Bicontinuous Nanoporous Metals with Self-Organized Functionalities

Abstract

The functional applications of bicontinuous nanoporous metals have been rapidly growing along with the fabrication methods of the materials. Besides the most common routes of electrochemical dealloying, liquid-metal dealloying, vapor-phase dealloying, and reduction-induced decomposition, all via similar mechanisms of interface-controlled selforganization have created a broad range of nanoporous structures made of noble metals (e.g., Au and Pt), refractory metals (e.g., Ti and Ta), and reactive metals (e.g., Al and Zn). They in turn enable new applications in catalysis, sensing, actuation, and electrochemical energy storage. Underlying the burgeoning development is the close connection between the functionalities and the structural evolution mechanism. In this perspective, I will dissect the structural complexity of bicontinuous nanoporous metal into three key features: the bicontinuity, the small length scale, and the compositional heterogeneity. I will discuss their roots in the self-organization process and their ties to properties such as mechanical strength, conductivity, and catalytic activity. The analysis will be centered around two aspects of the dealloying theory, namely, percolation and surface diffusion, showing how they can be applied to quantitatively understand the self-organized functionalities. In the end, I will also highlight emerging opportunities for structural designs to further advance the functional applications of the materials.

Homogenizing Zn Deposition in Hierarchical Nanoporous Cu for a High‐Current, High Areal‐Capacity Zn Flow Battery

“…The dealloying process creates a large population of surface defects and organizes the remaining surface Cu atoms into a bi‐continuous network, frozen typically in a few to a few hundred nanometers controlled by the kinetics of surface diffusion. [ 52 ] The SEM reveals that the dark red, dealloyed foam (inset of Figure 1C) indeed has a nanoporous surface morphology (Figure 1C; Figure S3B, Supporting Information), distinct from the smooth surface of pristine Cu foam (Figure S3A, Supporting Information). The mean ligament diameter is ≈180 nm (Figure S3C, Supporting Information) and the mean pore size is ≈175 nm (Figure S3D, Supporting Information), estimated using the open‐source code AQUAMI.…”

“…The ligament width (≈100 nm) is too large to induce any measurable Gibbs–Thomson effect given typical values of γ (on the order of 1 J m −2 ) and V m (9.16 cm 3 mol −1 for Zn), but finer pits as small as 2 nm are revealed on the ligament surface by scanning transmission electron microscopy (STEM) ( Figure B,C). We speculate that these fine pits, which are absent in other nanoporous metals of similar length scales, [ 52 ] evolve from the unique dealloying process; Cu might be spontaneously oxidized with Zn in NaOH in the first step to form an oxide, which was then removed in H 2 SO 4 in the second step to create the pits. Their existence helps explain the high deposition potential.…”

Nanoporous Dealloyed Metal Materials Processing and Applications─A Review

“…The definition of “noble metal” often used within dealloying-related publications may therefore appear to be controversial since, as in the case of Au/Pt or Au/Pd bulk alloys, both metals are de facto considered “noble”. The target metal to compose the porous matrix, as opposed to the sacrificial metal to be removed, may be referred to in the literature as being noble respectively, regardless of its true electrochemical nature . For the sake of clarity and precision, in the following discussion, the sacrificial metal will correspond to the main metal removed during the process, while the metal of interest, which may be referred to as the noble metal, is the one remaining and forming the core of the porous metal matrix.…”

Host‐Guest Chemistry of Chiral MOFs for Multicolor Circularly Polarized Luminescence Including Room Temperature Phosphorescence

“…To date, tremendous efforts have been made to obtain CPL‐active materials. Generally, the strategies are devoted widely to the design and synthesis of chiral metal complexes, [ 6 ] chiral organic small molecules [ 7 ], and chiral supramolecular systems. [ 8 ] Among these methods, the construction of multi‐component supramolecular systems, specifically, the host‐guest hierarchical systems, associating the incorporation of the guest luminophores into chiral host, has become a popular pathway to achieve the generation, delivery, amplification, and reversion of chirality, including CPL activity from chiral hosts to achiral guests.…”