Integrated and Binder-Free Air Cathodes of Co3Fe7 Nanoalloy and Co5.47N Encapsulated in Nitrogen-Doped Carbon Foam with Superior Oxygen Reduction Activity in Flexible Aluminum-Air Batteries

All-solid-sate Al-air batteries with features of high theoretical energy density, low cost, and environmental-friendliness are promising as power sources for next-generation flexible and wearable electronics. However, the sluggish oxygen reduction reaction (ORR) and poor interfacial contact in air cathodes cause unsatisfied performance. Herein, a free-standing Co(3)Fe(7)nanoalloy and Co5.47N encapsulated in 3D nitrogen-doped carbon foam (Co3Fe7@Co5.47N/NCF) is prepared as an additive-free and integrated air cathode for flexible Al-air batteries in both alkaline and neutral electrolytes. The Co3Fe7@Co5.47N/NCF outperforms commercial platinum/carbon (Pt/C) toward ORR with an onset potential of 1.02 V and a positive half-wave potential of 0.92 V in an alkaline electrolyte (0.59 V in sodium chloride solution), which is ascribed to the unique interfacial structure between Co(3)Fe(7)and Co5.47N supported by 3D N-doped carbon foam to facilitate fast electron and mass transfer. The high ORR performance is also supported by in-situ electrochemical Raman spectra and density functional theory calculation. Furthermore, the fabricated Al-air battery displays good flexibility and delivers a power density of 199.6 mW cm(-2), and the binder-free and integrated cathode shows better discharge performance than the traditionally slurry casting cathode. This work demonstrates a facile and efficient approach to develop integrated air cathode for metal-air batteries.