Hans Bongard

Controllable Synthesis of Mesoporous Peapod‐like Co3O4@Carbon Nanotube Arrays for High‐Performance Lithium‐Ion Batteries

Transition metal oxides are regarded as promising anode materials for lithium-ion batteries because of their high theoretical capacities compared with commercial graphite. Unfortunately, the implementation of such novel anodes is hampered by their large volume changes during the Li(+) insertion and extraction process and their low electric conductivities. Herein, we report a specifically designed anode architecture to overcome such problems, that is, mesoporous peapod-like Co3O4@carbon nanotube arrays, which are constructed through a controllable nanocasting process. Co3O4 nanoparticles are confined exclusively in the intratubular pores of the nanotube arrays. The pores between the nanotubes are open, and thus render the Co3O4 nanoparticles accessible for effective electrolyte diffusion. Moreover, the carbon nanotubes act as a conductive network. As a result, the peapod-like Co3O4 @carbon nanotube electrode shows a high specific capacity, excellent rate capacity, and very good cycling performance.

Direct imaging of surface topology and pore system of ordered mesoporous silica (MCM-41, SBA-15, and KIT-6) and nanocast metal oxides by high resolution scanning electron microscopy

We report here a detailed study on the surface topology of well-known ordered mesoporous silica (SBA-15, MCM-41, and KIT-6) and a series of nanocast Co 3O 4, Co 3O 4/CoFe 2O 4 composites by high resolution scanning electron microscopy (HR-SEM). Images of the MCM-41 structure were obtained at a resolution of the pore size, as well as a real space image of the gyroid silica surface of KIT-6 for two different aging temperatures, clearly revealing the differences of the aging procedures. By using the low voltage HR-SEM technique with extremely high resolution, we could very clearly show the influence of the template properties on the structure of the nanocast metal oxides.

Design criteria for stable Pt/C fuel cell catalysts.

Summary Platinum and Pt alloy nanoparticles supported on carbon are the state of the art electrocatalysts in proton exchange membrane fuel cells. To develop a better understanding on how material design can influence the degradation processes on the nanoscale, three specific Pt/C catalysts with different structural characteristics were investigated in depth: a conventional Pt/Vulcan catalyst with a particle size of 3–4 nm and two Pt@HGS catalysts with different particle size, 1–2 nm and 3–4 nm. Specifically, Pt@HGS corresponds to platinum nanoparticles incorporated and confined within the pore structure of the nanostructured carbon support, i.e., hollow graphitic spheres (HGS). All three materials are characterized by the same platinum loading, so that the differences in their performance can be correlated to the structural characteristics of each material. The comparison of the activity and stability behavior of the three catalysts, as obtained from thin film rotating disk electrode measurements and identical location electron microscopy, is also extended to commercial materials and used as a basis for a discussion of general fuel cell catalyst design principles. Namely, the effects of particle size, inter-particle distance, certain support characteristics and thermal treatment on the catalyst performance and in particular the catalyst stability are evaluated. Based on our results, a set of design criteria for more stable and active Pt/C and Pt-alloy/C materials is suggested.

Very Low Temperature CO Oxidation over Colloidally Deposited Gold Nanoparticles on Mg(OH)2 and MgO

The colloidal deposition method was used to prepare Au/Mg(OH)(2) (0.7 wt % gold) catalysts with gold particle sizes between 1.5 to 5 nm which exhibited very high activity for CO oxidation with specific rates higher than 3.7 mol(CO) x h(-1) x g(Au)(-1) even at temperatures as low as -89 degrees C.

An Aqueous Emulsion Route to Synthesize Mesoporous Carbon Vesicles and Their Nanocomposites

[*] Prof. D. Y. Zhao, D. Gu, Dr. Y. H. Deng, D. Feng, Z. X. Wu, Y. Fang, J. J. Mao, Prof. B. Tu Department of Chemistry Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials and Advanced Materials Laboratory Fudan University Shanghai 200433 (P. R. China) E-mail: dyzhao@fudan.edu.cn H. Bongard, Prof. F. Schüth MPI für Kohlenforschung Kasier-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr (Germany)

How recombinant swollenin from Kluyveromyces lactis affects cellulosic substrates and accelerates their hydrolysis

BackgroundIn order to generate biofuels, insoluble cellulosic substrates are pretreated andsubsequently hydrolyzed with cellulases. One way to pretreat cellulose in a safeand environmentally friendly manner is to apply, under mild conditions,non-hydrolyzing proteins such as swollenin - naturally produced in low yields bythe fungus Trichoderma reesei. To yield sufficient swollenin forindustrial applications, the first aim of this study is to present a new way ofproducing recombinant swollenin. The main objective is to show how swolleninquantitatively affects relevant physical properties of cellulosic substrates andhow it affects subsequent hydrolysis.ResultsAfter expression in the yeast Kluyveromyces lactis, the resultingswollenin was purified. The adsorption parameters of the recombinant swolleninonto cellulose were quantified for the first time and were comparable to those ofindividual cellulases from T. reesei. Four different insoluble cellulosicsubstrates were then pretreated with swollenin. At first, it could bequalitatively shown by macroscopic evaluation and microscopy that swollenin causeddeagglomeration of bigger cellulose agglomerates as well as dispersion ofcellulose microfibrils (amorphogenesis). Afterwards, the effects of swollenin oncellulose particle size, maximum cellulase adsorption and cellulose crystallinitywere quantified. The pretreatment with swollenin resulted in a significantdecrease in particle size of the cellulosic substrates as well as in theircrystallinity, thereby substantially increasing maximum cellulase adsorption ontothese substrates. Subsequently, the pretreated cellulosic substrates werehydrolyzed with cellulases. Here, pretreatment of cellulosic substrates withswollenin, even in non-saturating concentrations, significantly accelerated thehydrolysis. By correlating particle size and crystallinity of the cellulosicsubstrates with initial hydrolysis rates, it could be shown that theswollenin-induced reduction in particle size and crystallinity resulted in highcellulose hydrolysis rates.ConclusionsRecombinant swollenin can be easily produced with the robust yeast K.lactis. Moreover, swollenin induces deagglomeration of celluloseagglomerates as well as amorphogenesis (decrystallization). For the first time,this study quantifies and elucidates in detail how swollenin affects differentcellulosic substrates and their hydrolysis.

Deposition of Aluminum–Magnesium Alloys from Electrolytes Containing Organo-Aluminum Complexes

Organo-aluminum compounds have been used for many years as electrolytes in the coating industry. In this communication the development of a galvanic process for generating aluminum-magnesium coatings from organometallic electrolyte systems is reported as well as results on physical properties like adhesion, ductility and corrosion resistance. (orig.)

Surface Casting Synthesis of Mesoporous Zirconia with a CMK-5-like Structure and High Surface Area

About 15 years ago, the Ryoo group described the synthesis of CMK-5, a material consisting of a hexagonal arrangement of carbon nanotubes. Extension of the surface casting synthesis to oxide compositions, however, was not possible so far, in spite of many attempts. Here it is demonstrated, that crystalline mesoporous hollow zirconia materials with very high surface areas up to 400 m2  g-1 , and in selected cases in the form of CMK-5-like, are indeed accessible via such a surface casting process. The key for the successful synthesis is an increased interaction between the silica hard template surface and the zirconia precursor species by using silanol group-rich mesoporous silica as a hard template. The surface areas of the obtained zirconias exceed those of conventionally hard-templated ones by a factor of two to three. The surface casting process seems to be applicable also to other oxide materials.

Dual‐Templated Cobalt Oxide for Photochemical Water Oxidation

Mesoporous Co3 O4 was prepared using a dual templating approach whereby mesopores inside SiO2 nanospheres, as well as the void spaces between the nanospheres, were used as templates. The effect of calcination temperature on the crystallinity, morphology, and textural parameters of the Co3 O4 replica was investigated. The catalytic activity of Co3 O4 for photochemical water oxidation in a [Ru(bpy)3 ](2+) [S2 O8 ](2-) system was evaluated. The Co3 O4 replica calcined at the lowest temperature (150 °C) exhibited the best performance as a result of the unique nanostructure and high surface area arising from the dual templating. The performance of Co3 O4 with highest surface area was further examined in electrochemical water oxidation. Superior activity over high temperature counterpart and decent stability was observed. Furthermore, CoO with identical morphology was prepared from Co3 O4 using an ethanol reduction method and a higher turnover-frequency number for photochemical water oxidation was obtained.

Zeolite Beta Formation from Clear Sols: Silicate Speciation, Particle Formation and Crystallization Monitored by Complementary Analysis Methods

The formation of silicate nanoaggregates (NAs) at the very early stages of precursor sols and zeolite beta crystallization from silicate nanoparticles (NPs) are investigated in detail using a combination of different analysis methods, including liquid-state 29 Si, 27 Al, 14 N, and 1 H NMR spectroscopy, mass spectrometry (MS), small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), and transmission electron microscopy at cryogenic temperatures (cryo-TEM). Prior to hydrothermal treatment, silicate NAs are observed if the Si/OH ratio in the reaction mixture is greater than 1. Condensation of oligomers within the NAs then generates NPs. Aluminum doped into the synthesis mixtures is located exclusively in the NPs, and is found exclusively in a state that is fourfold connected to silicate, favoring their condensation and aggregation. These results are in agreement with general trends observed for other systems. Silicate NAs are essential intermediates for zeolite formation and are generated by the aggregation of hydrated oligomers, aluminate, and templating cations. Subsequent further intra-nanoaggregate silicate condensation results in the formation of NPs. 1 H and 14 N liquid NMR as well as diffusion ordered spectroscopy (DOSY) experiments provide evidence for weakly restricted rotational and translational mobility of the organic template within NAs as a consequence of specific silicate-template interactions. NAs thus appear as key species in clear sols, and their presence in the precursor sol favors silicate condensation and further crystallization, promoted either by increasing the Si/OH ratio or by heating.