A facile and scalable process for the in situ formation of Fe 3 O 4 nanocrystals in a pre-formed carbon foam (CF) (Fe 3 O 4 /CF) was developed, which involved impregnation of an aqueous iron nitrate solution onto CF followed by controlled thermal treatment in an inert atmosphere. N 2 adsorption/ desorption and BET measurements showed that the CF was a mesoporous carbon with a high pore volume and specific surface area. Transmission electron microscopy, scanning electron microscopy, X-ray diffraction measurement, thermogravimetric analysis, and X-ray photoelectron spectroscopy (XPS) revealed that 5-50 nm Fe 3 O 4 nanocrystals at a high loading of 78.7 wt% were formed preferentially in the confined pores of CF. When tested for anode material in a Li ion half-cell, the Fe 3 O 4 /CF composite was far superior to unsupported Fe 3 O 4 nanocrystals, exhibiting significantly improved Coulombic efficiencies and cycling stability and achieving >780 mA h g À1 after 50 deep charge-discharge cycles with >95% cycling efficiency.
Among lithium alloy metals, silicon is an attractive candidate to replace commercial graphite anode because silicon possesses about ten times higher theoretical energy density than graphite. However, electrically nonconducting silicon undergoes a large volume changes during lithiation/delithiation reactions, which causes fast loss of storage capacity upon cycling due to electrode pulverization. To alleviate these problems, electrodes comprising Si nanoparticles (20 nm) and graphene platelets, denoted as SiGP-1 (Si = 35.5 wt%) and SiGP-2 (Si = 57.6 wt%), have been prepared with low cost materials and using easily scalable solution-dispersion methods. X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) analyses indicated that Si nanoparticles were highly dispersed and encapsulated between graphene sheets that stacked into platelets in which portions of graphite phases were reconstituted. From the galvanostatic cycling test, SiGP-1 exhibited a reversible lithiation capacity of approximately 802 mAh/g with excellent capacity retention up to 30 cycles at 100 mA/g. Further cycling with a step-increase of current density (100-1,000 mA/g) up to 120 cycles revealed that it has an appreciable power capability as well, showing 520 mAh/g at 1,000 mA/g with capacity loss of 0.2-0.3% per cycle. The improved electrochemical performance is attributed to the robust electrical integrity provided by flexible graphene sheets that encapsulated dispersed Si nanopraticles and stacked into platelets with portions of reconstituted graphite phases in their structure.
− Silicon nanoparticles have attracted a great deal of scientific interests due to its intense photoluminescence in the visible spectral region and its potential applications in biological fluorescence maker, RGB (red, green, blue) display, photonics and photovoltaics etc. Practical applications making use of optical and physicochemical properties of Si nanoparticles requires an efficient synthetic method which allows easy modulation of their size, size distribution as well as surface functionalities etc. In this study, a one-pot solution reduction scheme is attempted to prepare alkyl-terminated Si nanoparticles (<10 nm) with Si precursors, (Octyl)SiCl 3 or mixture of (Octyl)SiCl 3 and SiCl 4 , containing alkyl-groups using Na(naphthalide) as reducing agent. The surface capping of Si nanoparticles with octyl-groups as well as Si nanoparticle formation was achieved in one-pot reaction. The hexane soluble Si nanoparticles with octyl-termination were in the range of 2-10 nm by TEM and some oxide groups (Si-O-Si) was present on the surface by EDS/FTIR analyses. The optical properties of Si nanoparticles measured by UV-vis and PL evidenced that photoluminescent Si nanoparticles with alkyl-termination was successfully synthesized by solution reduction of alkyl-containing Si precursors in one-pot reaction.Key words: Si Nanoparticles, Solution Reduction, Na(naphthalide), Photoluminescence, Tetrachlorosilane, Octyltrichlorosilane
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