Cross-scale consolidation of cobalt single atoms toward enhanced oxygen reduction reaction in zinc-air batteries

Abstract

Simultaneously enhancing intrinsic catalytic activity and oxygen diffusion is essential for developing high-performance oxygen reduction reaction electrocatalysts, yet achieving both remains challenging. Herein, a cross-scale consolidation strategy is developed to integrate atomically dispersed Co−N₄ sites and metallic atomic clusters (Co ACs) within a hollow carbon nanoflower framework (Co-SAAC@HCMF). The Co−N₄/Co AC microregions boost intrinsic activity through atomic-scale electronic modulation, while the hollow nanoflower architecture ameliorates oxygen diffusion at the architectural scale. As a result, the optimized Co-SAAC@HCMF catalyst delivers a high half-wave potential of 0.887 V vs. RHE and excellent durability with 97.4% current retention after 50 000 s. When applied in zinc-air batteries, Co-SAAC@HCMF exhibits a high peak power density of 241 mW cm⁻² and a specific capacity of 813 mAh g_Zn⁻¹. Moreover, the Co-SAAC@HCMF + RuO₂ air cathode enables stable charge-discharge cycling for over 1000 h. Theoretical calculations and in situ infrared spectroscopy reveal that neighboring Co ACs upshift the Co D-band center of adjacent Co−N₄ sites and lower the free-energy barrier for *OOH formation, thereby accelerating ORR kinetics. Complementary transport analyses and finite-element simulations further demonstrate that the hollow nanoflower framework facilitates O₂ diffusion and alleviates mass-transfer limitations. This work establishes a cross-scale design principle that integrates single-atom/atomic-cluster electronic interactions with oxygen diffusion-oriented nanostructure engineering for efficient energy-relative electrocatalysis.