A yolk–shell structured metal–organic framework with encapsulated iron-porphyrin and its derived bimetallic nitrogen-doped porous carbon for an efficient oxygen reduction reaction

Abstract

A yolk–shell structured metal–organic framework (MOF) with encapsulated 5,10,15,20-tetraphenylporphyrinatoiron (FeTPP) in a zeolitic imidazolate framework (ZIF)-L-ZIF-8 is reported. ZIF-L with leaf-like morphology is used as a core, and FeTPP molecules will induce the partial decomposition of ZIF-L. The ZIF-8 shell is formed and encapsulates FeTPP in the yolk–shell structure by adding Zn ions and 2-methylimidazole (Hmim). After pyrolysis, FeCo bimetallic nitrogen doped porous carbon (FeCo–C/N) exhibits ORR performance comparable to commercial Pt/C (20 wt%), with a significant decrease in cost. Density functional theory (DFT) calculations demonstrate that the Fe site in FeCo–C/N contributes to the improved ORR performance by reducing the formation energy of *OOH formation. Thus, a Zn–air battery with FeCo–C/N as an electrocatalyst exhibits significantly improved performance (a high peak power density of 397.25 mW cm⁻², and good rechargeable stability). The synthesis strategy presented in this work provides new opportunities for designing yolk–shell structured 2D MOFs for applications in energy conversion and storage.