Metal Nanoalloys Research Articles

Determining the chemical ordering in nanoalloys by considering atomic coordination types.

The energetically most favorable chemical ordering of bimetallic nanoparticles can be characterized by combining global optimization algorithms and surrogate energy models. The latter approximate the energy of nanoalloys relying on structural descriptors, training models, and data. Here, we systematically evaluate the performance of highly data-efficient topological descriptors [Kozlov et al., Chem. Sci. 6, 3868 (2015)] for predicting the energies of metal nanoalloys with different chemical orderings. We also introduce a new descriptor based on atomic coordination types, which results in a less data-efficient and interpretable approach, but improves the general accuracy and the quantification of orderings in the inner parts of nanoparticles. The capacity of both the original and new approaches in combination with a basin hopping algorithm is illustrated by generating convex hulls of PdZn nanoalloys and predicting the resulting active surface site distribution as a function of particle composition. Finally, we show how these approaches can be combined with machine-learning adsorption models in electrocatalysis studies for a fast evaluation of the reactivity landscape of targeted nanoalloys.

New Insights into the ORR Catalysis on Pt Alloy Nanoparticles from an Element Specific d-Band Analysis.

Bolstered by their unique atomic structures and tailored compositions, nanoalloys exhibit extraordinary properties making them ideal materials to solve challenges in energy storage and conversion catalysis. However, a quantitative description of the structure-property relationships using an accurate descriptor-based model for nanoalloys, ranging from bimetallic to multimetallic compositions, is needed to drive efficient material design toward high-performance catalysis. In this work, we highlight the electronic property and catalytic activity relationship from an element specific d-band analysis of Pt-based alloy catalysts using X-ray absorption near-edge spectroscopy (XANES). Using a series of L10-MPt/Pt (M = Fe, Co, Ni) core/shell alloy catalysts with well-defined atomic structures, we quantified subtle differences in the Pt d-electron states and correlated the Pt d-band structure to their superior catalytic activity toward the oxygen reduction reaction (ORR). Our analysis used the upper d-band edge position as a predictive descriptor for the mass activity toward the ORR instead of the commonly used d-band center position. Together with density functional theory calculations and Nørskov d-band theory, the upper d-band edge position for the Pt states, derived from experimental measurements, elucidates new physical insights into the ORR performance of the L10-MPt/Pt core/shell catalysts. An element specific Pt d-band analysis using XANES overcomes challenges in traditional X-ray photoelectron spectroscopy-based valence d-band analysis, which cannot distinguish signals from independent elements in nanoalloys. Thus, the insights from the element specific d-band analysis presented in this work are a promising approach to determine structure-property relationships in a variety of transition metal nanoalloys and will be useful in the design of future high-performance catalysts.

Medium entropy FeCoNi nanoalloy supported on reduced graphene oxide for efficient electrochemical detection of roxarsone in food samples

Herein, a novel FeCoNi(b)-800 ternary metal nanoalloy was uniformly mixed with reduced graphene oxide (RGO) to synthesize the FeCoNi(b)-800@RGO(2:1) composite. The addition of RGO not only stopped the accumulation of FeCoNi(b)-800 alloy, but also heightened the electrocatalytic activity of composite. Particularly, the FeCoNi(b)-800@RGO(2:1) composite displayed the significantly strong electrocatalytic capacity for the reduction of roxarsone (ROX). Furthermore, the FeCoNi(b)-800@RGO(2:1) composite possessed enough porosity and metal catalytic sites, facilitating the transport and electrochemical reduction of the ROX. Thus, the FeCoNi(b)-800@RGO(2:1) composite modified glassy carbon electrode (FeCoNi(b)-800@RGO(2:1)/GCE) showed the superb electrochemical detection effect for ROX with relatively wide working range (0.1–1500 μM) and low detection limit (0.013 μM). Importantly, the FeCoNi(b)-800@RGO(2:1)/GCE sensor could accurately determine the contents of ROX in actual pork, chicken, duck and egg samples, indicating that it had good suitability in food safety monitoring.

Layered Double Hydroxide-Based PdCux@LDH Alloy Nanozyme for a Singlet Oxygen-Boosted Sonodynamic Therapy.

Redox nanozymes have demonstrated tremendous promise in disrupting cellular homeostasis toward cancer therapy, but a dysfunctional competition of diverse activities makes it normally restricted by the complex tumor microenvironment (TME). As palladium nanocrystals can achieve the precise regulation of the enzyme-like activity by regulating exposed crystal planes, noble metal nanoalloys can enhance the enzyme-like activity by promoting electron transfer and enhanced active sites. Herein, bimetallic nanoalloys with optimized enzymatic activity were intelligently designed via the interaction between the Pd and layered double hydroxide, denoted as PdCux@LDH. This PdCux@LDH is able to produce long-lived singlet oxygen (1O2) with high efficiency and selectivity for ultrasound-improved cancer therapy. In addition, this PdCux@LDH nanozyme demonstrated unique surface-dependent multienzyme-mimicking activities for catalyzing cascade reactions: oxidase (OXD)- and catalase (CAT)-mimicking activities. Interestingly, ultrasound (US) stimulation can further improve the dual-enzyme-mimicking activities and impart superior reactive oxygen species (ROS) generation activity, thereby further consuming nicotinamide adenine dinucleotide (NADH) to cause mitochondrial dysfunction, resulting in a highly efficient alloy nanozyme-mediated cancer therapy. This work opens a new research avenue to apply nanozymes for effective sonodynamic therapies (SDT).

The composition effect on the structural and thermodynamic properties of Cu–Ag–Au ternary nanoalloys: a study via molecular dynamics approach

Metal ternary nanoalloys or trimetallic nanoparticles have emerged, in recent years, as novel and relevant materials in different fields due to the synergy of three metals in a single system that leads to unique physicochemical properties as compared to mono- and bimetallic nanoparticles. In this study, the influence of composition on the structural and thermodynamic properties of Cu–Ag–Au nanoalloys with 5083 atoms is analyzed using molecular dynamics simulations. Relevant thermodynamic quantities are used to describe the melting and solidification behaviors of three models of Cu–Ag–Au nanoalloys. Our results indicate that the melting temperature presents linear and quadratic dependencies with the composition, i.e. for Cu33Ag 67−x Au x , Ag33Cu 67−x Au x , and Au33Ag 67−x Cu x are Tm=912.6+1.9x , Tm=882.3+2.7x , and Tm=1056.6−4.9x+0.07x2 , respectively. In addition, most Ag atoms segregate to the surface and the Au and Cu atoms are localized in the center of the nanoalloy during the heating process, and this trend is maintained in the cooling process. The solidification temperature does not have an explicit correlation with the composition. Furthermore, the structural analysis of cooled nanoalloys exhibits local FCC and HCP symmetries, and the excess energy shows that Cu33Ag27Au40, Au33Ag17Cu50, and Ag33Cu37Au30 are relatively more stable to form nanoalloys. Finally, the possibility of controlling the composition in these metal nanoalloys opens up potential applications in plasmonic, catalysis, and bactericidal (by Ag surface segregation) fields.

A carbon-promoted galvanic replacement method to synthesize efficient PdNi nanoalloy catalyst

PdNi nanoalloy catalysts were prepared by a carbon-promoted galvanic replacement method. Characterizations and control experiments show the increased replacement rate of metal Ni with Pd2+ ion can be attributed to the higher electrode potential and smaller crystalline sizes caused by carbon doping. Introduction of carbon (C) into Ni particles not only accelerates the formation process of PdNi nanoalloys, but also enables C atoms to successfully enter the lattice interstices of PdNi nanoalloys. C regulates the surface electronic properties of PdNi nanoalloys by the electron transfer between different elements and improves their activity. The PdNi@C-650 exhibits extraordinary activity and long-term stability for hydrogenation reduction of hexavalent chromium (Cr (VI)) and hydrodechlorination of chlorophenols in comparison with PdNi/CNTs (carbon nanotubes) and commercial Pd/C. Density functional theory calculations together with investigations of mechanism reveal that the high electron-deficient PdNi nanoalloys from the redistribution of electron between Ni, Pd and C of the PdNi@C-650 promote the surface adsorption of substrate molecules and H2, which accordingly enhances the hydrogenation activity. This study brings a new method for the design and preparation of high active noble metal nanoalloy.

Metallic Nanoalloys on Vertical GaAs Nanowires: Growth Mechanisms and Shape Control of Ni-GaAs Compounds.

GaAs nanowires are promising candidates for emerging devices in a broad field of applications (e.g., nanoelectronics, photodetection, or photoconversion). These nanostructures benefit greatly from a vertical integration, as it allows for the exhibition of the entire nanowire surface. However, one of the main challenges related to vertical integration is the conception of an efficient method to create low resistive contacts at nanoscale without degrading the device performance. In this article, we propose a complementary metal-oxide-semiconductor (CMOS)-compatible approach to form alloyed contacts at the extremities of vertical GaAs nanowires. Ni-based and Pd-based alloys on different vertical GaAs nanostructures have been characterized by structural and chemical analyses to identify the phase and to study the growth mechanisms involved at the nanoscale. It is shown that the formation of the Ni3GaAs alloy on top of nanowires following the epitaxial relation Ni3GaAs(0001)∥GaAs(111) leads to a pyramidal shape with four faces. Finally, guidelines are presented to tune the shape of this alloy by varying the initial metal thickness and nanowire diameters. It will facilitate the fabrication of a nanoalloy structure with tailored shape characteristics to precisely align with a designated application.

PdCux Bimetallic Nanoalloys with “Hand‐in‐Hand” Collaboration in POD‐like Activity and “Back‐to‐Back” Confrontation in SPR Effect for Tumor Redox System Control

AbstractIn reactive‐oxygen‐species‐mediated tumor therapy, the generation and accumulation of ·OH is highly dependent on peroxidase (POD)‐like enzymatic activities and the antioxidant tumor microenvironment. As noble metal nanoalloys can enhance the POD‐like enzymatic activity by improving electron transfer and upgrading active sites, PdCux (x = 0.6–1.2) bimetallic nanoalloys with optimized enzymatic activity, enhanced photothermal conversion efficiency, and altered glutathione (GSH) consumption ability are synthesized by a facile co‐reduction method. The electron transfer between Pd and Cu in the PdCux nanoalloys and their new Cu+ catalytic centers contribute to a “hand‐in‐hand” collaboration in their POD‐like enzymatic activities, while their photothermal properties remain almost unchanged because of the “back‐to‐back” confrontation occurring owing to the excess Cu produced by the surface plasmon resonance effect. Moreover, the intrinsic GSH consumption of those nanoalloys and heat from their surface plasmon resonance effect tilt the tumor redox steady state. Therefore, the PdCu0.9 nanoalloy show excellent POD‐like enzymatic activity resulting from a bimetallic catalytic route, which involves electron transfer from electron‐enriched Pd to hydrogen peroxide and heat‐enhanced Cu+/Cu2+‐coupled Fenton‐like reactions. The synthesized PdCux bimetallic nanoalloys can shed light on the mechanism responsible for enhancing the POD‐like activity in nanoalloys and offer a typical model for constructing next‐generation alloy nanozymes.

(Invited) An Overview of Electrochemistry Application to Additive Manufacturing

Additive manufacturing (AM) is the process of creating three-dimensional (3D) objects from digital models through the sequential deposition of material in layers. This talk will highlight how researchers have used electrochemical research in additive manufacturing and will provide insights into how technology can be exploited to formulate novel microstructures and optimize the manufacturing process. Electrochemical 3D printing is a relatively new form of AM that creates metallic structures through the electrochemical reduction of metal ions from solutions onto conductive substrates. It involves localized electrochemical deposition of metals combined with additive manufacturing principles to achieve Electrochemical Additive Manufacturing (ECAM). The talk will also focus on the formulation of metal precursor inks to produce novel metallic microstructures and nanoalloys containing multiple metals. These inks are used with AM techniques to fabricate 2D and 3D printed conductive structures directly onto a substrate. Examples include aligned nickel nanowires over large areas, which provide opportunities to produce structures with enhanced anisotropic electrical and magnetic properties. Nanoalloy films printed using metal precursor inks have a variety of important applications involving local control of alloy composition in AM part. Examples include the facile formation of layered nanostructures and electrical conductivity with oxidative stability. The talk will conclude with current research on electropolishing of AM parts. AM while capable of producing complex-shaped metal parts with intricate internal geometries and lattice structures struggles to make parts with the smooth surface finish required for many applications. Polishing interior surfaces inaccessible to traditional surface polishing methods is a challenge. Electropolishing is increasingly being used as a post-treatment option for metal AM parts due to its non-contact nature and ability to finish complex internal features.

Double‐Tuned RuCo Dual Metal Single Atoms and Nanoalloy with Synchronously Expedited Volmer/Tafel Kinetics for Effective and Ultrastable Ampere‐Level Current Density Hydrogen Production

AbstractAlkaline water electrolysis system is of general interest but is impeded by the unsatisfactory hydrogen evolution reaction (HER) performance under ampere‐level current density. Herein, the synchronous modification of complicated Volmer/Tafel kinetics is effectuated for attaining ampere‐level current density hydrogen production via engineering double‐tuned RuCo nanoalloy and dual metal single atoms on hierarchical N‐doped mesoporous carbon (RuCo@RuSACoSA‐NMC). The electronic structure of Ru sites in dual metal single atoms can be synergistically tailored by adjacent Co atomic sites and nanoalloy, which makes it achieve faster Volmer kinetics with rapid water adsorption/dissociation and transfer rates toward adsorbed hydroxyl. While double‐tuned Ru sites in nanoalloy by adjacent alloyed Co sites and dual metal single atoms undertake optimized Tafel kinetics with boosted transfer rates toward adsorbed hydrogen. Accordingly, RuCo@RuSACoSA‐NMC exhibits ultralow HER overpotential of 255 mV at 1 A cm−2 with robust stability over 24 days, ultrahigh mass activity of 37.2 A mgRu−1, and turnover frequency of 19.5 s−1. More importantly, RuCo@RuSACoSA‐NMC can make water electrolysis system possess low power consumption of 5.34 kWh per Nm3H2 and estimated costs of 1.197 $ per kgH2. The concept emphasized in this study provides guidance for rational design of cost‐effective catalysts with ampere‐level current density hydrogen production.

Molten-Salt Electrochemical Deoxidation Synthesis of Platinum-Neodymium Nanoalloy Catalysts for Oxygen Reduction Reaction.

Platinum-rare earth metal (Pt-RE) nanoalloys are regarded as a potential high performance oxygen reduction reaction (ORR) catalyst. However, wet chemical synthesis of the nanoalloys is a crucial challenge because of the extremely high oxygen affinity of RE elements and the significantly different standard reduction potentials between Pt and RE. Here, this paper presents a molten-salt electrochemical synthetic strategy for the compositional-controlled preparation of platinum-neodymium (Pt-Nd) nanoalloy catalysts. Carbon-supported platinum-neodymium (Ptx Nd/C) nanoalloys, with distinct compositions of Pt5 Nd and Pt2 Nd, are obtained through molten-salt electrochemical deoxidation of platinum and neodymium oxide (Pt-Nd2 O3 ) precursors supported on carbon. The Ptx Nd/C nanoalloys, especially the Pt5 Nd/C exhibit a mass activity of 0.40Amg-1 Pt and a specific activity of 1.41mAcm-2 Pt at 0.9V versus RHE, which are 3.1 and 7.1 times higher, respectively, than that of commercial Pt/C catalyst. More significantly, the Pt5 Nd/C catalyst is remarkably stable after undergoing 20000 accelerated durability cycles. Furthermore, the density-functional-theory (DFT) calculations confirm that the ORR catalytic performance of Ptx Nd/C nanoalloys is enhanced by compressive strain effect of Pt overlayer, causing a suitable weakened binding energies of O* and .

Bimetallic Metal-Organic Frameworks as an Efficient Capture Probe in Signal On-Off-On Electrochemiluminescence Aptasensor for Microcystin-LR Detection.

To ensure drinking water quality, the development of rapid and accurate analytical methods is essential. Herein, a highly sensitive electrochemiluminescence (ECL) aptasensor-based on the signal on-off-on strategy was developed to detect the water pollutant microcystin-LR (MC-LR). This strategy was based on a newly prepared ruthenium-copper metal-organic framework (RuCu MOF) as the ECL signal-transmitting probe and three types of PdPt alloy core-shell nanocrystals with different crystal structures as signal-off probes. Compounding the copper-based MOF (Cu-MOF) precursor with ruthenium bipyridyl at room temperature facilitated the retention of the intrinsic crystallinity and high porosity of the MOFs as well as afforded excellent ECL performance. Since bipyridine ruthenium in RuCu MOFs could transfer energies to the organic ligand (H3BTC), the ultra-efficient ligand luminescent ECL signal probe was finally obtained, which greatly improved the sensitivity of the aptasensor. To further improve the sensitivity of the aptasensor, the quenching effects of noble metal nanoalloy particles with different crystal states were investigated, which contained PdPt octahedral (PdPtOct), PdPt rhombic dodecahedral (PdPtRD), and PdPt nanocube (PdPtNC). Among them, the PdPtRD nanocrystal exhibited higher activity and excellent durability, stemming from the charge redistribution caused by the hybridization of Pt and Pd atoms. Moreover, PdPtRD could also load more -NH2-DNA strands because it exposed more active sites with a large specific surface area. The fabricated aptasensor exhibited outstanding sensitivity and stability in MC-LR detection, with a linear detection range of 0.0001-50 ng mL-1. This study provides valuable directions for the application of alloy nanoparticles of noble metals and bimetallic MOFs in the field of ECL immunoassay.

Solution Plasma‐Assisted Multivariate Metal Nanoalloys Encapsulated with Carbon Dots for Efficient Oxygen Evolution Reaction

AbstractTo accelerate the reaction kinetics of electrocatalytic oxygen evolution reaction (OER), a multicomponent CDs@(PdFeNiCo)Nbx nanohybrid comprising multiple metal nanoalloys and carbon quantum dots (CDs) was in situ generated by treating the mixture of Nb2C quantum dots (Nb2C QDs) and a variety of metal ions (M2+=Pd2+, Fe2+, Co2+, Ni2+) through the solution plasma (SP) modification technique. The CDs@(PdFeNiCo)Nbx catalyst was further explored as an electrocatalyst for OER in alkaline solution. Under nitrogen plasma irradiation with high input power (200 W), diverse bimetallic nanoalloy particles, including NbPd3, FeNb, NbNi3, and CoNbO4 nanoalloys, were generated, accompanied with the decomposition of Nb2C QDs into CDs. In view of the synergic effect between multivariate metal active sites and highly conjugated CD network, the developed CDs@(PdFeNiCo)Nbx electrocatalyst showed a small overpotential of 240 mV for achieving the current density of 10 mA cm−2, together with a very low Tafel slope of 62 mV dec−1, which substantially outperformed those of the state‐of‐the‐art metal electrocatalysts and was competitive with most metal oxides. The CDs@(PdFeNiCo)Nbx electrocatalyst also showed a negligible overpotential change during 30 h chronopotentiometry measurement. The present work can provide a feasible alternative strategy for the development of an excellent OER electrocatalyst using the SP modification method.

A Versatile Route for Synthesis of Metal Nanoalloys by Discharges at the Interface of Two Immiscible Liquids.

Discharge in liquid is a promising technique to produce nanomaterials by electrode erosion. Although its feasibility was demonstrated in many conditions, the production of nanoalloys by in-liquid discharges remains a challenge. Here, we show that spark discharge in liquid cyclohexane that is in contact with conductive solution, made of a combination of Ni-nitrate and/or Fe-nitrate and/or Co-nitrate, is suitable to produce nanoalloys (<10 nm) of Ni-Fe, Ni-Co, Co-Fe, and Ni-Co-Fe. The nanoparticles are synthesized by the reduction of metal ions during discharge, and they are individually embedded in C-matrix; this latter originates from the decomposition of cyclohexane. The results open novel ways to produce a wide spectrum of nanoalloys; they are needed for many applications, such as in catalysis, plasmonic, and energy conversion.

(Invited) Alloy of Platinum with Rare Earth Metals for High Oxygen Reduction Reaction Activity and Durability

In the search for highly active and durable electrocatalysts for the oxygen reduction reaction (ORR), alloys of Pt with rare-earth metals (REM) have been demonstrated as one of the most promising candidates. However, their synthesis by conventional chemical methods is challenging, since REM have very low reduction potentials and high oxygen affinity leading to the formation of oxides rather than alloys.We prepared a series of carbon supported Pt-REM nanomaterials with a solid-state method[1], characterized by physico-chemical techniques and evaluated towards the ORR in acidic medium.The influence of the type of rare earth metal, of the Pt:REM ratio[2], of the post-synthesis treatment[3], and of the nature of the carbon support on the structural, morphological and electrochemical properties of the prepared electrocatalysts was investigated.In this presentation we will give an overview of the results obtained on these highly active and durable carbon-supported Pt-REM nanostructured electrocatalysts and of the challenges to be tackled for their application at the cathode of proton exchange membrane fuel cells.[1] Y. Hu, J.O. Jensen, L.N. Cleemann, B.A. Brandes, Q. Li, Synthesis of Pt–Rare Earth Metal Nanoalloys, J. Am. Chem. Soc. 142 (2020) 953–961.[2] C.A. Campos-Roldán, F. Pailloux, P.-Y. Blanchard, D.J. Jones, J. Rozière, S. Cavaliere, Rational Design of Carbon-Supported Platinum–Gadolinium Nanoalloys for Oxygen Reduction Reaction, ACS Catal. 11 (2021) 13519–13529.[3] C.A. Campos Roldán, F. Pailloux, P.-Y. Blanchard, D.J. Jones, J. Rozière, S. Cavaliere, Enhancing the Activity and Stability of Carbon-Supported Platinum-Gadolinium Nanoalloys towards the Oxygen Reduction Reaction, Nanoscale Adv. (2021). doi:10.1039/D1NA00740H.

Molten salt synthesis of carbon-supported Pt-rare earth metal nanoalloy catalysts for oxygen reduction reaction.

The synthesis of nano-sized alloys of Pt and rare earth (RE) metal catalysts has been a huge challenge due to a significantly large standard reduction potential difference of Pt and RE metals and the high synthesis temperature. PtxY/C catalysts with an average particle size of around 21 nm, were synthesized by mixing K2PtCl4 with Y2O3 (a molar ratio of Pt : Y = 1 : 1) with a carbon support in a molten LiCl–CaH2 system by a one-step molten salt synthesis method at 600 °C. The synthesis processes of the PtxY/C alloys are proposed as follows: Pt nanoparticles were first obtained by the reaction of K2PtCl4 and CaH2 at 210 °C, then Y ions were preferentially reduced on the Pt nanoparticle surface by the reduction of CaH2, followed by PtxY alloy formation in the molten LiCl–CaH2 system at 600 °C. Molten LiCl provides a strong reducing environment and lowers the formation temperature of alloys. Pt2Gd/C and Pt2La/C were also obtained with Gd2O3 and La2O3 as the starting raw materials, respectively by using the same process. When investigated as an electrocatalyst for the oxygen reduction reaction (ORR), the half-wave potentials of PtxRE/Cs are all more positive than that of commercial Pt/C catalyst (e.g., 0.905 V for PtxY/C while 0.880 V for JM Pt/C), and the nano-sized PtxY/C alloy shows higher electrocatalytic activity toward the ORR and preferable catalytic durability with respect to JM Pt/C catalysts. This facile synthesis method provides an effective strategy for the preparation of Pt–RE based multicomponent nanoalloys, especially in large-scale production.

Dendrimer stabilized nanoalloys for inkjet printing of surface-enhanced Raman scattering substrates

Research on paper substrates prepared by inkjet deposition of metal nanoparticles for sensing applications has become a hot topic in recent years; however, the design of such substrates based on the deposition of alloy nanoparticles remains less explored. Herein, we report for the first time the inkjet printing of dendrimer-stabilized colloidal metal nanoalloys for the preparation of paper substrates for surface-enhanced Raman scattering (SERS) spectroscopy. To this end, nanoassemblies containing variable molar ratios of Au:Ag were prepared in the presence of poly(amidoamine) dendrimer (PAMAM), resulting in plasmonic properties that depend on the chemical composition of the final materials. The dendrimer-stabilized Au:Ag:PAMAM colloids exhibit high colloidal stability, making them suitable for the preparation of inks for long-term use in inkjet printing of paper substrates. Moreover, the pre-treatment of paper with a polystyrene (PS) aqueous emulsion resulted in hydrophobic substrates with improved SERS sensitivity, as illustrated in the analytical detection of tetramethylthiuram disulfide (thiram pesticide) dissolved in aqueous solutions. We suggest that the interactions established between the two polymers (PAMAM and PS) in an interface region over the cellulosic fibres, resulted in more exposed metallic surfaces for the adsorption of the analyte molecules. The resulting hydrophobic substrates show long-term plasmonic stability with high SERS signal retention for at least ninety days.

Facile synthesis of Pt5La nanoalloys as the enhanced electrocatalysts for oxygen reduction reaction and methanol oxidation reaction

Platinum-rare earth metal (Pt-RE) nanoalloys are the most promising candidates for fuel cells because of their superior activity and stability for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). However, the preparation of Pt-RE nanoalloys with chemical method is still challenge due to their huge standard reduction potential differences and the oxophilicity of the latter. Herein, this work provides a novel and facile strategy for the chemical synthesis of Pt5La nanoalloys to apply in both ORR and MOR. Pt5La nanoalloys are synthesized by co-reduction of Pt2+ and La3+ in LaCl3 and H2PtCl6 solution containing carbon powder and C2H4N4 by first heating at 550 °C for 2 h under N2, and then heating to 700 °C under H2/Ar for 2 h. The as-synthesized Pt5La nanoalloys present a high alloying degree at 700 °C, with the average particle size of 7.8 nm. The results indicate Pt5La nanoalloys lead to a significant enhancement in ORR and MOR performances related to the commercial JM-Pt/C catalyst.

Hollow Multiple Noble Metallic Nanoalloys by Mercury-Assisted Galvanic Replacement Reaction for Hydrogen Evolution.

Hollow multimetallic noble nanoalloys with high surface area/volume ratio, abundant active sites, and relatively effective catalytic activity have attracted considerable research interest. Traditional noble nanoalloys fabricated by hydro-/solvothermal methods usually involve harsh synthetic conditions such as high temperatures and intricate processing. We proposed a simple and mild strategy to synthesize platinum- and palladium-decorated hollow gold-based nanoalloys by the galvanic replacement reaction (GRR) at room temperature using hollow gold nanoparticles as templates and mercury as an intermediate. The hollow gold nanoparticles were essential for increasing the number of surface-active sites of the obtained multimetallic nanoalloys, and the introduction of mercury can eliminate the influence of the electrochemical potential of Pt/Pd with Au in the GRRs, increase alloying degrees, and maintain the nanoalloys that exhibit the hollow nanostructures. The structural characterizations of the hollow nanoalloys were studied by means of high-angle annular dark-field scanning transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. On the basis of the electrochemical catalytic measurements, the platinum-exposed nanoalloys were found to have excellent electrocatalytic activities. Especially in the presence of palladium, owing to the synergistic effect, the quaternary AuHgPdPt hollow nanoalloy displayed a low overpotential of 38 mV at 10 mA cm-2 with a small Tafel slope of 56.23 mV dec-1 for the alkaline hydrogen evolution reaction. In addition, this approach not only expands the application range of the galvanic replacement reaction but also provides new ideas for the preparation of multialloys and even high-entropy alloys at room temperature.

The AuCu Phase Diagram at the Nano Scale: A Molecular Dynamics Approach

While phase diagrams for metal nanoalloys are important to know the conditions at which a nanoparticle keeps a particular shape and kind of surface, experiments to build phase diagrams at the nanoscale are difficult to implement; a posible alternative is the use of atomistic simulations. In this work, a set of molecular dynamics simulations is implemented to build the phase diagram of icosahedral, cuboctahedral, and decahedral AuCu nanoparticles of 2 to 4 nm in size, with several relative concentrations of the metals, using the quantum-corrected version of the Sutton and Chen interaction model. In the obtained phase diagrams, the congruent melting point shifts towards high concentrations of copper in accordance with previous theoretical results, and the local density mapping and bond-order analysis as function of temperature show that for the largest particles, partial premelting of the surface coexists with a pseudo-crystalline region that shrinks as the temperature is incremented, followed by the nucleation of a melted region in the inner volume of the particle that grows until the particle melts as a whole. After melting, it is found that gold has a tendency to migrate to the surface, but the alloy remains in the whole volume of the nanoparticle.