Stable Alloy Research Articles

Developing thermally stable high-entropy alloys using a phase-diagram method

Developing thermally stable high-entropy alloys using a phase-diagram method

Effects of Ta on the Structural, mechanical and electronic properties of the ternary alloys [formula omitted]: A computational study

The structural, elastic and electronic properties of the ternary transition metal nitrides alloys TaxHf1−xN at (0<x<1) in the rock-salt structure are investigated by ab initio calculations. The calculations were performed using the first-principles Exact Muffin-Tin Orbitals method using full charge density technique within the framework of density functional theory. The compositional disorder is treated within the coherent potential approximation. The estimated formation enthalpy indicates that Ta0.5Hf0.5N is thermodynamically the most stable alloy. The obtained lattice parameters of the TaxHf1−xN alloys are in good agreement with other available theoretical and experimental values. The predicted elastic stiffness constants C11, C12 and C44 indicate that the TaxHf1−xN alloys are mechanically stable and the addition of Ta increases their ductility. The Ta0.7Hf0.3N found to be hardest alloy. The correlation between Pettifor’s criterion (C12−C44) normalized by bulk modulus B and Pugh’s ratio G/B with increasing the degree of alloying x allowed us to predict that the critical value (G/B)=0.53, which correspond to x around 0.6±0.05, marks the brittle to ductile transition.

CO2-Assisted Controllable Synthesis of PdNi Nanoalloys for Highly Selective Hydrogenation of Biomass-Derived 5-Hydroxymethylfurfural.

The selective hydrogenation of 5-hydroxymethylfurfural (HMF) to 2,5-bishydroxymethyltetrahydrofuran (BHMTHF), a vital fuel precursor and solvent, is crucial for biomass refining. Herein, we report highly selective and stable PdNi nanoalloy catalysts for this deep hydrogenation process. A CO2-assisted green method was developed for the controllable synthesis of various bimetallic and monometallic catalysts. The PdNi/SBA-15 catalysts with various Pd/Ni ratios exhibited a volcano-like trend between BHMTHF yield and Pd/Ni ratio. Among all catalysts tested, Pd2Ni1/SBA-15 achieved the best performance, converting 99.0 % of HMF to BHMTHF with 96.0 % selectivity, surpassing previously reported catalysts. Additionally, the Pd2Ni1/SBA-15 catalyst maintained excellent stability even after five recycling runs. Catalyst characterizations (e. g., HAADF-STEM) and density functional theory (DFT) calculations confirmed the successful formation of the alloy structure with electron transfer between Ni and Pd, which accounts for the remarkable performance and stability of the catalyst. This work paves the way for developing highly selective and stable alloy catalysts for biomass valorization.

CO2‐Assisted Controllable Synthesis of PdNi Nanoalloys for Highly Selective Hydrogenation of Biomass‐Derived 5‐Hydroxymethylfurfural

AbstractThe selective hydrogenation of 5‐hydroxymethylfurfural (HMF) to 2,5‐bishydroxymethyltetrahydrofuran (BHMTHF), a vital fuel precursor and solvent, is crucial for biomass refining. Herein, we report highly selective and stable PdNi nanoalloy catalysts for this deep hydrogenation process. A CO2‐assisted green method was developed for the controllable synthesis of various bimetallic and monometallic catalysts. The PdNi/SBA‐15 catalysts with various Pd/Ni ratios exhibited a volcano‐like trend between BHMTHF yield and Pd/Ni ratio. Among all catalysts tested, Pd2Ni1/SBA‐15 achieved the best performance, converting 99.0 % of HMF to BHMTHF with 96.0 % selectivity, surpassing previously reported catalysts. Additionally, the Pd2Ni1/SBA‐15 catalyst maintained excellent stability even after five recycling runs. Catalyst characterizations (e. g., HAADF‐STEM) and density functional theory (DFT) calculations confirmed the successful formation of the alloy structure with electron transfer between Ni and Pd, which accounts for the remarkable performance and stability of the catalyst. This work paves the way for developing highly selective and stable alloy catalysts for biomass valorization.

ZnO Quantum Dots as PEO-Based Solid Electrolytes Fillers for Lithium Metal Batteries.

PEO-based solid polymer electrolyte (PEO SPE) is regarded as one of the most promising solid electrolytes due to its exceptional flexibility, cost-effectiveness, and ease of integration. However, its commercialization is hindered by inadequate ionic conductivity and unstable interface. By incorporating proper ZnO quantum-dots (QDs) fillers with enhanced surface activity, the ion transport inner the PEO-based electrolyte can be improved along with enhanced REDOX kinetics at the Li/PEO interface. The ionic conductivity reaches 5.97×10-4 S cm-1 at 60 °C. Moreover, ZnO QDs exhibit a quantum size effect and possess lithiophilic characteristics that promote uniform nucleation and redeposition of Li+ while forming a stable Li-Zn alloy. This inhibits lithium dendrite formation and enhances the stability of Li anode. Li//Li cell with 3 % ZnO QDs works steadily for more than 2100 h at 60 °C with 0.1 mA cm-2. The assembled Li//LiFePO4 cell provides a reversible capacity of 134.91 mAh g-1 after200 cycles at 0.1 C.

Interface kinetic manipulation enabling efficient and reliable Mg3Sb2 thermoelectrics

Development of efficient and reliable thermoelectric generators is vital for the sustainable utilization of energy, yet interfacial losses and failures between the thermoelectric materials and the electrodes pose a significant obstacle. Existing approaches typically rely on thermodynamic equilibrium to obtain effective interfacial barrier layers, which underestimates the critical factors of interfacial reaction and diffusion kinetics. Here, we develop a desirable barrier layer by leveraging the distinct chemical reaction activities and diffusion behaviors during sintering and operation. Titanium foil is identified as a suitable barrier layer for Mg3Sb2-based thermoelectric materials due to the creation of a highly reactive ternary MgTiSb metastable phase during sintering, which then transforms to stable binary Ti-Sb alloys during operation. Additionally, titanium foil is advantageous due to its dense structure, affordability, and ease of manufacturing. The interfacial contact resistivity reaches below 5 μΩ·cm2, resulting in a Mg3Sb2-based module efficiency of up to 11% at a temperature difference of 440 K, which exceeds that of most state-of-the-art medium-temperature thermoelectric modules. Furthermore, the robust Ti foil/Mg3(Sb,Bi)2 joints endow Mg3Sb2-based single-legs as well as modules with negligible degradation over long-term thermal cycles, thereby paving the way for efficient and sustainable waste heat recovery applications.

Strong and stable ultrafine-grained Al-Mg alloys via polymer-derived in situ nanoparticles

Ultrafine-grained Al-Mg alloys provide immense promise as lightweight metallic materials for load-bearing applications, contributing significantly to energy efficiency and CO2 emission reduction. However, for prevalent bulk ultrafine-grained Al-Mg alloys fabricated by a combined mechanical alloying and thermomechanical consolidation, the presence of remaining polymers, which are used as a process control agent during milling, jeopardizes the mechanical performance of the consolidated materials and thus significantly limit their broad applications. An ideal solution to overcome this critical issue is to turn these polymers into useful nanoparticles, enabling simultaneous improvements in strength and grain size stability. In this study, we present an approach to currently achieve strength enhancement and grain size control by incorporating polymer-derived in situ nanoparticles. Through a combined process involving polymer-assisted mechanical alloying, extrusion at the eutectic temperature, and annealing-driven solid-state phase transformation, we achieved a strong and stable ultrafine-grained Al-Mg alloy. After post-heat treatment at 440 °C (i.e. 0.76 Tm; Tm is the absolute melting temperature of pure Al) for 24 h, the compressive yield strength exhibited minimal reduction from ∼1.3 GPa for the as-extruded alloy to ∼1 GPa for the as-annealed alloy. Similarly, the average grain size only experienced a slight increase, from 106 to 145 nm after post-annealing. These findings offer practical insights into the design of mechanically robust and thermodynamically stable ultrafine-grained metallic materials via a new strategy of polymer-derived in situ nanoparticles.

Stable and homogeneous intermetallic alloys by atomic gas-migration for propane dehydrogenation

Intermetallic nanoparticles (NPs) possess significant potentials for catalytic applications, yet their production presents challenges as achieving the disorder-to-order transition during the atom ordering process involves overcoming a kinetic energy barrier. Here, we demonstrate a robust approach utilizing atomic gas-migration for the in-situ synthesis of stable and homogeneous intermetallic alloys for propane dehydrogenation (PDH). This approach relies on the physical mixture of two separately supported metal species in one reactor. The synthesized platinum-zinc intermetallic catalysts demonstrate exceptional stability for 1300 h in continuous propane dehydrogenation under industrially relevant industrial conditions, with extending 95% propylene selectivity and propane conversions approaching thermodynamic equilibrium values at 550–600 oC. In situ characterizations and density functional theory/molecular dynamics simulation reveal Zn atoms adsorb on the particle surface and then diffuse inward, aiding in the formation of ultrasmall and highly ordered intermetallic alloys. This in-situ gas-migration strategy is applicable to a wide range of intermetallic systems.

First principles study of structural and optoelectronic properties of semiconductor NaBeP[formula omitted]N[formula omitted] alloys for photovoltaic applications

In this paper, the structural and optoelectronic properties of semiconductor NaBePxN1−x (x=0,0.25,0.50,0.75 and 1) alloys in the half-Heusler structure were investigated using density functional theory with GGA approximation. The lattice parameter a, the formation energy Ef and the cohesive energy Ec were examined. The obtained results show that the lattice parameter as a function of x for NaBePxN1−x alloys obeys Vegard’s Law. The negative values of Ef and Ec indicate that NaBeN and NaBeP alloys have thermodynamic stability and strong chemical bonds, implying that they could be synthesized in future experimental research. The estimated optical properties revealed details for NaBePxN1−x alloys concerning the optoelectronic and photovoltaic applications. The high absorption α(x=0,1)≈1.6×106cm−1 and reflectivity coefficients (R(x=0,1)>55%), indicate their suitability for usage in optoelectronic devices. The promising power conversion efficiency (η≈15%) also predicts that the thermodynamically stable alloys NaBeN and NaBeP are good for solar cell applications.

Stable aluminum-lithium alloy fuels for solid propellants by facile surface modifying

As a highly reactive metal fuel, aluminum–lithium (Al-Li) alloy is an ideal candidate for replacing Al powders in solid propellants. However, the Li solid solution and AlLi compounds on the surface of Al-Li alloy powders display high reactivity, which can react with a large number of organic and inorganic reagents. Thus, the incompatibility of Al-Li alloy with other components of propellants makes it difficult to be further applied in propellants. In this study, surface-modified Al-Li alloy powders (Li content of 5 wt%) with 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (FAS17) were prepared by a facile self-assembly method, which made the alloy powders super-hydrophobic. The results of SEM, XPS and FIB-TEM show that the surface of Al-Li alloy powder is well-coated by an evenly distributed FAS17 layer. Due to the fluoroalkyl on the surface of the powders, the water contact angle increased by 91°and the intensity of the reaction between alloy powders and water is significantly reduced, which results in improved compatibility with other components of propellants.Meanwhile, the propellant grain of surface-modified powders had fewer defects than the sample before coating, and showed original excellent combustion performance. The average combustion pressure and pressurization rate increased by ∼114 kPa and ∼8613 kPa/s, and the steady burning rate increased by 0.24 mm/s. Therefore, the surface-modified Al-Li alloy powders with FAS17 are expected to be an attractive candidate as a highly active and stable fuel in solid propellants.

Efficient and stable NiMo alloy nanoparticles on ZSM-5 for alkene hydrosilylation

The hydrosilylation of alkene substrates bearing additional functionalities is difficult to achieve by heterogeneous non-noble catalysts and has not been extensively realized with heterogeneous earth-abundant transition metals. Herein, we report NiMo alloy nanoparticles (NPs) supported on ZSM-5 zeolite, which exhibits high activity and selectivity for the hydrosilylation of functionalized terminal and internal alkenes. Compared with the corresponding monometallic counterparts, the Ni3Mo/ZSM-5 catalyst shows a distinct enhancement in the hydrosilylation of alkene. The key to the catalytic performance is the formation of the NiMo alloy, where the electrons are transferred from Mo to Ni. The NiMo alloy NPs have been verified by XRD, XPS and TEM analysis, and further characterized by ICP, BET, NH3-TPD, and H2-TPR. In addition, the Ni3Mo/ZSM-5 catalyst exhibits good reusability for the hydrosilylation reaction with wide substrate scope.

An efficient and stable high-entropy alloy electrocatalyst for hydrogen evolution reaction

An efficient and stable high-entropy alloy electrocatalyst for hydrogen evolution reaction

Modulus-mismatch strategy optimized lightweight refractory high-entropy alloys for superior synergy of mechanical properties and thermostability

Lightweight refractory high-entropy alloys (LRHEAs) have received significant attention due to their excellent strength-plasticity matching. Generally, its strengthening mechanism mainly comes from solid solution strengthening caused by atomic radius mismatches, but excessive atomic radius mismatch can reduce the phase stability of solid solution and easily generate precipitated phases to reduce the plasticity. Here, we present a strategy to enhance the shear modulus mismatch while improving the mechanical properties and phase stability of LRHEAs. We chose the TiZrVNbAl system as the LRHEAs model. The addition of Mo resulted in a modulus mismatch induced strength contribution of 564 MPa, which accounts for ∼57 % of the total strength. Compared to the alloy without Mo, the strength increased by ∼42 % without any loss of ductility. More importantly, the addition of Mo significantly reduces the diffusion coefficient of the main element and realizes the effective kinetic suppression of the precipitated phase. This enables the alloy to avoid brittle precipitate generation even after aging at 500 °C for 5 h, and hence the excellent mechanical properties are well kept. Additionally, the strength of the LRHEA is increased by more than two times at 700 °C, demonstrating higher high temperature performance compared to RHEAs with tensile ductility. Utilizing the shear modulus mismatch strategy can effectively enhance the solid solution strengthening effect, improving the comprehensive mechanical properties of the alloy at room temperature and high temperature, while also improving phase stability. This provides a new approach to developing structurally stable high-performance alloys.

Ab-Initio study of substitution at alkaline earth site on quaternary Heusler alloys LiXNiSb

In this study, we have studied the quaternary Heusler alloys with the formula LiXNiSb (X = Be, Mg, Ca, Sr, Ba) to investigate the effect of alkaline earth elements at the X site. We explored the structural, lattice dynamics, electronic, and magnetic properties by employing the density functional theory framework in FPLAPW formalism. All the studied alloys are nonmagnetic with no magnetic moment on the Ni atom. LiBeNiSb and LiBaNiSb are dynamically unstable and exhibit imaginary phonon frequencies. The lattice constant of the studied alloys systematically increases with the size of the alkaline earth element, whereas the bulk modulus decreases. Among the stable alloys, LiMgNiSb is metallic, whereas LiCaNiSb and LiSrNiSb are semiconducting with band gap values of 0.43 and 0.34 eV, respectively. The lattice specific heat and optical properties of the semiconducting alloys have also been computed. Our results demonstrate that the studied LiXNiSb alloys can be good candidates for photovoltaic applications.

First‐principles calculations on LaX3 (X: Sb, Sn) as electrode material for lithium‐ion batteries

AbstractUsing first‐principle calculations, we investigate the rare‐earth intermetallic compound LaX3 (X = Sb and Sn) as a cathode material for rechargeable lithium‐ion batteries (LIBs). The calculations have been performed to look into the stability of the structure and the electronic properties of host LaX3 as well as its lithiated phases, LixLa1−xX3 (0 &lt; x ≤ 1). In this study, we have observed a structural phase transformation of these intermetallic compounds from a cubic to a tetragonal structure upon lithiation to host structure. The ground state energy is calculated using the WIEN2k package to determine the structure stability and volume change due to lithium addition, which is further used to calculate the formation energy, open circuit voltage (OCV), and lithium‐ion storage capacity. The equilibrium structural parameters for all the phases are determined by achieving a total energy convergence of 10−4 Ry. The estimated band structure along high‐symmetry lines in the first Brillouin zone and the total as well as partial density of states demonstrate unequivocally that the addition of lithium does not change the metallic nature of these electrode materials. We have also calculated the theoretical lithium‐ion storage capacity and OCV for all the compounds. Despite a higher value for OCV larger than 5 V, many of the investigated materials could not be found suitable from a synthesis point of view due to positive formation energies. The formation energy calculation shows that LaSb3, with a 50% concentration of Li, is the most stable compound out of those investigated here. The calculated OCV for Li0.5La0.5Sb3 is 4.27 V. This is substantially higher than the value obtained up to this point for LIBs, which ranges from 3.20 to 3.65 V/cell. These improved results related to the most stable alloy (Li0.5La0.5Sb3) investigated in this work indicate that it is necessary to check the experimental feasibility of its synthesis and actual device performance.

Silica Confinement for Stable and Magnetic Co-Cu Alloy Nanoparticles in Nitrogen-Doped Carbon for Enhanced Hydrogen Evolution.

Ammonia borane (AB) with 19.6 wt % H2 content is widely considered a safe and efficient medium for H2 storage and release. Co-based nanocatalysts present strong contenders for replacing precious metal-based catalysts in AB hydrolysis due to their high activity and cost-effectiveness. However, precisely adjusting the active centers and surface properties of Co-based nanomaterials to enhance their activity, as well as suppressing the migration and loss of metal atoms to improve their stability, presents many challenges. In this study, mesoporous-silica-confined bimetallic Co-Cu nanoparticles embedded in nitrogen-doped carbon (CoxCu1-x@NC@mSiO2) were synthesized using a facile mSiO2-confined thermal pyrolysis strategy. The obtained product, an optimized Co0.8Cu0.2@NC@mSiO2 catalyst, exhibits enhanced performance with a turnover frequency of 240.9 molH2 ⋅ molmetal ⋅ min-1 for AB hydrolysis at 298 K, surpassing most noble-metal-free catalysts. Moreover, Co0.8Cu0.2@NC@mSiO2 demonstrates magnetic recyclability and extraordinary stability, with a negligible decline of only 0.8 % over 30 cycles of use. This enhanced performance was attributed to the synergistic effect between Co and Cu, as well as silica confinement. This work proposes a promising method for constructing noble-metal-free catalysts for AB hydrolysis.

Alloy [FA,Cs]PbI3 perovskite surfaces: The role of surface cesium composition in stability and tolerance to defect formation

Halide-perovskite alloys that include cesium have achieved records of stability and efficiency in solar cells. Controlling the surface composition, defects, and electronic properties guarantees interface stability and improves performance. By using density functional theory and molecular dynamic simulations, we analyzed which surface compositions of the formamidinium (FA) and cesium (Cs) lead iodide perovskite FA1−xCsxPbI3 with 25 and 50% of Cs become more stable than pure perovskites. Structural and electronic properties and tolerance to defect formation were also evaluated. Surface energy calculations show that only the alloys with 25% Cs and FAI-enriched surfaces are more stable than pure FAPbI3 ones. The most stable alloy surface shows electronic energy levels similar to the FAPbI3 perovskite, suggesting that this alloy may also be efficient for charge transport in the cell. However, the presence of Cs on the alloy surface, although low, favors the formation of FAI vacancies, which is detrimental to the stability of the perovskite. These results suggest evaluating FA1−xCsxPbI3 alloys with small Cs compositions to mitigate the formation of defects or using a passivation scheme. This study delivers valuable information for efficiency device improvement from the perspective of interface stability.

Synthesis and electrocatalytic evaluation of PtNi catalyst supported on SBA-15 modified carbon

Maximizing catalyst activity and stability while minimizing costs remains a formidable challenge. In this study, we employed the straightforward and easily executed ethylene glycol reduction method to synthesize highly active and stable Pt-Ni alloy catalysts, utilizing SBA15-modified carbon as the supporting material. Subsequent meticulous examinations delved into their physicochemical properties and electrocatalytic activities.Transmission electron microscopy (TEM) analyses unveiled a uniform distribution of PtNi particles on the support, showcasing a narrow particle size distribution centered around approximately 1.91 nm with minimal aggregation. Electrochemical assessments demonstrated that Pt3Ni/SBA15-C outperforms Pt/C, exhibiting 56 and 167 mV higher half-wave potentials (E1/2) and onset potential (Eonset), respectively. Furthermore, our meticulously prepared Pt3Ni/SBA15-C, featuring a cage structure, displayed remarkable stability while sustaining superior catalytic durability under an applied potential of +0.7 V. These findings underscore the effectiveness of the cage structure catalyst, comprising porous nanoparticles, in ensuring both catalytic activity and stability. The results collectively contribute to advancing our understanding of catalyst design and performance optimization in electrochemical applications.

Robust Anode‐Free Sodium Batteries with Durably Sodophilic Interfaces by Suppressing Sodium‐Alloy Transformation

AbstractAnode‐free sodium batteries (AFSBs) are a desirable choice for high‐energy‐density and low‐cost battery systems. However, the rapid capacity decline resulting from irreversible sodium plating and stripping remains a big challenge for AFSBs. Herein, a copper‐dominated Cu2Sb composite coating employing a co‐sputtering strategy is designed to improve the sodophilicity of copper foils. The Cu2Sb coating can construct a durably sodophilic and stable interface by suppressing the alloying transition of the sodophilic phase and alleviating the volumetric deformation of the coating. This stable alloy interface can greatly enhance sodium nucleation and improve ion transport at the interface by forming homogeneous NaF‐rich solid electrolyte interphase (SEI) film. Ultimately, the AFSB assembled using this unique substrate with a highly loaded Na3V2(PO4)3 (NVP) cathode (≈10 mg cm−2) can cycle 600 cycles deliver a discharge capacity of 75.4 mAh g−1 with a capacity retention of 74.2%, which is much higher than those of the untreated one or antimony coating one (&lt;30% after 200 cycles). This co‐sputtering strategy provides new insights into the design of sodophilic coatings with sodium‐alloying ability and can be extended to the optimization of zinc‐metal batteries.

Impact of Heat Treatment on the Oxygen Reduction Reaction Performance of PtCo/C(N) Electrocatalyst in PEM Fuel Cell

AbstractThe synthesis of efficient and stable Pt alloy catalysts is a major challenge for the commercialization of PEMFC. Herein, we report a PtCo/C(N) electrocatalyst prepared by Na2CO3‐assisted urea liquid‐phase deposition strategy as an efficient cathodic oxygen reduction reaction electrocatalyst, and test its activity and stability in a rotating disc electrode and a single‐cell. The membrane electrode prepared with PtCo/C(N)‐800 °C catalyst has an output voltage of 0.652 V at 2 A/cm2 and a maximum power density of 1.501 W/cm2, which are 36 mV and 81 W/cm2 higher than those of commercial Pt/C catalyst, respectively. In addition, the mass activity and half‐wave potential of PtCo/C(N)‐800 °C are 2.44 times and 50 mV higher than those of commercial Pt/C, respectively. After 5000 voltammetric cycles, its mass activity and half‐wave potential only lose 35 A/gPt and 9 mV, respectively. XPS results show that the binding energy of Pt 4f is positively shifted relative to Pt/C‐TKK, and the d‐band center of Pt decreases, leading to weak chemical interaction between the oxygen‐containing intermediate and the surface of the electrocatalyst, which is conducive to the improvement of the ORR activity and stability of the catalyst.