Thermodynamic-Driven Reconstruction of a Block Mof into a Sea Urchin-Like Mof Superstructure and the Derived Co-N-C Nanofiber Catalyst for Orr

Abstract

Fabricating metal-organic frameworks (MOFs) or carbon-based materials with unique morphologies, such as one-dimensional nanofibers, is critical for energy storage and conversion applications due to their high surface area and efficient electron transport. This study presents a thermodynamic driven reconstruction strategy to synthesize sea urchin-like MOF superstructures. Through this method, MOF block crystals undergo a transformation into pure-phase sea-urchin-like superstructure composed of long, ultra-thin and uniform MOF nanorods. This transformation process involves a reorganization of the coordination mode between ligands and metal centers, leading to reconstructions in the crystal structure. Detailed investigation into the evolution process demonstrate that the addition of urea can significantly accelerate the reconstruction process. The free energy difference acts as the driven force of transformation from the initial kinetic intermediate state to the final thermodynamic stable state. Thanks to the special nanofiber morphology, the derived Co-N-co-doped carbon nanofibers (Co-N-CNF) exhibits exceptional advantages in boosting ORR performance, much superior to block-like Co-N-C catalysts in terms of half-wave potential, stability, and durability. The Zn-air battery test validates the outstanding ORR performance in practical applications, demonstrating the potential of this new electrocatalyst for ORR. The proposed MOF reconstruction strategy offers a new pathway for synthesizing functional MOFs or derivatives with one-dimensional or other type morphologies.

Keywords: Metal-organic frameworks, superstructure, structural reconstruction, M-N-C catalysts, oxygen reduction reaction