Macroscopic 3D Nanoporosity Formation by Dry Oxidation of AgAu Alloys

Abstract

3D nanoporous metals made by alloy corrosion have attracted much attention due to various promising applications ranging from catalysis and sensing to energy storage and actuation. In this work we report a new process for the fabrication of 3D open nanoporous metal networks that phenomenologically resembles the nano-Kirkendall hollowing process previously reported for Ag/Au nanowires and nanoparticles, with the difference that the involved length scales are 10–100 times larger. Specifically, we find that dry oxidation of Ag70Au30 bulk alloy samples by ozone exposure at 150 °C stimulates extremely rapid Ag outward diffusion toward the gas/alloy-surface interface, at rates at least 5 orders of magnitude faster than predicted on the basis of reported Ag bulk diffusion values. The micrometer-thick Ag depleted alloy region thus formed transforms into a 3D open nanoporous network morphology upon further exposure to methanol–O2 at 150 °C. These findings have important implications for practical applications of alloys, for example as catalysts, by demonstrating that large-scale compositional and morphological changes can be triggered by surface chemical reactions at low temperatures, and that dilute alloys such as Au97Ag3 are more resilient against such changes.

Three-dimensional bicontinuous nanoporous materials by vapor phase dealloying

“…This is consistent with the facts that VPD takes place in a reduction atmosphere at high temperatures because Zn vapor itself is a strong reducing medium, in addition to the usage of protection gas (pure Ar or Ar + H 2 ). It is worth noting that the VPD process is not caused by any gas–gas or gas–solid chemical reactions even with the presence of a very small amount of hydrogen in the protection flowing gases, which is fundamentally different from the newly developed drying dealloying method, which selectively removes one component from AgAu alloys by utilizing gas oxidation 21 .…”

Atom Probe Tomography for Catalysis Applications: A Review

“…Catalysts in the form of nanoporous bulk materials have recently attracted much attention due to their high surface-to-volume ratio, their mechanical stability, their porosity allowing for mass transport of reactants and products, their absence of support, and most of all, due to their activity towards oxidation reactions [104][105][106][107][167][168][169]. These structures are produced by dealloying methods, i.e., the selective etching of the least noble metals from an initial alloy [170,171], and the chemical nature, concentration and nanoscale spatial distribution of the residual elements greatly influences the dealloying kinetics, the morphology and the catalytic activity; nanoscale characterization is thus required. To investigate such open-cell structures and avoid overlapping ion trajectories and distorted reconstructions, specific sample preparation methods have been developed using electron-beam assisted deposition within the FIB system and using electrodeposition.…”

Dynamic Processes on Gold-Based Catalysts Followed by Environmental Microscopies

“…The conclusions of this work are: (1) an increase in Au content decreases the sticking probability of oxygen, (2) there is no oxygen detected on pure Au at 300 K, and (3) there is a decrease of the heat of adsorption with added gold. It is interesting to note that 40 years after this study, Au-Ag systems are still studied to understand the behaviour of Ag within an Au backbone and its influence on the catalytic behaviour [217,218], and that relatively simple studies by FEM enable the nanoscale effect of Au-Ag alloying on the energies of adsorption to be measured.…”