Ultrahigh-Loaded Fe Single Atoms and FeC Nanoparticle Catalysts as Air Cathodes for High-Performance Zn-Air Batteries.

Fe-based materials containing Fe-Nx sites have emerged as promising electrocatalysts in the oxygen reduction reaction (ORR), but they still suffer structural instability which may lead to loss of catalytic activity. Herein, a novel electrocatalyst FeC-FeSA@3DCN with the coexistence of FeC nanoparticles and Fe single atoms (FeSA) in a three-dimensional conductive network (3DCN) is prepared via lattice confinement and defect trapping strategies with an Fe atomic loading of as high as 4.36%. In the ORR process, the limiting current density of FeC-FeSA@3DCN reaches 5.72 mA cm, with an onset potential of 0.926 V and a Tafel slope of 66 mV/decade, showing better catalytic activity and stability than Pt/C catalysts. Notably, its assembled aqueous and solid-state Zn-air batteries (ZABs) achieve peak power densities of 166 and 56 mW cm, respectively, with a long service life of up to 200 h at a current density of 5 mA cm. In addition, the assembled ZAB can provide a constant voltage on activated carbon electrodes to perform capacitive deionization to adsorb different ions. The importance of the Fe species active sites generated by FeC and FeSA in the material for ORR activity to boost the electron transfer and mass transfer is demonstrated by a simple selective poisoning experiment.