Platinum Nanostructures Research Articles

Plasmonic Pt Nanocrystals by Using a Sacrificial In Component via the Enhanced Dewetting on Sapphire (0001): Improvement on Morphological and Localized Surface Plasmon Resonance Properties

Modulation of functional metallic nanoparticles (NPs) in terms of their size, configuration, and dimension can offer a promising route to control the optical, catalytic, magnetic, and sensing properties for a wide range of applications. Herein, the platinum (Pt) nanostructures of improved morphological and localized surface plasmon resonance properties are demonstrated via the enhanced solid-state dewetting by using a sacrificial indium (In) layer on sapphire (0001). Upon annealing, the concurrent occurrence of intermixing between In and Pt atoms, formation of In–Pt alloy and sublimation of In atoms plays major roles in accelerating the dewetting process, which results in the formation of definite Pt nanostructures. The alteration in the In and Pt ratio readily varies the shape, size, and areal density of the resulting Pt NPs. The optical characteristics reveal that the localized surface plasmon resonance (LSPR) response is sensitively affected by the resulting surface morphology of Pt NPs. Specifically, ...

Understanding contact between platinum nanocontacts at low loads: The effect of reversible plasticity

Metal nanocontacts play a critical role in atomic force microscopy, functional nanostructures, metallic nanoparticles, and nanoscale electromechanical devices. In all cases, knowledge of the area of contact, and its variation with load, is critical for the quantitative prediction of behavior. Often, the contact area is predicted using continuum mechanics models which relate contact size to geometry, material properties, and load. Here we show for platinum nanoprobes that the contact size deviates significantly from these continuum predictions, even at low applied loads and in the absence of irreversible shape change. We use in situ transmission electron microscopy (TEM) with matched molecular dynamics (MD) simulations to investigate the load-dependent size of the contact. Direct measurements of contact radius from MD and TEM exceed the predictions of continuum mechanics by 24%–164%, depending on the model applied. The physical mechanism for this deviation is found to be dislocation activity in the near-surface material, which is fully reversed upon unloading. These findings demonstrate that contact mechanics models are insufficient for predicting contact area in real-world platinum nanostructures, even at ultra-low applied loads.

Shape-Controlled Synthesis of Luminescent Hemoglobin Capped Hollow Porous Platinum Nanoclusters and their Application to Catalytic Oxygen Reduction and Cancer Imaging

Engineering hollow and porous platinum nanostructures using biomolecular templates is currently a significant focus for the enhancement of their facet-dependent optical, electronic, and electrocatalytic properties. However, remains a formidable challenge due to lack of appropriate biomolecules to have a structure-function relationship with nanocrystal facet development. Herein, human hemoglobin found to have facet-binding abilities that can control the morphology and optical properties of the platinum nanoclusters (Pt NCs) by regulation of the growth kinetics in alkaline media. Observations revealed the growth of unusual polyhedra by shape-directed nanocluster attachment along a certain orientation accompanied by Ostwald ripening and, in turn, yield well-dispersed hollow single-crystal nanotetrahedrons, which can easily self-aggregated and crystallized into porous and polycrystalline microspheres. The spontaneous, biobased organization of Pt NCs allow the intrinsic aggregation-induced emission (AIE) features in terms of the platinophilic interactions between Pt(II)-Hb complexes on the Pt(0) cores, thereby controlling the degree of aggregation and the luminescent intensity of Pt(0)@Pt(II)−Hb core−shell NCs. The Hb-Pt NCs exhibited high-performance electrocatalytic oxygen reduction providing a fundamental basis for outstanding catalytic enhancement of Hb-Pt catalysts based on morphology dependent and active site concentration for the four-electron reduction of oxygen. The as-prepared Hb-Pt NCs also exhibited high potential to use in cellular labeling and imaging thanks to the excellent photostability, chemical stability, and low cytotoxicity.

Synthesis of Platinum Nanocrystals within Iodine Ions Mediated

A liquid-phase reducing method of synthesizing Pt nanocrystals was demonstrated, and dendrite-, cube-, and cuboctahedron-shaped Pt nanocrystals (NCs) with well-defined monomorphic were successfully synthesized through iodine ions mediated with the CTAB agent. When the KI concentration was increased to thirty times of K2PtCl4 at the nucleation stage, the high-quality Pt nanodendrites could be obtained. However, no matter how many KI were added at the growth age, only cube- and cuboctahedron-shaped Pt nanocrystals formed. The results of high-resolution TEM, EDX, and XRD indicated that the size and shape of Pt NCs could be turned by changing the concentration and time of KI. In the nucleation stage, it might be due to that some iodine ions adsorb on the surfaces of Pt NCs, which probably cause the rapid growth process resulting in the formation of Pt nanodendrites. In the growth stage, although high concentrations of I− ions could contribute to the shape control and generate bigger particles of Pt NCs, small Pt particles do not grow into dendrites. The insight into the role of I− ions in synthesis of Pt NCs reported here provided a viewpoint for clearly understanding the formation mechanism of anisotropic platinum nanostructures.

Platinum and N-doped carbon nanostructures as catalysts in hydrodechlorination reactions

Novel Pt catalysts supported on undoped and N-doped (1% N, w) carbons with well interconnected and nanostructured mesoporosity (Vmesopore = 0.65 cm3 g−1, SEXT = 730 m2 g−1) were prepared and tested in the hydrodechlorination of 4-chlorophenol in water at 30–70 °C. The growth of Pt nanoparticles was achieved using incipient wetness impregnation and a modified colloidal synthesis. Total conversion of 4chlorophenol and 100% selectivity to cyclohexanol was achieved. The remarkable activity in the hydrogenation of the phenol resulting from hydrodechlorination has not been reported before with Pt catalysts and it is of high interest because it maximizes detoxification. When the Pt NPs were synthesized by incipient wetness impregnation some influence of the N-doping of the support was observed in the size and electronic state of the NPs. However, highly reproducible Pt NPs were prepared by in situ colloidal synthesis regardless the nature of the support. In this last case similar activity was observed for the catalysts with undoped and N-doped carbon support, although the activity increased more with temperature for the later. Apparent activation energies of 15–25 kJ mol−1 were obtained for the disappearance of 4-chlorophenol.

Electrochemical and Chemical Synthesis of Platinum Hierarchical Nanostructures Using Bicontinuous Microemulsions

Fabrication of hierarchical noble metal nanostructures is of interest due to the unique structural arrangement of nanoscale building blocks: nanocrystals or nanoparticles, composition and size are important in taking the physical and chemical usefulness of metal nanomaterials to a macroscopic scale. Various methods have been employed in achieving nanostructures of unique morphological arrangement. Amongst which are chemical and electrochemical reduction, or electrodeposition. In this research, platinum hierarchical nanostructures (PtHNs) were prepared using bicontinuous microemulsion (BC-ME) as soft templates. The PtHNs were synthesized using electrodeposition method as well as chemical reduction method. PtHNs was electrodeposited on Au macroelectrode from the bicontinuous microemulsion as well as from aqueous solution of chloroplatinic acid. Linear sweep voltammetry and chronopotentiometry was employed to achieve the deposition of Pt0 from the aqueous and bicontinuous platinum microemulsion electrolytic media. In the chemical method, sodium borohydride was used to reduce the hexachloroplatinic ions present in the bicontinuous microemulsion to platinum nanomaterial. In using bicontinuous microemulsions as a soft templates, the channels serve as continuous vessels for the converging growth of structures, which are dimensionally restricted by the diameter of the channels. PtHNs were characterized by SEM, EDX, TEM, XRD and cyclic voltammetry. The SEM images obtained, showed that the structure was unique, hierarchical with a regular morphology. From the SEM images, it was observed that the chemically synthesized PtHNs, were made up of interconnected spheres and self-assembled nanoneedles forming a nanocoral shape. The PtHNs XRD patterns confirm the polycrystalline nature of the platinum nanomaterials. Cyclic voltammetry (CV) of PtHNs synthesized through chemical reduction and electrodeposition method was conducted in degassed 0.5 M H2SO4. CV measurements (current voltage curve) essentially provide information about the electrochemical reactions that occurs on a working electrode surface. Electrochemical active surface area (ECSA) values of 35.1 m2/g and 20.9 m2/g were recorded for PtHNs synthesized by chemical reduction of 2% and 4% water soluble Pt precursor respectively. The highest ECSA value of 35.1 m2/g recorded from the PtHNs is higher than Pt dendritic tubes (23.3 m2/g) reported by Zhang et al. [1]. This clearly shows that the catalytic ability of the nanostructures synthesized in this work are highly desirable. The electrochemical surface area (ECSA) of 14.6 m2/g was recorded for the PtHNs electrodeposited on Au macroelectrode from aqueous Pt electrolyte while 12.2 m2/g was obtained when bicontinuous microemulsion of Pt was used as the platinum electrodeposition media. The PtHNs synthesized by the chemical method exhibited larger surface area than the platinum nanomaterial synthesized by electrodeposition. Broadly, this report presents a novel study of different synthetic methods for obtaining platinum nanostructures demonstrating the “template effect” of bicontinuous microemulsions towards the synthesis of metallic superstructures. Reference [1] Zhang, G., Sun, S., Cai, M., Zhang, Y., Li, R., and Sun, X., 2013, Porous dendritic platinum nanotubes with extremely high activity and stability for oxygen reduction reaction: Sci. Rep., 3, 1526. Figure 1

Synthesis of 3D Porous Nanostructured Platinum Using Atomic Layer Deposition

Platinum is known for its catalytic efficiency, exceptional electrical and electrochemical properties, and high resistance to corrosion. Pt nanostructures exposing large surface areas are widely used in catalytic converters, chemical production, and gas sensing and energy conversion technologies. Engineering porosity into Pt nanomaterials is an explored route to maximize the surface over volume ratio and to enhance the performance while reducing the Pt content and cost. It is well established that the properties of 3D-structured Pt nanomaterials are closely related to their geometrical configuration. Synthesis approaches that can produce well-defined porous Pt nanostructures are therefore attractive. Here, we present the creation of micrometer sized porous Pt nanostructures using atomic layer deposition (ALD) [1]. Robust and easy to handle porous Pt is fabricated by replication of an ordered mesoporous silica with a special pore architecture. After ALD of Pt in the unique 3D channel system of the silica material and digestion of the template, a fully connected ordered porous Pt network is obtained with a 3D structure corresponding to that of the host matrix, as revealed with high-resolution scanning transmission electron microscopy and electron tomography. The Pt nanostructure consists of hexagonal Pt rods (with a diameter of ca. 11 nm) originating from the straight mesopores of the host structure and linking features resulting from Pt replication of interconnecting slits. The Pt replica is evaluated for its potential use as electrocatalyst for the hydrogen evolution reaction (HER), one of the half-reactions of water electrolysis. The high activity displayed by the material is attributed to the 3D ordered, mesoporous structure with large surface area.

Platinum Nanostructure/Nitrogen-Doped Carbon Hybrid: Enhancing its Base Media HER/HOR Activity through Bi-functionality of the Catalyst.

The design and synthesis of an active catalyst for the hydrogen evolution reaction/hydrogen oxidation reaction (HER/HOR) are important for the development of hydrogen-based renewable technologies. The synthesis of a hybrid of platinum nanostructures and nitrogen-doped carbon [Pt-(PtOx )-NSs/C] for HER/HOR applications is reported herein. The HER activity of this Pt-(PtOx )-NSs/C catalyst is 4 and 6.5 times better than that of commercial Pt/C in acids and bases, respectively. The catalyst exhibits a current density of 10 mA cm-2 at overpotentials of 5 and 51 mV, with Tafel slopes of 29 and 64 mV dec-1 in 0.5 m H2 SO4 and 0.5 m KOH. This catalyst also showed superior HOR activity at all pH values. The HER/HOR activity of Pt-(PtOx )-NSs/C and PtOx -free Pt-nanostructures on carbon (PtNSs/C) catalysts are comparable in acid. The presence of PtOx in Pt-(PtOx )-NSs/C makes this Pt catalyst more HER/HOR-active in basic media. The activity of the Pt-(PtOx )-NSs/C catalyst is fivefold higher than that of the PtNSs/C catalyst in basic medium, although their activity is comparable in acid. The hydrogen-binding energy and oxophilicity are two equivalent descriptors for HER/HOR in basic media. A bifunctional mechanism for the enhanced alkaline HER/HOR activity of the Pt-(PtOx )-NSs/C catalyst is proposed. In the bifunctional Pt-(PtOx )-NSs/C catalyst, PtOx provides an active site for OH- adsorption to form OHads , which reacts with hydrogen intermediate (Hads ), present at neighbouring Pt sites to form H2 O; this leads to enhancement of the HOR activity in basic medium. This work may provide an opportunity to develop catalysts for various renewable-energy technologies.

Thermal transport during thin-film argon evaporation over nanostructured platinum surface: A molecular dynamics study

Investigation of thermal transport characteristics of thin-film liquid evaporation over nanostructured surface has been conducted using molecular dynamics simulation with particular importance on the effects of the nanostructure configuration for different wall–fluid interaction strengths. The nanostructured surface considered herein comprises wall-through rectangular nanoposts placed over a flat wall. Both the substrate and the nanostructure are of platinum while argon is used as the evaporating liquid. Two different wall–fluid interaction strengths have been considered that essentially emulate both hydrophilic and hydrophobic wetting conditions for three different nanostructure configurations. The argon–platinum molecular system is first equilibrated at 90 K and then followed by a sudden increase in the wall temperature at 130 K that induces evaporation of argon laid over it. Comparative effectiveness of heat and mass transfer for different surface wetting conditions has been studied by calculating the wall heat flux and evaporative mass flux. The results obtained in this study show that heat transfer occurs more easily in cases of nanostructured surfaces than in case of flat surface. Difference in behavior of argon molecules during and after the evaporation process, that is, wall adsorption characteristics, has been found to depend on the surface wetting condition as well as on presence and configuration of nanostructure. A thermodynamic approach of energy balance shows reasonable agreement with the present molecular dynamics study.

(Invited) Structure and Reactivity of Hybrid Functional Materials in Electrocatalysis

Our research interests aim at establishing structure/property relations leading to rational designs of functionalized materials for efficient electrocatalysis and electrochemical energy conversion and storage. There has been growing interest in the electrochemical reduction of carbon dioxide, a potent greenhouse gas and a contributor to global climate change. Given the fact that the CO2 molecule is very stable, its electroreduction processes are characterized by large overpotentials. To optimize the hydrogenation-type electrocatalytic approach, we have proposed to utilize nanostructured metallic centers (e.g. Pd, Pt or Ru) in a form of highly dispersed and reactive nanoparticles generated within supramolecular network of distinct nitrogen, sulfur or oxygen-coordination complexes. Among important issues are the mutual completion between hydrogen evolution and carbon dioxide reduction and specific interactions between coordinating centers and metallic sites. We have also explored the ability of biofilms to form hydro-gel-type aggregates of microorganisms attached to various surfaces including those of carbon electrode materials. Upon incorporation of various noble metal nanostructures and/or conducting polymer ultra-thin films, highly reactive and selective systems toward CO2-reduction have been obtained. Another possibility to enhance electroreduction of carbon dioxide is to explore direct transformation of solar energy to chemical energy using transition metal oxide semiconductor materials. We show here that, by intentional and controlled combination of metal oxide semiconductors (titanium (IV) oxide and copper (I) oxide), we have been able to drive effectively photoelectrochemical reduction of carbon dioxide mostly to methanol. Application of mixed-metal oxides as active matrices is also of particular importance to electrocatalytic oxidations of small organic molecules in low-temperature fuel cell technologies. The hydrous behavior, which favors proton mobility and affects overall reactivity, reflects not only the oxide’s chemical properties but its texture and morphology as well. For example, during oxidation of ethanol (e.g. at PtRu), when rhodium nanoparticles have been dispersed in between WO3 and ZrO2 layers, significant current enhancements are observed. The result can be rationalized in terms of the formation of nanoreactors in which Rh induces splitting of C-C bonds in C2H5OH molecules before the actual electrooxidtion steps. We also consider nanoelectrocatalytic systems permitting effective operation of the iodine-based charge relays in dye sensitized solar cells. The ability of palladium or platinum nanostructures to induce splitting of I-I bonds in the iodine (triiodide) molecules is explored here to enhance electron transfers in the triiodide/iodide-containing 1,3-dialkylimidazolium room-temperature ionic liquids.

(Energy Technology Division Research Award Address) Hydroxide Exchange Membrane Fuel Cells for Affordable Zero-Emission Cars

One of the grand challenges facing humanity today is the development of an alternative energy system that is safe, clean, and sustainable and where combustion of fossil fuels no longer dominates. A distributed renewable electrochemical energy and mobility system (DREEMS) could meet this challenge1. At the foundation of this new energy system, we have chosen to study a number of electrochemical devices including fuel cells, electrolyzers, and flow batteries. For all these devices electrocatalysis and polymer electrolytes play a critical role in controlling their performance, cost, and durability, and thus their economic viability. In this presentation, I will focus on our work on hydroxide exchange membrane fuel cells (HEMFCs)2 which can work with nonprecious metal catalysts3 and inexpensive hydrocarbon polymer membranes4. More specifically I will show the roadmap we have developed for HEMFCs to achieve performance parity with proton exchange membrane fuel cells5, the progress we have made in developing the most stable membranes and the most active nonprecious metal catalysts6. I will also discuss our work on addressing cell/system level issues like reverse current decay and water management7-9, and why hydrogen oxidation reactions are slower in base than in acid for precious metal catalysts10-12. References (1) S. Gu, B. Xu, Y. Yan. Electrochemical Energy Engineering: A New Frontier of Chemical Engineering Innovation. Annual Review of Chemical and Biomolecular Engineering 2014, 5: 429-454. (2) S. Gu, R. Cai, T. Luo, Z. Chen, M. Sun, Y. Liu, G. He, Y. Yan. A Soluble and Highly Conductive Ionomer for High-Performance Hydroxide Exchange Membrane Fuel Cells. Angewandte Chemie-International Edition 2009, 48(35): 6499-6502. (3) S. Gu, W. Sheng, R. Cai, S. M. Alia, S. Song, K. O. Jensen, Y. Yan. An efficient Ag-ionomer interface for hydroxide exchange membrane fuel cells. Chemical Communications 2013, 49(2): 131-133. (4) S. Gu, J. Wang, R. B. Kaspar, Q. Fang, B. Zhang, E. B. Coughlin, Y. Yan. Permethyl Cobaltocenium (Cp-2*Co+) as an Ultra-Stable Cation for Polymer Hydroxide-Exchange Membranes. Scientific Reports 2015, 5. (5) B. P. Setzler, Z. Zhuang, J. A. Wittkopf, Y. Yan. Activity targets for nanostructured platinum group-metal-free catalysts in hydroxide exchange membrane fuel cells. Nature Nanotechnology 2016, 11(12): 1020-1025. (6) Z. Zhuang, S. A. Giles, J. Zheng, G. R. Jenness, S. Caratzoulas, D. G. Vlachos, Y. Yan. Nickel supported on nitrogen-doped carbon nanotubes as hydrogen oxidation reaction catalyst in alkaline electrolyte. Nature Communications 2016, 7. (7) R. B. Kaspar, Y. Yan. Communication-Patterned Electrodes to Increase Water Back-Diffusion in Hydroxide Exchange Membrane Fuel Cells. Journal of the Electrochemical Society 2016, 163(7): F593-F595. (8) R. B. Kaspar, J. A. Wittkopf, M. D. Woodroof, M. J. Armstrong, Y. Yan. Reverse-Current Decay in Hydroxide Exchange Membrane Fuel Cells. Journal of the Electrochemical Society 2016, 163(5): F377-F383. (9) R. B. Kaspar, M. P. Letterio, J. A. Wittkopf, K. Gong, S. Gu, Y. Yan. Manipulating Water in High-Performance Hydroxide Exchange Membrane Fuel Cells through Asymmetric Humidification and Wetproofing. Journal of the Electrochemical Society 2015, 162(6): F483-F488. (10) W. Sheng, M. Myint, J. G. Chen, Y. Yan. Correlating the hydrogen evolution reaction activity in alkaline electrolytes with the hydrogen binding energy on monometallic surfaces. Energy & Environmental Science 2013, 6(5): 1509-1512. (11) W. Sheng, Z. Zhuang, M. Gao, J. Zheng, J. G. Chen, Y. Yan. Correlating hydrogen oxidation and evolution activity on platinum at different pH with measured hydrogen binding energy. Nature Communications 2015, 6. (12) J. Zheng, W. Sheng, Z. Zhuang, B. Xu, Y. Yan. Universal dependence of hydrogen oxidation and evolution reaction activity of platinum-group metals on pH and hydrogen binding energy. Science Advances 2016, 2(3).

Physicochemical Properties of Nanoparticles: Interaction of Supported Platinum Nanoparticles with Gaseous Reactants

The shapes, sizes, and electronic structures of platinum nanoparticles supported onto highly oriented pyrolytic graphite and oxidized silicon by different methods and their adsorptive properties with respect to hydrogen, oxygen, water, and ammonia were established. The apparent activation energy of the reduction of single oxidized platinum nanoparticles with molecular hydrogen was determined. The possibility of controlling the rate of ammonia decomposition by a nanostructured platinum coating by the application of electric potentials of different values and polarities to it was demonstrated.

Preparation and characterization of Pt loaded WO3 films suitable for gas sensing applications

This paper presents the preparation of nanostructured platinum (Pt) loaded tungsten oxide (WO3) thin films by radio frequency (RF) magnetron sputtering technique. Even though, Pt loading does not produce any phase change in WO3 lattice, it deteriorates the crystalline quality and induces defects on WO3 films. The Pt loading in WO3 has profound impact on structural and optical properties of the films by which the particle size, lattice strain and optical band gap energy are reduced. Nanoporous film with reduced particle size is obtained for 5 wt% Pt loaded WO3 sample which is crucial for gas sensors. Hence the sensing response of 5 wt% Pt loaded sample is tested towards carbon monoxide (CO) gas along with pure WO3 sample. The sensing response of Pt loaded sample is nearly 15 times higher than pure WO3 sample in non-humid ambience at an operating temperature 200 °C. This indicates the suitability of the prepared films for gas sensors. The sensing response of pure WO3 film depends on the humidity while the Pt loaded WO3 film shows stable response in both humid and non-humid ambiences.

Characterization of the Platinum-Hydrogen Bond by Surface-Sensitive Time-Resolved Infrared Spectroscopy.

The vibrational dynamics of Pt-H on a nanostructured platinum surface has been examined by ultrafast infrared spectroscopy. Three bands are observed at 1800, 2000, and 2090 cm-1, which are assigned to Pt-CO in a bridged and linear configuration and Pt-H, respectively. Lifetime analysis revealed a time constant of (0.8 ± 0.1) ps for the Pt-H mode, considerably shorter than that of Pt-CO because of its stronger coupling to the metal substrate. Two-dimensional attenuated total reflection infrared spectroscopy provided additional evidence for the assignment based on the anharmonic shift, which is large in the case of Pt-H (90 cm-1), in agreement with the density functional theory calculations. The absorption cross section of Pt-H is smaller than that of the very strong Pt-CO vibration by only a modest factor of ∼1.5-3. Because Pt-H is transiently involved in catalytic water splitting on Pt, the present spectroscopic characterization paves the way for in-operando kinetic studies of such reactions.

Shape-controlled fabrication of TiO2 hollow shells toward photocatalytic application

This paper introduces a droplet-based microfluidic approach, followed by several post-treatments, for the fabrication of TiO2 hollow shells with novel morphology and perfectly uniform size distribution, which were further decorated with platinum nanostructures to improve their photocatalytic activity and their ability to remove organic pollutants. In particular, a single-emulsion technique was used to emulsify an oil phase containing a titanium dioxide precursor, titanium n-butoxide (TBT), and a UV-curable polymer resin, trimethylolpropane triacrylate (ETPTA), into an aqueous phase. These emulsion droplets then readily underwent phase separation and sol-gel reaction at the emulsion interface, forming a TiO2 shell that would eventually rupture, release the ETPTA core, and form an anatase TiO2 hollow shell after UV, isopropanol, and thermal post-treatments. Compared with TiO2 hollow spheres reported in the literature, the TiO2 hollow shells produced here have a well-defined inner cavity that significantly improves their photocatalytic activity and allows for the selective introduction of advanced functions by the addition of metal co-catalysts like platinum. This new approach, by offering the ability to uniformly control the shape of the TiO2 photocatalyst and the ability to selectively introduce co-catalysts, offers an alternative platform for the design and fabrication of high-performance photocatalysts for efficient water purification.

Grafting of platinum nanostructures on biopolymer at elevated temperature

In this study, platinum colloidal nanoparticles of different concentrations were prepared by method of sputtering directly into polyethylene glycol. The properties including size, shape (TEM, HRTEM), distribution (DLS), and light absorption (UV–vis) of prepared nanoparticles were investigated. Stability of nanoparticles was observed immediately after preparation, after time delay or after application of thermal stress. In the next part of the study the PLLA foil was successfully modified under various conditions by platinum nanoparticles. The properties of modified PLLA foil were studied. The studied properties include in particular, surface chemistry (XPS), surface morphology (AFM), light absorption (UV–vis) and surface wettability. The results showed that nanoparticles are sufficiently stabilized at certain concentrations to modify the surface of poly-l-lactic acid. According to the XPS analysis, the surface of the modified film contained up to 3% at. of platinum. The metal clusters on the surface of the modified films were observed on images from the atomic force microscope, and the catalytic ability of the grafted platinum nanoparticles was observed by the decomposition of hydrogen peroxide.

Electron-driven and thermal chemistry during water-assisted purification of platinum nanomaterials generated by electron beam induced deposition.

Focused electron beam induced deposition (FEBID) is a versatile tool for the direct-write fabrication of nanostructures on surfaces. However, FEBID nanostructures are usually highly contaminated by carbon originating from the precursor used in the process. Recently, it was shown that platinum nanostructures produced by FEBID can be efficiently purified by electron irradiation in the presence of water. If such processes can be transferred to FEBID deposits produced from other carbon-containing precursors, a new general approach to the generation of pure metallic nanostructures could be implemented. Therefore this study aims to understand the chemical reactions that are fundamental to the water-assisted purification of platinum FEBID deposits generated from trimethyl(methylcyclopentadienyl)platinum(IV) (MeCpPtMe3). The experiments performed under ultrahigh vacuum conditions apply a combination of different desorption experiments coupled with mass spectrometry to analyse reaction products. Electron-stimulated desorption monitors species that leave the surface during electron exposure while post-irradiation thermal desorption spectrometry reveals products that evolve during subsequent thermal treatment. In addition, desorption of volatile products was also observed when a deposit produced by electron exposure was subsequently brought into contact with water. The results distinguish between contributions of thermal chemistry, direct chemistry between water and the deposit, and electron-induced reactions that all contribute to the purification process. We discuss reaction kinetics for the main volatile products CO and CH4 to obtain mechanistic information. The results provide novel insights into the chemistry that occurs during purification of FEBID nanostructures with implications also for the stability of the carbonaceous matrix of nanogranular FEBID materials under humid conditions.

Hydrogen adsorption on nano-structured platinum electrodes.

The "hydrogen region" of platinum is a powerful tool to structurally characterize nanostructured platinum electrodes. In recent years, the understanding of this hydrogen region has improved considerably: on Pt(111) sites, there is indeed only hydrogen adsorption, while on step sites, the hydrogen region involves the replacement of adsorbed hydrogen by adsorbed hydroxyl which interacts with co-adsorbed cations. However, the hydrogen region features an enigmatic and less well-understood "third hydrogen peak", which develops on oxidatively roughened platinum electrodes as well as on platinum electrodes with a high (110) step density that have been subjected to a high concentration of hydrogen. In this paper, we present evidence that the peak involves surface-adsorbed hydrogen (instead of subsurface hydrogen) on a locally "reconstructed" (110)-type surface site. This site is unstable when the hydrogen is oxidatively removed. The cation sensitivity of the third hydrogen peak appears different from other step-related peaks, suggesting that the chemistry involved may still be subtly different from the other features in the hydrogen region.

Pt nanotube network with high activity for methanol oxidation

Electrocatalysts with high performance, increased stability, and high surface area are essential for the widespread commercialization of fuel cells. Nanostructured materials emerge as potential candidates to meet these targets. We report on the synthesis and characterization of a nanostructured platinum electrocatalyst for methanol oxidation. Using a simple, one-step electroless method, an interconnected platinum nanotube network was prepared. The highly ordered, high-surface-area catalyst exhibited enhanced current density and durability for methanol oxidation. The catalyst shows a peak current density of 1.43 mA cm−2 at 50 mV s−1 and retained 25% of its initial activity after 1 h. The high catalytic activity is a result of increased Pt–OH formation on nanocrystal aggregates at lower potentials.

Electrochemically Co‐deposited Teeth‐like Virus‐Platinum Nanohybrids as an Electrocatalyst for Methanol Oxidation Reaction

AbstractM13 virus (M13) as scaffolds has a major appeal, owing to their mono‐dispersed, fibrillar morphology and engineerable surface reactive sites. Herein we had developed a facile electrocatalyst for energy application. Platinum nanostructures are directly co‐deposited from a wild‐type M13 (or) two different engineered M13 mixed electrolytes onto the ITO electrodes. The engineered M13 with 4E peptides could specifically nucleate Pt precursor thereby enables the efficient growth of teeth‐like structures at the ITO electrode. The electrocatalytic activity of the resulting electrocatalyst toward methanol oxidation in alkaline medium was investigated and found enhanced mass activity (0.321 A/mgPt) relative to the catalyst prepared from wild‐type M13, Y3E peptides engineered M13 and without M13. Our novel electrocatalyst fabrication can be extended to other metal and metal oxides and its application might be useful to develop novel clean and green energy generating and storage materials.