Ligand-induced hollow MOF-derived carbon nanomaterials with abundant Fe species for efficient oxygen reduction

The rational design and facile fabrication of cost-effective, efficient, and robust non-precious metal-based carbon nanomaterials are of great significance. Herein, under the control of temperature, the single-crystal-to-single-crystal transformation from MOF-5 to ZIF-8 via ligand exchange can be easily achieved with the intermediate and final structures of ZIF-8-M and ZIF-8-F, respectively. After pyrolysis of Fe-doped MOF (metal-organic framework) materials, Fe-ZIF-8-F-900 was obtained and featured large surface area, high degree of graphitization, a large number of carbon nanotubes, and highly active Fe species. All of these characteristics contribute to fast electron transfer and mass transport, resulting in a satisfactory oxygen reduction performance which is comparable to that of Pt/C, such as superior onset potential (0.982 V), limiting diffusion current density (5.41 mA cm−2), small Tafel slope (40.6 mV dec−1), and high current retention of 94.4% after 10 h. Furthermore, the experimental and simulation results both verify that the assembled zinc-air batteries possess excellent properties in practical applications. This study provides a rational design strategy for the development and preparation of high-efficiency and low-cost non-precious metal-based electrocatalysts, which further indicates new directions for energy-related practical applications.