Francisco C. Robles Hernandez

Interlayer-Expanded Molybdenum Disulfide Nanocomposites for Electrochemical Magnesium Storage

Mg rechargeable batteries (MgRBs) represent a safe and high-energy battery technology but suffer from the lack of suitable cathode materials due to the slow solid-state diffusion of the highly polarizing divalent Mg ion. Previous methods improve performance at the cost of incompatibility with anode/electrolyte and drastic decrease in volumetric energy density. Herein we report interlayer expansion as a general and effective atomic-level lattice engineering approach to transform inactive intercalation hosts into efficient Mg storage materials without introducing adverse side effects. As a proof-of-concept we have combined theory, synthesis, electrochemical measurement, and kinetic analysis to improve Mg diffusion behavior in MoS2, which is a poor Mg transporting material in its pristine form. First-principles simulations suggest that expanded interlayer spacing allows for fast Mg diffusion because of weakened Mg-host interactions. Experimentally, the expansion was realized by inserting a controlled amount of poly(ethylene oxide) into the lattice of MoS2 to increase the interlayer distance from 0.62 nm to up to 1.45 nm. The expansion boosts Mg diffusivity by 2 orders of magnitude, effectively enabling the otherwise barely active MoS2 to approach its theoretical storage capacity as well as to achieve one of the highest rate capabilities among Mg-intercalation materials. The interlayer expansion approach can be leveraged to a wide range of host materials for the storage of various ions, leading to novel intercalation chemistry and opening up new opportunities for the development of advanced materials for next-generation energy storage.

Low-cost carbon-silicon nanocomposite anodes for lithium ion batteries

The specific energy of the existing lithium ion battery cells is limited because intercalation electrodes made of activated carbon (AC) materials have limited lithium ion storage capacities. Carbon nanotubes, graphene, and carbon nanofibers are the most sought alternatives to replace AC materials but their synthesis cost makes them highly prohibitive. Silicon has recently emerged as a strong candidate to replace existing graphite anodes due to its inherently large specific capacity and low working potential. However, pure silicon electrodes have shown poor mechanical integrity due to the dramatic expansion of the material during battery operation. This results in high irreversible capacity and short cycle life. We report on the synthesis and use of carbon and hybrid carbon-silicon nanostructures made by a simplified thermo-mechanical milling process to produce low-cost high-energy lithium ion battery anodes. Our work is based on an abundant, cost-effective, and easy-to-launch source of carbon soot having amorphous nature in combination with scrap silicon with crystalline nature. The carbon soot is transformed in situ into graphene and graphitic carbon during mechanical milling leading to superior elastic properties. Micro-Raman mapping shows a well-dispersed microstructure for both carbon and silicon. The fabricated composites are used for battery anodes, and the results are compared with commercial anodes from MTI Corporation. The anodes are integrated in batteries and tested; the results are compared to those seen in commercial batteries. For quick laboratory assessment, all electrochemical cells were fabricated under available environment conditions and they were tested at room temperature. Initial electrochemical analysis results on specific capacity, efficiency, and cyclability in comparison to currently available AC counterpart are promising to advance cost-effective commercial lithium ion battery technology. The electrochemical performance observed for carbon soot material is very interesting given the fact that its production cost is away cheaper than activated carbon. The cost of activated carbon is about

High-toughness/low-friction ductile epoxy coatings reinforced with carbon nanostructures

15/kg whereas the cost to manufacture carbon soot as a by-product from large-scale milling of abundant graphite is about

Fullerene-Metal Composites: Phase Transformations During Milling and Sintering

1/kg. Additionally, here, we propose a method that is environmentally friendly with strong potential for industrialization.

Gold nanoparticle SERS substrates sustainable at extremely high temperatures

We present the results of an effective reinforcement of epoxy resin matrix with fullerene carbon soot. The optimal carbon soot addition of 1 wt. % results in a toughness improvement of almost 20 times. The optimized soot-epoxy composites also show an increase in tensile elongation of more than 13 %, thus indicating a change of the failure mechanism in tension from brittle to ductile. Additionally, the coefficient of friction is reduced from its 0.91 value in plain epoxy resin to 0.15 in the optimized composite. In the optimized composite, the lateral forces during nanoscratching decrease as much as 80 % with enhancement of the elastic modulus and hardness by 43 % and 94%, respectively. The optimized epoxy resin fullerene soot composite can be a strong candidate for coating applications where toughness, low friction, ductility and light weight are important.

Effect of Coarsening of Sonochemical Synthesized Anatase on BET Surface Characteristics

Composites of Fe-C60 and Al C60 produced by mechanical milling and sinterized by Spark Plasma Sintering are investigated with special attention to the mechanical properties of the products. The processing involves phase transformations of the fullerenes that are interesting to follow and characterize. This involves formation of tetragonal/rhombohedral diamond and carbides during sintering and milling. Transmission Electron Microscopy (TEM) and Raman Spectroscopy techniques are also used to confirm preliminary results of X Ray Diffraction (XRD) related to the formation of nanostructures i.e., grain size of the crystals during mechanical milling and after sintering, spatial distribution of phases and the different phases that are developed during processing.

Flame Retardant Effect of Nano Fillers on Polydimethylsiloxane Composites

We report a technology for supporting gold nanoparticles (GNPS) with preserved SERS activity in substrates capable of sustaining temperatures as high as the melting point of gold. The material processing involved dispersion of citrate-capped GNPS in colloidal pseudoboehmite. The suspension was dried at 100 °C followed by annealing in air at temperatures of up to 1000 °C. Thus prepared substrates crystallized in γ-Al2O3 or θ-Al2O3 phases depending on the annealing temperature. XRD, TEM, and Raman spectroscopy characterizations show that GNPS remain nano-crystalline with preserved SERS activity and no apparent changes in size or shape after being treated at high temperatures. These results were also corroborated by the substrate UV-Vis absorption spectra. The SERS enhancement factor for Rhodamine 6G remained stable across the samples and showed no dependence on exposure to harsh environments.

Room-temperature synthesis of χ-Al2O3 and ruby (α-Cr:Al2O3)

In the present paper TiO2 (anatase) nanoparticles were synthesized by ultrasonic radiation proving the potential of this method. The synthesized anatase is heat treated at a temperature of 500°C in open air to coarse it using times from 1 h to 72 h. The heat treatment conditions were selected to prevent phase transformation and to solely sponsor coarsening of anatase from 6.2 nm to 28.3 nm. The synthesized and heat treated anatase were characterized using Electron Microscopy (Transmission and Scanning), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) method, UV-vis, Raman and Infrared spectroscopy. In the preset work is presented an analysis of anatase that is complemented by the agreement in the different characterization methods. This helps in the understanding of anatase coarsening as a function of heat treatment time and grain size, being the late a more suitable approach. This work opens up new perspectives to produce synthetic nanoparticulate anatase with potential for various applications.

Liquid and Semisolid Melt Treatment: Electromagnetic Stirring

Polydimethylsiloxane has exceptional fire retardancy characteristics, which make it a popular polymer in flame retardancy applications. Flame retardancy of polydimethylsiloxane with different nano fillers was studied. Polydimethylsiloxane composite fire property varies because of the shape, size, density, and chemical nature of nano fillers. In house made carbon and bismuth oxide nano fillers were used in polydimethylsiloxane composite. Carbon from biochar (carbonised bamboo) and a carbon by-product (carbon soot) were selected. For comparative study of nano fillers, standard commercial multiwall carbon nano tubes (functionalised, graphitised and pristine) as nano fillers were selected. Nano fillers in polydimethylsiloxane positively affects their fire retardant properties such as total smoke release, peak heat release rate, and time to ignition. Charring and surface ceramization are the main reasons for such improvement. Nano fillers in polydimethylsiloxane may affect the thermal mobility of polymer chains, which can directly affect the time to ignition. The study concludes that the addition of pristine multiwall carbon nano tubes and bismuth oxide nano particles as filler in polydimethylsiloxane composite improves the fire retardant property.

Applications in the Automotive and Aerospace Industries

In this work, we present a unique crystal growth synthesis of χ-Al2O3 accompanied with α-Cr:Al2O3 at room temperature. Raman spectroscopy and additions of Cr2O3 are key to identifying α-Cr:Al2O3 in trace amounts by the room temperature synthesis of ruby (α-Cr:Al2O3). The presence of this phase is further confirmed with HRTEM. The raw materials are pseudoboehmite and Cr2O3 that are treated mechano-chemically for the successful synthesis of ruby and χ-Al2O3. A thermal analysis approach is provided to explain the significant temperature reduction for the complete transformation to α-Cr:Al2O3 during annealing. The α-Cr:Al2O3 synthesized at room temperature acts as the seed or hetero site for nucleation and is responsible for a temperature drop of approximately 200 °C (up to 867 °C). This material is ideal for optics, photonics, defense, energy storage and harvesting, among other strategic applications.