Evolution Of Surface Structure Research Articles

Elucidating the effect of annealing temperature on the atomic-level surface structure evolution and electrochemical performance of Mo doped LiMn2O4 cathode materials

Critical barriers to the extensive applications of the spinel LiMn2O4 cathodes include grievous capacity degradation and structural collapse. Bulk elemental doping combining surface modification, which is a common approach to address these challenges. Here, synchronous bulk Mo-doped and in-situ surface reconstructed layer coated LiMo0.02Mn1.98O4 cathodes are prepared by tuning the annealing temperatures. Using the spherical aberration-corrected scanning transmission microscopy (Cs-STEM) technique, we demonstrate that part of Mo6+ ions dopes into the octahedral Mn 16d sites to form LiMo0.02Mn1.98O4 that strengthens bulk structural stability. The other part of Mo6+ ions or the Mn atom occupying the Mn 16c sites of the spinel to form a surface reconstructed layer on the outermost surface that suppresses the side reaction and slows down the decomposition of the electrolyte. Specifically, the LiMo0.02Mn1.98O4 cathode calcined at 750 °C with an appropriate surface reconstructed layer exhibits an outstanding capacity retention of 76.28 % after 1000 cycles at 10C at 25 °C. Our work provides a simple and novel way toward high electrochemical performance tuning for spinel LiMn2O4 cathodes.

Alkali Metal Cations Induce Structural Evolution on Au(111) During Cathodic Polarization.

The activity of the electrocatalytic CO2 reduction reaction (CO2RR) is substantially affected by alkali metal cations (AM+) in electrolytes, yet the underlying mechanism is still controversial. Here, we employed electrochemical scanning tunneling microscopy and in situ observed Au(111) surface roughening in AM+ electrolytes during cathodic polarization. The roughened surface is highly active for catalyzing the CO2RR due to the formation of surface low-coordinated Au atoms. The critical potential for surface roughening follows the order Cs+ > Rb+ > K+ > Na+ > Li+, and the surface proportion of roughened area decreases in the order of Cs+ > Rb+ > K+ > Na+ > Li+. Electrochemical CO2RR measurements demonstrate that the catalytic activity strongly correlates with the surface roughness. Furthermore, we found that AM+ is critical for surface roughening to occur. The results unveil the unrecognized effect of AM+ on the surface structural evolution and elucidate that the AM+-induced formation of surface high-activity sites contributes to the enhanced CO2RR in large AM+ electrolytes.

Revealing the surface structure and morphology evolution of Co nanoparticle supported on ZrO2 surfaces

The optimization of structure-dependent activity of supported metal catalysts has driven the dynamic determination of the morphology of Co nanoparticles on ZrO2 using atomic-level simulations. Density functional theory (DFT) calculations combined with ab initio molecular dynamics (AIMD) simulations were used to investigate the surface structure, nucleation mechanism and morphology evolution of Con clusters supported on different ZrO2 facets. As the size of the Con (n = 1–5) cluster increases, the competition between Co-Co bonding and the interaction of Con clusters with the ZrO2 surface further promotes the nucleation of larger clusters. Co atoms prefer to nucleate into large clusters on both c-ZrO2(111) and t-ZrO2(101) surfaces, but this behavior is unfavorable on the m-ZrO2(-111) surface. The analysis of electric properties suggests that the types of hybrid orbitals and the number of electron transfer accounts for the difference in energies of Con clusters on ZrO2 surfaces. Further, the AIMD simulations verified the stable structure of small Co5 cluster obtained by DFT, and predicted the morphology of large Co13 clusters on ZrO2 surfaces under realistic reaction conditions, consistent with the experimental SAM images. Our work provides an intuitive understanding of structure and morphology evolution of catalysts for the targeted design of catalysts to achieve the desired activity and explore more reaction possibilities.

The evolution of granular surface structure and functional properties in rice starch during grain filling

The developmental changes in the granular surface structure and functional properties of starch during the entire grain filling period of rice (around 40 days) were investigated. The specific surface area of rice starch significantly decreased firstly then stabilized during growth due to increasing granular size. The pore volume decreased from 5.40 cm3/g at 6th day after anthesis (DAA-6) to 3.02 cm3/g (DAA-46). More starch granule-associated proteins (SGAPs) accumulated on the surface and in channels. Swelling power decreased by 46 %, whereas the flow behavior index (n) decreased by 32 % in upward curve during starch development from DAA-6 to DAA-30. Tan δ first dropped then remained steady at DAA 22–34 and lightly rebounded at the final stage, indicating that starch in the middle stage tended to have greater viscoelastic gel behavior at all sweeps. Mature starch showed lower in vitro hydrolysis rate and exhibited stronger enzymatic resistance. The results showed that granular surface features of rice starch may be an essential factor in determining rheological behavior and resistance to hydrolysis.

Interface Structures on Mechanically Polished Surface of Spinel Ferrite and Its Effect on the Magnetic Domains.

Soft magnetic spinel ferrites are indispensable parts in devices such as transformers and inductors. Mechanical surface processing is a necessary step to realize certain shapes and surface roughness in producing the ferrite but also has a negative effect on the magnetic properties of the ferrite. In the past few years, a new surface layer was always believed to form during the mechanical surface processing, but the change of atomic structure on the surface and its effect on the magnetic structure remain unclear. Herein, an interface structure consisting of a rock-salt sublayer, distorted NiFe2O4 sublayer, and pristine NiFe2O4 was found to form on mechanically polished single-crystal NiFe2O4 ferrite. Such an interface structure is produced by phase transformation and lattice distortion induced by the mechanical processing. The magnetic domain observation and electrical property measurement also indicate that the magnetic and electrical anisotropy are both enhanced by the interface structure. This work provides deep insight into the surface structure evolution of spinel ferrite by mechanical processing.

Elevated Water Oxidation by Cation Leaching Enabled Tunable Surface Reconstruction.

Water electrolysis is one promising and eco-friendly technique for energy storage, yet its overall efficiency is hindered by the sluggish kinetics of oxygen evolution reaction (OER). Therefore, developing strategies to boost OER catalyst performance is crucial. With the advances in characterization techniques, an extensive phenomenon of surface structure evolution into an active amorphous layer was uncovered. Surface reconstruction in a controlled fashion was then proposed as an emerging strategy to elevate water oxidation efficiency. In this work, Cr substitution induces the reconstruction of NiFexCr2-xO4 during cyclic voltammetry (CV) conditioning by Cr leaching, which leads to a superior OER performance. The best-performed NiFe0.25Cr1.75O4 shows a ~1500 % current density promotion at overpotential η=300 mV, which outperforms many advanced NiFe-based OER catalysts. It is also found that their OER activities are mainly determined by Ni : Fe ratio rather than considering the contribution of Cr. Meanwhile, the turnover frequency (TOF) values based on redox peak and total mass were obtained and analysed, and their possible limitations in the case of NiFexCr2-xO4 are discussed. Additionally, the high activity and durability were further verified in a membrane electrode assembly (MEA) cell, highlighting its potential for practical large-scale and sustainable hydrogen gas generation.

Elevated Water Oxidation by Cation Leaching Enabled Tunable Surface Reconstruction

AbstractWater electrolysis is one promising and eco‐friendly technique for energy storage, yet its overall efficiency is hindered by the sluggish kinetics of oxygen evolution reaction (OER). Therefore, developing strategies to boost OER catalyst performance is crucial. With the advances in characterization techniques, an extensive phenomenon of surface structure evolution into an active amorphous layer was uncovered. Surface reconstruction in a controlled fashion was then proposed as an emerging strategy to elevate water oxidation efficiency. In this work, Cr substitution induces the reconstruction of NiFexCr2‐xO4 during cyclic voltammetry (CV) conditioning by Cr leaching, which leads to a superior OER performance. The best‐performed NiFe0.25Cr1.75O4 shows a ~1500 % current density promotion at overpotential η=300 mV, which outperforms many advanced NiFe‐based OER catalysts. It is also found that their OER activities are mainly determined by Ni : Fe ratio rather than considering the contribution of Cr. Meanwhile, the turnover frequency (TOF) values based on redox peak and total mass were obtained and analysed, and their possible limitations in the case of NiFexCr2‐xO4 are discussed. Additionally, the high activity and durability were further verified in a membrane electrode assembly (MEA) cell, highlighting its potential for practical large‐scale and sustainable hydrogen gas generation.

Fast, Efficient Tailoring Growth of Nanocrystalline Diamond Films by Fine-Tuning of Gas-Phase Composition Using Microwave Plasma Chemical Vapor Deposition.

Nanocrystalline diamond (NCD) films are attractive for many applications due to their smooth surfaces while holding the properties of diamond. However, their growth rate is generally low using common Ar/CH4 with or without H2 chemistry and strongly dependent on the overall growth conditions using microwave plasma chemical vapor deposition (MPCVD). In this work, incorporating a small amount of N2 and O2 additives into CH4/H2 chemistry offered a much higher growth rate of NCD films, which is promising for some applications. Several novel series of experiments were designed and conducted to tailor the growth features of NCD films by fine-tuning of the gas-phase compositions with different amounts of nitrogen and oxygen addition into CH4/H2 gas mixtures. The influence of growth parameters, such as the absolute amount and their relative ratios of O2 and N2 additives; substrate temperature, which was adjusted by two ways and inferred by simulation; and microwave power on NCD formation, was investigated. Short and long deposition runs were carried out to study surface structural evolution with time under identical growth conditions. The morphology, crystalline and optical quality, orientation, and texture of the NCD samples were characterized and analyzed. A variety of NCD films of high average growth rates ranging from 2.1 μm/h up to 6.7 μm/h were successfully achieved by slightly adjusting the O2/CH4 amounts from 6.25% to 18.75%, while that of N2 was kept constant. The results clearly show that the beneficial use of fine-tuning of gas-phase compositions offers a simple and effective way to tailor the growth characteristics and physical properties of NCD films for optimizing the growth conditions to envisage some specific applications.

The fate of plastic wraps in constructed wetland: Surface structure and microbial community

The high use of plastic wraps leads to significant environmental pollution. In this study, the surface structure and microbial community evolution of commercially available plastic wraps [polyethylene (PE), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), and polylactic acid (PLA)] in constructed wetlands (CWs) were investigated. The results indicated that all plastic wraps gradually decreased in molecular weight, crystallinity, melting, and crystallization temperatures, whereas a gradual increase was observed in the surface roughness, polymer dispersity index (PDI), carbonyl index (CI) and Shannon index of microorganisms colonizing the CWs. The aging rate of the plastic wrap was in the order: PLA > PVC > PE > PVDC, at the same site in the CWs, and it was in the order: soil surface > plant roots > subsoil, for the same plastic wrap. The diversity of microorganisms colonizing the same plastic wrap was in the order: plant roots > subsoil > soil surface. The Shannon indices of microorganisms on plastic wraps were lower than those in the soil, indicating that the diversity of microorganisms colonizing plastic wraps is limited. Additionally, the microbial community structure on the plastic surface was co-differentiated by the plastic type, placement position in the CWs, and aging time. Significantly different microbial community structures were found on the PVC and PVDC wrap surfaces, revealing that the chlorine in plastics limits microbial diversity. Unclassified members of Rhizobiaceae and Pseudomonadaceae were the dominant genera on the surface of the plastic wraps, suggesting that they may be the microorganisms involved in plastic degradation processes. The study provides valuable perspectives to facilitate a comprehensive understanding of the migration, fate, and environmental risks associated with microplastics (MPs) in wetlands.

Surface structure evolution and measurement analysis of Ti6Al4V titanium alloy by electric arc electrochemical machining

In this study, a theoretical model about the conversion mechanism of material removal by electric arc electrochemical machining (EAECM) was derived. The limiting conversion rate of ECM-EAECM was measured on this basis. The current waveform, surface integrity, shape accuracy and process indexes during machining were measured and evaluated. The results showed that when the limiting conversion rate of ECM was exceeded, the material removal consisted of alternating effects of electric arc machining (EAM) and ECM. The proportion of EAM increased and the surface structure evolved into discharge defects, verifying the correctness of the theory. In addition, parametric crossover experiments were performed to clarify the degree of parametric response to EAECM modulation. Finally, the optimal combination of parameters resulted in a material removal rate of up to 5452 mm3/min, a relative electrode wear rate of 1.39 %, and a surface roughness of only 4.62 μm.

In Situ Creation of Surface Defects on Pd@NiPd with Core-shell Hierarchical Structure Toward Boosting Electrocatalytic Activity.

A deep insight into surface structural evolution of the catalyst is a challenging issue to reveal the structure-activity relationship. In this contribution, based on a surface alloying strategy, the dual-functional Pd@NiPd catalyst with a unique core-shell hierarchical structure is developed through selective crystal growth, surface cocrystallization, directional self-assembly, and reduction process. The surface defects are created in situ on the outer NiPd alloy layer in the electrochemical redox processes, which endow the Pd@NiPd catalyst with excellent electrocatalytic activity of hydrogen generation reaction (HER) and oxygen generation reaction (OER) in alkaline media. The optimal Pd@NiPd-2 catalyst requires an overpotential of only 18 mV that is far lower than Pt/C benchmark (43 mV) at the current density of 10 mA cm-2 for the HER, and 210 mV that is far lower than RuO2 benchmark (430 mV) at 50 mA cm-2 for the OER. Density functional theory (DFT) calculations reveal that the outstanding electrocatalytic activity is originated from the creation of surface defect structure that induces a significant reduction in the adsorption and dissociation energy barriers of H2O molecules in the HER and a decrease in the conversion energy from O* to OOH* that resulted from the synergy of two adjacent Pd sites by forming O-bridge. This work affords a typical paradigm for exploiting efficient catalysts and investigating the dependence of electrocatalytic activity on the surface structural evolution.

X‐ray imaging for structural evolution and phase transformation dynamics of battery electrodes

AbstractThe impending energy crisis entails sustainable battery technologies with improved energy density, reliability, safety and lifetime. Hence, it is essential to gain detailed insights into the surface reactions, ionic diffusion, structural and morphological evolution, and degradation mechanisms of battery electrodes. Recently, X‐ray techniques emerged as revolutionary tools to reveal an in‐depth understanding of the battery during operations. This review provides an overview of the use of in situ/operando X‐ray techniques to understand the different functionalities of electrode materials inside the battery. It will focus on the phase transformation, structural evolution and dynamic properties of the battery electrodes, and discuss the relationship between battery failure and electro‐chemo‐mechanical failure in the electrode. Finally, the limitations of these methods are also discussed with the prospects for effective use of these techniques in the development of advanced battery technologies.

Thermally Induced Surface Structure and Morphology Evolution in Bimetallic Pt-Au/HOPG Nanoparticles as Probed Using XPS and STM.

Bimetallic nanoparticles expand the possibilities of catalyst design, providing an extra degree of freedom for tailoring the catalyst structure in comparison to purely monometallic systems. The distribution mode of two metal species defines the structure of surface catalytic sites, and current research efforts are focused on the development of methods for their controlled tuning. In light of this, a comprehensive investigation of the factors which influence the changes in the morphology of bimetallic nanoparticles, including the elemental redistribution, are mandatory for each particular bimetallic system. Here we present the combined XPS/STM study of the surface structure and morphology of bimetallic Pt-Au/HOPG nanoparticles prepared by thermal vacuum deposition and show that thermal annealing up to 350 °C induces the alloying process between the two bulk-immiscible metal components. Increasing the treatment temperature enhances the extent of Pt-Au alloying. However, the sintering of nanoparticles starts to occur above 500 °C. The approach implemented in this work includes the theoretical simulation of XPS signal intensities for a more meticulous analysis of the compositional distribution and can be helpful from a methodological perspective for other XPS/STM studies of bimetallic nanoparticles on planar supports.

Effect of laser preparation strategy on surface wettability and tribological properties under starved lubrication

The preparation strategy determines the microstructure of surface textures, influencing the lubrication properties of surface. This paper proposes three laser scanning strategies aimed at achieving a sinusoidal textured surface, and discussed the evolution of surface structure and chemical composition. The subsequent investigation focuses on the impact of the transition in surface wettability on friction performance. The findings reveal that the ridge structures enhance surface anti-wear properties but concurrently elevates the friction coefficient. However, the oil cover preparation method prevents the formation of ridges and increases the water contact angle to 138°. The shift in wettability is determined by the combined effects of structure and the adsorption of organic compounds. Furthermore, the hydrophobic surface exhibits superior tribological properties in friction tests.

The facilitating effect of sulfide treatment coupled sol-gel method on NH3-SCR activity of Fe–Mn/TiO2 catalysts

The 5Fe–3Mn–S/TiO2-SG catalysts were synthesized by sulfide treatment coupled sol-gel method to develop new NH3-SCR catalysts with wide temperature window, good low-temperature activity and environment-friendly. The evolution of catalyst surface chemical state, morphology, structure, acidity and interaction forces were systematically investigated by XPS, BET, XRD, SEM, H2-TPR, NH3-TPD, UV, IR and steady-state kinetic tests. The influence of sulfide treatment coupled sol-gel method on NO conversion was explored. XRD, BET and SEM characterization revealed that sulfide treatment resulted in smaller catalyst particles and higher dispersion, which increased the specific surface area. XPS, NH3-TPD and steady-state kinetic tests results demonstrated that the sulfide treatment catalysts had a higher surface adsorbed oxygen (Oα) content, which could produce more oxygen vacancies on the catalyst surface, thus increasing the number of acid sites. H2-TPR and UV results demonstrated that the 5Fe–3Mn–S/TiO2-SG catalysts exhibited the strongest contact between the carrier and the active component. The 5Fe–3Mn–S/TiO2-SG catalyst obtained more than 80% NO conversion in the operational temperature range of 220–420 °C, according to the NH3-SCR reaction data. The temperature window was expanded by 120 °C compared to conventional Fe–Mn/TiO2 catalysts, and 98% conversion was achieved at 300 °C. Meanwhile, DFT calculations of the SO42--MnFe2O4(311) crystalline surface of the 5Fe–3Mn–S/TiO2-SG catalysts revealed that it could form stronger chemisorption for both NH3 and NO, which promoted the NH3-SCR reaction more effectively. The DFT calculation results and the experimental findings agreed well.

Assembly of Multisurfaced Van der Waals Layered Compound GaSe via Thermal Oxidation

AbstractThe investigation of the oxidation behavior of van der Waals chalcogenides holds significant importance in terms of preventing and controlling oxidation, utilizing surface oxidation structures to regulate properties, and advancing applications. Here, taking GaSe as a candidate, its thermal oxidation and surface structure evolution are intensively studied. Through systematic microscopic analyses, oxidized structures at multi‐scale (from atomic scale to millimeters) are resolved, and various assembly heterogeneous surfaces including Ga2Se3/Ga2O3 and Ga2O3 multilayers are uncovered at different oxidation temperatures. The temperature‐dependent oxidation behavior and surface structure evolution of the GaSe are revealed, and the oxidation mechanisms in the entire temperature range are also disclosed. Finally, the photoluminescence regulation of the GaSe is initially explored via thermal oxidation, demonstrating great potential for surface oxidation engineering. This study is not only of great importance for the deep understanding and utilization of GaSe oxidation, but also beneficial for materials/device design and development of relative systems.

Electrochemical corrosion behaviour of Zn-Sn-Cu-xNi lead-free solder alloys

Zn-30Sn-2Cu-xNi (x=0, 0.5, 1.0, 1.5, wt.%) lead-free solder alloys were prepared via the casting method. Subsequently, their microstructures and corrosion behaviors in 0.5 mol/L NaCl solution were investigated. The electrochemical behaviour was studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques, to evaluate the influence of Ni content on the corrosion performances of the Zn-Sn-Cu alloy. The corrosion mechanism of the Zn-Sn-Cu-Ni alloys was analyzed by observing surface structure evolution during the corrosion process. The results revealed that the addition of 0.5 wt.% Ni improved the corrosion resistance of Zn-30Sn-2Cu alloy due to forming a denser and more homogeneous corrosion layer, which acted as a physical barrier. The phase identification confirmed that the main corrosion products consisted of ZnO, Zn(OH)2, and Zn5(OH)8Cl2·H2O. As the Ni content reached 1.0 and 1.5 wt.%, the corrosion resistance of Zn-30Sn-2Cu alloy declined, which could mainly be attributed to the galvanic corrosion between the (Ni, Cu)5Zn21 intermetallics and Zn-rich phase, accelerating the dissolution of Zn-rich phase. Thus, Zn-30Sn-2Cu-0.5Ni solder alloy showed the best corrosion resistance.

Formation and modulation of multi-pulse femtosecond laser-induced periodic surface structures by electromagnetic and partial differential equation simulations.

In order to demonstrate the formation of laser-induced periodic surface structures (LIPSS), simulations were performed to investigate the effect of multiple femtosecond laser pulses with different laser energy densities on a Ti6Al4V surface. In this work, a set of partial differential equations calculating the electron and lattice temperature variations, followed by coupling with an electric field, is used to analyze the evolution of the periodic surface structure induced by the interaction of the femtosecond laser with the material. As the number of pulses increases, the surface structure of the material changes from none to produce LIPSS structure and from low spatial frequency LIPSS (LSFL) structure to high spatial frequency LIPSS (HSFL) structure. In order to compare the results, single-point laser scanning ablation experiments were carried out at femtosecond laser energy. The experimental results are consistent with the simulation results.

Electrochemical Enhancement of Lithium-Ion Diffusion in Polypyrrole-Modified Sulfurized Polyacrylonitrile Nanotubes for Solid-to-Solid Free-Standing Lithium-Sulfur Cathodes.

The energy density of lithium-sulfurized polyacrylonitrile (Li-SPAN) batteries has chronically suffered from low sulfur content. Although a free-standing electrode can significantly reduce noncapacity mass contribution, the slow bulk reaction kinetics still constrain the electrochemical performance. In this regard, a novel electrochemically active additive, polypyrrole (PPy), is introduced to construct PAN nanotubes as a sulfur carrier. This hollow channel greatly facilitates charge transport within the electrode and increases the sulfur content. Both electrochemical tests and simulations show that the SPANPPy-1% cathode possesses a larger lithium-ion diffusion coefficient and a more homogeneous phase interface than the SPAN cathode. Consequently, significantly improved capabilities and rate properties are achieved, as well as decent exportations under high-sulfur-loading or lean-electrolyte conditions. In-situ and semi-situ characterizations are further performed to demonstrate the nucleation growth of lithium sulfide and the evolution of the electrode surface structure. This type of electrochemically active additive provides a well-supported implementation of high-energy-density Li-S batteries.

The surface structure of nanosilica produced from sodium silicate by the carbonation process

CO2 was used to prepare nanosilica particles through a carbonization reaction in a Na2SiO3 solution, aiming to convert CO2 into value-added products. The relationship between the specific structure of the as-prepared nanosilica and the sodium silicate concentration, reaction temperature, reaction time, and aging time was explored by TEM, BET, and XRD analysis. The growth process of nanosilica particles was relatively slow with the increase in the Na2SiO3 concentration, which resulted in the formation of large primary particles, reducing the specific surface area. The decreasing temperature reduced the polymerization of Si(OH)4 and SiOSi(OH)3, reducing the specific surface area. Meanwhile, the effects of reaction time and aging time on the surface structure of silica nanoparticles were studied. Different surface structure of nanosilica particles were synthesized by controlling the carbonization process conditions, which expand the application of nanosilica products. At present, the research on the carbonization preparation of nanosilica mainly focused on the carbonization process conditions and modification technology, but the research of control mechanism of nanosilica surface structure and properties was insufficient. This study focused on the relationship between surface structure evolution and properties, and provided a theoretical basis for the mechanism of the influence factors of preparation process on the structure evolution of prepared nanosilica. And the process reduced CO2 emission, which had important environmental protection value.