Constrained C2 adsorbate orientation enables CO-to-acetate electroreduction.

The carbon dioxide and carbon monoxide electroreduction reactions, when powered using low-carbon electricity, offer pathways to the decarbonization of chemical manufacture1,2. Copper (Cu) is relied on today for carbon-carbon coupling, in which it produces mixtures of more than ten C2+ chemicals3-6: a long-standing challenge lies in achieving selectivity to a single principal C2+ product7-9. Acetate is one such C2 compound on the path to the large but fossil-derived acetic acid market. Here we pursued dispersing a low concentration of Cu atoms in a host metal to favour the stabilization of ketenes10-chemical intermediates that are bound in monodentate fashion to the electrocatalyst. We synthesize Cu-in-Ag dilute (about 1 atomic per cent of Cu) alloy materials that we find to be highly selective for acetate electrosynthesis from CO at high *CO coverage, implemented at 10 atm pressure. Operando X-ray absorption spectroscopy indicates in situ-generated Cu clusters consisting of <4 atoms as active sites. We report a 12:1 ratio, an order of magnitude increase compared to the best previous reports, in the selectivity for acetate relative to all other products observed from the carbon monoxide electroreduction reaction. Combining catalyst design and reactor engineering, we achieve a CO-to-acetate Faradaic efficiency of 91% and report a Faradaic efficiency of 85% with an 820-h operating time. High selectivity benefits energy efficiency and downstream separation across all carbon-based electrochemical transformations, highlighting the importance of maximizing the Faradaic efficiency towards a single C2+ product11.

Open-channel metal particle superlattices.

Although tremendous advances have been made in preparing porous crystals from molecular precursors1,2, there are no general ways of designing and making topologically diversified porous colloidal crystals over the 10-1,000 nm length scale. Control over porosity in this size range would enable the tailoring of molecular absorption and storage, separation, chemical sensing, catalytic and optical properties of such materials. Here, a universal approach for synthesizing metallic open-channel superlattices with pores of 10 to 1,000 nm from DNA-modified hollow colloidal nanoparticles (NPs) is reported. By tuning hollow NP geometry and DNA design, one can adjust crystal pore geometry (pore size and shape) and channel topology (the way in which pores are interconnected). The assembly of hollow NPs is driven by edge-to-edge rather than face-to-face DNA-DNA interactions. Two new design rules describing this assembly regime emerge from these studies and are then used to synthesize 12 open-channel superlattices with control over crystal symmetry, channel geometry and topology. The open channels can be selectively occupied by guests of the appropriate size and that are modified with complementary DNA (for example, Au NPs).

Uncovering the predictive pathways of lithium and sodium interchange in layered oxides.

Ion exchange is a powerful method to access metastable materials with advanced functionalities for energy storage applications. However, high concentrations and unfavourably large excesses of lithium are always used for synthesizing lithium cathodes from parent sodium material, and the reaction pathways remain elusive. Here, using layered oxides as model materials, we demonstrate that vacancy level and its corresponding lithium preference are critical in determining the accessible and inaccessible ion exchange pathways. Taking advantage of the strong lithium preference at the right vacancy level, we establish predictive compositional and structural evolution at extremely dilute and low excess lithium based on the phase equilibrium between Li0.94CoO2 and Na0.48CoO2. Such phase separation behaviour is general in both surface reaction-limited and diffusion-limited exchange conditions and is accomplished with the charge redistribution on transition metals. Guided by this understanding, we demonstrate the synthesis of NayCoO2 from the parent LixCoO2 and the synthesis of Li0.94CoO2 from NayCoO2 at 1-1,000 Li/Na (molar ratio) with an electrochemical assisted ion exchange method by mitigating the kinetic barriers. Our study opens new opportunities for ion exchange in predictive synthesis and separation applications.

Uncovering the crystal defects within aragonite CaCO3.

Knowledge of deformation mechanisms in aragonite, one of the three crystalline polymorphs of CaCO3, is essential to understand the overall excellent mechanical performance of nacres. Dislocation slip and deformation twinning were claimed previously as plasticity carriers in aragonite, but crystallographic features of dislocations and twins have been poorly understood. Here, utilizing various transmission electron microscopy techniques, we reveal the atomic structures of twins, partial dislocations, and associated stacking faults. Combining a topological model and density functional theory calculations, we identify complete twin elements, characters of twinning disconnection, and the corresponding twin shear angle (∼8.8°) and rationalize unique partial dislocations as well. Additionally, we reveal an unreported potential energy dissipation mode within aragonite, namely, the formation of nanograins via the pile-up of partial dislocations. Based on the microstructural comparisons of biogenic and abiotic aragonite, we find that the crystallographic features of twins are the same. However, the twin density is much lower in abiotic aragonite due to the vastly different crystallization conditions, which in turn are likely due to the absence of organics, high temperature and pressure differences, the variation in inorganic impurities, or a combination thereof. Our findings enrich the knowledge of intrinsic crystal defects that accommodate plastic deformation in aragonite and provide insights into designing bioengineering materials with better strength and toughness.

Laser Precise Synthesis of Oxidation-Free High-Entropy Alloy Nanoparticle Libraries.

High-entropy alloy nanoparticles (HEA-NPs) show exceptional properties and great potential as a new generation of functional materials, yet a universal and facile synthetic strategy in air toward nonoxidized and precisely controlled composition remains a huge challenge. Here we provide a laser scribing method to prepare single-phase solid solution HEA-NPs libraries in air with tunable composition at the atomic level, taking advantage of the laser-induced metastable thermodynamics and substrate-assisted confinement effect. The three-dimensional porous graphene substrate functions as a microreactor during the fast heating/cooling process, which is conductive to the generation of the pure alloy phase by effectively blocking the binding of oxygen and metals, but is also beneficial for realizing accurate composition control via microstructure confinement-endowed favorable vapor pressure. Furthermore, by combining an active learning approach based on an adaptive design strategy, we discover an optimal composition of quinary HEA-NP catalysts with an ultralow overpotential for Li-CO2 batteries. This method provides a simple, fast, and universal in-air route toward the controllable synthesis of HEA-NPs, potentially integrated with machine learning to accelerate the research on HEAs.

Implications and Optimization of Domain Structures in IV-VI High-Entropy Thermoelectric Materials.

High-entropy semiconductors are now an important class of materials widely investigated for thermoelectric applications. Understanding the impact of chemical and structural heterogeneity on transport properties in these compositionally complex systems is essential for thermoelectric design. In this work, we uncover the polar domain structures in the high-entropy PbGeSnSe1.5Te1.5 system and assess their impact on thermoelectric properties. We found that polar domains induced by crystal symmetry breaking give rise to well-structured alternating strain fields. These fields effectively disrupt phonon propagation and suppress the thermal conductivity. We demonstrate that the polar domain structures can be modulated by tuning crystal symmetry through entropy engineering in PbGeSnAgxSbxSe1.5+xTe1.5+x. Incremental increases in the entropy enhance the crystal symmetry of the system, which suppresses domain formation and loses its efficacy in suppressing phonon propagation. As a result, the room-temperature lattice thermal conductivity increases from κL = 0.63 Wm-1 K-1 (x = 0) to 0.79 Wm-1 K-1 (x = 0.10). In the meantime, the increase in crystal symmetry, however, leads to enhanced valley degeneracy and improves the weighted mobility from µw = 29.6 cm2 V-1 s-1 (x = 0) to 35.8 cm2 V-1 s-1 (x = 0.10). As such, optimal thermoelectric performance can be achieved through entropy engineering by balancing weighted mobility and lattice thermal conductivity. This work, for the first time, studies the impact of polar domain structures on thermoelectric properties, and the developed understanding of the intricate interplay between crystal symmetry, polar domains, and transport properties, along with the impact of entropy control, provides valuable insights into designing GeTe-based high-entropy thermoelectrics.

Trapping Layers Prevent Dopant Segregation and Enable Remote Doping of Templated Self-Assembled InGaAs Nanowires.

Selective area epitaxy is a promising approach to define nanowire networks for topological quantum computing. However, it is challenging to concurrently engineer nanowire morphology, for carrier confinement, and precision doping, to tune carrier density. We report a strategy to promote Si dopant incorporation and suppress dopant diffusion in remote doped InGaAs nanowires templated by GaAs nanomembrane networks. Growth of a dilute AlGaAs layer following doping of the GaAs nanomembrane induces incorporation of Si that otherwise segregates to the growth surface, enabling precise control of the spacing between the Si donors and the undoped InGaAs channel; a simple model captures the influence of Al on the Si incorporation rate. Finite element modeling confirms that a high electron density is produced in the channel.

Self-Assembled Homopolymeric Spherulites from Small Molecules in Solution.

Polymeric spherulites are typically formed by melt crystallization: spherulitic growth in solution is rare and requires complex polymers and dilute solutions. Here, we report the mild and unique formation of luminescent spherulites at room temperature via the simple molecule benzene-1,4-dithiol (BDT). Specifically, BDT polymerized into oligomers (PBDT) via disulfide bonds and assembled into uniform supramolecular nanoparticles in aqueous buffer; these nanoparticles were then dissolved back into PBDT in a good solvent (i.e., dimethylformamide) and underwent chain elongation to form spherulites (rPBDT) in 10 min. The spherulite geometry was modulated by changing the PBDT concentration and reaction time. Due to the step-growth polymerization and reorganization of PBDT, these spherulites not only exhibited robust structure but also showed broad clusterization-triggered emission. The biocompatibility and efficient cellular uptake of the spherulites further underscore their value as traceable drug carriers. This system provides a new pathway for designing versatile superstructures with value for hierarchical assembly of small molecules into a complicated biological system.

Unraveling the Role of Entropy in Thermoelectrics: Entropy-Stabilized Quintuple Rock Salt PbGeSnCdxTe3+x.

Entropy-engineered materials are garnering considerable attention owing to their excellent mechanical and transport properties, such as their high thermoelectric performance. However, understanding the effect of entropy on thermoelectrics remains a challenge. In this study, we used the PbGeSnCdxTe3+x family as a model system to systematically investigate the impact of entropy engineering on its crystal structure, microstructure evolution, and transport behavior. We observed that PbGeSnTe3 crystallizes in a rhombohedral structure at room temperature with complex domain structures and transforms into a high-temperature cubic structure at ∼373 K. By alloying CdTe with PbGeSnTe3, the increased configurational entropy lowers the phase-transition temperature and stabilizes PbGeSnCdxTe3+x in the cubic structure at room temperature, and the domain structures vanish accordingly. The high-entropy effect results in increased atomic disorder and consequently a low lattice thermal conductivity of 0.76 W m-1 K-1 in the material owing to enhanced phonon scattering. Notably, the increased crystal symmetry is conducive to band convergence, which results in a high-power factor of 22.4 µW cm-1 K-1. As a collective consequence of these factors, a maximum ZT of 1.63 at 875 K and an average ZT of 1.02 in the temperature range of 300-875 K were obtained for PbGeSnCd0.08Te3.08. This study highlights that the high-entropy effect can induce a complex microstructure and band structure evolution in materials, which offers a new route for the search for high-performance thermoelectrics in entropy-engineered materials.

Effects of the Encapsulation Membrane in Operando Scanning Transmission Electron Microscopy.

Nanoscale tailoring of catalytic materials and Li-battery alternatives has elevated the importance of in situ gas-phase electron microscopy. Such advanced techniques are often performed using an environmental cell inserted into a conventional S/TEM setup, as this method facilitates concurrent electrochemical and temperature stimulations in a convenient and cost-effective manner. However, these cells are made by encapsulating gas between two insulating membranes, which introduces additional electron scattering. We have evaluated strengths and limitations of the gas-phase E-cell S/TEM technique, both experimentally and through simulations, across a variety of practical parameters. We reveal the degradation of image quality in an E-cell setup from various components and explore opportunities to improve imaging quality through intelligent choice of experimental parameters. Our results underscore the benefits of using an E-cell STEM technique, due to its versatility and excellent ability to suppress the exotic contributions from the membrane device.

Ingrained: An Automated Framework for Fusing Atomic-Scale Image Simulations into Experiments.

To fully leverage the power of image simulation to corroborate and explain patterns and structures in atomic resolution microscopy, an initial correspondence between the simulation and experimental image must be established at the outset of further high accuracy simulations or calculations. Furthermore, if simulation is to be used in context of highly automated processes or high-throughput optimization, the process of finding this correspondence itself must be automated. In this work, "ingrained," an open-source automation framework which solves for this correspondence and fuses atomic resolution image simulations into the experimental images to which they correspond, is introduced. Herein, the overall "ingrained" workflow, focusing on its application to interface structure approximations, and the development of an experimentally rationalized forward model for scanning tunneling microscopy simulation are described.

Bulk Nanostructured Metal from Multiply-Twinned Nanowires.

Using chemically synthesized silver nanowires with 5-fold twinning planes as a model system, a bottom-up process to generate a bulk nanostructured metal has been demonstrated. Although the nanowires would be shortened and deformed during densification, they are chosen as a model system because they are currently the most scalable and convenient way to obtain Ag particles with high twinning densities. Direct cold pressing of a silver nanowire filter cake did not generate a sufficiently cohesive sample, while hot pressing at 190 °C for 8 h resulted in extensive sintering, eliminating the nanowire morphology. Copper was then electroplated on the silver nanowires as a binder and filler to increase the densification upon hot pressing; despite nonuniform plating across the thickness of the filter cake, the thermal stability of the nanowires was increased, allowing hot pressing at 390 °C. Finally, a uniform copper coating on silver nanowires was achieved by electroless plating, leading to cohesive bulk metal after hot pressing.

Two-Dimensional Pd Rafts Confined in Copper Nanosheets for Selective Semihydrogenation of Acetylene.

The development of highly selective and active catalysts to catalyze an industrially important semihydrogenation reaction remains an open challenge. Here, we report the design of a bimetallic Pd/Cu(111) catalyst with Pd rafts confined in a Cu nanosheet, which exhibits desirable catalytic performance for acetylene semihydrogenation to ethylene with the selectivity of >90%. Theory calculations show that Pd atoms replacing neighboring Cu atoms in Cu(111) can improve the catalytic activity by reducing the energy barrier of the semihydrogenation reaction, as compared to unsubstituted Cu(111), and can improve the selectivity by weakening the adsorption of C2H4, as compared to a Pd(111) surface. The presence of Pd rafts confined in Cu nanosheets effectively turns on Cu nanosheets for semihydrogenation of acetylene with high activity and selectivity under mild reaction conditions. This work offers a well-defined nanostructured Pd/Cu(111) model catalyst that bridges the pressure and materials' gap between surface-science catalysis and practical catalysis.

Degeneration Behavior of Cu Nanowires under Carbon Dioxide Environment: An In Situ/Operando Study.

Copper (Cu) is a catalyst broadly used in industry for hydrogenation of carbon dioxide, which has broad implications for environmental sustainability. An accurate understanding of the degeneration behavior of Cu catalysts under operando conditions is critical for uncovering the failure mechanism of catalysts and designing novel ones with optimized performance. Despite the widespread use of these materials, their failure mechanisms are not well understood because conventional characterization techniques lack the necessary time and spatial resolution to capture these complex behaviors. In order to overcome these challenges, we carried out transmission electron microscopy (TEM) with a specialized in situ gas environmental holder, which allows us to unravel the dynamic behavior of the Cu nanowires (NWs) in operando. The failure process of these nanoscale Cu catalysts under CO2 atmosphere were tracked and further rationalized based on our numerical modeling using phase-field methods.

Revealing High-Temperature Reduction Dynamics of High-Entropy Alloy Nanoparticles via In Situ Transmission Electron Microscopy.

Understanding the behavior of high-entropy alloy (HEA) materials under hydrogen (H2) environment is of utmost importance for their promising applications in structural materials, catalysis, and energy-related reactions. Herein, the reduction behavior of oxidized FeCoNiCuPt HEA nanoparticles (NPs) in atmospheric pressure H2 environment was investigated by in situ gas-cell transmission electron microscopy (TEM). The reduction reaction front was maintained at the external surface of the oxide. During reduction, the oxide layer expanded and transformed into porous structures where oxidized Cu was fully reduced to Cu NPs while Fe, Co, and Ni remained in the oxidized form. In situ chemical analysis showed that the expansion of the oxide layer resulted from the outward diffusion flux of all transition metals (Fe, Co, Ni, Cu). Revealing the H2 reduction behavior of HEA NPs facilitates the development of advanced multicomponent alloys for applications targeting H2 formation and storage, catalytic hydrogenation, and corrosion removal.

Vanadium-Substituted Tunnel Structured Silver Hollandite (Ag1.2VxMn8-xO16): Impact on Morphology and Electrochemistry.

A series of tunnel structured V-substituted silver hollandite (Ag1.2VxMn8-xO16, x = 0-1.4) samples is prepared and characterized through a combination of synchrotron X-ray diffraction (XRD), synchrotron X-ray absorption spectroscopy (XAS), laboratory Raman spectroscopy, and electron microscopy measurements. The oxidation states of the individual transition metals are characterized using V and Mn K-edge XAS data indicating the vanadium centers exist as V5+, and the Mn oxidation state decreases with increased V substitution to balance the charge. Scanning transmission electron microscopy of reduced materials shows reduction-displacement of silver metal at high levels of lithiation. In lithium batteries, the V-substituted tunneled manganese oxide materials reveal previously unseen reversible nonaqueous Ag electrochemistry and exhibit up to 2.5× higher Li storage capacity relative to their unsubstituted counterparts. The highest capacity was observed for the Ag1.2(V0.8Mn7.2)O16·0.8H2O material with an intermediate level of V substitution, likely due to a combination of the atomic composition, the morphology of the particle, and the homogeneous distribution of the active material within the electrode structure where factors over multiple length scales contribute to the electrochemistry.

Comparing two airway management strategies for moderately sedated patients undergoing awake craniotomy: A single-blinded randomized controlled trial.

BACKGROUND: In the monitored anesthesia care (MAC) setting for awake craniotomy (AC), maintaining airway patency in sedated patients remains challenging. This randomized controlled trial aimed to compare the validity of the below-epiglottis transnasal tube insertion (the tip of the tube placed between the epiglottis and vocal cords) and the nasopharyngeal airway (simulated by the above-epiglottis transnasal tube with the tip of the tube placed between the epiglottis and the free edge of the soft palate) with respect to maintaining upper airway patency for moderately sedated patients undergoing AC. METHODS: Sixty patients scheduled for elective AC were randomized to receive below-epiglottis (n = 30) or above-epiglottis (n = 30) transnasal tube insertion before surgery. Moderate sedation was maintained in the pre- and post-awake phases. The primary outcome was the upper airway obstruction (UAO) remission rate (relieved obstructions after tube insertion/the total number of obstructions before tube insertion). RESULTS: The UAO remission rate was higher in the below-epiglottis group [100% (12/12) vs 45% (5/11); P = .005]. The tidal volume values monitored through the tube were greater in the below-epiglottis group during the pre-awake phase (P < .001). End-tidal carbon dioxide (EtCO2 ) monitored through the tube was higher in the below-epiglottis group at bone flap removal (P < .001). During the awake phase, patients' ability to speak was not impeded. No patient had serious complications related to the tube. CONCLUSION: The below-epiglottis tube insertion is a more effective method to maintain upper airway patency than the nasopharyngeal airway for moderately sedated patients undergoing AC.

High-flow nasal cannula improves clinical efficacy of airway management in patients undergoing awake craniotomy.

BACKGROUND: Awake craniotomy requires specific sedation procedure in an awake patient who should be able to cooperate during the intraoperative neurological assessment. Currently, limited number of literatures on the application of high-flow nasal cannula (HFNC) in the anesthetic management for awake craniotomy has been reported. Hence, we carried out a prospective study to assess the safety and efficacy of humidified high-flow nasal cannula (HFNC) airway management in the patients undergoing awake craniotomy. METHODS: Sixty-five patients who underwent awake craniotomy were randomly assigned to use HFNC with oxygen flow rate at 40 L/min or 60 L/min, or nasopharynx airway (NPA) device in the anesthetic management. Data regarding airway management, intraoperative blood gas analysis, intracranial pressure, gastric antral volume, and adverse events were collected and analyzed. RESULTS: Patients using HFNC with oxygen flow rate at 40 or 60 L/min presented less airway obstruction and injuries. Patients with HFNC 60 L/min maintained longer awake time than the patients with NPA. While the intraoperative PaO2 and SPO2 were not significantly different between the HFNC and NPA groups, HFNC patients achieved higher PaO2/FiO2 than patients with NPA. There were no differences in Brain Relaxation Score and gastric antral volume among the three groups as well as before and after operation in any of the three groups. CONCLUSION: HFNC was safe and effective for the patients during awake craniotomy. TRIAL REGISTRATION: Chinese Clinical Trial Registry, CHiCTR1800016621 . Date of Registration: 12 June 2018.

Origin of Intrinsically Low Thermal Conductivity in Talnakhite Cu17.6Fe17.6S32 Thermoelectric Material: Correlations between Lattice Dynamics and Thermal Transport.

Understanding the nature of phonon transport in solids and the underlying mechanism linking lattice dynamics and thermal conductivity is important in many fields, including the development of efficient thermoelectric materials where a low lattice thermal conductivity is required. Herein, we choose the pair of synthetic chalcopyrite CuFeS2 and talnakhite Cu17.6Fe17.6S32 compounds, which possess the same elements and very similar crystal structures but very different phonon transport, as contrasting examples to study the influence of lattice dynamics and chemical bonding on the thermal transport properties. Chemically, talnakhite derives from chalcopyrite by inserting extra Cu and Fe atoms in the chalcopyrite lattice. The CuFeS2 compound has a lattice thermal conductivity of 2.37 W m-1 K-1 at 625 K, while Cu17.6Fe17.6S32 features Cu/Fe disorder and possesses an extremely low lattice thermal conductivity of merely 0.6 W m-1 K-1 at 625 K, approaching the amorphous limit κmin. Low-temperature heat capacity measurements and phonon calculations point to a large anharmonicity and low Debye temperature in Cu17.6Fe17.6S32, originating from weaker chemical bonds. Moreover, Mössbauer spectroscopy suggests that the state of Fe atoms in Cu17.6Fe17.6S32 is partially disordered, which induces the enhanced alloy scattering. All of the above peculiar features, absent in CuFeS2, contribute to the extremely low lattice thermal conductivity of the Cu17.6Fe17.6S32 compound.

Spatial Vulnerability of Network Systems under Spatially Local Hazards.

A hazard is often spatially local in a network system, but its impact can spread out through network topology and become global. To qualitatively and quantitatively assess the impact of spatially local hazards on network systems, this article develops a new spatial vulnerability model by taking into account hazard location, area covered by hazard, and impact of hazard (including direct impact and indirect impact), and proposes an absolute spatial vulnerability index (ASVI) and a relative spatial vulnerability index (RSVI). The relationship between the new model and some relevant traditional network properties is also analyzed. A case study on the spatial vulnerability of the Chinese civil aviation network system is conducted to demonstrate the effectiveness of the model, and another case study on the Beijing subway network system to verify its relationship with traditional network properties.