Thermally Reconstructed Ni–MoS ₂ /Ni ₂ Mo ₆ S ₈ Heterostructures on N-Doped CNT/Graphene for Durable Bifunctional Air Electrodes in Zn–Air Batteries

Developing bifunctional oxygen electrocatalysts that simultaneously provide catalytic activity, electronic transport, and operational durability remains a major challenge in the development of rechargeable zinc–air batteries (RZABs). Here, thermally reconstructed Ni–MoS 2 /Ni 2 Mo 6 S 8 heterostructures supported on N-doped CNT/graphene were investigated to clarify how defect-rich MoS 2 domains, conductive Ni–Mo–S interfacial species, and catalyst–support coupling collectively govern the bifunctional air-electrode behavior. Structural analyses revealed that thermal treatment regulates the balance between accessible defect-rich lamellae and more consolidated heterostructures containing Chevrel-type Ni 2 Mo 6 S 8 domains. Compared to the 900 °C sample (N9N), the 800 °C material (N8N) retained a more open lamellar architecture, a higher surface abundance of Ni–Mo–S species, and more favorable interfacial accessibility. This structural state translates into the best overall bifunctional response within the studied series, with an ORR limiting current density of 5.65 mA cm –2, OER potential of 1.572 V at 10 mA cm –2, and a bifunctional gap of 909 mV. When implemented as the air electrode in RZABs, N8N delivered a maximum power density of 90 mW cm –2 and sustained superior cycling durability relative to Pt/C + IrO 2 /C under repeated charge–discharge operations. The results show that durable RZAB performance is dictated not only by electrochemically active surface area or phase conductivity but also by the cooperative integration of catalytically accessible sulfide domains, conductive interfacial phases, and transport-compatible electrode architecture.