Microstructural Engineering of Bimetallic Co/Zn ZIF-Derived Hierarchically Porous Carbon Nanocubes for Advanced Oxygen Reduction Electrocatalysts

Designing the chemical composition and nanostructure of oxygen reduction catalysts is essential for the development of fuel cells and metal–air batteries. Herein, cetyltrimethylammonium bromide (CTAB) was introduced as a structure-directing agent in bimetallic Co/Zn zeolite imidazole frameworks (ZIFs), enabling the controllable construction of small-sized nanocubic carbon. The Kirkendall effect─outward volatilization of Zn and inward formation of Co–Nx active sites─imparts a hierarchical porosity to the bimetallic ZIF-derived catalyst that facilitates the multiscale mass transfer of the oxygen reduction reaction (ORR) and the exposure of efficient Co–Nx active sites. The CTAB-modified ZIF-derived catalyst catalyzed the ORR process through a near-ideal four-electron transfer pathway, achieving high half-wave potentials (E1/2 = 0.88 and 0.77 V in alkaline and acidic electrolytes, respectively). The rational design of the microstructure is an effective strategy for preparing high-performance oxygen reduction catalysts.