Ultra-long Pt nanolawns supported on TiO2-coated carbon fibers as 3D hybrid catalyst for methanol oxidation

In this study, TiO2 thin film photocatalyst on carbon fibers was used to synthesize ultra-long single crystalline Pt nanowires via a simple photoreduction route (thermally activated photoreduction). It also acted as a co-catalytic material with Pt. Taking advantage of the high-aspect ratio of the Pt nanostructure as well as the excellent catalytic activity of TiO2, this hybrid structure has the great potential as the active anode in direct methanol fuel cells. The electrochemical results indicate that TiO2 is capable of transforming CO-like poisoning species on the Pt surface during methanol oxidation and contributes to a high CO tolerance of this Pt nanowire/TiO2 hybrid structure

Direct growth of ultra-long platinum nanolawns on a semiconductor photocatalyst

A template- and surfactant-free process, thermally assisted photoreduction, is developed to prepare vertically grown ultra-long Pt nanowires (NWs) (about 30-40 nm in diameter, 5-6 μm in length, and up to 80 NWs/100 μm2 in the wire density) on TiO2 coated substrates, including Si wafers and carbon fibers, with the assistance of the photocatalytic ability and semiconductor characteristics of TiO2. A remarkable aspect ratio of up to 200 can be achieved. TEM analytical results suggest that the Pt NWs are single-crystalline with a preferred 〈111〉 growth direction. The precursor adopted and the heat treatment conditions are crucial for the yield of NWs. The photoelectrons supplied by TiO2 gives rise to the formation of nano-sized Pt nuclei from salt melt or solution. The subsequent growth of NWs is supported by the thermal electrons which also generated from TiO2 during the post thermal treatment. The interactions between the ions and the electrons in the Pt/TiO2 junction are discussed in this study

An in situ study on the coalescence of monolayer-protected Au-Ag nanoparticle deposits upon heating

The structural evolution of thiolate-protected nanoparticles of gold, silver, and their alloys with various Au/Ag ratios (3:1, 1:1, and 1:3) upon heating was investigated by means of in situ synchrotron radiation X-ray diffraction. The relationships between the coalescence and composition of nanoparticles, as well as the surfactant reactions, were clarified. Experimental results show that there existed a critical temperature ranging from 120°C to 164°C, above which the tiny broad X-ray diffraction peaks became sharp and strong due to particle coalescence. The coalescence temperatures for alloy nanoparticle deposits were clearly lower than those for pure metals, which can be ascribed to the rivalry between the thermodynamic effect due to alloying and the interactions between surface-assembled layers and the surface atoms of the nanoparticles. The strong affinity of thiolates to Ag and thus complex interactions give rise to a greater energy barrier for the coalescence of nanoparticles into the bulk and subsequent high coalescence temperature. The influences of particle coalescence on the optical and electrical properties of the nanoparticle deposits were also explored

Faceting Behavior of Primary Ag in Bi-Ag Alloys for High Temperature Soldering Applications

The solidification behavior and structure of Bi-Ag alloys with low Ag content (0 mass%11 mass%) which are now being applied as high temperature Pb-free solders were investigated. The results show that Bi-Ag alloys exhibited a nonequilibrium eutectic solidification feature and a considerably large undercooling. A longer cooling period to reach eutectic temperature enhanced the faceting of primary Ag crystals. The large value of the entropy of solution for Ag near the eutectic point should account for this

Effect of Ag Templates on the Formation of Au-Ag Hollow/Core-Shell Nanostructures

Au-Ag alloy nanostructures with various shapes were synthesized using a successive reduction method in this study. By means of galvanic replacement, twined Ag nanoparticles (NPs) and single-crystalline Ag nanowires (NWs) were adopted as templates, respectively, and alloyed with the same amount of Au+ ions. High angle annular dark field-scanning TEM (HAADF-STEM) images observed from different rotation angles confirm that Ag NPs turned into AuAg alloy rings with an Au/Ag ratio of 1. The shifts of surface plasmon resonance and chemical composition reveal the evolution of the alloy ring formation. On the other hand, single-crystalline Ag NWs became Ag@AuAg core-shell wires instead of hollow nanostructure through a process of galvanic replacement. It is proposed that in addition to the ratio of Ag templates and Au ion additives, the twin boundaries of the Ag templates were the dominating factor causing hollow alloy nanostructures

Plasma-Modified PI Substrate for Highly Reliable Laser-Sintered Copper Films Using Cu2O Nanoparticles

Plasma modification of polyimide (PI) substrates upon which electrical circuits are fabricated by the laser sintering of cuprous oxide nanoparticle pastes was investigated systematically in this study. Surface properties of the PI substrate were investigated by carrying out atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Experimental results show that surface characteristics of PI substrates, including surface energy, surface roughness, and surface binding significantly affected the mechanical reliability of the sintered copper structure. Among the plasma gases tested (air, O2, Ar-5%H2, and N2-30%H2), O2 plasma caused the roughest PI surface as well as the most C=O and C–OH surface binding resulting in an increased polar component of the surface energy. The combination of all those factors caused superior bending fatigue resistance

Nanomechanical Responses of an Intermetallic Compound Layer in Transient Liquid Phase Bonding Using Indium

Low-temperature transient liquid phase bonding (TLPB) can be achieved using indium, and the joints thus formed can withstand high temperatures. Since the joints that are formed with TLPB entirely consist of intermetallic compounds (IMCs), this study investigates the phase evolution and mechanical properties of IMCs that are obtained from isothermal reactions between In and commonly used substrate metals, Cu, Ag and Au. Using nanoindentation, the relationships between the yield strain, work hardening exponent and strain rate sensitivity of In-bearing and other frequently observed IMC phases were compared. Notably, the strain-induced precipitation of Ag3In occurred in the indent of Ag9In4