Dual-templates-assisted synthesis of hollow nanoreactors with hierarchically porous shell for efficient oxygen reduction reaction

Hollow-structured transition metal nitrogen-carbon (TM-N-C) materials synthesized from metal-organic frameworks (MOFs) have recently emerged as leading candidates in next-generation energy storage systems and conversion technologies. However, the controlled synthesis of hollow nanostructured TM–N–C materials, especially hollow nanoreactors with hierarchically porous shell, is rarely reported. Herein, we introduce a dual-template strategy where ZIF-8 crystals and SiO 2 serve as degradable and rigid templates within ZIF-67-based hybrid particles (ZIF-8@SiO 2 /ZIF-67). Pyrolysis-etching of these hybrid structures leads to the formation of Co/N-doped hollow nanocages with hierarchically porous shells (H-Co/NC-HS). Compared to ZIF-8@ZIF-67-derived samples, the H-Co/NC-HS structure offers a larger external surface area and greater exposure of active sites, which facilitate mass transfer and enhance ORR performance. The optimal H-Co/NC-HS(90) exhibits outstanding electrocatalytic activity, with a half-wave potential ( E 1/2 ) of 0.86 V vs. RHE, comparable to commercial Pt/C (20 wt% Pt). The material also shows excellent robustness, with E 1/2 and limiting current remaining stable after 1000 CV cycles, as well as superior methanol tolerance. This work pioneers a MOF/inorganic hybrid templating approach for hierarchical porous carbons and establishes a versatile platform for functional nanoreactor design.