A single-atom iron catalyst on hierarchical N-doped carbon for highly efficient oxygen reduction in Zn-air batteries

Single-atom iron electrocatalysts have emerged as up-and-coming alternatives to platinum-based catalysts for the oxygen reduction reaction. However, their further development has been impeded by complex fabrication procedures and limitations in long-term stability. This study developed a chemical vapor deposition approach for synthesizing an efficient iron single-atom electrocatalyst denoted as Fe-SA@NC, utilizing vaporized ferrocene to deposit on a hierarchical N-doped carbon derived from ZIF-8. The preparation process maintained the initial pore structure throughout the deposition process by utilizing a two-step pyrolysis, preventing the collapse or deformation of the pore structure and frameworks. The optimized catalyst exhibited an exceptional half-wave potential (0.932 V) and kinetic current density (28.38 mA cm⁻² at 0.9 V vs. RHE), along with high turnover frequency (36.37 s⁻¹) and mass activity (5.68 A mg⁻¹), and remarkable long-term stability in an alkaline electrolyte, exceeding those of commercial Pt/C and most previously reported iron-based electrocatalysts. Moreover, it also demonstrated outstanding practicability in both liquid and solid Zn-air batteries. The formation of well-dispersed Fe-N₄ with strong interaction on hierarchical N-doped carbon was verified in the correlation of the structural activity and the excellent performance of Fe-SA@NC. This work sheds some light on the facile synthesis of single-atom catalysts with effective efficiency and stability.