Rapid Synthesis and Microenvironment Optimization of Hierarchical Porous Fe─N─C Catalysts for Enhanced ORR in Microbial Fuel Cells.

Abstract

Here, an approach to produce a hierarchical porous Fe-N-C@TABOH catalyst with densely accessible high intrinsic active FeNx sites is proposed. The method involves a single-step pyrolysis of Zn/Fe-zeolitic imidazolate framework (Zn/Fe-ZIF-H) with tetrabutylammonium hydroxide (TABOH) micelles, which is obtained by utilizing TABOH as a structural template and electronic mediator at room temperature for a brief duration of 16min. Notably, the yield of Zn/Fe-ZIF-H is 3.5 times that of Zn/Fe-ZIF-N prepared by conventional method. Results indicate that in addition to expediting synthesis and increasing yield of the Zn/Fe-ZIF-H, the TABOH induces a hierarchical porous structure and fosters the formation of more and higher intrinsic active FeNx moieties in Fex-N-C@TABOH, showing that TABOH is a multifunctional template. Crucially, the increased mesoporosity/external surface area and optimized microenvironment of Fe-N-C@TABOH significantly enhance ORR activity by facilitating the formation of high intrinsic active FeNx sites, increasing accessible FeNx sites, and reducing mass transfer resistance. Through structure tailoring and microenvironment optimization, the resulting Fe-N-C@TABOH exhibits superior ORR performance. DFT calculation further validates that the synergistic effect of these two factors leads to low ORR barrier and optimized *OH adsorption energy. This study underscores the importance of structure and electronic engineering in the development of highly active ORR catalysts.