Heterostructure-Promoted Oxygen Electrocatalysis Enables Rechargeable Zinc–Air Battery with Neutral Aqueous Electrolyte

Neutral aqueous zinc-air batteries (ZABs) are an emerging type of energy devices with substantially elongated lifetime and improved recyclability compared to conventional alkaline ZABs. However, their development is impeded by the lack of robust bifunctional catalyst at the air-electrode for the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). Here, we report the controlled synthesis of NiFe₂O₄/FeNi₂S₄ heterostructured nanosheets (HNSs) that are highly efficient in catalyzing OER and ORR, therefore enabling neutral rechargeable ZABs. Associated with the formation of abundant oxide/sulfide interfaces over NiFe₂O₄/FeNi₂S₄ HNSs' surfaces, the catalyst's oxygen binding energy can be effectively tuned to enhance the OER and ORR activities, as revealed by the density functional theory calculations. In 0.2 M phosphate buffer solution, the optimized NiFe₂O₄/FeNi₂S₄ HNSs present an excellent oxygen electrocatalytic activity and stability, with much lower OER and ORR overpotentials than single-component FeNi₂S₄ or NiFe₂O₄ and with negligible performance decay in accelerated durability testing. When used as an air-electrode, the NiFe₂O₄/FeNi₂S₄ HNSs can deliver a power density of 44.4 mW cm^-2 and a superior cycling stability (only 0.6% decay after 900 cycles at 0.5 mA cm^-2), making the resultant ZAB the most efficient and robust one with a neutral aqueous electrolyte reported to date. This work highlights the essential function of the heterostructure interface in oxygen electrocatalysis, opening a new avenue to advanced neutral metal-air batteries.