Oriented Assembly of 2D Metal-Pyridylporphyrinic Framework to Regulate the Redox Kinetics in Li-S Batteries.

Developing the highly efficient catalysts is a great challenge for accelerating the redox reactions in Li-S batteries. Inspired by the single-atom catalysts and metalloproteins, it makes full use of the advantages of metal-organic frameworks (MOFs) as electrocatalysts. Herein, a series of 2D metal-bonded metalloporphyrin MOFs are prepared with 5,10,15,20-tetrakis(4-pyridyl) cobalt porphyrin (CoTPyP) as building blocks and transition metals (M═Mn, Fe, Co, Ni, and Cu) as nodes, respectively. The crystalline structures of the bimetallic 2D MOFs are confirmed by UV-vis spectra and X-ray diffraction analyses. According to DFT calculation, the peripheral metal nodes optimize the electronic state of Co in porphyrin core. Especially, CoTPyP-Mn facilitates the cleavage of S-S bond from both ends and promotes their conversion kinetics through Co-S and Li-N bonds. The Li-S cells with CoTPyP-Mn show the initial specific capacity of 1339 mA h g at 0.2 C. The capacity decay rate is only 0.0442% per cycle after 1000 cycles at 2 C. This work achieves the rational control of the central Co d electron state through the peripheral regulation and enriches the application of MOFs in accelerating the redox kinetics in Li-S batteries.