Solvent-assisted structural phase transition of Zn-MOF from 2D to 3D and its microflower-structured carbon for supercapacitors

Abstract

Green synthesis of two-dimensional metal–organic frameworks (2D MOFs) and their further modifications to hierarchical structures are of great interest in achieving sustainable and high-performing energy storage materials. However, the synthesis of 2D MOFs often involves complicated synthetic methods requiring modulators (e.g., templates and surfactants) or the interfacial growth strategy for anisotropic MOF growth. Moreover, 2D MOFs are prone to aggregation and restacking, thus losing accessible surface area and achieving only a limited performance for target applications. To address such challenges, this study demonstrates a recrystallization-guided structural phase transition of 2D MOF nanosheets to a superstructural three-dimensional (3D) MOF exhibiting a flower-like morphology. This synthesis strategy is highly sustainable as it effectively omits the use of harmful modulators, allowing significantly reduced contamination with simpler separation processes. Besides, it also adds the versatility of MOFs in achieving various morphologies which is a critical aspect of control in obtaining greater capacity and durability for electrochemical applications. After carbonization, the microflower superstructural morphology of the 3D MOF is well retained with abundant active sites and hierarchical distribution of nanopores, enhancing electrolyte ion transport to achieve excellent performance as electrode materials for supercapacitors.