F:Highly flammable;
7440-06-4Relevant articles and documents
Platinum nanofilm formation by EC-ALE via redox replacement of UPD copper: Studies using in-situ scanning tunneling microscopy
Kim, Youn-Geun,Kim, Jay Y.,Vairavapandian, Deepa,Stickney, John L.
, p. 17998 - 18006 (2006)
The growth of Pt nanofilms on well-defined Au(111) electrode surfaces, using electrochemical atomic layer epitaxy (EC-ALE), is described here. EC-ALE is a deposition method based on surface-limited reactions. This report describes the first use of surface-limited redox replacement reactions (SLR3) in an EC-ALE cycle to form atomically ordered metal nanofilms. The SLR 3 consisted of the underpotential deposition (UPD) of a copper atomic layer, subsequently replaced by Pt at open circuit, in a Pt cation solution. This SLR3 was then used a cycle, repeated to grow thicker Pt films. Deposits were studied using a combination of electrochemistry (EC), in-situ scanning tunneling microscopy (STM) using an electrochemical flow cell, and ultrahigh vacuum (UHV) surface studies combined with electrochemistry (UHV-EC). A single redox replacement of upd Cu from a PtCl42- solution yielded an incomplete monolayer, though no preferential deposition was observed at step edges. Use of an iodine adlayer, as a surfactant, facilitated the growth of uniformed films. In-situ STM images revealed ordered Au(111)-(√3 × √3)R30°-iodine structure, with areas partially distorted by Pt nanoislands. After the second application, an ordered Moire pattern was observed with a spacing consistent with the lattice mismatch between a Pt monolayer and the Au(111) substrate. After application of three or more cycles, a new adlattice, a (3 × 3)-iodine structure, was observed, previously observed for I atoms adsorbed on Pt(111). In addition, five atom adsorbed Pt-I complexes randomly decorated the surface and showed some mobility. These pinwheels, planar PtI4, complexes, and the ordered (3 × 3)-iodine layer all appeared stable during rinsing with blank solution, free of I- and the Pt complex (PtCl42-).
Cr(III) oxidation with lead dioxide-based anodes
Devilliers,Dinh Thi,Mahé,Le Xuan
, p. 4301 - 4309 (2003)
A procedure for preparing PbO2-based electrodes with a titanium substrate is proposed. A platinum underlayer is first deposited on Ti by metal organic chemical vapor deposition (MOCVD), followed by the electrodeposition of the PbO2 layer. The prepared Ti/Pt/PbO2 anodes were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD) before being used for oxidation of Cr(III) in sulphuric acid. The current efficiency was determined for that electrodes and the results were compared with those obtained with Pb/PbO2 and Ebonex/PbO 2 electrodes with different pH conditions. The Ti/Pt/PbO2 were found to have a very good electrochemical behaviour (current efficiency: φ=0.93 for pH 2), and may be used as dimensionally stable anodes for the oxidation of Cr(III).
High-resolution in situ and ex situ TEM studies on graphene formation and growth on Pt nanoparticles
Peng, Zhenmeng,Somodi, Ferenc,Helveg, Stig,Kisielowski, Christian,Specht, Petra,Bell, Alexis T.
, p. 22 - 29 (2012)
The formation of graphene layers on MgO-supported Pt nanoparticles was studied by both in situ and ex situ high-resolution transmission electron microscopy (HRTEM). The HRTEM images indicate that graphene sheets grow from steps in the surface of Pt nanoparticles. The subsequent morphology of the graphene sheets is a strong function of Pt particle size. For particles less than ～6 nm in diameter, the graphene sheets form nanotubes or move from the surface of Pt particles and accumulate on the MgO support. Complete particle envelopment by multiple graphene layers was only observed for particle greater than ～6 nm in diameter. The observed dependence of graphene morphology on Pt nanoparticle size and shape is associated with the strain energy generated between graphene layers during their growth and the overall free energy of the graphene-Pt system.
Effects of humidity on the performance of ionic polymer-metal composite actuators: Experimental study of the back-relaxation of actuators
Shoji, Eiichi,Hirayama, Daisuke
, p. 11915 - 11920 (2007)
This article focuses on the dependence of water uptake on the displacement, velocity, mechanical force, and charging profiles of perfluorinated ionomer-platinum/Li+-based actuators. Both the displacement and force generation were found to be strongly dependent on the humidity. The primary reason for this effect is a decrease in the stiffness as a result of the humidity. The actuators demonstrated a dramatic reverse motion and a negative force, and this subsequent relaxation was dramatically decreased by decreasing humidity. This relaxation process can be explained by the slow diffusion of water into the elastically softened anode and out of the stiffened camode. There are no clear inflection points on the charging profile during me reverse relaxation, and this suggests that the relaxation process does not involve a major redistribution of counter cations. An increase in water uptake resulted in an enhancement of the velocity of the displacement. A continuous generation of force was also examined by scanning potential, and the force was proportional to the potential. Humidities near 50-60% (i.e., water uptakes of ca. 5 wt %) gave a better actuator bending performance.
Fabrication and evaluation of platinum/diamond composite electrodes for electrocatalysis: Preliminary studies of the oxygen-reduction reaction
Wang, Jian,Swain, Greg M.
, p. E24-E32 (2003)
A catalytic electrode was prepared using a new electrically conducting and corrosion resistant carbon support material, boron-doped diamond. Fabrication of the composite electrode involves a three-step process: (i) continuous diamond thin-film deposition on a substrate, (ii) electrodeposition of Pt catalyst particles on the diamond surface, and (iii) short-term diamond deposition to entrap the metal particles into the surface microstructure. The process results in a conductive, morphologically, and microstructurally stable composite electrode containing metal particles of somewhat controlled composition, size, and catalytic activity. The metal catalyst particles were galvanostatically deposited from a K2PtCl6/HClO4 solution, with the metal particle size (50-350 nm) and distribution (～109 cm-2) being controlled by adjusting the galvanostatic deposition and secondary diamond-growth conditions. For a 300 s Pt deposition time, the estimated loading was 75.8 μg/cm2, assuming a 100% current efficiency. The composite electrode was extremely stable, both structurally and catalytically, during a 2 h polarization in 85% H3PO4 at 170°C and 0.1 A/cm2. The electrode's catalytic activity was evaluated using the O2 reduction reaction at room temperature in 0.1 M solutions of H3PO4, H2SO4, and HClO4. The kinetic parameters (Tafel slope and exchange current density) were obtained by cyclic voltammetry and were found to be comparable to those for a polycrystalline Pt electrode in the same media. Tafel slopes of -63 to -80 mV/dec were observed at low overpotentials, with the lowest slope in HClO4 and highest in H3PO4. The exchange current density ranged from 10-12 to 10-10 A/cm2, and increased in the order of H3PO4 2SO4 4. The potential advantages of the composite electrode, as compared with commercial sp2 carbon electrodes, are (i) the corrosion resistance of the diamond support, resulting in highly stable reaction centers at high potentials, current densities, and temperatures, and (ii) the fact that all of the catalyst particles are strongly anchored at the film surface and are not contained inside pores.
Synthesis, characterization of FAU/EMT intergrowths and its catalytic performance in n-pentane hydroisomerization reaction
Belandría,Gonzàlez,Aguirre,Sosa,Uzcátegui,González,Brito,González-Cortés,Imbert
, p. 164 - 172 (2008)
Zeolites FAU, EMT and their intergrowths were synthesized using 15-crown-5, 18-crown-6 and their equimolar mixture, respectively. The synthesized products were characterized by XRD, SEM-EDX, N2 adsorption and TPD-NH3. The solids obtained were all highly crystalline. The FAU samples were formed by octahedral submicrometric crystallites, EMT samples had hexagonal plate morphology of 2-5 μm. The intergrowth crystals were micrometric hexagonal plates through whose hexagonal faces, the octahedral FAU crystallites intergrow. The intergrowth proportion was evaluated by means of DIFFaX, resulting in different intergrowth proportions, depending on the molar ratio of template/Al2O3 and on the relative template proportion used in the synthesis gel. For a template/Al2O3 ratio of 0.70, a 50%FAU/50%EMT intergrowth proportion was obtained, with cluster-type stacking and for template/Al2O3 of 0.30 the intergrowth proportion was 12%FAU/88%EMT with two stacking arrangements: clusters and random. Platinum was incorporated to these zeolites and their intergrowths by solid ion exchange; the metal dispersion was evaluated by TEM. For most catalysts the platinum particles were between 4 and 10 nm. All the catalysts were active for n-pentane conversion. The activity was found to be a function of acidity. The intergrowth catalysts were the most active materials. The iso-pentane selectivity, at 350 °C and carrier gas composition of H2:N2 = 2:1, was 82% independent of time on stream, acidity, Pt/Al ratio and Pt dispersion. The selectivity increased with decreasing temperature and as carrier gas composition became richer in H2. The catalytic remaining activity (at 10 min) decreased in the following order: FAU > EMT > intergrowth.
Temperature effect on the electrode kinetics of ethanol oxidation on Pd modified Pt electrodes and the estimation of intermediates formed in alkali medium
Mahapatra,Dutta,Datta
, p. 9097 - 9104 (2010)
Ethanol has been recognized as the ideal fuel for direct alcohol fuel cell (DAFC) systems due to its high energy density, non-toxicity and its bio-generation. However the complete conversion of ethanol to CO2 is still met with challenges, due t
Platinum Electroless Deposition on Silicon from Hydrogen Fluoride Solutions: Electrical Properties
Kuznetsov,Skryshevsky,Vdovenkova,Tsyganova,Gorostiza,Sanz
, p. C528-C532 (2001)
Current transport through mesa structures formed by Pt electroless deposition on p-Si wafers has been studied. The silicon treatment in the solution of sodium chloroplatinate in dilute HF acid is shown to result in both Pt nucleation on the Si surface (cathodic process) and Si wafer etching by fluoride ions (anodic process). These processes occurred simultaneously, forming the developed Pt/Si interface. Auger electron spectroscopy and C-V curves reveal the formation of a dielectric interface layer between Pt and Si of hundreds of nanometers that extends with the time of treatment. The electrical properties of mesa structures exhibit Schottky barrier behavior. Both conditions of current transport along the deposited layer and parameters of Schottky contact are defined vs. the deposition time and compared with that for thermally deposited Pt contact.
In situ FTIR spectroscopic studies of (bi)sulfate adsorption on electrodes of Pt nanoparticles supported on different substrates
Zeng, Dong-Mei,Jiang, Yan-Xia,Zhou, Zhi-You,Su, Zhang-Fei,Sun, Shi-Gang
, p. 2065 - 2072 (2010)
Nanostructured Pt electrodes were prepared by electrodeposition of Pt nanoparticles on different substrates (GC, Pt and Au) under cyclic voltammetric conditions and with various number (n) of potential cycling, and were denoted as nm-Pt/S(n) (S = GC, Pt and Au). Adsorption of (bi)sulfate on the nm-Pt/S(n) was studied by in situ FTIR reflection spectroscopy. It has been revealed that the nanostructured Pt electrodes exhibit anomalous IR properties for (bi)sulfate adsorption regardless of the different reflectivity of substrate, i.e. the IR absorption of (bi)sulfate species adsorbed on all the nm-Pt/S(n) electrodes is significantly enhanced and the IR band direction is completely inverted in comparison with the same species adsorbed on a bulk Pt electrode. The two IR bands around 1200 and 1110 cm-1 attributed to adsorbed (bi)sulfate species are shifted linearly with increasing electrode potential, yielding Stark tuning rates (d over(ν, ?) / d ES) of 152.1 and 21.1 cm-1 V-1 on nm-Pt/GC(20), respectively. Along with increasing n, the Stark tuning rate of the IR band around 1200 cm-1 decreases quickly and declined to 7.6 cm-1 V-1 on nm-Pt/GC(80), while the Stark tuning rate of the IR band near 1100 cm-1 is fluctuated between 23.0 and 16.2 cm-1 V-1. It has determined that the enhancement of IR absorption of (bi)sulfate adsorbed on nanostructured Pt electrode is varied with substrate material and n, and a maximal 16-fold enhancement of the IR band near 1200 cm-1 has been measured on the nm-Pt/GC(30) electrode. The in situ FTIR studies illustrated that the adsorption of (bi)sulfate occurs mainly in the double layer potential region, and reaches a maximum around 0.80 V. The results demonstrated also that the competitive adsorption of CO and oxygen species can inhibit completely (bi)sulfate adsorption, which has evidenced a weak interaction of (bi)sulfate with nm-Pt/S(n) electrode surface.
Recovery of platinum with calcium oxide sorbent in ammonia oxidation
Zakharchenko
, p. 402 - 407 (2002)
The reaction of granulated CaO sorbent with platinum lost in high-temperature oxidation of ammonia was studied. Physicochemical properties of the product and conditions and mechanism of its formation are considered.
