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 (E-onset) of 1.03 V and half-wave potential (E-1/2) of 0.89 V, slightly better than commercial Pt/C (E-onset = 1.01 V, E-1/2 = 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 O-2 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.