Prussian Blue Analogue-Derived Bimetallic CoFe@NC as Effective and Extremely Stable Oxygen Reduction Electrocatalysts for Mg-Air Battery

The magnesium (Mg)-air battery is considered to be the most prospective electrochemical energy conversion and storage system because of its advantages of outstanding energy density, cost-effectiveness, remarkable safety, and environmental friendliness. Nevertheless, in the air cathode of the Mg-air battery, the slow dynamics of the oxygen reduction reaction (ORR) seriously hinders its development and application. Herein, the Prussian blue analogues (PBAs) with tunable chemical compositions and controllable morphology were used as precursors to prepare effective and stable ORR electrocatalysts for Mg-air batteries. The Fe@NC and bimetallic CoFe@NC electrocatalysts were derived from calcining FeFe-PBA and CoFe-PBA precursors at various temperatures under an argon atmosphere. Compared with an Fe@NC electrocatalyst, the bimetallic CoFe@NC electrocatalysts possess better ORR activities and stability under alkaline and neutral conditions. When the pyrolysis temperature was 600 °C, the CoFe@NC-600 displayed the best ORR activities. Meanwhile, the CoFe@NC-600 electrocatalyst exhibits the similar ORR reaction mechanism and activity compared to the Pt/C catalyst. After 5000 CV cycles in alkaline (0.1 M KOH) and neutral (3.5 wt % NaCl) electrolytes, the half-wave potentials of CoFe@NC-600 electrocatalyst merely appear at 2 and 5 mV negative deviations, respectively. Furthermore, the homemade Mg-air battery composed with CoFe@NC-600 exhibits superior discharge behaviors compared to that of the Mg-air battery assembled with Fe@NC. This research offers the groundwork for future research into the progress of nonprecious bimetallic ORR electrocatalysts for Mg-air battery.