Physical upcycling of spent artificial diamond accelerant into bifunctional oxygen electrocatalyst with dual-metal active sites for durable rechargeable Zn–air batteries

The low-cost and efficient bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is critical for advanced rechargeable Zn–air batteries (ZABs). Herein, we designed and fabricated a bifunctional m-Fe2.04Ni0.66 @GCFs catalyst using a sustainable physical upcycling strategy involving spent artificial diamond accelerants. Experiments and theoretical calculations verified that dual-metal active-site synergy between *Fe2.04Ni0.66 @GC and Fe2.04 *Ni0.66 @GC enhances the rapid adsorption/desorption of *OOH/*OH species, thereby improving ORR/OER performance. In situ Raman technique confirmed that ORR/OER activities are dependent on the FeOOH, Fe(OH)2, and β-NiOOH intermediates formed during the reaction. Impressively, the m-Fe2.04Ni0.66 @GCFs catalyst exhibited outstanding ORR/OER activities with a small potential difference of only 0.73 V in alkaline media. The assembled rechargeable ZAB exhibited high peak power density (115.2 mW cm−2), large specific capacity (786.9 mA h g−1), and long-term charge-discharge cycling stability of more than 1200 cycles. These results not only contribute to the design of efficient bifunctional catalysts, but also provide a new approach to the high-value utilisation of waste catalyst resources.