Electronic Properties of CrB/Co2CO2 Superlattices by Multiple Descriptor-Based Machine Learning Combined with First-Principles.

In recent times, newly unveiled 2D materials exhibiting exceptional characteristics, such as MBenes and MXenes, have gained widespread application across diverse domains, encompassing electronic devices, catalysis, energy storage, sensors, and various others. Nonetheless, numerous technical bottlenecks persist in the development of high-performance, structurally flexible, and adjustable electronic device materials. Research investigations have demonstrated that 2D van der Waals superlattices (vdW SLs) structures comprising materials exhibit exceptional electrical, mechanical, and optical properties. In this work, the advantages of both materials are combined and compose the vdW SLs structure of MBenes and MXenes, thus obtaining materials with excellent electronic properties. Furthermore, it integrates machine learning (ML) with first-principles methods to forecast the electrical properties of MBene/MXene superlattice materials. Initially, various configurations of MBene/MXene superlattice materials are explored, revealing that distinct stacking methods exert significant influence on the electronic structure of MBene/MXene materials. Specifically, the BABA-type stacking of CrB (layer A) and Co2CO2 MXene (layer B) is most stable configureation. Subsequently, multiple descriptors of the structure are constructed to predict the density of states  of vdW SLs through the employment of ML techniques. The best model achieves a mean absolute error (MAE) as low as 0.147 eV.

Double strengthening induced by grain boundary segregation of solute elements in gradient nano Ni-Co alloys.

Gradient induced unusual strain hardening achieves the equilibrium of the strength and plasticity of alloys, and is an important strategy for the optimization of the mechanical properties of metals and alloys. The segregation of solute elements can greatly improve the grain boundary stability, inhibit grain coarsening and promote the mechanical strength of the alloy. In our efforts, the segregation structure of the solute element Co was designed and added to the gradient nano Ni-Co alloy, and the two strengthening strategies were applied simultaneously in one structure. The mechanical strength of the alloy achieved a second increase based on the unique combination of gradient induced strain hardening and high plasticity, especially the yield strength of alloy increase amplitude reach to 42%. This provides a positive direction for the alloy strengthening strategy. In the process of secondary strengthening, the micro-mechanism is divided into two stages: in the first stage, the gradient strain provides the alloy with geometrically necessary dislocations and a multi-axial stress state, and the existence of large numbers of geometrically necessary dislocations creates good conditions for the second stage strengthening. In the second stage, the solute segregation induced stable grain boundaries produce a strong pinning effect on the geometrically necessary dislocation, which realizes the coupling of grain boundary strengthening and dislocation strengthening. This provides a new strengthening strategy and positive theoretical guidance for the experimental preparation of advanced alloys with excellent properties.

Strong yet flexible ceramic aerogel.

Ceramic aerogels are highly efficient, lightweight, and chemically stable thermal insulation materials but their application is hindered by their brittleness and low strength. Flexible nanostructure-assembled compressible aerogels have been developed to overcome the brittleness but they still show low strength, leading to insufficient load-bearing capacity. Here we designed and fabricated a laminated SiC-SiOx nanowire aerogel that exhibits reversible compressibility, recoverable buckling deformation, ductile tensile deformation, and simultaneous high strength of up to an order of magnitude larger than other ceramic aerogels. The aerogel also shows good thermal stability ranging from -196 °C in liquid nitrogen to above 1200 °C in butane blow torch, and good thermal insulation performance with a thermal conductivity of 39.3 ± 0.4 mW m-1 K-1. These integrated properties make the aerogel a promising candidate for mechanically robust and highly efficient flexible thermal insulation materials.

Insight into the Electronic Properties of Semiconductor Heterostructure Based on Machine Learning and First-Principles.

A first-principles approach is a powerful means of gaining insight into the intrinsic structure and properties of materials. However, with the implementation of material genetic engineering, it is still a challenging road to discover materials with high satisfaction. One alternative is to employ machine-learning techniques to mine data and predict performance. In this present contribution, the method is taken to predict the band gap opening value of graphene in a heterostructure. First, the data of 2076 binary compounds in the Materials Project library are used to achieve visual dimensionality reduction of the data set through a t-distributed stochastic neighbor embedding (t-SNE) algorithm in unsupervised learning. Then, a series of semiconductor components are screened out and form heterostructures with graphene. Second, by means of the ensemble learning EXtreme Gradient Boost (XGBoost) algorithm and support vector machine (SVM) technology, two prediction frameworks are built to predict the band gap opening value of the graphene in the system. Finally, density functional theory (DFT) is used to calculate the energy band and density of states for comparison. Analysis shows that the prediction model has an accuracy rate of 88.3%, and there is little difference between prediction results and calculation results. We anticipate that this framework model would have fascinating applications in predicting the electronic properties of various multiphase materials.

Influence of Grain Size and Its Distribution on Charpy Impact Properties of TA3 Alloy.

In practice, most components often receive impact loads during service. In order to ensure the service safety of components, impact toughness evaluation is essential. To the best of our knowledge, the previous studies were mainly focused on the quasi-static tensile deformation, and the impact toughness of bimodal grain structured metals have rarely been reported. Three different grain size characteristics TA3 alloy, i.e., fine grained sample (FG Ti), the mixture of coarse and fine grained sample (MG Ti), and coarse grained (CG Ti), were produced, and their tensile and Charpy impact properties were comparatively investigated. Owing to the strengthening of retained ß phase and the twining inducing plasticity effect, MG Ti display the highest tensile strength and impact absorbed energy, together with an intermediate tensile elongation. The impact deformed microstructures revealed that the primary deformation modes of FG Ti, MG Ti and CG Ti sample are: dislocation slips, a combination of dislocation slip in fine grained region and {101¯2} deformation twins in coarse grained region, and {112¯1} deformation twins in sequence.

Metal-Free Bifunctional Ordered Mesoporous Carbon for Reversible Zn-CO2 Batteries.

The fabrication of Zn-CO2 batteries is a promising technique for CO2 fixation and energy storage. Herein, nitrogen-doped ordered mesoporous carbon (NOMC) is adopted as a bifunctional metal-free electrocatalyst for CO2 reduction and oxygen evolution reaction in the near-neutral electrolyte. The ordered mesoporous structures and abundant N-dopings of NOMC facilitate the accessibility and utilization of the active sites, which endow NOMC with excellent electrocatalysis performance and outstanding stability. Especially, a nearly 100% CO Faradaic efficiency is achieved at an ultralow overpotential of 360 mV for CO2 reduction. When constructed as an aqueous rechargeable Zn-CO2 battery using NOMC as the cathode, it yields a high peak power density of 0.71 mW cm-2 , a good cyclability of 300 cycles, and excellent energy efficiency of 52.8% at 1.0 mA cm-2 .

Highly Stretchable, Crack-Insensitive and Compressible Ceramic Aerogel.

Ceramic aerogels are attractive candidates for high-temperature thermal insulation, catalysis support, and ultrafiltration materials, but their practical applications are usually limited by brittleness. Recently, reversible compressibility has been realized in flexible nanostructures-based ceramic aerogels. However, these modified aerogels still show fast and brittle fracture under tension. Herein, we demonstrate achieving reversible stretch and crack insensitivity in a highly compressible ceramic aerogel through engineering its microstructure by using curly SiC-SiOx bicrystal nanowire as the building blocks. The aerogel exhibits large-strain reversible stretch (20%) and good resistance to high-speed tensile fatigue test. Even for a prenotched sample, a reversible stretch at 10% strain is achieved, indicating good crack resistance. The aerogel also displays reversible compressibility up to 80% strain, ultralow thermal conductivity of 28.4 mW m-1 K-1, and excellent thermal stability even at temperatures as high as 1200 °C in butane blow torch or as low as -196 °C in liquid nitrogen. Our findings show that the attractive tensile properties arise from the deformation, interaction, and reorientation of the curly nanowires which could reduce stress concentration and suppress crack initiation and growth during tension. This study not only expands the applicability of ceramic aerogels to conditions involving complex dynamic stress under extreme temperature conditions but also benefits the design of other highly stretchable and crack-resistant porous ceramic materials for various applications.

Isolated copper single sites for high-performance electroreduction of carbon monoxide to multicarbon products.

Electrochemical carbon monoxide reduction is a promising strategy for the production of value-added multicarbon compounds, albeit yielding diverse products with low selectivities and Faradaic efficiencies. Here, copper single atoms anchored to Ti3C2Tx MXene nanosheets are firstly demonstrated as effective and robust catalysts for electrochemical carbon monoxide reduction, achieving an ultrahigh selectivity of 98% for the formation of multicarbon products. Particularly, it exhibits a high Faradaic efficiency of 71% towards ethylene at -0.7 V versus the reversible hydrogen electrode, superior to the previously reported copper-based catalysts. Besides, it shows a stable activity during the 68-h electrolysis. Theoretical simulations reveal that atomically dispersed Cu-O3 sites favor the C-C coupling of carbon monoxide molecules to generate the key *CO-CHO species, and then induce the decreased free energy barrier of the potential-determining step, thus accounting for the high activity and selectivity of copper single atoms for carbon monoxide reduction.

Highly Productive Electrosynthesis of Ammonia by Admolecule-Targeting Single Ag Sites.

The ambient electrocatalytic N2 reduction reaction (NRR) is a promising alternative to the Haber-Bosch process for producing NH3. However, a guideless search for single-atom-based and other electrocatalysts cannot promote the NH3 yield rates by NRR efficiently. Herein, our first-principles calculations reveal that the successive emergence of vertical end-on *N2 and oblique end-on *NNH admolecules on single metal sites is key to high-performance NRR. By targeting the admolecules, single Ag sites with the Ag-N4 coordination are found and synthesized massively. They exhibit a record-high NH3 yield rate (270.9 µg h-1 mgcat.-1 or 69.4 mg h-1 mgAg-1) and a desirable Faradaic efficiency (21.9%) in HCl aqueous solution under ambient conditions. The generation rate of NH3 is stable during 20 consecutive reaction cycles, and the reduction current density is almost constant for 60 h. This work provides an effective targeting-design principle to purposefully synthesize active and durable single-atom-based NRR electrocatalysts.

Cluster expansion Monte Carlo study of indium-aluminum segregation and homogenization in CuInSe2-CuAlSe2 pseudobinary alloys.

The influence of temperature and Al content on the segregation and homogenization behaviour of In-Al atoms in CuIn1-xAlxSe2 (CIAS) pseudobinary alloys is studied using a combination of cluster expansion Monte Carlo simulations and first-principles calculations. Such alloys are promising materials for a number of solar-energy-related applications. We found that the segregation of In-Al atoms in CIAS alloys with different Al contents occurs at relatively low temperatures. The cluster morphology of Al(In) atoms in CIAS alloys at 73 K appears in an ellipsoidal, rod-like or lamellar form, depending on the Al(In) content. The spatial distribution of In-Al atoms becomes homogeneous as the temperature increases. By determining the inhomogeneity degree σ of In-Al distributions in CIAS alloys at a series of temperatures, we found that the variation of σ with temperature (T) for all the considered CIAS alloys are sigmoidal in general and the sharp decrease in σ within a certain temperature range implies the occurrence of inhomogeneous-to-homogeneous phase transition. The inhomogeneity degree σ of CIAS alloys before or after the phase transition (phase segregation) increases as the content of Al(x) and In(1 - x) atoms gets closer. The σ(T) data points obtained by us can be well fitted with the Boltzmann function, which can give several physically meaningful parameters such as the phase transition temperature T0, temperature range of phase transition ΔT and so on. The fitted T0 and ΔT values for CIAS alloys with different Al content were proved to be reliable. The novel method for predicting the T0 and ΔT may be applied to many other binary or pseudobinary material systems with positive formation energy.

Boosting hydrogen evolution activity of vanadyl pyrophosphate nanosheets for electrocatalytic overall water splitting.

Herein, (VO)2P2O7 nanosheets function as a highly-active electrocatalyst for the hydrogen evolution reaction with an ultralow overpotential of 30 mV at 10 mA cm-2 in basic media, being close to Pt/C. Furthermore, as a bifunctional electrocatalyst, (VO)2P2O7 not only exhibits high activity but also good stability for overall water splitting.

AuCu Alloy Nanoparticle Embedded Cu Submicrocone Arrays for Selective Conversion of CO2 to Ethanol.

The CO2 reduction reaction (CO2 RR) driven by renewable electricity represents a promising strategy toward alleviating the energy shortage and environmental crisis facing humankind. Cu species, as one type of versatile electrocatalyst for the CO2 RR, attract tremendous research interest. However, for C2 products, ethanol formation is commonly less favored over Cu electrocatalysts. Herein, AuCu alloy nanoparticle embedded Cu submicrocone arrays (AuCu/Cu-SCA) are constructed as an active, selective, and robust electrocatalyst for the CO2 RR. Enhanced selectivity for EtOH is gained, whose Faradaic efficiency (FE) reaches 29 ± 4%, while ethylene formation is relatively inhibited (16 ± 4%) in KHCO3 aqueous solution. The ratio between partial current densities of EtOH and C2 H4 (jEtOH /jC2H4 ) can be tuned in the range from 0.15 ± 0.27 to 1.81 ± 0.55 by varying the Au content of the electrocatalysts. The combined experimental and theoretical calculation results identify the importance of Au in modifying binding energies of key intermediates, such as CH2 CHO*, CH3 CHO*, and CH3 CH2 O*, which consequently modify the activity and selectivity (jEtOH /jC2H4 ) for the CO2 RR. Moreover, AuCu/Cu-SCA also shows high durability with both the current density and FEEtOH being largely maintained for 24 h electrocatalysis.

Single-Atom Catalysts for the Electrocatalytic Reduction of Nitrogen to Ammonia under Ambient Conditions.

Powered by renewable electricity, the electrochemical reduction of nitrogen to ammonia is proposed as a promising alternative to the energy- and capital-intensive Haber-Bosch process, and has thus attracted much attention from the scientific community. However, this process suffers from low NH3 yields and Faradaic efficiency. The development of more effective electrocatalysts is of vital importance for the practical applications of this reaction. Of the reported catalysts, single-atom catalysts (SACs) show the significant advantages of efficient atom utilization and unsaturated coordination configurations, which offer great scope for optimizing their catalytic performance. Herein, progress in state-of-the-art SACs applied in the electrocatalytic N2 reduction reaction (NRR) is discussed, and the main advantages and challenges for developing more efficient electrocatalysts are also highlighted.

Unveiling the structural evolution of 1T SnS2 anode upon lithiation/delithiation by TEM.

Herein, the definite structure-dependent evolution process upon lithiation/delithiation and clear atomic images of pure 1T-phase SnS2 were obtained for the first time, illustrating the different insertion-conversion-desertion processes of discharge/charge plateaus. Also, 1T SnS2 exhibited advantages over commercial SnS2 (mixed with 1T and 1H phases) in cell resistance and lithium-storage performance.

Efficient Electroreduction CO2 to CO over MnO2 Nanosheets.

As a critical alternative step for the synthesis of important chemical feedstocks and complex carbon-based fuels, the electrochemical transformation of CO2 into CO holds great significance for the chemical industry. Here, MnO2 nanosheets array supported nickel foam has been synthesized and adopted as a binder-free catalyst for electrochemical CO2 reduction reaction (CO2RR). The well-distributed nanosheets of MnO2 impart a much higher density of accessible active sites for CO2RR, enabling the selective CO2 reduction to CO with a large current density (14.1 mA cm-2), excellent Faradaic efficiency (71%) and high electrochemical stability (10 h). This work first demonstrates the great potential of Mn-based oxides for electrocatalytic transformation of CO2 to valuable products.

Tensile mechanical performance of Ni-Co alloy nanowires by molecular dynamics simulation.

In this present contribution, tensile mechanical properties of Ni-Co alloy nanowires with Co content from 0 to 20% were studied by molecular dynamics. The simulation results show the alloy nanowire with the Co content of 5% has the highest yield value of 9.72 GPa. In addition, more Frank dislocations were generated during the loading process to improve the performance of the alloy nanowire. The Young's modulus increases little by little from 105.68 to 179.78 GPa with the increase of Co content. Secondly, with the increase of temperature, the yield strength gradually decreases to 2.13 GPa. Young's modulus tends to decrease linearly from 170.7 GPa to 48.21 GPa. At the temperatures of 500 K and 700 K, it is easier to form Frank dislocation and Hirth dislocation, respectively, in the loading process. The peak value of the radial distribution function decreases and the number of peaks decreases, indicating the disappearance of the ordered structure. Finally, after the introduction of the surface and inner void, the yield strength of the nanowire drops about to 8.97 and 6.6 GPa, respectively, and the yield strains drop to 0.056 and 0.043. In the case of the existence of internal void, perfect dislocation and Hirth dislocation can be observed in the structure.