Pd Icosahedra Research Articles

Highly dispersed Pd icosahedra and Ag nanocubes on ultrathin g-C3N4 nanosheet for boosting photocatalytic bacterial inactivation and organic pollutants degradation

Engineering surface facet of metallic nanoparticles that decorated on certain substants is an intriguing strategy to modulate photocatalytic capacity. Herein, a novel photocatalyst by doping g-C3N4 nanosheet with Pd icosahedra with {111} facets and Ag nanocubes with {100} facets were firstly synthesized through facile wet-chemical route. The successfully constructed g-C3N4/Pd/Ag composites were employed as a visible-light-driven dual-functional photocatalyst for bacterial inactivation and organic contaminant degradation. Result suggested that 1 × 108 CFU/mL E. coli strains can be totally inactivated by g-C3N4/Pd/Ag within 60 min, outperformed that of {100} faceted enclosed Pd nanocubes functioned g-C3N4/Ag. Also, the optimized g-C3N4/Pd/Ag exhibited ideal photocatalytic performance toward tetracycline and methylene blue degradation. The rate constant was found to be 8.74 × 10−3 and 7.08 × 10−3 min−1, respectively, which was higher than those of bare g-C3N4 and g-C3N4/Pd. Quenching experiment and electron paramagnetic resonance analysis suggested that hole (h+), electron (e−), and superoxide radical (O2−) exerted a key role in the improved capacity. Furthermore, the more positive Fermi level of Pd icosahedra and Ag nanocubes relative to that of g-C3N4 also contributed to the enhanced photocatalytic performance. Collectively, our work can provide in-depth insight into fabricate novel facet-engineering photocatalyst for environmental applications.

Shape Transformation via Etching and Regrowth: A Systematic Study of Pd Nanocrystals with Different Shapes and Twin Structures.

This article describes a systematic study of the oxidative etching and regrowth behaviors of Pd nanocrystals, including single-crystal cubes bounded by {100} facets, single-crystal octahedra and tetrahedra enclosed by {111} facets; and multiple-twinned icosahedra covered by {111} facets and twin boundaries. During etching, Pd atoms are preferentially oxidized and removed from the corners regardless of the type of nanocrystal, and the resultant Pd2+ ions are then reduced back to elemental Pd. For cubes and icosahedra, the newly formed Pd atoms are deposited on the {100} facets and twin boundaries, respectively, due to their relatively higher energies. For octahedra and tetrahedra, the Pd atoms self-nucleate in the solution phase, followed by their growth into small particles. We can control the regrowth rate relative to etching rate by varying the concentration of HCl in the reaction solution. As the concentration of HCl is increased, 18-nm Pd cubes are transformed into octahedra of 23, 18, and 13 nm, respectively, in edge length. Due to the absence of regrowth, however, Pd octahedra are transformed into truncated octahedra, cuboctahedra, and spheres with decreasing sizes whereas Pd tetrahedra evolve into truncated tetrahedra and spheres. In contrast, Pd icosahedra with twin boundaries on the surface are converted to asymmetric icosahedra, flower-like icosahedra, and spheres. This work not only advances the understanding of etching and growth behaviors of metal nanocrystals with various shapes and twin structures but also offers an alternative method for controlling their shape and size.

Exploring the Strain Effect in Single Particle Electrochemistry using Pd Nanocrystals.

Tuning the surface strain of heterogeneous catalysts are recognized as a powerful strategy for tailoring their catalytic activity. However, a clear understanding of the strain effect in electrocatalysis at single-particle resolution is still lacking. Here, we explore the electrochemical hydrogen evolution reaction (HER) of single Pd octahedra and icosahedra with the same surface bounded {111} crystal facets and similar sizes using scanning electrochemical cell microscopy (SECCM). It is revealed that tensely strained Pd icosahedra display significantly superior HER electrocatalytic activity. The estimated turnover frequency at -0.87 V vs RHE on Pd icosahedra is about two times higher than that on Pd octahedra. Our single-particle electrochemistry study using SECCM at Pd nanocrystals ambiguously highlights the importance of tensile strain on electrocatalytic activity and may offer new strategy for understanding the fundamental relationship between surface strain and reactivity.

Exploring the Strain Effect in Single Particle Electrochemistry using Pd Nanocrystals

AbstractTuning the surface strain of heterogeneous catalysts is recognized as a powerful strategy for tailoring their catalytic activity. However, a clear understanding of the strain effect in electrocatalysis at single‐particle resolution is still lacking. Here, we explore the electrochemical hydrogen evolution reaction (HER) of single Pd octahedra and icosahedra with the same surface bounded {111} crystal facet and similar sizes using scanning electrochemical cell microscopy (SECCM). It is revealed that tensilely strained Pd icosahedra display significantly superior HER electrocatalytic activity. The estimated turnover frequency at −0.87 V vs RHE on Pd icosahedra is about two times higher than that on Pd octahedra. Our single‐particle electrochemistry study using SECCM at Pd nanocrystals unambiguously highlights the importance of tensile strain on electrocatalytic activity and may offer new strategy for understanding the fundamental relationship between surface strain and reactivity.

Insight into Surface Electronic Effects on Pd Nanostructures as Efficient Electrocatalysts.

Although the unique properties of nanomaterials have endowed enzyme-mimic catalysts with broad applications, the development of catalysts still relies on trial-and-error strategies without predictive indicators. Surface electronic structures have rarely been studied in enzyme-mimic catalysts. Herein, we present a platform for understanding the impact of surface electronic structures on electrocatalysis toward H2O2 decomposition, using the Pd icosahedra (Pd ico), Pd octahedra (Pd oct) and Pd cubic nanocrystals as electrocatalysts. The electronic properties on Pd were modulated with a correlation of surface orientation. We revealed the relationship between the electronic properties and electrocatalytic performance, in which the surface electron accumulation can boost the electrocatalytic activity of the enzyme-mimic catalysts. As a result, the Pd icodimer exhibits the highest electrocatalytic and sensing efficiency. This work offers new perspectives for the investigation of structure-activity relationships and provides an effective knob for utilizing the surface electronic structures to boost the catalytic performance for enzyme-mimics.

An Integrated Electrochemistry Approach to the Design and Synthesis of Polyhedral Noble Metal Nanoparticles.

The synthesis of shaped metal nanoparticles to meet the precise needs of emerging applications requires intentional synthetic design directed by fundamental chemical principles. We report an integrated electrochemistry approach to nanoparticle synthetic design that couples current-driven growth of metal nanoparticles on an electrode surface-in close analogy to standard colloidal synthesis-with electrochemical measurements of both electrochemical and colloidal nanoparticle growth. A simple chronopotentiometry method was used to translate an existing colloidal synthesis for corrugated palladium (Pd) nanoparticles to electrochemical growth on a glassy carbon electrode, with minimal modification to the growth solution. The electrochemical synthesis method was then utilized to produce large Pd icosahedra, a shape whose synthesis is challenging in a colloidal growth environment. This electrochemical synthesis for Pd icosahedra was used to develop a corresponding colloidal growth solution by tailoring a weak reducing agent to the measured potential profile of the electrochemical synthesis. Finally, measurements of colloidal syntheses were employed as guides for the directed design of electrochemical syntheses for Pd cubes and octahedra. Together, this work provides a cyclical approach to shaped nanoparticle design that allows for the optimization of nanoparticles grown via a colloidal approach with a chemical reducing agent or synthesized with an applied current on an electrode surface as well as subsequent bidirectional translation between the two methods. The enhanced chemical flexibility and direct tunability of this electrochemical method relative to combinatorial design of colloidal syntheses have the potential to accelerate the synthetic design process for noble metal nanoparticles with targeted morphologies.

H-Implanted Pd Icosahedra for Oxygen Reduction Catalysis: From Calculation to Practice

Although palladium (Pd) has gradually emerged as the most likely candidate to replace platinum (Pt) in the oxygen reduction reaction (ORR), the specific electronic structure of conventional Pd resu...

Unexpected Kirkendall effect in twinned icosahedral nanocrystals driven by strain gradient

Nanoscale Kirkendall effect has been widely used for rationally fabricating high-quality hollow nanocrystals, but often requires the intrinsic diffusion coefficient of out-diffusion materials higher than that of in-diffusion components. Here we demonstrate an unexpected Kirkendall effect that occurs in diffusing intrinsically faster Cu atoms into Pd icosahedra, leading to the formation of PdCu alloyed hollow nanocrystals. The control experiment with Pd octahedra replacing icosahedra indicates the critical role of twin boundaries in facilitating such unexpected Kirkendall effect. In addition, geometric phase analysis and density functional theory calculation show that out-diffusion of Pd atoms in the icosahedra is faster than in-diffusion of Cu atoms, particularly through the twin boundaries, upon the strain gradient with an inward distribution from tensile to compressive strains. The unexpected Kirkendall effect is also found in the interdiffusion of Ag and Pd atoms in Pd icosahedra. Our finds break the limitation of the intrinsic diffusion coefficient for the synthesis of hollow nanocrystals through Kirkendall effect and are expected to enormously enrich the family of hollow nanocrystals which have shown great potential in broad areas, such as fine chemical production, energy storage and conversion, and environmental protection. This work also provides a deep understanding in the diffusion behavior of atoms upon the strain gradient.

Insights into the Pd nanocatalysts directed by morphology effect for CO and methyl nitrite coupling to dimethyl oxalate

CO coupling to dimethyl oxalate (DMO) has been considered as the most important part in industrial production of ethylene glycol (EG). Five kinds of Pd nanoparticles with various morphologies were successfully synthesized by liquid-phase reduction. The exposed crystal planes of these Pd nanoparticles were identified and quantified. The corresponding supported Pd/α-Al2O3 showed excellent catalytic activities for CO coupling reaction and the catalysts including Pd icosahedra can enhanced the selectivity of DMO to 98% and remained unchanged for 50 hours. The characterization results illustrated that the exposure of Pd (111) facets enhanced the intensities of bridged CO, which contributed to the high performance of the Pd-based catalysts. DFT calculations revealed CO adsorbed on Pd (111) facets had higher binding energies. This work systematically discussed the influence of Pd morphologies. Experimental and theoretical results confirmed that the Pd (111) facets showed better catalytic activities for CO coupling reaction.

Atomic-Level Construction of Tensile-Strained PdFe Alloy Surface toward Highly Efficient Oxygen Reduction Electrocatalysis.

Exploring the high-performance non-Pt electrocatalysts for oxygen reduction reaction (ORR), the bottleneck process in fuel cells, is desirable but challenging. Here, we report the Pd@PdFe core-shell icosahedra as an active and durable electrocatalyst toward ORR in alkaline conditions, which feature a three-atomic-layer tensile-strained PdFe overlayer on Pd icosahedra. Our optimized catalyst shows 2.8-fold enhancement in mass activity and 6.9-fold enhancement in specific activity than commercial Pt/C catalyst toward ORR, representing one of the best non-Pt electrocatalysts. Moreover, the boosted ORR catalysis is strongly supported by the assembled fuel cell performance using Pd@PdFe core-shell icosahedra as the cathode electrocatalyst. The density functional theory calculations reveal that the synergistic coupling of tensile strain and alloy effects enables the optimum binding strength for intermediates, thus causing the maximum activity. The present work suggests the coupling between multiple surface modulations endows larger room for the rational design of remarkable catalysts.

Strain Effect in Palladium Nanostructures as Nanozymes.

While various effects of physicochemical parameters (e.g., size, facet, composition, and internal structure) on the catalytic efficiency of nanozymes (i.e., nanoscale enzyme mimics) have been studied, the strain effect has never been reported and understood before. Herein, we demonstrate the strain effect in nanozymes by using Pd octahedra and icosahedra with peroxidase-like activities as a model system. Strained Pd icosahedra were found to display 2-fold higher peroxidase-like catalytic efficiency than unstrained Pd octahedra. Theoretical analysis suggests that tensile strain is more beneficial to OH radical (a key intermediate for the catalysis) generation than compressive strain. Pd icosahedra are more active than Pd octahedra because icosahedra amplify the surface strain field. As a proof-of-concept demonstration, the strained Pd icosahedra were applied to an immunoassay of biomarkers, outperforming both unstrained Pd octahedra and natural peroxidases. The findings in this research may serve as a strong foundation to guide the design of high-performance nanozymes.

Surface-modulated palladium-nickel icosahedra as high-performance non-platinum oxygen reduction electrocatalysts.

The search for high-performance non-platinum (Pt) electrocatalysts is the most challenging issue for fuel cell technology. Creating bimetallic non-Pt nanocrystals (NCs) with core/shell structures or alloy features has widely been explored as the most effective way for enhancing their electrochemical properties but still suffered from undesirable performance due to the limited interactions between the different components. By addressing the above issue, we report on a new class of active and stable bimetallic non-Pt electrocatalysts with palladium (Pd) icosahedra as the core and nickel (Ni) decorating the surface toward cathodic oxygen reduction reaction (ORR) under alkaline conditions. The optimized Pd6Ni icosahedra with unique interaction between an icosahedral Pd core and surface Ni yield the highest ORR activity with a mass activity of 0.22 A mgPd-1, which is better than those of the conventional Pd6Ni icosahedra with alloy surfaces or Pd-rich surfaces, and even two times higher than that of the commercial Pt/C (0.11 A mgPt-1), representing one of the best non-Pt electrocatalysts. Simulations reveal that the Pd icosahedra decorated with Ni atoms emerged in the subsurface can weaken the interaction between the adsorbed oxygen and Pd (111) facet and enhance the ORR activities due to an obvious shift of d-band center. More significantly, under electrochemical accelerated durability test, the Pd6Ni icosahedra can endure at least 10,000 cycles with negligible activity decay and structural change. The present work demonstrates an important advance in surface tuning of bimetallic NCs as high-performance non-Pt catalysts for catalysis, energy conversion, and beyond.

Scalable Synthesis of Palladium Icosahedra in Plug Reactors for the Production of Oxygen Reduction Reaction Catalysts

AbstractWe have synthesized Pd icosahedra with uniform, controllable sizes in plug reactors separated by air. The oxygen contained in the air segments not only contributed to the generation of a reductant from diethylene glycol in situ, but also oxidized elemental Pd back to the ionic form by oxidative etching and thus slowed down the reduction kinetics. Compared to droplet reactors involving silicone oil or fluorocarbon, the use of air as a carrier phase could reduce the production cost by avoiding additional procedures for the separation of products from the oil. The average diameters of the Pd icosahedra could be readily controlled in the range of 12–20 nm. The Pd icosahedra were further employed as seeds for the production of Pd@Pt2–3L core‐shell icosahedra, which could serve as a catalyst toward the oxygen reduction reaction with greatly enhanced activity. We believe that the plug reactors could be extended to other types of noble‐metal nanocrystals for their scale‐up production.

Polyol Syntheses of Palladium Decahedra and Icosahedra as Pure Samples by Maneuvering the Reaction Kinetics with Additives

This article reports a robust method based upon polyol reduction for the deterministic synthesis of Pd decahedra or icosahedra with tunable sizes and a purity approaching 100%. The success of such a selective synthesis relies on an ability to fine-tune the reaction kinetics through the addition of Na2SO4 and HCl for decahedra and icosahedra, respectively. In the absence of any additive, the product of a similar synthesis in diethylene glycol contained 10% decahedra and 90% icosahedra. By optimizing the amount of Na2SO4 (or HCl) added into the reaction solution, the percent of decahedra (or icosahedra) in the product could be increased up to 100%. The roles of Na2SO4 and HCl were also investigated in great detail, and two plausible mechanisms were proposed and validated through a set of experiments. In general, a faster reduction rate is needed for the synthesis of Pd decahedra when compared with what is needed for Pd icosahedra. This work not only offers a simple approach to the deterministic syntheses of Pd decahedra and icosahedra but also provides an in-depth understanding of the mechanisms involved in shape-controlled syntheses of noble-metal nanocrystals from the perspective of reaction kinetics. On the basis of the mechanistic understanding, we have also achieved successful synthesis of Pd decahedra as pure samples by adding a proper amount of NaOH into the system to speed up the reduction kinetics.

Controlled Synthesis of Nanosized Palladium icosahedra and Their Catalytic Activity towards Formic‐Acid Oxidation

Pd icosahedra with sizes controlled in the range of 5-35 nm were synthesized in high purity through a combination of polyol reduction and seed-mediated growth. The Pd icosahedra were obtained with purity >94 % and uniform sizes controlled in the range of 5-17 nm by using ethylene glycol as both the reductant and solvent. The studies indicate that the formation of Pd nanocrystals with an icosahedral shape was very sensitive to the reaction kinetics. The success of this synthesis relies on the use of HCl to manipulate the reaction kinetics and thus control the twin structure and shape of the resultant nanocrystals. The size of the Pd icosahedra could be further increased up to 35 nm by seed-mediated growth, with 17 nm Pd icosahedra serving as seeds. The multiply twinned Pd icosahedra could grow into larger sizes, and their shape and multiply twinned structure were preserved. Thanks to the presence of twin defects, the Pd icosahedra showed a catalytic current density towards formic-acid oxidation that was 1.9 and 11.6 times higher than that of single-crystal Pd octahedra, which were also fully covered by {111} facets, and commercial Pd/C, respectively.

The Effect of Lattice Strain on the Catalytic Properties of Pd Nanocrystals

The effect of lattice strain on the catalytic properties of Pd nanoparticles is systematically studied. Synthetic strategies for the preparation of a series of shape-controlled Pd nanocrystals with lattice strain generated from different sources has been developed. All of these nanocrystals were created with the same capping agent under similar reaction conditions. First, a series of Pd nanoparticles was synthesized that were enclosed in {111} surfaces: Single-crystalline Pd octahedra, single-crystalline AuPd core-shell octahedra, and twinned Pd icosahedra. Next, various {100}-terminated particles were synthesized: Single-crystalline Pd cubes and single-crystalline AuPd core-shell cubes. Different extents of lattice strain were evident by comparing the X-ray diffraction patterns of these particles. During electrocatalysis, decreased potentials for CO stripping and increased current densities for formic-acid oxidation were observed for the strained nanoparticles. In the gas-phase hydrogenation of ethylene, the activities of the strained nanoparticles were lower than those of the single-crystalline Pd nanoparticles, perhaps owing to a larger amount of cetyl trimethylammonium bromide on the surface.

Polyallylamine Functionalized Palladium Icosahedra: One-Pot Water-Based Synthesis and Their Superior Electrocatalytic Activity and Ethanol Tolerant Ability in Alkaline Media

Polyallylamine (PAH) functionalized Pd icosahedra are synthesized through a simple, one-pot, seedless and hydrothermal growth method. Herein, PAH is used efficiently as a complex-forming agent, capping agent, and facet-selective agent. The strong interaction between PAH and Pd atom sharply changes the electronic structure of Pd atom in the Pd icosahedra. The protective function of PAH layers and enhanced antietching capability of Pd atom are responsible for the formation of the Pd icosahedra. Very importantly, the as-prepared PAH functionalized Pd icosahedra exhibit superior electrocatalytic activity and ethanol tolerant ability toward the oxygen reduction reaction (ORR) compared to the commercially available Pt black in alkaline media. At 0.95 V (vs RHE), the ORR specific kinetic current density at the Pd icosahedra is 4.48 times higher than that at commercial Pt black. The fact demonstrates the appropriate surface modification of the Pd nanoparticles by nonmetallic molecules can be regarded as an effective way to enhance the electrocatalytic activity toward the ORR.

Pd Cluster Nanowires as Highly Efficient Catalysts for Selective Hydrogenation Reactions

Palladium is a key catalyst invaluable to many industrial processes and fine-chemical synthesis. Although recent progress has allowed the synthesis of Pd nanoparticles with various shapes by using different techniques, the facile synthesis of Pd nanocrystals and turning them into a highly active, selective, and stable catalyst systems still remain challenging. Herein, we report the highly selective one-pot synthesis of monodisperse Pd cluster nanowires in aqueous solution; these consist of interconnected nanoparticles and may serve as highly active catalysts because of the enrichment of high index facets on the surface, including {443}, {331}, and {221} steps. For the first time, carbon nanotube and γ-Al(2)O(3) immobilized Pd cluster nanowires showed highly enhanced catalytic performance in the liquid-phase selective hydrogenation of cinnamaldehyde and gas-phase hydrogenation of 1,3butadiene relative to immobilized Pd icosahedra and nanocubes, as well as commercial Pd catalysts.

Shape-controlled synthesis of palladium nanocrystals by microwave irradiation

AbstractThe controlled synthesis of Pd icosahedra in tetraethylene glycol (TEG) with H2PdCl4as a precursor and poly(vinylpyrrolidone) (PVP) as a stabilizer in the presence of an appropriate amount of KOH under microwave irradiation was demonstrated. TEG served as both solvent and reducing agent, and stable Pd icosahedra with uniform sizes and well-defined shapes could be prepared in a yield of over 90 % by microwave heating for 60 s. The sizes of Pd icosahedra can be well controlled by adjusting the concentration of the precursor H2PdCl4.

Controllable Polyol Synthesis of Uniform Palladium Icosahedra: Effect of Twinned Structure on Deformation of Crystalline Lattices

Tailored nanoparticles: Uniform Pd icosahedra (see TEM images) were controllably synthesized in high yield by a facile polyol process. Their size can be readily tailored from 15 to 42 nm by tuning the reaction parameters. The high density of twin boundaries and sharp edges on the surfaces of the Pd icosahedra could make them promising for many applications, for example, catalysis.