Direct Visualization of Atomic Structure in Multivariate Metal‐Organic Frameworks (MOFs) for Guiding Electrocatalysts Design

Abstract

The direct utilization of metal-organic frameworks (MOFs) for electrocatalytic oxygen evolution reaction (OER) has attracted increasing interests. Herein, we employ the low-dose integrated differential phase contrast-scanning transmission electron microscopy (iDPC-STEM) technique to visualize the atomic structure of multivariate MOFs (MTV-MOFs) for guiding the structural design of bulk MOFs for efficient OER. The iDPC-STEM images revealed that incorporating Fe 3 + or 2-aminoterephthalate (ATA) into Ni-BDC (BDC: benzenedicarboxylate) can introduce inhomogeneous lattice strain that weaken the coordination bonds, which can be selectively cleaved via a mild heat treatment to simultaneously generate coordinatively unsaturated metal sites, conductive Ni@C and hierarchical porous structure. Thus, excellent OER activity with current densities of 10 and 100 mA cm À 2 are achieved over the defective MOFs at small overpotentials of 286 mV and 365 mV, respectively, which is superior to the commercial RuO 2 catalyst and most of the bulk MOFs.

Interfacial chemistries in metal–organic framework (MOF)/covalent–organic framework (COF) hybrids

“…Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM), which can offer the highest resolution in real-space imaging, are able to directly visualize the local structures at the atomic scale. The development of low-dose high-resolution (HR) TEM/STEM by using the direct-detection electron-counting cameras has enabled the direct visualization of the atomic structure of electron beam sensitive MOFs, [146][147][148][149][150][151][152][153][154] which could be a powerful supplement to the resolution of the interfacial structures of MOF/ COF hybrids.…”

Defect engineering of two-dimensional materials for advanced energy conversion and storage

“…The OER technology is vital to many energy-related fields, e.g., water splitting, metalair batteries, and fuel cells. [267][268][269][270][271] As a complex 4e À transfer process, OER can be operated in either acidic (2H 2 O -O 2 + 4H + + 4e À ) or alkaline (4OH À -O 2 + 2H 2 O + 4e À ) environments, which involves multiple O-containing intermediates (such as OH*, OOH* and O*) during the reaction. Up to now, the OER catalytic ability has been generally believed to be mainly related to intermediate adsorption/desorption and their interactions with catalysts.…”

Applications of Transmission Electron Microscopy in Phase Engineering of Nanomaterials

“…Because the variations in the electron wave phase sensitively reflect the local electrostatic potential of the specimen, “phase contrast” is an ideal contrast mechanism for atomic-resolution imaging. The iDPC-STEM technique has achieved great success in imaging electron-beam-sensitive nanoporous materials, such as zeolites and MOFs. ,− For instance, it successfully identified abundant structural defects and intergrowth of three polymorphs in zeolite EMM-17 …”

“…The field of low-dose TEM has advanced significantly in recent years, owing to the development of highly efficient electron detectors and imaging techniques. As a result, atomic-resolution imaging of a broad array of highly sensitive materials has been accomplished. ,− ,,− …”