Mechanochemical synthesis of nanostructured metal-loaded graphene oxide for bifunctional electrocatalysis in rechargeable Zn-air batteries

Bifunctional electrocatalysts based on iron phthalocyanine (FePc) and metal hydroxides supported on low oxidised few layer graphene oxide were synthesized through a one-step mechanochemical process, under solvent-free conditions. Electrochemically expanded graphene oxide was directly incorporated into ball milling with metal precursors, yielding well-dispersed hybrid catalysts whose structure and composition confirm the efficiency of this straightforward method. The materials displayed promising activity and stability towards the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), with iron phthalocyanine and nickel hydroxide emerging as the most effective catalyst. Post-reaction analyses showed that OER conditions significantly degraded the FePc, whereas ORR cycling caused minimal structural changes. When applied as cathodes in rechargeable Zn-air batteries, the catalysts demonstrated superior charge-discharge durability compared to Pt/C + RuO 2 . These results highlight ball milling as an effective and environmentally friendly route for the scalable synthesis of high-performance bifunctional electrocatalysts for Zn-air batteries.