Formation of a C15 Laves Phase with a Giant Unit Cell in Salt-Doped A/B/AB Ternary Polymer Blends
Abstract not provided
Xie, Shuyi↗
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Controlling 3-D Morphology of Ni-Fe-Based Nanocatalysts for Oxygen Evolution Reaction
Controlling the 3-D morphology of nanocatalysts is one of the underexplored but important approaches for improving the sluggish kinetics of the oxygen evolution reaction (OER) in water electrolysis. This work reports a scalable, oil-based method based on thermal decomposition of organometallic complexes to yield highly uniform Ni–Fe-based nanocatalysts with a well-defined morphology (i.e. Ni–Fe core–shell, Ni/Fe alloy, and Fe–Ni core–shell). Transmission electron microscopy reveals their morphology and composition to be NiOx–FeOx/NiOx core-mixed shell, NiOx/FeOx alloy, and FeOx–NiOx core–shell. X-ray techniques resolve the electronic structures of the bulk and are supported by electron energy loss spectroscopy analysis of individual nanoparticles. These results suggest that the crystal structure of Ni is most likely to contain α-Ni(OH)2 and that the chemical environment of Fe is variable, depending on the morphology of the nanoparticle. The Ni diffusion from the amorphous Ni-based core to the iron oxide shell makes the NiOx–NiOx/FeOx core-mixed shell structure the most active and the most stable nanocatalyst, which outperforms the comparison NiOx/FeOx alloy nanoparticles expected to be active for the OER. This study suggests that the chemical environment of the mixed NiOx/FeOx alloy composition is important to achieve high electrocatalytic activity for the OER and that the 3-D morphology plays a key role in the optimization of the electrocatalytic activity and stability of the nanocatalyst for the OER.
Nanocatalysts↗
Wetting transition and fluid trapping in a microfluidic fracture
Immiscible fluid–fluid displacement in confined geometries is a fundamental process occurring in many natural phenomena and technological applications, from geological CO 2 sequestration to microfluidics. Due to the interactions between the fluids and the solid walls, fluid invasion undergoes a wetting transition from complete displacement at low displacement rates to leaving a film of the defending fluid on the confining surfaces at high displacement rates. While most real surfaces are rough, fundamental questions remain about the type of fluid–fluid displacement that can emerge in a confined, rough geometry. Here, we study immiscible displacement in a microfluidic device with a precisely controlled structured surface as an analogue for a rough fracture. We analyze the influence of the degree of surface roughness on the wetting transition and the formation of thin films of the defending liquid. We show experimentally, and rationalize theoretically, that roughness affects both the stability and dewetting dynamics of thin films, leading to distinct late-time morphologies of the undisplaced (trapped) fluid. Finally, we discuss the implications of our observations for geologic and technological applications.
42 ENGINEERING↗
Inoculated biocrust cover and functions diverged over a gradient of soil textures and water availability
Restoring biological crust (biocrust) in disturbed drylands is challenging due to the difficult environmental conditions, such as limited soil moisture, low soil nutrients, and extreme temperatures, that impede growth. Understanding how the key components of biocrust—mosses, lichens, and cyanobacteria—react to different environmental factors informs the optimal timing, locations, and species composition for biocrust reintroduction, thereby increasing the likelihood of establishment. Here, we inoculated soils with a diverse range of biocrust organisms, analogous to seeding an area with diverse vascular plant seeds, and varied environmental conditions to observe how these changes influenced the development and functions of reintroduced biocrust. We found that by manipulating soil texture and time spent wet, we can change the proportional cover of biocrust within a restoration‐like setting. Specifically, we found that 4 months after inoculation, finer textured soils that received more water become dominated by moss cover, while coarser textured soils with less water remained dominated by cyanobacteria cover, and the interactions between texture and time spent wet strongly influenced cover. We found biocrust morphological group cover had a small, but detectable, effect on ecosystem functions (soil stability and nitrogenase activity, a proxy for nitrogen fixation), but that environmental conditions had a stronger impact on the functions we measured. Manipulative experiments in controlled environments, like this one, can help elucidate the mechanisms underlying the establishment rate and patterns of biocrusts post‐inoculation, and inform implementation of inoculations in the field.
Environmental Sciences & Ecology↗
Focus Issue: Understanding Water-Oxide Interfaces to Harness New Processes and Technologies. Introduction
Water interaction with metal oxides plays a fundamentally important role across environmental chemistry, geochemistry, catalysis, and in the control and performance of functional nanocrystalline oxides. Water is found virtually everywhere on Earth, from bulk fluid to trace molecules, and its interaction with natural and engineered materials often defines or at least influences a key part of their chemical and physical behavior. In turn, metal oxides play a dominant role as mineral particles across most natural environments, while comprising a compelling and versatile platform for the development of new functional materials with tailored properties that benefit society. Given the intrinsic correlation of their properties to water interactions, it is a common goal across materials and chemical sciences to develop a comprehensive understanding of water adsorption, water film formation, and water-mediated reactions on metal oxide surfaces. This is certainly true in heterogeneous catalysis and electrocatalysis, where water is omnipresent either as a reactant, a medium, an inhibitor or as a trace component in the feed. The effect of water on the morphological evolution during synthesis, particle assembly, and sintering is also important to the stability and functional properties of oxide nanostructures. Such processes are intimately related to how water molecules interact with their surfaces and affect local physical-chemical conditions.
Rosso, Kevin M.↗
Developing a New Polyolefin Precursor for Low-Cost, High-Strength Carbon Fiber
Current high-strength carbon fibers (CFs) are mostly derived from PAN polymer precursor, which are very expensive with limited usage in the high-end products. On the other hand, it has also stimulated research interest to develop new low-cost precursors and manufacturing process. Despite numerous studies, researchers have yet to develop a new polymeric precursor that is less expensive, melt-spinnable, and offers a high C-yield. In this three-year R&D project, we proposed three consecutive research phases, including (i) the development of new polyolefin-based precursors that can be thermally transformed to C material in one heating step under inert atmosphere and achieved a C-yield >80%, which is more than 60% higher than that of current PAN precursor, (ii) With the suitable new polyolefin-based precursor, we can focus on CF manufacturing process, including fiber spinning, stabilization, and carbonization, to form high quality carbon fibers with the desirable polymorphous morphology, and (iii) the investigation of thermal conversion process under tension for converting polyolefin-based precursor fibers to high tensile strength carbon fibers with specific graphite crystallite size, orientation of basal line, order-disorder ratio, fiber diameter, and reduced structural defect (voids). composites.
08 HYDROGEN↗
Assessing the influence of processing parameters and external loading on the nanoporous structure and morphology of nanoporous gold toward catalytic applications
Nanoporous gold structure gains several unique physical and chemical properties from its nanoscale foam structure composed of ligaments and connected pores. The high specific surface area and interconnected pores make its structure ideal for gas catalysis. Catalytic activity arises in part from the high number density of surface steps and kinks at points of high curvature in the nanoporous structure. However, the structure also makes the material macroscopically brittle and unreliable for many applications due to poor mechanical stability. The ligament diameter, which regulates both desirable chemical properties and mechanical instability, can be tuned to over three orders of magnitude, but few morphology features can be adjusted independently of this. In this report we fabricate nanoporous gold with an average ligament diameter of around 10 nm while varying synthesis parameters and quantify the resulting morphology in order to evaluate the effect of processing on the resulting nanoscale foam structure. In situ tensile experiments are performed to observe how both individual ligaments and the foam structure's features change during deformation in real-time. We found two new morphology features that are independently controllable through synthesis parameters and are likely to influence mechanical stability while preserving or enhancing catalytic activity. The curvature of the ligaments can be increased by stirring the electrolyte during dealloying and the width of the ligament diameter size distribution can be adjusted by controlling the coarsening rate. In situ mechanical tests show that grain boundaries can influence crack propagation and that ligaments removed from the crack tip experience both elastic and plastic stress.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Morphological Transitions of a Photoswitchable Aramid Amphiphile Nanostructure
Self-assembly of small amphiphilic molecules in water can lead to nanostructures of varying geometries with pristine internal molecular organization. Here we introduce a photoswitchable aramid amphiphile (AA), designed to exhibit extensive hydrogen bonding and robust mechanical properties upon self-assembly, while containing a vinylnitrile group for photoinduced cis-trans isomerization. We demonstrate spontaneous self-assembly of the vinylnitrile-containing AA in water to form nanoribbons. Upon UV irradiation, trans-to-cis isomerizations occur concomitantly with a morphological transition from nanoribbons to nanotubes. The nanotube structure persists in water for over six months, stabilized by strong and collective intermolecular interactions. We demonstrate that the nanoribbon-to-nanotube transition is reversible upon heating and that switching between states can be achieved repeatedly. Finally, we use electron microscopy to capture the transition and propose mechanisms for nanoribbon-to-nanotube rearrangement and vice versa. This stability and switchability of photoresponsive AA nanostructures make them viable for a range of future applications.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Aggregation‐Induced Multilength Scaled Morphology Enabling 11.76% Efficiency in All‐Polymer Solar Cells Using Printing Fabrication
Abstract All‐polymer solar cells (all‐PSCs) exhibit excellent stability and readily tunable ink viscosity, and are therefore especially suitable for printing preparation of large‐scale devices. At present, the efficiency of state‐of‐the‐art all‐PSCs fabricated by the spin‐coating method has exceeded 11%, laying the foundation for the preparation and practical utilization of printed devices. A high power conversion efficiency (PCE) of 11.76% is achieved based on PTzBI‐Si:N2200 all‐PSCs processing with 2‐methyltetrahydrofuran (MTHF, an environmentally friendly solvent) and preparation of active layers by slot die printing, which is the top efficient for all‐PSCs. Conversely, the PCE of devices processed by high‐boiling point chlorobenzene is less than 2%. Through the study of film formation kinetics, volatile solvents can freeze the morphology in a short time, and a more rigid conformation with strong intermolecular interaction combined with the solubility limit of PTzBI‐Si and N2200 in MTHF results in the formation of a fibril network in the bulk heterojunction. The multilength scaled morphology ensures fast transfer of carriers and facilitates exciton separation, which boosts carrier mobility and current density, thus improving the device performance. These results are of great significance for large‐scale printing fabrication of high‐efficiency all‐PSCs in the future.
Zhu, Lei↗
Room temperature synthesis of high temperature stable lanthanum phosphate–yttria nano composite
Graphical abstract: A facile aqueous sol–gel route involving precipitation–peptization mechanism followed by electrostatic stabilization is used for synthesizing nanocrystalline composite containing lanthanum phosphate and yttria. Highlights: ► A novel lanthanum phosphate–Y{sub 2}O{sub 3} nano composite is synthesized for the first time using a modified facile sol gel process. ► The composite becomes crystalline at 600 °C and X-ray diffraction pattern is indexed for monoclinic LaPO{sub 4} and cubic yttria. ► The composite synthesized was tested up to 1300 °C and no reaction between the phases of the constituents is observed with the morphologies of the phases being retained. -- Abstract: A facile aqueous sol–gel route involving precipitation–peptization mechanism followed by electrostatic stabilization is used for synthesizing nanocrystalline composite containing lanthanum phosphate and yttria. Lanthanum phosphate (80 wt%)–yttria (20 wt%) nano composite (LaPO{sub 4}–20%Y{sub 2}O{sub 3}), has an average particle size of ∼70 nm after heat treatment of precursor at 600 °C. TG–DTA analysis reveals that stable phase of the composite is formed on heating the precursor at 600 °C. The TEM images of the composite show rod shape morphology of LaPO{sub 4} in which yttria is acquiring near spherical shape. Phase identification of the composite as well as the phase stability up to 1300 °C was carried out using X-ray diffraction technique. With the phases being stable at higher temperatures, the composite synthesized should be a potential material for high temperature applications like thermal barrier coatings and metal melting applications.
36 MATERIALS SCIENCE↗
A Top-Down Strategy to Engineer ActiveLayer Morphology for Highly Efficient and Stable All-Polymer Solar Cells
A major challenge hindering the further development of all-polymer solar cells (all-PSCs) employing polymerized small-molecule acceptors is the relatively low fill factor (FF) due to the difficulty in controlling the active-layer morphology. The issues typically arise from oversized phase separation resulting from the thermodynamically unfavorable mixing between two macromolecular species, and disordered molecular orientation/packing of highly anisotropic polymer chains. Herein, a facile top-down controlling strategy to engineer the morphology of all-polymer blends is developed by leveraging the layer-by-layer (LBL) deposition. Optimal intermixing of polymer components can be achieved in the two-step process by tuning the bottom-layer polymer swelling during top-layer deposition. Consequently, both the molecular orientation/packing of the bottom layer and the molecular ordering of the top layer can be optimized with a suitable top-layer processing solvent. A favorable morphology with gradient vertical composition distribution for efficient charge transport and extraction is therefore realized, affording a high all-PSC efficiency of 17.0% with a FF of 76.1%. The derived devices also possess excellent long-term thermal stability and can retain >90% of their initial efficiencies after being annealed at 65 °C for 1300 h. In conclusion, these results validate the distinct advantages of employing an LBL processing protocol to fabricate high-performance all-PSCs.
14 SOLAR ENERGY↗
Structure and Morphology of Phthalocyanine Films Grown in Electrical Fields by Vapor Deposition
Phthalocyanine is a very stable organic material in the atmosphere and has been used in numerous applications, such as optical switching and optical storage devices. Although this material has already been discovered for several decades and has had extensive studies conducted on it, many properties still need to be better understood, for example, the mechanisms of forming different solid phases and of changing film morphology by external forces. Phthalocyanine has two preferred solid phases (alpha and beta phases) for which the crystal structures, surface morphology and optical properties are different. In order to investigate these phenomena and the relationship among them, phthalocyanine films have been synthesized by vapor deposition on quartz substrates with and without an external electrical field. Some substrates were coated with a very thin gold film for the electrical field. These films have been characterized using x-ray diffraction, scanning electron microscopy, Fourier transfer infrared spectroscopy, and Z-scan technique. The films have excellent chemical and thermal stability. However, the surface of these films grown without the electrical field shows flower-like morphology. When films are deposited under an electrical field (approximately 3000 V/cm), an aligned structure is revealed on the surface. A comparison of the structure, morphology, optical properties, and the growth mechanism for these films with and without an electrical field will be discussed.
Zhu, Shen↗
Effect of Ni content on the morphological evolution of Ni-YSZ solid oxide fuel cell electrodes
The coarsening of Ni in Ni–yttria-stabilized zirconia (YSZ) anodes is a potential cause of long term solid oxide fuel cells (SOFC) performance degradation. The specifics of the Ni-YSZ structure—including Ni/YSZ ratio, porosity, and particle size distributions—are normally selected to minimize anode polarization resistance, but they also impact long-term stability. A better understanding of how these factors influence long-term stability is important for designing more durable anodes. The effect of structural details, e.g., Ni-YSZ ratio, on Ni coarsening has not been quantified. Furthermore, prior measurements have been done by comparing evolved structures with control samples, such that sample-to-sample variations introduce errors. Here in this paper, we report a four dimensional (three spatial dimensions and time) study of Ni coarsening in Ni-YSZ anode functional layers with different Ni/YSZ ratios, using synchrotron x-ray nano-tomography. The continuous structural evolution was observed and analyzed at sub-100 nm resolution. It is shown quantitatively that increasing the Ni/YSZ ratio increases the Ni coarsening rate. This is due to both increased pore volume and a decrease in the YSZ volume fraction, such that there is more free volume and a less obtrusive YSZ network, both of which allow greater Ni coarsening. The results are shown to be in good agreement with a power-law coarsening model. In conclusion, the finding is critical for informing the design of SOFC electrode microstructures that limit coarsening and performance degradation.
36 MATERIALS SCIENCE↗
Morphology control enables thickness-insensitive efficient nonfullerene polymer solar cells
Owing to the use of cost-effective materials and excellent stability, nonfullerene polymer solar cells (PSCs) have great potential for realizing large-area industrial production. In contrast to fullerene-based devices, non-fullerene PSCs have exhibited a superior photovoltaic performance with up to 12% efficiency and long-term thermal stability. Presently, one of the major factors hindering industrial production is the high sensitivity of the power conversion efficiency (PCE) to thickness variations, which can significantly affect the manufacturing yields and production costs of roll-to-roll processing. Specifically, the device fill factors and PCEs of many high-efficiency nonfullerene PSCs show a significant loss when the thickness of the active layer is over 100 nm. In order to achieve high output capabilities earlier, there is an urgent need to find a processing method to fabricate high-efficiency thick-film nonfullerene PSCs. Controlling the morphology and performance sensitivity in thick-film non-fullerene devices is a great challenge in the field. In this paper, we present a simple morphology optimization method via thermal annealing to fabricate highly efficient thickness-insensitive non-fullerene PSCs. After this treatment, PBDB-T/IT-M-based nonfullerene PSCs can afford an impressive PCE of up to ~9.4% at an active layer thickness of 250 nm. In addition, the devices with an active layer thickness of 400 nm still maintain a high efficiency close to 9%. The photovoltaic properties and morphology parameters resolved from hard and soft X-ray scattering clearly indicate that thermal annealing plays a key role in improving the film thickness insensitivity for non-fullerene PSCs.
14 SOLAR ENERGY↗
Mn-doped ZnFe{sub 2}O{sub 4} nanoparticles with enhanced performances as anode materials for lithium ion batteries
Highlights: • Mn-doped ZnFe{sub 2}O{sub 4} nanoparticles have been synthesized by hydrothermal method. • Zn{sub 0.96}Mn{sub 0.04}Fe{sub 2}O{sub 4} electrode shows the highest reversible capacity of 1157 mA h g{sup −1}. • The Zn{sub 0.96}Mn{sub 0.04}Fe{sub 2}O{sub 4} electrode shows promising cycling stability. - Abstract: Nanocrystalline Zn{sub 1−x}Mn{sub x}Fe{sub 2}O{sub 4} (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1) have been successfully synthesized by one-step hydrothermal method. The morphologies and electrochemical performance of Mn-doped ZnFe{sub 2}O{sub 4} in various proportions were investigated at room temperature, respectively. The Zn{sub 1−x}Mn{sub x}Fe{sub 2}O{sub 4} (x = 0.04) electrode in the as-synthesized samples showed the highest specific capacity of 1547 mA h g{sup −1} and 1157 mA h g{sup −1} in the initial discharge/charge process, with a coulombic efficiency of 74.8%. Additionally, excellent cycling stability was performed with a 1214 mA h g{sup −1} capacity retention at a current density of 100 mA g{sup −1} after 50 cycles. The corresponding mechanism was proposed which indicated that the Mn-doped ZnFe{sub 2}O{sub 4} nanoparticles experienced an aggregation thermochemical reaction among ZnO, MnO and Fe{sub 2}O{sub 3} subparticles.
36 MATERIALS SCIENCE↗
Halide perovskite-polymer composite film for bright and stable light-emitting devices
Stability is the primary hindrance for the application of halide perovskite material in light-emitting devices, solar cells, and other devices. In this work, halide perovskite and polymer composite film have been prepared for stable and bright light-emitting devices. Pure-phase Cs4PbBr6 crystals have been synthesized, and their photoluminescence (PL) properties and fluorescence lifetimes have been investigated. The Cs 4 PbBr 6 crystals exhibited high uniformity but underwent rapid photodegradation under light irradiation. To address this issue, we prepared bright light-emitting devices using composite of Cs 4 PbBr 6 crystals and polyethylene oxide (PEO) as the emission layer. The aim was to improve the optical and physical properties of halide perovskites, such as photodegradation and stability. PEO, with its excellent film-forming ability, created a uniform and dense film on the halide perovskite surface, filling microscopic defects and providing a protective barrier. FTIR, morphology, and PL analyses confirmed the protective role of the halide perovskite and polymer composite film. The composite film light-emitting devices demonstrated improved stability and higher PL brightness, with a peak brightness approaching 3 × 10 8 cd/m 2 , which was approximately 75% higher than the pure halide perovskite devices.
Composite film↗
Optical properties of fluorescent zigzag graphene quantum dots derived from multi-walled carbon nanotubes
Graphene quantum dots (GQDs), which are edge-bound nanometer-size graphene pieces, have fascinating electronic and optical properties due to their quantum confinement and edge effect. In this paper, GQDs were synthesized by using acid treatment and chemical exfoliation of multi-walled carbon nanotubes (MWCNTs). The structure of the GQDs was investigated by transmission electron microscope. The GQDs have a uniform size distribution, zigzag edge structure and two-dimensional morphology. The results indicated that the GQDs have bright blue emission upon UV excitation. The highly fluorescent GQDs exhibited high water solubility and good stability. It is shown that the acid treatment of MWCNTs leads to the formation of the functional group in zigzag sites, which results in the pH-dependent fluorescence of the GQDs.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Experimental investigation of the relationship between impact crater morphology and impacting particle velocity and direction
Interpretation of the wealth of impact data available from the Long Duration Exposure Facility, in terms of the absolute and relative populations of space debris and natural micrometeoroids, requires three dimensional models of the distribution of impact directions, velocities and masses of such particles, as well as understanding of the impact processes. Although the stabilized orbit of LDEF provides limited directional information, it is possible to determine more accurate impact directions from detailed crater morphology. The applicability of this technique has already been demonstrated but the relationship between crater shape and impactor direction and velocity has not been derived in detail. We present the results of impact experiments and simulations: (1) impacts at micron dimensions using the Unit's 2MV Van de Graaff accelerator; (2) impacts at mm dimensions using a Light Gas Gun; and (3) computer simulations using AUTODYN-3D from which an empirical relationship between crater shape and impactor velocity, direction and particle properties we aim to derive. Such a relationship can be applied to any surface exposed to space debris or micrometeoroid particles for which a detailed pointing history is available.
Mackay, N. G.↗