Diganta Saikia

A comparative study of ordered mesoporous carbons with different pore structures as anode materials for lithium-ion batteries

In this study, ordered mesoporous carbons (OMCs) with different pore structures, namely 2D hexagonal CMK-3 and 3D cubic CMK-8 prepared by the nanocasting method using mesoporous silicas SBA-15 and KIT-6 as hard templates, respectively, in their pure forms are used as anode materials in lithium ion batteries (LIBs) to evaluate the role of mesoporous structures in their electrochemical performances. The results demonstrate that the CMK-8 electrode exhibits a higher reversible capacity and better cycling stability and rate capability, as compared to the CMK-3 electrode, due to its unique 3D cubic mesostructure. The initial capacities of 1884 and 964 mA h g−1 are obtained for the CMK-8 and CMK-3 electrodes, respectively. The CMK-8 electrode exhibits a higher capacity value (around 37.4% higher) than the CMK-3 electrode at the 100th cycle. The enhanced electrochemical performance of CMK-8 is mainly attributable to its unique 3D channel networks, which are beneficial for efficient Li storage and volume change. Although CMK-3 is the most investigated OMCs used in LIBs, herein we demonstrate that CMK-8 is a better carbon matrix for the fabrication of the electrode materials composed of mesoporous carbons.

A new highly conductive organic-inorganic solid polymer electrolyte based on a di-ureasil matrix doped with lithium perchlorate

A new hybrid organic-inorganic polymer electrolyte based on poly(propylene glycol) tolylene 2,4-diisocyanate terminated (PPGTDI), poly(propylene glycol)-block–poly(ethylene glycol)-block-poly(propylene glycol) bis(2-aminopropyl ether) (ED2000) and 3-isocyanatepropyltriethoxysilane (ICPTES) has been synthesized and characterized. A maximum ionic conductivity value of 1.0 × 10−4 S cm−1 at 30 °C and 1.1 × 10−3 S cm−1 at 80 °C is achieved for the hybrid electrolyte with a [O]/[Li] ratio of 32. The conductivity mechanism changes from Arrhenius to Vogel-Tamman-Fulcher (VTF) behavior with the increase in temperature from 20 to 80 °C. The present hybrid electrolyte system offers a remarkable improvement in ionic conductivity by at least one order of magnitude higher than the previously reported organic-inorganic electrolytes. The 7Li NMR (nuclear magnetic resonance) results reveal that there exists a strong correlation between the dynamic properties of the charge carriers and the polymer matrix. Two Li+ local environments are identified, for the first time, in such a di-ureasil based polymer electrolyte. The electrochemical stability window is found to be in the range of 4.6–5.0 V, which ensures that the present hybrid electrolyte is a potential polymer electrolyte for solid-state rechargeable lithium ion batteries.

Functionalization of cubic mesoporous silica SBA-16 with carboxylic acid via one-pot synthesis route for effective removal of cationic dyes.

In this work, we demonstrate that a high density of −COOH groups loading, up to 60 mol% based on silica, is successfully incorporated into SBA-16 via a one-pot synthesis route, which involves co-condensation of carboxyethylsilanetriol sodium salt (CES) and tetraethylorthosilicate (TEOS) templated by Pluronic F127 and P123 in an acidic medium. A variety of characterization techniques are performed to confirm quantitative incorporation of carboxylic groups into ordered cubic mesostructures. These functionalized materials are used to effectively remove two cationic dyes methylene blue (MB) and phenosafranine (PF) with the maximum adsorption capacities of 561 and 519 mg g(-1), respectively, at pH 9. The zeta potential results reveal that the electrostatic interactions between cationic dye molecule and negatively charged surface of the adsorbent play a crucial role in their high adsorption capacities. For a binary component system consisting of MB and PF, competitive adsorption of these two dyes is observed with adsorption capacity values slightly lower than those of the corresponding single dye systems. The dye adsorbed material can be easily regenerated by simple acid washing and be reused for five times with MB removal efficiency still up to 98.6%, showing its great potentials in environmental remediation.

Highly enhanced electrochemical performance of ultrafine CuO nanoparticles confined in ordered mesoporous carbons as anode materials for sodium-ion batteries

Ultrafine CuO nanoparticles are successfully encapsulated into two ordered mesoporous carbons (OMCs) with different pore architectures, namely CMK-8 with a 3D cubic mesostructure and CMK-3 with a 2D hexagonal mesostructure, and used as anodes in sodium-ion batteries. The electrochemical test results demonstrate that the CuO@CMK-8 nanocomposite with ultra-small CuO nanoparticles (around 4 nm in diameter) and a high content of CuO (78%) exhibits superior electrochemical performance as compared to that of the CuO@CMK-3 nanocomposite and the pristine CuO electrodes. The CuO@CMK-8 anode delivers an initial discharge capacity of 1405 mA h g−1 with a reversible capacity of 768 mA h g−1 at a current density of 20 mA g−1. At a current density of 100 mA g−1, it provides a reversible capacity of 477 mA h g−1 after 200 cycles with coulombic efficiency over 99%. The remarkable enhancement of the electrochemical performance of the CuO@CMK-8 nanocomposite can be attributed to the electrically conductive network of CMK-8 in the CuO@CMK-8 nanocomposite wherein the ultra-small CuO nanoparticles supported on CMK-8 act as a synergistic elastic buffer. Furthermore, cyclic voltammetry, ex situ XRD, SEM and TEM measurements provide deeper insights to the reversible conversion reaction in the CuO@CMK-8 nanocomposite system during the sodiation/desodiation process.

Synthesis and characterization of a highly conductive organic–inorganic hybrid polymer electrolyte based on amine terminated triblock polyethers and its application in electrochromic devices

A new highly ion conductive organic–inorganic hybrid electrolyte based on the reaction of triblock co-polymer poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) bis(2-aminopropyl ether) (ED2003) with 3-(glycidyloxypropyl)trimethoxysilane (GLYMO) and followed by co-condensation with 2-methoxy(polyethyleneoxy)propyl trimethoxysilane (MPEOPS) in the presence of LiClO4 was synthesized by a sol–gel process and characterized by a variety of experimental techniques. The maximum ionic conductivities of 1.1 × 10−4 S cm−1 at 30 °C and 6.0 × 10−4 S cm−1 at 80 °C were obtained for the hybrid electrolyte with a [O]/[Li] ratio of 24. The conductivity mechanism changed from Arrhenius at lower temperatures to Vogel–Tamman–Fulcher (VTF) behavior at higher temperatures. The results of solid-state NMR confirmed the structural framework of the hybrids, and provided a microscopic view of the effects of salt concentrations on the dynamic behavior of the polymer chains. The electrochemical stability window was found to be around 3.7–4.5 V, which is sufficient for electrochemical device applications. Preliminary tests performed with prototype electrochromic devices (ECDs) comprising the hybrid electrolyte with various [O]/[Li] ratios and mesoporous WO3 as the cathode layer are extremely encouraging. The best performance device exhibits an optical density change of 0.58, coloration efficiency of 375 cm2 C−1 and a good cycle life with the hybrid electrolyte with a [O]/[Li] ratio of 24. The present hybrid electrolyte offers a remarkable ionic conductivity and coloration efficiency in the solid state than previously reported organic–inorganic hybrid electrolytes.

Highly carboxylic-acid-functionalized ethane-bridged periodic mesoporous organosilicas: synthesis, characterization, and adsorption properties.

Functionalization of periodic mesoporous organosilicas (PMOs) with high loadings of pendant organic groups to form bifunctional PMOs with ordered mesostructures remains a challenging objective. Herein, we report that well-ordered ethane-bridged PMOs functionalized with exceptionally high loadings of pendant carboxylic acid groups (up to 80 mol % based on silica) were synthesized by the co-condensation of 1,4-bis(trimethoxysilyl)ethane (BTME) and carboxyethylsilanetriol sodium salt (CES) with Pluronic P123 as the template and KCl as an additive under acidic conditions. The bifunctional materials were characterized by using a variety of techniques, including powder X-ray diffraction, nitrogen-adsorption/desorption, TEM, and solid-state (13)C and (29)Si NMR spectroscopy. Zeta-potential measurements showed that the surface negative charges increased with increasing the CES content. This property makes them potential candidates for applications in drug adsorption. The excellent adsorption capacity of these bifunctional PMOs towards an anticancer drug (doxorubicin) was also demonstrated.

Size dependence of silver nanoparticles in carboxylic acid functionalized mesoporous silica SBA-15 for catalytic reduction of 4-nitrophenol

In this study, the formation of silver nanoparticles (Ag NPs) with a particle size of about 3 nm was successfully achieved by using the mesoporous channels of carboxylic acid (–COOH) functionalized SBA-15 as the support. When pure silica SBA-15 (without –COOH groups) was employed, the Ag NPs were formed outside of the mesopore and their particle size was significantly larger, up to about 20 nm. The –COO− groups under basic conditions can effectively interact with the Ag+ ions, and thus allowed facile fabrication of Ag NPs. The catalytic activity of these Ag NPs based SBA-15 materials were tested for a model reaction, namely the reduction of 4-nitrophenol to 4-aminophenol. The results showed that the particle size of the Ag NPs play a key role in determining their catalytic activity. The apparent kinetic constant for the Ag NPs with a particle size of about 3 nm was 1.1 × 10−2 s−1, corresponding to the activity parameters of 12.2 and 4630 s−1 g−1 by considering the total mass of the catalyst used and the Ag NPs alone, respectively, which were remarkably high as compared to other matrices bearing Ag. Moreover, the Ag NP based materials exhibited good recyclability up to 5 cycles.

A new organic–inorganic hybrid electrolyte based on polyacrylonitrile, polyether diamine and alkoxysilanes for lithium ion batteries: synthesis, structural properties, and electrochemical characterization

A new type of organic–inorganic hybrid polymer electrolyte based on poly(propylene glycol)-block-poly(ethylene glycol)-block-poly-(propylene glycol)bis(2-aminopropyl ether), polyacrylonitrile (PAN), 3-(glycidyloxypropyl)trimethoxysilane (GLYMO) and 3-(aminopropyl)trimethoxysilane (APTMS) complexed with LiClO4 via the co-condensation of organosilicas was synthesized. The structural and electrochemical properties of the materials were systematically investigated by a variety of techniques including differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), multinuclear (13C, 29Si, 7Li) solid-state NMR, AC impedance, linear sweep voltammetry (LSV) and charge–discharge measurement. A maximum ionic conductivity value of 7.4 × 10−5 S cm−1 at 30 °C and 4.6 × 10−4 S cm−1 at 80 °C is achieved for the solid hybrid electrolyte. The 7Li NMR measurements reveal the strong correlation of the lithium cation and the polymer matrix, and the presence of two lithium local environments. After swelling in an electrolyte solvent, the plasticized hybrid membrane exhibited a maximum ionic conductivity of 6.4 × 10−3 S cm−1 at 30 °C. The good value of the electrochemical stability window (∼4.5 V) makes the plasticized hybrid electrolyte membrane promising for electrochemical device applications. The preliminary lithium ion battery testing shows an initial discharge capacity value of 123 mA h g−1 and a good cycling performance with the plasticized hybrid electrolyte.

Ni Nanoparticles Supported on Cage‐Type Mesoporous Silica for CO2 Hydrogenation with High CH4 Selectivity

Ni nanoparticles (around 4 nm diameter) were successfully supported on cage-type mesoporous silica SBA-16 (denoted as Ni@SBA-16) via wet impregnation at pH 9, followed by the calcination-reduction process. The Ni@SBA-16 catalyst with a very high Ni loading amount (22.9 wt %) exhibited exceptionally high CH4 selectivity for CO2 hydrogenation. At a nearly identical loading amount, the Ni@SBA-16 catalysts with smaller particle size of Ni NPs surprisingly exhibited a higher catalytic activity of CO2 hydrogenation and also led to a higher selectivity on CH4 formation than the Ni@SiO2 catalysts. This enhanced activity of the Ni@SBA-16 catalyst is suggested to be an accumulative result of the advantageous structural properties of the support SBA-16 and the well confined Ni NPs within the support; both induced a favorable reaction pathway for high selectivity of CH4 in CO2 hydrogenation.

Towards an understanding of the role of hyper-branched oligomers coated on cathodes, in the safety mechanism of lithium-ion batteries

Self-terminated hyper-branched oligomers (STOBA) were coated and then melted on a Li(Ni0.4Co0.2Mn0.4)O2 cathode to form a dense polymer film at high temperatures. The physical and structural changes of the polymer layer at different temperatures and charge conditions were investigated by nitrogen adsorption–desorption, X-ray photoelectron spectroscopy, resistance measurements, scanning electron microscopy, and solid-state 7Li-NMR and 13C-NMR spectroscopy in order to improve the understanding of the role of the STOBA layer in the enhancement of the safety mechanism of lithium ion batteries. The morphological change of the STOBA layer from the porous to nonporous state at the temperature of a thermal runaway of a battery was demonstrated. The change in the resistance values at high temperatures revealed that the STOBA coating is helpful for the prevention of internal short-circuiting and thermal runaway. Most importantly, the 7Li-NMR results acquired at a very high spinning speed (50 kHz) allow the monitoring of the subtle changes in the local environments of the Li+ ions and their interaction and mobility in the STOBA–cathode interface as functions of temperature and charge states. The combined characterization results improve the understanding of how the STOBA layer can contribute to the safety features of lithium ion batteries.