Nanocatalyst Superior to Pt for Oxygen Reduction Reactions: The Case of Core/Shell Ag(Au)/CuPd Nanoparticles

Discovering High Entropy Alloy Electrocatalysts in Vast Composition Spaces with Multiobjective Optimization

High entropy alloys (HEAs) are a highly promising class of materials for electrocatalysis as their unique active site distributions break the scaling relations that limit the activity of conventional transition metal catalysts. Existing Bayesian optimization (BO)-based virtual screening approaches focus on catalytic activity as the sole objective and correspondingly tend to identify promising materials that are unlikely to be entropically stabilized. Here, we overcome this limitation with a multiobjective BO framework for HEAs that simultaneously targets activity, cost-effectiveness, and entropic stabilization. With diversity-guided batch selection further boosting its data efficiency, the framework readily identifies numerous promising candidates for the oxygen reduction reaction that strike the balance between all three objectives in hitherto unchartered HEA design spaces comprising up to 10 elements.

One-pot Construction of Metal Nanoparticles Loaded COF Catalysts for Aqueous Hydrogenation Reactions

The catalysis performance of metal nanoparticles (NPs) will be significantly deteriorated because of their spontaneous agglomeration during practical applications. Covalent-organic frameworks (COFs) materials with functional groups and well-defined channels benefit for the dispersion and anchor of metal ions and the confined growth of metal NPs, working as an ideal platform to compose catalytic systems. In this article, we report a one-pot strategy for the preparation of metal NPs loaded COFs without the need of post-modification. During the polymerization process, the pre-added metal ions were stabilized by the rapidly formed COF oligomers and hardly disturb the construction of COFs. After reduction, metal NPs are uniformly anchored on the COF matrix. Eventually, a wide spectrum of metal NPs, including Au, Pd, Pt, AuPd, CuPd, CuPt and CuPdPt, loaded COFs are successfully prepared. The versatility and metal ions anchoring mechanism are verified with four different COF matrixes. Taking AuPd NPs as example, the resultant AuPd NPs loaded COF materials can selectively decompose ammonium formate and produce hydrogen in-situ, exhibiting over 99 % conversion of hydrodechlorination for chlorobenzenes and nitro-reduction reaction for nitroaromatic compounds under ambient temperature in aqueous solution.

Intermetallic Nanocrystals for Fuel-Cells-Based Electrocatalysis

Electrocatalysis underpins the renewable electrochemical conversions for sustainability, which further replies on metallic nanocrystals as vital electrocatalysts. Intermetallic nanocrystals have been known to show distinct properties compared to their disordered counterparts, and been long explored for functional improvements. Tremendous progresses have been made in the past few years, with notable trend of more precise engineering down to an atomic level and the investigation transferring into more practical membrane electrode assembly (MEA), which motivates this timely review. After addressing the basic thermodynamic and kinetic fundamentals, we discuss classic and latest synthetic strategies that enable not only the formation of intermetallic phase but also the rational control of other catalysis-determinant structural parameters, such as size and morphology. We also demonstrate the emerging intermetallic nanomaterials for potentially further advancement in energy electrocatalysis. Then, we discuss the state-of-the-art characterizations and representative intermetallic electrocatalysts with emphasis on oxygen reduction reaction evaluated in a MEA setup. We summarize this review by laying out existing challenges and offering perspective on future research directions toward practicing intermetallic electrocatalysts for energy conversions.

Photoelectrocatalytic oxidation of ethylene glycol on trimetallic PdAgCu nanospheres enhanced by surface plasmon resonance

The notable surface plasmon resonance (SPR) effect of some metals has been applied to improve the efficiency of alcohol oxidation reactions, whereas the comprehensive investigation of Cu-assisted photoelectrocatalysis remains challenging. We herein successfully prepared trimetallic PdAgCu nanospheres (NSs) with abundant surface bulges for the advanced ethylene glycol oxidation reaction (EGOR) and compared them with bimetallic PdAg NSs to investigate the performance enhancement mechanism. Impressively, the as-optimized PdAgCu NSs exhibited superb mass activity and electrochemical stability. Moreover, under visible light illumination, the mass activity of PdAgCu NSs increased to 1.62 times compared to that in the dark, and in contrast, the mass activity of PdAg NSs only increased to 1.48 times that in the dark. A mechanistic study indicated that the incorporation of Cu not only strengthens the whole SPR effect of PdAgCu NSs but also further modifies the electronic structure of Pd. This work highlighted that the incorporation of Cu into PdAg NSs further enhanced the photoelectrocatalytic performance and increased noble metal atom utilization, which may provide guidance to fabricate novel and promising nanocatalysts in the field of photoelectrocatalysis.

Ultrathin PdCu Nanosheet as Bifunctional Electrocatalysts for Formate Oxidation Reaction and Oxygen Reduction Reaction

The development of robust nonplatinum electrocatalysts to enhance the performance of formate oxidation reaction (FOR) and oxygen reduction reaction (ORR) is one of the key issues for the commercialization of direct formate fuel cells (DFFCs), but still challenging. Herein, a structurally controlled 3D flower-like PdCu nanosheet (NS) catalyst is synthesized by a method of oil bath reduction under mild conditions as a bifunctional electrocatalyst for DFFCs. Under the dual tuning on the composition and intermetallic phase, the PdCu nanosheet catalyst exhibits 8.67 times higher mass activity for anodic formate oxidation reaction than the commercial Pd/C. For the cathodic ORR, a positive shift half-wave potential is obtained for PdCu nanosheets exceeding Pt/C. Moreover, after a long-term stability test, the current density of the PdCu nanosheet catalyst for FOR and ORR can be well maintained with the least activity decay. When the PdCu NSs are used as optimized anode and cathode electrodes for DFFCs enable a peak power density as high as 53 mW cm^-2 at room temperature, which is about 1.3 times higher than that of the commercial Pd/C and Pt/C as anode and cathode electrodes. This work provides a potential strategy to improve the catalytic performance of non-Pt-based nanocatalysts.

Designing Sites in Heterogeneous Catalysis: Are We Reaching Selectivities Competitive With Those of Homogeneous Catalysts?

A critical review of different prominent nanotechnologies adapted to catalysis is provided, with focus on how they contribute to the improvement of selectivity in heterogeneous catalysis. Ways to modify catalytic sites range from the use of the reversible or irreversible adsorption of molecular modifiers to the immobilization or tethering of homogeneous catalysts and the development of well-defined catalytic sites on solid surfaces. The latter covers methods for the dispersion of single-atom sites within solid supports as well as the use of complex nanostructures, and it includes the post-modification of materials via processes such as silylation and atomic layer deposition. All these methodologies exhibit both advantages and limitations, but all offer new avenues for the design of catalysts for specific applications. Because of the high cost of most nanotechnologies and the fact that the resulting materials may exhibit limited thermal or chemical stability, they may be best aimed at improving the selective synthesis of high value-added chemicals, to be incorporated in organic synthesis schemes, but other applications are being explored as well to address problems in energy production, for instance, and to design greener chemical processes. The details of each of these approaches are discussed, and representative examples are provided. We conclude with some general remarks on the future of this field.

Quantitative Characterization of the Thermally Driven Alloying State in Ternary Ir-Pd-Ru Nanoparticles

Compositional and structural arrangements of constituent elements, especially those at the surface and near-surface layers, are known to greatly influence the catalytic performance of alloyed nanoparticles (NPs). Although much research effort often focuses on the ability to tailor these important aspects in the design stage, their stability under realistic operating conditions remains a major technical challenge. Here, the compositional stability and associated structural evolution of a ternary iridium-palladium-ruthenium (Ir-Pd-Ru) nanoalloy at elevated temperatures have been studied using interrupted in situ scanning transmission electron microscopy and theoretical modeling. The results are based on a combinatory approach of statistical sampling at the sub-nanometer scale for large groups of NPs as well as tracking individual NPs. We find that the solid solution Ir-Pd-Ru NPs (∼5.6 nm) evolved into a Pd-enriched shell supported on an alloyed Ir-Ru-rich core, most notably when the temperature exceeds 500 °C, concurrently with the development of expansive atomic strain in the outer surface and subsurface layers with respect to the core regions. Theoretically, we identify the weak interatomic bonds, low surface energy, and large atomic sizes associated with Pd as the key factors responsible for such observed features.

Noble Metal-Based Multimetallic Nanoparticles for Electrocatalytic Applications

Noble metal-based multimetallic nanoparticles (NMMNs) have attracted great attention for their multifunctional and synergistic effects, which offer numerous catalytic applications. Combined experimental and theoretical studies have enabled formulation of various design principles for tuning the electrocatalytic performance through controlling size, composition, morphology, and crystal structure of the nanoparticles. Despite significant advancements in the field, the chemical synthesis of NMMNs with ideal characteristics for catalysis, including high activity, stability, product-selectivity, and scalability is still challenging. This review provides an overview on structure-based classification and the general synthesis of NMMN electrocatalysts. Furthermore, postsynthetic treatments, such as the removal of surfactants to optimize the activity, and utilization of NMMNs onto suitable support for practical electrocatalytic applications are highlighted. In the end, future direction and challenges associated with the electrocatalysis of NMMNs are covered.

Interfacial Engineering of Metal/Metal Oxide Heterojunctions toward Oxygen Reduction and Evolution Reactions

Oxygen reduction reactions (ORR) and oxygen evolution reactions (OER) are two very important electrochemical processes for renewable energy conversion and storage devices. Electrocatalysts are needed to accelerate their sluggish kinetics to improve energy conversion efficiencies. Hence, extensive efforts have been devoted to the development of OER and ORR electrocatalysts with high activity and stability as well as low cost. Among these developed electrocatalysts, metal/metal oxide heterostructures attract a great deal of research interest because their catalytic performances can be tuned by interface engineering. In this Review, the latest achievements in interface engineering of metal/metal oxides heterostructures toward ORR and OER are described. The effects of the metal/metal oxide interface on catalysis are first discussed. Then, the approaches for interface engineering are illustrated. The developments of interface engineering in OER and ORR catalysis as well as bifunctional electrocatalysis are further introduced. Lastly, a perspective for future development of interface engineering in metal/metal oxide for OER and ORR is discussed.

Electronic and lattice strain dual tailoring for boosting Pd electrocatalysis in oxygen reduction reaction

Deliberately optimizing the d-band position of an active component via electronic and lattice strain tuning is an effective way to boost its catalytic performance. We herein demonstrate this concept by constructing core-shell Au@NiPd nanoparticles with NiPd alloy shells of only three atomic layers through combining an Au catalysis with the galvanic replacement reaction. The Au core with larger electronegativity modulates the Pd electronic configuration, while the Ni atoms alloyed in the ultrathin shells neutralize the lattice stretching in Pd shells exerted by Au cores, equipping the active Pd metal with a favorable d-band position for electrochemical oxygen reduction reaction in an alkaline medium, for which core-shell Au@NiPd nanoparticles with a Ni/Pd atomic ratio of 3/7 exhibit a half-wave potential of 0.92 V, specific activity of 3.7 mA cm^-2, and mass activity of 0.65 A mg^-1 at 0.9 V, much better than most of the recently reported Pd-even Pt-based electrocatalysts.

Integrating Pt16 Te Nanotroughs and Nanopillars into a 3D "Self-Supported" Hierarchical Nanostructure for Boosting Methanol Electrooxidation

To develop durable and low-price catalysts of methanol oxidation to commercialize direct methanol fuel cell, many attempts have been made at fabricating Pt-based hybrids by designing component-, morphology-, facet-, integration-pattern-varied nanostructures, and have achieved considerable successes. However, most of present catalysts still lack robust catalytic durability especially owing to the corrosion of mixed carbon and the poor mechanical stability of catalyst layer. Herein, Te nanowire array is transformed at an air/water interface into a 3D Pt₁₆ Te hierarchical nanostructure via an interface-confined galvanic replacement reaction. As-formed Pt₁₆ Te nanostructure has an asymmetrical architecture composed of nanotroughs and nanopillars, and nanopillars are perpendicular to nanotroughs with a loose arrangement. Pt₁₆ Te hierarchical nanostructure has a "self-supported" feature and, when directly used as the catalyst of methanol electrooxidation, exhibits superior catalytic activity (>four times larger in mass activity than state-of-the-art Pt/C in either acidic or basic solution) and long-term durability (after 500 cycles of cyclic voltammetric measurement, more than 55% of the initial specific activity remains whereas Pt/C only remains 22.2% in acidic solution and almost loses all activity in basic solution). This study fully demonstrates that designing "self-supported" catalyst film may be the next promising step for improving the catalytic performance of Pt-based hybrids.

Metal-Based Electrocatalysts for Methanol Electro-Oxidation: Progress, Opportunities, and Challenges

Direct methanol fuel cells (DMFCs) are among the most promising portable power supplies because of their unique advantages, including high energy density/mobility of liquid fuels, low working temperature, and low emission of pollutants. Various metal-based anode catalysts have been extensively studied and utilized for the essential methanol oxidation reaction (MOR) due to their superior electrocatalytic performance. At present, especially with the rapid advance of nanotechnology, enormous efforts have been exerted to further enhance the catalytic performance and minimize the use of precious metals. Constructing multicomponent metal-based nanocatalysts with precisely designed structures can achieve this goal by providing highly tunable compositional and structural characteristics, which is promising for the modification and optimization of their related electrochemical properties. The recent advances of metal-based electrocatalytic materials with rationally designed nanostructures and chemistries for MOR in DMFCs are highlighted and summarized herein. The effects of the well-defined nanoarchitectures on the improved electrochemical properties of the catalysts are illustrated. Finally, conclusive perspectives are provided on the opportunities and challenges for further refining the nanostructure of metal-based catalysts and improving electrocatalytic performance, as well as the commercial viability.

A theoretical investigation of 38-atom CuPd clusters: the effect of potential parameterisation on structure and segregation

Understanding the structure of bimetallic clusters is increasingly important due to their emerging practical applications. Herein we investigate the structure of 38-atom CuPd clusters using a genetic algorithm with cluster energies described by the semi-empirical Gupta potential. Selected clusters are then refined with density functional theory. Three different parameterisations of the Gupta potential are used and their performance assessed to understand what features of bulk and surfaces are necessary to capture for accurate description of small clusters. Three general regions of motif stability exist; for the Pd majority clusters (Pd38 to Cu4Pd34) the truncated octahedron is most stable, while for clusters of intermediate compositions (Cu5Pd33 to Cu25Pd13) a "pancake" icosahedron is most stable, and for the Cu majority clusters (Cu26Pd12 to Cu38) again the truncated octahedron is most stable. CuPd clusters tend to segregate to a Cu-core, Pd-shell structure if possible, and at higher Cu compositions, the Pd segregates to the faces of the cluster. Using multiple parameterisations of the Gupta potential ensures the full variety of possible structures is found, and improves the search for the most stable CuPd clusters.

Applications of bimetallic PdCu catalysts

Bimetallic PdCu nanoparticles can be applied as catalysts in a wide range of chemical and electrochemical reactions.

Tuning the activities of cuprous oxide nanostructures via the oxide-metal interaction

Despite tremendous importance in catalysis, the design of oxide-metal interface has been hampered by the limited understanding of the nature of interfacial sites and the oxide-metal interaction (OMI). Through construction of well-defined Cu₂O/Pt, Cu₂O/Ag and Cu₂O/Au interfaces, we find that Cu₂O nanostructures (NSs) on Pt exhibit much lower thermal stability than on Ag and Au, although they show the same structure. The activities of these interfaces are compared for CO oxidation and follow the order of Cu₂O/Pt > Cu₂O/Au > Cu₂O/Ag. OMI is found to determine the activity and stability of supported Cu₂O NSs, which could be described by the formation energy of interfacial oxygen vacancy. Further, electronic interaction between Cu⁺ and metal substrates is found center to OMI, where the d band center could be used as a key descriptor. Our study provides insight for OMI and for the development of Cu-based catalysts for low temperature oxidation reactions.

The design of oxide-metal interface for heterogeneous catalysis has been hampered by the limited fundamental understanding. Here, the authors demonstrate that the activities of cuprous oxide nanostructures for CO oxidation can be tuned via the oxide-metal (Cu2O/M, M = Pt, Ag, Au) interaction.

Trimetallic PdCuAu Nanoparticles for Temperature Sensing and Fluorescence Detection of H 2 O 2 and Glucose

The design of palladium-based nanostructures has good prospects in various applications. This paper reports a simple one-step synthesis method of PdCuAu nanoparticles (PdCuAu NPs) prepared directly in aqueous solution. PdCuAu NPs have attracted much attention owing to their unique synergistic electronic effect, optical and catalytic performance. As temperature sensor, PdCuAu NPs are sensitive to the fluorescence intensity change in the temperature range of 4-95°C, which is due to its unique optical properties. The prepared PdCuAu NPs have excellent catalytic performance for peroxidase-like enzymes. It can catalyze TMB rapidly in the presence of hydrogen peroxide and oxidize it to visible blue product (oxTMB). Based on its unique peroxidase-like properties, this study used PdCuAu NPs colorimetric platform detection of hydrogen peroxide and glucose. The linear ranges of hydrogen peroxide and glucose were 0.1-300 μM and 0.5-500 μM, respectively, and the detection limits (LOD) were 5 and 25 nM, respectively. This simple and rapid method provides a good prospect for the detection of H2O2 and glucose in practical applications.

Interlaced Pd-Ag nanowires rich in grain boundary defects for boosting oxygen reduction electrocatalysis

Given the high cost and poisoning issues of Pt, developing Pd-based catalysts as substitutes is highly essential. Although substantial progress has been made, the synthesis of Pd-based electrocatalysts with both high activity and stability in the oxygen reduction reaction (ORR) remains a challenge. In this work, we prepared Pd-Ag nanowires with up to micro-sized length and a diameter of ∼17 nm via a facile modified polyol method. The obtained Pd-Ag nanowires (NWs) exhibit interlaced features and are rich in grain boundary defects. Due to the continuous grain boundaries in the one-dimensional (1D) structure and the optimized composition, the synthesized Pd1Ag1 NWs show half-wave potential of 0.897 V and mass activity of 0.103 A mg-1 in alkaline media toward ORR, higher than those of both state-of-the-art Pt/C and other Pd-Ag counterparts. Significantly, after stability tests over 5000 cycles, Pd1Ag1 NWs shows a 2 mV positive shift, much better than that of Pt/C, exhibiting striking stability for ORR. This work may provide an avenue to construct advanced catalysts by surface defect engineering.

A Trimetallic Pt2NiCo/C Electrocatalyst with Enhanced Activity and Durability for Oxygen Reduction Reaction

Commercialization of the polymer electrolyte membrane fuel cell (PEMFC) requires that electrocatalysts for oxygen reduction reaction (ORR) satisfy two main considerations: materials must be highly active and show long-term stability in acid medium. Here, we describe the synthesis, physical characterization, and electrochemical evaluation of carbon-dispersed Pt2NiCo nanocatalysts for ORR in acid medium. We synthesized a trimetallic electrocatalyst via chemical route in organic medium and investigated the physical properties of the Pt2NiCo/C nanocatalyst by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy-scanning electron microscope (EDXS-SEM), and scanning transmission electron microscopy (STEM), whereas the catalytic activities of the Pt2NiCo/C and Pt/C nanocatalysts were determined through cyclic voltammetry (CV), CO-stripping, and rotating disk electrode (RDE) electrochemical techniques. XRD and EDXS-SEM results confirmed the presence of the three metals in the nanoparticles, and scanning transmission electron microscopy (STEM) allowed observation of the Pt2NiCo nanoparticles at ~10 nm. The measured specific activity for the synthesized nanocatalyst is ~6.4-fold higher than that of Pt/C alone, and its mass activity is ~2.2-fold higher than that of Pt/C, which is attributed to the synergistic interaction of the trimetallic electrocatalyst. Furthermore, the specific and mass activities of the synthesized material are maintained after the accelerated stability test, whereas the catalytic properties of Pt/C decreased. These results suggest that the Pt2NiCo/C trimetallic nanocatalyst is a promising candidate cathode electrode for use in PEMFCs.

All-metallic nanorattles consisting of a Pt core and a mesoporous PtPd shell for enhanced electrocatalysis

The fabrication of nanorattles with controllable compositions and structures is very important for catalytic applications. Herein, we propose a facile method for synthesis of very unique all-metallic nanorattle consisting of a Pt core and a mesoporous PtPd shell (named Pt@mPtPd). Owing to its spatially and locally separated active inner Pt core and mesoporous PtPd shell, the Pt@mPtPd nanorattle shows the enhanced performance for oxygen reduction reaction. The newly designed Pt@mPtPd nanorattle is quite different from traditional nanorattles with porous carbon and silica shell in its catalytically functional mesoporous metallic shell. The proposed facile method is highly valuable for the design of all-metallic nanorattle with controllable compositions and desired functions.

Defect Engineering of Palladium-Tin Nanowires Enables Efficient Electrocatalysts for Fuel Cell Reactions

The defect engineering of noble metal nanostructures is of vital importance because it can provide an additional yet advanced tier to further boost catalysis, especially for one-dimensional (1D) noble metal nanostructures with a high surface to bulk ratio and more importantly the ability to engineer the defect along the longitudinal direction of the 1D nanostructures. Herein, for the first time, we report that the defect in 1D noble metal nanostructures is a largely unrevealed yet essential factor in achieving highly active and stable electrocatalysts toward fuel cell reactions. The detailed electrocatalytic results show that the Pd-Sn nanowires (NWs) exhibit interesting defect-dependent performance, in which the defect-rich Pd₄Sn wavy NWs display the highest activity and durability for both the methanol oxidation reaction (MOR) and the oxygen reduction reaction (ORR). Density functional theory (DFT) calculations reveal that a large number of surface vacancies/agglomerated voids are the driving forces for forming surface grain boundaries (GBs) within Pd₄Sn WNWs. These electronic active GB regions are the key factors in preserving the number of Pd⁰ sites, which are critical for minimizing the intrinsic site-to-site electron-transfer barriers. Through this defect engineering, the Pd₄Sn WNWs ultimately yield highly efficient alkaline ORR and MOR. The present work highlights the importance of defect engineering in boosting the performance of electrocatalysts for potentially practical fuel cells and energy applications.

Recent Advances on Controlled Synthesis and Engineering of Hollow Alloyed Nanotubes for Electrocatalysis

The past decade has witnessed great progress in the synthesis and electrocatalytic applications of 1D hollow alloy nanotubes with controllable compositions and fine structures. Hollow nanotubes have been explored as promising electrocatalysts in the fuel cell reactions due to their well-controlled surface structure, size, porosity, and compositions. In addition, owing to the self-supporting ability of 1D structure, hollow nanotubes are capable of avoiding catalyst aggregation and carbon corrosion during the catalytic process, which are two other issues for the widely investigated carbon-supported nanoparticle catalysts. It is currently a great challenge to achieve high activity and stability at a relatively low cost to realize commercialization of these catalysts. An overview of the structural and compositional properties of 1D hollow alloy nanotubes, which provide a large number of accessible active sites, void spaces for electrolytes/reactants impregnation, and structural stability for suppressing aggregation, is presented. The latest advances on several strategies such as hard template and self-templating methods for controllable synthesis of hollow alloyed nanotubes with controllable structures and compositions are then summarized. Benefiting from the advantages of the unique properties and facile synthesis approaches, the capability of 1D hollow nanotubes is then highlighted by discussing examples of their applications in fuel-cell-related electrocatalysis. Finally, the remaining challenges and potential solutions in the field are summarized to provide some useful clues for the future development of 1D hollow alloy nanotube materials.

Advanced Technologies for High-Energy Aluminum-Air Batteries

Aluminum-air batteries are considered as next-generation batteries owing to their high energy density with the abundant reserves, low cost, and lightweight of aluminum. However, there are several hurdles to be overcome, such as the sluggish rate of the oxygen reduction reaction (ORR) at the air electrode, precipitation of aluminum hydroxides and oxides at the anode, and severe hydrogen evolution problems at the interface of the anode and the electrolyte. Here, recent advances in silver metal and metal-nitrogen-carbon-based ORR electrocatalysts, aluminum anodes, electrolytes, and the requirements of future research directions are mainly summarized.

In Situ Imaging Facet-Induced Spatial Heterogeneity of Electrocatalytic Reaction Activity at the Subparticle Level via Electrochemiluminescence Microscopy

Investigating catalytic behavior of heterogeneous catalysts, especially at the crystal facets level, is crucial for rational catalyst design in the energy and environmental fields. Here we demonstrate an efficient approach to in situ visualize and analyze the heterogeneity of electrocatalytic activity on different facets at the subparticle level via electrochemiluminescence (ECL) microscopy. ZnO crystals with various exposed facet proportions were synthesized, and the correlation between their electrocatalytic performance toward luminol analogue degradation and the exposed facets is established. It is clearly imaged that the ZnO (002) facet has superior catalytic performance compared to the ZnO (100) facet, which is supported by theoretical computation and electrochemical experiments as the facet-induced heterogeneity of the catalytic effect on oxygen reduction into the key reactant for ECL. Accordingly, the spatial heterogeneity of electrocatalytic activity at different facets on one particle is visualized for the first time. The realization of subparticle ECL imaging and kinetic analysis could provide a special approach to visualize facet-induced spatial heterogeneity of catalytic behavior and valuable information for the catalysis study and analysis.

Intrinsic effects of strain on low-index surfaces of platinum: roles of the five 5d orbitals

The inconsistent change in five 5d orbitals on strained Pt low-index induces abnormal species adsorption behaviours.

Golden single-atomic-site platinum electrocatalysts

Bimetallic nanoparticles with tailored structures constitute a desirable model system for catalysts, as crucial factors such as geometric and electronic effects can be readily controlled by tailoring the structure and alloy bonding of the catalytic site. Here we report a facile colloidal method to prepare a series of platinum-gold (PtAu) nanoparticles with tailored surface structures and particle diameters on the order of 7 nm. Samples with low Pt content, particularly Pt₄Au₉₆, exhibited unprecedented electrocatalytic activity for the oxidation of formic acid. A high forward current density of 3.77 A mg_Pt^-1 was observed for Pt₄Au₉₆, a value two orders of magnitude greater than those observed for core-shell structured Pt₇₈Au₂₂ and a commercial Pt nanocatalyst. Extensive structural characterization and theoretical density functional theory simulations of the best-performing catalysts revealed densely packed single-atom Pt surface sites surrounded by Au atoms, which suggests that their superior catalytic activity and selectivity could be attributed to the unique structural and alloy-bonding properties of these single-atomic-site catalysts.

Facile Synthesis of PtCu Alloy/Graphene Oxide Hybrids as Improved Electrocatalysts for Alkaline Fuel Cells

Morphology-controllable preparation of Pt-based nanoalloys supporting on carbonaceous materials is a potential strategy to enhance the catalytic properties for oxygen reduction reaction (ORR) and ethanol oxidation reaction (EOR); they are recognized as irreplaceable electrode reactions in proton-exchange membrane ethanol fuel cells. Herein, we exhibit a facile, one-step synthesis method to directly prepare composition-tunable PtCu alloy/graphene oxide (GO) hybrids. The structure of the as-synthesized PtCu alloy/GO hybrids has been analyzed using transmission electron microscopy, high resolution transmission electron microscopy, energy-dispersive X-ray, X-ray diffraction, inductively coupled plasma, and X-ray photoelectron spectroscopy. In the PtCu alloy/GO hybrids, the PtCu alloy nanoparticles well disperse on GO, and the size is below 5.0 nm. The catalysis for ORR and EOR of the as-synthesized PtCu/GO hybrids has been evaluated in alkaline solution. Compared to commercial Pt/C, the PtCu/GO hybrids exhibit much higher mass activity and stability. The mass activities toward ORR/EOR on Pt_75.4Cu_24.6/GO hybrids are 5.3/2.36 times higher than the commercial Pt/C. This study proves that the as-synthesized PtCu/GO hybrids can be used as improved catalysts for ORR and EOR in alkaline medium.

Shape-Controlled Synthesis of Platinum-Copper Nanocrystals for Efficient Liquid Fuel Electrocatalysis

Well-defined noble metal nanomaterials are attractive as catalysts for various applications because of abundant surface-active sites. However, the shape-controlled synthesis of high-performance Pt-based nanocatalysts remains a forbidden challenge. We herein demonstrate a versatile approach for realizing the systemically controlled syntheses of bimetallic Pt-Cu nanocrystals (NCs) from concave nanocubes (CNCs), to excavated nanocubes, to tripods via simply switching the amount of glycine (reducing agent). These Pt-Cu nanostructures supply a desirable platform for carrying out the structure-dependent electrocatalytic studies in the liquid fuel electro-oxidation. Impressively, all of the Pt-Cu NCs show high activity and outstanding durability for alcohol oxidation. In particular, the Pt-Cu CNCs display unprecedent high activity toward MOR and EOR, which are found to be 2041.1 and 5760.9 mA mg^-1 in mass activity, 7.9- and 11.5-folds greater than the commercial Pt/C catalysts, respectively, showing a promising class of electrocatalysts for fuel cells. This work sheds great promise for optimizing the electrochemical catalysis by precisely modulating the structure of catalysts.

Preparation of carbon-based AuAg alloy nanoparticles by using the heterometallic [Au4Ag4] cluster for efficient oxidative coupling of anilines

We herein report the preparation of unique heteroatom-doped and carbon-based AuAg alloy nanoparticles (NPs) via the pyrolysis of a structurally defined octanuclear heterometallic Au(i)-Ag(i) cluster [Au4Ag4(Dppy)4(Tab)4(MeCN)4](PF6)8 (2, Dppy = diphenylphosphine-2-pyridine and Tab = 4-(trimethylammonio)benzenethiolate). This cluster-precursor approach exerts a fine control over the spatial arrangement, size and uniformity of the AuAg alloy NPs as well as the doped heteroatoms (P, N, F and S). The optimized material prepared at 450 °C efficiently catalyzes the oxidative coupling of anilines to yield azobenzenes under mild conditions.