1. What is a nanoporous metal material?
Nanoporous Metals (NPM) is a class of metal materials with interconnected ligaments (positive curvature) and nanoporous channels (negative curvature), the porosity of which is not less than 50%, and the submicron pores ( Including micropores, mesopores and macropores with diameters of 50-1000 nm) have a significant contribution to the specific surface area of the foam. As shown in Figure 1, the pore size must be nanometer size!
Classification of porous materials of different sizes (from left to right, increasing in size)
Generally speaking, the synthesis of porous nanometals is mainly through top-down free chemical corrosion dealloying and electrochemical dealloying, and can also be prepared by bottom-up synthesis using template method. Here we mainly talk about the preparation method of dealloying to prepare porous metals. For some elements that are commonly used and dealloyed, the two components/multiple components that can be used for dealloying must meet the following points: 1. The equilibrium potential between the components must be quite different; 2. The content ratio of the components There is a threshold; 3. A single solid solution phase can be formed.
IUPAC Periodic Table of Elements, red and blue boxes are commonly used dealloyed metal elements
In addition, the nanopore distribution of nanoporous metals can be uniform or non-uniform, of course, both exist in most cases. Meanwhile, the crystallographic orientation and crystal defects of nanoporous metals depend on the microstructure of alloy precursors and the process of dealloying. Due to the unique microstructure, nanoporous metals can simultaneously exhibit the properties of metals and nanostructured materials, and their structures are closely related to the electrical, magnetic, optical, mechanical, catalytic and electrocatalytic properties.
a). TEM of np-AuAg, b) 3D reconstruction model
2. The microscopic characteristics of nanoporous metals?
In theory, one or more of the following three mechanisms might be at work when a metal dissolves preferentially.
(1) Both metals are ionized, and then the precious metal is redeposited;
(2) Only the base metal is ionized and enters the solution, while the atoms of the noble metal are aggregated by surface diffusion;
(3) Only the base metal ionizes and enters the solution, and the atoms of the two metals move in the solid phase by bulk diffusion.
Post time: Feb-14-2022
