Bridging crystalline MOFs with atomically dispersed metal–nitrogen–carbon catalysts via structure encoding

Abstract

Metal–organic frameworks (MOFs), and zeolitic imidazolate frameworks (ZIFs) in particular, have emerged as versatile precursors for metal–nitrogen–carbon (M–N–C) catalysts, in which atomically dispersed metal centers are coordinated by nitrogen within a carbon framework. Despite their widespread use, the mechanistic linkage between parent MOF structures and the catalysis-relevant properties of the derived carbons remains insufficiently defined. Here, using Fe–N–C catalysts for the oxygen reduction reaction (ORR) as a model system, we investigate how geometric factors inherent to ZIFs influence micropore formation, Fe–N_x site density, and electrochemical ORR performance. A geometric descriptor representing the linker-to-linker distance at the pore aperture, d_L–L, shows a stronger correlation with micropore volume than conventional pore descriptors such as the largest free sphere diameter (D_f) and largest included sphere diameter (D_i). The resulting micropore volume is further correlated with the density of formed Fe–N_x sites and ORR mass activity. As a practical validation, the Fe–N–C catalyst derived from MAF-6, identified by this descriptor-based selection, outperforms the widely used ZIF-8-derived analogue under polymer electrolyte fuel cell (PEFC) single-cell conditions, with approximately 1.5-fold higher mass activity at 0.8 V_iR-free. These results establish a structure–property–function relationship linking parent MOF structure, micropore evolution, Fe–N_x site formation, and ORR performance, enabling rational, high-throughput precursor selection from MOF databases.