An official website of the United States government
Abstract Mixing multimetallic elements in hollow‐structured nanoparticles is a promising strategy for the synthesis of highly efficient and cost‐effective catalysts. However, the synthesis of multimetallic hollow nanoparticles is limited to two or three elements due to the difficulties in morphology control under the harsh alloying conditions. Herein, the rapid and continuous synthesis of hollow high‐entropy‐alloy (HEA) nanoparticles using a continuous “droplet‐to‐particle” method is reported. The formation of these hollow HEA nanoparticles is enabled through the decomposition of a gas‐blowing agent in which a large amount of gas is produced in situ to “puff” the droplet during heating, followed by decomposition of the metal salt precursors and nucleation/growth of multimetallic particles. The high active sites per mass ratio of such hollow HEA nanoparticles makes them promising candidates for energy and electrocatalysis applications. As a proof‐of‐concept, it is demonstrated that these materials can be applied as the cathode catalyst for Li–O2battery operations with a record‐high current density per catalyst mass loading of 2000 mA gcat.−1, as well as good stability and durable catalytic activity. This work offers a viable strategy for the continuous manufacturing of hollow HEA nanomaterials that can find broad applications in energy and catalysis.
more »
« less
This content will become publicly available on June 17, 2026
In Situ TEM Studies on the Formation of High-Entropy Alloy Nanoparticles from Mixed Metal-Salt Precursors
Understanding the nucleation and growth mechanisms of highentropy alloy (HEA) nanoparticles is crucial for developing functional nanocrystals with tailored properties. This study investigates the thermal decomposition of mixed metal salt precursors (Fe, Ni, Pt, Ir, Ru) on reduced graphene oxide (rGO) using in situ transmission electron microscopy (TEM) when heated to 1000 °C at both slow (20 °C min−1) and fast (103 °C s−1) heating/cooling rates. Slow heating to 1000 °C revealed the following: (1) The nanoparticles' nucleation occurred through multistage decomposition at lower temperatures (250−300 °C) than single metal salt precursors (300−450 °C). (2) Pt-dominant nanocrystals autocatalytically reduced other elements, leading to the formation of multimetallic FeNiPtIrRu nanoparticles. (3) At 1000 °C, the nanoparticles were single-phase with noble metals enriched compared to transition metals. (4) Slow cooling induced structural heterogeneity and phase segregation due to element diffusion and thermodynamic miscibility. (5) Adding polyvinylpyrrolidone (PVP) suppressed segregation, promoting HEA nanoparticle formation even during slow cooling by limiting atomic diffusion. Under fast heating/cooling, nanoparticles formed as a solid solution of fcc HEA, indicating kinetic control and limited atomic diffusion. The density function theory (DFT) calculations illustrate that the simultaneous presence of metal elements on rGO, as expected by the fast heating process, favors the formation of an fcc HEA structure, with strong interactions between HEA nanoparticles and rGO enhancing stability. This study provides insights into how heating rates and additives like PVP can control phase composition, chemical homogeneity, and stability, enabling the rational design of complex nanomaterials for catalytic, energy, and functional applications.
more »
« less
- Award ID(s):
- 2311104
- PAR ID:
- 10638264
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- Langmuir
- Volume:
- 41
- Issue:
- 23
- ISSN:
- 0743-7463
- Page Range / eLocation ID:
- 14727 to 14742
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Metal nanoparticles of multi-principal element alloys (MPEA) with a single crystalline phase have been synthesized by flash heating/cooling of nanosized metals encapsulated in micelle vesicles dispersed in an oil phase (e.g., cyclohexane). Flash heating is realized by selective absorption of a microwave pulse in metals to rapidly heat metals into uniform melts. The oil phase barely absorbs microwave and maintains the low temperature, which can rapidly quench the high-temperature metal melts to enable the flash cooling process. The precursor ions of four metals, including Au, Pt, Pd, and Cu, can be simultaneously reduced by hydrazine in the aqueous solution encapsulated in the micelle vesicles. The resulting metals efficiently absorb microwave energy to locally reach a temperature high enough to melt themselves into a uniform mixture. The duration of microwave pulse is crucial to ensure the reduced metals mix uniformly, while the temperature of oil phase is still low to rapidly quench the metals and freeze the single-phase crystalline lattices in alloy nanoparticles. The microwave-enabled flash heating/cooling provides a new method to synthesize single-phase MPEA nanoparticles of many metal combinations when the appropriate water-in-oil micelle systems and the appropriate reduction reactions of metal precursors are available.more » « less
-
Abstract Understanding the thermal decomposition of metal salt precursors on carbon structures is essential for the controlled synthesis of metal‐decorated carbon nanomaterials. Here, the thermolysis of a Ni precursor salt, NiCl2·6H2O, on amorphous carbon (a‐C) and graphene oxide (GO) substrates is explored using in situ transmission electron microscopy. Thermal decomposition of NiCl2·6H2O on GO occurs at higher temperatures and slower kinetics than on a‐C substrate. This is correlated to a higher activation barrier for Cl2removal calculated by the density functional theory, strong Ni‐GO interaction, high‐density oxygen functional groups, defects, and weak van der Waals using GO substrate. The thermolysis of NiCl2·6H2O proceeds via multistep decomposition stages into the formation of Ni nanoparticles with significant differences in their size and distribution depending on the substrate. Using GO substrates leads to nanoparticles with 500% smaller average sizes and higher thermal stability than a‐C substrate. Ni nanoparticles showcase thefcccrystal structure, and no size effect on the stability of the crystal structure is observed. These findings demonstrate the significant role of carbon substrate on nanoparticle formation and growth during the thermolysis of carbon–metal heterostructures. This opens new venues to engineer stable, supported catalysts and new carbon‐based sensors and filtering devices.more » « less
-
For the first time, a fast heating–cooling process is reported for the synthesis of carbon‐coated nickel (Ni) nanoparticles on a reduced graphene oxide (RGO) matrix (nano‐Ni@C/RGO) as a high‐performance H2O2fuel catalyst. The Joule heating temperature can reach up to ≈2400 K and the heating time can be less than 0.1 s. Ni microparticles with an average diameter of 2 µm can be directly converted into nanoparticles with an average diameter of 75 nm. The Ni nanoparticles embedded in RGO are evaluated for electro‐oxidation performance as a H2O2fuel in a direct peroxide–peroxide fuel cell, which exhibits an electro‐oxidation current density of 602 mA cm−2at 0.2 V (vs Ag/AgCl), ≈150 times higher than the original Ni microparticles embedded in the RGO matrix (micro‐Ni/RGO). The high‐temperature, fast Joule heating process also leads to a 4–5 nm conformal carbon coating on the surface of the Ni nanoparticles, which anchors them to the RGO nanosheets and leads to an excellent catalytic stability. The newly developed nano‐Ni@C/RGO composites by Joule heating hold great promise for a range of emerging energy applications, including the advanced anode materials of fuel cells.more » « less
-
High entropy alloy (HEA) nanoparticles hold promise as active and durable (electro)catalysts. Understanding their formation mechanism will enable rational control over composition and atomic arrangement of multimetallic catalytic surface sites to maximize their activity. While prior reports have attributed HEA nanoparticle formation to nucleation and growth, there is a dearth of detailed mechanistic investigations. Here we utilize liquid phase transmission electron microscopy (LPTEM), systematic synthesis, and mass spectrometry (MS) to demonstrate that HEA nanoparticles form by aggregation of metal cluster intermediates. AuAgCuPtPd HEA nanoparticles are synthesized by aqueous co-reduction of metal salts with sodium borohydride in the presence of thiolated polymer ligands. Varying the metal : ligand ratio during synthesis showed that alloyed HEA nanoparticles formed only above a threshold ligand concentration. Interestingly, stable single metal atoms and sub-nanometer clusters are observed by TEM and MS in the final HEA nanoparticle solution, suggesting nucleation and growth is not the dominant mechanism. Increasing supersaturation ratio increased particle size, which together with observations of stable single metal atoms and clusters, supported an aggregative growth mechanism. Direct real-time observation with LPTEM imaging showed aggregation of HEA nanoparticles during synthesis. Quantitative analyses of the nanoparticle growth kinetics and particle size distribution from LPTEM movies were consistent with a theoretical model for aggregative growth. Taken together, these results are consistent with a reaction mechanism involving rapid reduction of metal ions into sub-nanometer clusters followed by cluster aggregation driven by borohydride ion induced thiol ligand desorption. This work demonstrates the importance of cluster species as potential synthetic handles for rational control over HEA nanoparticle atomic structure.more » « less
