Space‐Confined Yolk‐Shell Construction of Fe3O4 Nanoparticles Inside N‐Doped Hollow Mesoporous Carbon Spheres as Bifunctional Electrocatalysts for Long‐Term Rechargeable Zinc–Air Batteries

Abstract Development of efficient, durable and inexpensive oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts with accelerated kinetics and high‐performance remain a grand challenge in the context of reversible metal–air batteries. Herein, the Fe 3 O 4 nanoparticles inside N‐doped hollow mesoporous carbon spheres (N/HCSs) yolk‐shell structure (Fe x @N/HCSs) is constructed as an excellent bifunctional electrocatalyst for ORR and OER via an innovative approach. The N/HCSs effectively control and confine in situ growth of Fe 3 O 4 nanoparticles using the melting‐diffusion strategy via capillary force and significantly improve the conductivity and structural stability of the hybrid material. The constructed yolk‐shell structured Fe 20 @N/HCSs ecosystem with Fe–N x active sites exhibits excellent ORR and OER activity and stability, which even surpass commercial grade Pt/C, RuO 2 , IrO 2 and many reported catalysts. Moreover, the zinc–air battery assembled with Fe 20 @N/HCSs as a cathode achieves high open circuit voltage (1.57 V), large power density (140.8 mW cm −2 ), and excellent long‐term cycling performance (over 300 h), revealing superior performance compared to commercial Pt/C + RuO 2 . This work provides a new avenue for the design and optimization of other high‐performance yolk‐shell materials with nanoscale confinement structures.