Hitachi (Canada)

We report a facile synthesis of multiply twinned Pd@Pt core-shell concave decahedra by controlling the deposition of Pt on preformed Pd decahedral seeds. The Pt atoms are initially deposited on the vertices of a decahedral seed, followed by surface diffusion to other regions along the edges/ridges and then across the faces. Different from the coating of a Pd icosahedral seed, the Pt atoms prefer to stay at the vertices and edges/ridges of a decahedral seed even when the deposition is conducted at 200 °C, naturally generating a core-shell structure covered by concave facets. The nonuniformity in the Pt coating can be attributed to the presence of twin boundaries at the vertices, as well as the {100} facets and twin defects along the edges/ridges of a decahedron, effectively trapping the Pt adatoms at these high-energy sites. As compared to a commercial Pt/C catalyst, the Pd@Pt concave decahedra show substantial enhancement in both catalytic activity and durability toward the oxygen reduction reaction (ORR). For the concave decahedra with 29.6% Pt by weight, their specific (1.66 mA/cm(2)Pt) and mass (1.60 A/mgPt) ORR activities are enhanced by 4.4 and 6.6 times relative to those of the Pt/C catalyst (0.36 mA/cm(2)Pt and 0.32 A/mgPt, respectively). After 10,000 cycles of accelerated durability test, the concave decahedra still exhibit a mass activity of 0.69 A/mgPt, more than twice that of the pristine Pt/C catalyst.

Abstract 3D porous nanostructures built from 2D δ-MnO 2 nanosheets are an environmentally friendly and industrially scalable class of supercapacitor electrode material. While both the electrochemistry and defects of this material have been studied, the role of defects in improving the energy storage density of these materials has not been addressed. In this work, δ-MnO 2 nanosheet assemblies with 150 m 2 g −1 specific surface area are prepared by exfoliation of crystalline K x MnO 2 and subsequent reassembly. Equilibration at different pH introduces intentional Mn vacancies into the nanosheets, increasing pseudocapacitance to over 300 F g −1 , reducing charge transfer resistance as low as 3 Ω, and providing a 50% improvement in cycling stability. X-ray absorption spectroscopy and high-energy X-ray scattering demonstrate a correlation between the defect content and the improved electrochemical performance. The results show that Mn vacancies provide ion intercalation sites which concurrently improve specific capacitance, charge transfer resistance and cycling stability.

Graphene oxide (GO) is a layered material comprised of hierarchical features which possess vastly differing characteristic dimensions. GO nanosheets represent the critical hierarchical structure which bridges the length-scale of monolayer and bulk material architectures. In this study, the strength and fracture behavior of GO nanosheets were examined. Under uniaxial loading, the tensile strength of the nanosheets was measured to be as high as 12 ± 4 GPa, which approaches the intrinsic strength of monolayer GO and is orders of magnitude higher than that of bulk GO materials. During mechanical failure, brittle fracture was observed in a highly localized region through the cross-section of the nanosheets without interlayer pull-out. This transition in the failure behavior from interplanar fracture, common for bulk GO, to intraplanar fracture, which dominates failure in monolayer GO, is responsible for the high strength measured in the nanosheets. Molecular dynamics simulations indicate that the elastic release from the propagation of intraplanar cracks initiates global fracture due to interlayer load transmission through hydrogen bond networks within the gallery space of the GO nanosheets. Furthermore, the GO nanosheet strength and stiffness were found to be strongly correlated to the effective volume and thickness of the samples, respectively. These findings help to bridge the understanding of the mechanical behavior of hierarchical GO materials and will ultimately guide the application of this intermediate scale material.

Abstract We report the results of the first dynamic, in situ heating of lunar soils to simulate micrometeorite impacts on the lunar surface. We performed slow‐ and rapid‐heating experiments inside the transmission electron microscope to understand the chemical and microstructural changes in surface soils resulting from space‐weathering processes. Our slow‐heating experiments show that the formation of Fe nanoparticles begins at ~575 °C. These nanoparticles also form as a result of rapid‐heating experiments, and electron energy‐loss spectroscopy measurements indicate the Fe nanoparticles are composed entirely of Fe 0 , suggesting this simulation accurately mimics micrometeorite space‐weathering processes occurring on airless body surfaces. In addition to Fe nanoparticles, rapid‐heating experiments also formed vesiculated textures in the samples. Several grains were subjected to repeated thermal shocks, and the measured size distribution and number of Fe nanoparticles evolved with each subsequent heating event. These results provide insight into the formation and growth mechanisms for Fe nanoparticles in space‐weathered soils and could provide a new methodology for relative age dating of individual soil grains from within a sample population.

An adequate charging infrastructure advocates to ameliorate the range anxiety to propel the disparaged electric vehicle (EV) market. But, the high initial installation cost, requirement of suitable places and the anticipated immense load on the grid during peak times hinder to elongate the charging station network, especially in urban areas. Fortunately, the bidirectional energy transferring capability between vehicles (i.e., V2V) may act as an auxiliary solution to charge an EV at any place and at any time without leaning on a stationary charging infrastructure. In this work, we assume a market where charging providers each has a number of charging trucks equipped with a larger battery and a fast charger to charge a number of EVs at some particular parking lots. A provider intends to maximize the served number of EVs using its limited number of charging trucks, when an EV should be considered as served only if it would be fully charged during its declared charging window. All charging requests are assumed to be received by an agent which provisions a route and schedule for each charging truck and all trucks should return to the depot after serving EVs. We formulate this combinatorially hard problem as an integer linear program (ILP) to maximize the number of served EVs by determining the optimal trajectory of each truck. Owing to its complexity, we present a solution methodology by decomposing the problem using Dantzig-Wolfe decomposition approach; we divide the problem into one master problem and a set of pricing problems (one for each EV) and achieve the solution iteratively. Though the solution achieved from the decomposition might not be optimal, it is faster to be applicable in practice. We also compare the performance with two heuristic algorithms and report on the collected results.

Despite the remarkable success in controlling the synthesis of metal nanocrystals, it still remains a grand challenge to stabilize and preserve the shapes or internal structures of metastable kinetic products. In this work, we address this issue by systematically investigating the surface and bulk reconstructions experienced by a Pd concave icosahedron when subjected to heating up to 600 °C in vacuum. We used in situ high-resolution transmission electron microscopy to identify the equilibration pathways of this far-from-equilibrium structure. We were able to capture key structural transformations occurring during the thermal annealing process, which were mechanistically rationalized by implementing self-consistent plane-wave density functional theory (DFT) calculations. Specifically, the concave icosahedron was found to evolve into a regular icosahedron via surface reconstruction in the range of 200-400 °C, and then transform into a pseudospherical crystalline structure through bulk reconstruction when further heated to 600 °C. The mechanistic understanding may lead to the development of strategies for enhancing the thermal stability of metal nanocrystals.

Abstract Narrow bandgap semiconductor CuBi 2 O 4 microstructures such as three dimensional hierarchical microspheres, micro‐flowers, one dimensional microrods and nanorods were fabricated through a facile hydrothermal synthesis approach by systematically changing the synthesis conditions. Their optical properties and photocatalytical performances under visible light illumination were characterized. The hierarchical micro‐flower shaped CuBi 2 O 4 sample showed a high photodecay rate of 0.114 ± 0.002 h −1 with 1 mg/ml CuBi 2 O 4 concentration for methylene blue (30 μM). Under the illumination of an AM 1.5G solar simulator, a 0.02 mA/cm 2 stable cathodic photocurrent density was observed at a low negative bias voltage (‐0.25 V vs (Ag/AgCl)). The micro‐flower shaped CuBi 2 O 4 sample also showed a high antibacterial effect against Escherichia coli , with ∼ 93 % bacteria reduction after 6 h illumination by a commercial white LED light (10 mW/cm 2 ). These results indicate that CuBi 2 O 4 can be a promising candidate for visible light driven energy conversion and antimicrobial applications.

Microscopists demand better performance from their electron microscopes with every new instrument. With the advancement of new instrument technologies, better images, higher resolution, more precise analysis, and faster throughput are all benefits that are expected of expensive purchases. Still, in many cases, a well-known problem detrimentally affects the quality of results: specimen contamination.

An unexpected morphology comprising patchy nanofibers can be accessed from the self-assembly of an all-conjugated, polyselenophene-block-polythiophene copolymer. This morphology consists of very small (<10 nm), polythiophene- and polyselenophene-rich domains and is unprecedented for both conjugated polymers and diblock copolymers in general. We propose that the patchy morphology occurs from the enhanced miscibility of the blocks arising from the longer alkyl chains in comparison to similar block copolymers with shorter alkyl chains, which fully phase separate, as well as the difference in rigidity between the polythiophene and polyselenophene blocks. This work demonstrates a facile way to tune the self-assembly behavior of conjugated block copolymers by modification of the side chain substituents.

interface and that graphene serves as a reinforcement, providing the hetero-film with an ability to sustain significantly high stresses at the point of failure initiation. The results and methodology described herein can contribute to the rational design of strong and reliable ultrathin hetero-films for versatile applications.

In this work, we investigate that the abundance of Electric Vehicles (EVs) can be exploited to target the stability of the power grid. Through a cyber attack that compromises a lot of available EVs and their charging infrastructure, we present a realistic coordinated switching attack that initiates inter-area oscillations between different areas of the power grid. The threat model as well as linearized state-space representation of the grid are formulated to illustrate possible consequences of the attack. Two variations of switching attack are considered, namely, switching of EV charging and discharging power into the grid. Moreover, two possible attack strategies are also considered (i) using an insider to reveal the accurate system parameters and (ii) using reconnaissance activities in the absence of the grid parameters. In the former strategy, the system equations are used to compute the required knowledge to launch the attack. However, a stealthy system identification technique, which is tailored based on Eigenvalue Realization Algorithm (ERA), is proposed in latter strategy to calculate the required data for attack execution. The two-area Kundur, 39-Bus New England, and the Australian 5-area power grids are used to demonstrate the attack strategies and their consequences. The collected results demonstrate that by manipulation of EV charging stations and launching a coordinated switching attack to those portions of load, inter-area oscillations can be initiated. Finally, to protect the grid from this anticipated attack, a Support Vector Machine (SVM) based framework is proposed to detect and eliminate this attack even before being executed.

This paper reports in situ transmission electron microscopy (TEM) tensile testing of carbon-linked graphene oxide nanosheets using a monolithic TEM compatible microelectromechanical system device. The set-up allows direct on-chip nanosheet thickness mapping, high resolution electron beam linking of a pre-fractured nanosheet, and mechanical tensile testing of the nanosheet. This technique enables simultaneous mechanical and high energy electron beam characterization of 2D nanomaterials.

Self‐poling of ferroelectric films, i.e., a preferred, uniform direction of the ferroelectric polarization in as‐grown samples is often observed yet poorly understood despite its importance for device applications. The multiferroic perovskite BiFeO 3 , which crystallizes in two distinct structural polymorphs depending on applied epitaxial strain, is well known to exhibit self‐poling. This study investigates the effect of self‐poling on the monoclinic domain configuration and the switching properties of the two polymorphs of BiFeO 3 ( R ′ and T ′) in thin films grown on LaAlO 3 substrates with slightly different La 0.3 Sr 0.7 MnO 3 buffer layers. This study shows that the polarization state formed during the growth acts as “imprint” on the polarization and that switching the polarization away from this self‐poled direction can only be done at the expense of the sample's monoclinic domain configuration. The observed reduction of the monoclinic domain size is largely reversible; hence, the domain size is restored when the polarization is switched back to its original orientation. This is a direct consequence of the growth taking place in the polar phase (below T c ). Switching the polarization away from the preferred configuration, in which defects and domain patterns synergistically minimize the system's energy, leads to a domain state with smaller (and more highly strained and distorted) monoclinic domains.

Dispersion stability, ligand structure and conformation, and SERS activities of 1-alkanethiol (CnH2n+1SH, n = 2–14) functionalized gold and silver nanoparticles (AuNPs and AgNPs) were studied as a function of alkanethiol carbon chain length and nanoparticle (NP) type and size. The dispersion stability of alkanethiol functionalized NPs in water increases with increasing alkanethiol chain length and NP size, and the stabilities of the alkanethiol-containing AuNPs are higher than their AgNP counterparts. C3H7SH and longer alkanethiols are highly ordered on AgNPs but disordered on AuNPs. The SERS intensity of the C–S stretch band for the model alkanethiols on AgNPs and AuNPs decays exponentially (I = I0 exp(−Nc/N0)) with increasing number of carbon atoms (Nc). The empirical decay length N0, in terms of the number of the carbon atoms, is 1.29, 0.53, and 0.10 for AgNPs with diameters of 50, 30, and 10 nm, respectively. This decay length is less than 1 for AuNPs of difference sizes. These results show that changing the NP gap size by a distance equivalent to a single chemical bond can have a significant impact on the NP integrated SERS activities.

The influence of tool geometry on material flow during friction stir welding of dissimilar aluminium alloys is investigated. Sheets of Al 2024 and Al 6061 alloys are friction stir welded in lap and butt configurations using different welding conditions. Optical microscopy with serial sectioning is utilised to systematically study material flow when small variations are made to the tool pin. It is shown that three flat features on the pin impose vertical material flow which can promote intermixing. When a threaded tool is used, the material flow and formation of the intermixed region depends on the orientation of the base materials, since the differences in viscosity of material on the advancing versus retreating side of the tool will inhibit intermixing. Decreasing the travel speed will promote intermixing by increasing the residence time to compensate for the differences in material viscosity that otherwise limit intermixing.

Abstract We report a systematic study of the thermal stability of Pt‐based cubic, octahedral, and icosahedral nanocages using high‐resolution electron microscopy coupled with in situ heating. Our results indicate that all these nanocages could be used with no observable changes up to 150 °C, with their facets still preserved at even higher temperatures. We observed the same behavior in all the nanocages under thermal stress: hole enlargement and atom migration toward the edges to create nanoframes. This transformation could be rationalized by the thermodynamic driving force to minimize surface free energy. The octahedral nanocages were found to be more stable by 50 °C than the icosahedral nanocages, suggesting that the thermal stability of such catalysts can be potentially optimized to extend their usage toward different applications at elevated temperatures.

The impact of mercury (Hg) on human and ecological health has been known for decades. Although a treaty signed in 2013 by 147 nations regulates future large-scale mercury emissions, legacy Hg contamination exists worldwide and small-scale releases will continue. The fate of elemental mercury, Hg(0), lost to the subsurface and its potential chemical transformation that can lead to changes in speciation and mobility are poorly understood. Here, we show that Hg(0) beads interact with soil or manganese oxide solids and X-ray spectroscopic analysis indicates that the soluble mercury coatings are HgO. Dissolution studies show that, after reacting with a composite soil, >20 times more Hg is released into water from the coated beads than from a pure liquid mercury bead. An even larger, >700 times, release occurs from coated Hg(0) beads that have been reacted with manganese oxide, suggesting that manganese oxides are involved in the transformation of the Hg(0) beads and creation of the soluble mercury coatings. Although the coatings may inhibit Hg(0) evaporation, the high solubility of the coatings can enhance Hg(II) migration away from the Hg(0)-spill site and result in potential changes in mercury speciation in the soil and increased mercury mobility.

The repercussion of increased electric vehicle (EV) charging demand is notable at the distribution grid especially during the cold morning, while users tend to precondition their vehicles before leaving their premises. Moreover, due to the price declination, a tendency of installing level 2 chargers in residential premises is anticipated, which should stimulate the appearance of a new peak to the residential load profile. Hence, multiple scenarios of preconditioning are simulated, and the corresponding network’s quality metrics (e.g., voltage level and power losses) are assessed to analyze the impact. And a remarkable consequence is observed. As a consequence, to mitigate the consequences and manage the new peak load, the optimal reconfiguration of network is implemented, and unfortunately, with a larger number of EVs, this technique fails to attain the minimum voltage level. Therefore, leveraging this high number of EVs, instead of relying on the network reconfiguration, power is assumed to be injected from idle EVs through vehicle-to-grid (V2G) energy transmission. An integer linear program is formed to schedule a set of EVs in participating in V2G, and the outcome indicates that V2G alone could not compensate for the disturbance in the network. Accordingly, a hybrid method of V2G and reconfiguration is proposed and evaluated to assist the network in handling the new peak load, and this hybrid solution reduces power losses in the network by 50% on average and maintains the voltage level above the operational threshold of 0.95 p.u.

High-energy internal failures of transformers are catastrophic events which are hardly predictable. For this reason, a full-scale controlled experiment represents a valuable learning opportunity to gather accurate information about sequence of events during the very short time in which the failure occurs. Controlled parameters include tank design, material properties, experimental load and measurements. In this paper, we present a detailed investigation using nonlinear finite-element analysis of a 210-MVA transformer high-pressure experiment. We begin by evaluating the relationship between internal arcing pressure rise and tank expansion characteristics. Since this relationship is not linear due to geometric and material nonlinearities, an iterative process is proposed to ensure result accuracy. Stress–strain material properties are retrieved by tension experiments of specimens extracted from the tested tank to enable accurate comparison of numerical and experimental results. It is shown in this paper that nonlinear material parameters have a small influence on the tank pressure rise, but a significant one on large strain prediction and therefore the true stress-strain curve is recommended. In addition, the ductile rupture criterion based on the ultimate plastic strain of the material correlates with the experimental and explicit dynamic analysis results. This can ensure a certain design margin for tank rupture prevention.

Abstract We report a facile method for the synthesis of Pt–Pd nanocages and Pt nanorings by conformally coating Pd nanoplates with Pt‐based shells using polyol‐ and water‐based protocols, respectively, followed by selective removal of the Pd cores. For the polyol‐based system, Pd nanoplates were conformally coated with Pt–Pd alloy shells due to the use of a high reaction temperature of 200 °C and a slow injection rate for the Pt precursor. In comparison, Pt shells were formed on Pd nanoplates with a larger thickness on the side face than on the top/bottom face in the water‐based system due to the use of a low reaction temperature of 80 °C and the presence of twin boundaries on the side face. As such, the Pd@Pt nanoplates prepared using the polyol‐ and water‐based protocols evolved into Pt–Pd nanocages and Pt nanorings, respectively, when the Pd templates in the cores were selectively removed by wet etching. The wall thickness of the nanocages and the ridge thickness of the nanorings could be reduced down to 1.1 nm and 1.8 nm, respectively, without breaking the hollow structures.