioxide (PGC/MnO₂) nanocomposite adsorbent using calcium alginate as carbon precursor. Morphological and structural characterization using scanning electron microscopy equipped with energy dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray diffraction techniques confirmed the interconnected nanoporous architecture and birnessite (δ) MnO₂ polymorph evenly distributed on the PGC structure. The synergistic effect of PGC and MnO₂ was exploited for enhanced sulfide removal from wastewater via adsorptive oxidation. The effect of different experimental parameters, including solution pH, initial sulfide concentration, adsorbent dosage, and contact time on removal efficiency was investigated. The equilibrium and kinetic data for sulfide adsorption by PGC/MnO₂ nanocomposite fitted well with Langmuir isotherm and pseudo-second-order kinetic model, respectively. The maximum uptake capacity of sulfide by the nanocomposite was determined as 500 mg/g with complete sulfide removal. Further, it was estimated that a typical field application using the synthesized nanocomposite adsorbent would require 0.5-1 g/L per 200 mg/L of sulfide contaminated wastewater. Based on the experimental results, a schematic of the adsorptive oxidation mechanism of PGC/MnO₂ nanocomposite is proposed.

Modish Designation of Hollow-Tubular rGO-NiMoO4@Ni-Co-S Hybrid Core-shell Electrodes with Multichannel Superconductive Pathways for High-Performance Asymmetric Supercapacitors

The scrupulous designation of hollow and porous electroactive materials incorporating prolific redox-active polyphase transition-metal oxide decorated with polyphase transition-metal sulfide onto rGO (reduced graphene oxide)-supported conductive substrate has never been an easy task due to the very good coordination affair of sulfur toward transition metals. Herein, cost-effective hydrothermal growth followed by a metal-organic framework (MOF)-mediated sulfidation approach is employed to achieve burl-like Ni-Co-S nanomaterial-integrated hollow and porous NiMoO₄ nanotubes onto rGO-coated Ni foam (rGO-NiMoO₄@Ni-Co-S) as the electrode material for supercapacitors. The open framework of the rGO-Co-MOF template after the etching and sulfidation process not only enables the creation of a tubular structure of NiMoO₄ nanorods but also provides convenient ion-electron pathways to promote rapid faradic reactions for the hybrid composite electrode. Owing to the unique hollow and tubular structure, the as-fabricated rGO-NiMoO₄@Ni-Co-S electrode exhibits a high specific capacity of 318 mA h g^-1 at 1 A g^-1 and remarkable cyclic performance of 88.87% after 10,000 consecutive charge-discharge cycles in an aqueous 2 M KOH electrolyte on a three-electrode configuration. Moreover, the assembled rGO-NiMoO₄@Ni-Co-S//rGO-MDC (MOF-derived carbon) asymmetric supercapacitor device exhibits a satisfactory energy density of 57.24 W h kg^-1 at a power density of 801.8 W kg^-1 with an admirable life span of 90.89% after 10,000 repeated cycles.

Controlled Preparation of Hollow and Porous Co9S8 Microplate Arrays for High-Performance Hybrid Supercapacitors

The design and controlled preparation of hollow and porous metal sulfide arrays are an important issue for electrochemical energy storage and conversion because of their unique structural merits including large surface areas, shortened diffusion paths, and rich reaction sites. Herein, a hollow and porous Co₉S₈ microplate array (MPA) was successfully fabricated by a facile self-sacrifice template strategy, which involved the uniform growth of a metal-organic framework microplate template on Ni foam (NF) and annealing in air, followed by an anion-exchange reaction with S^2- ions. The resulting Co₉S₈-MPA/NF as a binder-free electrode for a supercapacitor shows a high specific capacitance of 1852 F g^-1 (926 C g^-1) at 1 A g^-1 and an excellent cycling stability (86% retention after 5000 cycles at 20 A g^-1). Moreover, a hybrid supercapacitor (HSC) constructed with Co₉S₈-MPA/NF and activated carbon exhibits an outstanding energy density of 25.49 Wh kg^-1 at a high power density of 800 W kg^-1 and a long-term stability of 92% capacitance retention after 5000 cycles at 10 A g^-1. It is worth noting that the prepared all-solid-state HSC can light a red light-emitting diode for 2 min, proving to be a great practical application prospect. These excellent electrochemical behaviors show that this effective conversion strategy offers more possibilities for the development of high-performance energy storage metal sulfide materials.

Retracted Article: Fabrication of hollow CoS1.097 prisms toward supercapactior performance

The controlled synthesis of a variety of microstructures is valuable for understanding the relationship between morphology and properties and exploring potential applications. In this paper, hollow CoS1.097 prisms were prepared by prismatic Co-precursors using thioacetamide (TAA) as a sulfidation treatment reagent. A plausible mechanism was proposed for the formation of the hollow prism structure. S2- comes from TAA to displace the anions in Co-precursors by adjusting temperature and pressure. The original prism morphology of the Co-precursor was maintained and a hollow prismatic structure was formed by an anion exchanging process. Interestingly, the composition of samples after sulfidation treatment can be controlled by changing the diffusion to obtain Co3O4/CoS1.097 and CoS1.097 materials. As electrode materials for supercapacitors, hollow CoS1.097 prisms revealed ideal electrochemical performance.

Kirkendall Growth and Ostwald Ripening Induced Hierarchical Morphology of Ni-Co LDH/MMoS x (M = Co, Ni, and Zn) Heteronanostructures as Advanced Electrode Materials for Asymmetric Solid-State Supercapacitors

By changing the mixed metal sulfide composition, morphology tuning of an active electrode material can be possible, which can have a huge impact on its electrochemical performance. Here, effective morphology tuning of Ni-Co layered double hydroxide (LDH)/MMoS _x (M = Co, Ni, and Zn) heteronanostructures is demonstrated by varying the composition of MMoS _x. Taking advantage of the benefits associated with Kirkendall growth and Ostwald ripening, tunable morphologies were successfully achieved. Among the Ni-Co LDH/MMoS _x (M = Co, Ni, and Zn) heteronanostructures, a Ni-Co LDH/NiMoS _x core-shell structured electrode delivered a high specific capacity of 404 mAh g^-1 at 3 mA cm^-2 and an extraordinary cycling stability (after 10 000 cycles) of 93.2% at 50 mA cm^-2. In addition, an asymmetric supercapacitor (ASC) device coupled with Ni-Co LDH/NiMoS _x as the cathode and Fe₂O₃/reduced graphene oxide as the anode exhibited excellent cell capacity and extraordinary cycling stability. Moreover, the ASC device provided a very high specific energy of 72.6 Wh kg^-1 at a specific power of 522.7 W kg^-1 and maintained the specific power of 23.5 Wh kg^-1 at 5357.6 W kg^-1, demonstrating its high applicability to energy storage devices.

Facile one-pot synthesis of NiCo2Se4-rGO on Ni foam for high performance hybrid supercapacitors

A facile, innovative synthesis for the fabrication of NiCo₂Se₄-rGO on a Ni foam nanocomposite via a simple hydrothermal reaction is proposed. The as-prepared NiCo₂Se₄-rGO@Ni foam electrode was tested through pxrd, TEM, SEM, and EDS to characterize the morphology and the purity of the material. The bimetallic electrode exhibited outstanding electrochemical performance with a high specific capacitance of 2038.55 F g⁻¹ at 1 A g⁻¹. NiCo₂Se₄-rGO@Ni foam exhibits an extensive cycling stability after 1000 cycles by retaining 90% of its initial capacity. A superior energy density of 67.01 W h kg⁻¹ along with a high power density of 903.61 W kg⁻¹ further proved the high performance of this electrode towards hybrid supercapacitors. The excellent electrochemical performance of NiCo₂Se₄-rGO@Ni foam can be explained through the high electrocatalytic activity of NiCo₂Se₄ in combination with reduced graphene oxide which increases conductivity and surface area of the electrode. This study proved that NiCo₂Se₄-rGO@Ni foam can be utilized as a high energy density-high power density electrode in energy storage applications.

A hybrid supercapacitor comprising a NiCo₂Se₄-rGO composite has been fabricated on Ni foam and shows high energy and power density and superior flexibility.

Triggering Cation Exchange Reactions by Doping

Cation exchange (CE) reactions have emerged as a technologically important route, complementary to the colloidal synthesis, to produce nanostructures of different geometries and compositions for a variety of applications. Here it is demonstrated with first-principles simulations that an interstitial impurity cation in CdSe nanocrystals weakens nearby bonds and reduces the CE barrier in the prototypical exchange of Cd²⁺ ions by Ag⁺ ions. A Wannier function-based tight binding model is employed to quantify microscopic mechanisms that influence this behavior. To support our model, we also tested our findings in a CE experiment: both CdSe and interstitially Ag-doped CdSe nanocrystals (containing 4% of Ag⁺ ions per nanocrystal on average) were exposed to Pb²⁺ ions at room temperature and it was observed that the exchange reaction proceeds further in doped nanocrystals. The findings suggest doping as a possible route to promote CE reactions that hardly undergo exchange otherwise, for example, those in III-V semiconductor nanocrystals.

Enhanced cycle stability of a NiCo2S4 nanostructured electrode for supercapacitors fabricated by the alternate-dip-coating method

Nanostructured nickel cobalt sulfide (NiCo2S4) electrodes are successfully fabricated using a simple alternate-dip-coating method. The process involves dipping a TiO2 nanoparticles-covered substrate in a nickel/cobalt precursor solution and sulfur precursor solution alternately at room temperature. The fabricated bimetallic sulfide electrode exhibits a synergetic improvement compensating for the disadvantages of the two single metal sulfide electrodes, i.e. the poor cycle stability of the nickel sulfide electrode and the low specific capacitance (Csp) of the cobalt sulfide electrode. The two capacitive properties are optimized by adjusting the ratio of nickel and cobalt concentrations in the metal precursor solution, reaching a Csp of 516 F g-1 at a current density of 1 mA cm-2, with its retention being 99.9% even after 2000 galvanostatic charge-discharge cycles.

CoNi2 S4 Nanoparticle/Carbon Nanotube Sponge Cathode with Ultrahigh Capacitance for Highly Compressible Asymmetric Supercapacitor

Compared with other flexible energy-storage devices, the design and construction of the compressible energy-storage devices face more difficulty because they must accommodate large strain and shape deformations. In the present work, CoNi₂ S₄ nanoparticles/3D porous carbon nanotube (CNT) sponge cathode with highly compressible property and excellent capacitance is prepared by electrodepositing CoNi₂ S₄ on CNT sponge, in which CoNi₂ S₄ nanoparticles with size among 10-15 nm are uniformly anchored on CNT, causing the cathode to show a high compression property and gives high specific capacitance of 1530 F g^-1 . Meanwhile, Fe₂ O₃ /CNT sponge anode with specific capacitance of 460 F g^-1 in a prolonged voltage window is also prepared by electrodepositing Fe₂ O₃ nanosheets on CNT sponge. An asymmetric supercapacitor (CoNi₂ S₄ /CNT//Fe₂ O₃ /CNT) is assembled by using CoNi₂ S₄ /CNT sponge as positive electrode and Fe₂ O₃ /CNT sponge as negative electrode in 2 m KOH solution. It exhibits excellent energy density of up to 50 Wh kg^-1 at a power density of 847 W kg^-1 and excellent cycling stability at high compression. Even at a strain of 85%, about 75% of the initial capacitance is retained after 10 000 consecutive cycles. The CoNi₂ S₄ /CNT//Fe₂ O₃ /CNT device is a promising candidate for flexible energy devices due to its excellent compressibility and high energy density.

(Fe0.2Ni0.8)0.96S tubular spheres supported on Ni foam as an efficient bifunctional electrocatalyst for overall water splitting

Earth-abundant and efficient bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are highly significant for renewable energy systems. However, the performance of existing electrocatalysts is usually restricted by the low electroic conductivity and the limited amount of exposed active sites. In this work, (Fe0.2Ni0.8)0.96S tubular spheres supported on Ni foam have been prepared by a sulfuration of FeNi layered double hydroxide spheres grown on Ni foam. Benefiting from the unique tubular sphere architecture, the rich inner defects and the enhanced electron interactions between Fe, Ni and S, this electrocatalyst shows low overpotential of 48 mV for HER at 10 mA cm-2 in 1.0 mol L-1 KOH solution, which is one of the lowest value of non-previous electrocatalyts for HER in alkaline electrolyte. Furthermore, assembled this versatile electrode as an alkaline electrolyzer for overall water splitting, a current density of 10 mA cm-2 is achieved at a low cell voltage of 1.56 V, and reach up to 30 mA cm-2 only at an operating cell voltage of 1.65 V.

Ion exchange for synthesis of porous CuxO/SnO2/ZnSnO3 microboxes as a high-performance lithium-ion battery anode

Integrating other oxides and ZnSnO₃ with porous structures can accommodate volume expansion and enhance the electrochemical performance.

Synthesis of a MnS/NixSy composite with nanoparticles coated on hexagonal sheet structures as an advanced electrode material for asymmetric supercapacitors

A MnS/Ni_xS_y composite with nanoparticles coated on hexagonal sheets was successfully synthesized and exhibited enhanced performance.

Acceleration of Kirkendall effect processes in silicon nanospheres using magnetic fields

We show that a magnetic field can act as an independent parameter to accelerate the Kirkendall effect in a liquid reaction system.

Solid-Solution Sulfides Derived from Tunable Layered Double Hydroxide Precursors/Graphene Aerogel for Pseudocapacitors and Sodium-Ion Batteries

Transition-metal sulfides (TMSs) are suggested as promising electrode materials for electrochemical pseudocapacitors and lithium- and sodium-ion batteries; however, they typically involve mixed composites or conventionally stoichiometric TMSs (such as NiCo₂S₄ and Ni₂CoS₄). Herein we demonstrate a preparation of solid-solution sulfide (Ni_0.7Co_0.3)S₂ supported on three-dimensional graphene aerogel (3DGA) via a sulfuration of NiCo-layered double hydroxide (NiCo-LDH) precursor/3DGA. The electrochemical tests show that the (Ni_0.7Co_0.3)S₂/3DGA electrode exhibits a capacitance of 2165 F g^-1 at 1 A g^-1, 2055 F g^-1 at 2 A g^-1, and 1478 F g^-1 at 10 A g^-1; preserves 78.5% capacitance retention upon 1000 cycles for pseudocapacitors; and in particular, possesses a relatively high charge capacity of 388.7 mA h g^-1 after 50 cycles at 100 mA g^-1 as anode nanomaterials for sodium-ion batteries. Furthermore, the electrochemical performances are readily tuned by varying the cationic type of the tunable LDH precursors to prepare different solid-solution sulfides, such as (Ni_0.7Fe_0.3)S₂/3DGA and (Co_0.7Fe_0.3)S₂/3DGA. Our results show that engineering LDH precursors can offer an alternative for preparing diverse transition-metal sulfides for energy storage.

Autotemplate Microcapsules of CaCO3/Pectin and Nonstoichiometric Complexes as Sustained Tetracycline Hydrochloride Delivery Carriers

New types of composites were obtained by an autotemplate method for assembling hollow CaCO₃ capsules by using pH-sensitive polymers. Five pectin samples, which differ in the methylation degree and/or amide content, and some nonstoichiometric polyelectrolyte complex dispersions, prepared with the pectin samples and poly(allylamine hydrochloride), were used to control the crystal growth. The morphology of the composites was investigated by scanning electron microscopy, and the polymorphs characteristics were investigated by FTIR spectroscopy. The presence of the polymer in the composite particles was evidenced by X-ray photoelectron spectroscopy, particle charge density, and zeta-potential. The new CaCO₃/pectin hollow capsules were tested as a possible matrix for a tetracycline hydrochloride carrier. The kinetics of the drug release mechanism was followed using Higuchi and Korsmeyer-Peppas mathematical models.

Synthesis of Mesoporous CoS2 and NixCo1-xS2 with Superior Supercapacitive Performance Using a Facile Solid-Phase Sulfurization

Synthesis of nanostructured transition metal sulfides is of particular interest in providing new methods to control their porosity and improve their surface area because those sulfides hold promising applications in high-energy density devices. Significant challenges remain currently to prepare metal sulfides having three-dimensional (3-D) continuous mesoporous structures, known to be critical for increasing their active surface sites and enhancing ion transport. We herein present a facile solid-phase sulfurization method to synthesize 3-D continuous mesoporous CoS₂, NiS₂, and their binary sulfides in a two-step nanocasting using bicontinuous KIT-6 as hard templates. The solid-phase sulfurization taking place at 400 °C yields mesoporous sulfides with highly crystalline frameworks and a stoichiometric ratio of metal-to-sulfur, 1:2 (mol), within 30 min. Elemental sulfur as an inexpensive sulfur source can be directly used for the solid-phase sulfurization of mesoporous oxides of Co₃O₄, NiO, and their binary oxides. This facile synthetic method is highly efficient to prepare mesoporous sulfides in the gram-scale production at a very low cost. Mesoporous sulfides are demonstrated to be superior electrode materials for pseudo-supercapacitors, given their high surface area and accessible bicontinuous mesopores, the suitable crystalline sizes, and the enhanced ion transport capability. The use of binary mesoporous sulfides presents interesting synergetic effect where the doping of metal ions can significantly enhance the capacitive performance of single-component sulfides. The binary sulfides of mNi_0.32Co_0.68S₂ show a specific capacitance up to 1698 F g^-1 at a current density of 2 A g^-1. The supercapacitor device of mNi_0.32Co_0.68S₂ has a high energy density of 37 Wh kg^-1 at a power density of 800 W kg^-1. We believe that the reported solid-phase synthesis offers a universal method toward the conversion of mesoporous oxides materials into various useful and functional forms for energy conversion and storage applications.

Synergistic effect in the heterostructure of ZnCo2O4 and hydrogenated zinc oxide nanorods for high capacitive response

Herein, a novel heterostructure was fabricated by combining electrochemically and optically active materials to achieve a high capacitive response of 896 F g^-1 at 5 A g^-1. A network of ZnCo₂O₄ nanorods (NRs) was directly grown on a three-dimensional matrix of H : ZnO NRs (ZnCo₂O₄/H : ZnO NRs) that offered synergistic advantages by providing an optimum ion/charge transportation path, large electrochemically active surface area, and stable capacitive response during the electrolytic process. Furthermore, the fabricated solid-state asymmetric supercapacitor ZnCo₂O₄/H : ZnO NRs//activated carbon induced a large potential window of 1.5 V that offered excellent energy and power densities. In addition, optically active ZnCo₂O₄/H : ZnO NRs were also used for the conversion of optical energy over a broad wavelength range; thus, the as-fabricated asymmetric solid-state supercapacitor could easily provide the required power for the operation of a photodetector. Therefore, the unique heterostructure of ZnCo₂O₄/H : ZnO NRs not only presents excellent capacitive response but also demonstrates great potential for energy conversion.

Role of the Crystal Structure in Cation Exchange Reactions Involving Colloidal Cu2Se Nanocrystals

Stoichiometric Cu₂Se nanocrystals were synthesized in either cubic or hexagonal (metastable) crystal structures and used as the host material in cation exchange reactions with Pb²⁺ ions. Even if the final product of the exchange, in both cases, was rock-salt PbSe nanocrystals, we show here that the crystal structure of the starting nanocrystals has a strong influence on the exchange pathway. The exposure of cubic Cu₂Se nanocrystals to Pb²⁺ cations led to the initial formation of PbSe unselectively on the overall surface of the host nanocrystals, generating Cu₂Se@PbSe core@shell nanoheterostructures. The formation of such intermediates was attributed to the low diffusivity of Pb²⁺ ions inside the host lattice and to the absence of preferred entry points in cubic Cu₂Se. On the other hand, in hexagonal Cu₂Se nanocrystals, the entrance of Pb²⁺ ions generated PbSe stripes "sandwiched" in between hexagonal Cu₂Se domains. These peculiar heterostructures formed as a consequence of the preferential diffusion of Pb²⁺ ions through specific (a, b) planes of the hexagonal Cu₂Se structure, which are characterized by almost empty octahedral sites. Our findings suggest that the morphology of the nanoheterostructures, formed upon partial cation exchange reactions, is intimately connected not only to the NC host material, but also to its crystal structure.

Mesocrystalline Zn-Doped Fe3O4 Hollow Submicrospheres: Formation Mechanism and Enhanced Photo-Fenton Catalytic Performance

Uniform and magnetic recyclable mesocrystalline Zn-doped Fe₃O₄ hollow submicrospheres (HSMSs) were successfully synthesized via a simple one-pot solvothermal route and were used for efficient heterogeneous photo-Fenton catalyst. XRD, XPS, Raman spectroscopy, Mössbauer spectroscopy, SEM, HRTEM, and EDX analyses revealed that the shell of HSMSs is highly porous and assembled by oriented attachment of magnetite nanocrystal building blocks with Zn-rich surfaces. Furthermore, a possible formation mechanism of mesocrystalline hollow materials was proposed. First, Fe₃O₄ mesocrystals were assembled by oriented nanocrystals, and a Zn-rich amorphous shell grew on the surfaces. Then, Zn gradually diffused into Fe₃O₄ crystals to form Zn-doped Fe₃O₄ due to the Kirkendall effect with increasing the reaction time. Meanwhile, the inner nanocrystals would be dissolved, and outer particles would grow larger owing to the Ostwald ripening process, leading to the formation of a hollow structure with porous shell. The Zn-doped Fe₃O₄ HSMSs exhibited high and stable photo-Fenton activity for degradation of rhodamine B (RhB) and cephalexin under visible-light irradiation in the presence of H₂O₂, which results from their hollow mesocrystal structure and Zn doping. It could be easily separated and reused by an external magnetic field. The results suggested that the as-obtained magnetite hollow mesocrystals could be a promising catalyst in the photo-Fenton process.

Sequential partial ion exchange synthesis of composite Ni3S2/Co9S8/NiSe nanoarrays with a lavender-like hierarchical morphology

A hierarchical Ni@Ni₃S₂/Co₉S₈/NiSe composite through sequential partial ion exchange for supercapacitor design.

Modified chemical synthesis of MnS nanoclusters on nickel foam for high performance all-solid-state asymmetric supercapacitors

Novel MnS nanoclusters were synthesized on nickel foam (NF) using a successive ionic layer adsorption and reaction (SILAR) method.