Narrow Results

The synthesis of bimetallic nanostructures using galvanic replacement displays a versatile route toward efficient catalysts for fuel cell reactions. We show that electrolessly plated Ag nanotubes (NTs) are a unique template for the synthesis of double-walled Ag–Pt NTs. After replacement reaction, different dealloying protocols are applied to adjust the residual Ag content. The structures were thoroughly characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy, providing evidence of a hollow tube structure composed of Ag–Pt alloy. Experiments under harsh conditions reveal, that a significant amount of Ag remain in the NTs, which strongly affects the methanol oxidation performance. With optimized Ag–Pt ratio, the specific activity of Pt/C catalysts can be outperformed. From the obtained results, we emphasize that each effort using galvanic replacement should be accompanied by detailed compositional analysis.

Bimetallic silver–gold composites are currently among the most studied substrates for detection based on surface-enhanced Raman scattering (SERS). Here, we developed Au–Ag composite films as high sensitivity, large-scale, chemically stable and reproducible SERS substrates. Au–Ag composite films were fabricated by chemical etching of Ag–Au alloy leaves with HAuCl₄ aqueous solutions. Along with galvanic replacement reaction and dealloying, films with distinct microstructural features exhibit dramatic improvement in the SERS intensity. Especially, the Au–Ag composite films with legible nano-ridges fabricated by alloy leaves of 9 carat present the strongest SERS enhancement. The superior SERS enhancement is attributed to the confluence effect of enhanced local surface plasmon fields and electromagnetic coupling within nanogaps, sharp edges and corners. In addition, results showed that features of the films mightily depend on the initial proportions of Ag–Au alloys.

Nanoporous copper (NPC) and nanoporous copper-nickel (NPC-Ni) can be prepared by free corrosion dealloying Mn${}_{72}$Cu${}_{28-x}$Ni_x ($x=0$, 1, 3at.% Ni) precursor alloys. Microscopic morphology characterization by scanning electron microscopy exhibited a three-dimensional bicontinuous porous structure with nanoscale ligaments and pores. NPC with a pore size of 48.7nm was obtained in 0.1M hydrochloric acid solution for 3.5h dealloyed at 25${}^{\circ }$C. Under the same free corrosion dealloying condition, NPC-Ni₁ and NPC-Ni₃ were obtained with the pore size of 36.6nm and 28.1nm, respectively. The results indicate that minor Ni atoms addition to the precursor greatly refined the dealloyed nanoporous structure. This effect could be attributed to the lower Ni surface diffusivity than that of Cu and resulted in slow down of the diffusion and rearrangement of Cu atoms during dealloying process. Post-dealloying heat treatment at 300${}^{\circ }$C, 450${}^{\circ }$C and 600${}^{\circ }$C made the ligaments coarsen in NPC and NPC-Ni.

In this work, a series of three dimensions nanoporous Pd/M_xO_y ($\mathrm{\text{M}}=\mathrm{\text{Zr}}$, Ti, Co, Ni) composites are directly prepared by a simple dealloying method, their electrocatalytic performances are investigated. The structure analysis results show that the pores size of the composites is distinctly reduced, and their specific surface area is obviously increased compared with the nanoporous Pd when adding M_xO_y. As an anode catalyst, these three-dimensional (3D) nanoporous Pd/M_xO_y composites exhibit remarkable electrocatalytic performance (activity and stability) than that of the nanoporous Pd for ethanol electrooxidation, the order of the performance is as follows: Pd/NiO $>$ Pd/Co₂O₃ s $>$ Pd/TiO₂ s $>$ Pd/ZrO${}_2>$ Pd. Among the composites, the nanoporous Pd/NiO composite shows the best performance, which is approximately 3.6 times that of the single nanoporous Pd. The performance improvement of the composites for the ethanol oxidation is attributed to the structure optimization, interfacial electronic effect and dual functional mechanism between Pd and M_xO_y.

The self-supporting three-dimensional (3D) nanoporous PdAg alloy (NP–PdAg) foams have been prepared by a simple one-step dealloying melt-spun Al–Pd–Ag ribbons in a 20wt.% NaOH aqueous solution at 90^∘C for 1.5h. The structure is advantageous to the diffusion and removal of the intermediate products and the transmission of the methanol molecules. The NP–PdAg foams exhibit better electrocatalytic performance than the NP-Pd foam toward the methanol oxidation in potassium hydroxide (KOH) solution. The optimal atomic ratio of Pd to Ag in the NP–PdAg foams is 1:1, and its electrocatalytic activity is about 2.6 times that of the NP–Pd foam. The significant improvement in the electrocatalytic performance is attributed to the addition of a moderate amount of Ag. In the whole electrocatalytic process, Ag can provide OH_ads to oxidize the intermediate products on the surface of active Pd sites into carbon dioxide or other cleaning products. Also, the Ag can increase electrochemical active surface area and the adsorption energy of Pd to methanol molecules and OH_ads. These significantly prevent the accumulation of poisoning intermediates on the surface of Pd and quickly release more active Pd sites.

A novel and simple method has been developed to prepare the Cu-Si composite as anode material for lithium-ion batteries. Nanoporous Cu-Si composite with pore sizes of 1~30 nm was prepared by dealloying the melt-spun Al-Cu-Si-Ce ribbons in a 5 wt.% HCl solution. Electrochemical tests revealed that the nanoporous Cu-Si electrodes exhibited highly reversible capacity of 2317 mAhg^-1 and retained a capacity of 1030 mAhg^-1 over 20 cycles. The excellent electrochemical performance is attributed to the unique porous structure of the Cu-Si composite. Our results demonstrate that this novel composite is a promising anode candidate for high-capacity rechargeable lithium-ion batteries.