In-Situ Visualization of Thermal Transformation Pathways in Leaf-Shaped Zeolitic Imidazolate Framework Derived Nanocarbon

Abstract

Metal–organic frameworks (MOFs) are versatile precursors for nanostructured, heteroatom-doped carbons. However, understanding the spatiotemporally resolved mechanisms that govern crystalline-to-amorphous framework collapse, diffusion-mediated reorganization of transient intermediates, and the subsequent formation of graphitic carbon remains challenging. Here, we elucidate the transformation of the 2D leaf-shaped zeolitic imidazolate framework ZIF-L into Zn-dispersed N-doped carbon using a combination of in situ transmission electron microscopy (TEM) and X-ray diffraction (XRD). These measurements directly capture the sequential collapse of the layered MOF framework and the associated morphological evolution under controlled heating, decoupled from beam-induced effects during electron microscopy. Complementary ex-situ pyrolysis (700–1100 °C), together with high-resolution TEM, synchrotron X-ray pair distribution function (X-PDF) analysis, and electron energy-loss spectroscopy (EELS), reveals the diffusion of Zn-containing species, ligand decomposition, and progressive graphitization within the amorphous matrix. We identify temperature-dependent stages involving ligand breakdown, migration of Zn–Nx species, followed by Zn loss, and ultimately forming porous N-doped carbon at 1000 °C that exhibits the strongest electrochemical response within this series. These findings establish temperature-dependent structure–property relationships that enable the thermal engineering of MOF-derived ORR catalysts.