Phase relationship in the Fe-Pt-Pr ternary system at 500°C

The phase relationship in the Fe-Pt-Pr ternary system at 500°C was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) energy dispersion spectroscopy techniques. The 500°C isothermal section consists of 13 single-phase regions, 23 two-phase regions and 11 three-phase regions. At 500°C, the maximum solid solubility of Pt in α-Fe is about 10 at.% and Fe in Pt is about 18 at.%; the maximum solubilities of Pr in α-(Fe,Pt), Fe₃Pt, FePt, FePt₃ and (Pt,Fe) (the solid solution of Fe in Pt) are about 6 at.% 1.5 at.% 2 at.%, 2.5 at.% and 1.5 at.%, respectively. No Pr₃Pt₄ binary compound and new ternary compounds were found.     

Influence of water-organic solvent composition on composition and structure of Pt/C and Pt<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ni/C electrocatalysts in borohydride synthesis

Nanostructured Pt/C and Pt _x Ni/C materials containing from 4 to 30 wt % Pt were prepared using the method of chemical reduction of platinum and nickel compounds in the liquid phase by sodium borohydride solution. The change in the nature of the organic component (ethylene glycol, dimethyl sulfoxide, dimethyl formamide, tetrahydrofuran, acetone, ethyl alcohol, and glycerin) of binary water-organic solvent influences considerably the reaction product yield, structural characteristics (average nanoparticle size) of the material, mass fraction of metals in the nanocomposite, and the PtNi alloy composition. The fundamental possibility of controlling the PtNi alloy composition and structural characteristics of Pt/C and Pt _x -Ni/C nanocomposites by variation of the water-organic solvent composition was demonstrated. The minimum average size of nanoparticles in synthesized metal-carbon materials promising as electrocatalysts in low-temperature fuel cells was 2 nm for Pt/C (for about 20 wt % Pt) and 1.8 nm for Pt₂Ni (for about 30 wt % Pt).     

Synthesis and electrocatalytic oxygen reduction properties of truncated octahedral Pt3Ni nanoparticles

Pt₃Ni nanoparticles have been obtained by shape-controlled synthesis and employed as oxygen reduction electrocatalysts for proton exchange membrane fuel cells (PEMFC). The effects of varying the synthesis parameters such as the types of the capping agent and the reducing agent, and the reaction time have been systematically studied. The as-prepared Pt₃Ni nanoparticles were subjected to a butylamine-based surface treatment in order to prepare carbon-supported electrocatalysts. The Pt₃Ni electrocatalysts show an areaspecific activity of 0.76 mA/cm²(Pt) at 0.9 V in an alkaline electrolyte, which is 4.5 times that of a commercial Pt/C catalyst (0.17 mA/cm² (Pt)). The mass activity reached 0.30 A/mg(Pt) at 0.9 V, which is about twice that of the commercial Pt/C catalyst. Our results also show that the area-specific activities of these carbon-supported Pt₃Ni electrocatalysts depend strongly on the (111) surface fraction, which is consistent with the results of a study based on Pt₃Ni extended single-crystal surfaces.     

Electrical enhancement of DMFC by Pt-M/C catalyst-assisted PVD

Direct methanol fuel cells (DMFC) are studied extensively owing to their simple cell configuration, high volume energy density, short start-up time and operation reliability. However, the major drawbacks include high production cost, catalyst and methanol crossover poisoning. This study presents a simple method for Pt-M/C catalyst preparation using a magnetron sputtering (MS) and metal-plasma ion implantation (MPII) technique. The Pt catalysts were sputtered onto a gas diffusion layer (GDL), followed by implanting Cr, Fe, Ni, and Mo catalysts using MPII (accelerating voltage is 20 kV and implantation fluence is 1 × 10¹⁶ ions/cm²). The crystallinity and microstructure of the catalyst films were analyzed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM). The cell performance was tested using potential stat/galvano station. The results indicate that the membrane electrode assembly for Pt-Ni/C, Pt-Fe/C and Pt-Cr/C catalysts can enhance DMFC cell performance, compared with traditional Pt/C and Pt-Ru/C. The maximum Pt-Ni/C power density is 2.4 mW/cm² with an open circuit voltage (OCV) 0.334 V when tested at a methanol concentration of 1 M.     

A comprehensive study on the effect of Ru addition to Pt electrodes for direct ethanol fuel cell

The electro-oxidation of ethanol was studied over nanosized Pt and different compositions of PtRu catalysts synthesized by the borohydride reduction method. Physicochemical characterizations of the catalyst material were made by X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with EDX analysis and transmission electron microscopy (TEM). XRD patterns showed that Ru induces a contraction of the Pt lattice. EDX provided the composition of binary catalysts while TEM images indicated uniform distribution of discrete nanoparticle of the catalysts with narrow range. The electro-catalytic activities of the materials towards ethanol oxidation were investigated through electrochemical techniques, viz. cyclic voltammetry (CV), potentiodynamic polarization, chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) at room temperature. The onset potential of ethanol electro-oxidation is lowered on bimetallic PtRu catalysts compared to that on Pt alone. Of the investigated catalyst compositions the one with the highest electrocatalytic activity was found to be Pt₈₂Ru₁₈. This enhancement towards ethanol oxidation is explained on the basis of a structural effect and modified bi-functional mechanism.     

Influence of underlayers on the c-axis distribution in Co80Pt20 thin films

A series of approximately 40 nm thick Co₈₀Pt₂₀ thin films have been sputter-deposited onto a combination of Ta, Pt and Ru underlayers grown at different layer thicknesses. The addition of a Ta seed layer to the Pt and Ru underlayers caused the {0002} hexagonal close packed (hcp) Co₈₀Pt₂₀'s c-axis dispersion's full width at half maximum to narrow from approximately 12° to approximately 2°. In-situ stress measurements taken during deposition showed that the Ta seed layer reduced the growth stresses for the Pt and an initial 1 nm of growth for the Ru underlayers. The Ru layer thickness controlled the c/a ratio of the hcp Co₈₀Pt₂₀ film which regulated the degree of magnetic easy-axis alignment in the Co₈₀Pt₂₀ film. The optimal underlayer material stack for Co₈₀Pt₂₀ with a narrow c-axis dispersion and a high degree of magnetic easy-axis alignment was 5 nm Ta/10 nm Pt/5 nm Ru.     

A study on phase relations and texture of Co1 − xPtx (0.09 < x < 0.86) nanowire arrays

Based on Rietveld refinement of X-ray diffraction patterns, the phase structure and microstructural parameters of Co_1 − xPt_x nanowires are determined for a range of Pt content. The phase structure of the as-deposited Co_1 − xPt_x(0.09 < x < 0.86) nanowire arrays changes progressively from hcp ε-Co to a mixture of the hcp ε-Co and fcc α-Co,Pt solid solution and finally to pure fcc Co,Pt solid solution with Pt content increasing . Moreover, the texture parameter P₍₁₁₁₎ has a maximum value with Pt content of 50% confirmed by the (111) pole figure measurement. It is suggested that this contributes to enhance magnetocrystalline anisotropy, resulting in a relatively high squareness and coercivity for the nanowires.     

Alloy-oxide equilibria in the system Pt-Rh-O

The composition of Pt-Rh alloys that co-exist with Rh₂O₃ in air have been identified by experiment at 1273 K. The isothermal sections of the phase diagram for the ternary system Pt-Rh-O at 973 K and 1273 K have been computed based on experimentally determined phase relations and recent thermodynamic measurements on Pt_1−X Rh _X alloys and Rh₂O₃. The composition dependence of the oxygen partial pressure for the oxidation of Pt_1−X Rh _X alloys at different temperatures, and temperature for the oxidation of the alloys in air are computed. The diagrams provide quantitative information for optimization of the composition of Pt_1−X Rh _X alloys for high temperature application in oxidizing atmospheres.     

Carbide and nanocomposite thin films in the Ti-Pt-C system

Thin films in the Ti-Pt-C system were deposited by non-reactive, DC-magnetron sputtering. Samples were characterised using X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscopy. A previously not reported metastable solid solution carbide, (Ti_1 − xPt_x)C_y with a Pt/Ti ratio of up to 0.43 was observed. This solid solution phase was present both as single phase in polycrystalline samples, and together with amorphous carbon (a-C) in nanocomposite samples. Annealing of nanocomposite samples leads to the decomposition of the solid solution phase and the formation of a nc-TiC_x/a-C/nc-Pt nanocomposite. Test sensors for automotive gas exhausts manufactured from such a three-phase material suffer from complete oxidation of the coating at 400 °C with no observed sensor activity.     

Ultrahigh Mass Activity Pt Entities Consisting of Pt Single atoms,Clusters, and Nanoparticles for Improved Hydrogen Evolution Reaction

Platinum is one of the best-performing catalysts for the hydrogen evolution reaction (HER). However, high cost and scarcity severely hinder the large-scale application of Pt electrocatalysts. Constructing highly dispersed ultrasmall Platinum entities is thereby a very effective strategy to increase Pt utilization and mass activities, and reduce costs. Herein, highly dispersed Pt entities composed of a mixture of Pt single atoms, clusters, and nanoparticles are synthesized on mesoporous N-doped carbon nanospheres. The presence of Pt single atoms, clusters, and nanoparticles is demonstrated by combining among others aberration-corrected annular dark-field scanning transmission electron microscopy, X-ray absorption spectroscopy, and electrochemical CO stripping. The best catalyst exhibits excellent geometric and Pt HER mass activity, respectively ≈4 and 26 times higher than that of a commercial Pt/C reference and a Pt catalyst supported on nonporous N-doped carbon nanofibers with similar Pt loadings. Noteworthily, after optimization of the geometrical Pt electrode loading, the best catalyst exhibits ultrahigh Pt and catalyst mass activities (56 ± 3 A mg⁻¹_Pt and 11.7 ± 0.6 A mg⁻¹_Cat at −50 mV vs. reversible hydrogen electrode), which are respectively ≈1.5 and 58 times higher than the highest Pt and catalyst mass activities for Pt single-atom and cluster-based catalysts reported so far.     

The interaction of oxygen with high loaded Ru/γ-Al2O3 catalyst

The interaction of oxygen with the Ru/γ-Al₂O₃ catalyst comprising metal particle with sizes of 1-16 nm, was examined over a temperature range 20-400 °C. The catalyst loaded with 10.8 wt.% Ru was prepared by incipient wetness from RuCl₃ precursor. The structure of the Cl-containing catalyst and the catalyst after elimination Cl⁻ ions was characterized using H₂ and O₂ chemisorption, O₂ uptake, BET, XRD and TEM. The Cl⁻ ions in the catalyst decreased the H₂ and O₂ chemisorption capacity of Ru and caused large discrepancies between the mean particle size calculated from gas chemisorption and from TEM. Exposure to O₂ at 100-200 °C caused oxidation of small Ru particles, while larger particles were covered with very thin Ru_xO_y skin (undetected by XRD and TEM). The O/Ru ratio increased up to 200 °C implying high affinity of the small Ru particles to oxygen. Oxidation at 250 °C led to the formation of poorly crystalline RuO₂ particles with a mean size of 4 nm, and coverage of large Ru particles with 1.6 nm thick oxide layer. At 300 and 400 °C crystallization of the RuO₂ phase, as well as significant agglomeration of oxide particles was observed. However, even at 400 °C, metallic Ru was detected by XRD, TEM and SAED suggesting that large metal particles were not fully oxidized under the used conditions. Also, the O₂ uptake at 400 °C was lower than expected for oxidation of Ru metal to RuO₂. For the catalyst after elimination Cl ions the O₂ uptake (O/Ru ratio = 1.50) was higher, than for sample with large amount of Cl ions (O/Ru ratio = 1.34), indicating that the presence of Cl inhibits ruthenium oxidation in the Ru/Al₂O₃ catalyst.     

Direct Synthesis of Ultrathin Pt Nanowire Arrays as Catalysts for Methanol Oxidation

High‐performance electrocatalysts are of critical importance for fuel cells. Morphological modulation of the catalyst materials is a rare but feasible strategy to improve their performance. In this work, Pt nanowire arrays are directly synthesized with a template‐less wet chemical method. The effects of surface functionalization and the reduction kinetics are revealed to be vital to the nanowire growth. The growth mechanism of the Pt nanowires is studied. By adjusting the concentration of the organic ligands, Pt nanowire arrays with tunable surface roughness can be obtained on various substrate surfaces. Such arrays avoid the contact resistance of randomly packed particles and allow open diffusion channels for reactants and products alike, making them excellent electrocatalysts for the methanol oxidation reaction. In particular, Pt nanowire arrays with rough surface have a mass activity of 1.24 A mg_Pt^?1 at 1.12 V (vs Ag/AgCl), 3.18‐fold higher than that of the commercial Pt/C catalysts. It also shows more resistant against poisoning, as indicated by the higher I_f/I_b ratio (2.06), in comparison to the Pt/C catalysts (1.30).     

Atomically Dispersed Ni–N4 Sites Assist Pt3Ni Nanocages with Pt Skin to Synergistically Enhance Oxygen Reduction Activity and Stability

Currently, the rarity and high cost of platinum (Pt)-based electrocatalysts seriously limit their commercial application in fuel cells cathode. Decorating Pt with atomically dispersed metal–nitrogen sites possibly offers an effective pathway to synergy tailor their catalytic activity and stability. Here active and stable oxygen reduction reaction (ORR) electrocatalysts (Pt₃Ni@Ni–N₄–C) by in situ loading Pt₃Ni nanocages with Pt skin on single-atom nickel–nitrogen (Ni–N₄) embedded carbon supports are designed and constructed. The Pt₃Ni@Ni–N₄–C exhibits excellent mass activity (MA) of 1.92 A mg_Pt⁻¹ and specific activity of 2.65 mA cm_Pt⁻², together with superior durability of 10 mV decay in half-wave potential and only 2.1% loss in MA after 30 000 cycles. Theoretical calculations demonstrate that Ni–N₄ sites significant redistribute of electrons and make them transfer from both the adjacent carbon and Pt atoms to the Ni–N₄. The resultant electron accumulation region successfully anchored Pt₃Ni, that not only improves structural stability of the Pt₃Ni, but importantly makes the surface Pt more positive to weaken the adsorption of *OH to enhance ORR activity. This strategy lays the groundwork for the development of super effective and durable Pt-based ORR catalysts.     

Complete oxidation of acetaldehyde on Pt/CeO2-ZrO2-Bi2O3 catalysts

Pt/CeO₂-ZrO₂-Bi₂O₃ catalysts for catalytic combustion of acetaldehyde, which is one of volatile organic compounds (VOCs), were prepared by a wet impregnation method in the presence of polyvinylpyrrolidone K25 (PVP). The addition of PVP in the preparation process was effective to enhance the specific surface area and the Pt²⁺ ratio on the surface. Additionally, the pore volume and size of the catalysts were modified by the PVP addition. The Pt/CeO₂-ZrO₂-Bi₂O₃ catalysts are specific for the total acetaldehyde oxidation and CO and any acetaldehyde-derivative compounds were not observed as by-products. The catalytic activity of the Pt/CeO₂-ZrO₂-Bi₂O₃ catalysts was significantly promoted by the PVP addition and the total oxidation temperature decreased. By the optimization of the amount of platinum, the complete oxidation of acetaldehyde was realized at a temperature as low as 140 °C on a 10 wt%Pt/CeO₂-ZrO₂-Bi₂O₃ catalyst.     

Magnetic properties and microstructures of single-layered Fe100 − xPtx films deposited onto heated substrates

The single-layered Fe_100 − xPt_x films of 30 nm thick with Pt contents (x) of 35-57 at.% are deposited on heated Si (100) substrate at a temperature (Ts) of 620 °C by magnetron co-sputtering. When the Pt content in the Fe-Pt alloy film is 35 at.%, the value of in-plane coercivity (Hc_//) is close to perpendicular coercivity (Hc_⊥) and both values are about 800 kA/m. The FePt films exhibit perpendicular magnetic anisotropy when the Pt content increases to the values of between 45 and 51 at.%. The perpendicular coercivity, saturation magnetization (Ms) and perpendicular squareness (S_⊥) for Fe₅₄Pt₄₆ film are as high as 1113 kA/m, 0.594 Wb/m² and 0.96, respectively. These magnetic properties reveal its significant potential as perpendicular magnetic recording media. Upon further increasing the Pt content to 57 at.%, the coercivity of the Fe-Pt film decreases drastically to below 230 kA/m and tends to be closer to in-plane magnetic anisotropy.     

Trimetallic Synergy in Intermetallic PtSnBi Nanoplates Boosts Formic Acid Oxidation

Platinum is the most effective metal for a wide range of catalysis reactions, but it fails in the formic acid electrooxidation test and suffers from severe carbon monoxide poisoning. Developing highly active and stable catalysts that are capable of oxidizing HCOOH directly into CO₂ remains challenging for commercialization of direct liquid fuel cells. A new class of PtSnBi intermetallic nanoplates is synthesized to boost formic acid oxidation, which greatly outperforms binary PtSn and PtBi intermetallic, benefiting from the synergism of chosen three metals. In particular, the best catalyst, atomically ordered Pt₄₅Sn₂₅Bi₃₀ nanoplates, exhibits an ultrahigh mass activity of 4394 mA mg^?1 Pt and preserves 78% of the initial activity after 4000 potential cycles, which make it a state‐of‐the‐art catalyst toward formic acid oxidation. Density functional theory calculations reveal that the electronic and geometric effects in PtSnBi intermetallic nanoplates help suppress CO* formation and optimize dehydrogenation steps.     

Preparation and characterization of Ba1 − xSrxTiO3 thin films deposited on Pt/SiO2/Si by sol-gel method

BST thin films have been investigated as potential candidates for use in frequency agile microwave circuit devices. Stoichiometric (Ba_1 − xSr_x)TiO₃ (BST) thin films have been prepared on Pt/SiO₂/Si substrates using sol-gel method. The BST films were characterized by X-ray fluorescence (XRF) spectroscopy analysis, X-ray diffraction (XRD), scanning electron microscope (SEM) and electrical measurements. The relationships of processing parameters, microstructures, and dielectric properties are discussed. The results show that the films exhibit pure perovskite phase through rapid thermal anneal at 700 °C and their grain sizes are about 20-40 nm. The dielectric constants of BST5, BST10, BST15 and BST20 are 323, 355, 382 and 405, respectively, at 80 kHz.     

Architecture of PtFe/C catalyst with high activity and durability for oxygen reduction reaction

A PtFe/C catalyst has been synthesized by impregnation and high-temperature reduction followed by acid-leaching. X-ray diffraction, X-ray photoelectron spectroscopy and X-ray atomic near edge spectroscopy characterization reveal that Pt₃Fe alloy formation occurs during high-temperature reduction and that unstable Fe species are dissolved into acid solution. The difference in Fe concentration from the core region to the surface and strong O-Fe bonding may drive the outward diffusion of Fe to the highly corrugated Pt-skeleton, and the resulting highly dispersed surface FeO _x is stable in acidic medium, leading to the construction of a Pt₃Fe@Pt-FeO _x architecture. The as prepared PtFe/C catalyst demonstrates a higher activity and comparable durability for the oxygen reduction reaction compared with a Pt/C catalyst, which might be due to the synergetic effect of surface and subsurface Fe species in the PtFe/C catalyst.      

Physical properties of very thin SnS films deposited by thermal evaporation

SnS films with thicknesses of 20-65 nm have been deposited on glass substrates by thermal evaporation. The physical properties of the films were investigated using X-ray diffraction (XRD), scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and ultraviolet-visible-near infrared spectroscopy at room temperature. The results from XRD, XPS and Raman spectroscopy analyses indicate that the deposited films mainly exhibit SnS phase, but they may contain a tiny amount of Sn₂S₃. The deposited SnS films are pinhole free, smooth and strongly adherent to the surfaces of the substrates. The color of the SnS films changes from pale yellow to brown with the increase of the film thickness from 20 nm to 65 nm. The very smooth surfaces of the thin films result in their high reflectance. The direct bandgap of the films is between 2.15 eV and 2.28 eV which is much larger than 1.3 eV of bulk SnS, this is deserving to be investigated further.     

Preparation and photoelectrochemical properties of KTa5O13 microcones

Potassium tantalate (KTa₅O₁₃) microcones with a maximum diameter of about 47-85 μm were prepared by anodic oxidation of tantalum in (15-20 M) KOH solutions at the temperature of 70 °C and applied voltage of 20 V for 3 h. Different factors affecting on the morphology of tantalum surface were discussed. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffractometry (XRD) were used to characterize the structure of the microcones. The photoelectrochemical properties were studied through electrochemical workstation. The experimental results indicate KTa₅O₁₃ microcones have a good performance in photoelectricity. The possible formation mechanism of as-prepared KTa₅O₁₃ microcones was also presented.