Nanoporous Alloy Research Articles

Nanoporous bimetallic Pt–Au alloy nanocomposites with superior catalytic activity towards electro-oxidation of methanol and formic acid

We present a facile route to fabricate novel nanoporous bimetallic Pt-Au alloy nanocomposites by dealloying a rapidly solidified Al(75)Pt(15)Au(10) precursor under free corrosion conditions. The microstructure of the precursor and the as-dealloyed sample was characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray (EDX) analysis. The Al(75)Pt(15)Au(10) precursor is composed of a single-phase Al(2)(Au,Pt) intermetallic compound, and can be fully dealloyed in a 20 wt.% NaOH or 5 wt.% HCl aqueous solution. The dealloying leads to the formation of the nanoporous Pt(60)Au(40) nanocomposites (np-Pt(60)Au(40) NCs) with an fcc structure. The morphology, size and crystal orientation of grains in the precursor can be conserved in the resultant nanoporous alloy. The np-Pt(60)Au(40) NCs consist of two zones with distinct ligament/channel sizes and compositions. The formation mechanism of these np-Pt(60)Au(40) NCs can be rationalized based upon surface diffusion of more noble elements and spinodal decomposition during dealloying. Electrochemical measurements demonstrate that the np-Pt(60)Au(40) NCs show superior catalytic activity towards the electro-oxidation of methanol and formic acid in the acid media compared to the commercial JM-Pt/C catalyst. This material can find potential applications in catalysis related areas, such as direct methanol or formic acid fuel cells. Our findings demonstrate that dealloying is an effective and simple strategy to realize the alloying of immiscible systems under mild conditions, and to fabricate novel nanostructures with superior performance.

Nanoporous alloy aggregates: synthesis and electrocatalytic activity

Nanoporous structures are widely used for many applications and hence there have been several efforts directed towards their synthesis. While several template-based and template-less approaches are available for monometallic systems, there is no general method for the synthesis of nanoporous multicomponent systems/alloys. We present a general template-less strategy for the synthesis of nanoporous alloy aggregates by controlled aggregation of nanoparticles in the solution phase with excellent control over morphology and composition as illustrated using AuPt, AuPd, PdPt and PtRu systems as examples. The Pt-based nanoporous clusters exhibit excellent activity for methanol oxidation with good long-term stability and CO tolerance. We show that the method can be extended to produce ternary catalysts and hence we expect our method to be widely used for the synthesis of multifunctional nanoporous structures for catalysis, sensor and drug-delivery applications.

A dramatic increase in the strength of a nanoporous Pt–Ni alloy induced by annealing

The microstructure and mechanical strength of a nanoporous Pt–Ni alloy were characterized before and after 300 °C annealing for 1 h. After annealing microhardness increased significantly from 2.1 to 3.8 GPa, while the relative density, ligament morphology and size remained unchanged. The annealing-induced strength increase is believed to be due to microstructure relaxation and grain growth. This study suggests that the mechanical properties of nanoporous metals depend not only on the relative density, ligament size and morphology, but also on the structure inside ligaments.

Marked Effects of Alloying on the Thermal Conductivity of Nanoporous Materials

We show that porous alloys can display thermal conductivity reductions at considerably larger pore sizes than nonalloyed porous materials of the same nominal porosity. The thermal conductivity of Si0.5Ge0.5 alloy with 0.1 porosity becomes half the nonporous value at 1000 nm pore sizes, whereas pores smaller than 100 nm are required to achieve the same relative reduction in pure Si or Ge. Using Monte Carlo simulations, we also show that previous models had overestimated the thermal conductivity in the small pore limit. Our results imply that nanoporous alloys should be advantageous with respect to nanoporous nonalloys, for applications requiring a low thermal conductivity, such as novel thermoelectrics.

Novel Nanoporous Au−Pd Alloy with High Catalytic Activity and Excellent Electrochemical Stability

A novel nanoporous gold−palladium alloy has been successfully fabricated by electrochemically dealloying a multicomponent metallic glass. In comparison with conventional nanoporous gold prepared by dealloying Au−Ag alloys, the nanoporous gold−palladium alloy shows much higher catalytic activity for electrooxidation of methanol as a free-standing electrode. Moreover, a small amount of palladium in the nanoporous alloy is found to dramatically improve the electrochemical stability of nanoporous gold.

Mechanoelectricity of a nanoporous monel–electrolyte solution system

The electrification of an electrolyte solution in a nanoporous alloy is investigated through a mechanoelectricity measurement experiment. As the liquid flows across the nanoporous electrode, charge separation occurs over the large nanopore surface, resulting in a significant output voltage, which is in-phase with the actuator motion. This phenomenon is different from the conventional streaming current effect, since the solid phase is conductive and no voltage can be developed along its surface.