Marcus Rose

High-Rate Electrochemical Capacitors Based on Ordered Mesoporous Silicon Carbide-Derived Carbon

Microporous carbons, produced by selective etching of metal carbides in a chlorine-containing environment, offer narrow distribution of micropores and one of the highest specific capacitances reported when used in electrical double layer capacitors (EDLC) with organic electrolytes. Previously, the small micropores in these carbons served as an impediment to ion transport and limited the power storage characteristics of EDLC. Here we demonstrate, for the first time, how the preparation and application of templated carbide-derived carbon (CDC) can overcome the present limitations and show the route for dramatic performance enhancement. The ordered mesoporous channels in the produced CDC serve as ion-highways and allow for very fast ionic transport into the bulk of the CDC particles. The enhanced transport led to 85% capacitance retention at current densities up to approximately 20 A/g. The ordered mesopores in silicon carbide precursor also allow the produced CDC to exhibit a specific surface area up to 2430 m(2)/g and a specific capacitance up to 170 F/g when tested in 1 M tetraethylammonium tetrafluoroborate solution in acetonitrile, nearly doubling the previously reported values.

Hierarchical Micro- and Mesoporous Carbide-Derived Carbon as a High-Performance Electrode Material in Supercapacitors

Ordered mesoporous carbide-derived carbon (OM-CDC) materials produced by nanocasting of ordered mesoporous silica templates are characterized by a bimodal pore size distribution with a high ratio of micropores. The micropores result in outstanding adsorption capacities and the well-defined mesopores facilitate enhanced kinetics in adsorption processes. Here, for the first time, a systematic study is presented, in which the effects of synthesis temperature on the electrochemical performance of these materials in supercapacitors based on a 1 M aqueous solution of sulfuric acid and 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid are reported. Cyclic voltammetry shows the specific capacitance of the OM-CDC materials exceeds 200 F g(-1) in the aqueous electrolyte and 185 F g(-1) in the ionic liquid, when measured in a symmetric configuration in voltage ranges of up to 0.6 and 2 V, respectively. The ordered mesoporous channels in the produced OM-CDC materials serve as ion-highways and allow for very fast ionic transport into the bulk of the OM-CDC particles. At room temperature the enhanced ion transport leads to 75% and 90% of the capacitance retention at current densities in excess of ∼10 A g(-1) in ionic liquid and aqueous electrolytes, respectively. The supercapacitors based on 250-300 μm OM-CDC electrodes demonstrate an operating frequency of up to 7 Hz in aqueous electrolyte. The combination of high specific capacitance and outstanding rate capabilities of the OM-CDC materials is unmatched by state-of-the art activated carbons and strictly microporous CDC materials.

Isosorbide as a Renewable Platform chemical for Versatile ApplicationsuQuo Vadis

Isosorbide is a platform chemical of considerable importance for the future replacement of fossil resource-based products. Applications as monomers and building blocks for new polymers and functional materials, new organic solvents, for medical and pharmaceutical applications, and even as fuels or fuel additives are conceivable. The conversion of isosorbide to valuable derivatives by functionalization or substitution of the hydroxyl groups is difficult because of the different configurations of the 2- and 5-positions and the resulting different reactivity and steric hindrance of the two hydroxyl groups. Although a substantial amount of work has been published using exclusively the endo or exo derivatives isomannide and isoidide, respectively, as starting material, a considerable effort is still necessary to transfer and adapt these methods for the efficient conversion of isosorbide. This Minireview deals with all aspects of isosorbide chemistry, which includes its production by catalytic processes, special properties, and chemical transformations for its utilization in biogenic polymers and other applications of interest.

Hydrogels and aerogels from noble metal nanoparticles.

Aerogels are fine inorganic superstructures with enormously high porosity and are known to be exceptional materials with a variety of applications, for example in the area of catalysis. The chemistry of the aerogel synthesis originated from the pioneering work from the early 1930s and was further developed starting from the 1960s. Attractive catalytic, thermoresistant, piezoelectric, antiseptic, and many other properties of the aerogels originate from the unique combination of the specific properties of nanomaterials magnified by macroscale self-assembly. Currently, the most investigated materials that form fine aerogel superstructures are silica and other metal oxides together with their mixtures. Recently, the possibility of creating aerogels and even light-emitting monoliths with densities 500 times less than their bulk counterparts from colloidal quantum dots and clusters of metal chalcogenides has attracted attention. These developments may open opportunities in areas such as semiconductor technology, photocatalysis, optoelectronics, and photonics. Quite a number of different approaches have focused on modifying oxide-based aerogels (silica, titania, alumina, etc.) with metal nanoparticles (such as of platinum) to carry the catalytic properties from the metal 15] into the porous structures of the aerogels. 16,17] Fine mesoporous assemblies of catalytically active metal nanoparticles were also created by using artificial opals and fungi as templates. Other superstructural materials derived from metal nanoparticles include mesoporous platinum–carbon composites, gold nanoparticles interlinked with dithiols, necklace nanochains of hybrid palladium–lipid nanospheres, electrocatalytically active nanoporous platinum aggregates, foams, and highly ordered twoand three-dimensional supercrystals. The creation of non-supported metal aerogels has however not been reported to date. Recently, the formation of highly porous spherical aggregates (“supraspheres”) of several hundred nanometers in diameter, where nanoparticles from one or two different metals were cross-linked with dithiols, was reported. 31] The metal aerogels presented herein exhibit an average density two orders of magnitude lower than that of the reported foams. Their primary structural units match the size range of single nanoparticles (5–20 nm), which is an order of magnitude smaller than that of the self-assembled supraspheres. Moreover, in the present case, no chemical cross-linkers are involved in the self-assembly process. The formation of such noble-metal nanoparticle-based mesoporous monometallic and bimetallic aerogels is an important step towards self-supported monoliths with enormously high catalytically active surfaces. Considering that metal nanoparticles possess very specific optical properties owing to their pronounced surface plasmon resonance, aerogels from metal nanoparticles may also find future applications in nanophotonics, for example, as advanced optical sensors and ultrasensitive detectors. In terms of size, shape, and composition control, the synthesis of colloidal metallic nanoparticles is nowadays a well-developed research field. For gel formation, various methods of slow destabilization, developed previously for quantum-dot-based gels, were systematically applied to aqueous colloidal solutions of gold, silver, and platinum nanoparticles. Supercritical drying of the hydrogels with liquid CO2 finally produces aerogels. Aqueous colloidal metal solutions are normally very stable in the dilute as-prepared state (below ca. 10 m particle concentration). To gelate these sols, efficient destabilization is initiated by concentrating the sols (see the Supporting Information). Gel formation is achieved by, for example, the addition of ethanol or hydrogen peroxide to the concentrated colloids. Different morphologies of the gels can be obtained depending on the type and amount of destabilizer, and also on the metal colloid. Figure 1 shows scanning electron microscopy (SEM; A and B) and transmission electron microscopy (TEM) images (C and D) of an aerogel manufactured from platinum nanoparticles with the use of ethanol as [*] A.-K. Herrmann, M. Vogel, Dr. N. Gaponik, Prof. Dr. A. Eychm ller Physical Chemistry/Electrochemistry, TU Dresden 01062 Dresden (Germany) Fax: (+ 49)351-37164 E-mail: Alexander.eychmueller@chemie.tu-dresden.de Homepage: http://www.chm.tu-dresden.de/pc2/index.shtml

Cellulose-Based Sustainable Polymers: State of the Art and Future Trends

Nowadays, nearly all polymeric materials are produced from crude oil-derived monomers. With the steadily increasing demand for oil-based products and their decreasing availability in the near future, one of the main challenges of mankind is the replacement of crude oil as raw material by renewable resources such as biomass. So far, only a few polymers are available derived directly from cellulose as a main component of biomass by regeneration. On the other hand, a significant potential lies in the production of polymers from cellulose-derived monomers. A huge variety of different monomers is already available by convenient catalytic processes. This feature article focuses on the current status of mono- and resulting polymers derived either directly from cellulose processing and regeneration or by catalytic conversion to a number of monomers for the production of novel polymers and co-polymers.

Twin Polymerization at Spherical Hard Templates: An Approach to Size‐Adjustable Carbon Hollow Spheres with Micro‐ or Mesoporous Shells

Kitset hollow spheres: The combination of twin polymerization with hard templates makes hollow carbon spheres (HCSs) with tailored properties easily accessible. The thickness and pore texture of the HCS shells and also the diameter of the spherical cavity can be varied. The application potential of synthesized HCS is substantiated by an excellent cycling stability of lithium-sulfur batteries.

Nanoporous Polymers: Bridging the Gap between Molecular and Solid Catalysts?

The combination of the advantageous properties of molecular and solid catalysts is considered the “Holy Grail” in catalysis research. Great potential is provided by nanoporous polymers. Chemically well‐defined moieties in combination with a high stability render these materials suitable as catalyst supports for liquid‐phase and even aqueous‐phase catalytic processes, especially regarding the transition from fossil resources to renewable resources. In this Minireview, recent developments are summarized, covering the three main approaches: solid metal‐free organocatalysts, immobilized molecular catalyst species, and supported metal nanoparticles and clusters. Their potential is evaluated and the question as to whether nanoporous polymers can bridge the gap between homogeneous and heterogeneous catalysis is critically discussed.

New element organic frameworks viaSuzuki coupling with high adsorption capacity for hydrophobic molecules

We present new highly microporous element organic frameworks synthesized by the Pd catalyzed Suzuki coupling reaction. They show specific surface areas of up to 1380 m2 g−1 with a strong hydrophobic character. Thus, they are interesting for the adsorption of non-polar substances. By variation of the organic linkers, the modular concept of the materials in analogy to the metal–organic frameworks is demonstrated. The polymeric materials have thermal stability up to 573 K and show no decomposition in aqueous environment, allowing excellent handling and processing. They are accessible by a basic synthetic approach, and by their chemical and thermal stabilities they may provide adequate properties for applications in many fields, especially in adsorptive separation processes and storage of non-polar gases.

Platinum induced crosslinking of polycarbosilanes for the formation of highly porous CeO2/silicon oxycarbide catalysts

A new synthesis scheme for the formation of porous CeO2/Pt-polycarbosilane composites using inverse microemulsions is presented. Aqueous hexachloroplatinic acid was used as a hydrosilylation catalyst causing crosslinking of allyl groups in a liquid polycarbosilane (PCS). The resulting polymers are temperature stable and highly porous. The Pt catalyst content and post-treatment of the polymer can be used to adjust the porosity. For the first time hydrophobic polymers with specific surface areas up to 896 m2/g were obtained by catalytic crosslinking of polycarbosilanes. Ceria nanoparticles 2–3 nm in diameter are well dispersed in the PCS matrix as proven using high resolution electron microscopy. Porosity of the hydrophobic materials could be increased up to 992 m2/g by adding divinylbenzene in the oil phase. Pyrolyses at 1200–1500 °C and post-oxidative treatment at various temperatures produce porous ceramic structures with surface areas up to 423 m2/g. X-Ray diffration investigations show that the crystallinity of the SiC matrix can be controlled by the pyrolysis temperature. Post-oxidative treatments cause silicon oxycarbide formation. Structure and morphology of the polymeric and ceramic composites were investigated using 29Si MAS NMR, FESEM, FT-IR and EDX techniques. The temperature programmed oxidation (TPO) of methane shows a high catalytic activity of CeO2/Pt-SiC(O) composites lowering the onset in the TPO to 400–500 °C.

A new route to porous monolithic organic frameworks via cyclotrimerization

Cyclotrimerization of bifunctional acetyl compounds is used to obtain highly porous organic frameworks. Syntheses in solution induced by silicon tetrachloride result in highly disperse powders while syntheses in molten 4-toluene sulfonic acid result in polymeric monoliths with a hierarchical pore structure containing micro- and macropores allowing for direct impregnation of textiles with a porous polymer. The materials show specific BET surface areas up to 895 m2 g−1 and large pore volume (1.99 cm3 g−1) combined with a highly hydrophobic character. The amorphous materials are thermally stable below 300 °C in air and show no decomposition effects in aqueous environment. These outstanding properties in combination with the opportunity to generate shapes of any kind desired for an application render the materials as highly promising for application in air filtration systems and individual protection, as well as gas storage and separation.