Surface Atoms Research Articles

Selective adsorption behavior of reducing gases on the NiO–In2O3 heterojunction under the interfacial effect

Gas sensors with the p–n heterojunction have demonstrated distinct sensing responses to reducing gases, yet a clear understanding of the reaction pathways and selective adsorption mechanisms for specific gas components remains elusive, impeding practical applications. In this study, we constructed an atomic-level NiO–In2O3 heterojunction and explored its adsorption behaviors and sensing properties for CO and H2 by first-principles calculations. Analysis of its electronic properties, focusing on binding energy, differential charge density, and density of states, confirmed the creation of a highly stable NiO–In2O3 heterojunction and alterations in the coordination environment of the surface-active atoms. These changes potentially led to differences in the affinity between the gas molecules and the adsorption sites. The calculations of the adsorption properties revealed that the adsorption capacity of H2 is relatively weak compared to the strong interactions between CO and heterojunction surface atoms, indicating a readily variable reaction pathway for H2. Consequently, the adsorption configuration at the interface site on the NiO–In2O3 heterojunction surface exhibited a predominantly p-type response for CO and a unique n-type response for H2. This interfacial effect of the heterojunction is crucial for the selective adsorption of CO and H2. Furthermore, the opposite response signal was verified by gas sensing tests, which also presented the superior stability of the NiO–In2O3 sensor. The p–n heterojunction of the corresponding composites was effectively characterized. This research offers new insights into the selective adsorption mechanism, paving the way for the development of gas sensors.

Investigating the Temperature Dependency of Trimethyl Aluminum Assisted Atomic Surface Reduction of Li and Mn-Rich NCM

Most next-generation electrode materials are prone to interfacial degradation, which eventually spreads to the bulk and impairs electrochemical performance. One promising method for reducing interfacial degradation is to surface engineer the electrode materials to form an artificial cathode electrolyte interphase as a protective layer. Nevertheless, the majority of coating techniques entail wet processes, high temperatures, or exposure to ambient conditions. These experimental conditions are only sometimes conducive and can adversely affect the material structure or composition. Therefore, we investigate the efficacy of a low-temperature, facile atomic surface reduction (ASR) using trimethylaluminum vapors as a surface modification strategy for Li and Mn-rich NCM (LMR-NCM). The results presented herein manifest that the extent of TMA-assisted ASR is temperature-dependent. All tested temperatures demonstrated improved electrochemical performance. However, ASR carried out at temperatures >100 °C was more effective in preserving the structural integrity and improving the electrochemical performance. Electrochemical testing revealed improved rate capabilities, cycling stability, and capacity retention of ASR-treated LMR-NCM. Additionally, post-cycling high-resolution scanning electron microscopy analysis verified that after extended cycling, ASR carried out at T > 100 °C showed no cracks or cleavage, demonstrating the efficiency of this method in preventing surface degradation.

Solar-driven highly selective conversion of glycerol to dihydroxyacetone using surface atom engineered BiVO4 photoanodes

Dihydroxyacetone is the most desired product in glycerol oxidation reaction because of its highest added value and large market demand among all possible oxidation products. However, selectively oxidative secondary hydroxyl groups of glycerol for highly efficient dihydroxyacetone production still poses a challenge. In this study, we engineer the surface of BiVO4 by introducing bismuth-rich domains and oxygen vacancies (Bi-rich BiVO4-x) to systematically modulate the surface adsorption of secondary hydroxyl groups and enhance photo-induced charge separation for photoelectrochemical glycerol oxidation into dihydroxyacetone conversion. As a result, the Bi-rich BiVO4-x increases the glycerol oxidation photocurrent density of BiVO4 from 1.42 to 4.26 mA cm−2 at 1.23 V vs. reversible hydrogen electrode under AM 1.5 G illumination, as well as the dihydroxyacetone selectivity from 54.0% to 80.3%, finally achieving a dihydroxyacetone production rate of 361.9 mmol m−2 h−1 that outperforms all reported values. The surface atom customization opens a way to regulate the solar-driven organic transformation pathway toward a carbon chain-balanced product.

Stabilizing magnetic order of cobalt-based anisotropic nanoparticles prepared using NaBH4 as a reducing agent

A one-pot chemical method was used to prepare cobalt nanoparticles (Co NPs) by employing sodium borohydride (NaBH4) as a reducing agent, as well as graphite and activated carbon as stabilizer materials. The resulting NPs were characterized by XRD, FE-SEM, EDX mapping and VSM measurements before and after annealing under a mixture of argon and hydrogen atmosphere at 600 ℃, in order to study their structural, morphological, and magnetic properties. This study focused on the shape and size of Co NPs, involving the formation of Co and Co3O4 phases with the effect of oxygen as the main factor that can significantly contribute to the magnetic anisotropy. Co NPs exhibited a high saturation magnetization (Ms) value after performing the annealing process, achieving Ms> 99 emu/g when using the graphite stabilizer. The results indicate that surface atoms play a significant role in the modification of magnetic characteristics of Co NPs.

Direct formation of copper nanoparticles from atoms at graphitic step edges lowers overpotential and improves selectivity of electrocatalytic CO2 reduction

A key strategy for minimizing our reliance on precious metals is to increase the fraction of surface atoms and improve the metal-support interface. In this work, we employ a solvent/ligand/counterion-free method to deposit copper in the atomic form directly onto a nanotextured surface of graphitized carbon nanofibers (GNFs). Our results demonstrate that under these conditions, copper atoms coalesce into nanoparticles securely anchored to the graphitic step edges, limiting their growth to 2–5 nm. The resultant hybrid Cu/GNF material displays high selectivity in the CO2 reduction reaction (CO2RR) for formate production with a faradaic efficiency of ~94% at -0.38 V vs RHE and a high turnover frequency of 2.78 × 106 h-1. The Cu nanoparticles adhered to the graphitic step edges significantly enhance electron transfer to CO2. Long-term CO2RR tests coupled with atomic-scale elucidation of changes in Cu/GNF reveal nanoparticles coarsening, and a simultaneous increase in the fraction of single Cu atoms. These changes in the catalyst structure make the onset of the CO2 reduction potential more negative, leading to less formate production at -0.38 V vs RHE, correlating with a less efficient competition of CO2 with H2O for adsorption on single Cu atoms on the graphitic surfaces, revealed by density functional theory calculations.

Structure evolution of Cu3Pd single-particles under CO2 hydrogenation

Encapsulating metal nanoparticles into a porous silica shell, forming a core–shell geometry, has been popularly applied to prevent the particles from sintering at the elevated temperatures and under reactive gases. However, structure evolution of the metal particles under reaction conditions is less known. Here, the dynamic behavior of Cu3Pd single-particles, confined by a permeable silica shell, during CO2 hydrogenation have been examined by microscopic and spectroscopic characterizations. It was found that H2-reduction of the bimetallic particle at 673 K led to the partial enrichment of Cu on the surface, while H2-treatment at 873 K resulted in the surface segregation of Pd owing to the stronger adsorption of H2 on Pd. When subjected to CO2 hydrogenation at 517–673 K, the enriched Pd surface atoms and the electron-deficient Cu atoms synergistically activated H2/CO2 molecules and promoted the activity for the reverse water–gas shift. However, the Cu atoms partially migrated onto the SiO2 shell and formed tiny Cu clusters, induced by the strong adsorption of O-containing reaction intermediates, forming a core@shell@satellite (CuPd@SiO2 @Cu) architecture.

Rapid synthesis of PdCu nanosheets with enhanced electrocatalytic activity toward polyalcohol oxidation reaction

Reasonable design of Pd-based catalysts with specific composition and morphology is of great importance for promoting the commercial application.of direct alcohol fuel cells (DAFCs). Recently, two-dimension (2D) with high density of defects and massive low-coordinated surface atom has become research highlights in the field of catalysis. Herein, we report a wet chemical method for synthesizing PdCu nanosheets with abundant wrinkles. The ultrathin two-dimensional structure endows catalysts plentiful catalytic active sites and large specific surface area, improving atomic utilization efficiency. The formation of bimetallic PdCu alloy structure leads to the adjustment of Pd electronic structure, resulting in lattice compression effect. Benefitting from the structural and compositional characteristics, PdCu nanosheets (NSs) exhibits excellent electrocatalytic performance for ethylene glycol oxidation reaction (EGOR) and glycerol oxidation reaction (GOR) with the mass activity of 7031 mA mg−1/5117 mA mg−1, which is 4.4/3.9 times higher than that of commercial Pd/C catalysts. Furthermore, the remained mass activity of PdCu NSs is 3991/3851 mA mg−1 after the durability measurement for EGOR/GOR, which confirm PdCu NSs possesses superior stability. We believe that our synthetic strategy could provide robust reference for the development of high-performance eletrocatalysts.

Influence of particle size on the magnetic and microwave absorption properties of magnetite via mechano-mechanical methods for micro-nano-spheres

The demand for innovative electromagnetic wave absorbers stems from the pressing need to mitigate electromagnetic interference and pollution emanating from electronic devices and communication technologies, which pose risks to human health and disrupt the functionality of electronic equipment. This study investigates how particle size influences the magnetic and microwave absorption properties of magnetite micron-nano-spheres. Utilizing ball milling (BM) and mechanochemical alloying (MA), particle sizes were controlled by varying the milling times, resulting in a reduction of magnetite's average particle size from 3 µm to 43 nm. The research uncovers the unique effects of blending micron and nano-sized particles, a phenomenon previously undocumented. It was observed that saturation magnetization and coercivity increase with larger particle sizes due to the small size effect. The complex permittivity, dielectric loss and attenuation constant of the magnetite nanocomposites were influenced by the larger interface area and increased defects in smaller-sized nano-filler composites. Decreasing the magnetite particle size leads to a lower frequency shift and a broader bandwidth of the reflection loss (RL) peak in the fixed absorber, with maximum RL achieved for thinner absorber layers. Notably, the mixed micron-nano magnetite composite exhibits promising microwave absorption capabilities, achieving a maximum RL of −35.36 dB at 16.8 GHz with a 1 mm thickness, making it suitable for lightweight microwave absorption. Resonance frequencies corresponding to RL below −20 dB extend to 3.63 GHz, meeting the 99 % wave absorption requirement due to the high loss tangent of antiferromagnetic resonance and significant magnetic relaxation peak over the 8–18 GHz frequency range. This study underscores the significant impact of adjusting the particle size on microwave absorption properties, where decreasing the size broadens the absorption bandwidth, shifts the RL peak to lower frequencies and maximizes RL with thinner thicknesses. Increasing the nano-filler content enhances the absorption bandwidth and microwave absorber performance by augmenting the dielectric loss, attenuation constant and impedance matching. Overall, controlling the particle size proves effective in tailoring microwave absorption, highlighting the potential of magnetite composites as ultra-thin, lightweight materials capable of absorbing a wide range of microwave frequencies. These composites find applications in microwave absorption, stealth technology and managing electromagnetic interference, leveraging the magnetic properties of ferrites and exploiting super-exchange interactions in microparticles-sized materials. Moreover, they benefit from the amplified dielectric or/magnetic losses resulting from the characteristics of nanoparticle-sized materials, including high surface area, greater surface atoms and multiple reflections, resulting in exceptional microwave absorption performance exceeding 99 % across an exceptionally broad bandwidth.

Distribution Tendencies of Noble Metals on Fe(100) Using Lattice Gas Cluster Expansions.

Fe-based catalysts are highly selective for the hydrodeoxygenation of biomass-derived oxygenates but are prone to oxidative deactivation. Promotion with a noble metal has been shown to improve oxidative resistance. The chemical properties of such bimetallic systems depend critically on the surface geometry and spatial configuration of surface atoms in addition to their coverage (i.e., noble metal loading), so these aspects must be taken into account in order to develop reliable models for such complex systems. This requires sampling a vast configurational space, which is rather impractical using density functional theory (DFT) calculations alone. Moreover, "DFT-based" models are limited to length scales that are often too small for experimental relevance. Here, we circumvent this challenge by constructing DFT-parametrized lattice gas cluster expansions (LG CEs), which can describe these types of systems at significantly larger length scales. Here, we apply this strategy to Fe(100) promoted with four technologically relevant precious metals: Pd, Pt, Rh, and Ru. The resultant LG CEs have remarkable predictive accuracy, with predictive errors below 10 meV/site over a coverage range of 0 to 2 monolayers. The ground state configurations for each noble metal were identified, and the analysis of the cluster energies reveals a significant disparity in their dispersion tendency.

Enhancing Bovine Embryo Development In Vitro Using Oil-in-Water Nanoemulsions as Specific Carriers for Essential Lipids.

Worldwide meat consumption and production have nearly quintupled in the last 60 years. In this context, research and the application of new technologies related to animal reproduction have evolved in an accelerated way. The objective of the present study was to apply nanoemulsions (NEs) as carriers of lipids to feed bovine embryos in culture media and verify their impact on the development of embryos produced in vitro. The NEs were characterized by particle size, polydispersity, size distribution, physical stability, morphology using atomic force microscopy (AFM), surface tension, density, pH, and rheological behavior. The NEs were prepared by the emulsification/evaporation technique. A central composite rotatable design (CCRD) was used to optimize the NE fabrication parameters. The three optimized formulations used in the embryo application showed an emulsion stability index (ESI) between 0.046 and 0.086, which reflects high stability. The mean droplet diameter analyzed by laser diffraction was approximately 70-80 nm, suggesting a possible transit across the embryonic zona pellucida with pores of an average 90 nm in diameter. AFM images clearly confirm the morphology of spherical droplets with a mean droplet diameter of less than 100 nm. The optimized formulations added during the higher embryonic genome activation phase in bovine embryos enhanced early embryonic development.

Impacts of hot electron diffusion, electron–phonon coupling, and surface atoms on metal surface dynamics revealed by reflection ultrafast electron diffraction

Metals exhibit nonequilibrium electron and lattice subsystems at transient times following femtosecond laser excitation. In the past four decades, various optical spectroscopy and time-resolved diffraction methods have been used to study electron–phonon coupling and the effects of underlying dynamical processes. Here, we take advantage of the surface specificity of reflection ultrafast electron diffraction (UED) to examine the structural dynamics of photoexcited metal surfaces, which are apparently slower in recovery than predicted by thermal diffusion from the profile of absorbed energy. Fast diffusion of hot electrons is found to critically reduce surface excitation and affect the temporal dependence of the increased atomic motions on not only the ultrashort but also sub-nanosecond times. Whereas the two-temperature model with the accepted physical constants of platinum can reproduce the observed surface lattice dynamics, gold is found to exhibit appreciably larger-than-expected dynamic vibrational amplitudes of surface atoms while keeping the commonly used electron–phonon coupling constant. Such surface behavioral difference at transient times can be understood in the context of the different strengths of binding to surface atoms for the two metals. In addition, with the quantitative agreements between diffraction and theoretical results, we provide convincing evidence that surface structural dynamics can be reliably obtained by reflection UED even in the presence of laser-induced transient electric fields.

Role of sulfur and phosphorous doping on the electrochemical performance of graphene oxide-based electrodes

Heteroatom doping of graphene oxide (GO) with phosphorous (P), and sulfur (S) was studied. In-situ grown binder-free electrodes of these doped and un-doped GO systems were developed via hydrothermal process. S-GO, P-GO, PS-GO, and un-doped hydrothermally treated GO (H-GO) electrodes were thoroughly investigated through physical and electrochemical characterization. The PS-GO electrode, comprising P (10.90 at%), S (0.3 at%), C (45.54 at%), O (36.36 at%), and Ni (2.38 at%) atoms, exhibited a mixed morphology of a few hundred nanometers doped GO flakes and dissolved Ni foam nanorods. Electrochemical analysis showed, this mixed morphology stimulates the charge storage ability of the PS-GO electrode and achieved a high specific capacity of 1218 C/g, compared to 647 C/g for H-GO at 1 mV/s. Electrochemical analysis revealed, charge was primarily stored through the capacitive charge storage mechanism, where only surface atoms are solely responsible for developing a double layer or facilitating redox reactions between electrode atoms and electrolyte ions. Additionally, the PS-GO electrode demonstrated an energy density of 76.94 Wh/kg at 1 A/g, which is much closer to that of batteries. We anticipate that PS-GO has the potential to be utilized as electrode material in modern energy storage devices.

A New centrosymmetric supramolecular Hybrid Antimony (III)-based material :X-ray characterization, vibrational studies, theoretical (DFT and TD-DFT) studies, thermal behavior, opto-electric properties and atomic Hirshfeld surface analysis.

The new centrosymmetric hybrid material (C8H12N)4[SbCl5]2 has been successfully elaborated at room temperature by slow evaporation in the centrosymmetric monoclinic space group P21/c with the following parameters: a = 29.0349(16) Å, b = 13.1241(7) Å, c = 12.0278(7) Å, β = 95.567(2) ° Z = 4 and V = 4561.7(4) Å3. The asymmetric unit consists of two isolated [Sb2Cl10]4- dimers and four protonated cations (C8H12N)+ was optimized d by density functional theory (DFT) using the B3LYP method. The cohesion of this supramolecular material was ensured by the means of N—H…Cl hydrogen-bonding interactions yield a three-dimensional network. The infrared IR and Raman studies which were performed at room temperature charge in the 4000–400 cm -1 and 10- 3000 cm -1 frequency regions, respectively, displayed the existence of vibrational modes that correspond to the organic and inorganic groups. The assignment of wavenumbers which were based on potential energy distribution (PED), were performed using Vibrational Energy Distribution Analysis (VEDA) software. Actually, the values obtained by the B3LYP/LanL2MB are in good agreement with the experimental data.Moreover, the Hirschfeld surfaces analysis which was employed to identify the different intermolecular interactions, showed that predominate interactions were H…Cl. The Thermogravimetric analysis (TGA) reveals the decomposition of the compound remains stable above 175 °C that confirms its great thermal stability. Furthermore, the optical property of the 0D hybrid Sb(III) based halide was studied with a focus on the band gap. Theoretical investigations on the electronic structure, Simulated UV–Visible spectrum, band gap, and frontier molecular orbitals (FMOs) were undertaken using density functional theory (DFT) and time-dependent DFT (TD-DFT). Therefore, our results indicate an acceptable consistency was found between calculations and experimental results leading to consistent vibrational and optical features assignments as well as the energy gap (Eg) and the chemical reactivity descriptors which are primarily linked to the ring of the organic cation and the inorganic anion.

Instantaneous fundamental modes and contact angles of droplets from surface atoms

Contact angle measurements of sessile or moving droplets are by far the most common way to characterize their wetting properties. The typical route to obtain contact angle estimates from atomistic molecular dynamics simulations requires the calculation of an isochore or the equimolar dividing surface, both of which need sizeable statistics to achieve acceptable accuracy and are less suitable in non-stationary conditions. Here, we propose an algorithm for estimating the contact angle that relies on the identification of interfacial molecules, which can determine the instantaneous location of the liquid surface. We apply this algorithm to calculate the contact angles of water droplets at equilibrium and out of equilibrium on graphite-like substrates, paying particular attention to modeling the presence of excited modes using general ellipses to fit the droplet surface. The algorithm is implemented in a user-friendly way in the Pytim software package.

Novel full-scale model verified by atomic surface and developed composite microfiber and slurry polishing system

Polishing mechanisms between fibers of a polishing pad and slurry are elusive, rising a challenge to develop high-performance composite polishing system. To solve this challenge, a novel full-scale model is proposed from mm to nm, consisting of macro, meso, micro and nanoscale. The model is verified by atomic surface and developed composite microfiber and slurry polishing system. Prior to chemical mechanical polishing, fused silica was polished by ceria slurry. A novel polishing pad was prepared using microfibers with a diameter of 2.5 μm, and a novel green slurry contained silica abrasives, hydrogen peroxide, sodium carbonate, sorbitol and xanthan gum. After CMP, an atomic surface with Ra of 0.108 nm was achieved, and the thickness of damaged layer is 1.95 nm. In terms of the macroscale model suggested, the maximum stress on the microfiber pad decreased 417.7 %, and the direct contact area increased 41.23 % compared with those of a commercial nonwoven pad. The peak stress exceeded 1 MPa on the commercial pad, while it reduced to about one fourth on the developed microfiber pad, according to the mesoscale fiber-slurry model proposed. Reactive force field molecular dynamics simulations, i.e. nanoscale model, reveal that a slurry layer existing at interface effectively impedes direct contact between abrasives and fused silica. With increasing the polishing load, material removal mode transformed from an atom to atomic chains. The constructed full-scale model and developed composite polishing system provide new insights to analyze, design and manufacture high-performance polishing pads, slurry and system.

Synthesis, spectral characterizations, computational studies and biological investigation of 4-(4-(2-hydroxyethyl)phenylamino)-4-oxobutanoic acid and its trimethyltin(IV) complex

The current manuscript contains the synthesis, biological evaluation, and theoretical investigations of 4-(4-(2-hydroxyethyl)phenylamino)-4-oxobutanoic acid (HPO) and its organotin(IV) complex (SnHPO). The synthesized compounds were characterized by FT-IR, NMR (1H and 13C), and mass spectrometry. Furthermore, the molecular structures of both compounds were probed by single-crystal X-ray diffraction (SC-XRD)analysis. The outcomes reveal that the chelation occurs by one of the O atoms of the carboxylate group and shows a distorted tetrahedral coordination geometry for the organotin(IV) complex. Both XRD and FT-IR data confirm the monodentate nature of the carboxylate group of HPO. The supramolecular assembly of ligand and complex was stabilized by various intermolecular interactions, which were travelled by Hirshfeld surface analysis (HSA). The experimental and theoretical (based on B3LYP/def2-SVP/6-311G(d,p) level of theory) structures were found to be nearly similar. Mulliken atomic charge and MEP surface indicated Sn, H-N1, and H-O4 atoms in SnHPO are appropriate targets for nucleophilic attacks. The molecular orbital energy gaps suggested that SnHPO possesses high biological activity and chemical reactivity and less stability than HPO. The docking simulation of the synthesized compounds against SARS-CoV-2 virus receptor protein (6LU7) was investigated, and the findings demonstrated that SnHPO has better binding affinity than HPO and favipiravir. The ligand and its complex were vetted for their antifungal and antibacterial activities. It can be concluded that the reported compounds have strong antimicrobial properties but weak hemolytic activity, and they may be studied extensively as potential therapeutic drugs for a variety of microbes.

Rapid Surface Reconstruction of In2S3 Photoanode via Flame Treatment for Enhanced Photoelectrochemical Performance.

Surface reconstruction, reorganizing the surface atoms or structure, is a promising strategy to manipulate materials' electrical, electrochemical, and surface catalytic properties. Herein, a rapid surface reconstruction of indium sulfide (In2S3) is demonstrated via a high-temperature flame treatment to improve its charge collection properties. The flame process selectively transforms the In2S3 surface into a diffusionless In2O3 layer with high crystallinity. Additionally, it controllably generates bulk sulfur vacancies within a few seconds, leading to surface-reconstructed In2S3 (sr-In2S3). When using those sr-In2S3 as photoanode for photoelectrochemical water splitting devices, these dual functions of surface In2O3/bulk In2S3 reduce the charge recombination in the surface and bulk region, thus improving photocurrent density and stability. With optimized surface reconstruction, the sr-In2S3 photoanode demonstrates a significant photocurrent density of 8.5mA cm-2 at 1.23V versus a reversible hydrogen electrode (RHE), marking a 2.5-fold increase compared to pristine In2S3 (3.5mA cm-2). More importantly, the sr-In2S3 photoanode exhibits an impressive photocurrent density of 7.3mA cm-2 at 0.6V versus RHE for iodide oxidation reaction. A practical and scalable surface reconstruction is also showcased via flame treatment. This work provides new insights for surface reconstruction engineering in sulfide-based semiconductors, making a breakthrough in developing efficient solar-fuel energy devices.

Real-time and highly responsive hydrogen mapping in pure Fe using TiO2 thin films

A hydrogen visualization method with high responsivity and chemical stability under atmospheric corrosion is necessary to inhibit hydrogen embrittlement, which can occur with hydrogen uptake of structural materials. In this study, a highly responsive hydrogen mapping technique for steels was successfully established using a TiO2 thin film and Pd intermediate layer. The color of the TiO2 film on the hydrogen-detection side changes during hydrogen charging on the hydrogen-entry side of the Fe specimen, indicating that the color changes were attributed to the hydrogen uptake of the Fe surface and subsequent introduction of hydrogen atoms to the TiO2 film. Considering the responsivity and visibility, the optimal thickness of the TiO2 film was determined to be 20 nm. As TiO2 is a chemically stable material, the proposed mapping technique can be used to monitor the hydrogen absorbed into metallic materials under outdoor conditions.

Surface evolution of thermoelectric material KCu4Se3 explored by scanning tunneling microscopy

Abstract Novel two-dimensional thermoelectric materials have attracted significant attention in the field of thermoelectric due to their low lattice thermal conductivity. A comprehensive understanding of their microscopic structures is crucial for driving further the optimization of materials properties and developing novel functional materials. Here, by using in situ scanning tunneling microscopy, we report the atomic layer evolution and surface reconstruction on the cleaved thermoelectric material KCu4Se3 for the first time. We clearly revealed each atomic layer, including the naturally cleaved K atomic layer, the intermediate Se2− atomic layer, and the Se− atomic layer that emerges in the thermodynamic-stable state. Departing from the majority of studies that predominantly concentrate on macroscopic measurements of the charge transport, our results reveal the coexistence of potassium disorder and complex reconstructed patterns of selenium, which potentially influences charge carrier and lattice dynamics. These results provide direct insight into the surface microstructures and evolution of KCu4Se3, and shed useful light on designing functional materials with superior performance.

Characterized on hydrogen properties and mechanism of Al–Sn–Bi composite powder in salt solutions

Using low-melting point elements to promote the Al/H2O reaction has garnered considerable attention because it is an economical approach to hydrogen supply. Herein, .Al–Sn–Bi composite powder was prepared through milling. The Al–Sn–Bi composite powder and the hydrolysate were investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM). The results show that the hydrolysis products is primarily AlOOH. The properties of the Al/H2O reaction were systematically characterized in salt solutions. Results show that the presence of Sn and Bi is beneficial to achieve short introduction times and large Al/H2O reaction rates. The hydrogen generation rate of the Al–Sn–Bi composite is 4566 mL min−1 g−1 and 3600 mL min−1·g−1 with NaCl and Na2SO4 solutions, respectively and the hydrogen production efficiency can reach 100% in 1 min. Additionally, the mechanism of Sn and Bi promoting Al/H2O reaction was characterized by density functional theory (DFT) calculations. The DFT calculations show that Sn and Bi replace 1/8 ML, 1/4 ML and 1/2 ML surface atoms of Al (111), the surface chemical potential increases with increasing doping concentration, and the electrode potential decreases with increasing doping concentration. The presence of Sn and Bi increases the surface chemical potential and reduces the electrode potential, this is conducive to the microcell reaction and promotes the Al/H2O reaction.