Hao Cui

The oxygen reduction reaction (ORR) at the cathode remains a major kinetic bottleneck for proton-exchange-membrane fuel cells, and Pt-Co alloying is a well-established strategy for boosting Pt-mass-normalized ORR activity. However, the long-term durability of such alloys is limited by two largely independent degradation pathways, dealloying-induced Co leaching and nanoparticle coalescence, that are rarely addressed simultaneously. Here, a series of Pt_xCo_y/C-H₂ catalysts with varying Pt:Co ratios were synthesized via gel-confined co-reduction of Pt and Co precursors, phosphoric-acid-assisted carbonization into a mesoporous carbon support, and a subsequent H₂-annealing step. XRD confirmed Pt-Co alloy formation with composition-dependent lattice contraction, while XPS showed that surface Pt:Co ratios consistently exceeded the nominal feed ratios across all compositions, indicating H₂-annealing-induced Pt surface segregation and the formation of a Pt-enriched, core–shell-like architecture, further supported by TEM/EDS line-scan profiles. Among the series, Pt₃Co₁/C-H₂ delivered ORR activity (E_1/2, mass activity, and specific activity) essentially comparable to commercial Pt/C while reducing Pt loading by approximately 9 wt%, and retained the intrinsic four-electron ORR pathway (n = 3.78). After accelerated durability testing (10,000 cycles), Pt₃Co₁/C-H₂ exhibited smaller E_1/2 decay than Pt/C (48 vs. 52 mV), which is attributed to the concurrent suppression of nanoparticle coalescence by mesopore confinement and of Co leaching by the Pt-enriched surface. These results establish a generalizable design principle for decoupling the dominant degradation pathways of Pt-transition-metal alloy ORR catalysts while reducing precious-metal content.

Silver-based alloys are irreplaceable in high-reliability electrical contacts because silver has the highest electrical conductivity of all metals, yet its low strength and the intrinsic strength–ductility trade-off limit their use under increasingly severe service conditions. Internal oxidation—the selective in situ oxidation of reactive solutes in a chemically inert Ag matrix—converts these solutes into fine, dispersed oxides, thereby strengthening the alloy. This review critically assesses internal oxidation in silver-based alloys. The thermodynamic and kinetic criteria for selective oxidation are summarized, together with the Wagner diffusion-controlled framework describing the oxidation front. Using Ag-Mg and Ag-Sn as archetypal systems, we trace the microstructural evolution from coherent Mg-O nanoclusters and dispersed SnO₂ particles to deleterious banded oxides, identifying band formation and under-oxidized cores as the two characteristic microstructural defects. The roles of temperature, time, oxygen partial pressure and third-element additions (Te, In, Sb, Bi, Ni) in widening the process window and refining the oxide dispersion are examined. Orowan bypassing, coherency strain and Hall–Petch grain refinement, and their coupling with microstructural characteristics, are discussed to provide guidelines for alloy design. Finally, outstanding questions and opportunities, including atomic-scale in situ characterization, predictive multiscale modeling and novel processing routes, are outlined.

Lattice strain engineering bridges atomic structure and electrocatalytic performance. This review explains how strain tunes electronic structure and optimizes adsorption, boosting activity and stability in key reactions.

A novel AgCuTi brazing foil with a unique microstructure was developed, which could achieve strong vacuum brazing of Ti6Al4V (TC4) and sapphire. The brazing foil was composed of Ag solid solution (Ag(s,s)), Cu solid solution (Cu(s,s)), and layered Ti-rich phases, and had a low liquidus temperature of 790 °C and a narrow melting range of 16 °C, facilitating the defect-free joining of TC4 and sapphire. The sapphire/TC4 joint fabricated by using this novel AgCuTi brazing foil exhibited an outstanding average shear strength of up to 132.2 MPa, which was the highest value ever reported. The sapphire/TC4 joint had a characteristic structure, featuring a brazing seam reinforced by TiCu particles and a thin Ti₃(Cu,Al)₃O reaction layer of about 1.3 μm. The fracture mechanism of the sapphire/TC4 joint was revealed. The crack originated at the brazing seam with TiCu particles, then propagated through the Ti₃(Cu,Al)₃O reaction layer, detached the reaction layer from the sapphire, and finally penetrated into the sapphire. This study offers valuable insights into the design of active brazing alloys and reliable metal–ceramic bonding.

Ruthenium (Ru) is a refractory metal that has applications in the semiconductor industry as a sputtering target material. However, conventional powder metallurgy methods cannot produce dense and fine-grained Ru targets with preferred orientation. Here, we present a novel method of hot-pressing deformation to fabricate Ru targets with high relative density (98.8%), small grain size (~4.4 μm) and strong (002) texture. We demonstrate that applying pressures of 30–40 MPa at 1400 °C transforms cylindrical Ru samples into disk-shaped targets with nearly full densification in the central region. We also show that the hardness and the (002)/(101) peak intensity ratio of the targets increase with the pressure, indicating enhanced mechanical and crystallographic properties. Our study reveals the mechanisms of densification and texture formation of Ru targets by hot-pressing deformation.

In this study, pure copper’s hot deformation behavior was studied through isothermal compression tests at deformation temperatures of 350~750 °C with strain rates of 0.01~5 s⁻¹ on a Gleeble-3500 isothermal simulator. Metallographic observation and microhardness measurement were carried out of the hot compressed specimens. By analyzing the true stress–strain curves of pure copper under various deformation conditions during the hot deformation process, the constitutive equation was established based on the strain-compensated Arrhenius model. On the basis of the dynamic material model proposed by Prasad, the hot-processing maps were acquired under different strains. Meanwhile, the effect of deformation temperature and strain rate on the microstructure characteristics was studied by observing the hot-compressed microstructure. The results demonstrate that the flow stress of pure copper has positive strain rate sensitivity and negative temperature correlation. The average hardness value of pure copper has no obvious change trend with the strain rate. The flow stress can be predicted with excellent accuracy via the Arrhenius model based on strain compensation. The suitable deforming process parameters for pure copper were determined to be at a deformation temperature range of 700~750 °C and strain rate range of 0.1~1 s⁻¹.

Silver nanodisks (AgNDs) have been successfully synthesized by using ferric chloride as an auxiliary agent in the presence of polyvinylpyrrolidone and N,N-dimethylformamide as both a solvent and a reducing agent. The mass ratio of reactants, temperature, and time were demonstrated to be the key factors determining the morphology of the product, and the conversion of Fe³⁺/Fe²⁺ ions played an important role in increasing the ratio of silver nanosheets (AgNSs). As the reaction prolonged, the etching effect of Cl^- ions on the tips of AgNSs became more and more obvious, which made the obtained typical polygonal AgNSs turn into AgNDs eventually. In addition, the prepared AgNDs exhibited a considerable catalytic activity in the reduction of 4-nitrophenol.

LuAG:Ce (Lu₃Al₅O₁₂:Ce) is one of the most important color converters in white lighting industry. Especially, LuAG:Ce film attracts more attention due to the outstanding advantages, such as the efficient heat dissipation, the saving of rare earth, and so on. Here, LuAG:Ce film on sapphire was successfully prepared by the ultrasonic spray pyrolysis process. The phase, microstructure and photoluminescence of LuAG:Ce films were investigated. LuAG:Ce films had a thickness of around 5 μm, which were well crystallized at 1000 °C in air atmosphere to form the typical garnet structure. Under the protection of CO atmosphere, increasing the annealing temperature greatly enhanced the photoluminescence performance. After annealing at 1500 °C for 5 h in CO atmosphere, 3.0 mol.% Ce³⁺ doped LuAG:Ce film exhibited the highest emission and excitation intensity. The emission intensity of 3.0 mol.% Ce³⁺ doped LuAG:Ce film annealed at 1500 °C in CO atmosphere increased up to five times, when compared with the best LuAG:Ce film annealed at 1000 °C in air atmosphere. The effects of Ce³⁺ doping concentration on the photoluminescence were also examined. As the Ce³⁺ doping concentration increased from 0.2 mol.% to 7.0 mol.%, the color of LuAG:Ce films changed from yellowish green to greenish yellow. When coupling the 3.0 mol.% Ce³⁺ doped LuAG:Ce film with a 0.5 W 450 nm blue laser, the formed device successfully emitted white light.

Ag/Y₂O₃ has excellent potential to replace Ag/CdO as the environmentally friendly electrical contact material. Using spherical Y₂O₃ as the starting material, Ag/Y₂O₃ contacts with a quasi-continuous network structure were successfully fabricated by a low-energy ball milling treatment. The mean size of Y₂O₃ used ranged from 243 to 980 nm. Due to the differences in the size of Y₂O₃, Ag/Y₂O₃ contacts had different primitive microstructures, thereby exhibiting distinctive anti-arc-erosion capabilities. Ag/Y₂O₃ contact prepared using 243 nm Y₂O₃ showed the best anti-arc-erosion capability and the most outstanding electrical performance measures, such as low contact resistance, less mass transfer, and no failure up to 10⁵ cycle times. The quasi-continuous network structure formed in the micro-scale was responsible for the excellent electrical performance. The short distance between Y₂O₃ particles in the network promoted the cathode arc motion, and thus alleviated the localized erosion. The results obtained herein may inspire further attempts to design electrical contacts rationally.

Ceria-modified Pt/Al₂O₃ catalyst has been commonly prepared by the impregnation of platinum on ceria-modified alumina and widely applied in the chemical industry and automotive industry. The in situ diffuse reflectance infrared Fourier transformed spectroscopy (DRIFTS), and thermogravimetric (TG) analysis techniques were employed to investigate the typical mechanisms of the bis(ethanolammonium)hexahydroxyplatinate(IV) and cerium nitrate decomposition catalyzed by Pt^δ+ species for the facile synthesis of CeO₂-Pt/Al₂O₃ catalyst. It was found that Pt⁴⁺-catalyzed decomposition of cerium nitrate leads to the higher dispersity of ceria and forming more active oxygen species, on the basis of X-ray diffraction (XRD) and H₂ temperature-programmed reduction (H₂-TPR) results. The in situ activity measurements were also performed to investigate the reaction mechanisms and the specific activities for the catalytic CO, NO, C₃H₆ and C₃H₈ co-oxidation. The results indicate that undesirable N₂O by-product is formed by the selective catalytic reduction (SCR) of NO by C₃H₆ below 350 °C. The cerium addition effectively improves the activity of catalytic oxidation, but exhibits an increased N₂O yield, due to the increased reducibility.