High‐Throughput Electron Diffraction Reveals a Hidden Novel Metal–Organic Framework for Electrocatalysis

Meng Ge,Francesco Carraro,Samira Siahrostami,Paolo Falcaro,Christian Doonan,Davide M Proserpio,Haoquan Zheng,Xiaodong Zou,Morteza Roostaeinia,Zhehao Huang,Yanzhi Wang,Weibin Liang

doi:10.1002/ange.202016882

Abstract

AbstractMetal‐organic frameworks (MOFs) are known for their versatile combination of inorganic building units and organic linkers, which offers immense opportunities in a wide range of applications. However, many MOFs are typically synthesized as multiphasic polycrystalline powders, which are challenging for studies by X‐ray diffraction. Therefore, developing new structural characterization techniques is highly desired in order to accelerate discoveries of new materials. Here, we report a high‐throughput approach for structural analysis of MOF nano‐ and sub‐microcrystals by three‐dimensional electron diffraction (3DED). A new zeolitic‐imidazolate framework (ZIF), denoted ZIF‐EC1, was first discovered in a trace amount during the study of a known ZIF‐CO3‐1 material by 3DED. The structures of both ZIFs were solved and refined using 3DED data. ZIF‐EC1 has a dense 3D framework structure, which is built by linking mono‐ and bi‐nuclear Zn clusters and 2‐methylimidazolates (mIm−). With a composition of Zn3(mIm)5(OH), ZIF‐EC1 exhibits high N and Zn densities. We show that the N‐doped carbon material derived from ZIF‐EC1 is a promising electrocatalyst for oxygen reduction reaction (ORR). The discovery of this new MOF and its conversion to an efficient electrocatalyst highlights the power of 3DED in developing new materials and their applications.

Highlights

Structural analysis is done by matching peak positions in the experimental Powder X-ray diffraction (PXRD) pattern with those calculated from possible structures in a crystallographic database, for example, the Cambridge Structure Database, which includes more than one million reported crystal structures.[22]
By applying high throughput structural analysis on single nanocrystals of a phase mixture, we discovered a new Metal-organic frameworks (MOFs), zeolitic-imidazolate framework (ZIF)-EC1
We present a proof-of-concept study that highlights the advantage of the 3DED technique in the development of MOF materials

Summary

Introduction

Metal-organic frameworks (MOFs), or porous coordination polymers (PCPs), are a class of highly crystalline and porous hybrid materials constructed by linking metal clusters (or ions) and organic ligands via coordination bonds.[1,2] In addition, their tunable structure metrics and topologies give rise to versatile properties,[3] and vast opportunities for applications in gas storage,[4,5] separation,[6,7,8,9] catalysis,[10,11,12] energy conversion and storage,[13,14,15,16,17,18,19] and bio-medical science.[20,21] With the access to almost unlimited combinations of inorganic building units and organic linkers, more than 80 000 different MOFs have been reported over the past two decades.[22] Interestingly, through the control of reaction kinetics or thermodynamics, different structures with distinct properties can be obtained even using the same building units.[23,24,25,26] A relevant example is the large sub-class of MOFs termed zeolitic imidazolate frameworks (ZIFs),[27] which are synthesized by connecting tetrahedrally-coordinated metal ions and linkers. Accompanied by the tiny crystal sizes which are inaccessible to single crystal Xray diffraction (SCXRD), structural characterization of these materials poses a major challenge, when in search for new materials

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Conclusion