A hierarchical Co3O4/CoS microbox heterostructure as a highly efficient bifunctional electrocatalyst for rechargeable Zn–air batteries.

Herein, we report the synthesis of a strongly coupled Co₃O₄/CoS microbox heterostructure, prepared through an annealing treatment with the subsequent hydrothermal sulfidation of a Co–Co Prussian blue analog (PBA) precursor. The unique 3D hierarchical architecture and potential synergies of Co₃O₄ and CoS provide benefits to the Co₃O₄/CoS heterostructure for both oxygen reduction and evolution reactions (ORR and OER). It displays comparable ORR catalytic activity (half-wave potential of 0.820 V) to state-of-the-art Pt/C but better durability and methanol tolerance. The Co₃O₄/CoS electrocatalyst also shows high OER activity with a relatively low overpotential (349 mV at 10 mA cm⁻²) and small Tafel slope (66.6 mV dec⁻¹), compared to those of commercial RuO₂ (366 mV at 10 mA cm⁻² and 86.3 mV dec⁻¹, respectively), making it a potential bifunctional electrocatalyst for both the ORR and the OER. Moreover, a rechargeable Zn–air battery with a Co₃O₄/CoS cathode shows a higher cell voltage (1.51 V), higher power density (168 mW cm⁻² at 269 mA cm⁻²), and better cycling stability (up to 150 cycles) than the same battery with the state-of-the-art Pt/C + RuO₂ catalyst. This PBA-based material with a strongly coupled interface between Co₃O₄ and CoS offers insights into the development of low-cost and highly efficient electrocatalysts for diverse energy-related applications. [ABSTRACT FROM AUTHOR]