84 Search Results

Using ai-GCMC simulations, operando WAXS, and kinetics analysis, we found that the high-rate performance of Sb as an alloy anode in Na-ion batteries is due to the presence of an amorphous intermediate phase formed during sodiation and desodiation.

One step pore diffusion mechanism of lithium ion transport in the solid electrolyte interphase (SEI) layer with discrete inorganic components enables the fast lithium conduction without slow solid state diffusion process.

Ferroelectric Al_1-xSc_xN has raised much interest in recent years due to its unique ferroelectric properties and complementary metal oxide semiconductor back-end-of-line compatible processing temperatures. Potential applications in embedded nonvolatile memory, however, require ferroelectric materials to switch at relatively low voltages. One approach to achieving a lower switching voltage is to significantly reduce the Al_1-xSc_xN thickness. In this work, ferroelectric behavior in 5-27 nm films of sputter deposited Al_0.72Sc_0.28N has been studied. We find that the 10 kHz normalized coercive field increases from 4.4 to 7.3 MV/cm when reducing the film thickness from 27.1 to 5.4 nm, while over the samemore » thickness range, the characteristic breakdown field of a 12.5 μm radius capacitor increases from 8.3 to 12.1 MV/cm. In conclusion, the 5.4 nm film demonstrates ferroelectric switching at 5.5 V when excited with a 500 ns pulse and a switching speed of 60 ns.« less

Earth-abundant metals have recently been demonstrated as cheap catalyst alternatives to scarce noble metals for polyethylene hydrogenolysis. However, high methane selectivities hinder industrial feasibility. Herein, we demonstrate that low-temperature ex-situ reduction (350 °C) of coprecipitated nickel aluminate catalysts yields a methane selectivity of <5% at moderate polymer deconstruction (25–45%). A reduction temperature up to 550 °C increases the methane selectivity nearly sevenfold. Catalyst characterization (XRD, XAS, 27Al MAS NMR, H₂ TPR, XPS, and CO-IR) elucidates the complex process of Ni nanoparticle formation, and air-free XPS directly after reaction reveals tetrahedrally coordinated Ni²⁺ cations promote methane production. Metallic and the specificmore » cationic Ni appear responsible for hydrogenolysis of internal and terminal C–C scissions, respectively. A structure-methane selectivity relationship is discovered to guide the design of Ni-based catalysts with low methane generation. It paves the way for discovering other structure–property relations in plastics hydrogenolysis. These catalysts are also effective for polypropylene hydrogenolysis.« less

The use of nanoporous metals as catalysts has attracted significant interest in recent years. Their high‐curvature, nanoscale ligaments provide not only high surface area but also a high density of undercoordinated step edge and kink sites. However, their long‐term stability, especially at higher temperatures, is often limited by thermal coarsening and the associated loss of surface area. Herein, it is demonstrated that the nanoscale morphology of nanoporous Cu can be regenerated by applying oxidation/reduction cycles at 250 °C. Specifically, the morphological evolution and H ₂ dissociation activity of hierarchical nanoporous Cu catalysts doped with Ti during structural rearrangement triggered by oxidativemore » and reductive atmospheres at elevated temperatures are studied. In addition to coarsening of the structure at elevated temperatures, oxidation at 400 °C causes an expansion of the ligaments. Subsequent reduction at 400 °C leads to the formation of particles and a drop in the H ₂ dissociation activity compared the fresh catalyst. However, performing the redox cycle at 250 °C reverses coarsening and boosts the H ₂ dissociation activity for the hydrogen–deuterium (H ₂ –D ₂ ) reaction. Herein, the possibility to reverse coarsening is demonstrated, thereby mitigating the loss of activity frequently observed in nanoporous catalysts.« less

We report dynamical restructuring effects in free-standing Au_0.75Pd_0.25 nanoparticles occurring in gaseous environments at elevated temperatures. The freshly prepared sample was found to have a core–shell structure with a Pd-rich phase on the surface. The evolution of sample composition and morphology under exposure to 1 bar of pure gases, namely O₂, H₂, air, CO, and CO₂, at different temperatures was studied using in situ scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS). We observed sharper facets on the surface of the particles under O₂ or air at 400 °C. Small islands of Pd were present on the surface,more » although some Pd was redistributed inside the bulk when the temperature was increased under O₂. Subtle changes in surface roughness were noted when O₂ was substituted with H₂ at 400 °C, an observation correlated to density functional theory (DFT) calculations. The particles lost clean surface facets when CO was introduced at room temperature and at 200 °C. No substantial changes could be observed after exposure to CO₂ at 250 °C. The adsorption of CO molecules on the surface modifies the surface of the particles and decreases the facet prevalence. Furthermore, these in situ observations show how gases can induce subtle modification of the surface of nanocatalysts, potentially impacting their chemical properties.« less

Abstract Ruthenium (Ru) is the one of the most promising catalysts for polyolefin hydrogenolysis. Its performance varies widely with the support, but the reasons remain unknown. Here, we introduce a simple synthetic strategy (using ammonia as a modulator) to tune metal-support interactions and apply it to Ru deposited on titania (TiO ₂ ). We demonstrate that combining deuterium nuclear magnetic resonance spectroscopy with temperature variation and density functional theory can reveal the complex nature, binding strength, and H amount. H ₂ activation occurs heterolytically, leading to a hydride on Ru, an H ⁺ on the nearest oxygen, and a partiallymore » positively charged Ru. This leads to partial reduction of TiO ₂ and high coverages of H for spillover, showcasing a threefold increase in hydrogenolysis rates. This result points to the key role of the surface hydrogen coverage in improving hydrogenolysis catalyst performance.« less

Machine learning and artificial intelligence (ML/AI) are rapidly becoming an indispensable part of physics research, with applications ranging from theory and materials prediction to high-throughput data analysis. In parallel, the recent successes in applying ML/AI methods for autonomous systems from robotics through self-driving cars to organic and inorganic synthesis are generating enthusiasm for the potential of these techniques to enable automated and autonomous experiment in imaging. Here, we discuss recent progress in application of machine learning methods in scanning transmission electron microscopy and scanning probe microscopy, from applications such as data compression and exploratory data analysis to physics learning tomore » atomic fabrication.« less

We report catalyst surface area and wetting behavior are key factors in determining the performance of gas diffusion electrode (GDE) electrolyzers for electrochemical CO₂ reduction. In this work, we report the integration of sub-1 μm thick nanoporous gold (npAu) catalyst coatings into a large-area (25 cm²) zero-gap electrolyzer. The npAu coatings were prepared by magnetron sputtering (MS) of thin AgAu alloy films on the microporous carbon layer of a gas diffusion layer (GDL) followed by Ag leaching. Compared to MS Au films of the same thickness, npAu catalyst coatings enable higher Faradaic efficiencies and improved catalyst stability for CO₂-to-CO reductionmore » with Faradaic efficiencies of up to 88% at 100 mA/cm². For a 800 nm npAu coating, the device level energy efficiency for CO₂ to CO conversion reaches 45% (52% for CO + H₂) at 100 mA/cm² with a single pass CO₂ conversion efficiency of ~12%. Contact angle measurements reveal that npAu coatings provide a more hydrophobic electrode interface compared to MS Au coatings, suggesting that the more hydrophobic interfacial environment of npAu coatings helps mitigating electrode flooding which is associated with performance deterioration over time.« less

Here, we report the synthesis, optimization, and characterization of Co/SiO₂ for ethane nonoxidative dehydrogenation. Co/SiO₂ is synthesized via strong electrostatic adsorption using the widely available Co(NO₃)₂ as the precursor. We demonstrate that high-temperature pretreatment (900 °C) in an inert atmosphere can significantly enhance the initial activity of the Co/SiO₂ catalyst. X-ray absorption near-edge spectroscopy (XANES), temperature-programmed reduction (TPR), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) suggest that highly dispersed Co(II) clusters are more active than Co⁰ or CoO_x nanoparticles. Fourier transform infrared (FTIR) and isopropanol (IPA) temperature-programmed desorption and density functional theory (DFT) calculations suggest that high-temperature treatmentmore » significantly increases the density of active Lewis acid sites, possibly via surface dehydroxylation of the catalyst.« less