Search

Hollow nanostructured materials are suitable for electrochemical reactions because of their unique internal cavity and short transport path. Carbon-based nanomaterials, including simplex carbon materials, heteroatom-doped carbon materials, carbon-transition metal nanoparticle composites, and carbon-transition metal compound composites, are promising electrode materials because of their high conductivity and stable structure. Hollow carbon-based nanomaterials, which possess the features of the aforementioned materials, have become a research hotspot in electrochemical energy storage and electrocatalysis. The excellent characteristics of metal–organic frameworks (MOFs) make them an ideal material for constructing hollow carbon-based nanomaterials. In this article, the process of preparing MOF-derived hollow carbon-based materials and their applications in electrochemical energy storage and electrocatalysis are reviewed. First, the various methods for preparing MOF-derived hollow carbon-based materials are introduced, and the characteristics of each method are analyzed. Second, the applications of MOF-derived hollow carbon-based materials in the oxygen evolution reaction, oxygen reduction reaction, hydrogen evolution reaction, lithium-ion batteries, sodium-ion batteries, lithium–sulfur batteries, and supercapacitors are analyzed and summarized. Finally, research directions for further development of MOF-derived hollow carbon-based materials are proposed. [ABSTRACT FROM AUTHOR]

Polypyrrole (PPy) coated hollow metal–organic framework (MOF) composites are synthesized through a simple melt-diffusion method followed by a water-phase dissolution process. Here, we used zeolitic imidazolate framework-67 (ZIF-67) as a precursor and then coated it with a PPy layer (ZIF-67-S-PPy) to prepare a lithium–sulfur battery (Li–S battery) electrode material. The special hollow structure can effectively inhibit device volumetric expansion caused by generated heat. Furthermore, this work also obtained a series of samples containing sulfur to explore the appropriate sulfur ratio. After electrochemical testing, the composites with a sulfur ratio of 60% achieved the highest specific capacity (1092.5 mA h g−1) among the tested samples, and 353.6 mA h g−1 remained after 200 cycles. The specific capacities of ZIF-67-S, S-PPy and sulfur without a host were 599.8 mA h g−1, 328.7 mA h g−1, and 364.8 mA h g−1, respectively, at 0.1C. The results indicated that the capacity of polymer-coated hollow MOF composite electrodes was obviously improved by the designed synthesis strategy, suggesting its potential for high-performance Li–S batteries. [ABSTRACT FROM AUTHOR]

Lithium–sulfur batteries (Li–S) have attracted considerable attention because of their high theoretical energy density (2600 W h kg−1). However, practical commercial applications of Li–S batteries are limited by the low conductivity of sulfur and discharge products, severe polysulfide shuttling effect, and large sulfur volume expansion during discharge. Various nanostructured carbon materials have been used as sulfur host materials to overcome these problems. Carbon nanotubes (CNTs) are superior to other nanostructured carbon materials because of their unique 1D nanostructure, good conductivity, excellent flexibility, and stable chemical properties. This article reviews the application of CNT-based materials, including simple CNT materials and CNT-based nanocomposites, in Li–S batteries and the particular roles of CNTs in this system. First, general information about the function of CNTs in Li–S batteries and the preparation method of CNT/sulfur composite is provided. Second, various simple CNTs are described, and their inherent characteristics are discussed. Third, CNT-based nanocomposites, including carbon material@CNTs, chemisorption host material@CNTs, and nanocomposites based on in situ formed CNTs, are summarized. The synergistic effect of components and the function of CNTs in the composite are discussed specifically. Fourth, further treatments for CNT/S nanocomposites to better control the diffusion of polysulfides are summarized. Finally, future directions and prospects are discussed. [ABSTRACT FROM AUTHOR]

Designing and preparing kinetically stable metal–organic frameworks through ligand functionalization can effectively improve their supercapacitive performances. Herein, we have successfully synthesized a novel polythreaded Co-based MOF by choosing a flexible N-donor ligand and a rigid multicarboxylate linker, [Co(HTATB)(dib)]·2H2O (1), where dib is the flexible N-donor 1,4-di(1H-imidazol-1-yl)butane linker and HTATB is the deprotonation mode from 4,4′,4′′-s-triazine-2,4,6-triyl-tribenzoic acid. The bulk Co-MOFs crystals and the corresponding nanorod powders have been evaluated as electrode materials for supercapacitors. The maximum gravimetric capacitance of the nanorod electrode is 2405 F g−1 at 0.75 A g−1 in 4 M KOH, which is higher than 1 M and 6 M KOH solution and seven times larger than that of the bulk-crystal electrode. Furthermore, the nanorod electrode also exhibits excellent Coulombic efficiency (92.2%), rate capability (53.5% after 20 times increase) and good cycling performance (93.5% after 3000 continuous cycles). The excellent electrochemical property may be ascribed to the 3D networks constructed from 2D entangled layered structures facilitating electron transport, sufficient interlayer spaces available for the storage and diffusion of OH− ions, and the small-size effect of the nanorods. Further, the dye adsorption performance of crystalline 1 for methyl orange and Congo red has also been investigated. [ABSTRACT FROM AUTHOR]

Rechargeable batteries are promising electrochemical energy storage devices that play a critical role in portable electronics, hybrid/pure electric vehicles, and smart grids. To achieve improved performance, considerable efforts have been focused on the investigation of new electrode materials. In recent years, coordination compound-derived materials, particularly including metal–organic framework (MOF) derivatives and Prussian blue (PB) derivatives, have received enormous attention as electrode materials of rechargeable batteries because of their nanoporous structure and hierarchical nanostructure. The features of coordination compound derivatives not only can facilitate the transport of the electrolyte, but also shorten the diffusion path of metal ions in the solid-state phase. In this study, we present a review on the recent developments in the application of coordination compound-derived materials (mainly including MOF- and PB-derivatives) in various rechargeable batteries, such as lithium-ion batteries, sodium-ion batteries, lithium–sulfur batteries, lithium–oxygen batteries, and zinc–air batteries. The synthesis, morphological characteristics, and electrochemical properties of the coordination compound derivatives are summarized. Furthermore, future outlooks regarding these developments are proposed. [ABSTRACT FROM AUTHOR]

Herein, hybrid Cu/Ni-based hexagonal rods were obtained through a competing reaction of dimethylglyoxime with copper acetate and nickel acetate. Using Cu2+ to intervene the coordination equilibrium between Ni2+ and dimethylglyoxime, the length of the rods was altered; moreover, the coordination environments were investigated by adjusting the concentration of Cu2+ and replacing the solvent. The decomposition products porous NiO and CuO/NiO were directly employed as SC electrodes. The CuO/NiO electrode delivered higher specific capacitance and energy with more excellent energy deliverable ability and better cycling stability than the pristine NiO electrode. After 2000 continuous cycles, the capacitance retention of the as-synthesized CuO/NiO electrode was 87.9%. The maximum specific capacitance and energy delivery efficiency of the CuO/NiO electrode were 344 F g−1 and 93.5%, respectively, at a current density of 0.625 A g−1. The better performance of the hybrid sample was mainly due to higher surface area, lower charge-transfer resistance, and possible synergistic effect. Furthermore, MgO/NiO nanoparticles were synthesized and compared to confirm the existence of a synergistic effect. [ABSTRACT FROM AUTHOR]

In this work, we report an ultrasensitive electrochemical biosensor for microRNA-21 (miRNA-21) detection by using a competitive RNA–RNA hybridization configuration. A biotinylated miRNA of the self-same sequence with the target miRNA is mixed with the samples, and allowed competition with the target miRNA for a thiolated RNA probe immobilized onto a tungsten diselenide (WSe2) nanosheet modified electrode. Thereafter the current response is obtained by forming the hybridized biotinylated miRNA with streptavidin–horseradish peroxidase (HRP) conjugates to catalyze the H2O2 + hydroquinone (HQ) system. Benefiting from the high specific surface area of WSe2 nanosheets, the competitive hybridization configuration and the signal amplification of the H2O2 + HQ detection system, the proposed assay exhibits a wide linear range of 0.0001–100 pM towards target miRNA with a detection limit of 0.06 fM (S/N = 3), and shows excellent discrimination ability for base-mismatched miRNA sequences. Therefore, the designed platform has promising prospects for the detection of miRNA in biomedical research and early clinical diagnosis. [ABSTRACT FROM AUTHOR]

As a promising technology, electrically rechargeable zinc–air batteries have gained significant attention in the past few years. Herein, in this review, we focused on the main challenges of the electrically rechargeable zinc–air batteries in alkaline electrolytes and the up-to-date progress from materials to technologies towards overcoming these technical barriers. We first overviewed the design and working mechanism of the battery and classified the hindrances into dendritic growth at the anode, lack of higher performance bifunctional catalysts at the air electrode, and electrolyte-related problems. Then, detailed discussions have been provided on the latest progress to address these technical issues based on the nano/micro-materials. Flexible zinc–air batteries as a new development have also been discussed in a separate section. Finally, conclusions have been provided followed by future perspective. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks have received increasing attention as promising electrode materials in supercapacitors. In this study, we have successfully synthesized a novel accordion-like Ni-MOF superstructure ([Ni3(OH)2(C8H4O4)2(H2O)4]·2H2O), for the first time, and used it as an electrode material for supercapacitors. The supercapacitors with the novel electrode exhibited excellent electrochemical performance. For example, the accordion-like Ni-MOF electrode showed specific capacitances of 988 and 823 F g−1 at current densities of 1.4 and 7.0 A g−1, respectively, while maintaining outstanding cycling stability (capacitance retention of 96.5% after 5000 cycles at a current density of 1.4 A g−1). More importantly, the accordion-like Ni-MOF and activated carbons were assembled into a high-performance flexible solid-state asymmetric supercapacitor with a specific capacitance of 230 mF cm−2 at a current density of 1.0 mA cm−2. The cycle test showed that the device can offer 92.8% capacity of the initial capacitance at 5.0 mA cm−2 after 5000 cycles with little decay. The maximum energy density of the device can achieve 4.18 mW h cm−3 and the maximum power density can also achieve 231.2 mW cm−3. [ABSTRACT FROM AUTHOR]

Mesoporous NiO nanosheets with a single-crystalline structure were investigated as an oxygen electrode catalyst in a non-aqueous Li–O2 battery. The recharge voltage plateau achieved for the NiO-based Li–O2 battery was ca. 3.95 V, ca. 200 mV negatively shifted compared with that for β-Ni(OH)2 and acetylene black. The reaction mechanism during the charge process for the NiO-based Li–O2 battery was intensively researched. The results of X-ray photoelectron spectroscopy characterization indicated that Li2O2 and Li2CO3 were formed during the discharge process, which can be decomposed after recharge. These demonstrated that the NiO nanosheet exhibited a good activity for the decomposition of Li2O2 and Li2CO3. Furthermore, the results of the gas chromatography-mass spectrometry test reflected two steps of the recharge process, i.e., the oxidation of Li2O2 when the potential was below 4.0 V and the decomposition of Li2O2 and Li2CO3 when the potential was above 4.0 V. Moreover, no obvious performance decay was observed in the NiO-based battery even after 40 cycles when the capacity was limited to 500 mA h g−1, indicating an impressive cycling performance. [ABSTRACT FROM AUTHOR]

A three-dimensional (3D) carbonaceous aerogel derived from sustainable bacterial cellulose (BC) is introduced as a flexible framework for sulfur in lithium–sulfur batteries. The 3D carbonized BC (CBC) with highly interconnected nanofibrous structure exhibits good electrical conductivity and mechanical stability. The intrinsic macroporous structure of CBC contributes to a high sulfur loading of 81 wt%. Microstructure and morphology characterization results demonstrate that the sulfur species wrapped around CBC nanofibers are well dispersed. Even at such a high loading, the S/CBC composite still contains sufficient free space to accommodate the volume expansion of sulfur during lithiation. Furthermore, with an ultralight CBC interlayer inserted between the sulfur cathode and separator, significant improvement is achieved in active material utilization, cycling stability, and coulombic efficiency. The CBC interlayer can provide an extra conductive framework and adsorb migrating polysulfides to a certain degree. The CBC interlayer can also act as an additional collector for sulfur and thus could prevent the over-aggregation of insulated sulfur on the cathode surface. The good electrochemical performance reported in this work can be ascribed to the flexible 3D-interconnected nanostructure of the carbon framework and the rational design of battery configuration. [ABSTRACT FROM AUTHOR]

Porous activated carbon with a ultrahigh specific surface area (3164 m2 g-1) and large pore volume (1.88 cm3 g-1) was prepared from waste litchi shells with channel-like macropores via a KOH activation method. The macroporous structure of litchi shells is believed to be conducive to distribute the activation agent, which enables sufficient activation. The as-prepared activated carbon was developed as a conducting framework for lithium-sulfur battery cathode materials. The resulting activated carbon/sulfur composite cathode possesses a high specific capacity, good rate capability, and long-term cycling performance. At 200 mA g-1 current density, the initial discharge capacity of the activated carbon/sulfur composite cathode with 60 wt% sulfur content is 1105 mA h g-1 At a current density of 800 mA g-1, the activated carbon/sulfur composite cathode shows 51% capacity retention over 800 cycles with a fade rate of 0.06% per cycle. The coulombic efficiency of the cell remains at approximately 95%. By adding LiNO3 in the electrolyte, the activated carbon/sulfur composite electrode tested at 800 mA g-1 shows a high coulombic efficiency (>99%). The activated carbon/sulfur composites exhibited similar capacity value and cycling trends with an increase in sulfur content from 60% to 68%. The good electrochemical performance can be attributed to the excellent structural parameters of the activated carbon. The ultrahigh specific surface area and large pore volume not only enhances the sulfur content but also ensures dispersion of elemental sulfur in the conducting framework, thereby improving sulfur utilization. The small nanopores of the activated carbon can effectively inhibit the diffusion of polysulfides during the charge/discharge process. [ABSTRACT FROM AUTHOR]

Network structured carbonized bacterial cellulose-supported Ru nanoparticles (CBC/Ru), which provide sufficient space for Li2O2 deposition without a significant volume effect and improve the transport of oxygen and electrons, were used as the binder-free oxygen electrode in a Li-O2 battery. The CBC/Ru exhibited high activities and good stability during discharge-recharge processes.

Li3VO4 nanoparticles embedded in graphene nanosheets (Li3VO4@GNS) were obtained using a sol-gel method. The composite presents excellent high-rate performance with a stable capacity of 133 mA h g(-1) at 50 C and long-life performance with a capacity retention rate of 63.1% after 5000 cycles at 5 C.