Sodiophilic Mg2+ -Decorated Ti3 C2 MXene for Dendrite-Free Sodium Metal Batteries with Carbonate-Based Electrolytes.

The advantages of sodium metal, such as abundant resources, low cost, high capacity, and high working potential, make it a promising metal anode. Unfortunately, the hazardous dendrite growth of sodium metal is one of the major hindrances for the practical application of sodium metal batteries (SMBs). By applying multifunctional Mg(II)@Ti3 C2 MXene as the protective layer for commercial Cu foil, the wettability of the electrolyte on the current collector is dramatically improved with the suppression of sodium dendrites. Moreover, the first-principles calculations prove that the surface of Mg(0001) is able to establish a connection with Na(111) growth, with Mg acting as the nucleation seed for sodium. The experimental results indicate that even when a high areal capacity of sodium (2 mAh cm-2 ) is deposited, no sodium dendrite is observed. Electrochemical tests, including symmetric cells, Na||Cu asymmetric cells, and full cells, prove the sodiophilic character of Mg2+ -decorated Ti3 C2 MXene. The results may also create a new pathway for developing other dendrite-free metal anodes, such as Li/K/Zn/Ca/Mg.

Scalable Synthesis of Nano-Sized Bi for Separator Modifying in 5V-Class Lithium Metal Batteries and Potassium Ion Batteries Anodes.

With the advantages of high theoretical-specific capacity and lowest working potential, lithium metal anode is considered as the most promising anode for next-generation batteries. Here, a scalable dealloying method is developed to prepare nano-sized bismuth (Bi). It is found that the Bi-modification can not only enhance the wettability of the commercial polyethylene separator but also suppresses the lithium dendrite growth. With the nano-sized Bi modified separator, 5V-class lithium metal batteries with commercial carbonate-based electrolyte show a 91% capacity retention ratio after 800 cycles. First-principle calculations prove that lithium atoms tend to deposit smoothly on the Bi surface. Moreover, for potassium ion batteries, nano-sized Bi shows a stable cycling performance and high capacity. The results may be useful for the development of high-energy and high-safety batteries.

A first-principles study of water adsorbed on flat and stepped silver surfaces.

The structural, electronic and vibrational properties of a water layer on Ag(100) and Ag(511) have been studied by first-principles calculations and ab initio molecular dynamics simulations. The most stable water structure on the Ag(100) and Ag(511) surfaces have been obtained. The AIMD results showed rather high stability of the water layer on the stepped surface at 140 K, indicating a crystal-like structure with long-range ordering. The calculated vibrational spectra at 140 K showed good agreement with the experimental results. On the Ag(100) surface, a red-shift was observed when the temperature increased from 140 K to 300 K caused by the change in the number of H-bonded (HB) hydrogen. On Ag(511), a three-fold splitting of the O-H stretch mode was observed. This can be explained by the special water structure at the stepped Ag surface: the relatively strong water-metal interaction at the step edge and weak water-terrace interaction/strong water-water interaction at the terrace, which can also explain the high stability of the water layer on the Ag(511) surface.

Theoretical design of platinum-sliver single atom alloy catalysts with CO adsorbate-induced surface structures.

In this work, by combining density functional theory calculations and Monte Carlo simulations with cluster expansion Hamiltonian methods, we investigate the surface aggregation of Pt atoms on the Pt/Ag(111) surface under vacuum conditions and in the presence of CO. The results show the decisive influence of CO-CO interactions and reveal the competition between CO-metal interactions and CO-CO repulsion. Thus, in addition to evidence of reverse Pt segregation caused by CO adsorption, two methods for tuning the surface Pt atomic system synthesis are found, where the surface can be adjusted by tuning the CO coverage to obtain a larger number of monomers (0.25 ML CO coverage) or a pure Pt layer (1 ML coverage) at Pt bulk concentrations above 10%. For highly dilute alloys, the Pt distribution can be controlled by adjusting the concentration. Indeed, for a Pt bulk concentration close to 8% and a CO coverage of about less than 1 ML, between 400 and 600 K, an ordered structure has been observed which maximized the number of Pt monomers and homogeneous distribution on the surface. The overpotential (η) of the ordered Pt3Ag(111) surface is 0.41 V, slightly lower than that of pure Pt(111) (η = 0.43 V), indicating a potential candidate for ORR catalysts with rich active sites and a low overpotential.

Theoretical and experimental study of the microstructure of a metallic melt in an In50Bi50 alloy based on the Wulff cluster model.

In this paper, the Wulff cluster model which has been proved to successfully describe the melt structure of pure metals, homogenous alloys and eutectic alloys has been extended to an alloy with intermetallic compounds (In50Bi50). According to the cohesive energy and the solid-state XRD patterns, the most possible types of clusters in the melt are Bi and InBi. At relatively high temperatures, the superimposed XRD (simulated) patterns of Bi and InBi clusters are in good agreement with the experimental HTXRD patterns in terms of the position and intensity of the peaks. With the decrease of temperature, there is an obvious deviation in the simulated XRD value at the second peak caused by the nucleation process of Bi clusters, which would be modified by adding simulated XRD patterns of the Bi bulk. The proportion of the superimposed Bi bulk XRD pattern increases with the decrease of temperature suggesting that the nucleation process of the Bi cluster begins at 160 °C.

A casting combined quenching strategy to prepare PdAg single atom alloys designed using the cluster expansion combined Monte Carlo method.

In this work, the surface structure of a PdAg alloy is investigated by cluster expansion (CE) combined Monte Carlo (MC) simulations. All systems with different component proportions show an obvious component segregation corresponding to the depth from the surface. A significant amount of Ag is observed on the first layer, and Pd is concentrated significantly on the second layer. The Pd distribution on the PdAg surfaces is closely related to the temperature and composition ascribed to the concentration and configurational entropy effects, which are explicitly treated in MC simulations. The vacancies mainly distribute separately. The simulation results show good agreement with the experimental evidence. Moreover, we demonstrated a general and highly effective casting combined quenching strategy for controlling the ensemble size and chemical composition of alloy surfaces which could successfully be applied to the large-scale production of SAA.

Aqueous MnV2 O6 -Zn Battery with High Operating Voltage and Energy Density.

Aqueous Zn ion batteries (AZIBs), featuring low cost, long-term cycling stability, and superior safety are promising for applications in advanced energy storage devices. However, they still suffer from unsatisfactory energy density and operating voltage, which are closely related to cathode materials used. Herein, the use of monoclinic MnV2 O6 (MVO) is reported, which can be activated for high-capacity Zn ions storage by electrochemically oxidizing part of the Mn2+ to Mn3+ or Mn4+ while the remaining Mn2+ ions act as binders/pillars to hold the layer structure of MVO and maintain its integrity during charging/discharging process. Moreover, after introducing carbon nanotubes (CNT), the MVO:CNT composite not only provides robust 3D Zn-ion diffusion channels but also shows enhanced structural integrity. As a result, a MVO:CNT cathode delivers a high midpoint voltage (1.38 V after 3000 cycles at 2 A g-1 ) and a high energy density of 597.9 W h kg-1 . Moreover, DFT analyses clearly illustrate stepwise Zn ion insertion into the MnV2 O6 lattice, and ex-situ analyses results further verify the highly structural reversibility of the MnV2 O6 cathode upon extended cycling, demonstrating the good potential of MnV2 O6 for the establishment of viable aqueous Zn ion battery systems.

The structure of metallic melts in eutectic alloys based on the Wulff cluster model: theory meets experiment.

In the present work, the Wulff cluster model, which has been proved to be successful for pure metals and homogeneous alloys, has been extended to eutectic alloys (Ag-Cu and Al-Si). In our model, the shapes of the clusters in melts were determined by the interfacial energy calculated by density functional theory (DFT) of different facet families based on Wulff theory. The cluster size was given by the pair distribution function (PDF) g(r), which was converted from experimental high-temperature X-ray diffraction (HTXRD). The simulated XRD curves in the high temperature region were in good agreement with the experimental results. For the Al-Si alloy, a deviation of the intensity and position of the second peak near the eutectic temperature was observed. The simulated results after structure and composition modification corresponded to the experimental ones. It indicates that the deviation is mainly related to the significant change of the cluster size during Si clusters' growth processes before nucleation. Differently, there are no such nucleation processes at temperatures near the eutectic point due to the relatively high nucleation barriers of the two components in the Ag-Cu alloy.

The structure of metallic melts in binary homogenous alloys: a thermodynamical understanding from the Wulff cluster model.

In the present work, a new liquid metal model (Wulff cluster model) which has been proved to describe the structures of pure metal melts has been extended to binary homogeneous alloy melts (Cu-Ni and Ag-Au). The shapes of the nano-particles are determined by surface energies of different families of crystal planes, calculated by density functional theory (DFT), whereas the size was given by the pair distribution function (PDF) g(r) which was converted from experimental high-temperature X-ray diffraction (HTXRD). We demonstrated that the simulated X-ray diffraction (XRD) curves from present models match the experimental results quite well at high temperatures above the liquid-solid two-phase region, including not only the position and width of the peaks but also the relative intensity of the first and second peaks. Moreover, when the temperature is near the liquid-solid two-phase region, our model also fits the experimental strength curve well after modification using the solid XRD pattern of a relatively high melting point metal instead of its nano-particle. The agreement indicates the nucleation processes in homogeneous alloy melts.

First-principles study for quasi-static growth model in FeAl intermetallic based on Wulff cluster model.

In order to investigate the structure of FeAl mesoscopic crystals segregating in liquid state alloys, we have determined their equilibrium structures (Wulff shape) based on the Wulff cluster model. For non-stoichiometric surface terminations, the chemical environment is taken into account through the chemical potential of the constituents. In this case, different cluster shapes change as a function of the chemical environment. In order to model the growth process in more detail, we propose a quasi-static growth model based on the sequential addition of (sub-)monolayers in the most favorable surface directions. Thus, a sequence of different Wulff shapes results in the growth process, as illustrated for the FeAl intermetallic compound. This model is proved preliminarily by calculating the concentration trend of Al/Fe atoms on both Al-terminated and Fe-terminated surfaces, and by simulating the most stable layer adsorbed on these two surfaces. This model might be helpful in analyzing the growth processes including nucleation barriers during nucleation processes theoretically.

Electrokinetic transport properties of deoxynucleotide monophosphates (dNMPs) through α-phase phosphorene carbide nanochannel for electrophoretic detection.

Electrokinetic identification of biomolecules is an effective analytical method in which an electric field drives the nucleic acids, peptides, and other species through a nanoscale channel and the time of flight (TOF) is recorded. The mobilities of the molecules are determined by the water/nanochannel interface, including the electrostatic interactions, surface roughness, van der Waals interactions, and hydrogen bonding. The recently reported α-phase phosphorus carbide (α-PC) has an intrinsically wrinkled structure that can efficiently regulate the migrations of biomacromolecules on it, making it a highly promising candidate for the fabrication of nanofluidic devices for electrophoretic detection. Herein, we studied the theoretical electrokinetic transport process of dNMPs in α-PC nanochannel. Our results clearly show that the α-PC nanochannel can efficiently separate dNMPs in a wide range of electric field strengths from 0.5 to 0.8 V nm-1. The electrokinetic speed order is deoxy thymidylate monophosphates (dTMP) > deoxy cytidylate monophosphates (dCMP) > deoxy adenylate monophosphates (dAMP) > deoxy guanylate monophosphates (dGMP) and is almost independent of the electric field strength. For a nanochannel with a typical height of 3.0 nm and an optimized electric field of 0.7-0.8 V nm-1, the difference in TOF is large enough to guarantee accurate identification. We find that dGMP is the weakest link among the four dNMPs for sensitive detection in the experiment because its velocity always shows large fluctuations. This is because of its significantly different velocities when dGMP is bound to α-PC in different orientations. In contrast, for the other three nucleotides, the velocities are independent of the binding orientations. The high performance of the α-PC nanochannel is attributed to its wrinkled structure in which the nanoscale grooves can form nucleotide-specific interactions that greatly regulate the transport velocities of the dNMPs. This study illustrates the high potential of α-PC for electrophoretic nanodevices. This could also provide new insights for the detection of other types of biochemical or chemical molecules.

A New Theoretical Method for Studying Effects of Microstructure on Effective Thermal Conductivity of Vermicular Graphite Cast Iron.

To provide the basis for thermal conductivity regulation of vermicular graphite cast iron (VGI), a new theoretical method consisting of shape interpolation, unit cell model and numerical calculation was proposed. Considering the influence of the graphite anisotropy and interfacial contact thermal conductivity (ICTC), the effective thermal conductivity of a series of unit cell models was calculated by numerical calculation based on finite difference. The effects of microstructure on effective thermal conductivity of VGI were studied by shape interpolation. The experimental results were in good agreement with the calculated ones. The effective thermal conductivity of VGI increases in power function with the decrease in graphite shape parameter, and increases linearly with the increase in graphite volume fraction and thermal conductivity of matrix. When the graphite volume fraction increases by 1%, the thermal conductivity of nodular cast iron increases by about 0.18 W/(m·K), while that of gray cast iron increases by about 3 W/(m·K). The thermal conductivity of cast iron has the same sensitivity to the thermal conductivity of matrix regardless of the graphite shape parameter. The thermal conductivity of matrix increased by 15 W/(m·K) and the thermal conductivity of cast iron increased by about 12 W/(m·K). Moreover, the more the graphite shape deviates from the sphere, the greater the enhancement effect of graphite anisotropy on thermal conductivity than the hindrance effect of interface between graphite and matrix. This work can provide guidance for the development of high thermal conductivity VGI and the study of thermal conductivity of composites containing anisotropic dispersed phase particles with complex shapes.

Hexaindium Heptasulfide/Nitrogen and Sulfur Co-Doped Carbon Hollow Microspindles with Ultrahigh-Rate Sodium Storage through Stable Conversion and Alloying Reactions.

Group IIIA-VA metal sulfides (GMSs) have attracted increasing attention because of their unique Na-storage mechanisms through combined conversion and alloying reactions, thus delivering large theoretical capacities and low working potentials. However, Na+ diffusion within GMSs anodes leads to severe volume change, generally representing a fundamental limitation to rate capability and cycling stability. Here, monodispersed In6 S7 /nitrogen and sulfur co-doped carbon hollow microspindles (In6 S7 /NSC HMS) are produced by morphology-preserved thermal sulfurization of spindle-like and porous indium-based metal organic frameworks. The resulting In6 S7 /NSC HMS anode exhibits theoretical-value-close specific capacity (546.2 mAh g-1 at 0.1 A g-1 ), ultrahigh rate capability (267.5 mAh g-1 at 30.0 A g-1 ), high initial coulombic efficiency (≈93.5%), and ≈92.6% capacity retention after 4000 cycles. This kinetically favored In6 S7 /NSC HMS anode fills up the kinetics gap with a capacitive porous carbon cathode, enabling a sodium-ion capacitor to deliver an ultrahigh energy density of 136.3 Wh kg-1 and a maximum power density of 47.5 kW kg-1 . The in situ/ex situ analytical techniques and theoretical calculation both show that the robust and fast Na+ charge storage of In6 S7 /NSC HMS arises from the multi-electron redox mechanism, buffered volume expansion, negligible morphological change, and surface-controlled solid-state Na+ transport.

PdAg/Ag(111) Surface Alloys: A Highly Efficient Catalyst of Oxygen Reduction Reaction.

In this article, the behavior of various Pd ensembles on the PdAg(111) surfaces was systematically investigated for oxygen reduction reaction (ORR) intermediates using density functional theory (DFT) simulation. The Pd monomer on the PdAg(111) surface (with a Pd subsurface layer) has the best predicted performance, with a higher limiting potential (0.82 V) than Pt(111) (0.80 V). It could be explained by the subsurface coordination, which was also proven by the analysis of electronic properties. In this case, it is necessary to consider the influence of the near-surface layers when modeling the single-atom alloy (SAA) catalyst processes. Another important advantage of PdAg SAA is that atomic-dispersed Pd as adsorption sites can significantly improve the resistance to CO poisoning. Furthermore, by adjusting the Pd ensembles on the catalyst surface, an exciting ORR catalyst combination with predicted activity and high tolerance to CO poisoning can be designed.

The safety and effectiveness comparison of Delta Medical's PEEK interface screw and Endobutton and that of Smith & Nephew's in arthroscopic anterior cruciate ligament reconstruction: A multicenter prospective double-blind randomized controlled clinical trial.

Background: To reduce the costs and financial burden in the ACLR treatment, we compare the early clinical outcomes and Magnetic Resonance Imaging (MRI) results of Delta Medical's PEEK (polyether ether ketone) interference screw and EndoButton with those of Smith & Nephew's PEEK interference screw and EndoButton in patients with arthroscopic anterior cruciate ligament reconstruction. Methods: A total of 104 patients in five different medical centers were randomly allocated into two groups: 1: Delta Medical's PEEK interference screw and EndoButton (53 patients); 2: Smith & Nephew's PEEK interference screw and EndoButton (51 patients). The modified Lysholm knee score, the laxity examination, and clinical and functional range of motion were evaluated at 3 and 6 months postoperatively. The clinical effective rate was calculated and classified as excellent and good at 6 months postoperatively. MRI examinations were performed at 3 and 6 months postoperatively to determine the healing process. Computerized tomography (CT) was performed at 2 weeks and 3 months postoperatively to evaluate the complications. Results: Significant improvements in knee function and functional scores were observed in both groups after surgery regardless of the fixation materials applied (P < 0.05). No differences were observed in the functional scores and range of motion. The assessments of Lysholm knee scores at 3 and 6 months produced no statistical differences (both P > 0.05). The clinical effective rate revealed no difference between the groups at 6 months postoperatively (non-inferiority analysis P = 0.0220). The differences of laxity examination between the groups were not statistically significant (Fisher's test, P = 0.6139, 0.2004, respectively). No significant differences in the functional range of motion were found at each follow-up time-point (P > 0.05). No major intra- or postoperative complications, such as infection, and vessel or nerve injury were observed. Conclusions: Knee function and functional scores were improved after ACLR in both groups, regardless of the PEEK interference screw and EndoButton applied. The difference in functional scores and range of motion were not significant in groups 1 and 2. Delta Medical's PEEK interference screw and EndoButton had a non-inferiority effect compared to Smith & Nephew's PEEK interference screw and EndoButton. Delta Medical's PEEK interference screw and EndoButton were suitable for arthroscopic ACLR.

Gold Carbide: A Predicted Nanotube Candidate from First Principle.

In the present work, density functional theory (DFT) calculations were applied to confirm that the gold carbide previously experimentally synthesized was AuC film. A crucial finding is that these kinds of AuC films are self-folded on the graphite substrate, leading to the formation of a semi-nanotube structure, which significantly diminishes the error between the experimental and simulated lattice constant. The unique characteristic, the spontaneous archlike reconstruction, makes AuC a possible candidate for self-assembled nanotubes. The band structure indicated, in the designed AuC nanotube, a narrow gap semiconductor with a bandgap of 0.14 eV. Both AIMD (at 300 and 450 K) results and phonon spectra showed a rather high stability for the AuC nanotube because a strong chemical bond formed between the Au-5d and C-2p states. The AuC nanotube could become a novel functional material.

Probing the Microstructure in Pure Al & Cu Melts: Theory Meets Experiment.

In the present work, a new model of the atomic cluster structure, which is determined by metal Wulff construction with the crystal structure inside, is proposed to describe the structures of metallic melts. The shapes of the structures are determined by surface energies of different crystal plane groups, calculated from density functional theory (DFT), while the size is given by the pair distribution function (PDF) of the experimental high-temperature X-ray diffraction (HTXRD). Taking Aluminum (Al) and Copper (Cu) as the representative examples, we demonstrate that the simulated XRD curves from present models match the experimental results quite well, not only regarding the position and width of the peaks but also the relative intensity of the first and second peaks. These results indicate a successful model to describe the properties of metallic melts. The model also explains a main peak deviation phenomenon between the XRD of metallic melt and the solid ones in pure metal Al. Finally, a physical picture of metallic melt is given, which is mainly composed of atomic cluster structures and free atoms around them.

First-principles study of the structure of water layers on flat and stepped Pb electrodes.

On the basis of perodic density functional theory (DFT) calculations, we have addressed the geometric structures and electronic properties of water layers on flat and stepped Pb surfaces. In contrast to late d-band metals, on Pb(111) the energy minimum structure does not correspond to an ice-like hexagonal arrangement at a coverage of 2/3, but rather to a distorted structure at a coverage of 1 due to the larger lattice constant of Pb. At stepped Pb surfaces, the water layers are pinned at the step edge and form a complex network consisting of rectangles, pentagons and hexagons. The thermal stability of the water layers has been studied by using ab initio molecular dynamics simulations (AIMD) at a temperature of 140 K. Whereas the water layer on Pb(111) is already unstable at this temperature, the water layers on Pb(100), Pb(311), Pb(511) and Pb(711) exhibit a higher stability because of stronger water-water interactions. The vibrational spectra of the water layers at the stepped surfaces show a characteristic splitting into three modes in the O-H stretch region.

Bottom-up formation of robust gold carbide.

A new phenomenon of structural reorganization is discovered and characterized for a gold-carbon system by in-situ atomic-resolution imaging at temperatures up to 1300 K. Here, a graphene sheet serves in three ways, as a quasi transparent substrate for aberration-corrected high-resolution transmission electron microscopy, as an in-situ heater, and as carbon supplier. The sheet has been decorated with gold nanoislands beforehand. During electron irradiation at 80 kV and at elevated temperatures, the accumulation of gold atoms has been observed on defective graphene sites or edges as well as at the facets of gold nanocrystals. Both resulted in clustering, forming unusual crystalline structures. Their lattice parameters and surface termination differ significantly from standard gold nanocrystals. The experimental data, supported by electron energy loss spectroscopy and density-functional theory calculations, suggests that isolated gold and carbon atoms form - under conditions of heat and electron irradiation - a novel type of compound crystal, Au-C in zincblende structure. The novel material is metastable, but surprisingly robust, even under annealing condition.