Synthesis of MgCo 2 O 4 -coated Li 4 Ti 5 O 12 composite anodes using co-precipitation method for lithium-ion batteries

Abstract(#br)In the present work, we report synthesis of MgCo 2 O 4 (MCO)/Li 4 Ti 5 O 12 (LTO) composites for Li-ion battery anodes by a co-precipitation method. The objective of this work is to replace expensive Co with Mg and also to exploit advantages of both MCO and LTO. Three samples of MCO/LTO particles with different MCO proportion have various average particle sizes of 38.1, 56.9, and 58.5 nm, confirmed by scanning electron microscopy. Electrochemical studies show that a MCO/LTO anode offers a discharge capacity of ca. 300 mAh g −1 , which is two times higher than that achieved by pristine LTO. The MCO/LTO anode also retains 75% of its initial capacity, even if the discharge rate is increased to 5 C. Cyclic stability test reveals that the composite anode still maintains nearly..

Fabrication and Properties of (Ti, W, Mo, Nb, Ta)(C, N)-Co-Ni Cermets

Abstract(#br)Fine single-phase (Ti, W, Mo, Nb, Ta)(C, N) solid solution powders were synthesized through the carbothermal reduction method. (Ti, W, Mo, Nb, Ta)(C, N)-Co-Ni cermets were fabricated via vacuum sintering.Micrographs of powders and microstructures of the cermets were observed using transmission electron microscopy and scanning electron microscopy in combination with energy-dispersive spectroscopy. Phase compositions were investigated using x-ray diffraction. The C and N contents were measured using elemental analysis (CHNS/O). The optimized conditions for the synthesis process of single-phase (Ti, W, Mo, Nb, Ta)(C, N) solid solution powders with high nitrogen content were 1500 °C for 2 h under a 2 kPa nitrogen atmosphere. Under such conditions, the particle size of the..

Thermal transport on composite thin films using graphene nanodots and polymeric binder

Abstract(#br)Series of composite thin films consisted of graphene nanodots (GNDs) and water-based binder (i.e., polyvinylpyrrolidone and polyvinyl alcohol) are designed and fabricated for nano-engineering devices with enhanced thermal and electrical conductivities. A thermal pyrolysis of citric acid and urea is adopted to synthesize crystalline GNDs under IR irradiation. The as-prepared GNDs are uniformly coated over three types of substrates including Cu foil, cotton cloth and filter paper. The GND thin films emit tunable fluorescence upon thermal treatment of GNDs at 400 °C in helium atmosphere. The thermally treated GND-based thin film exhibits excellent thermal as well as electrical conductivity compared to bare GNDs and reduced graphene oxide sheets. The enhanced conductivity is due to the reduced oxidation level induced by the thermal treatment on GNDs samples which subsequently decreases the photon scattering. With increasing weight loading, GNDs can serve not only as connective point but also as stuff, offering a well-developed conductive path for the heat dissipation. Accordingly, the design of GND thin film is promising for enhanced thermal management for electronic and photonic applications since it enables engineering the fluorescence emission with substantially increased thermal and electrical conductivities

Fluorescence of functionalized graphene quantum dots prepared from infrared-assisted pyrolysis of citric acid and urea

Abstract(#br)This paper reports an efficient fabrication of N-doped graphene quantum dots (GQDs) showing controllable chemical and fluorescence (FL) properties through infrared carbonization (IRC) of citric acid and urea. The GQDs prefer to form an equilibrium shapes of circle with an average particle size ranged from 5 to 10 nm. The N/C atomic ratio in GQDs can be precisely tailored in a range from 21.6 to 49.6 at.% by simply controlling the weight ratio of citric acid to urea. With increasing the urea content, the GQDs not only contain N-doped graphene but also incorporate with crystalline cyanuric acid, forming a binary crystallinity. The quantum yield of 22.2% is achieved by N-doped GQDs, prepared from the IRC synthesis of chemical precursor at the citric acid/urea at 3:1. Excessive N and cyanuric acid can lead to FL quenching, red shift and wide spectral distribution. The design of GQDs possesses a multiple chromophoric band-gap structure, originated from the presence of cyanuric acid, defect-related emissive traps, and functional group distributions. This work offers an effective and inspiring approach to engineering both chemical compositions and unique crystalline structures of GQDs, and will therefore facilitate their fundamental research and applications to optical, sensing, energy and biological fields

Microwave Deposition of Palladium Catalysts on Graphite Spheres and Reduced Graphene Oxide Sheets for Electrochemical Glucose Sensing

This work outlines a synthetic strategy inducing the microwave-assisted synthesis of palladium (Pd) nanocrystals on a graphite sphere (GS) and reduced graphene oxide (rGO) supports, forming the Pd catalysts for non-enzymatic glucose oxidation reaction (GOR). The pulse microwave approach takes a short period (i.e., 10 min) to fast synthesize Pd nanocrystals onto a carbon support at 150 °C. The selection of carbon support plays a crucial role in affecting Pd particle size and dispersion uniformity. The robust design of Pd-rGO catalyst electrode displays an enhanced electrocatalytic activity and sensitivity toward GOR. The enhanced performance is mainly attributed to the synergetic effect that combines small crystalline size and two-dimensional conductive support, imparting high accessibility to non-enzymatic GOR. The rGO sheets serve as a conductive scaffold, capable of fast conducting electron. The linear plot of current response versus glucose concentration exhibits good correlations within the range of 1–12 mM. The sensitivity of the Pd-rGO catalyst is significantly enhanced by 3.7 times, as compared to the Pd-GS catalyst. Accordingly, the Pd-rGO catalyst electrode can be considered as a potential candidate for non-enzymatic glucose biosensor

Fabrication of La₂O₃ Uniformly Doped Mo Nanopowders by Solution Combustion Synthesis Followed by Reduction under Hydrogen

This work reports the preparation of La2O3 uniformly doped Mo nanopowders with the particle sizes of 40⁻70 nm by solution combustion synthesis and subsequent hydrogen reduction (SCSHR). To reach this aim, the foam-like MoO2 precursors (20⁻40 nm in size) with different amounts of La2O3 were first synthesized by a solution combustion synthesis method. Next, these precursors were used to prepare La2O3 doped Mo nanopowders through hydrogen reduction. Thus, the content of La2O3 used for doping can be accurately controlled via the SCSHR route to obtain the desired loading degree. The successful doping of La2O3 into Mo nanopowders with uniform distribution were proved by X-ray photon spectroscopy and transmission electron microscopy. The preservation of the original morphology and size of the MoO2 precursor by the La2O3 doped Mo nanopowders was attributed to the pseudomorphic transport mechanism occurring at 600 °C. As shown by X-ray diffraction, the formation of Mo2C impurity, which usually occurs in the direct H2 reduction process, can be avoided by using the Ar calcination-H2 reduction process, when residual carbon is removed by the carbothermal reaction during Ar calcination at 500 °C

Influences of Ultrafine Ti(C, N) on the Sintering Process and Mechanical Properties of Micron Ti(C, N)-Based Cermets

For investigating the influence mechanism underlying ultrafine Ti(C, N) within micron Ti(C, N)-based cermets, three cermets including diverse ultrafine Ti(C, N) contents were employed. In addition, for the prepared cermets, their sintering process, microstructure, and mechanical properties were systematically studied. According to our findings, adding ultrafine Ti(C, N) primarily affects the densification and shrinkage behavior in the solid-state sintering stage. Additionally, material-phase and microstructure evolution were investigated under the solid-state stage from 800 to 1300 °C. Adding ultrafine Ti(C, N) enhanced the diffusion and dissolution behavior of the secondary carbide (Mo2C, WC, and (Ta, Nb)C) under a lower sintering temperature of 1200 °C. Further, as sintering temperature increased, adding ultrafine Ti(C, N) enhanced heavy element transformation behaviors in the binder phase and accelerated solid-solution (Ti, Me) (C, N) phase formation. When the addition of ultrafine Ti(C, N) reached 40 wt%, the binder phase had increased its liquefying speed. Moreover, the cermet containing 40 wt% ultrafine Ti(C, N) displayed superb mechanical performances

Measurement of non-equilibrium characteristics of thermoelectric materials

The study of material properties relies on accurate and reliable testing instruments. Sensitively capturing changes in material performance is key to understanding the mechanisms of material properties. The Seebeck coefficient and resistivity testing instrument are essential for research on many functional materials. However, the current instrument is limited in its ability to capture sensitive changes due to testing principles. Here, we prepared three different types of non-equilibrium Zn4Sb3. We found that the existing static testing instrument has problems with testing interruption or inaccuracy when the sample undergoes chemical reactions, rapid atomic diffusion, or phase transitions. The cause of interruption is that the temperature control setting cannot meet the accuracy requirements of the testing instrument. The instrument's large temperature difference setting will cause the determination of the phase transition temperature to become inaccurate. To address the limitations, we have developed a dynamic testing instrument and tested the Seebeck coefficient and resistivity of Zn4Sb3 and Ni in the range of 300 K–800 K. By ensuring the accuracy of each module of the instrument, optimizing the alternating temperature rise time, and improving the data acquisition calculation method, we have achieved accurate capture of sensitive performance changes in the non-equilibrium sample. Comparatively, dynamic testing reduces the measurement time by approximately 300 % compared to static testing. The standard deviation of measured Seebeck coefficient and resistivity is less than ±4 %. This study demonstrates that dynamic testing of the Seebeck coefficient and resistivity is an effective strategy for measuring non-equilibrium functional materials

Preparation of MgCo2O4/graphite composites as cathode materials for magnesium-ion batteries

Abstract Magnesium-ion batteries are fabricated with MgCo2O4/graphite composites as the cathode material. MgCo2O4 nanoparticles are prepared using a co-precipitation method. A three-dimensional mixing process is utilized to mechanically decorate MgCo2O4 nanoparticles on graphite particles. The MgCo2O4 spinel crystals of size ranging from 20 to 70 nm on micrometer-sized graphite chunks are analyzed by using X-ray diffraction and scanning electron microscopy. The electrochemical properties of the as-prepared composites are well characterized by cyclic voltammetry, charge and discharge cycling, and electrochemical impedance spectroscopy (EIS). Surprisingly, the MgCo2O4/graphite composite with a relatively low proportion of MgCo2O4, compared with the other as-prepared composites, achieves the highest specific capacity of 180 mAh g−1 at a C rate of 0.05 C. EIS results suggest that the electrical conductivity of the composite material is an increasing function of the graphite proportion. The superior performance of the MgCo2O4/graphite composite could be ascribed to the decoration of nanosized MgCo2O4 particles as well as to the increased conductivity provided by graphite

Sodium Super Ionic Conductor-Type Hybrid Electrolytes for High Performance Lithium Metal Batteries

Composite solid electrolytes (CSEs), composed of sodium superionic conductor (NASICON)-type Li1+xAlxTi2-x(PO4)3 (LATP), poly (vinylidene fluoride-hexafluoro propylene) (PVDF-HFP), and lithium bis (trifluoromethanesulfonyl)imide (LiTFSI) salt, are designed and fabricated for lithium-metal batteries. The effects of the key design parameters (i.e., LiTFSI/LATP ratio, CSE thickness, and carbon content) on the specific capacity, coulombic efficiency, and cyclic stability were systematically investigated. The optimal CSE configuration, superior specific capacity (~160 mAh g−1), low electrode polarization (~0.12 V), and remarkable cyclic stability (a capacity retention of 86.8%) were achieved during extended cycling (>200 cycles). In addition, with the optimal CSE structure, a high ionic conductivity (~2.83 × 10−4 S cm−1) was demonstrated at an ambient temperature. The CSE configuration demonstrated in this work can be employed for designing highly durable CSEs with enhanced ionic conductivity and significantly reduced interfacial electrolyte/electrode resistance