Structural Evolution Research Articles

Probing the structural evolution of cobalt hydroxide in electrochemical water splitting.

Transition-metal hydroxides are a category of earth-abundant and stable electrocatalysts for energy storage and conversion devices involving sluggish oxygen evolution reaction (OER). Understanding dynamic evolution at the solid/liquid interface of transition-metal hydroxides is crucial for the rational design of high-performance OER electrocatalysts. This study implemented in situ electrochemical atomic force microscopy (EC-AFM) to directly image the dynamic structural evolution of α-Co(OH)2 platelets during the electrochemical OER. Reconstruction of α-Co(OH)2, accompanied by ion insertion from the electrolyte, results in a volume expansion, which can be well confirmed from the X-ray diffraction patterns. Our findings are important for the fundamental understanding of transition-metal hydroxide oxygen-evolution catalysts, illustrating the dynamic nature of Co-based nanostructures under electrochemical conditions.

Investigation on the evolution of asphalt molecular structure under the salt erosion environment based on molecular dynamics simulation

Up to now, the underlying mechanism about the salt erosion aging of the asphalt has not been fully revealed yet, leading to the limitation of research on extending the lifespan of asphalt in salt erosion environment. Therefore, this work adopted the molecular dynamics (MD) method, aimed to investigate the potential mechanism of the salt erosion aging behavior of the asphalt from a molecular perspective. The asphalt models invaded by sodium sulfate and sodium chloride were established, and the invading salt amount was controlled to simulate the different aging degree. Various thermodynamics and energy parameters are output as simulation results. Results indicated that the potential energy and CED of the asphalt raise with the increasing amount of the salt invading into the asphalt, and the sodium sulfate exhibits a significant impact on increasing energy compared to the sodium chloride. Besides, the introduction of the salt increased the FFV of the asphalt, increasing the possibility of water damage in asphalt. Results of RDF exhibited that salt will intensify the self-assembly of the asphaltenes, which will endow asphalt with stronger elastic response. Moreover, at the same weight, sodium chloride had a larger number of ions, which formed wider connection with the asphaltenes, leading to a more serious self-assembly behavior compared to the sodium sulfate. In addition, the curve of relative concentration showed that the presence of salt prompted the weak or no polar fractions to separate from asphalt and enter the aqueous phase, which was called salt-out. Finally, an aging test in the laboratory was conducted, and the results prove the accuracy of the simulation.

Using Fractal Geometry Theory to Quantify Pore Structure Evolution and Particle Morphology of Stabilized Kaolinite

Using Fractal Geometry Theory to Quantify Pore Structure Evolution and Particle Morphology of Stabilized Kaolinite

Crystal structure evolution and solid solution mechanism of Al2O3-Cr2O3 system under different reaction conditions

Crystal structure evolution and solid solution mechanism of Al2O3-Cr2O3 system under different reaction conditions

Late Palaeozoic structural evolution of the Patch Bank Ridge and Utsira High, northern North Sea

AbstractThis study focuses on the Late Palaeozoic development of the area east of Utsira High in the North Sea, where the stratigraphic section below the late Permian Rotliegend Group is undrilled. We use regional 3D seismic data to study structuring, sediment distribution and geomorphology across the Patch Bank Ridge and Utsira High in the North Sea. The results show that the Stord Basin and the bounding Utsira East fault initially developed during the Late Palaeozoic extension, probably during the Devonian, and that the Utsira Shear Zone controlled the location of Late Palaeozoic depocentres. The Patch Bank Ridge is an uplifted part of the Stord Basin where we identify Late Palaeozoic growth strata along the southern and northern flanks, indicating a similar timing of the structural evolution in this area. Two key wells, in the Sele High and Ling Depression, are used to relate a Late Palaeozoic isopach map with regional structuring, surface tilt and basement morphology to the enigmatic parts of the Late Palaeozoic basin system. Our results supplement regional models for the Late Palaeozoic basin development, we suggest that the deeply eroded Devonian half‐grabens preserved on the Utsira High formed parts of an extensive basin system that show stratigraphic expansion towards their bounding faults. The Top Basement surface at these highs offers several distinct geomorphologies that evolved during three periods of exposure, expressed as (i) a tilted and rugose landscape, (ii) distinct drainage networks and (iii) peneplain surfaces. Cover sediments place these landscapes to the (i) Devonian, (ii) Carboniferous/Permian/Triassic and (iii) Late Triassic periods.

Microstructure and stress mapping in 3D at industrially relevant degrees of plastic deformation.

Strength, ductility, and failure properties of metals are tailored by plastic deformation routes. Predicting these properties requires modeling of the structural dynamics and stress evolution taking place on several length scales. Progress has been hampered by a lack of representative 3D experimental data at industrially relevant degrees of deformation. We present an X-ray imaging based 3D mapping of an aluminum polycrystal deformed to the ultimate tensile strength (32% elongation). The extensive dataset reveals significant intra-grain stress variations (36 MPa) up to at least half of the inter-grain variations (76 MPa), which are dominated by grain orientation effects. Local intra-grain stress concentrations are candidates for damage nucleation. Such data are important for models of structure-property relations and damage.

Electronic and Atomic Structural Properties Associated with Enhanced Photodegradation Activity in Mo-Doped TiO2 Nanoparticles.

The efficacy and structural evolution of Mo-doped titania nanoparticles (MTNPs) as advanced photocatalysts for degrading methyl blue (MB) are investigated by X-ray absorption spectroscopy (XAS). The 3 wt % MTNP, characterized by uniform size and anatase structure, exhibits higher efficiency. The spectral analyses unveiled structural variations in the TiO6 octahedral structure and revealed an active site of the distorted square pyramidal structure symmetry (C4v). The in situ XAS spectra illustrate that MTNPs, particularly at 3 wt % doping, effectively enhanced the hole carriers in Ti 3d orbitals with a charge transfer to Mo 4d orbitals and impeded electron-hole pair merging, significantly enhancing the photodegradation under light illumination. This study deepens our understanding of the crucial role of Mo doping in optimizing TiO2 nanoparticle performance for efficient environmental remediation, showcasing the potential of MTNPs as sustainable photocatalytic materials.

Microstructural evolution and mechanical behaviors of rock salt in energy storage: A molecular dynamics approach

The microstructure of rock salt significantly influences its macroscopic mechanical behaviors and deformation phenomena. Understanding the deformation and failure characteristics of rock salt at multiple scales is crucial for the secure and efficient functioning of energy storage in salt caverns. Although the macroscopic behaviors of rock salt are well understood, the microstructural changes occurring under uniaxial compression have not been thoroughly investigated. This study aims to investigate the evolving laws of rock salt microstructure and mechanical properties during the damage process, thereby providing a fundamental understanding of the underlying mechanism. To achieve this, a series of characterization tests on rock salt were conducted to study its microstructure and defects. Building on this, molecular dynamics simulations were utilized in rock mechanics to elucidate the mechanical behaviors, structural evolutions, and dislocation motions of rock salt during the damage process. The rock salt obtained from Qianjiang, China, is a polycrystalline material with an average subgrain size of 46 nm and an average dislocation density of 4.76 × 10−6 1/Å2. Uniaxial compression of single crystal NaCl exhibits three stages: elastic compression, rapid dislocation multiplication, and forest hardening. Scattered dislocations and isolated dislocation tangles trigger further plastic slippage, leading to decreased strength. Later, the formation of a dislocation cell network hinders further slip and reinforces the strength of rock salt. Plastic deformation is found to be a dominant factor in grain refinement and the formation of polycrystalline structures. Intergranular cracking results from cross-patterned dislocation lines on grain boundaries, which become vulnerable areas of the structure. This study describes the evolutionary process of rock salt microstructures and mechanical properties, identifies the micro-destruction mechanisms during the damage process at the ionic level, and provides insights into the micro-mechanical behavior of rock salt and for the design and stability assessment of underground energy storage facilities.

Microstructure and mechanical properties of multi-phase TiAl alloy matrix composites consolidated via field-assisted sintering technique

AbstractIn this study, fully densified Si3N4/TiAl composites were fabricated using the field-assisted sintering technique (FAST). Microstructural analysis showed the evolution of a continuous network structure consisting of minor fractions of in-situ formed Ti2AlN, unreacted Si3N4 ceramic particles and dominant Ti5Si3 intermetallic phases within the TiAl matrix at Si3N4 content above 1.5 wt%. The hardness of the developed composites increases with increasing Si3N4 content, with 7Si3N4/TiAl composite exhibiting the highest hardness of approximately 487 HV1.0, which was about 57% higher than that of the sintered pure TiAl alloy. Among the sintered samples, 1.5Si3N4/TiAl composite displayed the highest flexural strength of 832.65 ± 12.88 MPa (34.3% higher than pure TiAl matrix) with a deflection of 0.14 mm. In contrast, the lowest flexural strength and deflection of 535.44 ± 21.14 MPa and 0.09 mm were obtained in composite reinforced with 7 wt% Si3N4 ceramic content. The fractured surface of the sintered samples displayed predominantly cleavage fracture mode.

Deep learning-assisted characterization of nanoparticle growth processes: unveiling SAXS structure evolution

Deep learning-assisted characterization of nanoparticle growth processes: unveiling SAXS structure evolution

Structural evolution of ultrasonic microinjection molded sterecomplexes of poly(lactide) during heating process

Two stereocomplexes (SCs) with different molecular weights in poly(L-lactide) (PLLA-49k and PLLA-163k) were prepared by mixing equal amounts of poly(D-lactide) (PDLA) and PLLA via the solution method. The exclusive formation of SCs was achieved in SC-PLLA-49k, whereas both homocrystallites (HCs) and SCs were observed in SC-PLLA-163k. Two blends were subjected to further processing via the ultrasonic microinjection molding technique at varying mold temperatures, yielding amorphous samples. As the samples were heated, the heating induced structural reorganization occurs with the concurrent SCs and HCs for all samples at ca. 80 °C. The degree of crystallinity for HCs XHC exhibits a positive correlation with the mold temperature, whereas the degree of crystallinity for SCs XSC shows a negative dependence on mold temperature for both systems. This behavior can be tentatively explained as follows. Firstly, the demixing of enantiomeric PLA chains occurs in the melt state as evidenced by twice heating measurements of blends. The degree of chain segregation is expected to increase with the increase in mold temperature due to lower supercooling, resulting in a decrease of PLLA/PDLA clusters (SC nuclei). Secondly, a high mold temperature is beneficial for the formation of HC nuclei as the chain mobility is improved. The reformulation of SC nuclei is difficult because of a longer diffusion distance required for PLA molecules. The coexistence of SC and HC nuclei causes the simultaneous appearance of SCs and HCs during heating of samples. As HCs start to melt, a transition from HCs to SCs occurs accompanied by a continuous increase in XSC. For both systems, a maximum of XSC is reached when SCs begin to melt followed by a mold temperature independent evolution of XSC upon further heating. Such a maximum is larger in the low molar mass system because it is less entangled. The reservation of SC nuclei is demonstrated by a comparison of the structural evolution and isothermal cold crystallization behavior between the two blends and their ultrasonic microinjection molded samples.

Unveiling the Aggregation of M-N-C Single-Atom Electrocatalysts into Highly Efficient MOOH Nanoclusters during Alkaline Water Oxidation.

M-N-C-type single-atom catalysts (SACs) are highly efficient for the electrocatalytic oxygen evolution reaction (OER). And the isolated metal atoms are usually considered real active sites. However, the oxidative structural evolution of coordinated N during the OER will probably damage the structure of M-N-C, hence resulting in a completely different reaction mechanism. Here, we reveal the aggregation of M-N-C materials during the alkaline OER. Taking Ni-N-C as an example, multiple characterizations show that the coordinated N on the surface of Ni-N-C is almost completely dissolved in the form of NO3-, accompanied by the generation of abundant O functional groups on the surface of the carbon support. Accordingly, the Ni-N bonds are broken. Through a dissolution-redeposition mechanism and further oxidation, the isolated Ni atoms are finally converted to NiOOH nanoclusters supported by carbon as the real active sites for the enhanced OER. Fe-N-C and Co-N-C also have similar aggregation mechanism. Our findings provide unique insight into the structural evolution and activity origin of M-N-C-based catalysts under electrooxidative conditions.

Expediting Photo‐Charging of Semiconductors through a Bipolar Charge Storage Junction for Responsive Dark Photocatalysis

AbstractPhoto‐charging of semiconductors stores electrons for decoupled solar utilization, overcoming intermittent sunlight availability. However, the sluggish photo‐charging process impedes responsive charge storage. Herein, a bipolar charge storage junction is demonstrated to expedite the photo‐charging process within a renowned ionic‐CN/Co3O4 configuration, benefiting from their mismatched photo‐charging kinetics. Rapid photo‐hole storage associated with structural evolution at geometrically dependent Co sites in Co3O4 improves sluggish electron storage for ionic‐CN, while slow recovery of altered [CoO4] and [CoO6] structures delayed electron‐hole recombination. By passivating individual atomic sites, rapid hole storage is attributed to synergistic contributions of tetrahedral Co2⁺ and octahedral Co3⁺ species. The bipolar charge storage junction is photo‐charged at 0.86 A g−1, rivaling the electrical charging rate in ion batteries. With 60 s photo‐charging, the junction yields 0.27 mmol g−1 of “dark” hydrogen, the benchmark for such a short photo‐charging timeframe. This proof‐of‐concept design empowers the fast photo‐charging ability of bipolar charge storage junctions, advancing responsive photo‐charge storage for decoupled solar utilization.

Unveiling the Aggregation of M−N−C Single‐Atom Electrocatalysts into Highly Efficient MOOH Nanoclusters during Alkaline Water Oxidation

M−N−C‐type single‐atom catalysts (SACs) are highly efficient for the electrocatalytic oxygen evolution reaction (OER). And the isolated metal atoms are usually considered real active sites. However, the oxidative structural evolution of coordinated N during the OER will probably damage the structure of M−N−C, hence resulting in a completely different reaction mechanism. Here, we reveal the aggregation of M−N−C materials during the alkaline OER. Taking Ni−N−C as an example, multiple characterizations show that the coordinated N on the surface of Ni‐N‐C is almost completely dissolved in the form of NO3−, accompanied by the generation of abundant O functional groups on the surface of the carbon support. Accordingly, the Ni−N bonds are broken. Through a dissolution‐redeposition mechanism and further oxidation, the isolated Ni atoms are finally converted to NiOOH nanoclusters supported by carbon as the real active sites for the enhanced OER. Fe−N−C and Co−N−C also have similar aggregation mechanism. Our findings provide unique insight into the structural evolution and activity origin of M−N−C‐based catalysts under electrooxidative conditions.

Aqueous co-solvent synthesis of Zeolitic Imidazolate Frameworks: The impact of co-solvents in the crystal growth kinetics

Zeolitic Imidazolate Frameworks (ZIFs) have been widely studied in recent decades in a variety of applications. However, a fundamental understanding of crystal growth kinetics as well as their formation mechanisms has been very limited. Underpinning such mechanisms might be of key importance for the predictable synthesis of ZIFs to rationally tune the structural and morphological properties for respective applications. Herein, the crystal growth kinetics and structural evolution of ZIF-8 crystals in various aqueous co-solvent reaction environments were studied with respect to synthesis time. By tracking the nucleation, crystal growth, stabilization and ripening, three potential kinetic formation mechanisms were proposed. More specifically, with methanol, isopropanol and acetone, a fast nucleation rate and crystal growth occurred within 60 minutes (min) at room temperature. However, ethanol and n-propanol showed prolonged nucleation which resulted in the slow formation of ZIF-L/ZIF-8 mixed phases at the early stage. Phase transformation to pure ZIF-8 was observed in longer syntheses. Nitrogen-containing solvent, N, N–dimethyl formaldehyde (DMF), was found to induce both nucleation and growth, resulting in large crystals in less than 60 min of fabrication. In each case, the crystal formation follows Avrami's classical model. Hence, by understanding the effects of co-solvents in ZIF nucleation, crystallization and phase selection, one can rationally design the crystals with predictable crystallinity, size, morphology, purity and surface properties for targeted applications such as adsorption of small molecules from aqueous mixtures.

Co doping in NASICON-structured Na3.5MnTi(PO4)3 enables superior structural stabilization and rate performance

NASICON-type Na3MnTi(PO4)3 has been regarded as one of the most ideal cathodes due to its high earth content elements and considerable cycling stability. However, poor electrical conductivity, low redox potential of Ti3+/4+ and undesirable rate performance remain restrict its practical application. Herein, a series of Co-doping Na3.5MnTi1-xCox(PO4)3 (x = 0, 0.05, 0.07 and 0.10) cathode materials are designed via the sol-gel method. By partial substitution with Co, the capacity contribution of the Mn2+/3+and Mn3+/4+ is increased and the rate performance is significantly enhanced. The Na3.5MnTi0.93Co0.07(PO4)3 (NMTP-0.07) delivers a high capacity (150.5 mA h g−1 at 0.1 C), superior rate performance (112.0 mA h g−1 at 10 C) and excellent cycling performance (94.7 % capacity retention after 100 cycles at 1 C). Benefiting from Co doping, the EIS and GITT affirm the superior sodium ion diffusion ability of NMTP-0.07 and the enhancement of its own conductivity. Moreover, in situ XRD measurement validates the highly reversible structural evolution and both solid-solution reaction and two-phase reaction are involved in the sodiation/desodiation process. This contribution provides a new perspective on the doping studies of NASICON materials.

A- and B-type wheat starch granules: The multiscale structural evolution during digestion and the distinct digestion mechanisms

The digestive characteristics of wheat starch are closely related to human health. However, the digestive mechanisms of distinct wheat starch granules are not well understood. To address this problem, A- and B-type wheat starch granules (AWS and BWS, respectively) were digested in vitro and the structural evolution of the digestive remnants was compared. After stomach–intestinal digestion of AWS, its crystallinity decreased from 12.75 % to 6.65 %, its fractal dimension decreased from 3.12 to 2.35, and the median particle size decreased from 20.613 to 10.135 μm. Additionally, the number of short chains (polymerization degree<14) and thermodynamic stability decreased after digestion. For BWS, Fourier transform infrared ratio of 1047/1022 cm−1 and 995/1022 cm−1 increased from 0.665 and 0.725 to 0.990 and 0.800, respectively. The median particle size decreased from 5.480 to 4.769 μm. An enzyme-resistant scattering peak was observed in the 1.35 nm−1 lamellar structure. Additionally, the number of B2 and B3 chains and the thermodynamic stability increased after digestion. Our study confirmed that BWS is more likely than AWS to form enzyme-resistant structures during digestion. These findings provide insights into the distinct digestion mechanisms of AWS and BWS, and serve as a foundation for modifying wheat starch to increase its nutritional value.

Epoxy composite microspheres as a versatile platform for enhancement of chlorophyll dispersion and photostability in coatings

Chlorophyll (Chl), as a rich natural pigment, is limited in applications due to poor photostability. The hydrophobic properties of Chl attributed to the tetrapyrrole ring and terminal long-chain hydrocarbons further constrains its dispersion in aqueous coatings. In this work, chlorophyll/epoxy composite microspheres (Chl/EMs) were prepared as candidate pigments via emulsion polymerization to provide a versatile platform for enhanced dispersion and photostability. The optimal reaction temperature of 75 °C for achieving the appropriate particle size distribution of epoxy microspheres (EMs) was first determined. Chl/EMs were then prepared by (1) the combination of Chl and DGEBA in the emulsification process, or by (2) mixing Chl with m-xylylenediamine (MXDA) during curing. The effects of Chl introduction at different steps on the emulsification, curing agent diffusion, and curing process were studied using off-site microscopy observation and aggregation-induced emission technique, to clarify the structure and morphology evolution during emulsion polymerization. The particle size of the microspheres was mainly determined by the emulsification process of the epoxy precursor. Chl participates in emulsification of Chl/EMs in case (1), resulting in a large average particle size and poor particle size distribution. In case (2), the diffusion of MXDA into epoxy emulsion particles is completed within 30 min and does not impede the quicker diffusion process of Chl which was mixed with MXDA. The prepared Chl/EMs with size ranging from 1 to 10 μm create a conducive oxygen blocking environment. Compared to the complete degradation period of untreated Chl coatings, the photostability of Chl/EMs coatings increased nearly 7-fold. Remarkably, Chl/EMs exhibit superior dispersion capability in waterborne polyurethane coatings compared to pure Chl coatings. The EMs with controllable morphology and size can be used as a versatile platform for enhancing dispersion and photostability of other organic or natural dyes and pigments in waterborne coatings.

Effect of chemical structures and environmental factors on the thermal degradation mechanism of polyimide: Experiments and molecular dynamics simulations

The impact of chemical structure and environment on the thermal stability of polyimide (PI) was examined, and the degradation mechanism was determined using a combination of experiments and molecular simulations. Changes in mechanical properties and thermogravimetric analysis (TGA) were used to characterize the thermal stability of PI. Pyrolysis gas chromatography mass spectrometry (Py-GCMS) and thermogravimetric-infrared spectroscopy (TG-IR) were used to analyze the degradation products both qualitatively and quantitatively. Molecular simulation was employed to analyze the primary bond breakage and thermal degradation pathways of PI, as well as to investigate the effects of the chemical structure, atmosphere, and temperature on degradation properties. The findings indicated that p-benzene-structured 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA)/p-phenylenediamine (PDA) has the best thermal stability, whereas weak bonds like C–O–C in 4,4′-oxydianiline (ODA) and C–N in the 2-(4-aminophenyl)-1H-benzimidazol-5-amine (BIA) imidazole group decrease thermal stability. The formation path of low molecular weight products (CO2, CO, HCN, and NH3) and the potential degradation mechanism of PI were proposed. The process of PI thermal degradation accelerated by oxygen and high temperature was observed at the atomic level. Taken together, this work offers the possibility of monitoring the structural evolution of PI degradation process in real-time.

Microstructure evolution and mechanical properties of a lamellar AlCoCrFeNi2.1 eutectic high-entropy alloy processed by high-pressure torsion

High-pressure torsion (HPT) was applied to a lamellar eutectic high-entropy alloy (EHEA) to study the effect of severe plastic deformation (SPD) on the composite structure and mechanical properties. We found that the existence of multiple phases affects defect distribution and the fragmentation process during HPT. Structural evolution shows orientation dependence with respect to the shear plane, which finally leads to a refined multiphase structure with nanograins and vortex clusters after a shear strain γ of 24. In nanograins, dislocation-mediated deformation prevails. The high density of grain boundaries, forest dislocations, and the generation of deformation twins restrict dislocation movement. As a result, an EHEA with a yield strength of 1.75 GPa, an excellent tensile strength of 2.20 GPa, and an appreciable failure strain of 5 % is realized. Our results demonstrate that the HPT deformation process of the lamellar EHEA is significantly affected by the structure. SPD on the multiphase structure is a suitable route for designing high-strength yet ductile alloys.