Platinum-palladium-on-reduced graphene oxide as bifunctional electrocatalysts for highly active and stable hydrogen evolution and methanol oxidation reaction.

In the context of the gradual depletion of global fossil fuel resources, it is increasingly necessary to explore new alternative energy. Hydrogen energy has attracted great interest from researchers because of its green and pollution-free characteristics. Moreover, the methanol oxidation reaction (MOR) can combine the hydrogen evolution reaction (HER), replacing the anode reaction (oxygen evolution reaction-OER) in overall water splitting and efficiently producing hydrogen. In this study, platinum-palladium nanoparticles on reduced graphene oxide (PtPd/rGO) were successfully synthesized as HER and MOR bifunctional electrocatalysts under alkaline conditions by the stepwise loading of Pt and Pd bimetallic nanoparticles on rGO using a simple liquid-phase reduction method. PtPd/rGO-2 with 0.99 wt% Pt and 2.86 wt% Pd in the HER has the lowest overpotential (87.16 mV at 100 mA cm-2), with the smallest Tafel slope (18.9 mV dec-1). The exceptional mass activity of PtPd/rGO-2 in the MOR reaches 10.75 A mg-1PtPd, which is 18.22 and 53.75 times greater than that of commercial Pt/C (Pt/C) and commercial Pd/C (Pd/C), respectively. PtPd/rGO-2 is 0.935 V lower in the coupling reaction of HER and MOR (MOR ∥ HER) compared to the overall water splitting (OER ∥ HER) without methanol (10 mA cm-2). This is probably because appropriate Pt and Pd loading exposes many more catalytic sites, and the synergistic interaction between Pt, Pd, and Pt-Pd enhances the catalytic performance. This strategy can be used for the synthesis of novel bifunctional electrocatalysts.

Wet Etching of Quartz Using a Solution Based on Organic Solvents and Anhydrous Hydrofluoric Acid.

The quartz-crystal resonator is the core device for frequency control in modern communication systems and network technology. At present, in modern resonator blanks manufacturing, BOE solution is usually used as the etching solution, but its etching rate is relatively volatile, and the surface morphology of the blanks is prone to defects after etching, which brings certain difficulties to the deep-etching process of the wafer. To solve the above challenges, this paper systematically compares a BOE solution and anhydrous etching solution in terms of etching rate, surface morphology, and electrical properties of the blanks after etching. Seven groups of blanks were etched using different etching solutions with different etching conditions to verify their effect on the surface morphology and electrical properties of quartz blanks. The experimental results suggest that the application of anhydrous etching solution has achieved better surface morphology and electrical properties and can be more suitable for application in batch manufacturing. In general, when using anhydrous etching solution, it is possible to reduce surface roughness by up to 70% and equivalent resistance by 32%, and the etch rate is almost 10 times lower than BOE solution under the same temperature, which is more conducive to the rate control of wafers in the etching process.

Effect of remelting heat treatment on the microstructure and mechanical properties of SnBi solder under high-speed self-propagation reaction.

The heat source based on the self-propagation reaction of Al/Ni thin foil has the characteristics of concentrated heat, fast temperature rise/fall rate and small heat-affected zone; it can complete the melting and solidification crystallization of solder within milliseconds to realize solder interconnection, which can solve the problems of damage to heat-sensitive materials and components caused by monolithic heating of package structure. However, due to the highly non-stationary interconnection process, the resulting microstructure morphology may affect the service performance of the interconnected joints. In view of this, to investigate the post-solder microstructure of solder based on the self-propagation reaction, this paper analyzes the effect of the initial microstructure on the post-solder microstructure by heating 300-µm-thick SnBi solder with a 40-µm Al/Ni thin foil. The results indicated that the short melting time could resulted in the incomplete melting of heterogeneous phases and the non-uniform distribution of elements during the melting process, which had a significant effect on the morphology and composition distribution of the solidified microstructure, as well as the hardness distribution of the melted zone. The above conclusions have the potential to improve the interconnection process based on the self-propagation reaction, which is critical for both theoretical guidance and engineering application.

Rational Design of Pt-Pd-Ni Trimetallic Nanocatalysts for Room-Temperature Benzaldehyde and Styrene Hydrogenation.

Nanostructures of the multimetallic catalysts offer great scope for fine tuning of heterogeneous catalysis, but clear understanding of the surface chemistry and structures is important to enhance their selectivity and efficiency. Focussing on a typical Pt-Pd-Ni trimetallic system, we comparatively examined the Ni/C, Pt/Ni/C, Pd/Ni/C and Pt-Pd/Ni/C catalysts synthesized by impregnation and galvanic replacement reaction. To clarify surface chemical/structural effect, the Pt-Pd/Ni/C catalyst was thermally treated at X=200, 400 or 600 °C in a H2 reducing atmosphere, respectively termed as Pt-Pd/Ni/C-X. The as-prepared catalysts were characterized complementarily by XRD, XPS, TEM, HRTEM, HS-LEIS and STEM-EDS elemental mapping and line-scanning. All the catalysts were comparatively evaluated for benzaldehyde and styrene hydrogenation. It is shown that the "PtPd alloy nanoclusters on Ni nanoparticles" (PtPd/Ni) and the synergistic effect of the trimetallic Pt-Pd-Ni, lead to much improved catalytic performance, compared with the mono- or bi- metallic counterparts. However, with the increase of the treatment temperature of the Pt-Pd/Ni/C, the catalytic performance was gradually degraded, which was likely due to that the favourable nanostructure of fine "PtPd/Ni" was gradually transformed to relatively large "PtPdNi alloy on Ni" (PtPdNi/Ni) particles, thus decreasing the number of noble metal (Pt and Pd) active sites on the surface of the catalyst. The optimum trimetallic structure is thus the as synthesised Pt-Pd/Ni/C. This work provides a novel strategy for the design and development of highly efficient and low-cost multimetallic catalysts, e. g. for hydrogenation reactions.

Fabrication of fully covered Cu-Ag core-shell nanoparticles by compound method and anti-oxidation performance.

Cu-Ag core-shell nanoparticles with a size of 8 nm were synthesized by the compound method of replacement reaction and chemical reduction reaction. A fully covered Cu-Ag core-shell structure was obtained by controlling the two different silver sources and electroless silver plating time. The optimum condition uses silver ammonia reacted for 14 h. The process of electroless silver plating uses the mixed growth model of layered growth and island growth. Silver atoms firstly attach to the surface of the as-prepared copper nanoparticles to form the dotted Ag atom structure by galvanic displacement reaction between Cu and [Ag(NH3)2]+, and then more silver atoms, reduced by sodium citrate, gradually deposit on the copper surface to form a fully covered structure. The morphology and core-shell structure of the nanoparticles was observed by scanning electron microscopy, transmission electron microscopy and x-ray diffraction. The simultaneous thermal analyzer results confirmed that the weight gain of Cu-Ag core-shell nanoparticles was 2.2% when heated up to 400 °C, which was lower than pure Cu nanoparticles. According to the x-ray photoelectron spectroscopy results, the Cu-Ag core-shell nanoparticles exhibited good anti-oxidation performance compared with the pure copper nanoparticles after being stored for one month under the ambient conditions.

Ag3Sn Compounds Coarsening Behaviors in Micro-Joints.

As solder joints are being scaled down, intermetallic compounds (IMCs) are playing an increasingly critical role in the reliability of solder joints, and thereby an in-depth understanding of IMCs microstructure evolutions in micro-joints is of great significance. This study focused on coarsening behaviors of Ag3Sn compounds in Sn-3.0Ag-0.5Cu (SAC305) micro-joints of flip chip assemblies using thermal shock (TS) tests. The results showed that the Ag3Sn compounds grew and rapidly coarsened into larger ones as TS cycles increased. Compared with such coarsening behaviors during thermal aging, TS exhibited a significantly accelerating influence. This predominant contribution is quantitatively determined to be induced by strain-enhanced aging. Moreover, based on observations for Ag3Sn microstructure evolutions during TS cycling, one particular finding showed that there are two types of coarsening modes (i.e., Ostwald ripening and Necking coalescence) co-existing in the Ag3Sn coarsening process. The corresponding evolutions mechanism was elucidated in a combination of simulative analysis and experimental validation. Furthermore, a kinetic model of the Ag3Sn coarsening was established incorporating static aging and strain-enhanced aging constant, the growth exponent (n) was calculated to be 1.70, and the predominant coarsening mode was confirmed to be the necking coalescence.

[Superfine comminution of Glycyrrhiza uralensis roots by vibration mill].

OBJECTIVE: To discuss the mechanism of superfine comminution of traditional Chinese medicine (TCM) at low temperature. METHOD: Glycyrrhiza uralensis roots were at room superfinely comminuted temperature and at low temperature by cryogenic vibration mill. The superfine powders were observed and analyzed by laser particle size analyzer and SEM. RESULT: The powder processed at low temperature was of smaller effective diameter and narrower size distribution and was also with smoother surface and smaller angle of repose. CONCLUSION: The G. uralensis roots could be superfinely comminuted with high efficiency and simple procedure by vibration mill at low temperature.