Highly Oxidized Platinum Nanoparticles Prepared through Radio‐Frequency Sputtering: Thermal Stability and Reaction Probability towards CO

Platinum‐oxide nanoparticles were prepared through the radio‐frequency (RF) discharge sputtering of a Pt electrode in an oxygen atmosphere. The structure, particles size, electronic properties, and surface composition of the RF‐sputtered particles were studied by using transmission electron microscopy and X‐ray photoelectron spectroscopy. The application of the RF discharge method resulted in the formation of highly oxidized Pt⁴⁺ species that were stable under ultrahigh vacuum conditions up to 100 °C, indicating the capability of Pt⁴⁺–O species to play an important role in the oxidation catalysis under real conditions. The thermal stability and reaction probability of Pt⁴⁺ oxide species were analyzed and compared with those of Pt²⁺ species. The reaction probability of PtO₂ nanoparticles at 90 °C was found to be about ten times higher than that of PtO‐like structures.     

CO and methanol adsorption on (2 × 1)Pt(110) and ion‐eroded Pt(111) model catalysts

Methanol adsorption on ion‐sputtered Pt(111) surface exhibiting high concentration of vacancy islands and on (2 × 1)Pt(110) single crystal were investigated by means of photoelectron spectroscopy (PES) and thermal desorption spectroscopy. The measurements showed that methanol adsorbed at low temperature on sputtered Pt(111) and on (2 × 1)Pt(110) surfaces decomposed upon heating. The PES data of methanol adsorption were compared to the data of CO adsorbed on the same Pt single crystal surfaces. In the case of the sputtered Pt(111) surface, the dehydrogenation of H_xCO intermediates is followed by the CO bond breakage. On the (2 × 1)Pt(110) surface, carbon monoxide, as product of methanol decomposition, desorbed molecularly without appearance of any traces of atomic carbon. By comparing both platinum surfaces we conclude that methanol decomposition occurs at higher temperature on sputtered Pt(111) than on (2 × 1)Pt(110). Copyright © 2010 John Wiley & Sons, Ltd.     

One‐Pot Self‐Templating Synthesis of Pt Hollow Nanostructures and Their Catalytic Properties for CO Oxidation

Nanoporous Pt hollow nanostructures with octahedral and hexagonal frame‐like morphologies were prepared by a novel one‐pot self‐templating route with no assistance from a preformed template or shape‐directing agent. The hexagonal frame‐like Pt hollow structures exhibited significantly enhanced catalytic activity toward CO oxidation reaction compared to the octahedral Pt hollow nanostructures due to the higher oxidation state of Pt.     

Estimation of Surface Structure and Carbon Monoxide Oxidation Site of Shape‐Controlled Pt Nanoparticles

Surface structures of shape‐controlled Pt nanoparticles have been estimated using cyclic voltammetry (CV) and infrared reflection absorption spectroscopy (IRAS). Cubic and cuboctahedral Pt nanoparticles are prepared using a capping polymer. These nanoparticles give CVs similar to those of single crystal electrodes of Pt in sulfuric acid solution. The CV of cubic nanoparticles is similar to that of the Pt(510) [=5(100)–(110)] electrode, while the CV of cuboctahedral nanoparticles is reproduced well with the convolution of Pt(766) [=13(111)–(100)] and Pt(17 1 1) [=9(100)–(111)] electrodes. These results suggest that the planes of the cubic and cuboctahedral nanoparticles are composed of step‐terrace and atomically flat terraces, respectively. Adsorbed carbon monoxide (CO) on the shape‐controlled nanoparticles gives the IR bands that are assigned to on‐top and bridged CO. The band of on‐top CO is deconvoluted to two bands: the higher and the lower frequency bands are assigned to the CO on the plane and the edges of the nanoparticles, respectively. On‐top CO adsorbed on the edges is oxidized at more negative potential than that on the planes. Edge sites of the nanoparticles promote CO oxidation.     

Effects of Adsorbate Coverage and Bond‐Length Disorder on the d‐Band Center of Carbon‐Supported Pt Catalysts

Determination of the factors that affect the d‐band center of catalysts is required to explain their catalytic properties. Resonant inelastic X‐ray scattering (RIXS) enables direct imaging of electronic transitions in the d‐band of Pt catalysts in real time and in realistic environmental conditions. Through a combination of in situ, temperature‐resolved RIXS measurements and theoretical simulations we isolated and quantified the effects of bond‐length disorder and adsorbate coverage (CO and H₂) on the d‐band center of 1.25 nm size Pt catalysts supported on carbon. We found that the decrease in adsorbate coverage at elevated temperatures is responsible for the d band shifts towards higher energies relative to the Fermi level, whereas the effect of the increase in bond‐length disorder on the d‐band center is negligible. Although these results were obtained for a specific case of non‐interacting support and weak temperature dependence of the metal–metal bond length in a model catalyst, this work can be extended to a broad range of real catalysts.     

High‐Efficiency Encapsulation of Pt Nanoparticles into the Channel of Carbon Nanotubes as an Enhanced Electrocatalyst for Methanol Oxidation

Pt‐based nanostructures serving as anode catalysts for the methanol oxidation reaction (MOR) have been widely studied for many years. Nevertheless, challenging issues such as poor reaction kinetics and the short‐term stability of the MOR are the main drawbacks of such catalysts and limit their applications. Herein, we have developed a facile approach to encapsulate Pt nanoparticles (NPs) inside the nanochannels of porous carbon nanotubes (CNTs; Pt‐in‐CNTs) as a new enhanced electrocatalytic material. The as‐prepared CNTs offer simultaneously ordered diffusion channels for ions and a confinement effect for the NPs, which both facilitate the promotion of catalytic kinetics and avoid the Ostwald ripening of Pt NPs, thus leading to high activity and durable cycle life as an anode catalyst for MOR. This work provides a new approach for enhancing the stability and activity by optimizing the structure of the catalyst, and the Pt‐in‐CNTs represent the most durable catalysts ever reported for MOR.     

Direct Observation of the Collision of Single Pt Nanoparticles onto Single‐Crystalline Gold Nanowire Electrodes

We observed the collision of single Pt nanoparticles (NPs) onto an Au nanowire (NW) electrode by using electrocatalytic amplification. Previously, such observations had typically been performed by using a microscale disk‐type ultramicroelectrode (UME). The use of a NW electrode decreased the background noise current and provided a shielding effect, owing to adsorption of the NPs onto the insulating sheath. Therefore, the transient current signal that was caused by the collision of single NPs could be more clearly distinguished from the background current by using a NW electrode instead of a UME. Furthermore, the use of a NW electrode increased the collisional frequency and the magnitude of the transient current signal. The experimental data were analyzed by using a theoretical model and a random walk simulation model.     

Carbon Aerogels Supported Pt Nanoparticles as Electrocatalysts for Methanol Oxidation in Alkaline Media

Carbon aerogels (CAs) were prepared by sol‐gel polycondensation of resorcinol and formaldehyde with BET surface area of 616 m² g^?1 and the average pore size of 9.8 nm. The prepared CAs were used as supports for Pt nanoparticles for methanol oxidation in alkaline media. In comparison with Pt supported on commercial Vulcan XC‐72R carbon (Pt/C) electrocatalysts, Pt supported on CAs (Pt/CAs) electrocatalysts exhibited higher peak current density and more negative onset potential toward methanol oxidation. The effects of different parameters such as NaOH concentration, methanol concentration, and scan rate on the methanol oxidation reaction were investigated in detail. The results showed that the Pt/CAs electrocatalysts had promising application for methanol oxidation in alkaline media.     

An Amphiphilic Resin‐dispersion of Nanoparticles of Platinum (ARP‐Pt): A Highly Active and Recyclable Catalyst for the Aerobic Oxidation of a Variety of Alcohols in Water

Please recycle! An amphiphilic polystyrene‐poly(ethylene glycol) resin‐dispersion of nanoparticles of platinum (ARP‐Pt) is developed, with the nanoparticles exhibiting a narrow size distribution throughout the resin. ARP‐Pt offers a sustainable chemistry alternative as a useful and readily recyclable catalyst for the aerobic oxidation of a wide variety of alcohols.

     

Dark‐Field‐Based Observation of Single‐Nanoparticle Dynamics on a Supported Lipid Bilayer for In Situ Analysis of Interacting Molecules and Nanoparticles

Observation of single plasmonic nanoparticles in reconstituted biological systems allows us to obtain snapshots of dynamic processes between molecules and nanoparticles with unprecedented spatiotemporal resolution and single‐molecule/single‐particle‐level data acquisition. This Concept is intended to introduce nanoparticle‐tethered supported lipid bilayer platforms that allow for the dynamic confinement of nanoparticles on a two‐dimensional fluidic surface. The dark‐field‐based long‐term, stable, real‐time observation of freely diffusing plasmonic nanoparticles on a lipid bilayer enables one to extract a broad range of information about interparticle and molecular interactions throughout the entire reaction period. Herein, we highlight important developments in this context to provide ideas on how molecular interactions can be interpreted by monitoring dynamic behaviors and optical signals of laterally mobile nanoparticles.     

Pathways for the Non‐CO‐Involved Oxidation of Methanol on Pt(111)

The non‐CO‐involved oxidation of methanol (NCOIOM) on a Pt(111) surface is investigated by using density functional theory. Relative energy diagrams for the NCOIOM are established in which the reaction mechanisms for a catalytic cycle—including the associated barriers, the reactive energies, the intermediates, and the transient states—are shown. The results indicate that the reaction proceeds via the kinetically favored pathways: A) HCOH→HC(OH)₂→HCOOH→HCOO‐ [‐COOH]→CO₂ and B) CHO→HCOOH→HCOO‐ [‐COOH]→CO₂, with OH playing a key role in the entire process. The vibrational frequencies of the intermediate states derived from the calculations are in agreement with the experimental measurements.     

Catalytic Performance of Graphite Oxide Supported Au Nanoparticles in Aerobic Oxidation of Benzyl Alcohol: Support Effect

Various Au/GO catalysts were prepared by depositing Au nanoparticles on thermally- and chemically-treated graphite oxide (GO) supports using a sol-immobilization method. The surface chemistry and structure of GO supports were characterized by a series of analytical techniques including X-ray photoelectron spectroscopy, temperature-programmed desorption and Raman spectroscopy. The results show that thermal and chemical treatments have large influence on the presence of surface oxygenated groups and the crystalline structure of GO supports. A strong support effect was observed on the catalytic activity of Au/GO catalysts in the liquid phase aerobic oxidation of benzyl alcohol. Compared to the amount and the type of surface oxygen functional groups, the ordered structure of GO supports may play a more important role in determining the catalytic performance of Au/GO catalysts.     

表面增强拉曼光谱研究吸附电位对CO在Pt电极上氧化行为的影响

预吸附电势对CO在Pt上的氧化行为有重要影响. 在电势低于0.3 V（vs. RHE）下,预吸附的CO单层在Pt电极上0.4 V就开始氧化,并会在0.6 V左右出现1个较小的氧化峰,即所谓的“氧化前峰”,而在双电层电位区间饱和吸附的CO只有当电势正于0.6 V才氧化     

Chemical‐Reaction‐Induced Hot Electron Flows on Platinum Colloid Nanoparticles under Hydrogen Oxidation: Impact of Nanoparticle Size

Generation of hot electron flows and the catalytic activity of Pt nanoparticles (NPs) with different sizes were investigated using catalytic nanodiodes. We show that smaller Pt NPs lead to higher chemicurrent yield, which is associated with the shorter travel length for the hot electrons, compared with their inelastic mean free path. We also show the impact of capping on charge carrier transfer between Pt NPs and their support.     

碳纳米管电极上原位沉积Pt纳米颗粒

 本文利用原位离子交换法制备了碳纳米管(CNTs)载铂(Pt/CNTs)电极. X射线光电子能谱分析表明, Pt通过离子交换载于电化学功能化的CNTs表面. 扫描电镜照片显示, Pt高度分散于CNTs表面. X射线衍射分析表明, Pt的粒径约为4.0 nm. 离子交换法所制Pt/CNTs电极的电化学表面积和Pt的利用率均大于传统Pt/CNTs电极(Pt粒径约为2.5 nm), 其对氧还原的催化活性高于传统电极. 这归因于离子交换法所制电极的特殊结构,即Pt普遍载于电化学活性位上.