Harnessing interplay of Fe-Ni atom pairs embedded in nitrogen-doped carbon for bifunctional oxygen electrocatalysis

Abstract Oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) both have sluggish kinetics, which normally requires the use of noble metal-based catalysts (e.g. RuO2, IrOx and Pt). Unfortunately, the high cost of these noble metals has severely restricted their large-scale applications. Herein, we report the fabrication of a cost-effective OER/ORR bifunctional catalyst by embedding atomic Fe-Ni dual metal pairs into nitrogen-doped carbon hollow spheres (Fe-NiNC-50). The resultant catalyst shows exceptional catalytic performance towards both OER and ORR, which is even comparable to the noble metal-based benchmarks. By virtue of its bi-functionality, a rechargeable zinc-air battery is constructed and presents high power density (∼220 mW cm-2), stable discharge voltage and large specific energy density (∼932.66 Wh kgZn-1). Moreover, the rechargeable Zn-air battery exhibits long-term durability in a charge-discharge cycling test (100 h) with negligible performance degradation. The outstanding bifunctional catalytic performance can be ascribed to the formation of Fe-Ni atomic pairs, which imposes mutual effects for tuning electronic structures of both Fe and Ni sites. Experiments and theoretical calculations further unravel that the electronically modified Ni and Fe atoms are the active sites for OER and ORR, respectively, facilitating both OER and ORR by tuning the binding energy of the reaction intermediates.