Formation Of Interfacial Structure Research Articles

Highly Stable Pt/CeO2 Catalyst with Embedding Structure toward Water-Gas Shift Reaction.

Strong metal-support interaction (SMSI) has been extensively studied in heterogeneous catalysis because of its significance in stabilizing active metals and tuning catalytic performance, but the origin of SMSI is not fully revealed. Herein, by using Pt/CeO2 as a model catalyst, we report an embedding structure at the interface between Pt and (110) plane of CeO2, where Pt clusters (∼1.6 nm) are embedded into the lattice of ceria within 3-4 atomic layers. In contrast, this phenomenon is absent in the CeO2(100) support. This unique geometric structure, as an effective motivator, triggers more significant electron transfer from Pt clusters to CeO2(110) support accompanied by the formation of interfacial structure (Ptδ+-Ov-Ce3+), which plays a crucial role in stabilizing Pt nanoclusters. A comprehensive investigation based on experimental studies and theoretical calculations substantiates that the interfacial sites serve as the intrinsic active center toward water-gas shift reaction (WGSR), featuring a moderate strength CO activation adsorption and largely decreased energy barrier of H2O dissociation, accounting for the prominent catalytic activity of Pt/CeO2(110) (a reaction rate of 15.76 molCO gPt-1 h-1 and a turnover frequency value of 2.19 s-1 at 250 °C). In addition, the Pt/CeO2(110) catalyst shows a prominent durability within a 120 h time-on-stream test, far outperforming the Pt/CeO2(100) one, which demonstrates the advantages of this embedding structure for improving catalyst stability.

Characterization of the Interfacial Orientation and Molecular Conformation in a Glass-Forming Organic Semiconductor.

The ability to control structure in molecular glasses has enabled them to play a key role in modern technology; in particular, they are ubiquitous in organic light-emitting diodes. While the interplay between bulk structure and optoelectronic properties has been extensively investigated, few studies have examined molecular orientation near buried interfaces despite its critical role in emergent functionality. Direct, quantitative measurements of buried molecular orientation are inherently challenging, and many methods are insensitive to orientation in amorphous soft matter or lack the necessary spatial resolution. To overcome these challenges, we use polarized resonant soft X-ray reflectivity (p-RSoXR) to measure nanometer-resolved, molecular orientation depth profiles of vapor-deposited thin films of an organic semiconductor Tris(4-carbazoyl-9-ylphenyl)amine (TCTA). Our depth profiling approach characterizes the vertical distribution of molecular orientation and reveals that molecules near the inorganic substrate and free surface have a different, nearly isotropic orientation compared to those of the anisotropic bulk. Comparison of p-RSoXR results with near-edge X-ray absorption fine structure spectroscopy and optical spectroscopies reveals that TCTA molecules away from the interfaces are predominantly planar, which may contribute to their attractive charge transport qualities. Buried interfaces are further investigated in a TCTA bilayer (each layer deposited under separate conditions resulting in different orientations) in which we find a narrow interface between orientationally distinct layers extending across ≈1 nm. Coupling this result with molecular dynamics simulations provides additional insight into the formation of interfacial structure. This study characterizes the local molecular orientation at various types of buried interfaces in vapor-deposited glasses and provides a foundation for future studies to develop critical structure-function relationships.

Interfacial structure and wear properties of selective laser melted Ti/(TiC+TiN) composites with high content of reinforcements

• Titanium matrix composites reinforced with high-content TiC and TiN particulates are manufactured by SLM. • The constitution, interfacial structure and wear properties of SLM-fabricated Ti/(TiC+TiN) composites are investigated. • The formation mechanism of interfacial structure in the SLM-processed Ti/(TiC+TiN) composites is addressed. High-fraction ceramic particulate-reinforced titanium matrix composites were manufactured by selective laser melting (SLM) from starting powders containing Ti-TiC, Ti-TiN, Ti-TiC-TiN and Ti-TiN-graphene. The microstructures of the composites were characterized to reveal the constitution of the reinforcements, the matrix as well as the formation of interfacial structure via ex-situ and in-situ synthesis routes. The microhardness of the SLM-fabricated composites is at least three times higher than that of unreinforced Ti due to high density of hard ceramic reinforcements. A coefficient of friction (COF) value of 0.792 and a wear rate of 1.0 × 10 −4 mm 3 /N −1 m −1 were obtained for the SLM-processed Ti/(TiC+TiN) composites by ex-situ addition of TiC and TiN ceramic particles due to the favorable interfacial structure formed between these hybrid reinforcements and good manufacturing quality. This study proposes a unique interfacial structure by combination of hybrid reinforcements that allows to improve the manufacturing quality and wear properties of SLM-fabricated titanium matrix composites.

(Invited) A Real Time Platform for Observing Surface Processes at Activated Battery Cathodes:Resolving CO2 and O2 Evolution

Understanding the impact of surface catalysis on the interfacial evolution of battery electrodes during energy storage is key to developing reliable, efficient, and safe high-energy density technologies. The formation of interphases is essential for the operation at anodes, where the solid-electrolyte interphase (SEI) kinetically stabilizes the electrode; recently, the formation of interfacial structures at high-energy density cathodes has also garnered great interest due to the kinetic and Coulombic limitations it places on the performance of various promising materials. [1] Elucidating how electrode surface structure, composition, and potential-dependent behavior impact the degradation reactions of the electrolyte and solvent is a fundamental pursuit with significant practical implications, as it may be key to engineering safe devices and to improve the efficiency of growing and aging stable interfaces at an industrial scale. Thus, understanding how surface reactions prompt the evolution of interfaces is a pressing challenge. While X-ray and mass-spectrometric methods [2,3] have been used to characterize these chemistries, probing the surface chemistry of these electrodes with higher versatility, in situ and with high spatiotemporal and chemical resolution represents a formidable analytical challenge.Here, we present an analytical methodology based on the use of scanning electrochemical microscopy in various modes for quantitatively detecting the formation, in real time and with high spatial resolution, of gaseous by-products such as O2 and CO2 from the catalytic decomposition of the electrolyte/solvent at battery electrodes. Using the generation/collection mode we developed an analytical platform capable of resolving these two species in order to quantify material degradation processes as a function of state of charge, and by using the feedback mode we can simultaneously monitor their impact on the interfacial kinetics of the electrode. By insightfully using ultramicroelectrode methods, and principles of CO2 electroreduction, we evaluated the nonaqueous reaction mechanisms involved in the detection to provide quantitative guidance on the relationship between the detected signal and the quantification of the processes undergoing at the battery electrode. We tested the response of our probes on a model NMC cathode, confirming O2 and CO2 evolution processes under conditions reported to exhibit bulk decomposition and surface passivation, respectively. This work creates a foundation not only for the high spatiotemporal evolution of interfacial processes at battery electrodes, but also for the understanding of CO2-related mechanisms in nonaqueous solvents.[1] Li, W. et al. Nature Comm. 2017, 8, 14589[2] Li, Q. et al. ACS Appl. Mater. Interfaces 2020, 12, 2, 2319–2326[3] McCloskey, B.D. et al. J. Phys. Chem. Lett. 2012, 3, 997-1001

Influence of thermal treatment on oil-water interfacial properties and emulsion stabilization prepared by sono-assembled soy peptide nanoparticles

Sono-assembled soy peptide nanoparticles (SPN), originated from large peptide aggregates formed upon enzymatic proteolysis, were successfully fabricated and could act as bifunctional interfacial stabilizer as shown in our previous study. Herein, a continuous work on the potential stabilization mechanism of SPN in response to thermal treatment was carried out, from both the bulk and the interfacial aspect. Results indicated that SPN showed comparable or better surface activity than SPI and could form a stable viscoelastic layer at the oil-water interface. Thermal treatment on SPN considerably accelerated the particle aggregation, which facilitated the adsorption of SPN at the interface with enhanced inter-particle interactions and structural rearrangements, resulting in the formation of interfacial structure with enhanced thickness and stability against coalescence. To further explore how thermal treatment influence SPN at interface, SPN-stabilized emulsion was then subjected to the same thermal treatment. Results obtained showed that enhanced interactions among SPN adsorbed at the interface and so as in the continuous phase was discovered upon thermal treatment, which facilitated the formation of large particle clusters that wrapping the oil droplets. The steric hindrance caused by interfacial aggregation/particle fusion and greater distribution of peptide nanoparticles at the interface endowed the emulsion with extraordinary coalescence stability and enhanced oxidative stability.

Effects of solid fat content in fat particles on their adsorption at the air–water interface

The role of solid fat content (SFC) within fat particles was examined for its effects on adsorption behaviour at the air–water interface. Three kinds of vegetable oil with different SFC profiles were mixed with a sodium caseinate solution (2% w/w) to prepare the creams, whose fat contents were adjusted in the range of 0–40% w/w. The decrease of interfacial tension at the air–water interface was measured for creams and the sodium caseinate solution, and the ratio of the maximum decrease rate of creams (Δγmax)-to-the sodium caseinate solution (Δγ0max), Δγmax/Δγ0max, was calculated. The interfacial elastic modulus (E′) of creams and sodium caseinate solution was also measured and found to initially increase with time but decreased after the maximum value (E'max). Both Δγmax/Δγ0max and E'max were affected by the temperature, fat content of creams and SFC in fat particles. The largest increase for Δγmax/Δγ0max and E′max was observed when the SFC of creams was between 10 and 50% w/w. The microscopic structures of the air–water interface of creams after whipping were also affected by the SFC, such that fat particles containing 28.4% SFC were found to adsorb and aggregate at the air–water interface layer. These results suggest that the adsorption of fat particles onto the air–water interface and interfacial structure formation by adsorbed fat particles were promoted via partial coalescence.

Importance of microstructure and interface in designing metal oxide nanocomposites for supercapacitor electrodes

In this work, we demonstrate that designing metal oxide nanocomposite with an optimized nanocarbon to metal oxide ratio is required to realize the best electrochemical performance. Using carbon nano-onion (CNO) and TiO2 composite as a model system, it is evidenced that the formation of interfacial structure and the existence of electrical percolation networks are essential to enhance electrical performance of the composite. When the aforementioned conditions are satisfied, CNO/TiO2 hybrid nanocomposites (CTHNs) with only 11wt% TiO2 loading exhibits excellent electrochemical performance. The maximum specific capacitance obtained for this composite electrode is 386Fg−1 at a scan rate of 5mVs−1, which is the highest reported value till date in a TiO2 composite electrode measured in a two electrode cell configuration. At this composition, excellent electrochemical stability is obtained with only 5% capacitance degradation over 2000cycles. As the TiO2 loading increases the electrochemical performance decreases.

Effects of Al/Si ordering on feldspar dissolution: Part I. Crystallographic control on the stoichiometry of dissolution reaction

The incongruent dissolution of feldspar is associated with the formation and evolution of Si-rich amorphous interfacial structures during its chemical weathering. The stoichiometry of dissolution is compositionally dependent, and this dependence reflects the nature of dissolution reaction as a combination of surface renewal and heterogeneous chemical reaction. We hypothesize that during continuous surface renewal, reactive sites on a feldspar’s surface will inherit characteristics from the bulk structure of the primary mineral. Hence, the dissolution rate of feldspar depends not only on water chemistry but also on its crystallographic properties. We propose a new formalism to quantify the dependence of the dissolution rates of feldspars on their crystallographic properties. A correlation between the degree of Al/Si ordering and the stoichiometry of feldspar dissolution is predicted based on this formalism. This correlation is verified by a combination of water chemistry analysis, synchrotron X-ray diffraction with structure refinement (HR-XRD), and Fourier transform infrared spectroscopy (FTIR). We find that the rates of dissolution and the degree to which dissolution is incongruent depend on the frequency of SiOSi and SiOAl linkages (chemistry) and the crystallographic characteristics of these linkages (bond lengths, bond angles, and ordering) in the dissolving mineral. The knowledge of Al/Si ordering provides a means to quantify the relative abundances of Si atoms with different reactivities. Using a C1¯-based structure model, we show that the distribution of Al within the Al-rich (T1) type of tetrahedral sites has only a minor effect on dissolution stoichiometry, whereas the distribution of Al between the T1-type and the Si-rich (T2)-type of sites affects dissolution incongruence predominantly. A greater extent of disorder results in higher dissolution incongruence. As an implication, our results suggest that the formation of interfacial structures during silicate dissolution should at least be partially affected by reactivity differences among the framework atoms of a silicate.

Sol–gel mediated surface modification of nanocrystalline NiFe2O4 spinel powders with amorphous SiO2

Abstract Surface modification of nanocrystalline NiFe 2 O 4 spinel particles with amorphous SiO 2 by the sol–gel process at 350 °C was demonstrated. Amorphous phase of the SiO 2 layer was evaluated by X-ray diffraction technique. Structural coordination of the pristine and SiO 2 coated NiFe 2 O 4 particles as investigated by employing FTIR analysis. Thickness of the SiO 2 layer was investigated through transmission electron microscopy and it was identified to be ∼10–23 nm over nanocrystalline NiFe 2 O 4 particles. The magnetic behavior of pristine and surface modified NiFe 2 O 4 particles were investigated using vibrating sample magnetometer (VSM). Magnetic studies showed the retention of magnetic property of surface modified NiFe 2 O 4 particles with the reduced saturation magnetization and coercivity compared to the pristine NiFe 2 O 4 particles, which is respectively due to the lower fraction of the magnetic component and the formation of interfacial structure.

Effects of Zn additions on the structure of the soldered Sn-3.5Ag and Cu interfaces

Purpose The interfacial structure is vitally important for achieving a good joint reliability during service. The purpose of this paper is to systematically explore the effects of Zn addition into the Sn-3.5Ag eutectic solder on the formation of intermetallic compound (IMC) layer at the interface between Sn-3.5Ag-xZn (x = 0, 0.9 and 3) solders and Cu pad. Design/methodology/approach To obtain useful information on the formation of interfacial structure and to determine an effective way to avoid the formation of brittle joints, a series of Sn-Ag lead-free solders with different Zn contents were prepared and soldered. To investigate the IMC layers between Sn-3.5Ag-xZn (x = 0, 0.9 and 3) lead-free solders and the Cu pads, three specimens of the Sn-3.5Ag-xZn/Cu were soldered at 250°C for one min. Findings It is found that the addition of Zn in the Sn-3.5Ag eutectic solder can prompt the formation of Cu5Zn8 IMCs, and restrain the formation of the Cu6Sn5 IMCs. Moreover, the addition of Zn in the Sn-3.5Ag eutectic solder will reduce the solubility of Cu in the liquid solder, which accelerates the growth of the formed IMCs. Consequently, the thickness of IMC layer increases with increasing the content of Zn. Originality/value This paper usefully demonstrates how the addition of Zn favoured the formation of the Cu5Zn8 phase and restrained the formation of the Cu6Sn5 phase. Moreover, the addition of Zn in the Sn-Ag eutectic solder would reduce the solubility of Cu in the liquid solder, which accelerates the growth of the formed IMCs. Consequently, the thickness of the IMC layer increased with increasing concentration of Zn.

Formation of interfacial structure of Sn–3.7Ag–0.9Zn eutectic solder with different Al additions

The structural evolution of interfaces between the Sn–3.5Ag–0.9Zn–xAl (x = 0.5 and 1.0) solders and Cu substrate has been investigated by microstructural observations. The results suggest that the addition of Al in the Sn–3.5Ag–0.9Zn restrains the formation of Cu5Zn8 intermetallic compounds (IMCs) at the soldered interface. Moreover, the formation of Al2Cu and Cu9Al4 IMCs leads to a crack failure near the interface of the Sn–3.7Ag–0.9Zn–1Al and Cu pad. It is suggested that the increase of Al content (e.g. 1 wt%) in the Sn–Ag–Zn eutectic solder would do harm to the reliability of the solder joint.

Effect of the soldering time on the formation of interfacial structure between Sn–Ag–Zn lead-free solder and Cu substrate

The evolution of interfacial structure between the Sn–3.7%Ag–0.9%Zn lead-free solder and Cu substrate were systematically explored for different soldering times (1, 5, and 10 min). According to microstructural observations, it is found that the longer the soldering time is, the thicker the soldered interface becomes. The interface soldered for 1 min is composed of the Cu5Zn8 intermetallic compounds (IMCs) layer locating above the Cu6Sn5 IMCs layer. The interfaces soldered for 5 and 10 min are mainly made up of the Cu6Sn5 IMCs with some bulk Ag3Sn IMCs randomly distributing within it. The evolution of the IMCs layer in the soldered interface can be divided into three stages: the Cu5Zn8 IMCs firstly forms, then Cu6Sn5 IMCs separated out from the bottom (controlled by diffusion of Sn in the Cu5Zn8), finally, subsequent growth of the Cu6Sn5 IMCs layer is controlled by diffusion of Sn in Cu6Sn5 IMCs.

Effect of segregation on the formation of interface structures. Example of Cr-Doped CoO

This paper considers the formation of spinel-type structures at the surface of Cr-doped CoO. This structure, which is formed at elevated temperatures, decomposes during slow cooling and impoverishment of the surface layer in Cr occurs. Analysis of the effect of cooling rate on the Cr concentration profile in the boundary layer indicates that the decomposition of the surface structure is controlling the process of Cr desegregation during cooling rather than Cr lattice diffusion.

Modeling of internal stresses and interface effects in metals

Currently theoretical work is being carried out on the influence of internal stresses and the effect of interfaces on the microstructural development in metallic systems. Atomistic simulations provide an adequate description of nanoscale phenomena such as precipitation, interface-structure formation and adatom migration. Remarkable progress to predict microstructure evolution has also been achieved by appropriate continuum approaches.