Thomas Diemant

Synthesis and properties of hydroxyapatite-containing porous titania coating on ultrafine-grained titanium by micro-arc oxidation

Equal channel angular pressing results in ultrafine-grained (approximately 200-500 nm) Ti with superior mechanical properties without harmful alloying elements, which benefits medical implants. To further improve the bioactivity of Ti surfaces, Ca/P-containing porous titania coatings were prepared on ultrafine-grained and coarse-grained Ti by micro-arc oxidation (MAO). The phase identification, composition, morphology and microstructure of the coatings and the thermal stability of ultrafine-grained Ti during MAO were investigated subsequently. The amounts of Ca, P and the Ca/P ratio of the coatings formed on ultrafine-grained Ti were greater than those on coarse-grained Ti. Nanocrystalline hydroxyapatite and alpha-Ca(3)(PO(4))(2) phases appeared in the MAO coating formed on ultrafine-grained Ti for 20 min (E20). Incubated in a simulated body fluid, bone-like apatite was completely formed on the surface of E20 after 2 days, thus evidencing preferable bioactivity. Compared with initial ultrafine-grained Ti, the microhardness of the E20 substrate was reduced by 8% to 2.9 GPa, which is considerably more than that of coarse-grained Ti (approximately 1.5 GPa).

Single step transformation of sulphur to Li2S2/Li2S in Li-S batteries

Lithium-sulphur batteries have generated tremendous research interest due to their high theoretical energy density and potential cost-effectiveness. The commercial realization of Li-S batteries is still hampered by reduced cycle life associated with the formation of electrolyte soluble higher-order polysulphide (Li2Sx, x = 4–8) intermediates, leading to capacity fading, self-discharge, and a multistep voltage profile. Herein, we have realized a practical approach towards a direct transformation of sulphur to Li2S2/Li2S in lithium-sulphur batteries by alteration of the reaction pathway. A coconut shell derived ultramicroporous carbon-sulphur composite cathode has been used as reaction directing template for the sulphur. The lithiation/delithiation and capacity fading mechanism of microporous carbon confined sulphur composite was revealed by analyzing the subsurface using X-ray photoelectron spectroscopy. No higher-order polysulphides were detected in the electrolyte, on the surface, and in the subsurface of the cathode composite. The altered reaction pathway is reflected by a single-step profile in the discharge/charge of a lithium-sulphur cell.

Performance study of magnesium–sulfur battery using a graphene based sulfur composite cathode electrode and a non-nucleophilic Mg electrolyte

Here we report for the first time the development of a Mg rechargeable battery using a graphene-sulfur nanocomposite as the cathode, a Mg-carbon composite as the anode and a non-nucleophilic Mg based complex in tetraglyme solvent as the electrolyte. The graphene-sulfur nanocomposites are prepared through a new pathway by the combination of thermal and chemical precipitation methods. The Mg/S cell delivers a higher reversible capacity (448 mA h g(-1)), a longer cyclability (236 mA h g(-1) at the end of the 50(th) cycle) and a better rate capability than previously described cells. The dissolution of Mg polysulfides to the anode side was studied by X-ray photoelectron spectroscopy. The use of a graphene-sulfur composite cathode electrode, with the properties of a high surface area, a porous morphology, a very good electronic conductivity and the presence of oxygen functional groups, along with a non-nucleophilic Mg electrolyte gives an improved battery performance.

The interaction of CO with PdAg/Pd(111) surface alloys—A case study of ensemble effects on a bimetallic surface

The interaction of CO with structurally well-defined PdAg/Pd(111) surface alloys was investigated by temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS) to unravel and understand contributions from electronic strain, electronic ligand and geometric ensemble effects. TPD measurements indicate that CO adsorption is not possible on the Ag sites of the surface alloys (at 120 K) and that the CO binding strength on Pd sites decreases significantly with increasing Ag concentration. Comparison with previous scanning tunneling microscopy (STM) data on the distribution of Pd and Ag atoms in the surface alloy shows that this modification is mainly due to geometric ensemble effects, since Pd(3) ensembles, which are the preferred ensembles for CO adsorption on non-modified Pd(111), are no longer available on Ag-rich surfaces. Consequently, the preferred CO adsorption site changes with increasing Ag content from a Pd(3) trimer via a Pd(2) dimer to a Pd monomer, going along with a successive weakening of CO adsorption. Additionally, the CO adsorption properties of the surface alloys are also influenced by electronic ligand and strain effects, but on a lower scale. The results are discussed in comparison with previous findings on PdAg bulk alloys, supported PdAg catalysts and PdAu/Pd(111) model systems.

Pectin, Hemicellulose, or Lignin? Impact of the Biowaste Source on the Performance of Hard Carbons for Sodium-Ion Batteries

Hard carbons are currently the most widely used negative electrode materials in Na-ion batteries. This is due to their promising electrochemical performance with capacities of 200-300 mAh g-1 and stable long-term cycling. However, an abundant and cheap carbon source is necessary in order to comply with the low-cost philosophy of Na-ion technology. Many biological or waste materials have been used to synthesize hard carbons but the impact of the precursors on the final properties of the anode material is not fully understood. In this study the impact of the biomass source on the structural and electrochemical properties of hard carbons is unraveled by using different, representative types of biomass as examples. The systematic structural and electrochemical investigation of hard carbons derived from different sources-namely corncobs, peanut shells, and waste apples, which are representative of hemicellulose-, lignin- and pectin-rich biomass, respectively-enables understanding and interlinking of the structural and electrochemical properties.

Development of new anode composite materials for fluoride ion batteries

Due to their high theoretical energy density values, Fluoride Ion Batteries (FIB) are interesting alternatives to Li-ion batteries. Recently, results have been reported on the reversible charge and discharge of such systems using a solid electrolyte, various metal fluorides as cathode materials and Ce metal as the anode. The work in the present study is focused on the development of new anode materials which do not contain Li. To facilitate cell preparation and material handling, cells were prepared in the discharged state with Bi or Cu as the cathode material and CeF3, CaF2 or MgF2 as potential anode materials. The charge and discharge mechanisms were examined by detailed ex situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) experiments. The best cycling performances were obtained with MgF2 but prepared in the half-discharged state (i.e. mixed with Mg), thus forming a composite that could provide better interface contacts between the different reactive phases. The results showed that apart from choosing carefully the electrode active materials, it is also important to optimise the architecture of the electrodes.

From Adlayer Islands to Surface Alloy: Structural and Chemical Changes on Bimetallic PtRu/Ru(0001) Surfaces

The correlation between structural and chemical properties of bimetallic PtRu/Ru(0001) model catalysts and their modification upon stepwise annealing of a submonolayer Pt-covered Ru(0001) surface up to the formation of an equilibrated Pt(x)Ru(1-x)/Ru(0001) monolayer surface alloy was investigated by scanning tunneling microscopy and by the adsorption of CO and D(2) probe molecules. Both temperature-programmed desorption and IR measurements demonstrate the influence of the surface structure on the adsorption properties of the bimetallic surface, which can be explained by changes of the composition of the adsorption ensembles (ensemble effects) for D adsorption and by changes in the electronic interaction (ligand effects, strain effects) of the metallic constituents for CO and D adsorption upon alloy formation.

Vanadium oxychloride/magnesium electrode systems for chloride ion batteries

We report a new type of rechargeable chloride ion battery using vanadium oxychloride (VOCl) as cathode and magnesium or magnesium/magnesium chloride (MgCl2/Mg) as anode, with an emphasis on the VOCl-MgCl2/Mg full battery. The charge and discharge mechanism of the VOCl cathode has been investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and electrochemical measurements, demonstrating the chloride ion transfer during cycling. The VOCl cathode can deliver a reversible capacity of 101 mAh g(-1) at a current density of 10 mA g(-1) and a capacity of 60 mAh g(-1) was retained after 53 cycles in this first study.

In-Depth Interfacial Chemistry and Reactivity Focused Investigation of Lithium–Imide- and Lithium–Imidazole-Based Electrolytes

A comparative and in-depth investigation on the reactivity of various Li-based electrolytes and of the solid electrolyte interface (SEI) formed at graphite electrode is carried out using X-ray photoelectron spectroscopy (XPS), chemical simulation test, and differential scanning calorimetry (DSC). The electrolytes investigated include LiX (X = PF6, TFSI, TDI, FSI, and FTFSI), dissolved in EC-DMC. The reactivity and SEI nature of electrolytes containing the relatively new imide (LiFSI and LiFTFSI) and imidazole (LiTDI) salts are evaluated and compared to those of well-researched LiPF6(-) and LiTFSI-based electrolytes. The thermal reactivity of LixC6 in the various electrolytes is found to be in the order of LiFSI > LiTDI > LiTFSI > LiFTFSI > LiPF6 and LiFSI > LiFTFSI > LiPF6 > LiTFSI > LiTDI in terms of onset exothermic temperature and total heat generated, respectively. Surface and depth-profiling XPS analysis of the SEI formed with the diverse electrolyte formulations provide insight into the differences and similarities (composition, thickness, and evolution, etc.) emanating from the structure of the various salt anions.

Increasing the creation yield of shallow single defects in diamond by surface plasma treatment

Single Nitrogen-Vacancy (NV) centers in diamond close to the crystal surface are very promising magnetic field sensors with very high sensitivity. Here, we report the enhanced creation of very shallow (less than 3 nm below the diamond surface) NV centers by using fluorine and oxygen plasma treatment. We observe a four fold increase—from 0.11% to about 0.45% in the production yield when the sample surface is terminated with fluorine or oxygen atoms. This effect is explained by the stabilization of the NVs negative charge state which is influenced by the various defects present on the diamond surface.