Supplementary information files for FeNC catalysts decorated with NiFe2O4 to enhance bifunctional activity for Zn–Air batteries

Supplementary files for article FeNC catalysts decorated with NiFe2O4 to enhance bifunctional activity for Zn–Air batteries 

Rechargeable Zn–air battery is a promising next-generation energy storage device attributed to its high energy density, excellent safety, and low cost. However, its commercialization is hampered by sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at air electrodes. Herein, we have designed, fabricated, and demonstrated a highly efficient ORR/OER electrocatalyst, NiFe2O4/FeNC, using low-cost materials via a facile synthesis route. NiFe2O4 is successfully loaded on Fe/N-doped carbon (FeNC) through bonding to Fe3C in FeNC. Due to the existence of high ORR active sites such as FeN4 and Fe and N-doped carbon moieties, the half-wave potential of the ORR reaches a high value of 0.83 V. While benefited from NiFe2O4 with high OER activity and the synergistic effect between NiFe2O4 and FeNC, the overpotential is 310 mV at 10 mA cm–2 in the OER. The voltage difference between charging–discharging operations in the Zn–air battery employing the NiFe2O4/FeNC electrocatalyst only increases by 0.16 V after cycling for 100 h (600 cycles) at 10 mA cm–2, which is much lower than 1.28 V using the best commercial Pt/C and RuO2 catalysts.