Surface Density Of Atoms Research Articles

Surface Density Dependent Catalytic Activity of Single Palladium Atoms Supported on Ceria*.

The analogy between single-atom catalysts (SACs) and molecular catalysts predicts that the specific catalytic activity of these systems is constant. We provide evidence that this prediction is not necessarily true. As a case in point, we show that the specific activity over ceria-supported single Pd atoms linearly increases with metal atom density, originating from the cumulative enhancement of CeO2 reducibility. The long-range electrostatic footprints (≈1.5 nm) around each Pd site overlap with each other as surface Pd density increases, resulting in an observed deviation from constant specific activity. These cooperative effects exhaust previously active O atoms above a certain Pd density, leading to their permanent removal and a consequent drop in reaction rate. The findings of our combined experimental and computational study show that the specific catalytic activity of reducible oxide-supported single-atom catalysts can be tuned by varying the surface density of single metal atoms.

Surface Density Dependent Catalytic Activity of Single Palladium Atoms Supported on Ceria**

AbstractThe analogy between single‐atom catalysts (SACs) and molecular catalysts predicts that the specific catalytic activity of these systems is constant. We provide evidence that this prediction is not necessarily true. As a case in point, we show that the specific activity over ceria‐supported single Pd atoms linearly increases with metal atom density, originating from the cumulative enhancement of CeO2 reducibility. The long‐range electrostatic footprints (≈1.5 nm) around each Pd site overlap with each other as surface Pd density increases, resulting in an observed deviation from constant specific activity. These cooperative effects exhaust previously active O atoms above a certain Pd density, leading to their permanent removal and a consequent drop in reaction rate. The findings of our combined experimental and computational study show that the specific catalytic activity of reducible oxide‐supported single‐atom catalysts can be tuned by varying the surface density of single metal atoms.

Corrosion Behavior of Laser Powder Bed Fusion Fabricated Stainless Steel 316L

Metal additive manufacturing techniques have been recognized for their capability of controlling the crystallographic orientations of stainless steels. However, the inherent anisotropic corrosion behavior has not been extensively studied. In this study, the corrosion properties of 316L stainless steels prepared by Laser Powder Bed Fusion (LPBF) additive manufacturing were investigated. The effects of different crystallographic textures, namely {100}, {110} and {111} on both general and pitting corrosion were characterized by several electrochemical measurements, including Electrochemical Impedance Spectroscopy (EIS), potentiodynamic polarization and Mott-Schottky analysis. The results were also compared to the polycrystalline and wrought 316L counterparts. It was found that the LPBF-{111} sample offered the highest general corrosion resistance, followed by the LPBF-{100}, LPBF-polycrystalline and LPBF-{110} samples (Figure 1). The origin of this trend was related to the atomic surface density. The LPBF-{111} surface exhibited a stronger atomic bonding than that of LPBF-{100} and LPBF-{110} samples, resulting in a higher corrosion activation energy and thus a higher general corrosion resistance. All the LPBF samples also offered a significantly higher pitting corrosion resistance (Figure 2), which was attributed to the lower concentration of oxygen vacancies (donor levels) in the passive film that serve as pits nucleation sites, as observed by the Mott-Schottky analysis (Figure 3). Figure 1

Growth of Ba–O ultrathin films on Pt(1 1 1) followed by Ti incorporation to prepare oxide crystalline approximants and quasicrystals

In this study, three different precursor Ba–O films on Pt(111) are characterized and the oxide crystalline approximant (OCA) and oxide quasicrystal (OQC) films are prepared by annealing after Ti deposition on the films. The prepared Ba–O ultra-thin films are BaO(100)–(√2×√2)R3°:Pt(111), Ba–O:Pt(111)–(2 × 2) and Ba–O:Pt(111)–(√13×√13)R13.9°, as determined using scanning tunneling microscopy, low-energy electron diffraction, and X-ray photoelectron spectroscopy. The phase transformation from an OCA film to an OQC film likely follows the mechanism where Ti is reduced and its surface atomic density decreased, while Ba is oxidized. The schematic structural models of the OCA film as Ba4Ti4O10 and the OQC film as Ba12Ti5O12, where the Ba atoms form a cluster tiling, are proposed.

Importance of Defective and Nonsymmetric Structures in Silver Nanoparticles.

Scanning transmission electron microscopy experiments indicate that face-centered cubic (FCC) is the predominant ordered structure for Ag309 ± 7 nanoclusters, synthesized in vacuum. Historically, experiments do not present a consensus on the morphology at these sizes, whereas theoretical studies find the icosahedral symmetry for Ag309 and the decahedral shape for nearby sizes. We employ density functional theory calculations to rationalize these observations, considering both regular and defective Ag nanoparticles (281-321 atoms). The change of stability induced by the presence of defects, symmetry loss, and change of number of atoms is evaluated by the nanoparticle surface energy, which was measured previously. FCC and decahedral symmetries are found to be more favorable than icosahedral, consistent with our measurements of clusters protected from extended atmospheric exposure. In addition, an energy-free descriptor, surface atomic density, is proposed and qualitatively reproduces the surface energy data. Nonsymmetric and defective structures may be preferred over perfectly regular ones within a given size range.

Gas compression and stellar feedback in the tidally interacting and ram-pressure stripped Virgo spiral galaxy NGC 4654

Due to an environment that promotes gravitational interactions and ram pressure stripping, galaxies within clusters are particularly likely to present unusual interstellar medium (ISM) properties. NGC 4654 is a Virgo cluster galaxy seen almost face-on, which undergoes nearly edge-on gas ram pressure stripping and a fly-by gravitational interaction with another massive galaxy, NGC 4639. NGC 4654 shows a strongly compressed gas region near the outer edge of the optical disk, with H I surface densities (high H I surface density region) significantly exceeding the canonical value of 10−15 M⊙ pc−2. New IRAM 30 m HERA CO(2−1) data of NGC 4654 are used to study the physical conditions of the ISM and its ability to form stars in the region where gas compression occurs. The CO-to-H2 conversion factor was estimated by (i) simultaneously solving for the conversion factor and the dust-to-gas ratio by assuming that the latter is approximately constant on giant molecular cloud scales and (ii) by assuming that the dust-to-gas ratio is proportional to the metallicity. The CO-to-H2 conversion factor was found to be one to two times the Galactic value. Based on the comparison with a region of similar properties in NGC 4501, we favor the higher value. We observe a significant decrease in the ratio between the molecular fraction and the total ISM pressure in the high H I surface density region. The gas in this region is self-gravitating, with a Toomre parameter below the critical value of Q = 1. However, the star-formation efficiency (SFEH2 = ΣSFR/ΣH2) is 1.5 to 2 times higher, depending on the assumed conversion factor, in the high H I surface density region than in the rest of the disk. Analytical models were used to reproduce radial profiles of the SFR and the atomic and molecular surface densities to better understand which physical properties are mandatory to maintain such high H I surface density regions. We conclude that a Toomre parameter of Q ∼ 0.8 combined with an increase in the velocity dispersion of Δvdisp ∼ 5 km s−1 are necessary conditions to simultaneously reproduce the gas surface densities and the SFR. A dynamical model that takes into account both gravitational interactions and ram pressure stripping was used to reproduce the gas distribution of NGC 4654. While the ISM properties are well reproduced in the whole disk, we find that the model SFR is significantly underestimated in the high H I surface density region due to the absence of gas cooling and stellar feedback. The comparison between the velocity dispersion given by the moment 2 map and the intrinsic 3D velocity dispersion from the model were used to discriminate between regions of broader linewidths caused by a real increase in the velocity dispersion and those caused by an unresolved velocity gradient only. We found that the 5 km s−1 increase in the intrinsic velocity dispersion predicted by the model is compatible with the observed velocity dispersion measured in the high H I surface density region. During a period of gas compression through external interactions, the gas surface density is enhanced, leading to an increased SFR and stellar feedback. Our observations and subsequent modeling suggest that, under the influence of stellar feedback, the gas density increases only moderately (by less than a factor of two). The stellar feedback acts as a regulator of star-formation, significantly increasing the turbulent velocity within the region.

Covalent Surface Alteration of MXenes and Its Effect on Superconductivity

Surface functional groups such as F, O, and OH attached to MXenes have a profound impact on the electronic properties. Generally, MXenes are synthesized by the aqueous acidic etching of the MAX phase, and these functional groups are inherently incorporated during the synthesis. Recently, covalent surface modification of MXene has been demonstrated at low temperature using molten inorganic salts.

Self-assembled PMMA/ZnO nanocomposites with anti-staining and liquid barrier properties–their physicochemical perspectives and clinical implications as a biomaterial for Maxillofacial prosthetic rehabilitation

Wettability, stainability and diffusion properties of polymer (PMMA) based nanocomposites (PMMA/ZnO) have been explored with critical significance to their physicochemical perspectives and clinical implications in the maxillofacial rehabilitation of cancer and trauma patients. Wetting and diffusion of artificial saliva through the neat polymer and nano composites have been investigated in detail. The same protocol was adopted for water diffusion studies at different temperatures. Transportation mechanism and surface wettability and stainability by commonly used beverages like tea, coffee and turmeric on these composites are studied in detail. Inferences are correlated with morphological analysis by Atomic Force Microscopy (AFM) and surface roughness parameters and density measurements. No studies have been reported till date about correlating wetting enhancement to retentive qualities and diffusion resistance to anti-stainability of the prostheses in the biomedical field. Findings of the present study is highly relevant and promising as these membranes/composites offer better retention and adaptability for the prostheses on tissue base which stimulates blood circulation in that region which prevents further bone resorption. Anti-staining potential offer more acceptance and durability for the maxillofacial prostheses especially intra orally. This nano formulation is a highly durable, cost effective esthetic substitute for the conventional polymer PMMA.

Surface properties of heterogeneous polycyclic aromatic hydrocarbon clusters

In this paper we investigate the impact of molecular inhomogeneity on the surface properties of soot particles. Using replica exchange molecular dynamics and solvent-excluded surface analysis, we evaluate detailed surface properties directly from particles containing polycyclic aromatic hydrocarbon molecules of different sizes. The temperature-dependent behaviour of surface roughness and number densities of reactive sites are evaluated for particles from 1–5 nm in diameter. The percentage of carbon atoms and zig-zag sites on the particle surface are found to be independent of molecular composition, while molecule heterogeneity influences the accessible hydrogen atoms and free-edge sites. These relationships allow the prediction of surface composition for a given particle diameter. The surface densities of carbon and hydrogen atoms are explained by the morphological changes and molecule size contributions for solid-like and liquid-like configurations. Small molecules contribute significantly to the particle surface properties at low temperatures, regardless of the proportion of molecule sizes, which results in an increased density of accessible carbon atoms for heterogeneous particles. Interestingly, the surface density of edge carbon atoms and free-edge sites can be predicted from the average molecule size alone. The density of hydrogen atoms on the surface follows the average expected values from the constituent molecule sizes, suggesting that for particles containing many different molecule sizes the α parameter corresponding to the HACA mechanism converges to a linear temperature-dependent trend. This quantitative evaluation of the accessibility of reactive sites for heterogeneous particles provides important information for understanding soot particle growth and oxidation.

Probing the Irregular Lattice Strain-Induced Electronic Structure Variations on Late Transition Metals for Boosting the Electrocatalyst Activity.

Owing to the simplicity in practice and continuous fine-tuning ability toward the binding strengths of adsorbates, the strain effect is intensively explored, especially focused on the modulation of catalytic activity in transition metal (TM) based electrocatalysts. Recently, more and more abnormal cases have been found that cannot be explained by the conventional simplified models. In this work, the strain effects in five late TMs, Fe, Co, Ni, Pd, and Pt are studied in-depth regarding the facet engineering, the surface atom density, and the d-band center. Interestingly, the irregular response of Fe lattice to the applied strain is identified, indicating the untapped potential of achieving the phase change by precise strain modulation. For the complicated high-index facets, the surface atom density has become the pivotal factor in determining the surface stability and electroactivity, which identifies the potential of high entropy alloys (HEA) in electrocatalysis. The work supplies insightful understanding and significant references for future research in subtle modulation of electroactivity based on the precise facet engineering in the more complex facets and morphologies.

Equilibrium concentration of hydrogen at tungsten surface

In this work, numerical calculations have been employed to investigate the adsorption equilibrium state of hydrogen (H) atoms on tungsten (W) surface. The surface energy and relevant surface atomic density of different W surfaces are obtained through the empirical-potential model. The calculations show that the higher surface atomic densities correspond to the more stable surfaces, of which the most stable surface is the W (110) surface. The H adsorption energies are systematically analyzed by density functional theory. The equilibrium concentration dependence for adsorption upon H coverage, a temperature range from 300 K to 1100 K, and a pressure range from 10−6 Pa to 106 Pa is examined by employing a Monte Carlo model. Our results suggest that most of H atoms desorb from 700 K to 1100 K when the pressure region varies from 10−6 Pa to 102 Pa. The monolayer-adsorbed H density is estimated from ∼1.39 × 1018 m−2 to ∼1.40 × 1019 m−2 at the equilibrium state.

An Investigation on the role of crystallographic texture on anisotropic electrochemical behavior of a commercially pure nickel manufactured by laser powder bed fusion (L-PBF) additive manufacturing

The layer-wise deposition of the laser powder bed fusion (L-PBF) process offers a tailorable microstructure with anisotropic properties. This research aimed to investigate the contribution of crystallographic texture on the anisotropic electrochemical/corrosion behavior of a L-BPF processed commercially pure nickel (Ni) cube along surfaces oriented parallel and perpendicular to the building direction. In order to exclusively assess the role of crystallographic texture on the corrosion behavior, the electrochemical measurements were performed on different surfaces of the L-PBF processed cube in alkaline and acidic chloride-free solutions. Orientation microscopy analysis showed that the morphology of grains along the parallel surface to the building direction was columnar, and their crystallographic orientation distribution was uniform. In contrast, the morphology of grains on the surface aligned normal to the building direction was equiaxed and highly oriented toward [110]. This bias in the orientation distribution led to the highest residual affinity for oxidation in comparison to the other planes in the FCC (Face Centered Cubic) crystal structure. In the case of 1 M NaOH solution, the hydroxide layer formed at the exposed surface did not effectively control the cation ejection from the surface. Also, surfaces oriented normal to the building direction, with lower surface atomic density, showed an elevated dissolution rate. Conversely, in the case of 1 M H2SO4 solution, a more integrated and thicker oxide film formed in comparison to the surface aligned parallel to the building direction. This fact led to reduced surface dissolution. This study shows that engineering the topology and microstructure based on the desired properties can remarkably promote the performance of additively manufactured materials in extreme environments.

Investigations of chemical and atomic composition of native oxide layers covering SI GaAs implanted with Xe ions

Semi-insulating (100) oriented GaAs was irradiated with 250 keV Xe+ ions with different fluences. The native oxide layers formed in the air after implantation are investigated in this study. The surface density of atoms in the native oxide layer, determined using Rutherford backscattering spectroscopy with nuclear reaction (RBS/NR), increases with ion fluence in the range between 2 × 1013 cm−2 and 8 × 1014 cm−2. Using X-ray photoelectron spectroscopy (XPS) method, the chemical composition was analyzed. It has been found that the native oxide layer on GaAs samples is a mixture of Ga2O3, As2O3, As2O5 and GaAs compounds and the compounds concentration changes depend on ion fluences.

Non-Native Pyrite Performs Better Than Native Marcasite CoSe2 for Electrochemical Oxygen and Hydrogen Evolution Reaction: A Theoretical Investigation

Efficient bifunctional electrocatalyst for water splitting is essential for replacing fossil-fuel energy sources with clean energy-dense hydrogen fuel (142 MJ/kg). Efficient electrocatalyst can be obtained by either increasing active site density or specific activity on individual active sites. The active site densities can be increased through roughening the potential energy surface or exposing the facets which has higher active site densities. The specific activity can be increased through modulation of strain or charge densities on active sites which can be achieved through introduction of dopants, defects or stabilization of “non-native phases” that are all the other crystalline and amorphous states that differ in terms of discrete translational symmetry in the sub-surface region from the “native” phase (or bulk ground-state). While for a given composition, there is a unique native state for a given set of thermodynamic condition while, there can be many non-native structures having different bond-angles, bond-distances and surface atom densities from the native phase, leading to different electrocatalytic properties. In this context, polymorphic engineering via stabilizing ‘non-native phase’ offers a potential approach for improving both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrocatalysts and its activity. The beneficial effect of polymorphic engineering with regards to bifunctional electrochemical OER and HER is demonstrated by first principle calculation by taking CoSe2 as a model electrocatalyst which has marcasite (Space Group-58) and pyrite (Space Group-205) as the native (N) and non-native (NN) structures, respectively. The first principle computations predict pyrite (NN) structure of CoSe2 would have better electrochemical activity towards OER and HER than its marcasite (N) counterpart which is confirmed through experimental results in literature too. Though the co-ordination number of Co remains same in both the structures, the co-ordination symmetry surrounding Co atom varies. This results in differential charge distribution in constituting Co- and Se-atoms consequently resulting in variable density of state (DOS) near Fermi level (Figure 1) thereby affecting the binding energies (BE) of reaction intermediates of OER and HER. Pyrite (NN) phase of CoSe2 has a greater electron density near Fermi Level in comparison to its marcasite (N) counterpart due to differential co-ordination symmetry. A greater electron density near Fermi-level is indicative of lower work function and consequently lower polarization resistance during water splitting. A greater electron density near Fermi level is contributed by Co-3d orbitals which is the common active site for both OER and HER. The greater electron density and lower work function in Pyrite (NN) results in stronger metal-hydrogen BE (0.03 eV) resulting in lower overpotential of HER. Hydrogen adsorption on Se sites occurs only at higher HER overpotential due to weak Se-hydrogen BE (0.59 eV). This results in observation of twin Tafel slopes during HER on CoSe2 electrocatalyst as the potential determination step (PDS) switches from Volmer to Heyrovsky step with participation of Se during HER. The lower work function and higher electron density near Fermi level in Pyrite (NN) structure results in weaker metal-oxygen bond thereby promoting multi-electron OER activity. The OER intermediates (-OH, -O, -OOH) has a higher BE over Co- than Se-sites. The transformation of Oads à HOOads on Co-sites of CoSe2 (001) structure is the potential determination step with an onset potential of 1.66 V (vs RHE).The desorption of O2 from Se site is found to be the potential-determination-step (PDS) for OER (η=0.79 V). Furthermore, pristine CoSe2 acts as a precursor for OER which undergoes dissolution to form a surface Co-O structure which has a greater activity than pristine pyrite CoSe2 surfaces (η=0.31 V). This energetics is more favourable for pyrite (NN) structure than marcasite (N) structure for dissolution process to form surface Co-O structure due to stronger Co-Se bonds present in the latter case. Furthermore, point-defects which can aid both OER and HER, can be more easily formed in pyrite (NN) structure than marcasite (N) structure due to the aforementioned reason. The present study underlines the importance of stabilization of non-native structures which has a great potential to produce higher electrocatalytic activity thus providing greater options in search of better water splitting electrocatalyst. Figure 1

Atomistic simulation of agglomeration of metal nanoparticles considering the induced charge density of surface atoms

To simulate the agglomeration of nanoparticles subjected to an external electric field, we develop a method to calculate the induced charge density in surface atoms to account for the inter-particle attractions between metallic nanoparticles, based on classical electrodynamics. A polarizable particle is subjected to dielectrophoresis force in a non uniform AC electric field. The induced charge density in a surface atom layer is redistributed to minimize the electric field inside the particle, restricting the total charge density of nanoparticles during the molecular dynamics simulations via a Lagrange multiplier method. The developed method is implemented in the LAMMPS code, where Lorentz and Coulomb forces applying on partially charged surface atoms are embedded to correct atomic motions in response to the applied AC electric field. In numerical examples, the electric field around a spherical nanoparticle shows good agreement with the analytical solution under external electric field. The proposed method is turned out to be more efficient for the problems of large particles since the ratio of surface to bulk atoms decreases as the size of particle increases. When an external electric field isexerted, the ordered aggregation of gold nanoparticles is observed in physical experiments and investigated through the LAMMPS simulations. The developed method successfully simulates that the nanoparticles are not only aligned in the direction of electric field but also formed lattice bonds due to the charges induced by the electric field.

Interactions between hydrogen bubbles and prismatic interstitial dislocation loops in BCC iron

The interaction between the interstitial dislocation loop and the hydrogen bubble has been investigated using the molecular dynamics (MD) method, to understand the behavior of dislocation loops in iron-based alloys for the future nuclear systems in which high concentration of hydrogen is created in structural materials. Based on the simulation results, the pinning effect of hydrogen bubble on prismatic interstitial dislocation loop is proposed in bcc iron. The dislocation loop can be attracted to a hydrogen bubble and locked by it when the dislocation loop is in contacts with the bubble. The dislocation loop gliding is also impeded through the elastic interaction with a hydrogen bubble, but without directly colliding with it. When the attractive interaction between a hydrogen bubble and an interstitial dislocation loop is strong enough, the hydrogen bubble can capture the dislocation loop directly and they annihilate with each other. The switching of these interaction mechanisms depends on sizes of the dislocation loop and the hydrogen bubble, the anglen and the distance between the loop and the bubble, and the surface density of hydrogen atoms in the bubble. All these results provide new insight on hydrogen effect in irradiated iron-based materials.

Distribution of O atoms on partially oxidized metal targets, and the consequences for reactive sputtering of individual metal oxides

We investigate the oxidation of a wide range of metal surfaces by ab-initio calculations. We go through a wide range of metals (Sc, Y, La, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Cu, Ag, Au, Zn, Cd, Al) and surface oxygen coverages (ΘO). Calculations of the adsorption energy per O atom (Eads_min) are followed by characterizing the preferred distribution of O atoms on a partially oxidized surface (considering up to 329 distributions per metal). We find that individual metals exhibit qualitatively different Eads_min(ΘO) dependencies and thermodynamical preferences: (i) decreasing Eads_min(ΘO) and heterogeneous distribution of O atoms (stoichiometric oxide + metal; e.g. Al or La), (ii) increasing Eads_min(ΘO) and homogeneous distribution of O atoms (substoichiometric oxide; e.g. Ti or Zr), (iii) concave Eads_min(ΘO) and homogeneous distribution of O atoms at low ΘO and heterogeneous at high ΘO (e.g. Sc or Y), etc. This is of crucial importance for the quantities such as secondary electron emission yield, which are guaranteed to correspond to a weighted average of those of stoichiometric oxide and metal only in the case of heterogeneous O atom distribution. The results are correlated with formation enthalpies of oxides of various compositions, surface atomic densities of individual metals, and experimental results such as the time dependence of the magnetron voltage during sputter cleaning of oxidized metal targets. Furthermore, we demonstrate use of these results by presenting static and dynamic Monte Carlo simulations of sputtering.

Simulation of traveling interface pulses in bistable surface reactions.

A couple of bistable oxidation reactions on Rh(110), the CH_{3}OH+O_{2} and the NH_{3}+O_{2} reactions, exhibit localized excitations at the interface between oxygen-poor and oxygen-rich phase that propagate in a pulselike manner along the interface. A three-variable reaction-diffusion model is set up based on a mechanism that explains the localized excitations as being caused by temporary structural defects generated in the vicinity of the interface. The structural defects are a consequence of different densities of surface atoms in the oxygen-induced reconstruction phases and in the nonreconstructed (1×1) phase. One- and two-dimensional simulations show that traveling interface pulses (TIPs) exist in a region of so-called double metastability adjacent to the equistability point of the bistable system. As in the experiment, we observe triangular-shaped TIPs that move fast along the interface. Diffusional anisotropy is not required for the occurrence of TIPs. All essential features of the experiment are reproduced by the simulations.

Effect of the Random Defects Generated on the Surface of Pt(111) on the Electro-oxidation of Ethanol: An Electrochemical Study.

In the present work, the Pt(111) surface was disordered by controlling the density of {110}- and {100}-type defects. The cyclic voltammogram (CV) of a disordered surface in acid media consists of three contributions within the hydrogen adsorption/desorption region: one from the well-ordered Pt(111) symmetry and the other two transformed from the {111}-symmetry with contributions of {110}- and {100}-type surface defects. The ethanol oxidation reaction (EOR) was studied on these disordered surfaces. Electrochemical studies were performed in 0.1 M HClO4 +0.1 M ethanol using cyclic voltammetry and chronoamperometry. Changes in current densities associated to the specific potentials at which each oxidation peak appears suggest that different surface domains of disordered platinum oxidize ethanol independently. Additionally, as the surface-defect density increases, the EOR is catalysed better. This tendency is directly observed from the CV parameters because the onset and peak potentials are shifted to less positive values and accompanied by increases in the oxidation-peak current on disordered surfaces. Similarly, the CO oxidation striping confirmed this same tendency. Chronoamperometric experiments showed two opposite behaviors at short oxidation times (0.1 s). The EOR was quickly catalyzed on the most disordered surface, Pt(111)-16, and was then rapidly deactivated. These results provide fundamental information on the EOR, which contributes to the atomic-level understanding of real catalysts.

Hydrothermal stable ZIF-67 nanosheets via morphology regulation strategy to construct mixed-matrix membrane for gas separation

Mixed matrix membranes (MMMs) based on metal-organic frameworks (MOFs) have proven to have high separation performance, which has great potential in separation applications. However, unsatisfactory hydrothermal stability is the Achilles' heel of MOFs in practical applications, which seriously hinders the development of MOF based MMMs. Under the advantage of crystal anisotropy, a morphology regulation strategy without post-treatment is presented for the first time to efficiently improve the stability of MOF fillers in aqueous solution. Contrary to the regular dodecahedron ZIF-67 crystals, the [211] oriented ZIF-67 nanosheets (NS) can maintain an ordered microporous framework integrally in the aqueous solution of membrane preparation. The exposed [211] crystal face exhibits enhanced stability due to a lower proportion of Co–N bond and higher surface atomic density. The flake morphology of ZIF-67 with economic incorporation (5.0 wt %) offers the MMMs significantly enhanced CO2 permeability of 139.4 barrer and CO2/N2 ideal selectivity of 73.2, improved by 50.7% and 76.0% compared with the pristine polymer membrane. This strategy provides a new idea for improving the hydrothermal stability of MOF materials and extends their separation applications under aqueous conditions.