Rolf Jürgen Behm

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.

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.

Submicron-sized silicon oxycarbide spheres as anodes for alkali ion batteries

Submicron-sized silicon oxycarbide (SiCO) spheres were prepared by using a 2-step acid/base catalyzed sol–gel process of triethoxyphenylsilane (PhTES) with subsequent carbonization at 1000 °C under an argon atmosphere. To prevent the organosilica spheres from sintering during heating, small amounts of tetraethoxysilane (TEOS) were cocondensed with carbosilane. The resulting SiCO material retains the spherical morphology (average particle diameter of around 200–300 nm) of the organosilica material upon heating in contrast to the SiCO obtained from pure PhTES or from the cocondensation of PhTES with methyltriethoxysilane (MTES). X-ray photoelectron spectroscopy (XPS) measurements of the SiCO spheres revealed an absolute carbon content of 41 wt%, which is only slightly lower than the carbon content of the SiCO obtained from pure PhTES with 46 wt%. Together with the O/Si ratio, we determined the following composition for the SiCO spheres: SiC0.3O1.4 + 2.89Cfree. In order to elucidate the potential of the material as an anode material for sodium and lithium ion batteries, galvanostatic charge/discharge measurements were conducted and compared to the other SiCO materials. For the lithium system, capacities as high as 858 mA h g−1 at a lower current of 50 mA g−1 have been achieved. The spheres show significantly improved rate capability compared to the other SiCO samples. For instance, the material delivers reversible capacities of around 500 mA h g−1 at a specific current of 500 mA g−1. It is noteworthy that the spheres show the highest first cycle coulombic efficiency (73%) compared to the other SiCO materials (down to 51%) prepared throughout this work, which might be attributed to the higher material utilization due to the nanoscopic morphology. The SiCO nanostructure also significantly improved the sodium insertion properties compared to bulk SiCO. For the SiCO spheres we obtained a promising high reversible capacity of 200 mA h g−1 at a lower current of 25 mA g−1 (1st cycle efficiency of 47%). When increasing the current to 200 mA g−1, the material still delivered 111 mA h g−1.

Inhibitor-assisted synthesis of silica-core microbeads with pepsin-imprinted nanoshells

A novel approach for molecularly imprinting proteins, i.e. inhibitor-assisted imprinting, onto silica microspheres is discussed, which provides advanced functional materials addressing prevalent challenges in the field of protein purification and isolation from biotechnologically relevant media. Pepstatin-assisted surface-imprinted core-shell microbeads for the acidic protease pepsin were synthesized serving as selective sorbent materials for solid phase extraction (SPE) applications. The inorganic core, i.e. amino-functionalized silica spheres (AFSS), is prepared by the co-condensation of tetraethylorthosilicate (TEOS) and (3-aminopropyl) trimethoxysilane (APTMS) in water-in-oil (W/O) emulsion, which is then reacted with pepstatin, a selective inhibitor of pepsin, onto the surface of the AFSS via an amide bond. 3-Aminophenylboronic acid (APBA) serves as the functional monomer for establishing nanothin imprinted polymer films, i.e. poly(3-aminophenylboronic acid) (pAPBA) at the surface of the pepstatin-immobilized AFSS via oxidation by ammonium persulfate in aqueous solution in the presence (molecularly imprinted polymer, MIP) and absence (non-imprinted polymer; NIP) of pepsin. Thus obtained core-shell microbeads are packaged into SPE cartridges for evaluating the selectivity for pepsin. Each individual synthesis step is thoroughly characterized using x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and BET methods. Finally, the imprinted core-shell microbeads indeed provide specific binding.

Silicon carboxylate derived silicon oxycarbides as anodes for lithium ion batteries

A novel and facile procedure was developed to synthesize silicon oxycarbides which are suitable anode materials for lithium ion batteries. Silicon tetraacetate was thoroughly mixed with varying amounts of citric acid and the mixtures were thermally treated at lower temperatures of up to 250 °C for several hours. The mixtures start to melt at around 150 °C. Acetic acid and acetic anhydride may then continuously be removed via distillation until the mixture starts to solidify. The degree of substitution may be controlled by the amount of citric acid. The resulting solids were then carbonized under an inert gas atmosphere at a temperature of 1000 °C. Black solids were obtained whose chemical composition and morphology were characterized in detail. X-ray diffraction (XRD) confirmed the amorphous nature of the materials. With X-ray photoelectron spectroscopy (XPS) we were able to analyze the chemical environment of the silicon atoms in more detail. Compared to fumed silica the Si 2p detail spectra show another peak at lower binding energy, which can be attributed to oxycarbide species. XPS also allowed us to determine the O/Si ratio from which a chemical formula for the SiCO materials could be derived. The materials also contain a significant amount of free carbon, which improves electrical conductivity and thus the electrochemical properties. In order to elucidate the potential of the materials as anodes for lithium ion batteries, galvanostatic charge/discharge measurements were conducted. Within the cut off potentials of 0.005–1.5 V, the materials showed high capacities of up to 590 mA h g−1 at a current of 50 mA g−1. To overcome the irreversible capacities in this system, a prelithiation approach via spray coating with stabilized lithium metal powders (SLMP®) was successfully applied. The electrodes, fabricated with lithiated polyacrylic acid (LiPAA) as binder, maintained the cycling characteristics of their non-lithiated counterparts, even if the anode was almost completely lithiated.

Wie lange halten Edelstahlklebungen

Dass eine Laser-Vorbehandlung durchaus eine Alternative zu nasschemischen oder tribochemischen Prozessen darstellt, ist bereits bekannt. Die im Folgenden beschriebenen Untersuchungsergebnisse sollen das Verständnis für die Wechselwirkung des Lasers mit der Substratoberfläche und die Wirkung auf die Klebbarkeit werkstoffspezifisch vertiefen. Das Kleben empfiehlt sich für das Fügen von metallischen Teilen und damit auch von Edelstählen, da die Fügeteile thermisch wenig belastet werden und damit Nacharbeiten zur Korrektur von Verzug und Verfärbungen vermeidbar sind. Bild 1 zeigt exemplarisch den Vergleich einer Schweißung mit einer geklebten Verbindung. Deutlich sind bei der geschweißten Lösung die thermisch bedingten Anlauffarben sowie der Verzug erkennbar, welche die Gebrauchseigenschaften erheblich beeinträchtigen können. Der Vollständigkeit halber sei erwähnt, dass jeweils verfahrensspezifische Konstruktionen unerlässlich sind. Erste Erkenntnisse deuten darauf hin, dass die Laserbehandlung eines austenitischen Stahles zu einer deutlichen Verbesserung der Beständigkeit von Klebungen in Bezug auf feucht-warme Alterung führt [1]. Wie in vorangegangenen Untersuchungen wurde wieder auf Probekörper aus Edelstahl-rostfrei des Typs 1.4301 zurückgegriffen. Die Zusammensetzung ließ sich mittels optischer Emissionsspektroskopie ermitteln (Tabelle 1).

Infrared spectroscopy via substrate-integrated hollow waveguides: a powerful tool in catalysis research

Substrate-integrated hollow waveguides (iHWG) represent an innovative generation of photon conduits, which can simultaneously serve as highly miniaturized gas cells with low sample volume. In this communication, we introduce a novel concept for analyzing the performance of catalysts via infrared gas phase analysis based on iHWGs. Due to rapid gas exchange and sample transient times within the iHWG, compositional changes of a continuous gas stream after interaction with a catalyst assembly can be monitored with high time resolution.

The durability of stainless steel bondings

Laser pre-treatment is a well-known alternative to wet chemical or tribochemical processes. The results of this study, which relate specifically to stainless steel, are intended to give a more in-depth understanding of the interaction of the laser with the substrate surface and its effect on the bonding ability of the material. Adhesive bonding is an ideal means of joining metal components, including those made from stainless steel, because the bonded parts are not exposed to high temperatures and, therefore, no re-working is needed to correct distortion and discoloration. Figure 1 shows an example of the difference between a welded and a bonded joint. The welded component clearly demonstrates the discoloration and distortion caused by the high temperature of the welding process, which can have a significant impact on the usability of the part. It is worth mentioning here that parts must be designed to suit the process in question. Initial findings indicate that laser treatment of austenitic steels significantly improves the durability of bonds after moisture and heat ageing /1/. As in previous studies, test specimens made from 1.4301 grade stainless steel were used. The composition was identified using optical emission spectroscopy (Table 1).