Controlled-Size Hollow Magnesium Sulfide Nanocrystals Anchored on Graphene for Advanced Lithium Storage

Constructing CoNC coordination in Co9S8 embedded N,S-codoped carbon nanotube as an advanced electrode for supercapacitor and Na-ion battery

Yolk-shell-structured transition metal sulfides (TMSs)/carbon nanocomposites are highly desirable in advanced energy storage system, such as sodium-ion batteries (SIBs) and supercapacitors (SCs). Nevertheless, practical applications are still prevented by the loose attachment of TMSs with carbon caused by conversion stress, the aggregation of TMSs nanoparticles and the sluggish ion transport caused by high crystallinity of carbon. Here, the disperse hollow Co9S8 nanoparticles encapsulated into N,S-codoped carbon nanotubes (CNTs) with poor crystallinity through CoNC bond was synthesized (CS-NSCNT) to overcome the above obstacles. The designed CS-NSCNT can provide the short diffusion path and prevent the huge volume expansion of conversion reaction. Moreover, the established CoNC bond endows the strong interaction and regulates the electronic structure thus promote the stability and rate performance effectively. The CS-NSCNT SCs's electrode delivers a high specific capacitance of 1150 F g-1 at 1 A g-1, with a high cycling life stability and rate performance. For SIBs, the CS-NSCNT cathode demonstrates an initial reversible capacity of 475 mAh g-1 at 0.1 A g-1 and an excellent rate performance with a capacity retention of 53 % at 10 A g-1. This work may satisfy the long-stability, high-capacitance/capacity, high-power/energy density application requirements of future applications.

Formation of Core-Shell AuCu@Ag Nanocrystals through the Nanoscale Kirkendall Effect

Polymetallic nanocrystals (NCs) consist of multiple metal elements. A powerful platform to achieve the flexible construction of polymetallic NCs is highly desired but challenging. Herein, we devise a model system that realizes metal atom diffusion between different NCs, resulting in the formation of polymetallic NCs. The differential bond strength between different metal atoms is proposed to initiate such metal atom diffusion, and the specific high surface-to-volume ratio of the NCs can expedite the diffusion process. Taking the Au-Cu-Ag trimetallic system as an example, core-shell AuCu@Ag NCs were successfully formed by combining AgCu NCs with Au NCs. The evolution process was explored, and the gradual fusion of simple NCs into AuCu@Ag NCs was unambiguously observed, which could be attributed to the larger bond strength of Au-Cu than that of Ag-Cu. This work offers an opportunity/platform in theory and experiment to expand the synthesis framework as well as the polymetallic NC list.

An Ultra-Stable Electrode-Solid Electrolyte Composite for High-Performance All-Solid-State Li-Ion Batteries

The low ionic and electronic conductivity between current solid electrolytes and high-capacity anodes limits the long-term cycling performance of all-solid-state lithium-ion batteries (ASSLIBs). Herein, this work reports the fabrication of an ultra-stable electrode-solid electrolyte composite for high-performance ASSLIBs enabled by the homogeneous coverage of ultrathin Mg(BH₄ )₂ layers on the surface of each MgH₂ nanoparticle that are uniformly distributed on graphene. The initial discharge process of Mg(BH₄ )₂ layers results in uniform coverage of MgH₂ nanoparticle with both LiBH₄ as the solid electrolyte and Li₂ B₆ with even higher Li ion conductivity than LiBH₄ . Consequently, the Li ion conductivity of graphene-supported MgH₂ nanoparticles covered with ultrathin Mg(BH₄ )₂ layers is two orders of magnitude higher than that without Mg(BH₄ )₂ layers. Moreover, the thus-formed inactive Li₂ B₆ with strong adsorption capability toward LiBH₄ , acts as a stabilizing framework, which, coupled with the structural support role of graphene, alleviates the volume change of MgH₂ nanoparticles and facilitates the intimate contact between LiBH₄ and individual MgH₂ nanoparticles, leading to the formation of uniform stable interfaces with high ionic and electronic conductivity on each MgH₂ nanoparticles. Hence, an ultrahigh specific capacity of 800 mAh g^-1 is achieved for MgH₂ at 2 A g^-1 after 350 cycles.

Size-Controllable Nickel Sulfide Nanoparticles Embedded in Carbon Nanofibers as High-Rate Conversion Cathodes for Hybrid Mg-Based Battery

The integration of highly-safe Mg anode and fast Li+ kinetics endows hybrid Mg2+ /Li+ batteries (MLIBs) a promising future, but the practical application is circumvented by the lack of appropriate cathodes that enable the realization of an enough participation of Mg2+ in the reactions, resulting in a high dependence on Li+ . Herein, the authors develop a series of size-controllable nickel sulfide nanoparticles embedded in carbon nanofibers (NiS@C) with synergistic effect of particle diameter and carbon content as the cathode material for MLIBs. The optimized particle size is designed to maximize the utilization of the active material and remit internal stress, and appropriate carbon encapsulation efficiently inhibiting the pulverization of particles and accelerates the ability of conducting ions and electrons. In consequence, the representative NiS@C delivers superior electrochemical performance with a highest discharge capacity of 435 mAh g-1 at 50 mA g-1 . Such conversion cathode also exhibits excellent rate performance and remarkable cycle life. Significantly, the conversion mechanism of NiS in MLIBs is unambiguously demonstrated for the first time, affirming the corporate involvement of both Mg2+ and Li+ at the cathodic side. This work underlines a guide for developing conversion-type materials with high rate capability and cyclic performance for energy storage applications.

Hollow MoS2/Co nanopillars with boosted Li-ion diffusion rate and long-term cycling stability

Hollow MoS₂/Co-0.1 nanopillars were successfully synthesized by sulfurizing CoMoO₄ and subsequent acid etching, which were used as the anode material for lithium ion batteries. The introduction of suitable metal Co into MoS₂ nanopillars effectively accelerates electron/ion transport kinetics, leading to high specific capacity and superior rate capability and cycling stability.

Carbon nanotubes coupled with layered graphite to support SnTe nanodots as high-rate and ultra-stable lithium-ion battery anodes

SnTe exhibits a layered crystal structure, which enables fast Li-ion diffusion and easy storage, and is considered to be a promising candidate for an advanced anode material. However, its applications are hindered by the large volume variation caused by intercalation/deintercalation during the electrochemical reaction processes. Herein, topological insulator SnTe and carbon nanotubes (CNTs) supported on a graphite (G) carbon framework (SnTe-CNT-G) were prepared as a new, active and robust anode material for high-rate lithium-ion batteries by a scalable ball-milling method. Remarkably, the SnTe-CNT-G composite used as a lithium-ion battery anode offered an excellent reversible capacity of 840 mA h g-1 at 200 mA g-1 after 100 cycles and high initial coulombic efficiencies of 76.0%, and achieved a long-term cycling stability of 669 mA h g-1 at 2 A g-1 after 1400 cycles. The superior electrochemical performance of SnTe-CNT-G is attributed to the stable design of its electrode structure and interesting topological transition of SnTe, combined with multistep conversion and alloying processes. Furthermore, in situ X-ray diffraction and ex situ X-ray photoelectron spectroscopy were employed to study the reaction mechanism. The results presented here provide new insights to design and reveal the reaction mechanisms of transition metal telluride materials in various energy-storage materials.

Levofloxacin Detection Using l-Cysteine Capped MgS Quantum Dots via the Photoinduced Electron Transfer Process

Antibiotics resistance is becoming one of the biggest problems of the 21st century. The prior detection of antibiotics resistance can help human beings in better treatment of diseases. Here, we have used l-Cysteine capped magnesium sulfide quantum dots (L-Cyst-MgS QDs) to detect Levofloxacin antibiotic. L-Cyst-MgS QDs were synthesized using the hydrothermal method. Transmission electron microscopy study showed monodispersed L-Cyst-MgS QDs of 2–4 nm in size. Energy dispersive x-ray photoemission spectroscopy study confirmed the elemental composition of the L-Cyst-MgS QDs without any impurity. UV-vis absorption study showed a peak centered around 340 nm. The photoluminescence study exhibited the maximum peak at 410 nm for 340 nm of excitation wavelength. L-Cyst-MgS QDs were studied with thirteen antibiotics, namely Thiamphenicol, Gentamicin, Erythromycin, Ofloxacin, Ampicillin, Ciprofloxacin, Tetracycline, Chloramphenicol, Florfenicol, Amoxicillin, Moxifloxacin, Norfloxacin, and Levofloxacin. Among these, Levofloxacin showed the most significant change in the peaks’ intensity and was further used for the interaction study. In the interaction study, the peak corresponding to MgS showed a continuous decrease, while the peak corresponding to Levofloxacin showed an increase with the increased concentrations (0–100 μg/ml) of Levofloxacin. Linear behavior was obtained in the range of 1–90 μg/ml. FT-IR study confirmed the interaction of the Levofloxacin with L-Cyst-MgS QDs. The Time-resolved fluorescence spectroscopy showed identical lifetime for both the samples and no spectral overlap confirm the FRET free system. The underlying mechanism is explained based on the electron transfer from the conduction band of the L-Cyst-MgS QDs to the HOMO of Levofloxacin. The limit of detection was found to be 0.21 μg/ml.