Formation of CoS2Nanobubble Hollow Prisms for Highly Reversible Lithium Storage

ZnS-Sb2S3@C Core-Double Shell Polyhedron Structure Derived from Metal-Organic Framework as Anodes for High Performance Sodium Ion Batteries

Taking advantage of zeolitic imidazolate framework (ZIF-8), ZnS-Sb₂S₃@C core-double shell polyhedron structure is synthesized through a sulfurization reaction between Zn²⁺ dissociated from ZIF-8 and S^2- from thioacetamide (TAA), and subsequently a metal cation exchange process between Zn²⁺ and Sb³⁺, in which carbon layer is introduced from polymeric resorcinol-formaldehyde to prevent the collapse of the polyhedron. The polyhedron composite with a ZnS inner-core and Sb₂S₃/C double-shell as anode for sodium ion batteries (SIBs) shows us a significantly improved electrochemical performance with stable cycle stability, high Coulombic efficiency and specific capacity. Peculiarly, introducing a carbon shell not only acts as an important protective layer to form a rigid construction and accommodate the volume changes, but also improves the electronic conductivity to optimize the stable cycle performance and the excellent rate property. The architecture composed of ZnS inner core and a complex Sb₂S₃/C shell not only facilitates the facile electrolyte infiltration to reduce the Na-ion diffusion length to improve the electrochemical reaction kinetics, but also prevents the structure pulverization caused by Na-ion insertion/extraction. This approach to prepare metal sulfides based on MOFs can be further extended to design other nanostructured systems for high performance energy storage devices.

Metal-Organic Framework Derivatives for Improving the Catalytic Activity of the CO Oxidation Reaction

Metal-organic framework (MOF)-based derivatives have attracted an increasing interest in various research fields. However, most of the reported papers mainly focus on pristine MOF-based derivatives, and research studies on functional MOF-based derivative composites are rare. Here, a simple strategy has been reported to design functional MOF-based derivative composites by the encapsulation of metal nanoparticle (MNP) in MOF matrixes (MNP@MOF) and the high-temperature calcination of MNP@MOF composites. The as-prepared MNP@metal oxide composites with a hierarchical pore structure exhibited excellent catalytic activity and high stability for the CO oxidation reaction.

Morphology memory but reconstructing crystal structure: porous hexagonal GeO2 nanorods for rechargeable lithium-ion batteries

Hexagonal GeO₂, with high theoretical reversible capacity and low operating voltage, is regarded as a promising anode material for Li ion batteries. Being similar to other alloy type anode materials, the practical application of GeO₂ is confronted with large volume change and fast capacity fading during lithiation/delithiation cycles. Constructing unique GeO₂ nanostructures is proposed as an effective strategy to address this issue of fast capacity degradation. However, the controllable synthesis of GeO₂ nanomaterials is challenged due to the fast hydrolysis of Ge precursors in aqueous solution. In this work, we report a simple strategy to synthesize GeO₂ nanorods by using orthorhombic Ca₂Ge₇O₁₆ nanorods as the sacrificial template with HNO₃ as the etching agent. With the morphology memory of orthorhombic Ca₂Ge₇O₁₆ nanorods, the as-prepared porous hexagonal GeO₂ nanorods exhibit excellent electrochemical performance with a high capacity of 747 mA h g^-1 after 50 cycles, which should be attributed to the porous and one dimensional nanostructure of GeO₂ nanorods. This facile 'morphology memory but restructuring crystal structure' method could be extended to the controllable preparation of other GeO₂ nanostructures, and achieve more efficient anode materials.

Interfacial engineering of renewable metal organic framework derived honeycomb-like nanoporous aluminum hydroxide with tunable porosity

Novel honeycomb-like mesoporous aluminum hydroxide (pATH) was synthesized via a facile one-step reaction by employing ZIF-8 as a template.

Novel honeycomb-like mesoporous aluminum hydroxide (pATH) was synthesized via a facile one-step reaction by employing ZIF-8 as a template. This self-decomposing template was removed automatically under acidic conditions without the need for any tedious or hazardous procedures. Meanwhile, the pore size of pATH was easily modulated by tuning the dimensions of the ZIF-8 polyhedrons. Of paramount importance was the fact that the dissolved ZIF-8 in solution was regenerated upon deprotonation of the ligand under mild alkali conditions, and was reused in the preparation of pATH, thus forming a delicate synthesis cycle. The renewable template conferred cost-effective and sustainable features to the as-synthesized product. As a proof-of-concept application, the fascinating nanoporous structure enabled pATH to load more phosphorous-containing flame retardant and endowed better interaction with epoxy resin over that of commercial aluminum hydroxide. The limiting oxygen index, UL-94 vertical burning test and cone calorimeter test showed that the results of epoxy with the modified pATH rivalled those of epoxy with two times the loading amount of the commercial counterpart, while the former presented better mechanical properties. The proposed “amorphous replica method” used in this work will advance the potential for launching a vast area of research and technology development for the preparation of porous metal hydroxides for use in practical applications.

Preparation of NiCoP Hollow Quasi-Polyhedra and Their Electrocatalytic Properties for Hydrogen Evolution in Alkaline Solution

Double metal phosphide (NiCoP) with hollow quasi-polyhedron structure was prepared by acidic etching and precipitation of ZIF-67 polyhedra and further phosphorization treatment with NaH₂PO₂. The morphology and microstructure of NiCoP quasi-polyhedron and its precursors were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and a micropore and chemisorption analyzer. Electrocatalytic properties were examined by typical electrochemical methods, such as linear sweep voltammetry, cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy in 1.0 M KOH aqueous solution. Results reveal that, compared with CoP hollow polyhedra, NiCoP hollow quasi-polyhedra exhibit better electrochemical properties for hydrogen evolution with a low onset overpotential of 74 mV and a small Tafel slope of 42 mV dec^-1. When the current density is 10 mA cm^-2, the corresponding overpotential is merely 124 mV, and 93% of its electrocatalytic activity can be maintained for 12 h. This indicates that NiCoP with hollow quasi-polyhedron structure, bimetallic merit, and low cost may be a good candidate as electrocatalyst in the practical application of hydrogen evolution.

Self-Templated Formation of Hollow Structures for Electrochemical Energy Applications

The rational design and synthesis of hollow structured functional materials are of great significance as both fundamental challenges in materials science and practical solutions for efficient energy utilization in modern society. The unique structural features of hollow functional materials bring outstanding electrochemical properties for both energy storage and electrocatalysis. However, conventional templating methods are normally less efficient in constructing hollow structures with desirable compositions and architectures. In the past decade, many novel synthetic approaches directly converting templates into hollow structures have been developed. Collectively termed as the "self-templated" strategy, it makes use of various physical/chemical processes to transform solid templates into hollow structures of target materials. Of particular note is the outstanding capability to construct complex hollow architectures of a wide variety of inorganic or hybrid functional materials, thus providing effective solutions for various electrochemical energy applications. In this Account, we present the recent progress in self-templated formation of hollow structures especially with complex architectures, and their remarkable performance in electrochemical energy-related technologies. These advanced self-templated methods are summarized as three categories. "Selective etching" creates hollow structures from solid templates of same materials by removing some of the internal parts, forming multishelled or unusual hollow architectures. "Outward diffusion" utilizes the relocation of mass in templates from inner region to outer region driven by various mechanisms, to construct hollow structures with multiple or hierarchical shells. "Heterogeneous contraction" typically applies to thermally decomposable templates and generates various hollow structures under nonequilibrium heating conditions. We further demonstrate some remarkable electrochemical properties of such hollow structures in virtue of their exceptional composition-/structure-induced merits. As electrode materials for lithium-ion batteries, hybrid or multishelled metal oxides exhibit high cyclability because of their capability to well accommodate the lithium insertion strain. Also the rate capability is effectively improved by the fast lithium insertion/deinsertion in multishelled or hierarchical hollow structures. These exceptional structural merits also significantly enhance the reaction kinetics and prolong the cycling lifetime of metal-sulfides-based electrodes, which enables the assembly of hybrid supercapacitors with high energy and power densities. On the other hand, multicompositional hollow structures with large exposed surface area and rich open pore channels offer abundant robust active sites and fast charge/mass transport for electrocatalytic reactions. These studies demonstrate that the versatility and superiority of self-templated methods for hollow structured functional materials have greatly promoted their applications for electrochemical energy storage and conversion. With continued research efforts, we are expecting greater and broader impacts brought by the rapidly growing family of hollow structures formed by self-templated methods.

Coaxial MoS₂@Carbon Hybrid Fibers: A Low-Cost Anode Material for High-Performance Li-Ion Batteries

A low-cost bio-mass-derived carbon substrate has been employed to synthesize MoS₂@carbon composites through a hydrothermal method. Carbon fibers derived from natural cotton provide a three-dimensional and open framework for the uniform growth of MoS₂ nanosheets, thus hierarchically constructing coaxial architecture. The unique structure could synergistically benefit fast Li-ion and electron transport from the conductive carbon scaffold and porous MoS₂ nanostructures. As a result, the MoS₂@carbon composites-when serving as anodes for Li-ion batteries-exhibit a high reversible specific capacity of 820 mAh·g-1, high-rate capability (457 mAh·g-1 at 2 A·g-1), and excellent cycling stability. The use of bio-mass-derived carbon makes the MoS₂@carbon composites low-cost and promising anode materials for high-performance Li-ion batteries.

Hollow-sphere ZnSe wrapped around carbon particles as a cycle-stable and high-rate anode material for reversible Li-ion batteries

Hollow-sphere ZnSe is successfully obtained through Ostwald ripening. Carbon nanoparticles are designed and utilized to form a wrapped carbon network as a conductive buffering matrix by subsequent annealing.

Formation of graphene-encapsulated CoS2 hybrid composites with hierarchical structures for high-performance lithium-ion batteries

Hierarchical structure CoS₂ nanospheres with graphene (CoS₂/G) composite is fabricated by a simple hydrothermal method. This composite exhibits excellent electrochemical performance, especially long cycle life.

Templated and template-free fabrication strategies for zero-dimensional hollow MOF superstructures

Fabrication strategies for hollow MOF superstructures are classified based on the existence of external templates and the types and properties of templates, and their advantages and disadvantages are reviewed.

Bimetallic phosphide hollow nanocubes derived from a prussian-blue-analog used as high-performance catalysts for the oxygen evolution reaction

Bimetallic phosphide (Ni_xFe_1−x)₂P hollow nanocubes were prepared from PBAs as highly active and stable OER electrocatalysts.

Two-dimensional transition metal dichalcogenide-based counter electrodes for dye-sensitized solar cells

Dye-sensitized solar cell using counter electrode based on transition metal dichalcogenides.

Fabrication of zero to three dimensional nanostructured molybdenum sulfides and their electrochemical and photocatalytic applications

Transition metal dichalcogenides (TMDs) are emerging as promising materials, particularly for electrochemical and photochemical catalytic applications, and among them molybdenum sulfides have received tremendous attention due to their novel electronic and optoelectronic characteristics. Several review articles have summarized the recent progress on TMDs but no critical and systematic summary exists about the nanoscale fabrication of MoS₂ with different dimensional morphologies. In this review article, first we will summarize the recent progress on the morphological tuning and structural evolution of MoS₂ from zero-dimension (0D) to 3D. Then the different engineering methods and the effect of synthesis conditions on structure and morphology of MoS₂ will be discussed. Moreover, the corresponding change in the electronic and physicochemical properties of MoS₂ induced by structure tuning will also be presented. Further, the applications of MoS₂ in various electrochemical systems e.g. hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and supercapacitors as well as photocatalytic hydrogen evolution will be highlighted. The review article will also critically focus on challenges faced by researchers to tune the MoS₂ nanostructures and the resulting electrochemical mechanism to enhance their performances. At the end, concluding remarks and future prospects for the development of better MoS₂ based nanostructured materials for the aforementioned applications will be presented.