A Gradient Composite Structure Enables a Stable Microsized Silicon Suboxide-Based Anode for a High-Performance Lithium-Ion Battery.

The practical application of microsized anodes is hindered by severe volume changes and fast capacity fading. Herein, we propose a gradient composite strategy and fabricate a silicon suboxide-based composite anode (d-SiO@SiOx/C@C) consisting of a disproportionated microsized SiO inner core, a homogeneous composite SiOx/C interlayer (x ≈ 1.5), and a highly graphitized carbon outer layer. The robust SiOx/C interlayer can realize a gradient abatement of stress and simultaneously connect the inner SiO core and carbon outer layer through covalent bonds. As a result, d-SiO@SiOx/C@C delivers a specific capacity of 1023 mAh/g after 300 cycles at 1 A/g with a retention of >90% and an average Coulombic efficiency of >99.7%. A full cell assembled with a LiNi0.8Co0.15Al0.05O2 cathode displays a remarkable specific energy density of 569 Wh/kg based on total active materials as well as excellent cycling stability. Our strategy provides a promising alternative for designing structurally and electrochemically stable microsized anodes with high capacity.

Tuning Mass Transport in Electrocatalysis Down to Sub-5†nm through Nanoscale Grade Separation.

Nano and single-atom catalysis open new possibilities of producing green hydrogen (H2 ) by water electrolysis. However, for the hydrogen evolution reaction (HER) which occurs at a characteristic reaction rate proportional to the potential, the fast generation of H2 nanobubbles at atomic-scale interfaces often leads to the blockage of active sites. Herein, a nanoscale grade-separation strategy is proposed to tackle mass-transport problem by utilizing ordered three-dimensional (3d) interconnected sub-5 nm pores. The results reveal that 3d criss-crossing mesopores with grade separation allow efficient diffusion of H2 bubbles along the interconnected channels. After the support of ultrafine ruthenium (Ru), the 3d mesopores are on a superior level to two-dimensional system at maximizing the catalyst performance and the obtained Ru catalyst outperforms most of the other HER catalysts. This work provides a potential route to fine-tuning few-nanometer mass transport during water electrolysis.

Preparation of Hollow Core-Shell Fe3O4/Nitrogen-Doped Carbon Nanocomposites for Lithium-Ion Batteries.

Iron oxides are potential electrode materials for lithium-ion batteries because of their high theoretical capacities, low cost, rich resources, and their non-polluting properties. However, iron oxides demonstrate large volume expansion during the lithium intercalation process, resulting in the electrode material being crushed, which always results in poor cycle performance. In this paper, to solve the above problem, iron oxide/carbon nanocomposites with a hollow core-shell structure were designed. Firstly, an Fe2O3@polydopamine nanocomposite was prepared using an Fe2O3 nanocube and dopamine hydrochloride as precursors. Secondly, an Fe3O4@N-doped C composite was obtained by means of further carbonization treatment. Finally, Fe3O4@void@N-Doped C-x composites with core-shell structures with different void sizes were obtained by means of Fe3O4 etching. The effect of the etching time on the void size was studied. The electrochemical properties of the composites when used as lithium-ion battery materials were studied in more detail. The results showed that the sample that was obtained via etching for 5 h using 2 mol L-1 HCl solution at 30 °C demonstrated better electrochemical performance. The discharge capacity of the Fe3O4@void@N-Doped C-5 was able to reach up to 1222 mA g h-1 under 200 mA g-1 after 100 cycles.

Amorphous Intermediate Derivative from ZIF-67 and Its Outstanding Electrocatalytic Activity.

Increasing active sites is an effective method to enhance the catalytic activity of catalysts. Amorphous materials have attracted considerable attention in catalysis because of their abundant catalytic active sites. Herein, a series of derivatives is prepared via the low-temperature heat treatment of ZIF-67 hollow sphere at different temperatures. An intermediate product with an amorphous structure is formed during transformation from ZIF-67 to Co3 O4 nanocrystallines when ZIF-67 hollow sphere is heat treated at 260 °C for 3 h. The chemical composition of the amorphous derivative is similar to that of ZIF-67, and the carbon and nitrogen contents of the amorphous derivative are obviously higher than those of crystalline samples obtained at 270 °C or higher. As electrocatalysts for the oxygen evolution reaction (OER) and nonenzymatic glucose sensing, the amorphous derivative exhibits significantly better catalytic activity than crystalline Co3 O4 samples. The amorphous sample as an OER catalyst has a low overpotential of 352 mV at 10 mA cm-2 . The amorphous sample as an enzyme-free glucose sensing catalyst can provide a low detection limit of 3.9 × 10-6 m and a high sensitivity of 1074.22 µA mM-1 cm-2 .

Oxygen-Deficient Ferric Oxide as an Electrochemical Cathode Catalyst for High-Energy Lithium-Sulfur Batteries.

Lithium-sulfur batteries, as one of promising next-generation energy storage devices, hold great potential to meet the demands of electric vehicles and grids due to their high specific energy. However, the sluggish kinetics and the inevitable "shuttle effect" severely limit the practical application of this technology. Recently, design of composite cathode with effective catalysts has been reported as an essential way to overcome these issues. In this work, oxygen-deficient ferric oxide (Fe2 O3- x ), prepared by lithiothermic reduction, is used as a low-cost and effective cathodic catalyst. By introducing a small amount of Fe2 O3- x into the cathode, the battery can deliver a high capacity of 512 mAh g-1 over 500 cycles at 4 C, with a capacity fade rate of 0.049% per cycle. In addition, a self-supporting porous S@KB/Fe2 O3- x cathode with a high sulfur loading of 12.73 mg cm-2 is prepared by freeze-drying, which can achieve a high areal capacity of 12.24 mAh cm-2 at 0.05 C. Both the calculative and experimental results demonstrate that the Fe2 O3- x has a strong adsorption toward soluble polysulfides and can accelerate their subsequent conversion to insoluble products. As a result, this work provides a low-cost and effective catalyst candidate for the practical application of lithium-sulfur batteries.

Iron oxide-based nanomaterials for supercapacitors.

As highly efficient and clean electrochemical energy storage devices, supercapacitors (SCs) have drawn widespread attention as promising alternatives to batteries in recent years. Among various electrode materials, iron oxide materials have been widely studied as negative SC electrode materials due to their broad working window in negative potential, ideal theoretical specific capacitance, good redox activity, abundant availability, and eco-friendliness. However, iron oxides still suffer from the problems of low stability and poor conductivity. In this review, recent progress in iron oxide-based nanomaterials, including Fe2O3, Fe3O4, FexOy, and FeOOH, as electrode materials of SCs, is discussed. The nanostructure design and various synergistic effects of nanocomposites for improving the electrochemical performance of iron oxides are emphasized. Research on iron oxide-based symmetric/asymmetric SCs is also discussed. Future outlooks regarding iron oxides for SCs are likewise proposed.

Stable Voltage Cutoff Cycle Cathode with Tunable and Ordered Porous Structure for Li-O2 Batteries.

Ordered porous RuO2 materials with various pore structure parameters are prepared via a hard-template method and are used as the carbon-free cathodes for Li-O2 batteries under the voltage cutoff cycle mode. The influences of pore structure parameters of porous RuO2 on electrochemical performance are systematically studied. Results indicate that specific surface area and pore size determine the specific capacity and round-trip efficiency of Li-O2 batteries. Too small pores cause pore blockage and hinder the diffusion pathways of Li+ and O2 , thereby causing small specific capacity and high overpotentials. Too large pores weaken the mechanical property of porous RuO2 , thereby causing the rapid decrease in capacity during electrochemical reaction. The Li-O2 battery based on the RuO2 cathode with an average pore size of 16 nm (RuO2 -16) exhibits a high round-trip efficiency of ≈75.6% and an excellent cycling stability of up to 70 cycles at 100 mA g-1 with a voltage window of 2.5-4.0 V. The superior performance of RuO2 -16 can be attributed to its optimal pore structure parameters. Furthermore, the in situ differential electrochemical mass spectrometry test demonstrates that RuO2 can effectively reduce parasitic reactions compared with carbon materials.

Subcellular-Scale Drug Transport via Ultrasound-Degradable Mesoporous Nanosilicon to Bypass Cancer Drug Resistance.

Delivering and releasing anticancer agents directly to their subcellular targets of action in a controlled manner are almost the ultimate goal of pharmacology, but it is challenging. In recent decades, plenty of efforts have been made to send drugs to tumor tissue or even specifically to cancer cells; however, at the subcellular scale, cancer cells have multiple cunning ways to hinder drugs from reaching their final action targets. Here, we demonstrate a strategy to bypass the last defense of cancer drug resistance by contolling the drug transportation and release at subcellular scale. We developed a platform based on ultrasound-degradable mesoporous nanosilicon, which allows drug delivery towards, ultrasound controlled drug release into the cell nucleus. This strategy altered the drug distribution within cells and remarkably enhanced the drug accumulation ratio at the action target, i.e. nucleus. In vitro and in vivo studies proved that this strategy reduced the drug dosage by an order of magnitude, prolonged drug retention and amplified therapeutic efficacy in tumor-bearing mice. These results offer new insights into bypassing cancer drug resistance through transport and release drugs directly to their action targets in a controlled manner.

An electrochemical microRNA sensing platform based on tungsten diselenide nanosheets and competitive RNA-RNA hybridization.

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.

A multi-layered Fe2O3/graphene composite with mesopores as a catalyst for rechargeable aprotic lithium-oxygen batteries.

Aprotic Li-O2 batteries have attracted a huge amount of interest in the past decade owing to their extremely high energy density. However, identifying a desirable cathodic catalyst for this promising battery system is one of the biggest challenges at present. In this work, a multi-layered Fe2O3/graphene nanosheets (Fe2O3/GNS) composite with sandwich structure was synthesized using an easy thermal casting method, and served as a cathodic catalyst for aprotic Li-O2 batteries. The aprotic Li-O2 cell with the Fe2O3/GNS catalyst demonstrated a better reversibility, lower overpotential for oxygen evolution, and a higher Coulombic efficiency (close to 100%) than those of pure GNS. An excellent rate performance and good cycle stability were also confirmed. The results, characterized by ex and in situ methods, revealed that the dominant discharge product Li2O2 was decomposed below 4.35 V. This superior electrochemical performance is mainly attributed to the unique sandwich structure of the Fe2O3/GNS catalyst with mesopores, which can provide substantially more catalytic sites and prevent direct contact between carbon and Li2O2.

Indirect transformation of coordination-polymer particles into magnetic carbon-coated MN3O4 (MN3O4@C) nanowires for supercapacitor electrodes with good cycling performance.

Carbon-coated Mn3O4 nanowires (Mn3O4@C NWs) have been synthesized by the reduction of well-shaped carbon-coated bixbyite networks and characterized by TEM, X-ray diffraction, X-ray photoelectron spectroscopy, and electrochemical experiments. To assess the properties of 1D carbon-coated nanowires for their use in supercapacitors, cyclic voltammetry and galvanostatic charging-discharging measurements were performed. Mn3O4 @C NWs could be charged and discharged faster and had higher capacitance than bare Mn3O4 nanostructures and other commercial materials. The capacitance of the Mn3O4@C NWs was 92% retained after 3000 cycles at a charging rate of 5 Ag(-1). This improvement can be attributed to the carbon shells, which promote fast Faradaic charging and discharging of the interior Mn3O4 core and also act as barriers to protect the inner core. These Mn3O4@C NWs could be a promising candidate material for high-capacity, low-cost, and environmentally friendly electrodes for supercapacitors. In addition, the magnetic properties of the as-synthesized samples are also reported to investigate the influence of the carbon coating.

The transaction behavior of cryptocurrency and electricity consumption.

Rapidly increasing cryptocurrency prices have encouraged cryptocurrency miners to participate in cryptocurrency production, increasing network hashrates and electricity consumption. Growth in network hashrates has further crowded out small cryptocurrency investors owing to the heightened costs of mining hardware and electricity. These changes prompt cryptocurrency miners to become new investors, leading to cryptocurrency price increases. The potential bidirectional relationship between cryptocurrency price and electricity consumption remains unidentified. Hence, this research thus utilizes July 31 2015-July 12 2019 data from 13 cryptocurrencies to investigate the short- and long-run causal effects between cryptocurrency transaction and electricity consumption. Particularly, we consider structural breaks induced by external shocks through stationary analysis and comovement relationships. Over the examined time period, we found that the series of cryptocurrency transaction and electricity consumption gradually returns to mean convergence after undergoing daily shocks, with prices trending together with hashrates. Transaction fluctuations exert both a temporary effect and permanent influence on electricity consumption. Therefore, owing to the computational power deployed to wherever high profit is found, transactions are vital determinants of electricity consumption.

Preparation of hierarchical hollow CoFe Prussian blue analogues and its heat-treatment derivatives for the electrocatalyst of oxygen evolution reaction.

The microstructure of materials importantly affects their performance. As electrocatalyst materials, the performance of hollow-structure materials is usually better than that of solid materials because of the larger specific surface area, lower density, and more exposed active sites of hollow structure. Bimetallic catalysts usually exhibit better catalytic activity than monometallic catalysts because of the synergistic effects between different metal elements. Prussian blue and its analogues (PB/PBAs) are ideal precursors for preparing hollow-structure bimetallic catalysts due to their structure and composition characteristics. In this study, ZIF-67 hollow sphere (HS) was used as the template to prepare hierarchical hollow CoFePBA (H-SCP) through anion-exchange method. The oxygen evolution reaction (OER) catalytic performance of H-SCP was further improved by low-temperature heat treatment in N2 atmosphere. The H-SCP-350 sample, which was obtained at a heat-treatment temperature of 350 ℃, was a bimetallic nanocomposite. Part of H-SCP was converted into metallic cobalt and cobalt-iron alloy during heat treatment. The synergistic effect among the different components effectively improved the electrocatalytic activity of the material. Therefore, H-SCP-350 showed the best OER catalytic performance among all samples. The overpotential was only 291mV at a current density of 10 mA cm-2 when tested in 1 M KOH electrolyte.

Microwave-assisted synthesis of Sb2Se3 submicron tetragonal tubular and spherical crystals.

Sb(2)Se(3) submicron tetragonal tubes have been prepared by a microwave-assisted polyol method using antimony trichloride and sodium selenite as the Sb and Se precursors. Scanning electron microscopy (SEM) results showed a novel transformation of Sb(2)Se(3) microstructures from submicron tubes to submicron spheres during the microwave heating process. The potential growth mechanism has been investigated by analyzing the samples at different growth stages. Transmission electron microscopy (TEM) analyses confirmed that samples prepared under 10 min microwave heating possessed tetragonal tubular structure with lengths in the range of 10-30 microm, thicknesses in the range of 0.5-1 microm and wall thicknesses in the range of 100-200 nm. High-resolution TEM (HRTEM) and selected area electron diffraction (SAED) results revealed that Sb(2)Se(3) submicron tubes were single-crystalline along the [001] direction. The optical properties of Sb(2)Se(3) submicron tubes and submicron spheres were characterized by UV-vis diffuse reflectance spectroscopy, and the band gap (E(g)) derived to be 1.161 and 1.173 eV, respectively.

Applications of MxSey (M = Fe, Co, Ni) and Their Composites in Electrochemical Energy Storage and Conversion.

Transition-metal selenides (MxSey, M = Fe, Co, Ni) and their composites exhibit good storage capacities for sodium and lithium ions and occupy a unique position in research on sodium-ion and lithium-ion batteries. MxSey and their composites are used as active materials to improve catalytic activity. However, low electrical conductivity, poor cycle stability, and low rate performance severely limit their applications. This review provides a comprehensive introduction to and understanding of the current research progress of MxSey and their composites. Moreover, this review proposes a broader research platform for these materials, including various bioelectrocatalytic performance tests, lithium-sulfur batteries, and fuel cells. The synthesis method and related mechanisms of MxSey and their composites are reviewed, and the effects of material morphologies on their electrochemical performance are discussed. The advantages and disadvantages of MxSey and their composites as well as possible strategies for improving the storage and conversion of electrochemical energy are also summarized.

Boosting the performance of broccoli-like Ni-triazole frameworks through a CNTs conductive-matrix.

Different approaches for the fabrication of CNT-supported Ni-triazole composites, such as room-temperature stirring and hydrothermal treatment for a distinct reaction time has been presented. As a result, various morphologies, MMOF wrapped CNTs, CNTs entangled with an MMOF and CNTs attached on an MMOF, were synthesized and investigated through electrochemical measurements. The as-synthesized CNTs/MMOF-based hybrids, especially for the CNTs/MMOF-8H structure, show a good rate capability after 20 times increase, a superior coulombic efficiency and an excellent long-term cycling stability (more than 98% retained after 2000 cycles). This enhancement can be ascribed to the introduction of the CNT conductive additives, which promote the fast charge-transfer ability of ions and electrons. Even for the other CNTs/MMOF-based composites, the overall electrochemical performances are still superior to those of pristine MMOF electrodes.

Hierarchically Nanostructured Transition Metal Oxides for Lithium-Ion Batteries.

Lithium-ion batteries (LIBs) have been widely used in the field of portable electric devices because of their high energy density and long cycling life. To further improve the performance of LIBs, it is of great importance to develop new electrode materials. Various transition metal oxides (TMOs) have been extensively investigated as electrode materials for LIBs. According to the reaction mechanism, there are mainly two kinds of TMOs, one is based on conversion reaction and the other is based on intercalation/deintercalation reaction. Recently, hierarchically nanostructured TMOs have become a hot research area in the field of LIBs. Hierarchical architecture can provide numerous accessible electroactive sites for redox reactions, shorten the diffusion distance of Li-ion during the reaction, and accommodate volume expansion during cycling. With rapid research progress in this field, a timely account of this advanced technology is highly necessary. Here, the research progress on the synthesis methods, morphological characteristics, and electrochemical performances of hierarchically nanostructured TMOs for LIBs is summarized and discussed. Some relevant prospects are also proposed.

Facile fabrication of magnetic nanocomposites of ordered mesoporous carbon decorated with nNickel nanoparticles.

A magnetic nanocomposite of ordered mesoporous carbon (CMK-3) decorated with nickel nanoparticles was synthesized successfully by a simple chemistry method. Nickel nanoparticles were prepared and uniformly supported on ordered mesoporous carbon CMK-3 by reduction route with CMK-3 as a reducing agent at 673 K. The Ni/CMK-3 composite materials were characterized by powder X-ray diffraction, nitrogen sorption, and transmission electron microscopy. As-prepared nickel nanoparticles supported on CMK-3 were crystalline with a face-center-cubic phase and a size distribution ranging from 10 to 60 nm. The BET special surface area and pore volume of Ni/CMK-3 were as high as 797 m2 g(-1) and 0.72 cm3 g(-1), respectively. The formation mechanism of the nickel nanoparticles outside the surface of CMK-3 was preliminarily discussed. The hysteresis loops of the CMK-3 decorated with nickel nanoparticles were measured by vibrating sample magnetometer (VSM), and the results showed that the composite was ferromagnetism with the saturated magnetization of 15 emu/g, and the coercivity value of 214 Oe. Furthermore, the application of Ni/CMK-3 as magnetically separable adsorbent for vitamin B2 was primarily examined in this study.

Highly cross-linked Cu/a-Si core-shell nanowires for ultra-long cycle life and high rate lithium batteries.

Seeking long cycle lifetime and high rate performance are still challenging aspects to promote the application of silicon-loaded lithium ion batteries (LIBs), where optimal structural and compositional design are critical to maximize a synergistic effect in composite core-shell nanowire anode structures. We here propose and demonstrate a high quality conformal coating of an amorphous Si (a-Si) thin film over a matrix of highly cross-linked CuO nanowires (NWs). The conformal a-Si coating can serve as both a high capacity storage medium and a high quality binder that joins crossing CuO NWs into a continuous network. And the CuO NWs can be reduced into highly conductive Cu cores in low temperature H2 annealing. In this way, we have demonstrated an excellent cycling stability that lasts more than 700 (or 1000) charge/discharge cycles at a current density of 3.6 A g(-1) (or 1 A g(-1)), with a high capacity retention rate of 80%. Remarkably, these Cu/a-Si core-shell anode structures can survive an extremely high charging current density of 64 A g(-1) for 25 runs, and then recover 75% initial capacity when returning to 1 A g(-1). We also present the first and straightforward experimental proof that these robust highly-cross-linked core-shell networks can preserve the structural integrity even after 1000 runs of cycling. All these results indicate a new and convenient strategy towards a high performance Si-loaded battery application.