Engineering iron single atomic sites with adjacent ZrO2 nanoclusters via ligand–assisted strategy for effective oxygen reduction reaction and high–performance Zn–air batteries

Abstract

• SA Fe@ZrO 2 /NC is synthesized by ligand–assisted strategy with single Fe atoms and adjacent ZrO 2 . • The SA Fe@ZrO 2 /NC exhibits much better catalytic performance toward ORR. • A Zn-air battery based on SA Fe@ZrO 2 /NC shows excellent performance. • DFT reveals the role of ZrO 2 in modulating electron structure of single Fe atoms and ORR activity. Atomically dispersed iron–nitrogen–carbon (Fe–N–C) catalyst is a promising candidate to replace Pt for oxygen reduction reaction (ORR). To enhance ORR activity of Fe–N–C catalysts, the density and distribution of isolated Fe–N 4 sites should be further optimized. Herein, a ligand–assisted strategy to synthesis of single atomic Fe–N–C derived from Zr–metal–organic frameworks (Zr–MOFs) is proposed. During preparation, –NO 2 (from 2–nitroterephthalic acid ligands) in Zr–MOFs not only acts as the anchoring sites to capture Fe–polydopamine (FePDA) source but also plays a crucial role in modulating the Fe − N 4 configuration. The resulting SA Fe@ZrO 2 /NC catalyst consists of FeN 4 sites with adjacent ZrO 2 in N–doped carbon, in which in–situ introduction of ZrO 2 positively enhance O 2 adsorption ability. Due to the moderate pore structure, atomically dispersed Fe–N 4 active sites, and the strong interface interaction between isolated Fe atoms and ZrO 2 nanocluster, the as–prepared catalyst exhibits comparable ORR activity and outstanding stability in alkaline solution. When assembled in a rechargeable Zn–air battery, the battery with SA Fe@ZrO 2 /NC air electrode delivers a stable open circuit voltage, high–power density (250 mW cm −2 ) and discharge specific capacity (730 mA h g Zn −1 ). It also demonstrates a long cycle life and good rate performance. Density functional theory calculation results reveals that the adjacent ZrO 2 nanocluster modulates the electron structure of Fe atoms in FeN 4 sites with an improved ORR process and activity. This work provides a facile strategy for preparing efficient single atomic Fe–N–C catalyst to drive the oxygen reduction reaction in Zn–air batteries.