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

Li-ion battery materials: present and future

The family of 2D transition metal carbides, carbonitrides and nitrides (collectively referred to as MXenes) has expanded rapidly since the discovery of Ti3C2 in 2011. The materials reported so far always have surface terminations, such as hydroxyl, oxygen or fluorine, which impart hydrophilicity to their surfaces. About 20 different MXenes have been synthesized, and the structures and properties of dozens more have been theoretically predicted. The availability of solid solutions, the control of surface terminations and a recent discovery of multi-transition-metal layered MXenes offer the potential for synthesis of many new structures. The versatile chemistry of MXenes allows the tuning of properties for applications including energy storage, electromagnetic interference shielding, reinforcement for composites, water purification, gas- and biosensors, lubrication, and photo-, electro- and chemical catalysis. Attractive electronic, optical, plasmonic and thermoelectric properties have also been shown. In this Review, we present the synthesis, structure and properties of MXenes, as well as their energy storage and related applications, and an outlook for future research. More than twenty 2D carbides, nitrides and carbonitrides of transition metals (MXenes) have been synthesized and studied, and dozens more predicted to exist. Highly electrically conductive MXenes show promise in electrical energy storage, electromagnetic interference shielding, electrocatalysis, plasmonics and other applications.

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2D metal carbides and nitrides (MXenes) for energy storage

Worldwide commercial interest in carbon nanotubes (CNTs) is reflected in a production capacity that presently exceeds several thousand tons per year. Currently, bulk CNT powders are incorporated in diverse commercial products ranging from rechargeable batteries, automotive parts, and sporting goods to boat hulls and water filters. Advances in CNT synthesis, purification, and chemical modification are enabling integration of CNTs in thin-film electronics and large-area coatings. Although not yet providing compelling mechanical strength or electrical or thermal conductivities for many applications, CNT yarns and sheets already have promising performance for applications including supercapacitors, actuators, and lightweight electromagnetic shields.

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Carbon Nanotubes: Present and Future Commercial Applications

A fundamental change has been achieved in understanding surface electrochemistry due to the profound knowledge of the nature of electrocatalytic processes accumulated over the past several decades and to the recent technological advances in spectroscopy and high resolution imaging. Nowadays one can preferably design electrocatalysts based on the deep theoretical knowledge of electronic structures, via computer-guided engineering of the surface and (electro)chemical properties of materials, followed by the synthesis of practical materials with high performance for specific reactions. This review provides insights into both theoretical and experimental electrochemistry toward a better understanding of a series of key clean energy conversion reactions including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). The emphasis of this review is on the origin of the electrocatalytic activity of nanostructured catalysts toward the aforementioned reactions by correlating the apparent electrode performance with their intrinsic electrochemical properties. Also, a rational design of electrocatalysts is proposed starting from the most fundamental aspects of the electronic structure engineering to a more practical level of nanotechnological fabrication.

Design of electrocatalysts for oxygen- and hydrogen-involving energy conversion reactions

http://www.chemeng.tsinghua.edu.cn/scholars/zhangqiang/Carbon_2010-Layered%20double%20hydroxides%20as%20catalysts%20for%20the%20efficient%20growth%20of%20high%20quality%20single-walled%20carbon%20nanotubes%20in%20a%20fluidized%20bed%20reactor.pdf

Layered double hydroxides as catalysts for the efficient growth of high quality single-walled carbon nanotubes in a fluidized bed reactor

Improvement of oil adsorption performance by a sponge-like natural vermiculite-carbon nanotube hybrid

The arrangement and construction of 1D carbon nanotubes (CNTs) into frameworks with two or more levels of structures is an essential step to demonstrate their intrinsic properties and promising applications for energy storage. Single-walled CNTs (SWCNTs) are considered to have more excellent properties compared with multiwalled CNTs (MWCNTs), however, how to appropriately use SWCNTs as building blocks for nanocomposite electrodes is not well understood. Here, a composite cathode containing SWCNT@S coaxial nanocables for Li-S battery is fabricated by a facile melt-diffusion strategy. Beneficial from its sp2 carbon nanostructure, higher specific surface area, larger aspect ratio, and interconnected electron pathway, the SWCNT@S cathode have reversible capacities of 676, 441 and 311 mAh g−1 for the first discharging at 0.5 C, 100th discharging at 1.0 C, and discharging at 10.0 C, respectively. These capacities are much higher than the corresponding capacities of the MWCNT@S cathode. By introducing polyethylene glycol (PEG) as a physical barrier to trap the highly polar polysulfide species, the PEG modified SWCNT@S cathode afforded improved reversible capacities. The cycling stability of the reversible capacities is expected to be further improved. The SWCNTs can serve as scaffolds for Li-S battery with much improved energy storage performance.

Composite Cathodes Containing SWCNT@S Coaxial Nanocables: Facile Synthesis, Surface Modification, and Enhanced Performance for Li‐Ion Storage

Super tough carbon nanotube (CNT) reinforced nanocomposites require both the unique interaction and effective stress transfer between CNTs and polymer chains. When CNT reinforced nanocomposites are stretched, the crack interfaces are usually bridged by CNTs, and energy can be absorbed during deformation before fracture and bring high toughness. However, developing super-tough CNT/polymer nanocomposites which can withstand high matrix deformation yet exploit the superior strength of CNTs is still a great challenge. In this contribution, an ultra-tough CNT/polyimide (PI) nanocomposite was fabricated by a facile in situ polymerization. Super-long vertically aligned CNTs were dispersed into N,N-dimethylacetamide, which is the feedstock for in situ PI polymerization. A long-CNT-induced three-dimensional, continuous, and heterogeneous network is formed to toughen the nanocomposites. By incorporating 0.27 wt% CNTs into a PI matrix, the tensile strength and elongation at break of the nanocomposites reached 156.4 MPa and 140%, respectively, which are 90% and 250% increased compared with the values of pristine PI. Thus, the toughness of the nanocomposites improved 470% and approached 127.4 J g−1, well exceeding state-of-the-art tough materials. The reinforcement mechanism reveals that robust tapered fibrils are formed around high-aspect-ratio CNTs to facilitate energy dissipation and enhance the energy absorbing capability. The length of CNTs and the interfacial bonding are important to initiate long-range creep and form robust heterogeneous tapered fibrils to toughen the nanocomposites. The CNT/PI composite film with high toughness, much improved electrical conductivity, as well as high thermal stability, and transparency, broadened their advanced applications in aerospace, aviation, buildings, bulletproof vests, and so on.

Meng-Qiang Zhao

Papers

Layered double hydroxides as catalysts for the efficient growth of high quality single-walled carbon nanotubes in a fluidized bed reactor

Improvement of oil adsorption performance by a sponge-like natural vermiculite-carbon nanotube hybrid

Composite Cathodes Containing SWCNT@S Coaxial Nanocables: Facile Synthesis, Surface Modification, and Enhanced Performance for Li‐Ion Storage

Dramatic enhancements in toughness of polyimide nanocomposite via long-CNT-induced long-range creep

Resilient aligned carbon nanotube/graphene sandwiches for robust mechanical energy storage