Metal-Organic Framework Template Synthesis of NiCo2S4@C Encapsulated in Hollow Nitrogen-Doped Carbon Cubes with Enhanced Electrochemical Performance for Lithium Storage

Three-dimensional nano assembly of nickel cobalt sulphide/polyaniline@polyoxometalate/reduced graphene oxide hybrid with superior lithium storage and electrocatalytic properties for hydrogen evolution reaction

Engineering hierarchical nanostructures with enhanced charge storage capacity and electrochemical activity are vital for the advancement of energy devices. Herein, a highly ordered mesoporous three-dimensional (3D) nano-assembly of Nickel Cobalt Sulphide/Polyaniline @Polyoxometalate/Reduced Graphene Oxide (NiCo₂S₄/PANI@POM/rGO) is prepared first time via a simple route of oxidative polymerization followed by a hydrothermal method. Morphological analysis of the resulting hybrid reveals the sheet-like structures containing a homogeneous assembly of PANI@POM and NiCo₂S₄ on the graphene exterior maintaining huge structural integrity, large surface area and electrochemically active centres. The electrochemical analysis of the nanohybrid as the anode of the lithium-ion battery (LIB) has delivered ultra-huge reversible capacity of 735.5 mA h g^-1 (0.1 A g^-1 after 200 cycles), superb capacity retention (0.161% decay/per cycle at 0.5 A g^-1 for 1000 cycles), and significant rate capability (355.6 mA h g^-1 at 2 A g^-1). The hydrogen evolution reaction (HER) measurement also proves remarkable activity, extremely low overpotential and high durability. The extraordinary performance of the nanohybrid is due to the presence of abundant electroactive centres, high surface area and a large number of ion exchange channels. These outstanding results prove the advantages of a combination of NiCo₂S₄, graphene sheets, and PANI@POM in energy devices.

Statistical Multiobjective Optimization of Thiospinel CoNi2S4 Nanocrystal Synthesis via Design of Experiments

Thiospinels, such as CoNi₂S₄, are showing promise for numerous applications, including as catalysts for the hydrogen evolution reaction, hydrodesulfurization, and oxygen evolution and reduction reactions; however, CoNi₂S₄ has not been synthesized as small, colloidal nanocrystals with high surface-area-to-volume ratios. Traditional optimization methods to control nanocrystal attributes such as size typically rely upon one variable at a time (OVAT) methods that are not only time and labor intensive but also lack the ability to identify higher-order interactions between experimental variables that affect target outcomes. Herein, we demonstrate that a statistical design of experiments (DoE) approach can optimize the synthesis of CoNi₂S₄ nanocrystals, allowing for control over the responses of nanocrystal size, size distribution, and isolated yield. After implementing a 2^5-2 fractional factorial design, the statistical screening of five different experimental variables identified temperature, Co:Ni precursor ratio, Co:thiol ratio, and their higher-order interactions as the most critical factors in influencing the aforementioned responses. Second-order design with a Doehlert matrix yielded polynomial functions used to predict the reaction parameters needed to individually optimize all three responses. A multiobjective optimization, allowing for the simultaneous optimization of size, size distribution, and isolated yield, predicted the synthetic conditions needed to achieve a minimum nanocrystal size of 6.1 nm, a minimum polydispersity (σ/d̅) of 10%, and a maximum isolated yield of 99%, with a desirability of 96%. The resulting model was experimentally verified by performing reactions under the specified conditions. Our work illustrates the advantage of multivariate experimental design as a powerful tool for accelerating control and optimization in nanocrystal syntheses.

Three-Dimensional Porous Nitrogen-Doped Carbon Nanosheet with Embedded NixCo3-xS4 Nanocrystals for Advanced Lithium-Sulfur Batteries

The shuttle effect of lithium polysulfides (Li₂S_n) in electrolyte and the low conductivity of sulfur are the two key hindrances of lithium sulfur (Li-S) batteries. In order to address the two issues, we propose a three-dimensional porous nitrogen-doped carbon nanosheet with embedded Ni_xCo_3-xS₄ nanocrystals derived from metal-organic frameworks for the durable-cathode host material in Li-S batteries. Experiments and density functional theory simulations show that the large porosity, robust N-doped carbon framework, and evenly embedded Ni_xCo_3-xS₄ nanocrystals with high polarity act as strong "traps" for the immobilization of Li₂S_n, which leads to an effective suppressing of the shuttle effect and promotes efficient utilization of sulfur. The Ni_xCo_3-xS₄/N-doped carbon hybrid material exhibits a high reversible capacity of 1122 mAh g^-1 at a current density of 0.5 C after 100 cycles. Even at high areal sulfur loadings of 10 and 12 mg cm^-2, the hybrid cathode materials can maintain good areal capacities of 7.2 and 7.6 mAh cm^-2 after 100 cycles. The present study sheds light on the principles of the anchoring behaviors of Li₂S_n species on bimetallic sulfide hybrid materials and reveals an attractive route to design the highly desirable cathode materials for Li-S batteries.

Nanostructured metal chalcogenides confined in hollow structures for promoting energy storage

The engineering of progressive nanostructures with subtle construction and abundant active sites is a key factor for the advance of highly efficient energy storage devices. Nanostructured metal chalcogenides confined in hollow structures possess abundant electroactive sites, more ions and electron pathways, and high local conductivity, as well as large interior free space in a quasi-closed structure, thus showing promising prospects for boosting energy-related applications. This review focuses on the most recent progress in the creation of diverse confined hollow metal chalcogenides (CHMCs), and their electrochemical applications. Particularly, by highlighting certain typical examples from these studies, a deep understanding of the formation mechanism of confined hollow structures and the decisive role of microstructure engineering in related performances are discussed and analyzed, aiming at prompting the nanoscale engineering and conceptual design of some advanced confined metal chalcogenide nanostructures. This will appeal to not only the chemistry-, energy-, and materials-related fields, but also environmental protection and nanotechnology, thus opening up new opportunities for applications of CHMCs in various fields, such as catalysis, adsorption and separation, and energy conversion and storage.

Graphitic Carbon Quantum Dots Modified Nickel Cobalt Sulfide as Cathode Materials for Alkaline Aqueous Batteries

Carbon quantum dots (CQDs) as a new class of emerging materials have gradually drawn researchers' concern in recent years. In this work, the graphitic CQDs are prepared through a scalable approach, achieving a high yield with more than 50%. The obtained CQDs are further used as structure-directing and conductive agents to synthesize novel N,S-CQDs/NiCo₂S₄ composite cathode materials, manifesting the enhanced electrochemical properties resulted from the synergistic effect of highly conductive N,S-codoped CQDs offering fast electronic transport and unique micro-/nanostructured NiCo₂S₄ microspheres with Faradaic redox characteristic contributing large capacity. Moreover, the nitrogen-doped reduced graphene oxide (N-rGO)/Fe₂O₃ composite anode materials exhibit ultrahigh specific capacity as well as significantly improved rate property and cycle performance originating from the high-capacity prism-like Fe₂O₃ hexahedrons tightly wrapped by highly conductive N-rGO. A novel alkaline aqueous battery assembled by these materials displays a specific energy (50.2 Wh kg^-1), ultrahigh specific power (9.7 kW kg^-1) and excellent cycling performance with 91.5% of capacity retention at 3 A g^-1 for 5000 cycles. The present research offers a valuable guidance for the exploitation of advanced energy storage devices by the rational design and selection of battery/capacitive composite materials.

A rational design of nanoporous Cu–Co–Ni–P nanotube arrays and CoFe2Se4 nanosheet arrays for flexible solid-state asymmetric devices

A facile method was developed to synthesize nanoporous Cu–Co–Ni–P nanotube arrays and hierarchical CoFe₂Se₄ nanosheet arrays for a flexible asymmetric device.

Encapsulating MnSe Nanoparticles Inside 3D Hierarchical Carbon Frameworks with Lithium Storage Boosted by in Situ Electrochemical Phase Transformation

Electrode materials that act through the electrochemical conversion mechanism, such as metal selenides, have been considered as promising anode candidates for lithium-ion batteries (LIBs), although their fast capacity attenuation and inadequate electrical conductivity are impeding their practical application. In this work, these issues are addressed through the efficient fabrication of MnSe nanoparticles inside porous carbon hierarchical architectures for evaluation as anode materials for LIBs. Density functional theory simulations indicate that there is a completely irreversible phase transformation during the initial cycle, and the high structural reversibility of β-MnSe provides a low energy barrier for the diffusion of lithium ions. Electron localization function calculations demonstrate that the phase transformation leads to high charge transfer kinetics and a favorable lithium ion diffusion coefficient. Benefitting from the phase transformation and unique structural engineering, the MnSe/C chestnut-like structures with boosted conductivity deliver enhanced lithium storage performance (885 mA h g^-1 at a current density of 0.2 A g^-1 after 200 cycles), superior cycling stability (a capacity of 880 mA h g^-1 at 1 A g^-1 after 1000 cycles), and outstanding rate performance (416 mA h g^-1 at 2 A g^-1).

Engineering Unique Ball-In-Ball Structured (Ni0.33Co0.67)9S8@C Nanospheres for Advanced Sodium Storage

Constructing hollow architectures based on metal sulfides is of great interest for high-performance electrode materials for sodium-ion batteries because of their intriguing properties and various applications. However, the relatively low volumetric density and high fragile structure are the obstacles blocking the development of hollow-structured electrode materials. In this work, ball-in-ball structured (Ni_0.33Co_0.67)₉S₈@C nanospheres have been synthesized by using NiCo-glycerate as the precursor via solvothermal reaction, which was followed by a carbon coating treatment. In this structural design, hollow cavities are generated between the inner and outer balls to effectively accommodate the volume changes of the metal sulfides in the processes of charging/discharging, whereas the uniform carbon coating can increase the electrical conductivity and maintain the structural stability during repeated cycling. The Rietveld refinement, in situ X-ray diffraction, and ex situ X-ray photoelectron spectroscopy analyses provide evidence for an enlarged lattice parameter, weaker Co-S and Ni-S bondings, and a synergistic effect in (Ni_0.33Co_0.67)₉S₈@C toward boosting the conversion reaction and reversible formation of sulfur in the fully charged state, with sulfur trapped within the composite to additionally account for the superior cycling stability of this material. Capacitive behavior has been verified to dominate the electrochemical reaction, enabling fast charge-transport kinetics. Impressively, the double structural protection combined with the free hollow space and complete carbon layer endows the (Ni_0.33Co_0.67)₉S₈@C nanospheres with good electrochemical performance, featuring high cyclability and good rate capability.

In-situ synthesis of Ni-Co-S nanoparticles embedded in novel carbon bowknots and flowers with pseudocapacitance-boosted lithium ion storage

We design a facile approach to prepare a bimetallic transition-metal-sulphide-based 3D hierarchically-ordered porous electrode based on bimetallic metal-organic frameworks (Ni-Co-MOFs) by using confinement growth and in-situ sulphurisation techniques. In the novel resulting architectures, Ni-Co-S nanoparticles are confined in bowknot-like and flower-like carbon networks and are mechanically isolated but electronically well-connected, where the carbon networks with a honeycomb-like feature facilitate electron transfer with uninterrupted conductive channels from all sides. Moreover, these hierarchically-ordered porous structures together with internal voids can accommodate the volume expansion of the embedded Ni-Co-S nanoparticles. The pseudocapacitive behaviours displayed in the NCS@CBs and NCS@CFs occupied a significant portion in the redox processes. Because of these merits, both the as-built bowknot and flower networks show excellent electrochemical properties for lithium storage with superior rate capability and robust cycling stability (994 mAh g^-1 for NCS@CBs and 888 mAh g^-1 for NCS@CFs after 200 cycles). This unique 3D hierarchically-ordered structural design is believed to hold great potential applications in propagable preparation of carbon networks teamed up with sulphide nanocrystals for high energy storage.

Rational design of few-layer MoSe2 confined within ZnSe-C hollow porous spheres for high-performance lithium-ion and sodium-ion batteries

Rechargeable battery systems, including Li-ion batteries and Na-ion batteries, have attracted great interest in energy storage because of their high energy density, low cost, efficient energy storage and suitable redox potential. Nevertheless, their rapid development is still greatly hampered by some typical constraints including low coulombic efficiency, large volume changes and severe particle agglomeration and pulverization during the charge-discharge process. Here, we fabricate a few-layer MoSe2 confined within a ZnSe-C hollow porous sphere nanocomposite through a simple self-assembly strategy followed by selenization, which efficiently circumvents these problems. The fabricated ZnSe/MoSe2@C electrode demonstrates diverse advantages, including the existence of a few-layer structure, an in situ porous carbon matrix, multicomponent coordination and excellent pseudocapacitive behavior. When used as an anode material, it displays extraordinarily attractive electrochemical performance for both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). The reversible capacity of ZnSe/MoSe2@C for LIBs reaches as high as 1051 mA h g-1 at 0.2 A g-1 (150 cycles). A long-term high-rate cycling test reveals an excellent stability of 524 mA h g-1 at 4 A g-1 after 600 cycles. In addition, for SIBs, ZnSe/MoSe2@C also manifests a high initial coulombic efficiency of 89% at 0.2 A g-1 and a remarkable reversible capacity of 381 mA h g-1 at a high current density of 4 A g-1 even after 250 cycles with negligible capacity loss. This is one of the best performances of ZnSe-based anode materials for SIBs reported so far. The regulation strategy reported in the present work is expected to offer new insights into the fabrication of high performance anode materials for SIBs.

Formation of nickel-cobalt sulphide@graphene composites with enhanced electrochemical capacitive properties

Here, nickel-cobalt sulphide particles embedded in graphene layers (porous Ni-Co-S@G), were successfully prepared by one-step annealing of metallocene/metal-organic framework (MOF) hybrids involving simultaneous carbonization and sulfidation. Benefiting from the porous structure, highly conductive graphene layers and large loading of super-capacitive Ni-Co-S, the obtained Ni-Co-S@G composites exhibited excellent electrochemical performance with a specific capacitance of 1463 F g-1 at a current density of 1 A g-1. A flexible solid-state asymmetric supercapacitor (ASC), assembled with Ni-Co-S@G and active carbon, demonstrated a high energy density of 51.0 W h kg-1 at a power density of 650.3 W kg-1. It is noteworthy that the ASC offered robust flexibility and excellent performance that was maintained when the devices were bent at various angles. The results indicate that the as-prepared materials could potentially be applied in high-performance electrochemical capacitors.

Resorcinol-Formaldehyde Resin-Coated Prussian Blue Core-Shell Spheres and Their Derived Unique Yolk-Shell FeS2@C Spheres for Lithium-Ion Batteries

The practical applications of transition metal sulfides as electrode materials for lithium-ion batteries (LIBs) is greatly hindered by the fast capacity fading owing to the large volume expansion. To address this issue, construction of transition metal sulfide and carbon nanocomposites with unique yolk-shell structures is an effective strategy but also remains a great challenge. In this work, we reported a facile approach to synthesize the unique yolk-shell FeS₂@carbon (FeS₂@C) spheres via calcination treatment of the resorcinol-formaldehyde (RF) resin-coated Prussian blue (FeFe PB) core-shell spheres in Ar atmosphere and a subsequent sulfidation treatment. The synthetic method herein was quite simple and convenient. Such unique structure design could effectively prevent the large volume expansion and dissolution of the active materials in the electrolytes during lithiation. As expected, the yolk-shell FeS₂@C spheres exhibited good electrochemical performance as anode materials for LIBs, which displayed a high discharge capacity of 560 mA h g^-1 at 100 mA g^-1 for 100 cycles. When the current density increased to 1000 mA g^-1, a reversible discharge capacity of 269 mA h g^-1 was still retained after 500 cycles. The present work demonstrated an extraordinary synthetic strategy to construct transition metal sulfide and carbon nanocomposites with unique yolk-shell structure. In addition, this RF resin coating strategy can be further extended to synthesize other RF resin-coated PB analogue (PBA) core-shell nanostructures, demonstrating the generality of this RF resin coating strategy.

Hollow Ni-CoSe2 Embedded in Nitrogen-Doped Carbon Nanocomposites Derived from Metal-Organic Frameworks for High-Rate Anodes

Developing high-rate anode materials with large capacity for lithium ion batteries (LIBs) is quite necessary for the booming electric vehicles industry. The utilization of stable and conductive hollow structures for electrode composite materials could make the desired performances possible in the future. Thus, in this study, a hollow structured Ni-CoSe₂ embedded in N-doped amorphous carbon nanocomposite (Ni-CoSe₂@NC) has been successfully synthesized with metal-organic frameworks (MOFs) as precursors. Such strategy integrates both the merits of the multicomponents and the hollow structure; the latter could facilitate both mass and charge transport, and the former (the N-doped carbon) could not only offer plenty of surface defects, improving the surface capacitive contributions, but also stabilize the electrode structure during the charge/discharge processes. As a result, the metal selenide composite delivers outstanding high-rate properties with good stability as the anode for LIBs. The structure and components design could also be extended to other anode composites in the future.

Facile synthesis of NiCo2S4/CNTs nanocomposites for high-performance supercapacitors

Herein, porous NiCo2S4/CNTs nanocomposites were synthesized via a simple hydrothermal method followed by the sulphurization process using different sulfide sources. By comparing two different sulfur sources, the samples using thioacetamide as sulfide source delivered more remarkable electrochemical performance with a high specific capacitance of 1765 F g-1 at 1 A g-1 and an admirable cycling stability with capacitance retention of 71.7% at a high current density of 10 A g-1 after 5000 cycles in 2 M KOH aqueous electrolyte. Furthermore, an asymmetric supercapacitor (ASC) device was successfully fabricated with the NiCo2S4/CNTs electrode as the positive electrode and graphene as the negative electrode. The device provided a maximum energy density of 29.44 W h kg-1 at a power density of 812 W kg-1. Even at a high power density of 8006 W kg-1, the energy density still reaches 16.68 W h kg-1. Moreover, the ASC presents 89.8% specific capacitance retention after 5000 cycles at 5 A g-1. These results reveal its great potential for supercapacitors in electrochemical energy storage field.

Morphological control of lanthanide ferrocyanides and their highly efficient catalytic degradation performance toward organic dyes under dark ambient conditions

KCe[FeII(CN)6]·4H2O (CePBA), a Prussian blue analogue, was successfully synthesized with various morphologies and different sizes. CePBA, when used as a heterogeneous catalyst, can rapidly and completely degrade a large number of methylene blue molecules in 30 seconds: 14.5 mg of MB (for each 5 mg of catalyst). The CePBA catalyst is reusable. These are very important parameters for practical applications.

The development of MOFs-based nanomaterials in heterogeneous organocatalysis

Metal-organic framework (MOF) is a class of inorganic-organic hybrid material assembled periodically with metal ions and organic ligands. MOFs have always been the focuses in a variety of frontier fields owing to the advantageous properties, such as large BET surface areas, tunable porosity and easy-functionalized surface structure. Among the various application areas, catalysis is one of the earliest application fields of MOFs-based materials and is one of the fastest-growing topics. In this review, the main roles of MOFs in heterogeneous organocatalysis have been systematically summarized, including used as support materials (or hosts), independent catalysts, and sacrificial templates. Moreover, the application prospects of MOFs in photocatalysis and electrocatalysis frontiers were also mentioned. Finally, the key issues that should be conquered in future were briefly sketched in the final parts of each item. We hope our perspectives could be beneficial for the readers to better understand these topics and issues, and could also provide a direction for the future exploration of some novel types of MOFs-based nanocatalysts with stable structures and functions for heterogeneous catalysis.

Template synthesis of nitrogen-doped carbon nanocages–encapsulated carbon nanobubbles as catalyst for activation of peroxymonosulfate

Nitrogen-doped carbon nanocages–encapsulated carbon nanobubbles were employed as high-performance peroxymonosulfate activators for the degradation of organic pollutants.

Synthesis of TiO2@α-Fe2O3 core–shell heteronanostructures by thermal decomposition approach and their application towards sunlight-driven photodegradation of rhodamine B

TiO₂@α-Fe₂O₃ core–shell heteronanostructures that act as a good photocatalyst for the degradation of RhB were synthesized by a novel thermal decomposition approach.

Encapsulating CoS2–CoSe2 heterostructured nanocrystals in N-doped carbon nanocubes as highly efficient counter electrodes for dye-sensitized solar cells

The CoS₂–CoSe₂@N-doped carbon nanocubes were synthesized through simultaneous sulfurization and selenization of polydopamine coated Prussian blue analogs.