There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

Electrolytes and interphases in Li-ion batteries and beyond.

Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal–support interaction, and metal–reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results o...

Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles.

Supercapacitors have drawn considerable attention in recent years due to their high specific power, long cycle life, and ability to bridge the power/energy gap between conventional capacitors and batteries/fuel cells. Nanostructured electrode materials have demonstrated superior electrochemical properties in producing high-performance supercapacitors. In this review article, we describe the recent progress and advances in designing nanostructured supercapacitor electrode materials based on various dimensions ranging from zero to three. We highlight the effect of nanostructures on the properties of supercapacitors including specific capacitance, rate capability and cycle stability, which may serve as a guideline for the next generation of supercapacitor electrode design.

/pdf/supercapacitor-electrode-materials-nanostructures-from-0-to-3zlm6qeqf5.pdf

Supercapacitor electrode materials: nanostructures from 0 to 3 dimensions

Novel nanotechnologies have allowed great improvements in the syn-thesis of catalysts with well-controlled size, shape, and surface properties. Transition metal nanostructures with specific sizes and shapes, for instance, have shown great promise as catalysts with high selectivities and relative ease of recycling. Researchers have already demonstrated new selective catalysis with solution-dispersed or supported-metal nanocatalysts, in some cases applied to new types of reactions. Several challenges remain, however, particularly in improving the structural stability of the catalytic active phase. Core–shell nanostructures are nanoparticles encapsulated and protected by an outer shell that isolates the nanoparticles and prevents their migration and coalescence during the catalytic reactions. The synthesis and characterization of effective core–shell catalysts has been at the center of our research efforts and is the focus of this Account.Efficient core–shell catalysts require porous shells that allow free a...

Core–Shell Nanostructured Catalysts

In real life applications, supercapacitors (SCs) often can only be used as part of a hybrid system together with other high energy storage devices due to their relatively lower energy density in comparison to other types of energy storage devices such as batteries and fuel cells. Increasing the energy density of SCs will have a huge impact on the development of future energy storage devices by broadening the area of application for SCs. Here, we report a simple and scalable way of preparing a three-dimensional (3D) sub-5 nm hydrous ruthenium oxide (RuO2) anchored graphene and CNT hybrid foam (RGM) architecture for high-performance supercapacitor electrodes. This RGM architecture demonstrates a novel graphene foam conformally covered with hybrid networks of RuO2 nanoparticles and anchored CNTs. SCs based on RGM show superior gravimetric and per-area capacitive performance (specific capacitance: 502.78 F g−1, areal capacitance: 1.11 F cm−2) which leads to an exceptionally high energy density of 39.28 Wh kg−1 and power density of 128.01 kW kg−1. The electrochemical stability, excellent capacitive performance, and the ease of preparation suggest this RGM system is promising for future energy storage applications.

https://cyberleninka.org/article/n/529338.pdf

Hydrous Ruthenium Oxide Nanoparticles Anchored to Graphene and Carbon Nanotube Hybrid Foam for Supercapacitors

A catalytic process for the selective formation of cis olefins would help minimize the production of unhealthy trans fats during the partial hydrogenation of edible oils. Here we report on the design of such a process on the basis of studies with model systems. Temperature programmed desorption data on single crystals showed that the isomerization of trans olefins to their cis counterparts is promoted by (111) facets of platinum, and that such selectivity is reversed on more open surfaces. Quantum mechanics calculations suggested that the extra stability of cis olefins seen on hydrogen-saturated Pt(111) surfaces may be due to a lesser degree of surface reconstruction, a factor found to be significant in the adsorption on close-packed platinum surfaces. Kinetic data using catalysts made out of dispersed tetrahedral Pt nanoparticles corroborated the selective promotion of the trans-to-cis isomerization on the (111) facets of the metal. Our work provides an example for how catalytic selectivity may be controlled by controlling the shape of the catalytic particles.

Tuning selectivity in catalysis by controlling particle shape

The crystallization of nanometer-scale materials during high-temperature calcination can be controlled by a thin layer of surface coating. Here, a novel silica-protected calcination process for preparing mesoporous hollow TiO2 nanostructures with a high surface area and a controllable crystallinity is presented. This method involves the preparation of uniform silica colloidal templates, sequential deposition of TiO2 and then SiO2 layers through sol–gel processes, calcination to transform amorphous TiO2 to crystalline anatase, and finally etching of the inner and outer silica to produce mesoporous anatase TiO2 shells. The silica-protected calcination step allows crystallization of the amorphous TiO2 layer into anatase nanocrystals, while simultaneously limiting the growth of anatase grains to within several nanometers, eventually producing mesoporous anatase shells with a high surface area (∼311 m2 g−1) and good water dispersibility upon chemical etching of the silica. When used as photocatalysts for the degradation of Rhodamine B under UV irradiation, the as-synthesized mesoporous anatase shells show significantly enhanced photocatalytic activity with greater enhancement for samples calcined at higher temperatures thanks to their improved crystallinity.

Mesoporous Anatase Titania Hollow Nanostructures though Silica-Protected Calcination

Traditionally, gold has been considered a fairly inert metal. However, Bond and Haruta challenged that view a few decades ago by showing that, when dispersed as small nanoparticles, gold can catalyze several hydrogenation and oxidation reactions. Many reports have been published since on the usefulness of gold catalysis for the promotion of a wide variety of reactions. 5] Unfortunately, this has not translated into many practical applications. One of the main limitations has been that supported gold catalysts are often unstable under reaction conditions: they tend to sinter and grow into larger particles, and that leads to the loss of the unique properties seen in the original nanoparticles. Although several schemes have been advanced to address this shortcoming, no satisfactory solution has been found yet. This is particularly true for the case of gold catalysts dispersed on titania, a support of interest because of its synergistic effect in further facilitating the promotion of oxidation 8] and photocatalytic reactions. Here we report on the preparation and characterization of a Au@TiO2 catalyst with a new yolk@shell nanostructure. The new catalyst shows an activity comparable to that of other more conventional Au/TiO2 catalysts but an increased stability against sintering. The growth of titania hollow shells encapsulating metal nanoparticles is more difficult than with silica, the material with which most reported yolk@shell nanostructures have been made to date. However, we have now accomplished this by following a sol–gel-based templating protocol where citrate-stabilized gold nanoparticles are first coated with a sacrificial layer of silica using tetraethyl orthosilicate (TEOS). An outer shell of titania is then grown on top using tetrabutyl titanate (TBOT), and the silica etched away using an aqueous solution of NaOH. 13] The size of the void space inside the titania shells can be controlled by the amount of TEOS used during the growth of the silica layer, and the thickness of the shell by repeating the TBOT sol–gel step multiple times. Figure 1a,c displays typical transmission electron microscopy (TEM) images of the Au@TiO2 yolk@ shell nanostructure used herein, which consist of gold nano-

Ilkeun Lee

Papers

Core–Shell Nanostructured Catalysts

Hydrous Ruthenium Oxide Nanoparticles Anchored to Graphene and Carbon Nanotube Hybrid Foam for Supercapacitors

Tuning selectivity in catalysis by controlling particle shape

Mesoporous Anatase Titania Hollow Nanostructures though Silica-Protected Calcination

A Yolk@Shell Nanoarchitecture for Au/TiO2 Catalysts