source materials were heated to between 60 and 200 C. The pressure in the source vessels was between 80 and 196 hPa. The carrier gas was Ar and the flow rate was in the range 70±300 sccm, depending on the source materials, which were loaded individually into the source vessels. The pipes connected to the reactor were heated to above 200 C in order to avoid vapor condensation. Oxygen was supplied to the reactor at 36 hPa and the total pressure in the reactor was 65 hPa. The deposition temperature was 800 C. The as-prepared thin films had a cation composition of Bi/Sr/Ca/Cu = 1:1:1:(1.5±1.7). The composition and thickness of the thin films were determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES) (SPS 7700, Seiko Instruments Inc.). X-ray diffraction patterns (D500, Siemens) have shown that that films were epitaxial, c-axis aligned, and formed from the Bi 2 Sr 2 Ca 2 Cu 3 O 10±x phase. The morphology of the thin films was inspected by optical microscopy on large areas, and by atomic force microscopy (AFM) (SPA 300, Seiko Instruments Inc.) locally. The superconductivity of the thin films was checked by the standard four-probe method.

Supported Au nanoclusters are well-known for their unusual properties in catalysis. We describe here that nanostructured porous Au made via dealloying represents a new class of unsupported catalysts with extraordinary activities in important reactions such as CO oxidation. Although nanoporous Au may contain some oxides on the surface, our results demonstrate that it is metallic Au that plays the main role in this catalytic reaction. Furthermore, this material has good low-temperature catalytic stability and is extremely CO tolerant.

Dealloying single phase alloys is known to generate a type of nanostructured porous metals with intriguing properties. In this study, nanoporous gold (NPG) made by dealloying Au-Ag is investigated as a novel electrode material for methanol electro-oxidation. Compared to bulk Au electrode, oxidation and subsequent reduction of NPG occur at significantly negative potentials in both acid and alkaline solutions. NPG shows great catalytic activity for methanol electro-oxidation, but the structure quickly coarsens upon long time potential cycling. Interestingly, after surface modification with only a tiny amount of platinum, NPG exhibits greatly enhanced electrocatalytic activity toward methanol oxidation in the alkaline solutions, which is exemplified by a broad and high anodic peak during the positive scan and two secondary oxidation peaks in the subsequent reverse scan. At the same time, SEM observation and long-time potential cycling both prove that Pt-NPG has much enhanced structure stability as compared with bare NPG.

A simple two-step dealloying strategy is described to make free-standing metal membranes with hierarchical porous architecture. This structure has a bimodal pore size distribution composed of large porosity channels and small porosity channel walls, where each pore size can be tailored independently of the others. A new gas-phase electroless plating technique was also developed here that could be used to uniformly fill porous structures with pore size as small as 10 nm.

We describe the fabrication, characterization, and applications of ultrathin, free-standing mesoporous metal membranes uniformly decorated with catalytically active nanoparticles. Platinum-plated nanoporous gold leaf (Pt-NPG) made by confining a plating reaction to occur within the pores of dealloyed silver/gold leaf is 100 nm thick and contains an extremely high, uniform dispersion of 3 nm diameter catalytic particles. This nanostructured composite holds promise as a prototypical member of a new class of fuel cell electrodes, showing good electrocatalytic performance at low platinum loading (less than 0.05 mg cm-2), while also maintaining long-term stability against coarsening and aggregation of catalytic nanoparticles.