Autogenous Production and Stabilization of Highly Loaded Sub‐Nanometric Particles within Multishell Hollow Metal–Organic Frameworks and Their Utilization for High Performance in Li–O₂ Batteries

Abstract

Despite sub-nanometric particles (SNPs) having unique abilities such as maximized atom-utilization efficiency and governable catalytic selectivity, [1,2] a breakthrough solution that allows not only to originate SNPs and also to preserve single or a few atoms is still required. SNPs are typically stabilized through agglomeration due to their unsaturated surface bonds, [3] even after being synthesized by complex processes, so that the strong interactions with solid supports have been quite successful in stabilizing them. [4][5][6] Meanwhile, this method was possible only at low mass loadings where the collision frequency of SNPs can be inhibited. [7] In another way, the pyroly sis of organometallic compounds induces the formation of heterogeneous SNPs at nonuniform particle sizes. [8] However, as agglomeration is driven by surface energy differences attributed to different particle sizes, [9] these heterogeneous SNPs also grow to become larger particles.We hypothesize that the key requisite to make homogeneous and robust SNPs Sub-nanometric particles (SNPs) of atomic cluster sizes have shown great promise in many fields such as full atom-to-atom utilization, but their precise production and stabilization at high mass loadings remain a great challenge. As a solution to overcome this challenge, a strategy allowing synthesis and preservation of SNPs at high mass loadings within multishell hollow metal-organic frameworks (MOFs) is demonstrated. First, alternating waterdecomposable and water-stable MOFs are stacked in succession to build multilayer MOFs. Next, using controlled hydrogen bonding affinity, isolated water molecules are selectively sieved through the hydrophobic nanocages of water-stable MOFs and transferred one by one to water-decomposable MOFs. The transmission of water molecules via controlled hydrogen bonding affinity through the water-stable MOF layers is a key step to realize SNPs from various types of alternating water-decomposable and water-stable layers. This process transforms multilayer MOFs into SNP-embedded multishell hollow MOFs. Additionally, the multishell stabilizes SNPs by π-backbonding allowing high conductivity to be achieved via the hopping mechanism, and hollow interspaces minimize transport resistance. These features, as demonstrated using SNP-embedded multishell hollow MOFs with up to five shells, lead to high electrochemical performances including high volumetric capacities and low overpotentials in Li-O 2 batteries.

Pristine Hollow Metal–Organic Frameworks: Design, Synthesis and Application

“…Chemie stable ZIF-8 shell and water-unstable ZIF-67 core to prepare the hollow structures. [79] They found that unstable ZIF-67 core could be transformed into sub-nano Co(OH) 2 ,l eaving ac avity and aZ IF-8 shell, when exposed to am inority of water. Even multi-shell hollow MOF could be obtained by selective transformation of the unstable MOF.T his work provides an idea to precisely transform the targeted unstable MOF core phase to get the hollow structure.…”

Rational Design of MOF-Based Materials for Next-Generation Rechargeable Batteries

“…Recently, dinuclear Co(OH) 2 sub-nanometric particles (SNP) within multishell hollow ZIF-8 (H-ZIF-8[nS], where n is the number of shells) were autogenously synthesized by Kang and co-workers (Fig. 3d) [85]. First, the stable MOF (ZIF-8) layers effectively transferred ethylene glycol (EG) isolated water molecules to the decomposable MOF (ZIF-67) layers through hydrophobic micropores.…”

Pristine Hollow Metal–Organic Frameworks: Design, Synthesis and Application

“…stable ZIF-8 shell and water-unstable ZIF-67 core to prepare the hollow structures. [79] They found that unstable ZIF-67 core could be transformed into sub-nano Co(OH) 2 ,l eaving ac avity and aZ IF-8 shell, when exposed to am inority of water. Even multi-shell hollow MOF could be obtained by selective transformation of the unstable MOF.T his work provides an idea to precisely transform the targeted unstable MOF core phase to get the hollow structure.…”