Zeolitic Imidazolate Framework-Derived Co-Fe@NC for Rechargeable Hybrid Sodium–Air Battery with a Low Voltage Gap and Long Cycle Life

Developing low-cost, efficient electrocatalysts for the air electrode of high-performance rechargeable hybrid sodium–air batteries (HSABs) remains challenging. Herein, efficient bimetallic nanoparticles encapsulated in nitrogen-doped carbon (Co-Fe@NC) were developed for the oxygen reduction and evolution reactions in HSABs. The bimetallic Co-Fe@NC catalyst outperformed its monometallic counterparts in the oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) activity. The assembled HSAB, utilizing the Co-Fe@NC in the air electrode, exhibited a smaller voltage gap of 0.27 V and a higher power density of 5.39 mW/cm2 compared with the air electrode utilizing Pt/C + RuO2 (0.55 V, 4.79 mW/cm2). Furthermore, the round-trip efficiency of the assembled HSAB is up to 75.37% after 700 h of cycling at 0.1 mA/cm2, outperforming the benchmark HSAB with Pt/C + RuO2 (65.76% after 400 h). This work presents a promising strategy to prepare low-cost, efficient electrocatalysts to substitute the precious catalyst Pt/C + RuO2 in HSABs or other metal–air batteries for practical applications.