Trimethyl Platinum Research Articles

Electrochemical hydrogen pumping using a platinum catalyst made in a fluidized bed via atomic layer deposition

Platinum nanoparticle catalysts for electrochemical hydrogen pumping were synthesized on a functionalized powder carbon substrate (XC72R) using atomic layer deposition (ALD) in a fluidized bed reactor (FBR). Trimethyl(methylcyclopentadienyl)platinum(IV) (MeCpPtMe3) was used as the reagent for platinum delivery. Following deposition, MeCpPtMe3 ligands were combusted or hydrogenated to yield platinum on the XC72R surface. Reactions throughout the ALD cycle were monitored using mass spectrometry and IR spectroscopy to clarify the deposition chemistry. The resultant platinum catalysts were compared to commercial products in hydrogen pumping tests. Hydrogenation made finer, more dispersed, platinum nanoparticles that performed similarly to their commercial equivalent when pumping hydrogen. Conversely, oxygenation made a coarser catalyst that underperformed its commercial equivalent. Thus, altering chemistries shows potential for improving ALD catalyst performance.

Nanostructured Pt–TiO2 composite thin films obtained by direct liquid injection metal organic chemical vapor deposition: Control of chemical state by X-ray photoelectron spectroscopy

Nanostructured Pt–TiO2 composite thin films were synthesized by direct liquid injection metal organic chemical vapor deposition process, using trimethyl(methylcyclopentadienyl)platinum and titanium isopropoxide as precursors. Surface and cross-sectional morphologies obtained by scanning electron microscopy and transmission electron microscopy evidenced the uniform distribution of platinum nanoparticles in the TiO2 matrix. At higher Pt content, the X-ray diffraction analysis showed that the face-centered cubic phase of platinum appeared together with an anatase TiO2 structure. In addition, as far as the platinum chemical state is concerned, the co-deposition of TiO2 and Pt allowed obtaining Pt2+ or Pt°, in a ratio strongly dependent on the Pt content. Indeed, X-ray photoelectron spectroscopy characterization evidenced the presence of only Pt2+ for lower Pt content and only Pt° for higher one. The variation of platinum content in the TiO2 films resulted in a change of the chemical state of platinum.

MOCVD growth of Pt films using a novel Pt(IV) compound as a precursor

AbstractThe Me3Pt(acac)Py compound, trimethyl(pentane‐2,4‐dionato)platinum(IV)pyridine, is synthesized and, for the first time, characterized by physico‐chemical methods to determine its chemical composition (elemental analysis, IR‐spectroscopy) and thermal behavior (thermogravimetric (TG), differential thermal analyses (DTA), differential scanning calorimetry (DSC), tensometric flow method). Due to its good volatility ln(p/p°) = 16.47–9699/T(K) at moderate temperatures (393–414 K) the compound is offered as a promising precursor for growth of Pt films by metal‐organic chemical vapour deposition (MOCVD). The Pt films deposited on various substrates including Si(100), Ta, Ti substrates, cathodes and anodes of the electrodes for pacemakers are investigated by X‐ray diffraction (XRD), scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS). The electrochemical characteristics of Pt films are also determined. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural investigation of Ru/Pt nanocomposite films prepared by plasma-enhanced atomic layer depositions

We have fabricated Ru and Pt nanocomposite films using plasma-enhanced atomic layer deposition (PE-ALD), and characterized their structure by means of analytical electron microscopy. Pt and Ru were deposited in Ar/O2 plasma using trimethyl(methylcyclopentadienyl) platinum(IV) and bis(cyclopentadienyl)Ru(II) or bis(ethylcyclopentadienyl)Ru(II) as precursors, respectively. The resistivity of a Pt film deposited on a Si substrate at 300°C was 16.2μΩcm, and that of a Ru film was as low as 11μΩcm, showing the film to be metallic and not oxidized. It was revealed that the film prepared by successive PE-ALDs of Pt and Ru on a thin amorphous carbon substrate for electron microscopy analysis is a nanocomposite of Ru ribbons and PtRu (7:3) alloy ribbons with 2–3nm in width. The Ru ribbon comprised small particles with poor crystallinity of the hcp A3 structure and the PtRu ribbon comprised crystallites with good crystallinity of the fcc Al structure. The atomic layer deposition would be one of potential techniques to produce Ru/Pt nanocomposites for fuel cell catalysts.

Mechanistic studies for depositing highly dispersed Pt nanoparticles on carbon by use of trimethyl(methylcyclopentadienyl)platinum(IV) reactions with O2 and H2

A fundamental understanding is developed for the chemical reaction mechanism that underlies platinum atomic layer deposition (ALD) on a carbon support, XC72R, for use as a fuel cell catalyst. Specifically, trimethyl(methylcyclopentadienyl)platinum(IV) (MeCpPtMe3) was fed as the 1st reactant for ALD on high surface area particles using a well-instrumented fluidized bed reactor equipped with an in-line mass spectrometer. The precursor’s organic ligands were removed by reaction with the 2nd reactant, either oxygen or hydrogen. These experiments were performed on both unmodified and functionalized XC72R. Carbon modification involved reflux with nitric acid, which oxygenated the XC72R. Platinum weight loading, average particle size, and particle dispersion depended on carbon treatment and on the reactant used for ligand removal (oxygen or hydrogen). Deposited platinum particle sizes ranged from 2.6 to 6.7 nm. Transmission electron microscopy, chemisorption, and diffuse reflectance infrared Fourier transform spectroscopy were used to characterize the Pt deposition and carbon support functionalization. More discrete and non-agglomerated platinum nanoparticles were produced using hydrogen, rather than oxygen, as a reactant and when deposition was conducted on functionalized, rather than unmodified, XC72R carbon. The platinum nanoparticles are stabilized by the underlying oxygen added during substrate functionalization and the avoidance of carbon substrate combustion when using hydrogen, instead of oxygen, as the 2nd reactant to remove residual ligands.

Size-controlled platinum nanoparticles prepared by modified-version atomic layer deposition for ethanol oxidation

This study adopts a modified atomic layer deposition (ALD) process to prepare size-controlled Pt nanoparticles on the surface of carbon black, showing superior catalytic activity toward ethanol oxidation. Two types of ALD precursors, (methylcyclopentadienyl) trimethyl platinum (MeCpPtMe3) and oxygen (O2), were used to grow Pt deposits at 250 °C. For 30 ALD cycles, the pulse period of MeCpPtMe3 serves as a key factor in controlling the particle size and the weight loading of Pt deposits. The Pt growth rates over the carbon support can be attributed to the surface coverage of Pt–O* sites, diffusion rate of MeCpPtMe3, and lateral interaction between each active site. Since the MeCpPtMe3 dose strongly affects the Pt particle size and the deposit density, the growth of ALD–Pt can be assumed as being diffusion-limited. Because of the surface-catalyzed reaction steps, the small-sized ALD-Pt catalysts offer better catalytic activity, CO tolerance, and long-term stability as compared with the large-sized ones. On the basis of the results, the modified ALD technique exhibits a great potential for tuning the Pt particle size and weight loading onto the carbon support for fuel cell application.

Size Effect of Pt Nanoparticles Deposited By Plasma-Enhanced Atomic Layer Deposition on the Electrocatalytic Activity Toward the Methanol Oxidation Reaction

Platinum is the most important catalyst used for direct methanol fuel cells (DMFC) because its excellent electrocatalytic activity toward the methanol oxidation reaction (MOR). Most of recent research on DMFC focuses on the size minimization of the Pt catalyst, which can reduce the use of the precious Pt catalyst and increase the electroactive surface area. Moreover, nanosized Pt catalyst can significantly enhance the electrocatalytic activity toward MOR. In this study, we used plasma-enhanced atomic layer deposition (PEALD) to deposit Pt nanoparticles of different sizes on the TiO2substrate, and studied the electrocatalytic activity of Pt nanoparticles toward MOR as a function of the particle size. Pt nanoparticles were deposited on the TiO2 substrate by PEALD with a plasma power of 5W at 200oC using (methylcyclopentadienyl) trimethyl platinum (MeCpPtMe3) as the Pt precursor. Due to the self-limiting growth kinetics of ALD reactions, the size of Pt nanoparticles can be controlled by the number of the PEALD cycle, which was varied from 8 to 50 cycles in this study. The TiO2 was the nature oxide layer on a 100 nm thick Ti thin film sputter-deposited on the Si(100) wafer. Transmission electron microscopy (TEM) reveals that Pt nanoparticles has a size in the range between 3 nm and 7 nm depending on the number of the PEALD cycle. Cyclic voltammetry (CV) and CO stripping analysis were performed to study the electrocatalytic activity of the Pt/TiO2 electrode toward MOR in acidic media. The Pt/TiO2 electrode prepared with 15 PEALD cycles has a Pt particle size distribution peaking at ~4 nm, and has the best electrochemical performance, including electrocatalytic activity and CO tolerance. With the PEALD cycle number increased to 50, Pt nanoparticles trend to coalesce, and the electrode exhibits an electrochemical performance similar to a continuous Pt thin film. The better electrocatalytic activity of Pt nanoparticles prepared with a smaller number of the PEALD cycle can be ascribed to the synergistic effect of the nanosized Pt catalyst and the electronic interaction between Pt nanoparticles and the TiO2support. A schematic model describing the role of Pt nanoparticle size in the synergistic effect will be presented at the meeting. Keywords: direct methanol fuel cells, DMFC, plasma-enhanced atomic layer deposition, PEALD, methanol oxidation reaction, Pt nanoparticles, TiO2.

Electrocatalytic activity of atomic layer deposited Pt–Ru catalysts onto N-doped carbon nanotubes

Pt–Ru catalysts of various compositions, between 0 and 100at.% of Ru, were deposited onto N-doped multi-walled carbon nanotubes (N-CNTs) by atomic layer deposition (ALD) at 250°C. The Pt and Ru precursors were trimethyl(methylcyclopentadienyl)platinum (MeCpPtMe3) and bis(ethylcyclopentadienyl)ruthenium (Ru(EtCp)2), respectively. O2 was used as the reactant in both processes. The composition of the catalysts was easily tuned by varying the Pt-to-Ru ALD cycle ratio. The catalysts were tested toward the CO oxidation and methanol oxidation reaction (MOR) in a three-electrode electrochemical set-up. For the compositions investigated, the catalysts with a Ru content of 29at.% exhibited highest catalytic activity.

Synthesis of Pt/SiO2 Catalyst Nanoparticles from a Continuous Aerosol Process using Novel Cyclo‐octadienylplatinum Precursors

Investigations on the metal‐organic (MO)CVD of platinum nanoparticles on spherical, chemical vapor synthesis (CVS)‐produced SiO2 substrates are discussed in this paper. Commercially available methylcyclopentadienyl trimethyl platinum (MeCpPtMe3) (1) and three newly synthesized cyclooctadienyl platinum precursors are chosen and tested during a continuous CVD/CVS process. The synthesis of this new class of stable, halogen‐free precursors for atmospheric pressure (AP)CVD is presented. The complexes [PtMe2(R‐COD)], where R = Et (2a), nBu (2b), and iBu (2c), are shown to be highly suitable for the preparation of platinum nanoparticles. The precursors are characterized and their thermal properties are studied by thermogravimetric analysis (TGA) and infrared (IR). Investigations of the precursor decomposition mechanism, the effect of oxygen, and the autocatalytic effect during CVD are also carried out. Finally, transmission electron microscopy (TEM) and X‐ray photoelectron spectroscopy (XPS) analyses prove that continuous CVS of gas‐borne support particles combined with MOCVD of these newly synthesized platinum precursors gives ordered, defined platinum nanocatalysts with high dispersion and narrow size distribution (2 − 3 nm).

Ru-decorated Pt nanoparticles on N-doped multi-walled carbon nanotubes by atomic layer deposition for direct methanol fuel cells

We present atomic layer deposition (ALD) as a new method for the preparation of highly dispersed Ru-decorated Pt nanoparticles for use as catalyst in direct methanol fuel cells (DMFCs). The nanoparticles were deposited onto N-doped multi-walled carbon nanotubes (MWCNTs) at 250 °C using trimethyl(methylcyclopentadienyl)platinum MeCpPtMe3, bis(ethylcyclopentadienyl)ruthenium Ru(EtCp)2 and O2 as the precursors. Catalysts with 5, 10 and 20 ALD Ru cycles grown onto the CNT-supported ALD Pt nanoparticles (150 cycles) were prepared and tested towards the electro-oxidation of CO and methanol, using cyclic voltammetry and chronoamperometry in a three-electrode electrochemical set-up. The catalyst decorated with 5 ALD Ru cycles was of highest activity in both reactions, followed by the ones with 10 and 20 ALD Ru cycles. It is demonstrated that ALD is a promising technique in the field of catalysis as highly dispersed nanoparticles of controlled size and composition can be deposited, with up-scaling prospects.

Synthesis of nanowires via helium and neon focused ion beam induced deposition with the gas field ion microscope

The ion beam induced nanoscale synthesis of platinum nanowires using the trimethyl (methylcyclopentadienyl)platinum(IV) (MeCpPtIVMe3) precursor is investigated using helium and neon ion beams in the gas field ion microscope. The He+ beam induced deposition resembles material deposited by electron beam induced deposition with very small platinum nanocrystallites suspended in a carbonaceous matrix. The He+ deposited material composition was estimated to be 16% Pt in a matrix of amorphous carbon with a large room-temperature resistivity (∼3.5 × 104–2.2 × 105 μΩ cm) and temperature-dependent transport behavior consistent with a granular material in the weak intergrain tunnel coupling regime. The Ne+ deposited material has comparable composition (17%), however a much lower room-temperature resistivity (∼600–3.0 × 103 μΩ cm) and temperature-dependent electrical behavior representative of strong intergrain coupling. The Ne+ deposited nanostructure has larger platinum nanoparticles and is rationalized via Monte Carlo ion-solid simulations which show that the neon energy density deposited during growth is much larger due to the smaller ion range and is dominated by nuclear stopping relative to helium which has a larger range and is dominated by electronic stopping.

A comparison of neon versus helium ion beam induced deposition via Monte Carlo simulations

The ion beam induced nanoscale synthesis of PtCx (where x ∼ 5) using the trimethyl (methylcyclopentadienyl)platinum(IV) (MeCpPtIVMe3) precursor is investigated by performing Monte Carlo simulations of helium and neon ions. The helium beam leads to more lateral growth relative to the neon beam because of its larger interaction volume. The lateral growth of the nanopillars is dominated by molecules deposited via secondary electrons in both the simulations. Notably, the helium pillars are dominated by SE-I electrons whereas the neon pillars are dominated by SE-II electrons. Using a low precursor residence time of 70 μs, resulting in an equilibrium coverage of ∼4%, the neon simulation has a lower deposition efficiency (3.5%) compared to that of the helium simulation (6.5%). At larger residence time (10 ms) and consequently larger equilibrium coverage (85%) the deposition efficiencies of helium and neon increased to 49% and 21%, respectively; which is dominated by increased lateral growth rates leading to broader pillars. The nanoscale growth is further studied by varying the ion beam diameter at 10 ms precursor residence time. The study shows that total SE yield decreases with increasing beam diameters for both the ion types. However, helium has the larger SE yield as compared to that of neon in both the low and high precursor residence time, and thus pillars are wider in all the simulations studied.

Direct-write 3D nanolithography at cryogenic temperatures

Direct-write three-dimensional nanolithography is demonstrated using cryogenic electron beam-induced deposition (EBID). Cryogenic cooling and an electron beam were used to condense and expose the precursor methylcyclopentadienyl(trimethyl)platinum (MeCpPtMe3). The exposure process was modeled by Monte Carlo simulations of electron–condensate interactions, which were used to develop two approaches for the fabrication of three-dimensional self-supporting structures with incorporated gaps. Vertical and lateral resolutions of approximately 150 and 22 nm are demonstrated, and underlying mechanisms that limit resolution and throughput are identified. Resolution can be traded off for condensate exposure efficiency, which is shown to be up to four orders of magnitude greater than that of conventional, room temperature EBID.

Atomic Layer Deposition of Platinum Nanocatalysts onto Three-Dimensional Carbon Nanotube/Graphene Hybrid

Nanoparticulate platinum (Pt) has been well dispersed onto a three-dimensional carbon framework, consisting of carbon nanotubes (CNTs) and graphene oxide (GO) sheets, through an atomic layer deposition (ALD) route. One liquid-phase homogenizing process is capable of inserting a number of CNTs into the interspacing of GO sheets, forming the CNT#GO hybrid. Two types of ALD precursors, methylcyclopentadienyl-(trimethyl) platinum and oxygen were used to grow Pt deposits at 250 °C. The ALD cycle number acts as a key parameter in affecting the growth of Pt into the CNT#GO framework, showing growth rates of 0.054 nm cycle–1 and 0.00081 mg cm–2 cycle–1 for particle size and weight loading, respectively. The particle size of as-grown Pt deposits exhibits an increase from 2.27 to 12.32 nm within 50–200 ALD cycles. Single-stack cell test confirms the novel design of Pt catalyst electrodes with ultralow Pt loading displaying a superior catalytic activity, showing a promising feasibility for application in fuel cells.

Fabrication of platinum electrocatalysts on carbon nanotubes using atomic layer deposition for proton exchange membrane fuel cells

Platinum (Pt) has been synthesized by atomic layer deposition (ALD) onto the surface of multi-layered carbon nanotubes (CNTs) in order to investigate catalytic activity and durability of the ALD-Pt catalyst electrode in proton exchange membrane fuel cells (PEMFCs). Methylcyclopentadienyl-(trimethyl) platinum (MeCpPtMe3) and oxygen serve as precursors at a deposition temperature of 250°C. One growth mechanism involving two self-limiting reactions is proposed to clarify the decoration of ALD-Pt nanoparticles over the CNT support. The resultant ALD-Pt catalyst displays not only the fairly good electrochemical activity (electrochemically active surface area) but also the stability after potential cycling >1000cycles. Experimental results also show that the CNTs decorated with the ALD-Pt catalysts exhibit low-equivalent series resistance (∼3.55Ω), high-power density (∼2.95kWgPt−1 at 80°C) and long-term durability. On the basis of the results, the ALD approach is capable of synthesizing well-dispersed Pt nanoparticles onto CNTs, forming the advanced design of catalyst electrode for PEMFCs.

Gas phase low energy electron induced decomposition of the focused electron beam induced deposition (FEBID) precursor trimethyl (methylcyclopentadienyl) platinum(iv) (MeCpPtMe3)

Relative cross sections for dissociative electron attachment (DEA) and dissociative ionization (DI) of the FEBID precursor, trimethyl (methylcyclopentadienyl) platinum(iv), MeCpPtMe(3), are presented. The most pronounced DEA process is the loss of one methyl radical, while the loss of two or three methyl groups along with hydrogen is the main pathway in DI. Further fragments are formed in DEA and through DI by more complex rearrangement reactions but complete dissociation to bare Pt(-) in DEA or Pt(+) in DI is minor. The transient negative ion (TNI) formation in DEA is discussed and fragmentation mechanisms are proposed for individual processes. From the thermodynamics of the DEA processes we derive a lower limit for the electron affinity of the MeCpPtMe(2) radical (1.7 eV). Appearance energies (AE) of MeCpPtMe(3)(+) (7.7 eV) and Pt(+) (18.6 eV) formation through electron impact ionisation (EI) and through DI, respectively, are determined. Finally, the current DEA and DI results are compared and brought into context with earlier surface science studies on electron-induced decomposition of adsorbed MeCpPtMe(3) as well as gas phase and surface science studies on the FEBID precursors [Co(CO)(3)NO] and [Pt(PF(3))(4)]. These comparisons strongly indicate that DEA is an important process in the electron-induced decomposition of these molecules in FEBID.

Nucleation and Growth of Platinum Films on High-k/Metal Gate Materials by Remote Plasma and Thermal ALD

Platinum films were grown on Si wafers, SiO2, Al2O3 and high-k dielectric HfO2 ALD films on Si substrates by both remote plasma and thermal atomic layer deposition (ALD) at 300°C, using methylcyclopentadienyl_trimethyl platinum (MeCpPtMe3) and O2 as precursors. The ALD Pt-films deposited were homogeneous and resulted in a low resistivity of 12.8 μΩ-cm. AES studies revealed high quality Pt films deposited by both thermal and plasma ALD with carbon impurity less than 1.5% and oxygen found only in the interface. SEM and EDX were used to investigate Pt nucleation and growth in ALD processes. It is remarkable that the nucleation delay of between thermal and plasma ALD Pt was different though they are a similar growth rate of 0.45 Å/cycle. In this work, the Pt ALD nucleation and growth behaviours with precursor dose times, O2 or O2 plasma exposures and substrates are also investigated.

Binary Pt–Si Nanostructures Prepared by Focused Electron-Beam-Induced Deposition

Binary systems of Pt-Si are prepared by electron-beam-induced deposition using the two precursors, trimethyl(methylcyclopentadienyl)platinum(IV) (MeCpPt(Me)(3)) and neopentasilane (Si(SiH(3))(4)), simultaneously. By varying the relative flux of the two precursors during deposition, we are able to study composites containing platinum and silicon in different ratios by means of energy-dispersive X-ray spectroscopy, atomic force microscopy, electrical transport measurements, and transmission electron microscopy. The results show strong evidence for the formation of a binary, metastable Pt(2)Si(3) phase, leading to a maximum in the conductivity for a Si/Pt ratio of 3:2.

Nucleation and growth of Pt atomic layer deposition on Al2O3 substrates using (methylcyclopentadienyl)-trimethyl platinum and O2 plasma

The nucleation and growth of Pt atomic layer deposition (ALD) on Al2O3 substrates was studied using (methylcyclopentadienyl)-trimethyl platinum (MeCpPtMe3) and O2 plasma as the reactants. The nucleation of Pt ALD was examined on Al2O3 ALD substrates at 300 °C using a variety of techniques including spectroscopic ellipsometry, x-ray reflectivity, x-ray photoelectron spectroscopy, and scanning electron microscopy. These techniques revealed that Pt ALD does not nucleate and grow immediately on the Al2O3 ALD substrates. There was negligible Pt ALD during the first 38 ALD cycles. The Pt ALD growth rate then increased substantially during the next 12 ALD cycles. Subsequently, the Pt ALD growth rate reached a steady state linear growth regime for >50 ALD cycles. These measurements suggest that the Pt ALD first forms a number of nanoclusters that grow slowly during the first 38 ALD cycles. These islands then merge during the next 12 cycles and yield a steady state Pt ALD growth rate of ∼0.05 nm/cycle for >50 ALD cycles. The Pt ALD film at the onset of the steady state linear growth regime was approximately 2–3 nm in thickness. However, the SEM images of these Pt ALD films appeared corrugated and wormlike. These films also had a density that was only 50–70% of bulk Pt. Film densities that were consistent with bulk Pt were not observed until after >100 ALD cycles when the Pt ALD films appeared much smoother and were 4–5 nm in thickness. The Pt ALD nucleation rate could be enhanced somewhat using different O2 plasma parameters.

Transmission electron microscopy study of damage layer formed through ion beam induced deposition of platinum on silicon substrate

Ion beam induced deposition is used for nanofabrication operations (e.g., transmission electron microscopy sample preparation) but is still not perfectly understood. Here, the authors describe the use of a wide variety of analytical instruments to develop such an understanding. Pt-films were deposited on native oxide films on silicon (Si) by decomposing trimethyl platinum C5H4CH3Pt(CH3)3 with focused electron or gallium ion beams. Unlike electron beam induced deposition, ion beam induced deposition produces a deep and complex damage layer below the deposition. It is revealed that the damaged area can be divided into three layers: (1) a “white-band” with a lower Pt-concentration and concurrent higher carbon (C)-concentration; (2) a-Pt–Si region where amorphized silicon crystal is mixed with Pt, and Pt-particle formation starts somewhere in the middle area; and (3) a-Si, which is silicon amorphized by Ga ions. The change in the diffusion rate of platinum into the amorphized silicon layer plays a crucial role in the formation of the distinct layers. The diffusions are affected by interatomic chemical affinity as well as by concentration, so that the Pt–Si combination initially dominates Pt agglomeration and the combination of C–Si, resulting in the creation of the novel white-band.