Preparation and Exceptional Lithium Anodic Performance of Porous Carbon-Coated ZnO Quantum Dots Derived from a Metal–Organic Framework

Ternary TiO2/SiOx@C nanocomposite derived from a novel titanium-silicon MOF for high-capacity and stable lithium storage

A novel titanium-silicon MOF precursor was first designed and constructed via a facile solvothermal process. After subsequent pyrolysis, the derived ternary TiO₂/SiO_x@C nanocomposite exhibited superior lithium storage performances, which was attributed to their all-in-one architecture of synergistic components, including stable-cycling nanostructured TiO₂, high-capacity SiO_x and high-conductivity carbon matrix.

Rational Design of Unique ZnO/ZnS@N-C Heterostructures for High-Performance Lithium-Ion Batteries

Conversion-type anodes with high theoretical capacity have attracted enormous interest for lithium storage, although their extremely poor conductivity and volume variations during lithiation-delithiation processes seriously limit their practical applications. Herein, a facile strategy to fabricate ZnO/ZnS@N-C heterostructures decorated on carbon nanotubes (ZnO/ZnS@N-C/CNTs) with metal-organic framework assistance is developed. The as-prepared anodes display higher reversible capacity of 1020.6 mAh g^-1 at 100 mA g^-1 after 200 cycles and excellent high-cyclability with 386.6 mAh g^-1 at 1000 mA g^-1 over 400 cycles. The conductive CNT network and N-doped carbon shell could successfully improve the electrical conductivity and avoid the aggregation of ultrasmall ZnO/ZnS nanoparticles. The results calculated from density functional theory also suggest that the ZnO/ZnS heterostructures could promote electron-transfer capability.

Coupling of a conductive Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2 metal-organic framework with silicon nanoparticles for use in high-capacity lithium-ion batteries

A composite of Si nanoparticles (SiNPs) and a two-dimensional (2D) porous conductive Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2 (Ni3(HITP)2) metal-organic framework (MOF), namely Si/Ni3(HITP)2, is suggested as a potential anode material for Li-ion batteries (LIBs). The Ni3(HITP)2 MOF with a carbon backbone and evenly dispersed Ni and N heteroatoms showed high potential for mitigating the volume expansion of Si and enhancing the electronic conductivity as well as Li storage ability of the Si/Ni3(HITP)2 anode. The Si/Ni3(HITP)2 electrode delivered a reversible capacity of 2657 mA h g-1 after 100 cycles of discharge-charge at a rate of 0.1C. Moreover, at a high rate of 1C, the Si/Ni3(HITP)2 electrode maintained a reversible capacity of 876 mA h g-1 even after 1000 cycles. The different rate capacities were 1655, 1129, and 721 mA h g-1 at 5C, 10C and 20C, respectively. The excellent electrochemical performance of the Si/Ni3(HITP)2 electrode in terms of improved cycle life and rate capability results from the open channels of the MOF network, which are beneficial for the movement of Li+ ions through the electrolyte to the electrode and the mitigation of stress by volume expansion of Si. We believe that the coupling of conductive Ni3(HITP)2 with Si is a potential way to make an anode for high-performance LIBs.

Crystallization of zinc oxide quantum dots on graphene sheets as an anode material for lithium ion batteries

A zinc oxide quantum dot/reduced graphene oxide (ZnO/RGO) composite is prepared for the first time by a stepped graphene oxide (GO) reduction strategy.

Graphite-like polyoxometalate-based metal–organic framework as an efficient anode for lithium ion batteries

A new porous POM supported graphite-like MOF (Cu-POM) as a LIB anode material was designed and synthesized, and its lithium storage mechanism was explored using impedance spectra.

Template-free synthesis and lithium-ion storage performance of multiple ZnO nanoparticles encapsulated in hollow amorphous carbon shells

Due to the limited utilization of electrode materials, the rational design and facile synthesis of composite structures are still challenging issues for lithium-ion batteries (LIBs). Herein, a simple approach has been developed to prepare multiple core–shell structures of ZnO nanoparticles (NPs) encapsulated in hollow amorphous carbon (AC) shells. The as-synthesized ZnO@AC composites showed a uniform dispersion of ZnO NPs, compliant buffer AC shells, and nanoscale void spaces between the ZnO NP cores and AC shells. As a result of their structural merits, the ZnO@AC composites were evaluated as anode materials for LIBs and delivered enhanced coulombic efficiency, high reversible capacity, high rate capability, and improved cycling stability.

Core–shell structure of ZnO@amorphous carbon shell was synthesized using a simple and effective method, and exhibited excellent electrochemical performance as anode of lithium-ion batteries.

Controlling the morphology of metal–organic frameworks and porous carbon materials: metal oxides as primary architecture-directing agents

We give a comprehensive overview of how the morphology control is an effective and versatile way to control the physicochemical properties of metal oxides that can be transferred to metal–organic frameworks and porous carbon materials.

From coordination polymers to nanocrystals: general and facile synthesis of ultra-small metal oxide nanocrystals

Ultrasmall and well-dispersed ZnO QDs with special optical properties and polymerization activity were synthesised by using coordination polymers as templates.

Neuron-Mimic Smart Electrode: A Two-Dimensional Multiscale Synergistic Strategy for Densely Packed and High-Rate Lithium Storage

Conventional microsized and nanosized secondary battery electrodes inevitably suffer from poor rate capability and low tap density, respectively. Inspired by a multipolar neuron consisting of a centric micron-soma and multiple divergent nanodendrites, we propose a smart electrode design based on a two-dimensional (2D) multiscale synergistic strategy, for addressing both of the above problems. As a proof of concept, multiple Zn-doped Co-based regional-nanoarrays are grown on one Co-doped Zn-based micron-star in a 2D mode via a facile one-pot liquid-phase process, serving as a representative neuron-mimic anode for lithium-ion batteries. The 2D assembly well retains the tap density advantage derived from the micron-star subunit. Combined analysis of three-dimensional tomographic reconstruction, Li-storage kinetics, and in situ transmission electron microscopy reveal a smart electrochemical behavior similar to a neuron working mechanism, which significantly enhances rate capability as compared to the single micron-star subunit. A mutual-doping effect also benefits high-rate lithium storage as verified by density functional theory calculations. As expected, superior reversible areal capacity (2.52 mA h cm^-2), high long-term capacity retention (<0.024% loss per cycle over 800 cycles after initial 5 cycles), and enhanced rate capability (1 order of magnitude higher than the microsized electrode) are obtained, accompanied by considerable high-temperature endurance.

Boosting High-Rate Li-S Batteries by an MOF-Derived Catalytic Electrode with a Layer-by-Layer Structure

Rechargeable high-energy lithium-sulfur batteries suffer from rapid capacity decay and poor rate capability due to intrinsically intermediate polysulfides' shuttle effect and sluggish redox kinetics. To tackle these problems simultaneously, a layer-by-layer electrode structure is designed, each layer of which consists of ultrafine CoS2-nanoparticle-embedded porous carbon evenly grown on both sides of reduced graphene oxide (rGO). The CoS2 nanoparticles derived from metal-organic frameworks (MOFs) have an average size of ≈10 nm and can facilitate the conversion between Li2S6 and Li2S2/Li2S in the liquid electrolyte by a catalytic effect, leading to improved polysulfide redox kinetics. In addition, the interconnected conductive frameworks with hierarchical pore structure afford fast ion and electron transport and provide sufficient space to confine polysulfides. As a result, the layer-by-layer electrodes exhibit good rate capabilities with 1180.7 and 700 mAh g-1 at 1.0 and 5.0 C, respectively, and maintain an impressive cycling stability with a low capacity decay of 0.033% per cycle within ultralong 1000 cycles at 5.0 C. Even with a high sulfur loading of 3.0 mg cm-2, the electrodes still show high rate performance and stable cycling stability over 300 cycles.

Transformation of Metal-Organic Frameworks into Stable Organic Frameworks with Inherited Skeletons and Catalytic Properties

Metal-organic frameworks (MOFs) are an emerging class of porous materials with attractive properties, however, their practical applications are heavily hindered by their fragile nature. We report herein an effective strategy to transform fragile coordination bonds in MOFs into stable covalent organic bonds under mild annealing decarboxylative coupling reaction conditions, which results in highly stable organic framework materials. This strategy successfully endows intrinsic framework skeletons, porosity and properties of the parent MOFs in the daughter organic framework materials, which exhibit excellent chemical stability under harsh catalytic conditions. Therefore, this work opens a new avenue to synthesize stable organic framework materials derived from MOFs for applications in different fields.

In situ formation and superior lithium storage properties of tentacle-like ZnO@NC@CNTs composites

As a typical conversion-type electrode, ZnO has high theoretical Li⁺ storage capacity and is low cost. However, its practical application is far away due to its limited rate performance and cycle stability. Herein, a novel structure of double carbon coated tentacle-like ZnO composite has been synthesized, which features in situ grown carbon nanotubes (CNTs) embedded in yolk-shell polyhedra, consisting of nitrogen-doped carbon layer (NC) coated ZnO nanoparticles (ZnO@NC@CNTs). Excellent rate performance and good cycling stability are observed in the obtained ZnO@NC@CNTs, including a high reversible capacity of 800 and 617 mA h g^-1 at 0.1 and 1.0 A g^-1 and a low capacity decay of only 0.019% per cycle during 1000 cycles at 1.0 A g^-1. The unique structure of this double carbon NC@CNTs host can not only enhance electron transport throughout the whole electrode but also well accommodate the volume changes of ZnO during cycling, resulting in improved rate capability and cycle stability. In addition, the porous yolk-shell structure of the ZnO@NC@CNTs composite provides better contact between the electrolyte and active material, which enhances both capacity and rate performance of the electrode.

ZnO Nanosheets Abundant in Oxygen Vacancies Derived from Metal-Organic Frameworks for ppb-Level Gas Sensing

Surmounting the inhomogeniety issue of gas sensors and realizing their reproducible ppb-level gas sensing are highly desirable for widespread deployments of sensors to build networks in applications of industrial safety and indoor/outdoor air quality monitoring. Herein, a strategy is proposed to substantially improve the surface homogeneity of sensing materials and gas sensing performance via chip-level pyrolysis of as-grown ZIF-L (ZIF stands for zeolitic imidazolate framework) films to porous and hierarchical zinc oxide (ZnO) nanosheets. A novel approach to generate adjustable oxygen vacancies is demonstrated, through which the electronic structure of sensing materials can be fine-tuned. Their presence is thoroughly verified by various techniques. The sensing results demonstrate that the resultant oxygen vacancy-abundant ZnO nanosheets exhibit significantly enhanced sensitivity and shortened response time toward ppb-level carbon monoxide (CO) and volatile organic compounds encompassing 1,3-butadiene, toluene, and tetrachloroethylene, which can be ascribed to several reasons including unpaired electrons, consequent bandgap narrowing, increased specific surface area, and hierarchical micro-mesoporous structures. This facile approach sheds light on the rational design of sensing materials via defect engineering, and can facilitate the mass production, commercialization, and large-scale deployments of sensors with controllable morphology and superior sensing performance targeted for ultratrace gas detection.

MOF-derived metal oxide composite Mn2Co1Ox/CN for efficient formaldehyde oxidation at low temperature

A novel MOF-derived MnCoO_x nanoparticles embedded in porous N-doped carbon catalyst exhibits excellent catalytic activity for the low-temperature oxidation of formaldehyde.

Ultrafine ternary metal oxide particles with carbon nanotubes: a metal–organic-framework-based approach and superior lithium-storage performance

A metal–organic-framework template approach was used to fabricate ultrafine ternary metal oxide nanoparticles embedded in CNTs, which exhibit larger-than-theoretical reversible capacities for lithium-ion batteries.

In Situ Synthesis and Unprecedented Electrochemical Performance of Double Carbon Coated Cross-Linked Co3O4

Improving the structural stability and the electron/ion diffusion rate across whole electrode particles is crucial for transition metal oxides as next-generation anodic materials in lithium-ion batteries. Herein, we report a novel structure of double carbon-coated Co₃O₄ cross-linked composite, where the Co₃O₄ nanoparticle is in situ covered by nitrogen-doped carbon and further connected by carbon nanotubes (Co₃O₄ NP@NC@CNTs). This double carbon-coated Co₃O₄ NP@NC@CNTs framework not only endows a porous structure that can effectively accommodate the volume changes of Co₃O_4, but also provides multidimensional pathways for electronic/ionic diffusion in and among the Co₃O₄ NPs. Electrochemical kinetics investigation reveals a decreased energy barrier for electron/ion transport in the Co₃O₄ NP@NC@CNTs, compared with the single carbon-coated Co₃O₄ NP@NC. As expected, the Co₃O₄ NP@NC@CNT electrode exhibits unprecedented lithium storage performance, with a high reversible capacity of 1017 mA h g^-1 after 500 cycles at 1 A g^-1, and a very good capacity retention of 75%, even after 5000 cycles at 15 A g^-1. The lithiation/delithiation process of Co₃O₄ NP@NC@CNTs is dominated by the pseudocapacitive behavior, resulting in excellent rate performance and durable cycle stability.

The Research Development of Quantum Dots in Electrochemical Energy Storage

Quantum dots, which are made from semiconductor materials, possess tunable physical dimensions and outstanding optoelectronic characteristics, and they have aroused widespread interest in recent years. In addition to applications in biomolecular analysis, sensors, organic photovoltaic devices, fluorescence, solar cells, photochemical reagents, light-emitting diodes, and catalysis, quantum dots have attracted mounting attention in the field of electrochemical energy storage owing to their size confinement and anisotropic geometry. In this review, a comprehensive summary is given and the research progress of the study of quantum dots for batteries and electrochemical capacitors in recent years, including their synthesis methods, micro/nanostructural features, and electrochemical performance, is appraised.

Ultrasmall Ru/Cu-doped RuO2 Complex Embedded in Amorphous Carbon Skeleton as Highly Active Bifunctional Electrocatalysts for Overall Water Splitting

Developing highly active electrocatalysts with superior durability for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in the same electrolyte is a grand challenge to realize the practical application of electrolysis water for producing hydrogen. In this work, an ultrasmall Ru/Cu-doped RuO₂ complex embedded in an amorphous carbon skeleton is synthesized, through thermolysis of Ru-modified Cu-1,3,5-benzenetricarboxylic acid (BTC), as a highly efficient bifunctional catalyst for overall water splitting electrocatalysis. The ultrasmall Ru nanoparticles in the complex expose more activity sites for hydrogen evolution and outperform the commercial Pt/C. Meanwhile, the ultrasmall RuO₂ nanoparticles exhibit superior oxygen evolution performance over commercial RuO₂, and the doping of Cu into the ultrasmall RuO₂ nanoparticles further enhances the oxygen evolution performance of the catalyst. The outstanding OER and decent HER catalytic activity endow the complex with impressive overall water splitting performance superior to that of the state-of-the-art electrocatalysts, which just require 1.47 and 1.67 V to achieve a current density of 10 mA cm^-2 and 100 mA cm^-2. The density functional theory calculations reveal that a Cu dopant could effectively tailor the d-band center, thereby tuning electronic structure of Ru activity sites on the RuO₂ (110) plane and ultimately improving the OER performance of RuO₂.

Advances in the integration of quantum dots with various nanomaterials for biomedical and environmental applications

Quantum dots (QDs) are semiconductor nanocrystals with distinct characteristics of high brightness, large Stokes shift and broad absorption spectra, large molar extinction coefficients, high quantum yield, good photostability and long fluorescence lifetime. The QDs have replaced the conventional fluorophores with wide applications in immunoassays, microarrays, fluorescence imaging, targeted drug delivery and therapy. The integration of QDs with various nanomaterials such as noble metal nanoparticles, carbon allotropes, upconversion nanoparticles (UCNPs), metal oxides and metal-organic frameworks (MOFs) brings new opportunities and possibilities in nanoscience and nanotechnology. In this review, we summarize the recent advances in the integration of QDs with various nanomaterials for biomedical and environmental applications including sensing, bioimaging, theranostics and cancer therapy. We highlight the involved interactions such as fluorescence resonance energy transfer (FRET), plasmon enhanced fluorescence (PEF), and nanometal surface energy transfer (NSET) as well as the synergistic effect resulting from the integration of QDs with nanomaterials. In addition, we discuss the sensing and imaging mechanisms of different strategies and give new insight into the challenges and future direction as well.

Cobalt Disulfide Nanoparticles Embedded in Porous Carbonaceous Micro-Polyhedrons Interlinked by Carbon Nanotubes for Superior Lithium and Sodium Storage

Transition metal sulfides are appealing electrode materials for lithium and sodium batteries owing to their high theoretical capacity. However, they are commonly characterized by rather poor cycling stability and low rate capability. Herein, we investigate CoS₂, serving as a model compound. We synthesized a porous CoS₂/C micro-polyhedron composite entangled in a carbon-nanotube-based network (CoS₂-C/CNT), starting from zeolitic imidazolate frameworks-67 as a single precursor. Following an efficient two-step synthesis strategy, the obtained CoS₂ nanoparticles are uniformly embedded in porous carbonaceous micro-polyhedrons, interwoven with CNTs to ensure high electronic conductivity. The CoS₂-C/CNT nanocomposite provides excellent bifunctional energy storage performance, delivering 1030 mAh g^-1 after 120 cycles and 403 mAh g^-1 after 200 cycles (at 100 mA g^-1) as electrode for lithium-ion (LIBs) and sodium-ion batteries (SIBs), respectively. In addition to these high capacities, the electrodes show outstanding rate capability and excellent long-term cycling stability with a capacity retention of 80% after 500 cycles for LIBs and 90% after 200 cycles for SIBs. In situ X-ray diffraction reveals a significant contribution of the partially graphitized carbon to the lithium and at least in part also for the sodium storage and the report of a two-step conversion reaction mechanism of CoS₂, eventually forming metallic Co and Li₂S/Na₂S. Particularly the lithium storage capability at elevated (dis-)charge rates, however, appears to be substantially pseudocapacitive, thus benefiting from the highly porous nature of the nanocomposite.

Zeolite-templated carbons - three-dimensional microporous graphene frameworks

Zeolite-templated carbons (ZTCs) are ordered microporous carbons synthesized by using zeolite as a sacrificial template. Unlike well-known ordered mesoporous carbons obtained by using mesoporous silica templates, ZTCs consist of curved and single-layer graphene frameworks, thereby affording uniform micropore size (ca. 1.2 nm), developed microporosity (∼1.7 cm3 g-1), very high surface area (∼4000 m2 g-1), good compatibility with chemical modification, and remarkable softness/elasticity. Thus, ZTCs have been used in many applications such as hydrogen storage, methane storage, CO2 capture, liquid-phase adsorption, catalysts, electrochemical capacitors, batteries, and fuel cells. Herein, the relevant research studies are summarized, and the properties as well as the performances of ZTCs are compared with those of other materials including metal-organic frameworks, to elucidate the intrinsic advantages of ZTCs and their future development.

Tuning Pseudocapacitance via C-S Bonding in WS2 Nanorods Anchored on N,S Codoped Graphene for High-Power Lithium Batteries

Pseudocapacitance plays an important role in high-power lithium-ion batteries (LIBs). However, it is still lack of effective methods to tailor the pseudocapacitance contribution in electrode materials for LIBs. Herein, pseudocapacitance tuned by the strength of C-S bonding has been rendered in WS₂ nanorods anchored on the N,S codoped three-dimensional graphene hybrid (WS₂@N,S-3DG) for the first time. The pseudocapacitive contributions in the charge storage can be enhanced effectively with the increased strength of C-S bonding. As expected, the enhanced extrinsic pseudocapacitance makes WS₂@N,S-3DG a fascinating electrode material for high-power LIBs, with a high reversible capacity of 509 mA h g^-1 over 500 cycles at a current density as high as 2 A g^-1. These encouraging results of pseudocapacitance tailored by chemical bonding provide new opportunities for designing advanced electrode materials.

Metal-Organic Framework-Derived ZnO/ZnS Heteronanostructures for Efficient Visible-Light-Driven Photocatalytic Hydrogen Production

Developing highly active, recyclable, and inexpensive photocatalysts for hydrogen evolution reaction (HER) under visible light is significant for the direct conversion of solar energy into chemical fuels for various green energy applications. For such applications, it is very challenging but vitally important for a photocatalyst to simultaneously enhance the visible-light absorption and suppress photogenerated electron-hole recombination, while also to maintain high stability and recyclability. Herein, a metal-organic framework (MOF)-templated strategy has been developed to prepare heterostructured nanocatalysts with superior photocatalytic HER activity. Very uniquely, the synthesized photocatalytic materials can be recycled easily after use to restore the initial photocatalytic activity. It is shown that by controlling the calcination temperature and time with MOF-5 as a host and guest thioacetamide as a sulfur source, the chemical compositions of the formed heterojunctions of ZnO/ZnS can be tuned to further enhance the visible-light absorption and photocatalytic activity. The nanoscale heterojunction ZnO/ZnS structural feature serves to reduce the average free path of charge carriers and improve the charge separation efficiency, thus leading to significantly enhanced HER activity under visible-light irradiation (λ > 420 nm) with high stability and recyclability without any cocatalyst.