Enhancing ORR/OER active sites through lattice distortion of Fe-enriched FeNi intermetallic nanoparticles doped N-doped carbon for high-performance rechargeable Zn-air battery.

Low-cost, high-activity, non-precious metal electrocatalysts are needed to enhance the bifunctional oxygen activities of rechargeable Zn-Air batteries. In this study, a Fe-enriched FeNi inter-metallic nanoparticle/nitrogen-doped carbon (Fe-enriched-FeNi/NC) electrocatalyst was designed and prepared using a facile method based on plasma engineering. The excess Fe-ions in the Fe-enriched FeNi nanoparticles led to a high degree of lattice distortion that produced abundant oxygen-active sites. The electrocatalyst exhibited excellent oxygen evolution reaction (OER) activity as well as favorable oxygen reduction reaction (ORR) activity in an alkaline electrolyte. In addition, the electrocatalyst revealed a lower potential difference (ΔE = 0.80 V vs. RHE) in a bifunctional oxygen reaction compared to that of the benchmark 20 wt% Pt/C + Ir/C (ΔE = 0.84 V vs. RHE), and most of the reported FeNi alloy-doped carbon catalysts. Based on DFT calculations, the lattice distortion in Fe-enriched-FeNi/NC promoted a higher density of active electrons around the Fermi level. Owing to its great bifunctional oxygen activities, Fe-enriched FeNi/NC was applied as an ORR/OER catalyst in the air cathode in a homemade zinc-air battery and exhibited an excellent discharge-charge voltage gap (0.89 V), peak power density (89 mW/cm), and high specific capacity of 734 mAh/g at 20 mA/cm, which outperformed the benchmark 20 wt% Pt/C + Ir/C electrocatalyst. In summary, this research provides a novel strategy to enhance the OER/ORR activities of transition metal-based alloys through lattice distortion defects. In addition, it provides a new pathway for achieving noble metal-free air cathode materials for the next generation Zn-air battery.