Alexander G. Medvedev

High-capacity antimony sulphide nanoparticle-decorated graphene composite as anode for sodium-ion batteries

Sodium-ion batteries are an alternative to lithium-ion batteries for large-scale applications. However, low capacity and poor rate capability of existing anodes are the main bottlenecks to future developments. Here we report a uniform coating of antimony sulphide (stibnite) on graphene, fabricated by a solution-based synthesis technique, as the anode material for sodium-ion batteries. It gives a high capacity of 730 mAh g(-1) at 50 mA g(-1), an excellent rate capability up to 6C and a good cycle performance. The promising performance is attributed to fast sodium ion diffusion from the small nanoparticles, and good electrical transport from the intimate contact between the active material and graphene, which also provides a template for anchoring the nanoparticles. We also demonstrate a battery with the stibnite-graphene composite that is free from sodium metal, having energy density up to 80 Wh kg(-1). The energy density could exceed that of some lithium-ion batteries with further optimization.

Nanocrystalline tin disulfide coating of reduced graphene oxide produced by the peroxostannate deposition route for sodium ion battery anodes

A highly stable sodium ion battery anode was prepared by deposition of hydroperoxostannate on graphene oxide from hydrogen-peroxide-rich solution followed by sulfidization and 300 °C heat treatment. The material was characterized by electron microscopy, powder X-ray diffraction and X-ray photoelectron spectroscopy which showed that the active material is mostly rhombohedral SnS2 whose (001) planes were preferentially oriented in parallel to the graphene oxide sheets. The material exhibited >610 mA h g−1 charge capacity at 50 mA g−1 (with >99.6% charging efficiency) between 0 and 2 V vs. Na/Na+ electrode, high cycling stability for over 150 cycles and very good rate performance, >320 mA h g−1 at 2000 mA g−1.

Crystal structures of natural amino acid perhydrates

The structures of various natural amino acid hydrogen peroxide solvates are presented. All “active” hydrogen atoms (amino, hydroxy, peroxy, and water) in the studied amino acid perhydrates are involved in hydrogen bonding. Peroxide molecules form at least two donor hydrogen bonds. In the most common case, the H2O2 molecule is engaged in four hydrogen bonds (two donors with –CO2−groups and two acceptors with –NH3+groups). In peroxosolvates of amino acids bearing hydrocarbon side-chains, double layers were observed. These bilayers are hydrophilic inside, while their outer surfaces are hydrophobic. It was found that donor hydrogen bonds formed by hydrogen peroxide in amino acid perhydrates are significantly stronger than those formed by water molecules in amino acid hydrates.

Zinc dioxide nanoparticulates: a hydrogen peroxide source at moderate pH.

Solid peroxides are a convenient source of hydrogen peroxide, which once released can be readily converted to active oxygen species or to dissolved dioxygen. A zinc peroxide nanodispersion was synthesized and characterized, and its solubility was determined as a function of pH and temperature. We show that zinc peroxide is much more stable in aqueous solutions compared to calcium and magnesium peroxides and that it retains its peroxide content down to pH 6. At low pH conditions H2O2 release is thermodynamically controlled and its dissolution product, Zn(2+), is highly soluble, and thus, hydrogen peroxide release can be highly predictable. The Gibbs free energy of formation of zinc peroxide was found to be -242.0 ± 0.4 kJ/mol and the enthalpy of formation was -292.1 ± 0.7 kJ/mol, substantially higher than theoretically predicted before. The biocidal activity of zinc peroxide was determined by inactivation studies with Escherichia coli cultures, and the activity trend agrees well with the thermodynamic predictions.

Biocomposite Based on Reduced Graphene Oxide Film Modified with Phenothiazone and Flavin Adenine Dinucleotide-Dependent Glucose Dehydrogenase for Glucose Sensing and Biofuel Cell Applications

A novel composite material for the encapsulation of redox enzymes was prepared. Reduced graphene oxide film with adsorbed phenothiazone was used as a highly efficient composite for electron transfer between flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase and electrodes. Measured redox potential for glucose oxidation was lower than 0 V vs Ag/AgCl electrode. The fabricated biosensor showed high sensitivity of 42 mA M(-1) cm(-2), a linear range of glucose detection of 0.5-12 mM, and good reproducibility and stability as well as high selectivity for different interfering compounds. In a semibiofuel cell configuration, the hybrid film generated high power output of 345 μW cm(-2). These results demonstrate a promising potential for this composition in various bioelectronic applications.

Graphene oxide supported sodium stannate lithium ion battery anodes by the peroxide route: low temperature and no waste processing

Since there has been a notable improvement in the performance of graphene-supported tin-based lithium ion battery anodes, they have become a viable alternative to state of the art graphite anodes. However, currently these anodes are produced by energy-demanding thermal processes and generate lithium chloride or other wastes. In this research, we demonstrate the formation of efficient and stable lithium ion battery anodes based on sodium stannate-coated reduced graphene oxide. Coating is performed at low temperatures and when a sodium peroxostannate precursor is used, the process can be carried out with zero waste discharge. Thermal treatment is required only for the solid material. The anode exhibited a charge capacity of 610 mA h g−1 after 140 cycles at 100 mA g−1. This is the first characterization of a sodium stannate-based anode for LIBs.

Potassium, Cesium, and Ammonium Peroxogermanates with Inorganic Hexanuclear Peroxo Bridged Germanium Anion Isolated from Aqueous Solution

Potassium (K6[Ge6(μ-OO)6(μ-O)6(OH)6]·14H2O, 1), cesium ammonium (Cs4.2(NH4)1.8[Ge6(μ-OO)6(μ-O)6(OH)6]·8H2O, 2), and potassium ammonium (K2.4(NH4)3.6[Ge6(μ-OO)6(μ-O)6(OH)6]·6H2O, 3) peroxogermanates were isolated from 3% hydrogen peroxide aqueous solutions of the corresponding hydroxogermanates and characterized by single crystal and powder X-ray diffraction studies and by Raman spectroscopy and thermal analysis. The crystal structure of all three compounds consists of cations of potassium and/or ammonium and cesium, water molecules, and centrosymmetric hexanuclear peroxogermanate anion [Ge6(μ-OO)6(μ-O)6(OH)6](6-) with six μ-oxo- and six μ-peroxo groups. Peroxogermanates demonstrate relatively high thermal stability: the peroxide remains in the structure even after water release after heating to 100-120 °C. DFT calculations of the peroxogermanate [Ge6(μ-OO)6(μ-O)6(OH)6](6-) anion confirm its higher thermodynamic stability compared to the hydroperoxo- and oxogermanate analogues.

GeO2 Thin Film Deposition on Graphene Oxide by the Hydrogen Peroxide Route: Evaluation for Lithium-Ion Battery Anode

A peroxogermanate thin film was deposited in high yield at room temperature on graphene oxide (GO) from peroxogermanate sols. The deposition of the peroxo-precursor onto GO and the transformations to amorphous GeO2, crystalline tetragonal GeO2, and then to cubic elemental germanium were followed by electron microscopy, XRD, and XPS. All of these transformations are influenced by the GO support. The initial deposition is explained in view of the sol composition and the presence of GO, and the different thermal transformations are explained by reactions with the graphene support acting as a reducing agent. As a test case, the evaluation of the different materials as lithium ion battery anodes was carried out revealing that the best performance is obtained by amorphous germanium oxide@GO with >1000 mAh g-1 at 250 mA g-1 (between 0 and 2.5 V vs Li/Li+ cathode), despite the fact that the material contained only 51 wt % germanium. This is the first demonstration of the peroxide route to produce peroxogermanate thin films and thereby supported germanium and germanium oxide coatings. The advantages of the process over alternative methodologies are discussed.

Antimony and antimony oxide@graphene oxide obtained by the peroxide route as anodes for lithium-ion batteries

Abstract Zero-valent antimony and antimony oxide were deposited on graphene oxide by the recently introduced peroxide deposition route. The antimony@graphene oxide (GO) anode exhibits a charging capacity of 340 mAh g-1 with excellent stability at a current rate of 250 mA g-1 after 50 cycles of lithiation, which is superior to all other forms of antimony anodes that have been reported thus far. The electrode also exhibits a good rate performance, with a capacity of 230 and 180 mAh g-1 at a rate of 500 and 1000 mA g-1, respectively. We attribute the superior performance of the antimony@GO anodes to our coating protocol, which provides a thin layer of nanometric antimony coating on the graphene oxide, and to a small amount of antimony oxide that is left in the anode material after heat treatment and imparts some flexibility. The efficient charge distribution by the large surface area of reduced GO and the expansion buffering of the elastic graphene sheets also contributed to the superior stability of the anode.

Peroxide Coordination of Tellurium in Aqueous Solutions

Tellurium-peroxo complexes in aqueous solutions have never been reported. In this work, ammonium peroxotellurates (NH4 )4 Te2 (μ-OO)2 (μ-O)O4 (OH)2 (1) and (NH4 )5 Te2 (μ-OO)2 (μ-O)O5 (OH)⋅1.28 H2 O⋅0.72 H2 O2 (2) were isolated from 5 % hydrogen peroxide aqueous solutions of ammonium tellurate and characterized by single-crystal and powder X-ray diffraction analysis, by Raman spectroscopy and thermal analysis. The crystal structure of 1 comprises ammonium cations and a symmetric binuclear peroxotellurate anion [Te2 (μ-OO)2 (μ-O)O4 (OH)2 ](4-) . The structure of 2 consists of an unsymmetrical [Te2 (μ-OO)2 (μ-O)O5 (OH)](5-) anion, ammonium cations, hydrogen peroxide, and water. Peroxotellurate anions in both 1 and 2 contain a binuclear Te2 (μ-OO)2 (μ-O) fragment with one μ-oxo- and two μ-peroxo bridging groups. (125) Te NMR spectroscopic analysis shows that the peroxo bridged bitellurate anions are the dominant species in solution, with 3-40 %wt H2 O2 and for pH values above 9. DFT calculations of the peroxotellurate anion confirm its higher thermodynamic stability compared with those of the oxotellurate analogues. This is the first direct evidence for tellurium-peroxide coordination in any aqueous system and the first report of inorganic tellurium-peroxo complexes. General features common to all reported p-block element peroxides could be discerned by the characterization of aqueous and crystalline peroxotellurates.