Core-Shell Polydopamine@Zr-Hemin MOFs Derived Fe-N-Doped Porous Carbon Nanospheres Electrocatalysts for the Oxygen Reduction

Abstract

At present, the M-N-C electrocatalysts for ORR are the most promising candidates to replace precious metal catalysts. However, their performances are still needed to improve. In this study, we attempt to prepare highly effective Fe-N-C catalysts by designing a novel metal organic framework (MOF) based precursor. In detail, the low-cost Zr-hemin MOFs were firstly synthesized by an easy solvothermalmethod with hemin as an organic linker and Zr4+ as a node. Then, the composites of polydopamine sphere and Zr-hemin MOFs with core-shell structure (PDA@Zr-hemin MOFs) were prepared using the same method. In spite of the co-existence of Fe, N and C source for both Zr-hemin MOFs and PDA@Zr-hemin MOFs, the derivates of them by pyrolyzing at high temperature and the following leaching by HF were very different in composition which leaded to different ORR catalytic activity. The result and the corresponding reason have been discussed. Notably, the products derived from core-shell PDA@Zr-hemin MOFs are Fe-N-doped porous carbon nanospheres (FeN-PCS) with large specific surface area. On the optimum condition, the FeN-PCS displayed good ORR catalytic activities, 4e-selectivity, long-term stability and methanol tolerance in alkaline medium, holding great promise in the application of alkaline fuel cells and metal-air batteries.