Hierarchically ordered macro-microporous metal-organic framework derived oxygen reduction electrocatalyst

The electrocatalytic performance of carbon-based materials determined by the active sites' density, accessibility, and utilization rate. In this work, ordered macroporous Fe-containing zeolitic-imidazole frameworks (Fe-ZIF) single-crystalline was carefully synthesized by confined growing Fe-ZIF in the interior space of closely-packed polystyrene sphere template. Then ordered macro-microporous carbon with atomically dispersed Fe-N_x sites (Fe-N_x/HPC) were successfully fabricated by direct carbonizing the ordered macroporous Fe-ZIF. The optimized catalyst Fe-N_x/HPC-1000 shows a high specific surface area of 1293 m²·g⁻¹, a nitrogen and iron doping of 3.4 and 0.12 at.%, respectively. Thanks to the open and hierarchically porous structure, high specific surface area, and rich Fe-N_x moieties, Fe-N_x/HPC-1000 demonstrates outstanding oxygen reduction reaction (ORR) performance with an onset potential of 0.97 V, a half-wave potential of 0.881 V, and excellent durability. Secondary sulfur-doping was carried out to modify the properties of Fe-N_x/HPC-1000, which is favorable for ORR. These findings provide new insight into producing atomically dispersed Fe-N_x- and sulfur-modified MOF-derived ordered macroporous carbon electrocatalyst.