Unravelling the Role of Fe–Mn Binary Active Sites Electrocatalyst for Efficient Oxygen Reduction Reaction and Rechargeable Zn-Air Batteries

Transition-metal atoms and/or heteroatom-doped carbon nanostructures is a crucial alternative to find a nonprecious metal catalyst for electrocatalytic oxygen reduction reaction (ORR). Herein, for the first time, we demonstrated the formation of binary (Fe–Mn) active sites in hierarchically porous nanostructure composed of Fe, Mn, and N-doped fish gill derived carbon (Fe,Mn,N-FGC). The Fe,Mn,N-FGC catalyst shows remarkable ORR performance with onset potential (Eonset) of 1.03 V and half-wave potential (E1/2) of 0.89 V, slightly better than commercial Pt/C (Eonset = 1.01 V, E1/2 = 0.88 V) in alkaline medium (pH > 13), which is attributed to the synergistic effect of Fe–Mn dual metal center as evidenced from X-ray absorption spectroscopic study. We proposed that the presence of Fe–Mn binary sites is actually beneficial for the O2 binding and boosting the ORR by weakening the O═O bonds. The homemade rechargeable Zn–air battery performance reveals the open-circuit voltage of 1.41 V and a large power density of 220 mW cm–2 at 260 mA cm–2 current density outperforming Pt/C (1.40 V, 158 mW cm–2) with almost stable charge–discharge voltage plateaus at high current density. The present strategy enriches a route to synthesize low-cost bioinspired electrocatalyst that is comparable to/better than any nonprecious-metal catalysts as well as commercial Pt/C.