Patent Application
20240326127
The invention generally relates to methods and/or apparatuses capable of synthesizing ultrafine nano-alloys and fabricating powder precursors for use in such syntheses. The invention particularly relates to methods for photo-thermo-chemical synthesis of ultrafine nano-alloys with pulsed laser.
Metal nanoalloys are widely used as catalysts in many chemical reactions ranging from environmental to energy fields. Conventional bottom-up methods for the synthesis of metal nanoalloys, such as wet-chemistry methods, usually need to consider the miscibility (or more accurately, the immiscibility) of each metallic element in the phase diagrams to avoid the phase segregation during the formation of the particles. This immiscibility issue of metals restricts the realm of nanoalloys and precludes the discovery of new nanoalloys with superior functionalities.
High entropy alloy (HEA) is a term used to refer to alloys that contain multiple (more than two) base elements in equi-atomic concentrations. High-entropy alloys can be designed and made that have excellent properties, such high levels of hardness, fatigue resistance, and strength at ambient and high temperatures, as well as desirable tensile properties.
In recent years, high-entropy nanoalloys (HENAs) containing equal stoichiometric ratios of various metals in each particle in a well-mixed manner have attracted considerable interest because of their unusual physical and chemical properties. These unique properties make them attractive as catalysts, such as in an oxygen reductive reaction (ORR), which has great potential for applications in energy and environmental science.
The conventional synthesis of HENAs is challenged by slow reaction kinetics that leads to phase segregation, sophisticated pretreatment of precursors, and inert conditions that preclude scalable fabrication of HENAs. The slow reaction kinetics in traditional methods of forming HENAs that leads to the phase segregation in nanoalloys is a major obstacle. To overcome this challenge, fast synthetic methods of creating HENAs, such as carbothermal, fast-moving bed heating, pulsed electrochemical reduction, electrical sparkling, laser ablation, and microwave heating, have been developed by reduction of the metal ions in the time range from milliseconds to seconds. Nevertheless, sophisticated procedures for the precursor, aggregation issue of HENAs, and the inert atmosphere requirement still restrict the scalable production of high-quality HENAs.
Therefore, it would be desirable to have methods and/or apparatus that can improve on one or more of these characteristics in the conventional technology in order to allow for scalable fabrication of HENAs, for example, by simplifying the fabrication of the precursor, providing better control over the aggregation of the HENAs, and/or being accomplished in standard atmospheric conditions.
The intent of this section of the specification is to briefly indicate the nature and substance of the invention, as opposed to an exhaustive statement of all subject matter and aspects of the invention. Therefore, while this section identifies subject matter recited in the claims, additional subject matter and aspects relating to the invention are set forth in other sections of the specification, particularly the detailed description, as well as any drawings.
The present invention provides, but is not limited to, methods capable of synthesizing ultrafine nano-alloys and fabricating powder precursors for use in such syntheses.
According to a nonlimiting aspect, a method of synthesizing an ultrafine nano-alloy includes providing a powder precursor formed of powder grains including at least one metal salt on particles of a carbonaceous support, and laser irradiating the powder precursor with a plurality of laser pulses delivered at a high frequency to reduce metal atoms in the powder precursor to form the ultrafine nano-alloy.
According to another nonlimiting aspect, a method of fabricating a powder precursor for synthesizing an ultrafine nano-alloy is provided in which the powder precursor is formed of powder grains having at least one metal salt on particles of a carbonaceous support. The method includes dissolving the at least one metal salt in a liquid solvent, adding the particles of a carbonaceous support to the dissolved metal salt(s) and liquid solvent, dispersing the particles of the carbonaceous support in the dissolved metal salt(s) and liquid solvent to form a dispersion solution, and drying and degassing the dispersion solution to form the powder precursor.
Technical aspects of methods having features as described above preferably include the ability to provide a practical and economical method of producing ultrafine nano-alloys at a commercial industrial scale.
Other aspects and advantages will be appreciated from the following detailed description.
The intended purpose of the following detailed description of the invention and the phraseology and terminology employed therein is to describe one or more nonlimiting embodiments of the invention, and to describe certain but not all aspects of the embodiment(s). The following detailed description also describes certain investigations relating to the embodiment(s). As nonlimiting examples, the invention encompasses additional or alternative embodiments in which one or more features or aspects described as part of a particular embodiment could be eliminated, and also encompasses additional or alternative embodiments that combine two or more features or aspects described as part of different embodiments. Therefore, the appended claims, and not the detailed description, are intended to particularly point out subject matter regarded to be aspects of the invention, including certain but not necessarily all of the aspects and alternatives described in the detailed description.
The present application discloses methods and apparatus for direct conversion of metal salts into ultrafine high-entropy nano-alloys (HENAs) on a carbonaceous support using a nanosecond-pulsed laser that implements a laser-induced emission reduction (LITER) process. Advantageously, the methods can be performed in air at standard atmospheric conditions. In general, the LITER process includes providing metal salts loaded onto carbonaceous supports to form a precursor, and then subsequent laser treatment of the precursor. Due to a unique laser-induced thermionic emission and etch on carbon, the reduced metal elements can be gathered to ultrafine HENAs and stabilized by defect sites on the carbonaceous support. According to preferred but nonlimiting aspects, methods disclosed herein are capable of being scalable, facile, low-cost, and/or overcome immiscible issues typically encountered with conventional technology in this area. The methods disclosed herein are preferably capable of producing various HENAs with relatively uniform sizes of about 1 to about 3 nm and including up to eleven different metal elements with productivity of up to at least about 7 g HENA per hour.
In investigations leading to the invention, a senary HENA produced in accordance with the present methodology exhibited excellent catalytic performance in oxygen reduction reaction (ORR), which may have significant potential in a variety of practical applications. Investigations leading to the present invention utilized powder carbonaceous materials (e.g., graphene flakes or CNTs) and the laser reduction method (LITER process) was performed on what is referred to herein as a powder (or powdery) precursor that was formed of particles of a carbonaceous material (also referred to herein as a carbonaceous support) and the metal salts thereon. During the laser reduction process on the powder precursor, electron flow propelled the powder precursor across a container in which the method was performed, thus promoting an even and homogeneous reaction. In certain nonlimiting examples, the methods were used to directly fabricate supported ultrafine HENAs in air under atmospheric conditions using nanosecond-pulsed laser reduction of metal salts on a carbonaceous support. An ultrafast laser reaction achievable with a nanosecond-pulsed laser appears to preclude or at least inhibit the phase separation of alloys that tend to occur with conventional methods and is capable of synthesizing libraries of alloys with a good dispersion on the particles of the carbonaceous support. Methods disclosed herein are relatively straightforward and convenient compared with previous methods where sophisticated precursor preparation, inert reaction atmosphere, and high energy cost are necessary.
With reference to
As illustrated in
Certain nonlimiting aspects of the methods include the fabrication of the powder precursors 18 capable of use in the LITER synthesizing methods described herein. The powder precursor 18 used for the LITER process may be prepared for laser treatment by means of wet-impregnation of metal salts on particles of a carbonaceous support followed by vacuum drying. For example, a powder precursor 18 (see, e.g.,
In a particular but nonlimiting example of the wet-impregnation process used for preparation of the precursor powders for investigations leading to the methods disclosed herein, metal salts were dissolved in ethanol by sonication bath and then added to a glass vial with a specific volume to make a mixed solution. Then, the carbonaceous powder of graphene flakes or CNTs was added and evenly dispersed in the mixed solution under a sonication bath for twenty minutes. The obtained dispersion solution was then dried and degassed under a vacuum at room temperature overnight. Last, the powdery precursor was obtained and sealed to prevent moisture.
The powder precursor 18 is then laser irradiated utilizing the LITER method to form the HENAs from the powder precursor obtained by the wet-impregnations process. In the nonlimiting example shown in
It is believed that the nanosecond-pulsed laser reduction method entails the absorption of laser photons by the powder precursor 18 comprising the metal salts 22 on surfaces of particles of a carbonaceous support 12, as represented in
A laser-induced reduction using the LITER process as described above is ultrafast, in that the reduction and cooling steps occur in nanoseconds, which allows for the rapid reduction of the various metal salts 22 to form the HENAs 24 with uniform sizes and even distribution on the carbonaceous support 12. The LITER method can also provide a non-contact laser interaction that is suitable for the processing of powder precursors, which is compatible with industry fabrication techniques and may drastically reduce the cost of manufacturing HENAs. The LITER method can be used to fabricate HENAs with up to at least eleven different elements, and more elements may also be possible under certain conditions.
In experiments conducted to investigate the LITER method, HENAs stabilized on few-layered graphene synthesized by scalable LITER fabrication exhibited high catalytic activity in oxygen reduction reactions (ORR), manifesting the potential of this method to produce HENAs in practical applications. The experiments included certain trials that were performed to produce ultrafine nano-alloys (HENAs) utilizing the LITER method. In one particular example, an ultrafine nano-alloy was synthesized by providing a powder precursor having metal salts on particles of a carbonaceous support, and then laser irradiating the powder precursor with multiple laser pulses delivered at a high frequency to reduce metal ions of the metal salt in the powder precursor to metal atoms and form the ultrafine nano-alloy. Residual metal salts are then removed from the ultrafine nano-alloy, for example, by dissolving the residual metal salts in ethanol or other suitable solvent. Advantageously, the laser irradiation can be conducted in air at standard atmospheric pressure. The high frequency of the laser pulses from the LITER process is preferably in the range of nanoseconds (e.g., about 1-100 nanoseconds). The powder grains of the powder precursor may include at least from one to eleven different metal salts supported on the carbonaceous support. With this method, HENAs can be created using a powder carbonaceous support and five or more different metal salts. Example powder carbonaceous supports that are suitable include graphene (e.g., graphene flakes) and/or carbon nanotubes (CNTs), though the use of other suitable carbonaceous supports is foreseeable. The ultrafine nano-alloy is preferably cooled immediately after reducing the metal atoms with the laser pulses. The laser pulses may provide a dose of between about 1 and about 10 pulses per mg of the powder precursor, although larger or smaller doses may be used depending on the particle size of the powder precursor and/or other considerations.
Next, specific examples from trials leading to the development of the methods are described to illustrate at least certain successful implementations using the LITER process. The following examples are not intended as limiting, but rather to show some of the many variations that may be implemented.
Example 1: Fabrication of few-layered graphene supported HENAs. In a first example, the fabrication of few-layered graphene supported HENAs demonstrated the advantage of the LITER process. A powder of few-layered graphene flakes was dispersed in ethanol solvent containing corresponding chloride metal salts under stirring. Then, the ethanol solvent was evaporated under vacuum to obtain the graphene-supported metal salt precursor. Next, the precursor was loaded in a glass vial and subjected to nanosecond laser pulses in air (e.g.,
Example 2: Synthesis of ultrafine Pt nanoparticles. In a second example, the LITER process was used to synthesize ultrafine Pt nanoparticles decorated on few-layered graphene flakes. The precursor was prepared by wet-impregnation of PtCl4 salt on the surface of few-layered graphene flakes and then dried under vacuum to obtain a black powdery precursor. The black powdery precursor was loaded in a glass vial, and a glass cover was placed on the opening of the vial to prevent leakage of a product during the laser treatment (e.g.,
Additional similar experiments using the LITER process were used to fabricate a variety of different nanoalloys on graphene by loading designated metal salts in the powder precursor.
Example 3: In one example, ternary PtPdNi nanoparticles were successfully fabricated on graphene formed using the LITER process described herein. These PtPdNi nanoalloys exhibited excellent uniformity in particle size and distribution and exhibited a similar fcc crystalline structure as Pt and had an average particle size of 2.2 nm.
Example 4: In other examples, quaternary (PtPdNiCo), senary (PtPdNiCoCuAu), and octonary (PtPdNiCoCuAuFeSn) nanoalloys were fabricated using the LITER process. Each of these nanoalloys also had ultrafine sizes of around 2 nm, substantially uniform distribution, and well-matched elemental mappings across a graphene support. Tests suggested that no phase segregation occurred and there was high-entropy mixing of elements. These HENAs had a relatively uniform particle size of about 2 nm, which is substantially smaller than HENAs synthesized by previously known methods that have typical sizes from 10 to 100 nm.
Example 5: In yet another example, quinary PtAuRhIrSn nanoalloys were synthesized with a larger particle size of around 15 nm using the LITER process with much more laser pulses. Nanoparticles of the resulting quinary PtAuRhIrSn nanoalloys were uniformly dispersed on the graphene substrate, and all metallic elements exhibited uniform distribution on the graphene. In addition, the metallic elements in each nanoparticle were well mixed.
Example 6: In a still further example, a precursor powder with eleven metallic elements was prepared for the fabrication of FeCoNiCuPtRhPdAgSnIrAu nanoalloys and subjected to the LITER process. The resulting metallic elements showed identical distribution across each nanoparticle, confirming the successful fabrication of the HENAs across a large variety of metals. Furthermore, even though some of the metal elements were immiscible with each other (e.g., Au versus Ni, Cu versus Sn, and Pd versus Fe), the LITER process overcame the immiscible issue in nanoalloy fabrication via ultrafast reduction of the precursors in nanoseconds, precluding the immigration of atoms that leads to the phase separation. Subsequent testing of the resulting eleven-metal nanoalloy suggested that no phase segregation occurred in the HENAs fabricated by LITER.
Example 7: In still another example, PtPdRhFeCoNi HENAs were successfully formed on CNTs using the LITER process. The resulting HENAs showed superior ORR catalytic activity.
The wet-impregnation process disclosed herein provides a simple and scalable way to form a suitable metal salt precursor in a powder form from which many different HENAs can be fabricated. The LITER process disclosed herein provides a relatively easy way to refine uniform HENAs from their corresponding metal salt precursors under ambient conditions by direct laser-induced thermionic emission on graphene and CNTs in nanoseconds. The unique electron emission induced reduction and simultaneously formed defects on the carbonaceous support can instantly reduce the metal ions to ultrafine HENAs stabilized on the defect sites. These HENA nanoclusters with sizes down to several nanometers can deliver good catalytic performance in ORR. The LITER process may also be useful for mixing various elements into ultrasmall alloys in a scalable and energy-efficient manner. Given the rich combination of elements, the ultrafast laser technology, and the scalable feature, the LITER process provides a new way to produce alloy libraries with unique properties to meet the needs in various energy, environmental, and other applications.
As previously noted above, though the foregoing detailed description describes certain aspects of one or more particular embodiments of the invention, alternatives could be adopted by one skilled in the art. For example, the methods and ultrafine nano-alloys could differ in appearance and construction from the embodiments described herein, functions of certain components used in the methods could be performed by components of different construction but capable of a similar (though not necessarily equivalent) function, and various materials could be used in the fabrication of the ultrafine nano-alloys and/or their components. It should also be understood that the invention is not necessarily limited by descriptions, results, conclusions, or other statements that may be contained in documents cited above as incorporated herein by reference, though such statements may have been reasonably based on information and opinions that existed at the time these documents were written. As such, and again as was previously noted, it should be understood that the invention is not necessarily limited to any particular embodiment described herein or illustrated in the drawings.
This application claims the benefit of provisional U.S. Patent Application No. 63/493,212 filed Mar. 30, 2023, the contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63493212 | Mar 2023 | US |
