Aqueous Synthesis of Zn/Co-BMZIF-Derived Carbon Electrocatalysts for Oxygen Re-duction and Rechargeable Zinc–Air Batteries

Solvent-benign synthesis of MOF-derived carbon electrocatalysts with controlled graphitiza-tion and hierarchical porosity is essential for improving oxygen reduction reaction (ORR) performance in alkaline media, but remains challenging. Herein, bimetallic zeolitic imid-azolate framework precursors (BMZIFs) were synthesized in water and converted into N-doped porous carbon electrocatalysts by pyrolysis. The Zn/Co molar ratio was systemati-cally tuned at 3:1, 1:1, and 1:3 to regulate phase evolution, carbon ordering, and pore-structure development. XRD results revealed the formation of metallic Co nanoparti-cles in Co-containing derivatives, as evidenced by characteristic reflections at approximately 44o, 51 o, and 76 o, which are associated with Co-catalyzed graphitization and carbon nano-tube growth. Among the prepared samples, CBMZIF13 with a Zn/Co molar ratio of 1:3 ex-hibited the lowest Raman I_D/I_G ratio of 0.96, indicating the highest degree of graphitiza-tion. This sample also showed a CNT-rich morphology and a hierarchical micro–meso–macroporous texture, with a BET surface area of 270 m2 g-1 and an average pore diameter of approximately 7.7 nm, providing improved electronic and ionic transport pathways. In O₂-saturated 0.1 M KOH electrolyte, CBMZIF13 delivered a half-wave potential of 0.80 V, slightly higher than that of commercial 20 wt% Pt/C (0.79 V) under identical testing condi-tions. When used as an air cathode in rechargeable zinc–air batteries, CBMZIF13 maintained stable charge–discharge cycling for 1000 cycles at 10 mA cm-2. These results demonstrate that the synergistic effect of Zn-enabled pore formation and Co-catalyzed graphitization is an effective strategy for constructing highly graphitized, hierarchically porous, and CNT-containing carbon electrocatalysts for rechargeable zinc–air battery applications.