Growth of new ternary intermetallic phases from Ca/Zn eutectic flux

The eutectic 7.3:2.7 molar ratio mixture of calcium and zinc metal melts at 394 °C and was explored as a solvent for the growth of new intermetallic phases for potential use as hydrogen storage materials. The reaction of nickel in this molten mixture produces two new phases—the CaCu₅-related structure CaNi₂Zn₃ (P6/mmm, a=8.9814(5) Å, c=4.0665(5) Å) and a new cubic structure Ca₂₁Ni₂Zn₃₆ (Fd-3m, a=21.5051(4) Å). Palladium-containing reactions produced CaPd_0.85Zn_1.15 with the orthorhombic TiNiSi structure type (Pnma, a=7.1728(9) Å, b=4.3949(5) Å, c=7.7430(9) Å). Reactions of platinum in the Ca/Zn mixture produce Ca₆Pt₃Zn₅, with an orthorhombic structure related to that of W₃CoB₃ (Pmmn, a=13.7339(9) Å, b=4.3907(3) Å, c=10.7894(7) Å).     

Formation and hydrogenation of p(2 × 2)-N on Pt(1 1 1)

The formation of a well-ordered p(2 × 2) overlayer of atomic nitrogen on the Pt(1 1 1) surface and its reaction with hydrogen were characterized with reflection absorption infrared spectroscopy (RAIRS), temperature programmed desorption (TPD), low energy electron diffraction (LEED), Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS). The p(2 × 2)-N overlayer is formed by exposure of ammonia to a surface at 85 K that is covered with 0.44 monolayer (ML) of molecular oxygen and then heating to 400 K. The reaction between ammonia and oxygen produces water, which desorbs below 400 K. The only desorption product observed above 400 K is molecular nitrogen, which has a peak desorption temperature of 453 K. The absence of oxygen after the 400 K anneal is confirmed with AES. Although atomic nitrogen can also be produced on the surface through the reaction of ammonia with an atomic, rather than molecular, oxygen overlayer at a saturation coverage of 0.25 ML, the yield of surface nitrogen is significantly less, as indicated by the N₂ TPD peak area. Atomic nitrogen readily reacts with hydrogen to produce the NH species, which is characterized with RAIRS by an intense and narrow (FWHM ∼ 4 cm⁻¹) peak at 3322 cm⁻¹. The areas of the H₂ TPD peak associated with NH dissociation and the XPS N 1s peak associated with the NH species indicate that not all of the surface N atoms can be converted to NH by the methods used here.     

Activity evaluation of carbon paste electrodes loaded with pt nanoparticles prepared in different radiolytic conditions

Three Pt-based catalysts prepared in different radiolytic conditions and supported on graphite powder were packed into a carbon paste electrode configuration. They were compared to each other, to the commercial (Pt) deposited on activated carbon powder (Johnson Matthey) and to pure Vulcan XC-72 for their respective abilities toward the hydrogen evolution reaction (HER). The Tafel parameters were determined for all these electrodes. From the I–V curves and their quantitative treatment, the following order of activity emerged unambiguously and reads: (PtCO)₂ (fcc structure) > (PtCO)₁ (Chini cluster) > (Pt)_neat > (Pt)_JM (Johnson Matthey) ≫ (Vulcan XC-72). As expected, all the Pt-loaded electrodes were more efficient than Vulcan XC-72. The classification appears to be linked with the mean nanoparticle size, and for comparable sizes, with the surface morphology of the materials. The results and the stability of the electrodes suggest that the small particle sizes and the good dispersity on the carbon support were maintained during the HER.     

Study of adsorption of oxygen on β-Al2O3 + Au and β-Al2O3 + Pt: Work function measurements—proposition of a model

To improve the understanding of the electrochemical effects observed on an original potentiometric gas sensor, interactions of oxygen with the device were investigated. This gas sensor is made of a solid electrolyte (treated Na-β-alumina) associated with two metallic electrodes (gold and platinum) located in the same gas mixture. Adsorption of charged oxygen species, considered responsible for the electrical response developed by the sensor, was investigated by work function measurements. Results showed that charged oxygen species only form on partially gold or platinum covered solid electrolyte. Comparison of these results with those obtained in a previous calorimetric study of interactions between oxygen and the same materials suggests the existence of at least two different oxygen species adsorbed on the surface of the sensitive element. The first one, located on the solid electrolyte surface, is neutral and characterized by an endothermal reaction of formation. The second one is charged and probably produced at the gas/solid electrolyte/metallic electrode interface. A mechanism based on the concept of “three phase boundary” and similar to the “reverse spillover” phenomenon is proposed to account for the adsorption of these oxygen species.     

三元混配铂(Ⅱ)配合物的稳定性和分子内芳环堆积效应研究

用 pH电位滴定法测定了铂 (Ⅱ )与核苷酸NTP (NTP为腺苷 5′ 三磷酸和尿苷 5′ 三磷酸 )和另一芳环系列配体ArL形成的三元混配配合物Pt(ArL) (NTP) n -(ArL =Phen ,Bpy和Trp ;n =2或 3)在水溶液中的稳定常数 (I=0 .1mol/L ,KNO3 ;2 5℃ ) .用ΔlogKPt比较了二元和三元混配配合物的稳定性差异 ,认为三元混配配合物稳定性的增加可归因于π 酸与π 碱之间的合作效应和分子内芳环配体的堆积作用     

氯磺酚偶氮硫代若丹宁光度法测定铂

本文研究了氯磺酚偶氮硫代若丹宁 (HSCT)与铂的显色反应 ,在盐酸介质中 ,HSCT与铂反应生成 2∶ 1稳定络合物 ,λmax=5 3 5 nm,ε=6.2 4× 1 0 4 L· mol-1· cm-1。铂含量在 0— 5 0 μg/2 5 m L范围内符合比耳定律 ,方法用于催化剂中铂含量的测定     

Response to high acidity and basicity at a platinum electrode in chronopotentiometry

A simple and rapid method is developed to determine the high acidity and the basicity of solutions by chronopotentiometry with a platinum working electrode. The acidity range from 5.0 mol/l H⁺ to 1.0 mol/l OH⁻ can be measured by the adjustment of deposition potential and time. The response mechanism to acidity and basicity has been explored. The transition potential plateau in chronopotentiograms is caused from the oxidation of hydrogen adsorbed on electrode surface.     

Effects of surface step on molecular propane adsorption

We have studied the effects of surface step on molecular propane adsorption using molecular-dynamics simulations and a model stepped surface, Pt(6 5 5). Incidences along the step edge (smooth azimuth) and perpendicular to the step edge with upstairs momentum (upstairs azimuth) and downstairs momentum (downstairs azimuth) are considered. In general, the surface step enhances the initial trapping probability of propane except for the downstairs incidences. The most efficient zone in facilitating adsorption is near the bottom of the surface step on the lower terrace where incident molecules experience stronger attraction and an “additional-layer” effect when crossing the step. The least efficient zone is the top of the surface step on the upper terrace due to an opposite “missing-layer” effect. Surface step also creates steric effects such that more incident molecules along the upstairs azimuth but significantly less molecules along the downstairs azimuth impact the step-bottom zone. The latter steric effect, a shadowing effect, undermines the high trapping efficiency of the step-bottom zone to cause the downstairs incidences to have the lowest trapping probabilities. While the shadowing effect can be enhanced by larger incident angles and lower incident energies, the other steric effect on the upstairs incidences is relatively insensitive to the incident energy. Overall, the influence of surface step on molecular adsorption diminishes at low incident energies and large incident angles because longer contact times and less normal momenta result in high trapping probability across the entire stepped surface.     

Angle-dependent infrared absorption spectroscopy at electrode/electrolyte interfaces

Angle-dependent internal reflection spectroscopy is performed in the attenuated total reflection setup for an electrochemical cell with a Fourier transform infrared spectrometer. The working electrode is a thin Pt film evaporated onto a hemispherical Si prism. The refractive index of the Pt film obtained from the experiment is found to differ from the value for bulk material. The difference is ascribed to the surface corrugation of the Pt surface and the film thickness in the nanometer range. The function of reflection intensity versus angle of incidence changes significantly when a resonant absorption occurs in the electrolyte medium. The angle-dependent absorption band intensity of CO adsorbed on the Pt film under potential control reveals changes in magnitude and an inversion of the band for different angles of incidence. This behaviour is explained by the excitation of resonant surface plasmon waves at the Pt/electrolyte interface and by multiple reflections occurring at the interfaces. A simulation for the three-layer system Si/Pt/electrolyte agrees with the experimental results.     

Synthesis and Crystal Structure of Pivalamidate-Bridged Trinuclear Platinum–Copper Complex with a Linear Pt–Cu–Pt Core

Abstract The heterotrimetallic complex [Cu{trans-Pt(NH₃)₂(NHCO^tBu)₂}₂](NO₃)₂ was synthesized and structurally characterized by X-ray crystallography. The cationic complex consists two trans-[Pt(NH₃)₂(NHCO^tBu)₂] units and one Cu²⁺ ion, which are linearly held together by four bridging pivalamidate ligands. The compound crystallizes in the monoclinic space group P2₁/c with a = 13.18(1) ?, b = 13.12(1) ?, c = 21.38(2) ?, β = 116.88(3)°?, V = 3674(5) ?³, and Z = 4. The trimeric Pt–Cu–Pt cation further aggregates into a dimer of trimer via a weak Pt···Pt interaction. Graphical abstract Synthesis and crystal structure of pivalamidate-bridged trinuclear platinum–copper complex with a linear Pt–Cu–Pt core Chao Chen, Huayu Qiu*, Fenghui Liu and Wanzhi Chen* A heterotrimetallic complex [Cu{trans-Pt(NH3)₂(NHCO^tBu)₂}₂](NO₃)₂ was synthesized and structurally characterized by X-ray crystallography.