Transition Metal Nanoparticles Research Articles

Crystal Structure and Composition-Dependent Electrocatalytic Activity of Ni–Mo Nanoalloys for Water Splitting To Produce Hydrogen

Electrocatalytic water splitting presents an exciting opportunity to produce environmentally benign fuel to power human activities and reduce reliance on fossil fuels. Transition metal nanoparticle...

Coordination-Directed Growth of Transition-Metal-Crystalline-Carbon Composites with Controllable Metal Composition.

Transition-metal-carbon (CTM) composites show ample activity in many catalytic reactions. However, control of composition, distribution, and properties is challenging. Now, a straightforward path for the synthesis of transition-metal nanoparticles engulfed in crystalline carbon is presented with excellent control over the metal composition, amount, ratio, and catalytic properties. This approach uses molten monomers that coordinate metals ions at high temperature. At high temperatures, strong coordination bonds direct the growth of carbon material with homogeneous metals distribution and with negligible losses, owing to the liquid-like reaction compared to the traditional solid-state reaction. The strength of the approach is demonstrated by the synthesis of mono, binary, and trinary transition-metal-crystalline-carbon composites with tunable and precise elemental composition as well as good electrochemical properties as oxygen evolution reaction electrocatalysts.

(Invited) Electrochemical Preparation of Pd Nanoparticles in Different Ionic Liquids

Aprotic ionic liquids have been recognized as the potential electrolytes for electrodeposition of various metals due to wide electrochemical potential window and intrinsic ionic conductivity. In addition, the ability of the ionic liquids to disperse variety of nanomaterials without any stabilizing reagents makes it possible to prepare metal nanoparticles simply by electrochemical reduction of metal species dissolved in the ionic liquids. We have already reported the electrochemical preparation of the metal nanoparticles of such transition metals as Fe, Co, Ni, Pd, Ag, Cd, Pt, and Au in some ionic liquids composed of bis(trifluoromethylsulfonyl)amide (TFSA–) and dialkylpyrrolidinium cations.1-10 The average size of the nanoparticles prepared in the ionic liquids was found to be a few nanometers. However, the factors determining the average size of the nanoparticles have not been clarified yet. In the present study, the effects of the cations and anions on the size distribution of Pd nanoparticles has been investigated in the TFSA–- and FSA– (bis(fluorosulfonyl)amide)-based ionic liquids. The TFSA–-based ionic liquids composed of 1-butyl-, 1-hexyl-, and 1-decylpyrrolidinium (BMP+, HMP+, and DMP+) with bromides of the corresponding organic cations were used as the electrolytes. BMPFSA was prepared by the metathesis reaction of BMPBr and LiFSA. PdBr2 was dissolved in the electrolyte as a Pd(II) source. Glassy carbon was used as a working electrode. A rotating glassy carbon electrode was also used as a working electrode. A platinum wire was used as a counter electrode. A silver wire immersed in 0.1 M AgCF3SO3/BMPTFSA was used as a reference electrode. Pd nanoparticles were prepared by potentiostatic cathodic reduction using a double-compartment cell. The nanoparticles dispersed in the ionic liquids were characterized by transmission electron microscopy. Potentiostatic cathodic reduction on a GC electrode in BMPTFSA containing [PdCl4]2– resulted in deposition of Pd metal on the electrode and formation of Pd nanoparticles dispersed in the ionic liquid. The amount of Pd deposited on the GC electrode in BMPTFSA decreased with lowering the electrode potential, indicating the adsorption of Pd atom formed at the electrode-electrolyte interface onto the electrode surface is considered to be inhibited by accumulation of BMP+ at the interface at negative potentials.1 Pd nanoparticles were prepared using a rotating GC electrode with different rotating rates in order to examine the effects of the current density on the average size of Pd nanoparticles. The average size of Pd nanoparticles prepared at –2.5 V in 10 mM [PdBr4]2–/BMPTFSA was independent of the rotating rate, indicating the supply rate of Pd atoms at the electrode surface has no influence on the average size of Pd nanoparticles.10 The average size of Pd nanoparticles prepared in BMPTFSA, HMPTFSA, and DMPTFSA increased with an increase in the alkyl chain length of the cation.7 In addition, the average size of Pd nanoparticles prepared in BMPTFSA with excess Br–or in BMPFSA was smaller than that in BMPTFSA. These results suggested that the average size of Pd nanoparticles is mainly affected not by the current density and the electrode potential but by the size of the cations and anions composing the ionic liquids. References R. Fukui, Y. Katayama, and T. Miura, J. Electrochem. Soc., 158, D567 (2011). Y.-L. Zhu, Y. Katayama, and T. Miura, Electrochem. Solid-State Lett., 14, D110 (2011). Y. Katayama, R. Fukui, and T. Miura, Electrochemistry, 81, 532 (2013). Y. Katayama, T. Endo, T. Miura and K. Toshima, J. Electrochem. Soc., 160, D423 (2013). Y. Katayama, T. Endo, T. Miura, and K. Toshima, J. Electrochem. Soc., 161, D87 (2014). K. Yoshii, Y. Oshino, N. Tachikawa, K. Toshima, and Y. Katayama, Electrochem. Commun., 52, 21 (2015). Y. Katayama, Y. Oshino, N. Ichihashi, N. Tachikawa, K. Yoshii, and K. Toshima, Electrochim. Acta,183, 37 (2015). S. Saha, T. Taguchi, N. Tachikawa, K. Yoshii, Y. Katayama, Electrochim. Acta,183, 42 (2015). S. Sultana, N. Tachikawa, K. Yoshii, L. Magagnin, K. Toshima, and Y. Katayama, J. Electrochem. Soc., 163, D401 (2016). S. Sultana, N. Tachikawa, K. Yoshi, K. Toshima, L. Magagnin, and Y. Katayama, Electrochim. Acta, 249, 263 (2017).

Synthesis of Metal–Carbon Composites with Transition Metal Nanoparticles Distributed as Metal Core–Graphite-Like Shell Structures in the Bulk of an Amorphous Carbon Matrix

A method for the synthesis of metal–carbon nanocomposites in which metal-centered particles of the core–graphite-like shell type are distributed in the bulk of an amorphous sp2-carbon matrix is proposed. Polyvinyl chloride (PVC) was used as a carbon matrix precursor. The synthesis procedure included the following stages: The dehydrochlorination of PVC with diethylamine in a dimethyl sulfoxide solution in the presence of Co, Ni, Fe, or Cu nitrates; the carbonization of the product at 400°C; metal reduction with hydrogen at 500–620°C; and methane conversion at 620–850°C. The metal concentrations in the resulting composites were the following (%): Fe, 10; Ni, 10.8; Co, 11; and Cu, 21. The structure of the final metal–carbon nanocomposites was studied by transmission electron microscopy. The size of a metal core was 20–100 nm, and the number of graphene layers in a shell was to 50.

Uniform, Scalable, High-Temperature Microwave Shock for Nanoparticle Synthesis through Defect Engineering

Summary Here we demonstrate a thermal shock synthesis method triggered by microwave irradiation for the rapid synthesis of nanoparticles on reduced graphene oxide (RGO) substrate. With properly controlled reduction, RGO has high electrical conductivity while maintaining functional groups, leading to an extremely efficient microwave absorption of ∼70%. The high utilization of microwaves results in the ability to raise the temperature to 1,600 K in just 100 ms, which is followed by rapid quenching to room temperature. The defects on the RGO are crucial for achieving this record-high microwave-induced temperature as these defects play a fundamental role in absorbing the radiation as well as the self-quenching mechanism. By loading precursors onto RGO, we can utilize rapid temperature change to synthesize nanoparticles. The nanoparticles are ∼10 nm with uniform distribution. This facile, rapid, and universal synthesis technique has the potential to be employed in large-scale production of nanomaterials and suggests a new direction for nanosynthesis.

Surface enriched palladium on palladium-copper bimetallic nanoparticles as catalyst for polycyclic triazoles synthesis

Transition-metal nanoparticles (NPs) gained interest as a catalyst due to their high reactivity and recyclability. Monometallic NPs are less catalytic active compared to homogeneous counterparts as less number of catalytic active metal atoms are present on the surface of NPs and metal atoms present in the core part of the NPs are not utilized. It is necessary to synthesize a stable, reusable, highly reactive and economic catalyst which contain a more number of catalytic active precious metal atoms on the surface of NPs. Here in we have synthesized metal-carbon bond stabilized, alloy structured Pd/Cu bimetallic nanoparticles using binaphthyl moiety as a stabilizer (Pd/Cu-BNP). The enrichment of catalytically active precious Pd atoms over inexpensive Cu on the surface was observed with a narrow size distribution of the nanoparticles (average diameter 3 ± 0.5 nm). The Pd/Cu-BNP was used as an efficient and recyclable catalyst for the synthesis of polycyclic triazoles through domino alkyne insertion and CH bond functionalization reaction sequence.

Enhanced electrocatalytic activity of palladium nanochains by modifying transition metal core-shell nanoparticles (TMcore-shell = Ni@NiO, Co@CoO) on reduced graphene oxide for methanol electro-oxidation

Palladium nanochains with uniform dispersion supported transition metal core-shell nanoparticles (TMcore-shell, TMcore-shell = Ni@NiO, Co@CoO) modified reduced graphene oxide (rGO) are synthesized through a facile two-step method as the catalysts for methanol electro-oxidation. The transition metal nanoparticle consists of transition metal core and transition metal oxide shell layer with an average particle diameter of about 35 nm, which can play an important role in adjusting the electronic structure of Pd. It can be attributed to the different support-metal synergistic interaction (SMSI) between TMcore-shell-rGO support and Pd metal. In addition, the Pd/Co@CoO-rGO catalyst exhibits the highest electrocatalytic activity for methanol electro-oxidation, with the mass activity of 1786 mA mg−1, which is 7.01 times and 1.49 times as high as those of the commercial Pd/C and the commercial Pt/C, respectively. Furthermore, the Pd/Co@CoO-rGO catalyst keeps the best stability than the commercial Pd/C, the commercial Pt/C, Pd/rGO and Pd/Ni@NiO-rGO catalysts during all the test time. TMcore-shell-rGO support provide us a new strategy of structure engineering for highly efficient methanol oxidation.

Development of Metal Nanoparticle Catalysis toward Drug Discovery.

Transition-metal nanoparticles (NPs) catalysts supported on solid material represent one of the most important subjects in organic synthesis due to their reliable carbon-carbon or carbon-heteroatom bond-forming cross-coupling reactions. Therefore methodologically and conceptually novel immobilization methods for nonprecious transition-metal NPs are currently required for the development of organic, inorganic, green, materials, and medicinal chemistry. We discovered a self-assembled Au-supported Pd NPs catalyst (SAPd(0)) and applied it as a catalyst to Suzuki-Miyaura coupling, Buchwald-Hartwig reaction, Carbon(sp2 and sp3)-Hydrogen bond functionalization, double carbonylation, removal of the allyl protecting groups of allyl esters, and redox switching. SAPd(0) comprises approximately 10 layers of self-assembled Pd(0) NPs, whose size is less than 5 nm on the surface of a sulfur-modified Au. The Pd NPs are wrapped in a sulfated p-xylene polymer matrix. We thought that the self-assembled Au-supported Pd NPs could be made by in situ metal NP and nanospace simultaneous organization (PSSO). This methodology involves 4 kinds of simultaneous procedures: i) reduction of a higher valence metal salt, ii) growth of metal NPs with appropriate size, iii) growth of a matrix with appropriate pores, and iv) wrapping of the metal NPs by matrix nanopores. This methodology is different from previously reported metal NPs-immobilizing methods, which use solid supports with preformed pores or coordination sites. We also applied the in situ PSSO method to prepare various immobilized transition-metal NPs, including base metals. For example, the in situ PSSO method can be applicable to easily prepare Ni, Ru, and Fe NPs with good recyclability and low metal leaching for use in organic synthesis.

Facile fabrication of polypyrrole-coated silver nanoparticles: A novel and efficient surface-enhanced Raman scattering support for molecule detection

Conducting polymer coated noble metal particles, particularly polypyrrole (PPy)-coated silver (Ag) nanoparticles can be efficient and unprecedented surface-enhanced Raman scattering (SERS) electrodes. Here in this work, a very simple and robust strategy has been adopted to achieve PPy-coated Ag nanoparticles and thereafter used for molecular detection through SERS technique. PPy-coated Ag nanoparticles were synthesized by polymerizing pyrrole in presence of Ag nanoparticles via a facile oxidative chemical polymerization approach. Field emissions scanning electron microscopy, energy dispersive spectroscopy, elemental mapping analysis, Fourier transform infrared spectroscopy and UV–Visible diffuse reflectance spectroscopy data revealed the formation and structure of PPy-coated Ag nanoparticles. Strong interaction between PPy and PPy-coated Ag nanoparticles was observed. As-synthesized PPy-coated Ag nanoparticles were utilized as SERS-active substrate for molecule detection. Rhodamine 6G was used as an analyte and a detection limit up to part per billion was achieved. A plausible mechanism has been highlighted in this regard. The SERS-active electrodes as investigated in this study not only provide an effective means to molecule detection in reactive environment but also facilitate a viable strategy to coat sensitive nanoparticles, such as noble and transition metal nanoparticles, with conductive polymers. To the best of our knowledge, there is no attempt taken yet to use PPy-coated Ag nanoparticles as SERS-active substrate through photodynamic approach for molecule detection.

Transition-metal Nanoparticles Catalyzed Carbon-Carbon Coupling Reactions in Water

The use of transition-metal nanoparticles in catalysis has attracted much interest, and their use in carbon-carbon coupling reactions such as Suzuki, Heck, Sonogashira, Stille, Hiyama, and Ullmann coupling reactions constitutes one of their most important applications. The transition-metal nanoparticles are considered as one of the green catalysts because they show high catalytic activity for several reactions in water. This review is devoted to the catalytic system developed in the past 10 years in transition-metal nanoparticles-catalyzed carbon-carbon coupling reactions such as Suzuki, Heck, Sonogashira, Stille, Hiyama, and Ullmann coupling reactions in water.

Enhanced performance of well-dispersed Co species incorporated on porous carbon derived from metal-organic frameworks in 1,3-butadiene hydrogenation

Abstract Transition metal nanoparticles (TM NPs) have attracted much significant attention due to their low cost, excellent physicochemical properties and promising applications in a variety of fields. However, there are still great challenges when exploring a cost-effective and straightforward strategy to prepare TM NPs with optimal supports for maximizing their catalytic efficiency. Herein, we develop a facile route to prepare well-dispersed Co species incorporated onto porous carbon derived from metal-organic frameworks (MOFs). The composites are characterized carefully to understand their phase, particle size, porosity, and graphitization degree. As a result, with the increasing of carbonization temperatures, the particle size increased, and metallic cobalt formed apparently. When being used as catalysts in the hydrogenation of 1,3-butadiene, the catalysts exhibit high catalytic performance. Particularly, Co-BTC-500 displays the highest catalytic ability with turnover frequency (TOF) of 0.059 S-1 owing to the small particle size and the active sites of metallic Co. In addition, the conversion of 1,3-butadiene has no obvious change after reacting for 30 h at 60 °C. The highest selectivity of monobutenes (95%) and 1-butene (69%) is obtained over Co-BTC-700, which is comparable with Pd catalysts.

Nanoconfined Growth of Carbon-Encapsulated Cobalts as Cocatalysts for Photocatalytic Hydrogen Evolution

Transition metal nanoparticles encapsulated in carbon nanostructures (M@Carbon, M = Fe, Co, Ni, et al.) exhibit excellent catalytic performance toward the hydrogen evolution reaction (HER). However...

General Method for Synthesizing Transition-Metal Phosphide/N-Doped Carbon Nanomaterials for Hydrogen Evolution.

Applications of effective and steady metal catalysts for the hydrogen evolution reaction (HER) via electrolysis of water have a huge potential to relax energy crisis and reduce carbon dioxide emission. Herein, we design a simple, facile, and general approach for the synthesis of a series of transition-metal phosphide nanoparticles embedded in N-doped carbon (NC) nanomaterials using metal salts, abundantly available hexamethylene diamine tetra(methyl phosphonic acid), and urea as precursors. The resultant transition-metal phosphide nanoparticles can serve as high-efficiency and steady HER catalysts. Particularly, when the current density is 10 mA cm-2, the overpotentials of the obtained RhP2@NC are 30, 85, and 70 mV in acid (0.5 M H2SO4), neutral (1 M PBS), and alkaline (1 M KOH) solutions, respectively. Besides, the RhP2@NC exhibits good stability after 10 h in aforementioned solutions. More importantly, it is suited to fabricate other transition-metal phosphide nanoparticles/NC heterostructures by this synthetic strategy. The obtained CoP@NC, FeP@NC, Ni2P@NC, and Cu3P@NC also show relatively high efficiency for HER. Hence, the versatile synthesis strategy opens a new route for the research and fabrication of transition-metal phosphide-based catalysts for HER.

Reducing the Barrier Energy of Self-Reconstruction for Anchored Cobalt Nanoparticles as Highly Active Oxygen Evolution Electrocatalyst.

It is crucial for leaping forward renewable energy technology to develop highly active oxygen evolution reaction (OER) catalysts with fast OER kinetics, and the novel design of high-performance catalysts may come down to unveiling the origin of high catalytic behavior. Herein, a new class of heterogeneous OER electrocatalyst (metallic Co nanoparticles anchored on yttrium ruthenate pyrochlore oxide) is provided for securing fast OER kinetics. In situ X-ray absorption spectroscopy (in situ XAS) reveals that fast OER kinetics can be achieved by the harmonious catalytic synergy of a pyrochlore oxide support to Co nanoparticles. By the facile oxidation of yttrium (A-site) and ruthenium (B-site) cations, the pyrochlore oxide support helps to expel the electrons generated from the catalytic behavior of Co to the inner layers of the support, facilitating the electrostatic adsorption of OH- ions and reducing the barrier energy for the formation of CoOOH intermediates. This work affords the rational design of transition metal nanoparticles anchored on pyrochlore oxide heterogeneous catalysts and the fundamental insight of catalytic origin associated with self-reconstruction of OER electrocatalysts.

Magnetically separable rhodium nanoparticles as catalysts for releasing hydrogen from the hydrolysis of ammonia borane

Magnetically separable catalysts attract considerable attention in catalysis due to their facile separation from the reaction medium. This propensity is crucial for efficient multiple use of precious noble metal nanoparticles in catalysis. In fact, the isolation of catalysts from the reaction medium by filtration and washing results usually in the loss of huge amount of activity in the subsequent run of catalysis. Although many transition metal nanoparticle catalysts have been reported for the H2 generation from the hydrolysis of ammonia borane, there is no study reporting the magnetically separable rhodium based catalysts for the hydrolytic dehydrogenation of ammonia borane. Here, we report the preparation of rhodium(0) nanoparticles supported on the surface of Fe3O4 and CoFe2O4 magnetic nanopowders as the first example of magnetically separable rhodium nanocatalysts. The resulting magnetically separable Rh0/Fe3O4 and Rh0/CoFe2O4 nanoparticles are highly active, long-lived and reusable catalysts in H2 generation from the hydrolysis of ammonia borane providing a turnover frequency value of 273 and 720 min−1, respectively, at 25.0 ± 0.1 °C. These magnetically separable catalysts show high reusability and long-term stability in the hydrolysis reaction. They retain their complete initial activity even after the 5th use releasing exactly 3.0 equivalent H2 gas per mole of ammonia borane. The long-term stability tests show that Rh0/Fe3O4 and Rh0/CoFe2O4 nanoparticles provide a total turnover number of 125,000 and 245,000, respectively, in releasing H2 from the hydrolysis of ammonia borane at room temperature. The long term stability and reusability of magnetically separable Rh0/Fe3O4 and Rh0/CoFe2O4 nanoparticles make them attractive catalysts for hydrogen generation in fuel cell applications.

Molecular Signature of Asthma-Enhanced Sensitivity to CuO Nanoparticle Aerosols from 3D Cell Model.

More than 5% of any population suffers from asthma, and there are indications that these individuals are more sensitive to nanoparticle aerosols than the healthy population. We used an air–liquid interface model of inhalation exposure to investigate global transcriptomic responses in reconstituted three-dimensional airway epithelia of healthy and asthmatic subjects exposed to pristine (nCuO) and carboxylated (nCuOCOOH) copper oxide nanoparticle aerosols. A dose-dependent increase in cytotoxicity (highest in asthmatic donor cells) and pro-inflammatory signaling within 24 h confirmed the reliability and sensitivity of the system to detect acute inhalation toxicity. Gene expression changes between nanoparticle-exposed versus air-exposed cells were investigated. Hierarchical clustering based on the expression profiles of all differentially expressed genes (DEGs), cell-death-associated DEGs (567 genes), or a subset of 48 highly overlapping DEGs categorized all samples according to “exposure severity”, wherein nanoparticle surface chemistry and asthma are incorporated into the dose–response axis. For example, asthmatics exposed to low and medium dose nCuO clustered with healthy donor cells exposed to medium and high dose nCuO, respectively. Of note, a set of genes with high relevance to mucociliary clearance were observed to distinctly differentiate asthmatic and healthy donor cells. These genes also responded differently to nCuO and nCuOCOOH nanoparticles. Additionally, because response to transition-metal nanoparticles was a highly enriched Gene Ontology term (FDR 8 × 10–13) from the subset of 48 highly overlapping DEGs, these genes may represent biomarkers to a potentially large variety of metal/metal oxide nanoparticles.

Porphyrin‐Stabilized Transition Metal Nanoparticles and Their Applications in the Reduction of 4‐Nitrophenol and the Generation of Hydroxyl Radicals

The synthesis of robust transition metal nanoparticles (TMNPs) are still intensively investigated because of multiple up‐to date applications in catalysis, solar cells, nonlinear optics, biological labeling, nanoelectronics, medicine and energy storage devices. Here we report synthesis of tetrahydroxyphenylporphyrin (TPP‐OH)‐stabilized TMNPs (including AuNPs, AgNPs and PdNPs) by mixing TPP‐OH and simple commercial metal salt and followed by the addition of sodium borohydride at 0 °C. The as‐synthesized nanocomposites show high catalytic activity in the reduction of 4‐nitrophenol, a pertinacious pollutant occurring in industrial waste water. In addition, it is evident that a drastic absorption change has been observed in UV/Vis spectra, confirming that generation of hydroxyl radicals induced by AgNPs and further oxidized methylene blue (MB) to hydroxymethylene blue (MB‐OH).

Role of Polymer Structures in Catalysis by Transition Metal and Metal Oxide Nanoparticle Composites.

Nanoparticle (NP)/polymer nanocomposites received considerable attention because of their important applications including catalysis. Metal and metal oxide NPs may impart catalytic properties to polymer nanocomposites, while polymers with a different structure, functionality, and architecture control the NP formation (size, shape, location, composition, etc.) and in this way, govern catalytic properties of nanocomposites. In this review we will discuss the influence of the polymer nanostructure (thin or grafted layers, polymer ordering, polymer nanopores), architecture (branched vs linear), functional groups (coordinating or ionic), specific properties (reducing, stimuli responsive, conductive), etc. on the formation of metal or metal oxide NPs and the catalytic behavior of the nanocomposites. The development of novel and efficient catalysts is crucial for progress in chemical sciences, and this explains a huge number of publications in this area in recent years. Taking into consideration previous review articles on NP/polymer catalysts, we limited this review to a discussion of a narrow temporal scope (2017-April 2019), while embracing a broad subject scope, i.e., considering any polymers and NPs which form catalytic nanocomposites. This gives us a unique view of the field of catalytic polymer nanocomposites and allows understanding of where the field is going.

Novel CdFe Bimetallic Complex-Derived Ultrasmall Fe- and N-Codoped Carbon as a Highly Efficient Oxygen Reduction Catalyst.

During the development of oxygen reduction reaction electrocatalysts, transition-metal nanoparticles embedded in N-doped graphene have attracted increasing attention owing to their low-priced, minimal environmental impact, and satisfying performance. In this study, a new organic-cadmium (Cd) complex formed through Cd2+ coordination with p-phenylenediamine (PPD) was used to synthesize highly active Fe-embedded N-doped carbon catalysts for the first time. It is significant that with the decreasing molar ratio of Cd/Fe, an obvious microstructure evolution was observed in Cd-Fe-PPD from diamond-like blocks to thick flakes, and further bloomed into flowerlike shapes with ultrathin petals and then eventually exhibited large block starfish-like shapes. After carbonization, Cd was removed, slack and porous N-doped carbon was formed, and Fe was assembled in the N-doped carbon. Similar phenomenon was also observed in Co-PPD. The optimized Fe/NPC-2 material featuring uniform and well-dispersed 3-5 nm Fe nanoparticles embedded in two-dimensional ultrathin carbon nanosheets delivered excellent electrocatalytic performance ( Eonset: 0.96 V vs reversible hydrogen electrode (RHE), E1/2: 0.84 V vs RHE), which is very close to those of commercial platinum on carbon (Pt/C) ( Eonset: 0.95 V vs RHE, E1/2: 0.84 V vs RHE), and its methanol tolerance and durability also surpass those of Pt/C.

Nanoparticle Formation Kinetics and Mechanistic Studies Important to Mechanism-Based Particle-Size Control: Evidence for Ligand-Based Slowing of the Autocatalytic Surface Growth Step Plus Postulated Mechanisms

Ligands are known to affect the formation, stabilization, size, and size-dispersion control of transition-metal and other nanoparticles, yet the kinetic and mechanistic basis for such ligand effects remains to be elucidated and then coupled to predictions for improved particle size and narrower particle size distribution syntheses. Toward this broad goal, the effect of the added excess ligand (L) and the stabilizer, L = POM9– (= the polyoxometalate, P2W15Nb3O629–) is studied for the formation of POM9–-stabilized Ir(0)n nanoparticles, {Ir(0)n·(POM9–)m}9m−, synthesized from an atomically characterized precatalyst (COD)Ir·POM8– under H2. First, the balanced reaction stoichiometry and characterization of the nanoparticle products are established. Next, the kinetics of nanoparticle formation is analyzed initially by the FW 2-step minimum mechanism consisting of slow, continuous nucleation, A → B (rate constant k1obs), and autocatalytic surface growth, A + B → 2B (rate constant k2obs), where A is nominally (COD...