High-entropy Alloy Nanoparticles Research Articles

In-Situ Formation of High-Entropy Alloy Nanoparticles as a Hydrogen Pump for Boosting Hydrogen Storage in Mg-Based Alloy

In-Situ Formation of High-Entropy Alloy Nanoparticles as a Hydrogen Pump for Boosting Hydrogen Storage in Mg-Based Alloy

Tuning the near room temperature oxidation behavior of high-entropy alloy nanoparticles

Tuning the near room temperature oxidation behavior of high-entropy alloy nanoparticles

Colloids of HEA nanoparticles in an imidazolium-based ionic liquid prepared by magnetron sputtering: Structural and magnetic properties

Colloids consisting of the CoCrCuFeNi high-entropy alloy nanoparticles in ionic liquid with the 1-butyl-3-methylimidazolium ([BMIM]+) cation and the tetrafluorborate ([BF4]-) anion were obtained by the DC magnetron sputtering of high-entropy alloy target in vacuum, onto the surface of [BMIM.BF4] ionic liquid. The method of the nanoparticle colloid preparation is based on negligibly small vapour pressure of the ionic liquid, which allows its application in vacuum. The high-entropy alloy nanoparticle colloids were studied by HRTEM microscopy and SQUID magnetometry. Results of the structural and magnetic analyses show that the colloids contain ultra-small single-crystalline nanoparticles of an uneven shape and typical size of (2−3) nm. The nanoparticles have relatively narrow size distribution which is typical for this preparation method. The high-entropy alloy nanocolloids show complex magnetic properties that are a function of temperature, applied magnetic field and mass content of the nanoparticles in the colloids. The obtained results imply significant magnetic interactions between the ionic liquid and the high-entropy alloy nanoparticles.

High entropy nanoparticles of CoCrXFeNi (X=Al, Cu, Mn) loaded on activated carbon for efficient degradation of methylene blue

Different from the reported catalysts such as metallic glasses ribbons and ball-milled high entropy alloy powder, high entropy alloy nanoparticles (HEA NPs) have attracted wide attention for compelling and functional catalytic properties to degrade methylene blue (MB) dye. CoCrXFeNi (X = Al, Cu, Mn) HEA NPs with different loadings were synthesized by impregnation-adsorption method on activated carbon (AC). Nanoscale HEA NPs with maximized configuration mixing entropy are composed of a single solid-solution face-centered cubic (FCC) phase and the nanocomposites show distinctive porous architectures and large specific surface area (average S BET = 632.7 m 2 /g) for 10 wt.% loadings. The reaction rates ( k o b s ) of 10 wt.% CoCrAlFeNi and CoCrMnFeNi HEA NPs-AC for MB degradation are 0.1998 and 0.1830 min −1 and show comparable intrinsic catalytic performance to amorphous ribbons and HEA powders. The HEA NPs can effectively decompose MB molecule via nanoscale galvanic cell effect which provides a promising material in dye decomposition and mineralization.

Composition-dependent structure and properties of 5- and 15-element high-entropy alloy nanoparticles

High-entropy alloy nanoparticles (HEA NPs) are an area of interest due to their interesting structural features, large compositional space, and high potential for catalytic applications. While many HEA NPs have been successfully synthesized and characterized, little is known about the impact of composition on structural features. This work utilizes element-specific X-ray spectroscopy techniques to compare 5- and 15-element HEA NPs with shared elements, aiming to understand the impact that adding additional elements to an HEA has on its structure and properties. Here, we report significant differences between HEA-5 and HEA-15. In particular, the 3d elements show different oxidation behavior associated with different bonding properties. Varied bonding properties are also observed in the 4d and 5d elements. These results provide an understanding of the impact composition plays on the HEA structure, which will serve to aid in the fine-tuning of structure and properties of HEAs through adjusting their composition.

CoNiCuMgZn high entropy alloy nanoparticles embedded onto graphene sheets via anchoring and alloying strategy as efficient electrocatalysts for hydrogen evolution reaction

Great interests have been focused on high entropy alloys, a new class of single-phase solid solution materials, because of their unique physical and chemical properties. Herein, CoNiCuMgZn high entropy alloy (HEA) has been homogeneously embedded onto ultrathin two-dimensional (2D) holey graphene conducting substrates via a simple anchoring and alloying strategy. During the growth of the HEA, graphene oxide is employed as both direct template and reductant. By modulating the initial input amounts of metal sources, the particle sizes of HEA can be finely regulated from 40 to 200 nm. Benefiting from the synergistic effect between the excellent electronic conductivity of graphene and the abundant catalytic sites of HEA particles, the obtained material displays remarkable catalytic activity and stability for hydrogen evolution reaction compared to previous reported non-noble-metal catalysts. The density functional theory calculation unveils that the unique embedded structure of HEA onto graphene benefits to the H* sorption and promotes the catalytic kinetics. This work is of great importance in the practical utilization of HEA and indeed give a brilliant perspective in fabricating HEA as efficient electrocatalysts for water splitting.

Scalable Synthesis of High Entropy Alloy Nanoparticles by Microwave Heating

High entropy alloy nanoparticles (HEA-NPs) are reported to have superior performance in catalysis, energy storage, and conversion due to the broad range of elements that can be incorporated in these materials, enabling tunable activity, excellent thermal and chemical stability, and a synergistic catalytic effect. However, scaling the manufacturing of HEA-NPs with uniform particle size and homogeneous elemental distribution efficiently is still a challenge due to the required critical synthetic conditions where high temperature is typically involved. In this work, we demonstrate an efficient and scalable microwave heating method using carbon-based materials as substrates to fabricate HEA-NPs with uniform particle size. Due to the abundant functional group defects that can absorb microwave efficiently, reduced graphene oxide is employed as a model substrate to produce an average temperature reaching as high as ∼1850 K within seconds. As a proof-of-concept, we utilize this rapid, high-temperature heating process to synthesize PtPdFeCoNi HEA-NPs, which exhibit an average particle size of ∼12 nm and uniform elemental mixing resulting from decomposition nearly at the same time and liquid metal solidification without diffusion. Various carbon-based materials can also be employed as substrates, including one-dimensional carbon nanofibers and three-dimensional carbonized wood, which can achieve temperatures of >1400 K. This facile and efficient microwave heating method is also compatible with the roll-to-roll process, providing a feasible route for scalable HEA-NPs manufacturing.

Ultrasound-driven fabrication of high-entropy alloy nanocatalysts promoted by alcoholic ionic liquids

High-entropy alloy nanoparticles (HEA-NPs) are highly underutilized in heterogeneous catalysis due to the absence of a reliable, sustainable, and facile synthetic method. Herein, we report a facile synthesis of HEA nanocatalysts realized via an ultrasound-driven wet chemistry method promoted by alcoholic ionic liquids (AILs). Owing to the intrinsic reducing ability of the hydroxyl group, AILs were synthesized and utilized as environmentally friendly alternatives to conventional reducing agents and volatile organic solvents in the synthetic process. Under high-intensity ultrasound irradiation, Au3+, Pd2+, Pt2+, Rh3+, and Ru3+ ions were co-reduced and transformed into single-phase HEA (AuPdPtRhRu) nanocrystals without calcination. Characterization results reveal that the as-synthesized nanocrystals are composed of elements of Au, Pd, Pt, Rh, and Ru as expected. Compared to the monometallic counterparts such as Pd-NPs, the carbon-supported HEA nanocatalysts show superior catalytic performance for selective hydrogenation of phenol to cyclohexanone in terms of yield and selectivity. Our synthetic strategy provides an improved and facile methodology for the sustainable synthesis of multicomponent alloys for catalysis and other applications.

Laser powder bed fusion of high-entropy alloy particle-reinforced stainless steel with enhanced strength, ductility, and corrosion resistance

In additive manufacturing of metal matrix composites, it is difficult to ensure high strength as well as high ductility simultaneously. In this study, a FeCoNiCr high-entropy alloy was used as the strengthening phase to improve the performance of austenitic stainless steel processed via laser powder bed fusion. The microstructure of the as-printed parts was composed of high-entropy alloy nanoparticles, a solid solution matrix, and high-density dislocations. The strengthening effect caused by the microstructures resulted in a tensile strength of 627 MPa with a maximum elongation of 50%. The semi-obstructive effect of the interface on the dislocations improved the ductility, as proved through molecular dynamics analysis. The Cr, Ni, and Co elements in the high-entropy alloy melted into the stainless-steel matrix, facilitating the formation of a passive film; this improved the corrosion resistance of the composite. Thus, simultaneous improvements in strength, ductility, and corrosion resistance of the stainless-steel composites were realized. The composites inherited the performance characteristics of high-entropy alloys. This research also provides a new strategy to select the strengthening phase for composite materials. High-performance high-entropy alloy particles with lattice structures and element types similar to the stainless steel matrix have substantial potential to be used as strengthening phases.

Hydrogen spillover-driven synthesis of high-entropy alloy nanoparticles as a robust catalyst for CO2 hydrogenation

High-entropy alloys (HEAs) have been intensively pursued as potentially advanced materials because of their exceptional properties. However, the facile fabrication of nanometer-sized HEAs over conventional catalyst supports remains challenging, and the design of rational synthetic protocols would permit the development of innovative catalysts with a wide range of potential compositions. Herein, we demonstrate that titanium dioxide (TiO2) is a promising platform for the low-temperature synthesis of supported CoNiCuRuPd HEA nanoparticles (NPs) at 400 °C. This process is driven by the pronounced hydrogen spillover effect on TiO2 in conjunction with coupled proton/electron transfer. The CoNiCuRuPd HEA NPs on TiO2 produced in this work were found to be both active and extremely durable during the CO2 hydrogenation reaction. Characterization by means of various in situ techniques and theoretical calculations elucidated that cocktail effect and sluggish diffusion originating from the synergistic effect obtained by this combination of elements.

Noble metal-based high-entropy alloys as advanced electrocatalysts for energy conversion

Noble metal-based high-entropy alloy nanoparticles (NM-HEA NPs) have exhibited brilliant catalytic performance toward electrocatalytic energy conversion and attracted increasing attention. The near-equimolar mixed elements of NM-HEA NPs may result in the unique properties including cocktail effect, high entropy effect and lattice distortion effect, which are beneficial for improving the catalytic performance and reducing the amount of noble metal. Herein, several advanced NM-HEA NPs as electrocatalysts for energy conversion are systematically summarized. The preparation methods of NM-HEA NPs are evaluated as well as the catalytic properties and mechanism are discussed classified by electrocatalytic reactions. Finally, the challenges and prospects in this field are carefully discussed. This review provides an overview on recent advances of NM-HEA electrocatalysts for energy conversion and draws more attention in this infant research field.

Revealing High-Temperature Reduction Dynamics of High-Entropy Alloy Nanoparticles via In Situ Transmission Electron Microscopy.

Understanding the behavior of high-entropy alloy (HEA) materials under hydrogen (H2) environment is of utmost importance for their promising applications in structural materials, catalysis, and energy-related reactions. Herein, the reduction behavior of oxidized FeCoNiCuPt HEA nanoparticles (NPs) in atmospheric pressure H2 environment was investigated by in situ gas-cell transmission electron microscopy (TEM). The reduction reaction front was maintained at the external surface of the oxide. During reduction, the oxide layer expanded and transformed into porous structures where oxidized Cu was fully reduced to Cu NPs while Fe, Co, and Ni remained in the oxidized form. In situ chemical analysis showed that the expansion of the oxide layer resulted from the outward diffusion flux of all transition metals (Fe, Co, Ni, Cu). Revealing the H2 reduction behavior of HEA NPs facilitates the development of advanced multicomponent alloys for applications targeting H2 formation and storage, catalytic hydrogenation, and corrosion removal.

Spontaneously Forming Oxide Layer of High Entropy Alloy Nanoparticles Deposited on Porous Carbons for Supercapacitors

AbstractHigh‐entropy alloy nanoparticles with a thin metal oxide layer, deposited onto hypercrosslinked polymer‐based carbon (HCPC), were synthesized through the adsorption of five metal ions in the hypercrosslinked polymers and subsequent in situ reduction of such ions (Fe2+, Co2+, Ni2+, Cu2+ and Sn2+), followed by a carbonization process. The as‐prepared composites exhibit an excellent specific capacitance (495.4 F/g at 0.5 A/g in 1 M KOH), a superior cycling stability (94.7 % of initial capacitance after 15000 cycles at 10 A/g), and ultrafast charge transport kinetics (88.9 % fast kinetic capacitance at 200 mV/s). These excellent electrochemical behaviors are attributed to the pseudocapacitance of the metal oxide layer spontaneously formed on the outermost surface of the composite, having a thickness at the nanometer scale. Such findings suggest that this simple strategy, combining multimetallic nanoparticles with porous carbon materials, has promising potential to improve specific capacitance and paves the way to develop both the preparation of high‐entropy alloys and supercapacitors with improved performance.

A novel synergistic confinement strategy for controlled synthesis of high-entropy alloy electrocatalysts.

We report a synergistic confinement strategy for the synthesis of high-entropy alloy nanoparticles (HEA-NPs). The carbon nitride substrate and polydopamine coating layer synergistically confine the growth of NPs and contribute to the formation of homogeneous HEA-NPs. The HEA-NPs exhibit superior electrocatalytic performance for oxygen reduction and evolution reactions. This work demonstrates the great potential of HEA-NPs for electrocatalysis.

Elemental Core Level Shift in High Entropy Alloy Nanoparticles via X-ray Photoelectron Spectroscopy Analysis and First-Principles Calculation.

High entropy alloy nanoparticles (HEA-NPs) are expanding their influence in many fields. To explore the electronic structures in such multielemental systems, HEA-NPs were synthesized on two different carbon substrates through carbothermal shock and in situ reduction methods. The relationship between the apparent core level energy shifts (negative or positive) and the electron density changes among the components of quinary-metal HEA-NPs was investigated by X-ray photoelectron spectroscopy (XPS) analysis and first-principles electronic structure calculations. It was found that Cu displays a negative core level shift while Fe, Co, Mg, Cr, and Mn display a positive core level shift. While experiments show an apparent positive core level shift for Ni, electronic structure calculations reveal that this arises from shifts in the Fermi level and that the electron density redistribution in Ni behaves more like Cu than the other elements. The findings show that the electron density redistribution in the NPs occurs from less electronegative elements to more electronegative ones. This work should guide the design of HEA-NPs to expand their potential applications in mechanical structures, medicine, catalysis, and energy storage/conversion.

Melting mechanism of Pt–Pd–Rh–Co high entropy alloy nanoparticle: An insight from molecular dynamics simulation

The temperature elevation process by the molecular dynamics (MD) simulation was used to investigate the melting mechanism of PtPdRhCo and Pt41Pd18Rh5Co32 high-entropy alloy nanoparticles (HEA-NPs) with diameters of 5, 10, and 15 nm in the FCC arrangement. The second-nearest neighbor modified embedded-atom method (2NN MEAM) potential was used and the cross-element parameters were parametrized by the guaranteed convergence particle swarm optimization (GCPSO) based on the reference data prepared by the density functional theory (DFT) calculation. According to the MD results, three characteristic temperatures during the heating process are found, which include the surface local shear resistance temperature Tslsr, surface pre-melting temperature Tsm, and melting point Tm. By observing the distribution of atomic local shear strain ηiMises with the increasing temperature, the definition of Tslsr is first proposed, below which atoms with high local shear strains are blocked at the surface of HEA-NPs. As the system temperature is above Tslsr, the interior atoms near the surface begin to possess higher local shear strains and this influence continuously spread toward the core of HEA-NPs at higher temperatures. At Tsm, a certain amount of atoms within the thin surface shell are melted, leading to the first discontinuity of binding energy-temperature profile. At Tm, the HEA-NPs structure completely becomes liquid phase and the second discontinuity of binding energy-temperature profile can be found. Although the binding energies of these two HEA-NPs types of the same size are almost identical, the Tslsr, Tsm, and Tm values of PtPdRhCo are relatively higher than those of Pt41Pd18Rh5Co32. Each element type of PtPdRhCo shows a collective behavior during the heating process, resulting in a similar local structural evolution at different temperatures. For Pt41Pd18Rh5Co32, Co and Pd atoms tend to be distorted more easily than Pt and Rh atoms during the heating process, which can be regarded as a kind of defect. This is the main reason for relatively lower Tslsr, Tsm, and Tm values of Pt41Pd18Rh5Co32.

Autocatalytic Formation of High-Entropy Alloy Nanoparticles.

High-entropy alloy (HEA) nanoparticles hold great promise as tunable catalysts. Despite the fact that alloy formation is typically difficult in oxygen-rich environments, we found that Pt-Ir-Pd-Rh-Ru nanoparticles can be synthesized under benign low-temperature solvothermal conditions. In situ X-ray scattering and transmission electron microscopy reveal the solvothermal formation mechanism of Pt-Ir-Pd-Rh-Ru nanoparticles. For the individual metal acetylacetonate precursors, formation of single metal nanoparticles takes place at temperatures spanning from ca. 150 °C for Pd to ca. 350 °C for Ir. However, for the mixture, homogenous Pt-Ir-Pd-Rh-Ru HEA nanoparticles can be obtained around 200 °C due to autocatalyzed metal reduction at the (111) facets of the forming crystallites. The autocatalytic formation mechanism suggests that many types of HEA nanocatalysts should accessible with scalable solvothermal reactions, thereby providing broad availability and tunability.

Carbon Encapsulation of High Entropy Alloy Nanoparticles with Extraordinary Coercivity and Saturation at Room Temperature

AbstractOwing to their unique properties and technological potential, high entropy alloys (HEAs) have become the subject of great interest in the materials science community. HEAs consist of more than four principle elements in equimolar ratio so their configurational entropy is intrinsically greater than one‐principle element based. The increasing surface energy and chemical tendency toward clustering of like atoms at low dimension, however, make production of HEA‐nanoparticles (HEA‐NPs) extremely difficult. A facile production of HEA‐NPs inside carbon nanotubes and nanoparticles is demonstrated in this work. Electron microscopic and elemental analyses confirm encapsulated to be solution phase; some embrace carbides and form multidomains with chemical composition ranging from quaternary to quinary phase. Multidomains and nonmagnetic centers create hardening thus promoting coercivity significantly at room temperature. Alloying induces electron redistribution into high spin states, accounting for observed high saturation. Configurational entropy of encapsulated HEA‐NPs lies on a range comparable with bulk.

Interface characteristics of high-entropy alloy/Al-Mg composites by underwater friction stir processing

A novel high-entropy alloy (HEA) reinforced Al-Mg composite has been produced by employing underwater friction stir processing (UFSP). A study of the HEA-Al interface reveals that Mg aggregation and Cr segregation occur at the interface, resulting in the formation of a dual interface composed of the FCC phase with a nanotwins structure, Al18Cr2Mg3, and HEA nanoparticles with the depletion of Cr. The tensile strength of the fabricated composites was enhanced to 401 MPa, which is 22.6% higher than that of the UFSPed Al-Mg alloy, and the friction coefficient was reduced from 0.45 to 0.29. Thus, the formed interface is beneficial to the load transfer from the matrix to the HEA particles.

Synthesis of high-entropy alloy nanoparticles on supports by the fast moving bed pyrolysis

High-entropy alloy nanoparticles (HEA-NPs) are important class of materials with significant technological potential. However, the strategies for synthesizing uniformly dispersed HEA-NPs on granular supports such as carbon materials, γ-Al2O3, and zeolite, which is vital to their practical applications, are largely unexplored. Herein, we present a fast moving bed pyrolysis strategy to immobilize HEA-NPs on granular supports with a narrow size distribution of 2 nm up to denary (MnCoNiCuRhPdSnIrPtAu) HEA-NPs at 923 K. Fast moving bed pyrolysis strategy ensures the mixed metal precursors rapidly and simultaneously pyrolyzed at high temperatures, resulting in nuclei with a small size. The representative quinary (FeCoPdIrPt) HEA-NPs exhibit high stability (150 h) toward hydrogen evolution reaction with high mass activity, which is 26 times higher than the commercial Pt/C at an overpotential of 100 mV. Our strategy provides an improved methodology for synthesizing HEA-NPs on various supports.