Concave Cubes Research Articles

Strain engineering of PtMn alloy enclosed by high-indexed facets boost ethanol electrooxidation

Surface strain engineering has proven to be an efficient strategy to enhance catalytic properties of platinum (Pt)-based catalysts for electrooxidation reactions. Herein, the S-doped PtMn concave cubes (CNCs) enclosed with high index facets (HIFs) and regulatable surface strain are successfully fabricated by two steps hydrothermal method. The S element with electrophilic property can modify the near-surface of PtMn nanocrystals, altering the electronic structure of Pt to effectively regulate the adsorption/desorption of intermediates in the ethanol electrooxidation reaction (EOR). The PtMnS1.1 catalyst with optimal surface strain delivered extraordinary catalytic performance on EOR in acidic media, with a specific activity of 2.88 mA/cm2 and mass activity of 1.10 mA/μgPt, which is 4.1 and 2.2 times larger than that of state-of-the-art Pt/C catalyst, respectively. Additionally, the PtMnS1.1 catalyst also achieve excellent catalytic properties in alkaline electrolyte for EOR. The results of kinetic studies indicated that the surface strain and modified electronic structure can degrade the activation energy barrier during the process of EOR, which is beneficial for enhance the reaction rate. This work provides a promising approach to construct highly efficient electrocatalysts with tunable surface strain effects for clean energy electro-chemical reactions.

ZIF-67 template-assisted porous carbon based Ru-Co synergistic effect for efficient NH3BH3 hydrolysis & 4-nitrophenol reduction: Effect of morphology and pore structure adjustment

Herein, dodecahedron, concave cube with a cavity and leaf-like ZIF were prepared through water hydrogen bond induced coordination structure engineering. MOF-derived C materials, with feature of generally maintained ZIF morphology, adjustable mesoporous structure and in situ N doping, were constructed with simple pyrolysis under N2 and phosphoric acid etching strategies. Ru loaded ZIF template-assisted mesoporous carbon materials were utilized for the ammonia borane hydrolysis and p-nitrophenol reduction. Up to 1031 min−1 TOF in ammonia borane hydrolysis and as high as 1.602 min−1p-nitrophenol reduction efficiency could be achieved over Ru loaded dodecahedron ZIF-67 template-assisted mesoporous carbon. Above excellent catalytic performance should be ascribed to the partial retained coordination structure engineering based catalytic active center optimization, the phosphoric acid etching assisted mesoporous structure construction for hydrophilicity and mass transfer promotion, as well as the Ru–Co synergistic structure induced charge transfer improvement.

Lactoferrin functionalized concave cube Au nanoparticles as biocompatible antibacterial agent

Gold nanoparticles (AuNPs) are one of the most extensively studied nanomaterials and their distinct physicochemical properties make them suitable for versatile applications. Herein, we synthesized concave cube-shaped gold nanoparticles (CCAuNPs) and functionalized them with lactoferrin (Lf), a natural antimicrobial protein, through electrostatic interaction as well as weak covalent formation. The functionalization of CCAuNPs was confirmed through UV–Visible (i.e., bathochromic shift of the surface plasmon resonance peak by 7 nm), Fourier transform infrared (FTIR) and X-ray diffraction (XRD) spectroscopy, and their surface zeta potential. The concave cusp of CCAuNPs was confirmed through atomic force microscopy (AFM). The Lf-functionalized CCAuNPs (Lf-CCAuNPs) exhibited superior antibacterial propensity against a series of bacteria when compared to that of CCAuNPs. However, they didn't demonstrate any antibacterial activity against Lactobacillus plantarum, one of the key beneficial gut bacteria. The lipid peroxidation (LPO) assay confirmed the oxidation of fatty acids in the bacterial membrane upon interaction with AuNPs, which made the bacterial membrane porous. The resultant membrane-impaired dead bacteria were visualized through CellTox™ Green assay as well as the Trypan Blue dye exclusion assay. Both the nanoparticles demonstrated excellent hemocompatibility as well as biocompatibility (both in vitro and in vivo) as confirmed by MTT assay and the levels of important functional biomarkers of liver (e.g., ALT, AST, and ALP) and kidney (e.g., creatinine, uric acid, and BUN) in the serum. Overall, Lf-CCAuNPs with excellent hemocompatibility, and biocompatibility can be deployed as potential antibacterial agents to tackle the menace of pathogenic bacteria.

Controllable synthesis of Pt nanoparticles on graphene oxide nanosheets and its application for electrochemical determination of dopamine

AbstractEstablishing effective strategies to improve the performance of catalyst is a major area of interest within the field of electrochemical detection. In this paper, the nanocomposites of Pt catalyst with different morphologies decorated GO surface were successfully synthesized. The feature and diversity of Pt nanoparticles were confirmed by transmission electron microscope. The electrocatalytic performance and electroactive area of various modified electrodes were examined by cyclic voltammetry. According to Randles‐Sevick equation, the active area of electrode modified with the shape of concave cube Pt nanoparticles is the largest. Moreover, compared with the other common stable planes, the concave cube Pt nanoparticles bound by high‐index facets have the strongest current response. Furthermore, dopamine can be detected by amperometry at a typical working potential of 0.2 V (versus SCE) with a detection limit of 0.74 μM (at the signal‐to‐noise ratio of 3), over two wide linear ranges (3 μM–0.7 mM and 0.7 mM–4 mM). The sensing electrode also exhibited good reproducibility, stability and selectivity for dopamine determination.

An Alloy Platform of Dual‐Fingerprints for High‐Performance Stroke Screening

AbstractA multi‐modal serum profiling platform holds promise for precision diagnosis of diseases. Still, advanced tools are in demand to deliver the multi‐modal serum profiling. Herein, a bimodal spectrometric protocol is designed for stoke serum profiling using an alloy platform, by integrating label‐free surface‐enhanced Raman spectroscopy (SERS) and laser desorption/ionization mass spectrometry (LDI‐MS). The PdAu@Au concave cube with a wide localized surface plasmonic resonance (LSPR) range simultaneously enhances the signals from SERS and LDI‐MS, enabling high‐throughput co‐detection of vibrational and metabolic fingerprints of 0.1 µL serum in 2 min with simple pretreatment. Further, a dual‐fingerprints screening model of stroke is constructed, by adaptive machine learning with a programming nonlinear fitting model. The area under the curve are 0.949 (0.917–0.977, 95% confidence interval (CI)) and 0.911 (0.812–0.984, 95% CI), in the discovery and validation cohorts, respectively. Finally, five metabolites are identified that correlated to SERS signals and mapped the relevant pathways. This study features high performance in terms of throughput, speed, sample volume, and accuracy, providing new insight into the construction of multiplexed characterization platforms for precision diagnostic.

High-Throughput Color Imaging Hg2+ Sensing via Amalgamation-Mediated Shape Transition of Concave Cube Au Nanoparticles.

Mercury, as one type of toxic heavy metal, represents a great threat to environmental and biological metabolic systems. Thus, reliable and sensitive quantitative detection of mercury levels is particularly meaningful for environmental protection and human health. We proposed a high-throughput single-particle color imaging strategy under dark-field microscopy (DFM) for mercury ions (Hg2+) detection by using individual concave cube Au nanoparticles as optical probes. In the presence of ascorbic acid (AA), Hg2+ was reduced to Hg which forms Au–Hg amalgamate with Au nanoparticles, altering their localized surface plasmon resonance (LSPR). Transmission electron microscopy (TEM) images demonstrated that the concave cube Au nanoparticles were approaching to sphere upon increasing the concentration of Hg2+. The nanoparticles underwent an obvious color change from red to yellow, green, and finally blue under DFM due to the shape-evolution and LSPR changes. In addition, we demonstrated for the first time that the LSPR of Au–Hg amalgamated below 400 nm. Inspired by the above-mentioned results, single-particle color variations were digitalized by converting the color image into RGB channels to obtain (green+blue)/red intensity ratios [(G+B)/R]. The concentration-dependence change was quantified by statistically analyzing the (G+B)/R ratios of a large number of particles. A linear range from 10 to 2000 nM (R2 = 0.972) and a limit of detection (LOD) of 1.857 nM were acquired. Furthermore, many other metal ions, like Cu2+, Cr3+, etc., did not interfere with Hg2+ detection. More importantly, Hg2+ content in industrial wastewater samples and in the inner regions of human HepG2 cells was determined, showing great potential for developing a single-particle color imaging sensor in complex biological samples using concave cube Au nanoparticles as optical probes.

Functionalized Concave Cube Gold Nanoparticles as Potent Antimicrobial Agents against Pathogenic Bacteria.

Gold (Au) is an inert metal in a bulk state; however, it can be used for the preparation of Au nanoparticles (i.e., AuNPs) for multidimensional applications in the field of nanomedicine and nanobiotechnology. Herein, monodisperse concave cube AuNPs (CCAuNPs) were synthesized and functionalized with a natural antioxidant lipoic acid (LA) and a tripeptide glutathione (GSH) because different crystal facets of AuNPs provide binding sites for distinct ligands. There was an ∼10 nm bathochromic shift of the UV-vis spectrum when CCAuNPs were functionalized with LA, and the size of the as-synthesized monodisperse CCAu nanoparticles was 76 nm. The LA-functionalized CCAu nanoparticles (i.e., CCAuLA) showed the highest antibacterial activity against Bacillus subtilis. Both fluorescence images and scanning electron microscopy images confirm the damage of the bacterial cell wall as the mode of antibacterial activity of CCAuNPs. CCAuNPs also cause the oxidation of bacterial cell membrane fatty acids to produce reactive oxygen species, which pave the way for the death of bacteria. Both CCAu nanoparticles and their functionalized derivatives showed excellent hemocompatibility (i.e., percentage of hemolysis is <5% at 80 μg of AuNPs) to human red blood cells and very high biocompatibility to HeLa, L929, and Chinese hamster ovary-green fluorescent protein (CHO-GFP) cells. Taken together, LA and GSH enhance the antibacterial activity and biocompatibility, respectively, of CCAu nanoparticles that interact with the bacteria through Coulomb as well as hydrophobic interactions before demonstrating antibacterial propensity.

Facile synthesis of MOF-derived concave cube nanocomposite by self-templated toward lightweight and wideband microwave absorption

The green and facile strategy of producing high efficiency microwave absorption materials (MAMs) has attracted wide attention, but remains a challenge. In this work, polydopamine (PDA) was used as carbon source and nitrogen source, polyvinylpyrrolidone (PVP) was used as protective layer and dispersant, and nanoparticles with concave cube morphology were prepared by self-template eco-friendly method. By adjusting the addition amount of PDA and PVP, the MOF derived materials with three morphologies of pure ZIF-67 nanoparticles, core-shell adhesion cube and concave cube can be precisely controlled. Compared with the other two kinds of absorbers, the sample with concave cube morphology shows excellent electromagnetic wave absorption (EMA) performance. Furthermore, the excellent EMA performance comes from the efficient electron transport channel with unique concave cube morphology, multi-interface polarization process and Co nanoparticles high impedance matching. The analysis demonstrates that when the filling ratio of the concave cube sample is 15%, its effective absorption bandwidth is 5.97 GHz, which can basically cover the Ku band (12.0–18.0 GHz), and the corresponding thickness is 1.88 mm. Our research provides a meritorious approach for the design and preparation of high efficiency MAMs by considering the effects of the morphology and filling ratio of the absorber comprehensively.

Synthesis of Branched Au‐PdAg Hybrid Nanosheets by Controlled Reduction in a Galvanic Replacement Reaction

AbstractWe report a niche strategy to fabricate planar trimetallic nanocrystals with in‐plane branches and a unique hybrid structure. The success of current work relies on the use of seeded growth to produce Au@Ag core‐shell nanocubes, followed by the reaction with an excessive third metal precursor (i. e., Pd) via galvanic replacement reaction (GRR) in the presence of controlled reduction. The morphology of resulting products varied in the order of cube, concave cube, hollow cage, yolk‐shell frame, and finally branched nanoplates with Au‐PdAg hybrid structure. The controlled reduction involved in the GRR process, together with the use of Au seed at appropriate amounts and docosyltrimethylammonium chloride as the capping agent, is demonstrated to be crucial for the formation of such unique structure. When loaded on carbon black and working as electrocatalysts for electroxidation of ethanol in alkaline media, the current products exhibit satisfying electrocatalytic activity (e. g., 591 mA mgPd−1 in mass activity and 10.01 A m−2 in specific activity), improved kinetics, and long‐term durability, as compared to commercial Pt/C. The present study offers a feasible route to applying precise spatial control over elemental metals for two‐dimensional dendritic noble metal nanocrystals and could be potentially extended to other metals or alloy.

Evolution of stellated gold nanoparticles: New conceptual insights into controlling the surface processes

Understanding the surface processes (deposition and surface diffusion) that occur at or close to the surface of growing nanoparticles is important for fabricating reproducibly stellated or branched gold nanoparticles with precise control over arm length and spatial orientation of arms around the core. By employing a simple seed-mediated strategy, we investigate the key synthetic variables for precise tuning of in situ surface processes (competition between the deposition and surface diffusion). These variables include the reduction rate of a reaction, the packing density of molecules/ions on the high surface energy facets, and temperature. As a result, the thermodynamically stabilized nanoparticles (cuboctahedron and truncated cube) and kinetic products (cube, concave cube, octapod, stellated octahedron, and rhombic dodecahedron) in different sizes with high quantitative shape yield (> 80%) can be obtained depending on the reduction rate of reaction and the packing density of molecules/ions. With computer simulation, we studied the stability of stellated (branched structure) and non-stellated (non-branched structure) gold nanoparticles at high temperature. We construct a morphology phase diagram by varying different synthetic parameters, illustrating the formation of both stellated and non-stellated gold nanoparticles in a range of reaction conditions. The stellated gold nanoparticles display shape-dependent optical properties and can be self-assembled into highly ordered superstructures to achieve an enhanced plasmonic response. Our strategy can be applied to other metal systems, allowing for the rational design of advanced new stellated metal nanoparticles with fascinating symmetry dependent plasmonic, catalytic, and electronic properties for technological applications.

One-Pot Synthesis of Monodisperse Single-Crystalline Spherical Gold Nanoparticles for Universal Seeds

Synthesis of uniform polyhedral gold nanoparticles (Au NPs) by the seed-mediated method is often limited by the difficulties in preparing uniform seeds. Here, we report a facile one-pot synthesis of highly monodisperse single-crystalline spherical Au NPs, which can be used as universal seeds. This method only involves simple mixing of cetyltrimethyl ammonium 4-vinylbenzoate, HAuCl4, AgNO3, and HCl in water at a fixed temperature. The single crystallinity of particles is achieved by the interplay between oxidative etching and controlled surface capping by silver atoms. As-synthesized Au NPs show uniform single crystallinity, shape yield of nearly 100%, and size polydispersity less than 5%. The as-synthesized single-crystalline Au NPs are used as universal seeds to grow monodisperse polyhedral Au NPs of different shapes including octahedra, cubes, rhombic dodecahedra, concave cubes, and concave rhombic dodecahedra with size polydispersity as small as 1.5–4.2% depending on the particle shape, the smallest values for any shape reported so far. This clearly shows the importance of seed uniformity achieved by the present method.

Microstructure Evolution of Primary γ′ Phase in Ni3Al-Based Superalloy

In this work, water cooling, air cooling (AC) and furnace cooling (FC) were applied to investigate the effect of cooling rate on microstructure evolution of primary γ′ in a newly designed Ni3Al-based alloy. The results showed that nucleation rate of primary γ′ increased with increasing cooling rate. In addition, higher cooling rate shortened growth period of primary γ′, which made its morphology close to the initial precipitated γ′. For AC and FC specimens, due to the lower cooling rate, primary γ′ possessed longer growth period and its morphology was mainly due to the evolution of lattice misfit between γ and primary γ′. Meanwhile, growth of primary γ′ depended on lattice misfit distribution between its corner and edge area. Moreover, primary γ′ morphologies of sphere, cube and concave cube with tip corners were illustrated by considering interaction between elemental diffusion and elastic strain energy.

Facet-dependent antibacterial activity of Au nanocrystals

Engineered nanomaterials have attracted significantly attention as one of the most promising antimicrobial agents for against multidrug resistant infections. The toxicological responses of nanomaterials are closely related to their physicochemical properties, and establishment of a structure-activity relationship for nanomaterials at the nano-bio interface is of great significance for deep understanding antibacterial toxicity mechanisms of nanomaterials and designing safer antibacterial nanomaterials. In this study, the antibacterial behaviors of well-defined crystallographic facets of a series of Au nanocrystals, including {100}-facet cubes, {110}-facet rhombic dodecahedra, {111}-facet octahedra, {221}-facet trisoctahedra and {720}-facet concave cubes, was investigated, using the model bacteria Staphylococcus aureus. We find that Au nanocrystals display substantial facet-dependent antibacterial activities. The low-index facets of cubes, octahedra, and rhombic dodecahedra show considerable antibacterial activity, whereas the high-index facets of trisoctahedra and concave cubes remained inert under biological conditions. This result is in stark contrast to the previous paradigm that the high-index facets were considered to have higher bioactivity as compared with low-index facets. The antibacterial mechanism studies have shown that the facet-dependent antibacterial behaviors of Au nanocrystals are mainly caused by differential bacterial membrane damage as well as inhibition of cellular enzymatic activity and energy metabolism. The faceted Au nanocrystals are unique in that they do not induce generation of reactive oxygen species, as validated for most antibiotics and antimicrobial nanostructures. Our findings may provide a deeper understanding of facet-dependent toxicological responses and suggest the complexities of the nanomaterial-cell interactions, shedding some light on the development of high performance Au nanomaterials-based antibacterial therapeutics.

Relaxometric Studies of Gd-Chelate Conjugated on the Surface of Differently Shaped Gold Nanoparticles.

Nowadays, magnetic resonance imaging (MRI) is one of the key, noninvasive modalities to detect and stage cancer which benefits from contrast agents (CA) to differentiate healthy from tumor tissue. An innovative class of MRI CAs is represented by Gd-loaded gold nanoparticles. The size, shape and chemical functionalization of Gd-loaded gold nanoparticles appear to affect the observed relaxation enhancement of water protons in their suspensions. The herein reported results shed more light on the determinants of the relaxation enhancement brought by Gd-loaded concave cube gold nanoparticles (CCGNPs). It has been found that, in the case of nanoparticles endowed with concave surfaces, the relaxivity is remarkably higher compared to the corresponding spherical (i.e., convex) gold nanoparticles (SPhGNPs). The main determinant for the observed relaxation enhancement is represented by the occurrence of a large contribution from second sphere water molecules which can be exploited in the design of high-efficiency MRI CA.

“Ship-in-Bottle” Strategy to Encapsulate Shape-Controllable Metal Nanocrystals into Metal–Organic Frameworks: Internal Space Matters

“Ship-in-bottle” strategy used for encapsulating small metal clusters into metal–organic frameworks (MOFs) has been well established in the past decades, whereas immobilizing shape-controllable metal nanocrystals’ (MNCs) which was expected to show “shape effects” in catalysis remains as a challenging work. Herein, by the new developed pore-expanding pattern of digging holes in the central of MOFs crystals to create mesopores-concentrated structure, a successful metal nanocrystal shapes manipulation (cubes, rods, triangular bipyramids, icosahedrons, truncated octahedrons, and concave cubes) in the cavities was accomplished. Meanwhile, the tight relations among MOFs internal space types, sizes, and the reduced MNCs’ location and shape evolutions in the encapsulation process were revealed for the first time. In catalyzing the reaction of hydrogenation of o-chloronitrobenzene to produce o-chloroaniline, the as-prepared shape-controllable MNCs@MOFs exhibited excellent synergistic effects on both raw materials conversion and byproducts inhabitation efficiencies.

Syntheses of Colloidal F:In2O3 Cubes: Fluorine-Induced Faceting and Infrared Plasmonic Response

Cube-shaped nanocrystals (NCs) of conventional metals like gold and silver generally exhibit localized surface plasmon resonance (LSPR) in the visible region with spectral modes determined by their faceted shapes. However, faceted NCs exhibiting LSPR response in the infrared (IR) region are relatively rare. Here, we describe the colloidal synthesis of nanoscale fluorine-doped indium oxide (F:In2O3) cubes with LSPR response in the IR region, wherein fluorine was found to both direct the cubic morphology and act as an aliovalent dopant. Single-crystalline 160 nm F:In2O3 cubes terminated by (100) facets and concave cubes were synthesized using a colloidal heat-up method. The presence of fluorine was found to impart higher stabilization to the (100) facets through density functional theory calculations that evaluated the energetics of F-substitution at surface oxygen sites. These calculations suggest that the cubic morphology results from surface binding of F atoms. In addition, fluorine acts as an anionic al...

Oxygen vacancies in concave cubes Cu2O-reduced graphene oxide heterojunction with enhanced photocatalytic H2 production

A novel composite heterojunction based on concave cubes Cu2O-reduced graphene oxide (Cu2O-RGO) was synthesized via one-pot hydrothermal method. The anionic surfactant dioctyl sulfosuccinate sodium salt (AOT) can act as the soft template to build the novel Cu2O-based microstructure. The ascorbic acid serves as reductant and etching agent in the Cu2O growing process. The facet etching of Cu2O and reduction of GO can take place simultaneously in the reaction system. The concave cubes Cu2O with average edge length of ~ 1.55 µm were well-dispersed on the surface of RGO. The Cu2O-RGO (2 wt%) heterojunction exhibited superior photocatalytic performance and recyclability with the highest amount of H2 yields of 64.3 µmol/g, which was fivefold more than the pure Cu2O (12.8 µmol/g). The enhanced photocatalytic performances were attributed to the oxygen vacancies in Cu2O and a flexible conducting channel supported by RGO. Furthermore, the synergistic effect of Cu2O and graphene caused broader absorption in visible light region and lower recombination of photogenerated electron–hole pairs. It is believed that the Cu2O-RGO heterojunction could provide an alternative method to design excellent photocatalysts for energy application.

Novel RGO and Concave Cube Cu2O Co-Modified BiVO4 Nanosheets with Enhanced Photocatalytic and Surface Adsorption Performances of Tetracycline

A novel ternary Cu2O/BiVO4/RGO photocatalyst is successfully constructed by hydrothermal and evaporation-induced method, and it exhibits superior photocatalytic performance for degradation tetracycline (TC). Meanwhile, the visible light absorption range of composite photocatalyst is effectively broadened by the formation of heterojunction with narrow band gap semiconductor Cu2O. And the separation efficiency of the photogenerated electron–hole pairs is significantly enhanced by the synergistic effect of Cu2O and RGO. More importantly, the adsorption of TC by ternary Cu2O/BiVO4/RGO possesses high adsorption capacity, which is 23.73 times higher than that of pure BiVO4. Additionally, the possible reaction mechanism is clearly revealed by radical trapping experiment, electron spin-resonance (ESR) spectroscopy. This work provides a new insight to design a photocatalyst with excellent adsorption to remove organic contaminants in water.

Thein situetching assisted synthesis of Pt–Fe–Mn ternary alloys with high-index facets as efficient catalysts for electro-oxidation reactions

Pt-Based alloys enclosed with high-index facets (HIFs) generally show much higher specific catalytic activities than their counterparts with low-index facets in electro-catalytic reactions. However, the exposure of a certain Pt surface would require a well-defined nanostructure, which usually can only be obtained at larger sizes. Therefore, a low dispersion of Pt atoms in Pt-based alloys with HIFs would affect the atomic utilization of Pt, resulting in most of these Pt-based alloys exhibiting lower mass activity than commercial Pt/C and Pt black catalysts for electro-catalytic reactions. Herein, we address a novel strategy to divide the surface areas of larger sized nanocrystals into small surface area nanocrystals by in situ etching Pt-Fe-Mn concave cubes (CNCs) while maintaining the morphology of the Pt-Fe-Mn alloys to improve the utilization of Pt atoms and thus increase the mass activity. Remarkably, the Pt-Fe-Mn unique concave cube (UCNC) nanocrystals (NCs) showed much higher specific and mass activities toward the methanol oxidation reaction (MOR) than the Pt-Fe-Mn CNCs, commercial Pt black and Pt/C. The kinetic analysis from Tafel plots indicated that UCNC Pt-Fe-Mn NCs had the lowest Tafel slope at whole potentials and the splitting of the first C-H bond of a CH3OH molecule with the first electron transfer was the rate-determining step at high potentials (above 0.45 V). In situ Fourier transform infrared reflection (FTIR) spectroscopic investigation at the molecular level indicated that methanol chemical absorption took place at a low potential of -0.2 V at the UCNC NC electrode. Meanwhile, much higher CO2 productivity was observed at the UCNC NC electrode, indicating the strong anti-poisoning ability of the UCNC Pt-Fe-Mn NCs during methanol electrooxidation. Furthermore, in the formic acid oxidation (FAOR) test, the activity and long-term durability of the Pt-Fe-Mn UCNC NCs were also found to be superior to those of the Pt-Fe-Mn CNCs, commercial Pt black and Pt/C. The enhanced catalytic performance in both the MOR and FAOR is most probably due to the unique HIF structure consisting of small sized particles, enhanced Pt utilization, the richness of crystalline defects and synergetic effects of Pt, Fe, and Mn metals. Our present work provides an insight into the rational design of Pt based alloys with HIFs to improve the catalytic performance of electro-catalytic reactions for fundamental study.

Synthesis of Pt nanocrystals with different shapes using the same protocol to optimize their catalytic activity toward oxygen reduction

Abstract Engineering the shape and thus surface structure of Pt nanocrystals is an effective strategy for optimizing their catalytic activities toward various reactions. However, different protocols are typically used to produce Pt nanocrystals with distinctive shapes, making it difficult to directly compare their catalytic activities owing to the complication of surface contamination. Here we demonstrate that Pt nanocrystals with a variety of shapes, including those enclosed with low- or high-index facets, can be synthesized using the same protocol by simply adjusting the concentration of reducing agent and/or the reaction time. Specifically, when the reducing agent was used at a relatively low concentration, Pt truncated cubes, cuboctahedrons, truncated octahedrons, and octahedrons were produced sequentially upon the increase in reaction time. When 67% more reducing agent was used, Pt cubes and concave cubes were obtained consecutively as the reaction time was prolonged. Our quantitative analysis suggests that the diversity of shape and difference in size can be resulted from the difference in reduction kinetics. In evaluating their structure–activity relationship for oxygen reduction, it was established that the high-index facets on Pt concave cubes possessed a specific activity of 6.3 and 1.3 times greater than those of Pt cubes and octahedrons exposed by {1 0 0} and {1 1 1} facets, respectively. This work not only offers a general method for the synthesis of Pt nanocrystals having diverse shapes and thus different types of facets but also highlights the significance of reduction kinetics in controlling the structure evolution of other metal nanocrystals.