Nano-Engineered High-Entropy Intermetallic Compounds for Catalysis: From Designs to Catalytic Applications

Multi-metal nanoparticles, particularly alloys and intermetallic compounds, are useful catalysts for a variety of chemical transformations. Supported intermetallic nanoparticle catalysts are usually prepared by depositing precursors onto a support followed by high-temperature annealing, which is necessary to generate the intermetallic compound but causes sintering and minimizes surface area. Here we show that solution chemistry methods for converting metal nanoparticles into intermetallic compounds are applicable to supported nanoparticle catalyst systems. Unsupported nanocrystalline Pt can be converted to nanocrystalline PtSn, PtPb, PtBi, and FePt3 by reaction with appropriate metal salt solutions under reducing conditions. Similar reactions convert Al2O3, CeO2, and carbon-supported Pt nanoparticles into PtSn, PtPb, PtSb, Pt3Sn, and Cu3Pt. These reactions generate supported alloy and intermetallic nanoparticles directly in solution without the need for high temperature annealing or additional surface stabilizers. These supported intermetallic nanoparticles are catalytically active for chemical transformations such as formic acid oxidation (PtPb/Vulcan) and CO oxidation (Pt3Sn/graphite). Notably, PtPb/Vulcan XC-72 was found to electrocatalytically oxidize formic acid at a lower onset potential (0.1 V) than commercial PtRu/Vulcan XC-72 (0.4 V).

Toward Phase and Catalysis Control: Tracking the Formation of Intermetallic Nanoparticles at Atomic Scale

Intermetallic compounds (IMCs) have attracted significant attention in recent years due to their unique properties and potential applications in various fields, particularly in catalysis. This review aims to provide an in-depth understanding of IMCs, including their synthesis methods, structural characteristics, and diverse catalytic applications. The review begins with an introduction to IMCs, highlighting their distinct features and advantages over traditional catalyst materials. It then delves into the synthesis techniques employed to prepare IMCs and explores their structural properties. Subsequently, catalytic applications of the IMCs are introduced, focusing on the key reactions and highlighting their superior catalytic performance compared to conventional catalysts. Future perspectives for, and challenges to, the catalysis of IMCs are then proposed.

Liquid Metals in Catalysis for Energy Applications

Characterized by long-range atomic ordering, well-defined stoichiometry, and controlled crystal structure, intermetallics have attracted increasing attention in the area of chemical synthesis and catalytic applications. Liquid-phase synthesis of intermetallics has arisen as the promising methodology due to its precise control over size, shape, and resistance toward sintering compared with the traditional metallurgy. This short review tends to provide perspectives on the liquid-phase synthesis of intermetallics in terms of both thermodynamics and methodology, as well as its applications in various catalytic reactions. Specifically, basic thermodynamics and kinetics in the synthesis of intermetallics will be first discussed, followed by discussing the main factors that will affect the formation of intermetallics during synthesis. The application of intermetallics in electrocatalysis will be demonstrated case by case at last. We conclude the review with perspectives on the future developments with respect to both synthesis and catalytic applications.

Recent advances of Rh-based intermetallic nanomaterials for catalytic applications

Mutagenicity, carcinogenicity and teratogenicity of cobalt metal and cobalt compounds

Synthesis of Intermetallic Compounds and Their Catalytic Applications

A considerable interest in nanostructured thin films from intermetallic compounds of noble metals (Ag and Au) and post-transition metals is raised due to their unique plasmonic properties, which makes them potential materials for application in photonics, catalysis and biosensing systems. In this work the possibility for deposition of polycrystalline AuSn thin films was investigated, as thin films with the same composition and different thicknesses (10-100 nm) were obtained by co-depositing of Au and Sn metals. The chemical composition was determined by X-ray microanalysis. The X-ray diffraction patterns indicated formation of the intermetallic compound AuSn in the thin films. The complex permittivity ε = ε′ - i.ε″ of the thin AuSn films as function of the thickness was investigated by spectroscopic ellipsometry. The possibility for application of nanostructures from the AuSn intermetallic compound as suitable substrates for the needs of surface-enhanced Raman and fluorescence spectroscopy in the spectral interval 2.8 - 4.7 eV was analysed.

Zinc-included intermetallic compound catalysts of RhZn, PtZn, and PdZn with a molar ration of Zn/metal = 1/1, which are generally prepared using a hydrogen reduction approach, are known to show excellent catalytic performance in some selective hydrogenations of organic compounds. In this study, in order to reduce the incorporated mounts of the expensive noble metals, we attempted to prepare zinc-rich intermetallic compounds via a CaH2-assisted molten salt synthesis method with a stronger reduction capacity than the common hydrogen reduction method. X-ray diffraction results indicated the formation of RhZn13 and Pt3Zn10 in the samples prepared by the reduction of ZnO-supported metal precursors. In a hydrogenation reaction of p-nitrophenol to p-aminophenol, the ZnO-supported RhZn13 and Pt3Zn10 catalysts showed a higher selectivity than the RhZn/ZnO and PtZn/ZnO catalysts with the almost similar conversions. Thus, it was demonstrated that the zinc-rich intermetallic compounds of RhZn13 and Pt3Zn10 could be superior selective hydrogenation catalysts compared to the conventional intermetallic compound catalysts of RhZn and PtZn.

Platinum metal is not inert as it undergoes irreversible surface oxidation1. Platinum oxide (PtO) formation and corresponding reduction brings irreversibility on the surface due to famous place-exchange phenomena. Rise of this irreversibility during PtO reduction results in Pt dissolution2. Pt dissolution has been investigated upto an appreciable extent, in rigorous fuel cell conditions, which gives immense opportunity to restrain it by controlling accessible electrochemical operational parameters3. Advantageousness of modulated electrochemical dissolution of Pt, deployed as sacrificial electrode (S.E), renders ultra-low amount of simultaneous Pt electrodeposition through electrolyte on an anchoring substrate electrode (A.S.E). Thereby isolated atoms and subnanometric clusters becomes achievable over suitable A.S.E, utilizing altered rates of dissolution and deposition, by a four-electrode assembly (FEA). Presently, field of electrochemical energy conversion is evolving with highly active and stable electrocatalysts for Hydrogen Evolution Reaction (HER). One such pinnacle group of electrocatalysts emerged as metal-based single-atom catalysts (SACs) are quite efficient as well as stable for HER4. Current research work is focussed on using Pt dissolution phenomena to prepare SACs over certain stable substrates by using four-electrode assembly (FEA).Electrochemically assisted Dissolution-Deposition (EADD) by using FEA is utilized in present work to prepare Pt SACs supported by Intermetallic compounds. EADD being a novel, controlled and efficient synthesis technique has helped to evaluate the insitu Pt dissolution-deposition mechanism by Alternating Current Voltammetry. Authors also demonstrates that typical three-electrode assembly (TEA) used for Pt dissolution from Pt counter electrode is an uncontrolled method for Pt deposition over working electrode. In TEA, Open Circuit Potential (OCP) measurements of counter electrode conducted during cyclic voltammetry (CV) has helped to evaluate the scan rates experienced by Pt counter electrode. Finally, scan rates has given the insights about Pt dissolution and redeposition kinetics demonstrating the problems associated with TEA in context of dissolution-deposition synthesis. While using FEA the challenges experienced in TEA has also overcome. Synthesized Pt SACs tested for HER showed onset potential (η0) of 0mV and over potential at 10mA/cm2 (η10) of 50mV with a quite stable performance for 20h. Ultimately, EADD is summarized as a general, unique and effective surface synthesis technique in the domain of single atom catalysis availing immense opportunities for various other catalytic applications too.(1) H. ANGERSTEIN-KOZLOWSKA; B. E. CONWAY and W. B. A. SHARP. Faraday Trans. I, 1973. Langmuir 1973, 43, 9–36.(2) Gómez-Marín, A. M.; Clavilier, J.; Feliu, J. M. Sequential Pt(1 1 1) Oxide Formation in Perchloric Acid: An Electrochemical Study of Surface Species Inter-Conversion. J. Electroanal. Chem. 2013, 688, 360–370. https://doi.org/10.1016/j.jelechem.2012.07.016.(3) Topalov, A. A.; Cherevko, S.; Zeradjanin, A. R.; Meier, J. C.; Katsounaros, I.; Mayrhofer, K. J. J. Towards a Comprehensive Understanding of Platinum Dissolution in Acidic Media. Chem. Sci. 2014, 5 (2), 631–638. https://doi.org/10.1039/c3sc52411f.(4) Ji, S.; Chen, Y.; Wang, X.; Zhang, Z.; Wang, D.; Li, Y. Chemical Synthesis of Single Atomic Site Catalysts. Chem. Rev. 2020. https://doi.org/10.1021/acs.chemrev.9b00818. Figure 1

Metastable intermetallic compound Zn3Co alloying from porous coordination polymer pyrolysis

Prussian blue (PB) and its analogues (PBAs) are promising coordination polymers (CPs) with an adjustable composition and open framework. Nonetheless, their intrinsic electrochemical activity and electrical conductivity are poor, which hinder their applications in energy conversion and storage. In catalytic applications, metal compounds derived from PB/PBAs have a lot of advantages, such as outstanding stability, selectivity, and electrical conductivity. Furthermore, they can be used as electrode materials for electrochemical energy storage and conversion, while having preferable electronic conductivity, sufficient catalytic active sites, as well as a larger specific surface area and tunable size to achieve an optimized performance. This review summarizes the current achievements of PB/PBA-derived metallic nanomaterials, as well as the existing limitations, urgent challenges and future development.

Rapid fabrication of ultra-fine grain intermetallic compound powder in milliseconds under ultrasonic vibrations

The development of highly active, durable, and cost-effective catalysts is of paramount importance for the fuel cell industry. Most catalysts for relevant applications contain Pt that is known as one of the most expensive metals.1 To date, the best way to reduce the total catalyst cost is associated with the use of an inert support coated by a small amount of Pt-based catalyst. A good candidate for the support is nanoporous Au (NPG).1-3 As highly conductive material, NPG has an open, 3D interconnected porous framework with surface area that even in ultrathin NPG layer configuration could be tens to hundreds of times larger than the area of planar Au. Once developed on a C-based support, the NPG can be terminated with Pt or Pt-containing alloys by surface-limited redox replacement (SLRR), and then applied as the catalyst in the key catalytic reactions.4 In our previous work, we established an all-electrochemical synthetic approach for a NPG-based catalyst.4 The fabrication procedure entails AgxAu(1−x) alloy electrodeposition followed by selective dissolution of Ag (de-alloying) ultimately generating the desired NPG structure with a thickness of less than 20 nm. To further study the NPG applicability in catalysis, in this report we switch our focus to a CuxAu(1−x) precursor alloy synthesized for this work in different size and shape through various routes. Generally, the precursor is subjected to de-alloying and the resulting NPG is structurally and morphologically characterized and assessed for performance and durability in formic acid oxidation tests after platinization with ultra thin catalytically active layer. More specifically, CuxAu(1−x) bulk alloys, electrodeposited alloys, and chemically synthesized Cu3Au nanorods (intermetallic and random alloy)5-7 are subjected to a comparative de-alloying study with emphasis on their parting behavior and resulting structures. The de-alloying curves exhibit quite unique behavior owing to size and structural differences. Overall, the de-alloying curves for the system of interest illustrate multiple peaks that indirectly suggest phase coexistence dependent upon the synthetic route of the precursor alloy (melting, electrodeposition nanoparticle synthesis). The NPG resulting from the de-alloying process has been studied for surface area development by Pb underpotential deposition (Pb UPD). XRD is used to study the potential presence of different phases. SEM and TEM images display the morphology before and after de-alloying. Finally, basic activity and durability tests of the catalytic properties of various Pt-coated de-alloyed structures during formic acid oxidation are presented and discussed as well. In these tests the assessment of accordingly prepared catalysts in standard HCOOH oxidation experiments attests to their high catalytic activity which in some aspects exceeds the performance of recently studied nanoparticle based catalysts.