Ru-Pt core-shell nanoparticles for preferential oxidation of carbon monoxide in hydrogen

Shape Changes in AuPd Alloy Nanoparticles Controlled by Anisotropic Surface Stress Relaxation

The shape of AuPd nanoparticles is engineered by surface stress relaxation, achieved by varying the Au content in nanoparticles of Pd-rich compositions. AuPd nanoparticles are grown in the gas phase for several compositions and growth conditions. Their structure is atomically resolved by HRTEM/STEM and EDX. In pure Pd distributions the dominant structures are FCC truncated octahedra (TO), while increasing the Au content there is a transition to icosahedral (Ih) structures in which Au atoms are preferentially placed at the nanoparticle surface. The transition is sharper for growth conditions closer to equilibrium. The physical origin of the transition is determined with the aid of computer simulations. Global optimization searches and free energy calculations confirm that Ih become the equilibrium structure for increasing the Au content. Atomic stress calculations demonstrate that the TO → Ih shape change is caused by a better relaxation of anisotropic surface stress in icosahedra.

Melting Behavior of Bimetallic and Trimetallic Nanoparticles: A Review of MD Simulation Studies

In recent years, bimetallic and trimetallic nanoparticles (NPs) have become attractive materials for many researchers especially in the field of catalysis due to their interesting physical and chemical properties. These unique properties arise mainly from simultaneous effects of two different metal atoms in their structure. In this review, recent theoretical studies on these NPs using molecular dynamics simulation are presented. Since investigation of thermodynamic stabilities of metallic NPs is a critical factor in their construction for catalytic applications, our focus in this review is on the thermal stability of bimetallic and trimetallic NPs. The melting behavior of these materials with different atomic arrangements including core-shell, three-shell, crown-jewel, ordered and disordered alloy, and Janus materials are discussed. Other factors including stress, strain, atomic radius, thermal expansion coefficient, cohesive energy, surface energy, size, composition, and morphology are described in detail, because these properties lead to complexity in the melting behavior of bimetallic and trimetallic NPs.

New-phase retention in colloidal core/shell nanocrystals via pressure-modulated phase engineering

Core/shell nanocrystals (NCs) integrate collaborative functionalization that would trigger advanced properties, such as high energy conversion efficiency, nonblinking emission, and spin-orbit coupling. Such prospects are highly correlated with the crystal structure of individual constituents. However, it is challenging to achieve novel phases in core/shell NCs, generally non-existing in bulk counterparts. Here, we present a fast and clean high-pressure approach to fabricate heterostructured core/shell MnSe/MnS NCs with a new phase that does not occur in their bulk counterparts. We determine the new phase as an orthorhombic MnP structure (B31 phase), with close-packed zigzagged arrangements within unit cells. Encapsulation of the solid MnSe nanorod with an MnS shell allows us to identify two separate phase transitions with recognizable diffraction patterns under high pressure, where the heterointerface effect regulates the wurtzite → rocksalt → B31 phase transitions of the core. First-principles calculations indicate that the B31 phase is thermodynamically stable under high pressure and can survive under ambient conditions owing to the synergistic effect of subtle enthalpy differences and large surface energy in nanomaterials. The ability to retain the new phase may open up the opportunity for future manipulation of electronic and magnetic properties in heterostructured nanostructures.

Bimetallic nanocatalysts supported on graphitic carbon nitride for sustainable energy development: the shape-structure-activity relation

The catalytic performance of metal nanoparticles (NPs), including activity, selectivity, and durability, depends on their shape and structure at the molecular level. Consequently, metal NPs of different size and shape, e.g., nanobelts, nanocubes, nanoflakes, and nanowires, demonstrate different reactivity and provide different reaction rates depending on the facet exposed. In this context, the present review aims to summarize the shape-structure-activity relation of metallic nanocatalysts. Moreover, keeping in mind that the application of noble metal catalysts is expensive, we would like to draw the reader's attention to bimetallic nanocatalysts supported on graphitic carbon nitride. One of the advantages of these systems is the possibility to minimize the use of noble metals by introducing another metal either to the parent NPs and/or modifying the support materials. The development and optimization of bimetallic nanocatalysts might provide the new class of materials with superior, tunable performance, thermal stability and reduced costs compared to presently available commercial catalysts. Therefore, further application of these bimetallic composites for sustainable development in energy, green chemicals/fuels and environmental protection will be discussed.

Bridging Structural Inhomogeneity to Functionality: Pair Distribution Function Methods for Functional Materials Development

The correlation between structure and function lies at the heart of materials science and engineering. Especially, modern functional materials usually contain inhomogeneities at an atomic level, endowing them with interesting properties regarding electrons, phonons, and magnetic moments. Over the past few decades, many of the key developments in functional materials have been driven by the rapid advances in short-range crystallographic techniques. Among them, pair distribution function (PDF) technique, capable of utilizing the entire Bragg and diffuse scattering signals, stands out as a powerful tool for detecting local structure away from average. With the advent of synchrotron X-rays, spallation neutrons, and advanced computing power, the PDF can quantitatively encode a local structure and in turn guide atomic-scale engineering in the functional materials. Here, the PDF investigations in a range of functional materials are reviewed, including ferroelectrics/thermoelectrics, colossal magnetoresistance (CMR) magnets, high-temperature superconductors (HTSC), quantum dots (QDs), nano-catalysts, and energy storage materials, where the links between functions and structural inhomogeneities are prominent. For each application, a brief description of the structure-function coupling will be given, followed by selected cases of PDF investigations. Before that, an overview of the theory, methodology, and unique power of the PDF method will be also presented.

Probing Kinetics and Mechanism of Formation of Mixed Metallic Nanoparticles in a Polymer Membrane by Galvanic Replacement between Two Immiscible Metals: Case Study of Nickel/Silver Nanoparticle Synthesis

Galvanic replacement between metals has received notable research interest for the synthesis of heterometallic nanostructures. The growth pattern of the nanostructures depends on several factors such as extent of lattice mismatch, adhesive interaction between the metals, cohesive forces of the individual metals, etc. Due to the difficulties in probing ultrafast kinetics of the galvanic replacement reaction and particle growth in solution, real-time mechanistic investigations are often limited. As a result, the growth mechanism of one metal on the surface of another metal at the nanoscale is poorly understood so far. In the present work, we could successfully probe the galvanic replacement of silver ions with nickel nanoparticles, stabilized in a polymer membrane, using two complementary methods, namely, small-angle X-ray scattering (SAXS) and radiolabeling, and the results are supported by density functional theory (DFT) computations. The silver-nickel system has been chosen for the present investigation because of the high degree of bulk immiscibility caused by the large lattice mismatch (15.9%) and the weak adhesive interaction, which makes it a perfect model system for immiscible metal pairs. Membrane, as a host medium, plays a crucial role in retarding the kinetics of atomic and particle rearrangements (nucleation and growth) due to slower mobility of the atoms (monomers) and particles within the polymer network. This allowed us to examine the real-time concentration of silver monomers during galvanic replacement of silver ions with nickel nanoparticles and evolution of Ni/Ag nanoparticles. From combined experiment and DFT computations, it has been demonstrated, for the first time to the best of our knowledge, that the majority of silver atoms, which are produced on the nickel nanoparticle surface by galvanic reactions, do not form traditional core-shell nanostructures with nickel and undergo a self-governing sequential nucleation and growth of silver nanoparticles via formation of intermediate prenucleation silver clusters, leading to the formation of mixed metallic nanoparticles in the membrane. The surface of NiNPs has a heterogeneous effect on the silver nucleation pathway, which is evident from the reduced critical free energy barrier of nucleation (ΔG_crit). The present work establishes an original mechanistic pathway based on a sequential nucleation model for formation of mixed metallic nanoparticles by the galvanic replacement route, which opens up future possibilities for size-controlled synthesis in mixed systems.

Roles of highly ordered mesoporous structures of Fe–Ni bimetal oxides for an enhanced high-temperature water-gas shift reaction activity

Highly ordered mesoporous Fe–Ni bimetal oxide (m-FeNi) catalysts synthesized using KIT-6 as a hard-template by a nanocasting method were investigated for an alternative high-temperature water-gas shift (HT-WGS) reaction.

Unravelling the cooperative role of lattice strain on MnO2/TiO2 and MnO2/ZnO catalysts for the fast decomposition of hydrogen peroxide

The rate of decomposition of hydrogen peroxide was directly correlated with lattice strain, as derived from strain calculations.

Hemin-based conjugated effect synthesis of Fe–N/CNT catalysts for enhanced oxygen reduction

Fe/N-codoped carbon nanotubes fabricated through the π–π stacking effect and olefin oxidation polymerization-induced hemin assembly on PPy shows a potential application for ORR.

Interplay between CO Disproportionation and Oxidation: On the Origin of the CO Reaction Onset on Atomic Layer Deposition-Grown Pt/ZrO2 Model Catalysts

Pt/ZrO₂ model catalysts were prepared by atomic layer deposition (ALD) and examined at mbar pressure by operando sum frequency generation (SFG) spectroscopy and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) combined with differentially pumped mass spectrometry (MS). ALD enables creating model systems ranging from Pt nanoparticles to bulk-like thin films. Polarization-dependent SFG of CO adsorption reveals both the adsorption configuration and the Pt particle morphology. By combining experimental data with ab initio density functional theory (DFT) calculations, we show that the CO reaction onset is determined by a delicate balance between CO disproportionation (Boudouard reaction) and oxidation. CO disproportionation occurs on low-coordinated Pt sites, but only at high CO coverages and when the remaining C atom is stabilized by a favorable coordination. Thus, under the current conditions, initial CO oxidation is found to be strongly influenced by the removal of carbon deposits formed through disproportionation mechanisms rather than being determined by the CO and oxygen inherent activity. Accordingly, at variance with the general expectation, rough Pt nanoparticles are seemingly less active than smoother Pt films. The applied approach enables bridging both the “materials and pressure gaps”.

Operando Surface Characterization on Catalytic and Energy Materials from Single Crystals to Nanoparticles

Modern surface science faces two major challenges, a materials gap and a pressure gap. While studies on single crystal surface in ultrahigh vacuum have uncovered the atomic and electronic structures of the surface, the materials and environmental conditions of commercial catalysis are much more complicated, both in the structure of the materials and in the accessible pressure range of analysis instruments. Model systems and operando surface techniques have been developed to bridge these gaps. In this Review, we highlight the current trends in the development of the surface characterization techniques and methodologies in more realistic environments, with emphasis on recent research efforts at the Korea Advanced Institute of Science and Technology. We show principles and applications of the microscopic and spectroscopic surface techniques at ambient pressure that were used for the characterization of atomic structure, electronic structure, charge transport, and the mechanical properties of catalytic and energy materials. Ambient pressure scanning tunneling microscopy and X-ray photoelectron spectroscopy allow us to observe the surface restructuring that occurs during oxidation, reduction, and catalytic processes. In addition, we introduce the ambient pressure atomic force microscopy that revealed the morphological, mechanical, and charge transport properties that occur during the catalytic and energy conversion processes. Hot electron detection enables the monitoring of catalytic reactions and electronic excitations on the surface. Overall, the information on the nature of catalytic reactions obtained with operando spectroscopic and microscopic techniques may bring breakthroughs in some of the global energy and environmental problems the world is facing.

Nanocrystals of platinum-group metals as peroxidase mimics for in vitro diagnostics

Peroxidase mimics of nanoscale materials as alternatives to natural peroxidases have found widespread uses in biomedicine. Among various types of peroxidase mimics, platinum-group metal (PGM) nanocrystals have drawn considerable attention in recent years due to their superior properties. Particularly, PGM nanocrystals display high catalytic efficiencies, allow for facile surface modifications, and possess excellent stabilities. This feature article summarizes our recent work on development of PGM nanocrystals as peroxidase mimics and exploration of their applications in in vitro diagnostics. We begin with a brief introduction to controlled synthesis of PGM nanocrystals in solution phase. We then elaborate on a variety of physicochemical parameters that can be carefully tuned to optimize the peroxidase-like properties of PGM nanocrystals. Then, we highlight the applications of PGM nanocrystals in different in vitro diagnostic platforms. We conclude this article with personal perspectives on future research directions in this emerging field, where challenges and opportunities are remarked.

Synthesis of Quasi-Bilayer Subnano Metal-Oxide Interfacial Cluster Catalysts for Advanced Catalysis

Planar metal clusters possess high metal utilization, distinct electronic properties, and catalytic functions from their 3D counterparts. However, synthesis of these materials is challenging due to much elevated surface free energies. Here it is reported that silica supported planar bilayer Pt-CoO_x subnano clusters, consisting of approximately one atomic layer of Pt and one CoO_x layer on top, can be achieved by employing strong-electrostatic interactions during impregnation and precisely-controlled CoO_x coating using atomic layer deposition. Such bilayer structure is unambiguously confirmed by electron microscopy and in situ X-ray absorption fine spectroscopy which is never reported before. This synthetic approach can be extended to another eight permutations of planar metal-oxide subnano clusters. The resulting bilayer catalysts, owing to unique electronic properties and the abundant metal-oxide interfaces created, exhibit excellent catalytic performances in the reactions of preferential oxidation of CO in H₂ and selective hydrogenation of acetylene, by showing much higher selectivity and intrinsic activities at least 8 and 48 times greater than those conventional oxide coated 3D metal clusters/nanoparticles, highlighting the advances of bilayer interfacial structure. These findings open a new avenue to design abundant and highly active metal-oxide interfaces for advanced metal catalysis.

Biomimetic Au/CeO2 Catalysts Decorated with Hemin or Ferrous Phthalocyanine for Improved CO Oxidation via Local Synergistic Effects

Biomimetic catalysts have drawn broad research interest owing to both high specificity and excellent catalytic activity. Herein, we report a series of biomimetic catalysts by the integration of biomolecules (hemin or ferrous phthalocyanine) onto well-defined Au/CeO₂, which leads to the high-performance CO oxidation catalysts. Strong electronic interactions among the biomolecule, Au, and CeO₂ were confirmed, and the CO uptake over hemin-Au/CeO₂ was roughly about 8 times greater than Au/CeO₂. Based on the Au/CeO₂(111) and hemin-Au/CeO₂(111) models, the density functional theory calculations reveal the mechanisms of the biomolecules-assisted catalysis process. The theoretical prediction suggests that CO and O₂ molecules preferentially bind to the surface of noncontacting Au atoms (low-coordinated sites) rather than the biomolecule sites, and the accelerating oxidation of Au-bound CO occurs via either the Langmuir-Hinshelwood mechanism or the Mars-van Krevelen mechanism. Accordingly, the findings provide useful insights into developing biomimetic catalysts with low cost and high activity.

Large area Al2O3-Au raspberry-like nanoclusters from iterative block-copolymer self-assembly

In the field of functional nanomaterials, core-satellite nanoclusters have recently elicited great interest due to their unique optoelectronic properties. However, core-satellite synthetic routes to date are hampered by delicate and multistep reaction conditions and no practical method has been reported for the ordering of these structures onto a surface monolayer. Herein we show a reproducible and simplified thin film process to fabricate bimetallic raspberry nanoclusters using block copolymer (BCP) lithography. The fabricated inorganic raspberry nanoclusters consisted of a ∼36 nm alumina core decorated with ∼15 nm Au satellites after infusing multilayer BCP nanopatterns. A series of cylindrical BCPs with different molecular weights allowed us to dial in specific nanodot periodicities (from 30 to 80 nm). Highly ordered BCP nanopatterns were then selectively infiltrated with alumina and Au species to develop multi-level bimetallic raspberry features. Microscopy and X-ray reflectivity analysis were used at each fabrication step to gain further mechanistic insights and understand the infiltration process. Furthermore, grazing-incidence small-angle X-ray scattering studies of infiltrated films confirmed the excellent order and vertical orientation over wafer scale areas of Al2O3/Au raspberry nanoclusters. We believe our work demonstrates a robust strategy towards designing hybrid nanoclusters since BCP blocks can be infiltrated with various low cost salt-based precursors. The highly controlled nanocluster strategy disclosed here could have wide ranging uses, in particular for metasurface and optical based sensor applications.

Ambient Temperature CO Oxidation Using Palladium–Platinum Bimetallic Catalysts Supported on Tin Oxide/Alumina

A series of Pt-based catalysts were synthesised and investigated for ambient temperature CO oxidation with the aim to increase catalytic activity and improve moisture resistance through support modification. Initially, bimetallic PtPd catalysts supported on alumina were found to exhibit superior catalytic activity compared with their monometallic counterparts for the reaction. Following an investigation into the effect of Pt/Pd ratio, a composition of 0.1% Pt/0.4% Pd was selected for further studies. Following this, SnO2/Al2O3 supports were synthesised from a variety of tin oxide sources. Catalytic activity was improved using sodium stannate and tin oxalate precursors compared with a traditional tin oxide slurry. Catalytic activity versus tin concentration was found to vary significantly across the three precursors, which was subsequently investigated by X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX).

Ultra-Fine CeO2 Particles Triggered Strong Interaction with LaFeO3 Framework for Total and Preferential CO Oxidation

Interactions between the active components with the support are one of the fundamentally factors in determining the catalytic performance of a catalyst. In contrast to the comprehensive understanding on the strong metal-support interactions (SMSI) in metal-based catalysts, it remains unclear for the interactions among different oxides in mixed oxide catalysts due to its complexity. In this study, we investigated the interaction between CeO₂ and LaFeO₃, the two important oxygen storage materials in catalysis area, by tuning the sizes of CeO₂ particles and highlight a two-fold effect of the strong oxide-oxide interaction in determining the catalytic activity and selectivity for preferential CO oxidation in hydrogen feeds. It is found that the anchoring of ultra-fine CeO₂ particles (<2 nm) at the framework of three-dimensional-ordered macroporous LaFeO₃ surface results in a strong interaction between the two oxides that induces the formation of abundant uncoordinated cations and oxygen vacancy at the interface, contributing to the improved oxygen mobility and catalytic activity for CO oxidation. Hydrogen spillover, which is an important evidence of the strong metal-support interactions in precious metal catalysts supported by reducible oxides, is also observed in the H₂ reduction process of CeO₂/LaFeO₃ catalyst due to the presence of ultra-fine CeO₂ particles (<2 nm). However, the strong interaction also results in the formation of surface hydroxyl groups, which when combined with the hydrogen spillover reduces the selectivity for preferential CO oxidation. This discovery demonstrates that in hybrid oxide-based catalysts, tuning the interaction among different components is essential for balancing the catalytic activity and selectivity.

Probing the Microstructure in Pure Al & Cu Melts: Theory Meets Experiment

In the present work, a new model of the atomic cluster structure, which is determined by metal Wulff construction with the crystal structure inside, is proposed to describe the structures of metallic melts. The shapes of the structures are determined by surface energies of different crystal plane groups, calculated from density functional theory (DFT), while the size is given by the pair distribution function (PDF) of the experimental high-temperature X-ray diffraction (HTXRD). Taking Aluminum (Al) and Copper (Cu) as the representative examples, we demonstrate that the simulated XRD curves from present models match the experimental results quite well, not only regarding the position and width of the peaks but also the relative intensity of the first and second peaks. These results indicate a successful model to describe the properties of metallic melts. The model also explains a main peak deviation phenomenon between the XRD of metallic melt and the solid ones in pure metal Al. Finally, a physical picture of metallic melt is given, which is mainly composed of atomic cluster structures and free atoms around them.

Au Nanoparticles Modified with Pt, Ru and SnO2 as Electrocatalysts for Ethanol Oxidation Reaction in Acids

The anodic reaction in direct ethanol fuel cells (DEFCs), ethanol oxidation reaction (EOR) faces challenges, such as incomplete electrooxidation of ethanol and high cost of the most efficient electrocatalyst, Pt in acidic media at low temperature. In this study, core-shell electrocatalysts with an Au core and Pt-based shell (Au@Pt) are developed. The Au core size and Pt shell thickness play an important role in the EOR activity. The Au size of 2.8 nm and one layer of Pt provide the most optimized performance, having 6 times higher peak current density in contrast to commercial Pt/C. SnO₂ as a support also enhances the EOR activity of Au@Pt by 1.73 times. Further modifying the Pt shell with Ru atoms achieve the highest EOR current density that is 15 and 2.5 times of Pt/C and Au@Pt. Our results suggest the importance of surface modification in rational design of advanced electrocatalysts.

Facile Direct Seed-Mediated Growth of AuPt Bimetallic Shell on the Surface of Pd Nanocubes and Application for Direct H2O2 Synthesis

The selective enhancement of catalytic activity is a challenging task, as catalyst modification is generally accompanied by both desirable and undesirable properties. For example, in the case of the direct synthesis of hydrogen peroxide, Pt on Pd improves hydrogen conversion, but lowers hydrogen peroxide selectivity, whereas Au on Pd enhances hydrogen peroxide selectivity but decreases hydrogen conversion. Toward an ideal catalytic property, the development of a catalyst that is capable of improving H-H dissociation for increasing H2 conversion, whilst suppressing O-O dissociation for high H2O2 selectivity would be highly beneficial. Pd-core AuPt-bimetallic shell nanoparticles with a nano-sized bimetallic layer composed of Au-rich or Pt-rich content with Pd cubes were readily prepared via the direct seed-mediated growth method. In the Pd-core AuPt-bimetallic shell nanoparticles, Au was predominantly located on the {100} facets of the Pd nanocubes, whereas Pt was deposited on the corners of the Pd nanocubes. The evaluation of Pd-core AuPt-bimetallic shell nanoparticles with varying Au and Pt contents revealed that Pd-core AuPt-bimetallic shell that was composed of 2.5 mol% Au and 5 mol% Pt, in relation to Pd, exhibited the highest H2O2 production rate (914 mmol H2O2 gmetal−1 h−1), due to the improvement of both H2O2 selectivity and H2 conversion.

High-loading single Pt atom sites [Pt-O(OH) x ] catalyze the CO PROX reaction with high activity and selectivity at mild conditions

The preferential oxidation of CO (PROX) in hydrogen-rich fuel gas streams is an attractive option to remove CO while effectively conserving energy and H2. However, high CO conversion with concomitant high selectivity to CO2 but not H2O is challenging. Here, we report the synthesis of high-loading single Pt atom (2.0 weight %) catalysts with oxygen-bonded alkaline ions that stabilize the cationic Pt. The synthesis is performed in aqueous solution and achieves high Pt atom loadings in a single-step incipient wetness impregnation of alumina or silica. Promisingly, these catalysts have high CO PROX selectivity even at high CO conversion (~99.8% conversion, 70% selectivity at 110°C) and good stability under reaction conditions. These findings pave the way for the design of highly efficient single-atom catalysts, elucidate the role of ─OH species in CO oxidation, and confirm the absence of a support effect for our case.

Bimetallic and postsynthetically alloyed PtCu nanostructures with tunable reactivity for the methanol oxidation reaction

Designing effective catalysts by controlling morphology and structure is key to improving the energy efficiency of fuel cells. A good understanding of the effects of specific structures on electrocatalytic activity, selectivity, and stability is needed. Here, we propose a facile method to synthesize PtCu bimetallic nanostructures with controllable compositions by using Cu nanowires as a template and ascorbic acid as a reductant. A further annealing process provided the alloy PtCu with tunable crystal structures. The combination of distinct structures with tunable compositions in the form of PtCu nanowires provides plenty of information for better understanding the reaction mechanism during catalysis. HClO₄ cyclic voltammetry (CV) tests confirmed that various phase transformations occurred in bimetallic and alloy samples, affecting morphology and unit cell structures. Under a bifunctional synergistic effect and the influence of the insertion of a second metal, the two series of structures show superior performance toward methanol electrooxidation. Typically, the post-product alloy A-Pt₁₄Cu₈₆ with a cubic structure (a = 3.702 Å) has better methanol oxidation reaction (MOR) catalysis performance. Density functional theory (DFT) calculations were performed to determine an optimal pathway using the Gibbs free energy and to verify the dependence of the electrocatalytic performance on the lattice structure via overpotential changes. Bimetallic PtCu has high CO tolerance, maintaining high stability. This work provides an approach for the systematic design of novel catalysts and the exploration of electrocatalytic mechanisms for fuel cells and other related applications.

Ethanol Electrooxidation at Platinum-Rare Earth (RE = Ce, Sm, Ho, Dy) Binary Alloys

Proton exchange membrane fuel cells and direct alcohol fuel cells have been extensively studied over the last three decades or so. They have emerged as potential systems to power portable applications, providing clean energy, and offering good commercial viability. Ethanol is considered one of the most interesting fuels in this field. Herein, platinum-rare earth (Pt-RE) binary alloys (RE = Ce, Sm, Ho, Dy, nominal composition 50 at.% Pt) were produced and studied as anodes for ethanol oxidation reaction (EOR) in alkaline medium. A Pt-Dy alloy with nominal composition 40 at.% Pt was also tested. Their electrocatalytic performance was evaluated by voltammetric and chronoamperometric measurements in 2 M NaOH solution with different ethanol concentrations (0.2–0.8 M) in the 25–45 °C temperature range. Several EOR kinetic parameters were determined for the Pt-RE alloys, namely the charge transfer and diffusion coefficients, and the number of exchanged electrons. Charge transfer coefficients ranging from 0.60 to 0.69 and n values as high as 0.7 were obtained for the Pt0.5Sm0.5 electrode. The EOR reaction order at the Pt-RE alloys was found to vary between 0.4 and 0.9. The Pt-RE electrodes displayed superior performance for EOR than bare Pt, with Pt0.5Sm0.5 exhibiting the highest electrocatalytic activity. The improved electrocatalytic activity in all of the evaluated Pt-RE binary alloys suggests a strategy for the solution of the existing anode issues due to the structure-sensitive EOR.

SO2 Electrocatalytic Oxidation Properties of Pt-Ru/C Bimetallic Catalysts with Different Nanostructures

Electrocatalytic oxidation of SO₂ has been applied in many fields, and electrocatalyst is the focus of the research. Platinum-based electrocatalysts are the hot spot in this reaction. Although the properties of these materials have been optimized to a certain extent, there is still room for improvement in activity and long-term durability. In light of this, two kinds of carbon-supported Pt-Ru bimetallic electrocatalysts (PtRu/C alloy catalyst and Ru@Pt/C core-shell catalyst) were prepared by the microwave reduction method. The experiments demonstrate that the enhancement in the activity of bimetallic catalysts originates from the electronic effect and bifunctional effect between Pt and Ru. Bimetallic catalyst contains a large number of RuO_xH_y, which promotes the reaction. Because of the high Pt utilization, Ru@Pt/C catalyst with the Pt shell has a higher performance than alloy catalyst. The unit Pt mass activity of PtRu/C and Ru@Pt/C is 1.73 and 2.43 times that of Pt/C, respectively. Ru@Pt/C exhibits excellent stability in the high acid environment and is a promising SO₂ electrocatalyst.

Predicting metal-metal interactions. I. The influence of strain on nanoparticle and metal adlayer stabilities

Strain-engineering of bimetallic nanomaterials is an important design strategy for developing new catalysts. Herein, we introduce an approach for including strain effects into a recently introduced, density functional theory (DFT)-based alloy stability model. The model predicts adsorption site stabilities in nanoparticles and connects these site stabilities with catalytic reactivity and selectivity. Strain-based dependencies will increase the model's accuracy for nanoparticles affected by finite-size effects. In addition to the stability of small nanoparticles, strain also influences the heat of adsorption of epitaxially grown metal-on-metal adlayers. In this respect, we successfully benchmark the strain-including alloy stability model with previous experimentally determined trends in the heats of adsorption of Au and Cu adlayers on Pt (111). For these systems, our model predicts stronger bimetallic interactions in the first monolayer than monometallic interactions in the second monolayer. We explicitly quantify the interplay between destabilizing strain effects and the energy gained by forming new metal-metal bonds. While tensile strain in the first Cu monolayer significantly destabilizes the adsorption strength, compressive strain in the first Au monolayer has a minimal impact on the heat of adsorption. Hence, this study introduces and, by comparison with previous experiments, validates an efficient DFT-based approach for strain-engineering the stability, and, in turn, the catalytic performance, of active sites in bimetallic alloys with atomic level resolution.

Engineering stable electrocatalysts by synergistic stabilization between carbide cores and Pt shells

Core-shell particles with earth-abundant cores represent an effective design strategy for improving the performance of noble metal catalysts, while simultaneously reducing the content of expensive noble metals^1-4. However, the structural and catalytic stabilities of these materials often suffer during the harsh conditions encountered in important reactions, such as the oxygen reduction reaction (ORR)^3-5. Here, we demonstrate that atomically thin Pt shells stabilize titanium tungsten carbide cores, even at highly oxidizing potentials. In situ, time-resolved experiments showed how the Pt coating protects the normally labile core against oxidation and dissolution, and detailed microscopy studies revealed the dynamics of partially and fully coated core-shell nanoparticles during potential cycling. Particles with complete Pt coverage precisely maintained their core-shell structure and atomic composition during accelerated electrochemical ageing studies consisting of over 10,000 potential cycles. The exceptional durability of fully coated materials highlights the potential of core-shell architectures using earth-abundant transition metal carbide (TMC) and nitride (TMN) cores for future catalytic applications.

High-Performance Pt Catalyst with Graphene/Carbon Black as a Hybrid Support for SO2 Electrocatalytic Oxidation

In the electrochemical Bunsen reaction, which is the key reaction of the sulfur-iodide cycle, the main overpotential corresponds to the oxidation of SO₂. The catalysts currently used for the liquid phase electrocatalytic oxidation of SO₂ are mainly based on noble metals, which have excellent corrosion resistance and catalytic activity in an acidic environment. To improve the performance of the commercial Pt catalyst, a Pt catalyst with reduced graphene oxide (RGO) and carbon black as a hybrid support was synthesized by the microwave-assisted polyol reduction process. The large two-dimensional planar structure of RGO was a better anchor for Pt nanoparticles, and a catalyst with fine and uniform distribution of Pt particles was obtained. The carbon black interior prevented the agglomeration of RGO, forming a stereoscopic catalyst structure. The electrochemical test results showed that the RGO/carbon black hybrid support catalyst possessed a higher electrocatalytic activity than the single support catalysts and could be used as an efficient and stable catalyst for the SO₂ electrolyzer.

Two-Dimensional Electrocatalysts for Efficient Reduction of Carbon Dioxide

Two-dimensional (2D) materials are attractive catalysts for the electrochemical reduction of carbon dioxide reaction (eCO₂ RR) by virtue of their tunable atomic structures, abundant active sites, enhanced conductivity, suitable binding affinity to carbon dioxide and/or reaction intermediates, and intrinsic scalability. Herein, recent advances in 2D catalysts for the eCO₂ RR are reviewed. Structural features and properties of 2D materials that contribute to their advanced electrocatalytic properties are summarized, and strategies for enhancing their activity and selectivity for the eCO₂ RR are reviewed. Prospects and challenges of applications of 2D catalysts for the eCO₂ RR on an industrial scale are highlighted.

Resource utilization of waste V2O5-based deNOx catalysts for hydrogen production from formaldehyde and water via steam reforming

The harmless disposal of abandoned and toxic V₂O₅(WO₃)/TiO₂ (VWT) deNO_x catalysts has become a worldwide great demand, a new resource path for hydrogen production from steam reforming of formaldehyde and water using the waste VWT deNOx catalysts as catalyst carriers was proposed. The waste V₂O₅-based catalysts supported NiO (N/VWT) catalysts prepared by impregnation method were comparatively studied for hydrogen production. The H₂ and CO selectivity of the optimum N/VWT separately reached 100% and 72.5%, and the formaldehyde conversion of the N/VWT reached 86.3% at 400 ℃ and higher than 93.0% at 450-600 ℃. Analysis showed that the hydroxyl species played the most important role, and its richness determined the catalytic performance directly. The high acid sites and excellent redox properties were beneficial to enhance the catalytic performance. The in situ DRIFT study verified that the hydrogen bonds between formate species and hydroxyl groups reduced reaction steps, which accelerated the progress of the reaction. The adsorbed formaldehyde transformed to formate species firstly, and then produced H₂ and CO₂ (or CO) by dehydrogenation. Ultimately, the resource utilization path not only completely solved the harmless problems of the waste V₂O₅-based deNO_x catalysts and formaldehyde, but also contributed to the hydrogen production.

Selective oxidation of crotyl alcohol by AuxPd bimetallic pseudo-single-atom catalysts

Pseudo single-atom Pd catalysts dispersed in gold nanoparticle matrices show high selectivity and activity for room temperature crotyl alcohol oxidation.

Colloidal bimetallic platinum–ruthenium nanoparticles in ordered mesoporous carbon films as highly active electrocatalysts for the hydrogen evolution reaction

Ordered mesoporous carbon films with high surface area, good electrical conductivity and an improved distribution of NPs with tunable composition show high electrocatalytic activity in HER.

Toward a comparative description between transition metal and zeolite catalysts for methanol conversion

A general description for zeolites and transition metal catalysts has been established for methanol conversion.

Single-atom Pt supported on holey ultrathin g-C3N4 nanosheets as efficient catalyst for Li-O2 batteries

As for electrocatalysis, single-atom metal catalysts have been proved to lower the cost and utilize precious metals more efficiently. Herein, single-atom Pt catalyst supported on holey ultrathin g-C₃N₄ nanosheets (Pt-CNHS) was synthesized via a facile liquid-phase reaction of g-C₃N₄ and H₂PtCl₆. The single-atom Pt can achieve high dispersibility and stability, which can promote the utilization efficiency as well as enhance the electrochemical activity. When employed as Li-O₂ batteries' cathode catalyst, Pt-CNHS exhibits excellent electrocatalytic activity. Li-O₂ batteries utilizing Pt-CNHS show much higher discharge specific capacities than those with pure CNHS. Li-O₂ batteries with Pt-CNHS cathode can be cycled stably for 100 times under the discharge capacity of 600 mAh g^-1. Based on experimental results and density functional theory calculations, the superior electrocatalytic activity of Pt-CNHS can be ascribed to the large surface area, the enhanced electrical conductivity and the efficient interfacial mass transfer through Pt atoms and porous structure of CNHS.