Jinping Wu

Enabling Prominent High‐Rate and Cycle Performances in One Lithium–Sulfur Battery: Designing Permselective Gateways for Li+ Transportation in Holey‐CNT/S Cathodes

A cathode material composed of h-CNT/S/ZrO2 is developed for lithium-sulfur batteries. By incorporating ZrO2 into the S-incorporated h-CNT, permselective gateways for free Li(+) transportation can be assembled at the mesopore openings, which deny the penetration of lithium polysulfides. At the ultrahigh rate of 10 C, the discharge capacity averages to be 870 mA h g(-1) within 200 cycles.

Hydrogen dissociative chemisorption and desorption on saturated subnano palladium clusters (Pdn, n = 2–9)

H2 sequential dissociative chemisorption on small palladium clusters was studied using density functional theory. The chosen clusters Pdn (n = 2-9) are of the lowest energy structures for each n. H2 dissociative chemisorption and subsequent H atom migration on the bare Pd clusters were found to be nearly barrierless. The dissociative chemisorption energy of H2 and the desorption energy of H atom in general decrease with the coverage of H atoms and thus the catalytic efficiency decreases as the H loading increases. These energies at full cluster saturation were identified and found to vary in small energy ranges regardless of cluster size. As H loading increases, the clusters gradually change their bonding from metallic character to covalent character. For the selected Pd clusters, the capacity to adsorb H atoms increases almost proportionally with cluster size; however, it was found that the capacity of Pd clusters to adsorb H atoms is, on average, substantially smaller than that of small Pt clusters, suggesting that the catalytic efficiency of Pt nanoparticles is superior to Pd nanoparticles in catalyzing dissociative chemisorption of H2 molecules.

A first principles study of water dissociation on small copper clusters

Water dissociation on copper is one of the rate-limiting steps in the water-gas-shift (WGS) reaction. Copper atoms dispersed evenly from freshly made catalyst segregate to form clusters under the WGS operating conditions. Using density functional theory, we have examined water adsorption and dissociation on the smallest stable 3-dimensional copper cluster, Cu(7). Water molecules are adsorbed on the cluster sequentially until full saturation at which no direct water-copper contact is sterically possible. The adsorption is driven mainly by the overlap between the p-orbital of O atom occupied by the lone pair and the 3d-orbitals of copper, from which a fractional charge is promoted to the 4s-orbital to accommodate the charge transfer from water. Water dissociation on the Cu(7) cluster was investigated at both low and high water coverage. It was found that water dissociation into OH and H is exothermic but is inherently a high temperature process at low coverage. At high coverage, the reaction becomes more exothermic with fast kinetics. In both cases, water can catalyze the reaction. It was found that direct dissociation of the OH species is endothermic with a significantly higher barrier at both low and high coverage. However, the OH species can readily react with another adjacent hydroxyl group to form an O adatom and water molecule. Our studies indicate that the basic chemical properties of water dissociative chemisorption may not change significantly with the size of small copper clusters. Similarities between water dissociation on copper clusters and on copper crystalline surfaces are discussed.

High-performance lithium/sulfur batteries by decorating CMK-3/S cathodes with DNA

Prohibiting lithium polysulfides from being dissolved to electrolyte is the most critical challenge for pursuing high-performance Li/S batteries. Taking full advantage of interactions between polysulfides and functional groups of third-party additives has been proven to be an efficient strategy. In the present work, we selected DNA to decorate CMK-3/S cathodes. The –PO and N– sites of the constituent deoxyribonucleotides of DNA are demonstrated to be capable of anchoring polysulfides through our DFT calculations. The experimental results show that adding a small amount of DNA into the CMK-3/S composite significantly improved the cyclic performance. In particular, with a moderate DNA loading rate, the DNA post-loading procedure resulted in a discharge capacity of 771 mA h g−1 at 0.1 C after 200 cycles (70.7% retention of the initial), which yielded slightly improved performance as compared to the DNA pre-loading procedure. The proposed DNA decorating scheme may provide an applicable technical solution for developing high-performance Li/S batteries.

First‐Principles Simulations of Conditions of Enhanced Adhesion Between Copper and TaN(111) Surfaces Using a Variety of Metallic Glue Materials

Particle aggregation and film agglomeration have been among the main technical hurdles for solid-state thin film development and have been observed in many semiconductor and catalytic systems. In heterogeneous catalysis, particle aggregation leads to reduction of effective surface area and degradation of catalytic performance. 8–10] On semiconductor surfaces, film agglomeration may give rise to electric short, electron migration, and device degradation. 11,12] Prevention of these effects presents a great technical challenge and has been one of the most active research areas in recent years. One approach towards reducing surface agglomeration is to insert a thin interfacial layer, often referred to as a “glue layer”, between the substrate and the adlayer of concern. Herein, we report three necessary fundamental conditions for a glue layer to be effective in promoting adhesion of a thin-film material to the substrate and to suppress agglomeration of the film at the interface. Copper agglomeration and adhesion enhancement on a TaN(111) surface, which was found to be the preferred orientation upon physical vapor deposition (PVD) growth, will serve as the model system to demonstrate the theoretical approach. Firstprinciples simulations were utilized to predict adhesion strength of various glue layer formulations. This approach allows us to make objective comparison of interaction energies between film interfaces and a set of performance criteria for material selection that augments empirically driven material selection processes, which have been largely trial-and-error in experiments to date. TaN has been used effectively as a barrier to prevent diffusion of the copper metal interconnect into the insulating dielectric and ultimately into the gate dielectric of CMOSbased transistors (CMOS = complementary metal oxide semiconductor). Atomic layer deposition (ALD) is a powerful thin-film deposition technique that provides atomistic control over deposition to support the continued scaling of the TaN barrier with a copper seed layer for advanced-generation CMOS devices. However, seed-layer copper agglomeration on the TaN surfaces has been a bottleneck in the development of this approach. Numerous attempts have been made to stabilize the copper thin film against agglomeration directly on the barrier with limited success. 21] Recently, Kim et al. proposed to insert a thin ruthenium layer between the copper film and the TaN substrate to enhance copper adhesion. The concept was also demonstrated for a Cu/WN interfacial system. Unfortunately, a Ru-based process is expensive, and thus its applications are limited. Herein, we show that first-principles simulations are capable of providing quantitative information to aid material selection to allow broad applications of glue-layer-based technology using ALD. The TaN(111) surface is described by a slab model containing four alternating layers of tantalum and nitrogen, with nitrogen on top (Figure 1). In between slabs, there is a

Force fields for metallic clusters and nanoparticles

Atomic force fields for simulating copper, silver, and gold clusters and nanoparticles are developed. Potential energy functions are obtained for both monatomic and binary metallic systems using an embedded atom method. Many cluster configurations of varying size and shape are used to constrain the parametrization for each system. Binding energies for these training clusters were computed using density functional theory (DFT) with the Perdew‐Wang exchange‐correlation functional in the generalized gradients approximation. Extensive testing shows that the many‐body potentials are able to reproduce the DFT energies for most of the structures that were included in the training set. The force fields were used to calculate surface energies, buk structures, and thermodynamic properties. The results are in good agreement with the DFT values and consistent with the available experimental data.

Hydrogen sequential dissociative chemisorption on Ni n(n = 2~9,13) clusters: comparison with Pt and Pd.

Hydrogen dissociative chemisorption and desorption on small lowest energy Nin clusters up to n = 13 as a function of H coverage was studied using density functional theory. H adsorption on the clusters was found to be preferentially at edge sites followed by 3-fold hollow sites and on-top sites. The minimum energy path calculations suggest that H2 dissociative chemisorption is both thermodynamically and kinetically favorable and the H atoms on the clusters are mobile. Calculations on the sequential H2 dissociative chemisorption on the clusters indicate that the edge sites are populated first and subsequently several on-top sites and hollow sites are also occupied upon full cluster saturation. In all cases, the average hydrogen capacity on Nin clusters is similar to that of Pdn clusters but considerably smaller than that of Ptn clusters. Comparison of hydrogen dissociative chemisorption energies and H desorption energies at full H-coverage among the Ni family clusters was made.

Weak Chemical Complexation of PH3 with Ionic Liquids

We present a combined theoretical and experimental study on weak chemical complexation between PH(3) and a few selected Cu(I)- and Al-based ionic liquids (ILs). PH(3) molecules were found to covalently bind with the cationic sites of the ILs. Effects of cations, anions, ion pairing, and solvents on the binding strength were systematically examined. The weak coordination of PH(3) on the ILs allows the PH(3) gas to be stored at near ambient conditions with a high capacity.

Force field for copper clusters and nanoparticles

An atomic force field for simulating copper clusters and nanoparticles is developed. More than 2000 cluster configurations of varying size and shape are used to constrain the parametrization of the copper force field. Binding energies for these training clusters were computed using density functional theory. Extensive testing shows that the copper force field is fast and reliable for near‐equilibrium structures of clusters, ranging from only a few atoms to large nanoparticles that approach bulk structure. Nonequilibrium dissociation and compression structures that are included in the training set are also well described by the force field. Implications for molecular dynamics simulations and extensions to other metallic and covalent systems are discussed.

Growth mechanism of curved Mg–Al–CO3 layered double hydroxide nanostructures in a one-pot assembly procedure under ambient pressure

We show that the amount of peroxide added is a governing factor, leading to the curved or amorphous morphologies of Mg–Al-LDH products in a reflux system under ambient pressure. A concerted growth mechanism is proposed to elucidate the formation of the unconventional nano-features of the products.