Ex-situ Transmission Electron Microscopy Research Articles

Strain-induced continuous transition from orthorhombic to hexagonal-like phase in Ti-36Zr-6Nb alloy with abnormally high strain hardening

The deformation mechanism of the α″-type Ti-36Zr-6Nb alloy exhibiting an abnormal strain hardening behavior was investigated using in-situ high-energy X-ray diffraction and ex-situ transmission electron microscopy under tensile tests. It was discovered that the orthorhombic α″ phase distorts successively toward hexagonal symmetry during tension through coupled atomic shear and shuffle, and the successive distortion of the α″ lattice contributes to the abnormally high strain hardening of the Ti-36Zr-6Nb alloy. Notably, the orthorhombic α″ phase does not transform into an ideal hexagonal phase during tension but instead transforms into a hexagonal-like phase. The hexagonal-like phase exhibits shear and shuffle components that are very close to those of the ideal hexagonal phase. Additionally, the strain-induced α″ to hexagonal-like martensitic transition was found to be partially reversible during unloading. The present study offers an in-depth understanding of the abnormal strain hardening behavior and the strain-induced phase transition behavior of the α″-type titanium alloys.

Amorphous nanoscale antimony-vanadium oxide: A high capacity anode material for potassium ion batteries

Antimony (Sb)-based materials, as a kind of potential high capacity and low cost materials, are the focus of attention in the anode materials of potassium ion batteries. However, at present, studies on Sb-based anode materials mainly focus on Sb metal, Sb alloy and Sb chalcogenides, while reports on Sb-based oxides are relatively rare. In addition, the development of Sb-based materials is limited by their large volume variation and poor reaction kinetics for potassium storage. Herein, a novel amorphous Sb2VO5 (A-SbVO) as bimetallic antimony vanadium oxide has been synthesized by solvothermal method. The A-SbVO exhibits high K storage activity and capacity due to its nanoscale and amorphous structure. Moreover, ex-situ transmission electron microscopy and X-ray photoelectron spectroscopy revealed the evolution of the A-SbVO in the potassium storage process as follows: A-SbVO → Sb → K3Sb → Sb → Sb + Sb2VO5. After compounding with reduced graphene oxide (rGO), the as-prepared A-SbVO/rGO shows better K storage stability, with discharge specific capacities of 313.0 and 248. 8 mAh/g at 500 and 1000 mA g−1, respectively. After 300 cycles at 200 mA g−1, the A-SbVO/rGO still has a high discharge specific capacity of 382.1 mAh/g.

Ion-beam assisted synthesis and thermal oxidation of TiN thin films combined with in-situ, depth-resolved characterization using MeV ions

We present an in-situ, depth-resolved and non-destructive approach to assess the chemical composition of titanium nitride (TiN) thin films during synthesis and controlled oxidation. Ion beam assisted deposition was used to deposit a TiN sample of approximately 120 nm thickness. The chemical composition was characterized in the deposition environment using non-destructive Rutherford/Elastic Backscattering Spectrometry (RBS/EBS), with a depth resolution of ca. 25 nm. The high sensitivity of the measurements to the non-metallic species was ensured by the use of elastic resonances. Analysis revealed a few percent oxygen incorporated in the films due to residual gases during growth. After deposition, the TiN film was exposed to oxygen at step-wise increasing temperatures, and the composition of the film was analyzed after every annealing step. The measurements provide a direct proof of inward oxidation with associated concentration gradients, starting with oxygen absorption without significant nitrogen release when using moderate annealing temperatures (250–310 °C), where the oxygen content tends to saturation. At 710 °C, above the oxidation onset temperature, atomic composition data indicate N loss parallel to the O uptake. However, ex-situ transmission electron microscopy showed no evidence of any oxide phase, implying that oxidation starts without crystallite formation.

Strongly coupled C@MoSe2@OMWCNT heterostructure as an anode for sodium-ion batteries

MoSe2, with its extraordinary theoretical capacity, has emerged as a profoundly auspicious anode material for Sodium-ion Batteries (SIBs). However, the actual realization of SIBs encounters hurdles arising from insufficient electron and ion transportation capabilities, along with the irreversible transformation of Mo/Na2Se into MoSe2, eventually substituted by Mo/Se. In this investigation, By employing Mo-based complexes, we have achieved a triumphant synthesis of C@MoSe2@OMWCNT (oxidized multiwall carbon nanotubes) materials, wherein OMWCNTs serve as the fundamental substrate. Theoretical analysis has revealed that the utilization of OMWCNTs not only enhances the structural stability of the anode materials but also improves the electrical conductivity and Na+ ion mobility (the Na+ diffusion barrier: (MoSe2) 0.91 eV vs (C@MoSe2@OMWCNT) 0.41 eV) of the C@MoSe2@OMWCNT. These properties make C@MoSe2@OMWCNT a promising candidate for the development of high-performance SIBs. Furthermore, the Ex-situ Transmission Electron Microscopy (TEM) examination, unveils the emergence of Se and MoSe2 within the C@MoSe2@OMWCNT. The findings indicate that the outer carbon coating layer efficiently prevents contact between Se and the electrolyte, thereby impeding the formation of polyselenides. When C@MoSe2@OMWCNT is employed as the anode for the SIB, it exhibits exceptional cycle stability, with a capacity of 303 mA h g−1 and 189 mA h g−1 after 500 and 3000 cycles, respectively, under a current density of 5 A g−1. Overall, this investigation provides valuable insights into the design and synthesis of advanced anode materials for SIBs, which could have significant implications for the development of next-generation energy storage devices.

Modulating Co[sbnd]Co bonds average length in Co0.85Se1−xSx to enhance conversion reaction for potassium storage

While alloying transition metal chalcogenides (TMCs) with other chalcogen elements can effectively improve their conductivity and electrochemical properties, the optimal alloying content is still uncertain. In this study, we study the influence of dopant concentration on the chemical bonds in TMC and reveal the associated stepwise conversion reaction mechanism for potassium ion storage. According to density function theory calculations, appropriate S-doping in Co0.85Se (Co0.85Se1−xSx) can reduce the average length of CoCo bonds because of the electronegativity variation, which is thermodynamically favourable to the phase transition reactions. The optimal Se/S ratio (x = 0.12) for the conductivity has been obtained from experimental results. When assembled as an anode in potassium-ion batteries (PIBs), the sample with optimized Se/S ratio exhibits extraordinary electrochemical performance. The rate performance (229.2 mA h g−1 at 10 A g−1) is superior to the state-of-the-art results. When assembled with Prussian blue (PB) as a cathode, the pouch cell exhibits excellent performance, demonstrating its great potential for applications. Moreover, the stepwise K+ storage mechanism caused by the coexistence of S and Se is revealed by in-situ X-ray diffraction and ex-situ transmission electron microscopy techniques. Hence, this work not only provides an effective strategy to enhance the electrochemical performance of transition metal chalcogenides but also reveals the underlying mechanism for the construction of advanced electrode materials.

Investigation of the microstructure of He+ ion-irradiated TiBe12 and CrBe12 using ex-situ transmission electron microscopy

Titanium and chromium beryllides, TiBe12 and CrBe12, are materials of potential future importance as neutron multipliers for tritium breeding in nuclear fusion reactors. Beryllium experiences extremely high transmutation according to a n →2n transmutation reaction in which both tritium and helium are produced, which normally form bubbles in solids at the relevant concentration range. Neutron irradiation from the fusion plasma also introduces point defects into solids. The ensuing effect of this environment on the beryllides’ microstructure is poorly characterised, but important for understanding beryllides’ mechanical properties and their evolution in the irradiative environment inside a fusion reactor. This study is intended to initially determine and describe the microstructural features that occur in TiBe12 and CrBe12 when He and fast-particle-induced point defects have been introduced at fusion reactor neutron breeder relevant temperatures. In this study, beryllide samples were implanted with 300 kV He at a range of temperatures between 387 and 900 °C, sectioned down through the implantation surface with a focused ion beam post-irradiation, and the resulting microstructures examined using transmission electron microscopy, electron-dispersive X-ray spectroscopy (EDX/EDS) and precession diffraction mapping.Nanometre-scale bubbles grew in both TiBe12 and CrBe12 at 600 °C and larger (100+ nm) bubbles, some faceted, grew at 900 °C. Some bubbles in CrBe12 were lined with Cr, with some of the Cr oxidised. TiBe12 developed planar faults, on {110} planes at 600 °C and below but on to {111} at 900 °C. Faults were preferentially associated with large bubbles. The displacement vectors of faults on the {110} planes had some commonality with previous studies that found displacement vectors of the two types R=12〈011〉 and R=12〈110〉; the present study also found faults that did not match either previously found type. CrBe12 also developed planar faults but the appearance of these was quite different from the typical striped appearance of planar stacking faults and their nature remains unknown. Oxide particles from manufacture were found in both beryllides, most prominently in CrBe12.

Atomic layer deposition of aluminum-doped zinc oxide onto MoO3 nanorods toward enhanced lithium storage performance

An atomic layer deposition (ALD) of aluminum-doped zinc oxide (AZO) onto MoO3 nanorods (denoted as MoO3@AZO) was developed to enhance the lithium storage performance of MoO3 anode. Thanks to the highly conductive and robust AZO layer, the MoO3@AZO electrode demonstrated high pseudocapacitive contribution (76.2 % at 1.0 mV s−1), enhanced electron/ion transferability, outstanding rate performance (708 mAh g−1 at 2 A g−1) and excellent cycling stability (973 mAh g−1 after 100 cycles at 0.2 A g−1 with a high capacity retention of 92.8 %) when applied as an anode for lithium-ion batteries. Ex-situ transmission electron microscopy analysis revealed that the rod feature of MoO3@AZO was well retained with the protection of the AZO layer even after 100 cycles. Moreover, the ALD-AZO coating may also be commonly used for other metal oxides to enhance their electron conductivity and structural stability.

Use of Boron Doped Diamond Corrosion Free Supports to Evaluate Fuel Cell Electrocatalyst Stability Under Accelerated Stress Testing

Proton exchange membrane fuel cell (PEMFC) electrocatalysts are typically Pt or Pt alloy nanoparticles (NPs) supported on high surface area carbon black powders, the latter which contain a significant sp2 carbon component. One of the barriers to PEMFC commercialisation is the lifetime of the catalyst-support system, which should be at least 5,000 hours for automotive applications.[1] During the start-up and shut-down of the PEMFC, the cathode is subjected to significant oxidative potentials (greater than 1 V vs RHE) which can lead to corrosion of the predominantly sp2 bonded carbon support, a key factor which can limit the lifetime of PEMFCs. [2] High quality boron doped diamond (BDD) is an sp3 bonded network with above 1:1000 B:C ratio, which is required for metal-like electronic conductivity. BDD has many favourable properties for electrochemical experiments, most notably: higher electrochemical corrosion resistance with respect to sp2 carbons, low background currents, and a wide aqueous solvent window.[3] In this work we first explore the electrochemical corrosion stability of BDD when undergoing electrochemical cycling in acid solutions. To achieve this BDD substrates (BDD TEM grid) suitable for both electrochemical experiments and high magnification (single atom resolution) transmission electron microscopy (TEM) experiments were produced using precision ion polishing (Gatan PIPS-II). The surface was characterised using X-ray photoelectron spectroscopy to ensure the polishing process did not significantly alter the diamond substrate. Under aggressive electrochemical potential cycling in perchloric acid and sulfuric acid solutions, both TEM morphological analysis and Electron Energy Loss Spectroscopy (EELS) thickness measurements showed no evidence of BDD corrosion. [4] The BDD-TEM substrate was then used as a platform for investigating the degradation of a PEMFC electrocatalyst (Pt NPs) under accelerated stress testing (AST) [1] conditions on an atomic level, using the corrosion free carbon support. This enables the influence of other degradation pathways [2] (such as aggregation, Ostwald Ripening & direct dissolution) to be explored in more detail, free from issues associated with corrosion of the support. Pt NPs, in the size range 1 – 4 nm, were sputter coated onto the BDD TEM grid. Identical location ex-situ TEM (IL-TEM)[5] in combination with image analysis was used to probe NP changes e.g. size, shape, position, on an individual basis before, and after, AST (Fig. 1, which contains c.a. 200 NPs for analysis). Such measurements were complemented by Inductively Coupled Plasma – Optical Emission Spectroscopy analysis for any dissolved Pt, and electrochemical cyclic voltammetry measurements of the Pt to highlight changes in electrocatalytic behaviour (hydrogen evolution reaction and oxygen reduction reaction) due to AST cycling.Figure 1 – High magnification annular dark field (ADF) identical location images of Pt NPs, a) Pt/BDD before AST, b) Pt NPs after AST, c) Cyclic voltammogram of the 1000 cycle AST from 0.8 to 1.4 V vs Ag|AgCl (1.6 to 1.6 V vs RHE).

Constructing strain-alleviated structures in ultrathin FeS/C composites for durable lithium and sodium storage

Iron sulfide (FeS) is a competitive anode material for Li-/Na-ion batteries (LIBs/SIBs) with high specific capacity and excellent environmental benignity. Nevertheless, its practical application is greatly hindered by the sluggish charge transfer dynamics and large volume variations upon cycling. Herein, by constructing a strain-alleviated (bubble film-like) structure in an ultrathin FeS/C composite, the sluggish transfer kinetics and huge volume variations of FeS were fundamentally solved. The bubble film-like carbon matrix serves as the protective shell to alleviate the huge volume changes of FeS and enhance its electronic conductivity, as verified by finite element simulation and ex-situ transmission electron microscopy results. Benefiting from this unique design, the as-designed electrode exhibited a significantly enhanced performance with a high discharge capacity of 469 mA h g−1 at 5 A g−1 for LIBs and 354 mA h g−1 after 1500 cycles at 1 A g−1 for SIBs. Moreover, the full cell with this electrode and LiFePO4 cathode can deliver outstanding cycling stability of 558 mA h g−1 even after 100 cycles. We expect that this strategy can also be applied to other anode materials plagued by poor conductivity and huge volume changes and remarkably spur the development of batteries with high rate capability and long lifespan.

Root characterization of Fe-based catalyzed carbon nanotube forests

For the purpose of understanding the process of forming carbon nanotube forests catalyzed by Fe nanoparticles, a combination of ex-situ transmission electron microscopy observations and molecular dynamics simulation methods were used to study the rooting path of C in Fe and its motion evolution mechanism. The results show that C first reacts with Fe to form Fe3C, and C enters from Fe (110) crystal plane, thus Fe (110) crystal plane transferring to Fe3C (013) crystal plane; then C in Fe3C precipitates and grows into carbon nanotubes, and C precipitates from Fe3C (013) crystal plane, thus creating the relationship of the direction of carbon nanotubes growth parallel to Fe3C (013) crystal plane. The results of the microstructure snapshot over time and radial distribution function calculated by molecular dynamics simulation also show that the motion path of C is the same as the results deduced in the experiment, which confirms the correctness of the results.

Crystallization of SrAl12O19 Nanocrystals from Amorphous Submicrometer Particles.

Advanced instrumentation and modern analysis tools such as transmission electron microscopy (TEM) have led to phenomenal progress in understanding crystallization, in particular from solution, which is a prerequisite for the design-based preparation of a target crystal. Nevertheless, little has been understood about the crystallization pathway under high-temperature annealing (HTA) conditions. Metal oxide crystals are prominent materials that are usually obtained via HTA. Despite the widespread application of hydro-/solvothermal methods on the laboratory scale, HTA is the preferred method in many industries for the mass production of metal oxide crystals. However, poor control over the morphology and grain sizes of these crystals under extreme HTA conditions limits their applications. Here, applying ex-situ TEM, the transformation of a single amorphous spherical submicrometer precursor particle of SrAl12O19 (SA6) at 1150 °C toward a nanosized thermodynamically favored hexagonal crystal is explored. It is illustrated in real space, step by step, how both kinetic and thermodynamic factors contribute to this faceting and morphology evolution. These results demonstrate a nonclassical nucleation and growth process consisting of densification, crystallite domain formation, oriented attachment, surface nucleation, 2-dimensional (2D) growth, and surface diffusion of the atoms to eventually result in the formation of a hexagonal platelet crystal. The TEM images further delineate a parent crystal driving the crystal lattice and morphological orientation of a network of interconnected platelets.

Lithium storage behavior and mechanism of hexagonal FePO4/C composite as a novel anode material for lithium-ion batteries

Exploring novel electrode materials is crucial for the development of high-performance lithium-ion batteries (LIBs). Herein, hexagonal FePO4/N-doped carbon (FP/C-600) composite is synthesized by a facile precipitation method and subsequent heat treatment process; the lithium ions storage performance and mechanism of hexagonal FePO4 as a novel anode material for LIBs are systematically investigated for the first time. The as-prepared FP/C-600 composite gives a high specific capacity (761.1 mA h g−1 at 0.2 A g−1), superior cyclability (433.5 mA h g−1 after 400 cycles at 0.5 A g−1), and outstanding rate capability (240.3 mA h g−1 at 5.0 A g−1) for a half cell. Ex-situ transmission electron microscopy (TEM) characterization demonstrates that the lithium storage reactions in the FePO4 anode proceed via a conversion reaction mechanism. The FP/C-600 nanocomposite has a much smaller electrochemical reaction resistance and larger Li+ diffusion coefficient than the pure FePO4 (FP-600) sample. More importantly, when evaluated as an anode material in a Li-ion full cell, the FP/C-600 composite still maintains a high specific capacity of 456.2 mA h g−1 after 50 cycles at 0.2 A g−1, implying that such FP/C-600 composite is a novel anode material with significant potential for future practical applications in LIBs.

Nano-Crystallites of P2-Type Layered Transition Metal Oxide High Voltage Cathode for Sodium-Ion Battery

In this era of transitioning from conventional sources of energy to non-conventional, sodium-ion battery research has been burgeoning as an indigenous solution to energy storage applications, considering the sustainability, cost effectiveness, high availability and a familiar redox chemistry 1. P2-type Na2/3Ni1/3Mn2/3O2 is one of the preeminent cathode for sodium-ion batteries because of their environmental friendliness, open framework, superior specific capacity, higher operating voltage and air-moisture stability. However, rapid capacity decay on charging it to a higher voltage because of P2 to O2 phase transition and a large volume change leading to exfoliation of the layers have impeded the practicability of this as an electrode material for Na-ion battery 2,3,4.Here in this work, we report the preparation of hexagonal nanocrystals of P2-type Na2/3Ni1/3Mn1/2Ti1/6O2, which is titanium doped in pristine Na2/3Ni1/3Mn2/3O2 via a novel and quick microwave synthesis technique. This provides sharp and clear facets that allows accelerated sodium-ion migration within the crystal during extraction and insertion of Na-ions, making this material a highly efficient cathode. Unlike conventional heating, which requires around 12-20 hours of synthesis time and high energy consumption, microwave radiation induces rapid solid-state reaction that heats the material on molecular level leading to uniform heating, thus retaining the nanocrystallinity of the structure 5. The distinctive hierarchical nanostructure having large surface area could efficiently facilitate the transportation of Na+ ions, fast utilization of active materials, overcome the effect of internal strain generated inside and reduces the pulverization of active materials, thereby restraining the P2 to O2 phase transition at higher voltage 6. Aiding from the combined effect of titanium doping at manganese site and designing hierarchical nanocrystrals of P2-type Na2/3Ni1/3Mn1/2Ti1/6O2, we obtained a rate capability of 145 mAh g-1 at 0.1 C and a prolonged cycling life (87.3% capacity retention after 500 cycles at 1C) within a voltage range of 2.5 – 4.2 V, restraining the P2 to O2 type phase transition at higher potential. The combined analysis of X-ray diffraction, scanning electron microscopy and transmission electron microscopy along with density functional theory (DFT) calculations demonstrated the optimization of the structure and the physical properties of pristine Na2/3Ni1/3Mn2/3O2 and Ti doped structure along with their Bader charge analysis and electronic properties. Further the mechanical integrity of the nano Na2/3Ni1/3Mn1/2Ti1/6O2 and micro Na2/3Ni1/3Mn1/2Ti1/6O2 were analyzed through micro-compression test of the as prepared pellets. The underlying mechanism for the suppression of phase transition in Na2/3Ni1/3Mn1/2Ti1/6O2 was elucidated by ex-situ X-ray diffraction (XRD) and ex-situ Transmission electron microscopy (TEM). The electrochemical kinetics regarding Na+ diffusion coefficient was further studied through galvanostatic intermittent titration technique (GITT). An analytical model was established to probe deeper into the reason for exfoliation and thus, support our hypothesis. In addition, a sodium-ion full cell was constructed by pairing the as-prepared P2-type Na2/3Ni1/3Mn1/2Ti1/6O2 with a hard carbon anode. This modification of P2-type Na2/3Ni1/3Mn1/2Ti1/6O2 nanocrystallites with comprehensive electrochemical performance can be a path breaking, highly efficient cathode material for large-scale energy storage applications.

Pomegranate-inspired porous SnSe/ZnSe@C anode: A stress-buffer nanostructure for fast and ultrastable sodium-ion storage

Tin selenide (SnSe) is considered as a potential anode for sodium-ion batteries (SIBs) owing to its high theoretical specific capacity. Unfortunately, it suffers from drastic volume expansion/contraction during sodium ions insertion/extraction, resulting in poor cycling stability. Herein, a pomegranate-inspired porous carbon shell wrapped heterogeneous SnSe/ZnSe composite (SnSe/ZnSe@C) is exquisitely designed and fabricated through electrostatic spraying followed by high-temperature selenization. The polyacrylonitrile-derived carbon shell acts as an adhesive to link the porous cubic SnSe/ZnSe and form highly interconnected microcircuits to improve the electron/ion transfer efficiency and inhibit the bulk volume change of internal metallic selenide nanoparticles and polyselenides dissolution during repeated cycling. Moreover, the abundant heterostructure interface of SnSe/ZnSe further significantly accelerates the electrons/ions transport. As a result, the as-prepared SnSe/ZnSe@C electrode exhibits a high specific capacity (508.3 mAh g−1 at 0.05 A g−1), excellent rate performance (177.8 mAh g−1 at 10.0 A g−1), and remarkable cycling stability (195.9 mAh g−1 after 10,000 cycles at 5.0 A g−1). Furthermore, in-situ X-ray diffraction (XRD)/Raman, ex-situ transmission electron microscopy, and kinetic analysis clearly reveal a four-step electrochemical reaction process and battery-capacitor dual-mode sodium storage mechanism. This work provides a new perspective for developing commercial SIBs anode materials with high capacity and long lifespan.

Heterostructured Ni3S4/Co9S8 Encapsulated in Nitrogen-Doped Carbon Nanocubes for Advanced Potassium Storage

Potassium-ion batteries (PIBs), act as an emerging renewable secondary battery technology, have drawn substantial attention because of the easily available potassium resources and excellent electrochemical properties. At present, exploiting desirable anode materials is still a challenge. Transition metal sulfides (TMSs) are considered as the advanced anode materials for PIBs due to the high theoretical specific capacity and abundant resources. But they experience large deformation during the potassiation/depotassiation process resulting in the unsatisfying long-term cyclability, which impedes their widespread applications in PIBs. Hence, we report a bimetallic sulfide heterostructure confined in nitrogen-doped carbon nanocubes (NCS@NC) as the host for PIBs, which delivers an inspiring capacity (637.5 mAh g−1 at 0.1 A g−1) and the remarkable lifespan (417.7 mAh g−1 at 2 A g−1 after 1000 cycles). We show that the nano-heterojunction can not only accelerate the K+ diffusion, but also promote charge transfer at heterointerfaces. Moreover, scanning electron microscopy after cycling reveals that the carbon shell can tolerate the volume expansion during cycling, resulting in the robust structural stability. NCS@NC anode experiences a four-stage K+-storage mechanism of combined intercalation and conversion reactions, as demonstrated by in-situ X-ray diffraction and ex-situ transmission electron microscopy techniques. This strategy of combining morphology engineering with heterostructure construction may enlighten the design of desirable anode materials towards the development of advanced PIBs.

Impact of Nanoparticle Size and Surface Chemistry on Peptoid Self-Assembly.

Self-assembled organic nanomaterials can be generated by bottom-up assembly pathways where the structure is controlled by the organic sequence and altered using pH, temperature, and solvation. In contrast, self-assembled structures based on inorganic nanoparticles typically rely on physical packing and drying effects to achieve uniform superlattices. By combining these two chemistries to access inorganic-organic nanostructures, we aim to understand the key factors that govern the assembly pathway and structural outcomes in hybrid systems. In this work, we outline two assembly regimes between quantum dots (QDs) and reversibly binding peptoids. These regimes can be accessed by changing the solubility and size of the hybrid (peptoid-QD) monomer unit. The hybrid monomers are prepared via ligand exchange and assembled, and the resulting assemblies are studied using ex-situ transmission electron microscopy as a function of assembly time. In aqueous conditions, QDs were found to stabilize certain morphologies of peptoid intermediates and generate a final product consisting of multilayers of small peptoid sheets linked by QDs. The QDs were also seen to facilitate or inhibit assembly in organic solvents based on the relative hydrophobicity of the surface ligands, which ultimately dictated the solubility of the hybrid monomer unit. Increasing the size of the QDs led to large hybrid sheets with regions of highly ordered square-packed QDs. A second, smaller QD species can also be integrated to create binary hybrid lattices. These results create a set of design principles for controlling the structure and structural evolution of hybrid peptoid-QD assemblies and contribute to the predictive synthesis of complex hybrid matter.

Graphene-like ultrathin bismuth selenide nanosheets as highly stable anode material for sodium-ion battery

Sodium-ion batteries have high potential for next-generation battery system because of their cost-effective and similar energy-storage mechanism to lithium-ion batteries. However, the commercial graphite anode for lithium-ion batteries cannot be applied to sodium-ion batteries. The lower rate performance and poor cycling life of existing anode materials are major bottlenecks to prospective application in sodium-ion batteries. To address this issues, we synthesize a novel ultrathin Bi2Se3 layered nanosheets that enhance sodium-ion storage performance due to its stable graphene-like structure. Benefiting from the layered nanosheets morphology, as-prepared anode material exhibit excellent electrochemical performance, which can deliver an initial high capacity of 650 mA h g−1 (Na+ storage) at 0.1 A/g along with outstanding stability. The ultrathin Bi2Se3 layered nanosheets with a thickness of ~6 nm offer a large electrode-electrolyte contact interface due to its porous morphology. Ex-situ transmission electron microscopy analysis and electrochemical impedance spectroscopy measurement reveals the structural stability of bismuth selenide nanosheets during repeated sodium-ion insertion and extraction process. The superior electrochemical performance and unique graphene-like architecture of the layered bismuth selenide nanosheets offer a promising anode for commercial sodium-ion batteries.

Structural transformation of Na2Mn2(SO4)3 alluaudite into orthorhombic Li2Mn2(SO4)3 induced after lithium intercalation

Double sulfate salts of sodium and manganese, Na2Mn2(SO4)3, with an alluaudite-type of structure has been shown to intercalate Li+ ions reversibly, but the mechanism is still unclear. This study aims to examine the structure transformation of the alluaudite sodium manganese sulfate Na2Mn2(SO4)3 after Li+ intercalation by means of ex-situ transmission electron microscopy. We demonstrate that lithium intercalation into alluaudite Na2Mn2(SO4)3 proceeds at a nano-scale and leads to a formation of orthorhombic phase Li2Mn2(SO4)3. Although the alluaudite and orthorhombic structures possess common Mn2O10 entities, they are completely different. Because of the nano-structure, in-situ generated phase Li2Mn2(SO4)3 displays better capacity in comparison with the phase obtained before the electrochemical experiment. The orthorhombic Li2Mn2(SO4)3 is obtained by freeze-drying method, followed by thermal treatment at 500 °C. The revised electrochemical property shows that orthorhombic Li2Mn2(SO4)3 is able to intercalate reversible at least 1 mol of Li only in the case when electrolyte based on ionic liquid is used.

Effect of Zr on the as-cast microstructure and mechanical properties of lightweight Ti2VNbMoZrx refractory high-entropy alloys

Refractory high-entropy alloys (RHEAs) have attracted extensive attention due to their outstanding high-temperature performance. However, high density and poor ductility are the two bottleneck problems in industrial application. This study aims to exploit novel RHEAs with high specific strength and good ductility by adding light Group IVB elements. The effect of Zr on the as-cast microstructure, density, and mechanical properties of Ti2VNbMoZrx (x = 1, 1.5, 2, and 3) RHEAs was investigated in detail. All Ti2VNbMoZrx RHEAs exhibited a disordered body-centered-cubic solid-solution phase. The as-cast microstructures changed from dendritic morphology (x = 1 and 1.5) to equiaxed dendritic morphology grain (x = 2 and 3) with the increasing Zr content. The Ti2VNbMoZr2 RHEA displayed optimal mechanical properties with a compressive yield strength of 1421 MPa, a plastic strain of 31.6%, and a specific yield strength of 211 kPa · m3 · kg−1, superior to the most-reported RHEAs. The microbands along {110} and {112} slip planes, which was a typical poly slip configuration, were observed in the Ti2VNbMoZr2 alloy after compression test using ex-situ transmission electron microscopy. Furthermore, the Ti2VNbMoZr2 RHEA exhibited good high-temperature mechanical properties, showing a yield strength of 977 MPa at 600 °C and 386 MPa at 800 °C without fracture at a plastic strain of 50%. The solution strengthening model revealed that the high yield strength of Ti2VNbMoZrx RHEAs was mainly derived from the atomic radius misfit and shear modulus misfit of the Zr atoms.

Soot Formation and Growth in Toluene/Ethylene Combustion Catalyzed by Ruthenium Acetylacetonate

ABSTRACT Ruthenium-based compounds are efficient catalysts to enhance combustion performance and suppress soot emission. However, systematic mechanism and in-situ research on reducing soot are rarely addressed. In this study, ruthenium acetylacetonate (Ru(C5H7O2)3, Ru(acac)3) was utilized as the catalyst precursor in different concentration conditions to investigate its impacts on the size, volume, and morphology of the soot particles in the ethylene flames with central toluene injection. The soot particles were detected by in-situ small-angle X-ray scattering (SAXS) and ex-situ transmission electron microscopy (TEM). This study confirms that Ru(acac)3 can suppress the surface growth for the primary soot particles, but no significant change of the morphology has been discovered for the aggregates. Compared with the undoped flame, the volume of the soot particles in the Ru(acac)3-doped flames is lower and the particle size is smaller, indicating a valid inhibition effect of Ru(acac)3 on the soot emission by affecting its surface growth and oxidation process. Despite the remarkable distinction between the undoped and doped flames, no obvious difference is found between the flames with different catalyst concentrations.