The promotional effect of multiple active sites on Fe-based oxygen reduction electrocatalysts for a zinc–air battery

The in-depth understanding of the functions and interactions of multiple transition metal-based species in non-noble metal electrocatalysts is still obscure and challenges the oxygen reduction reaction (ORR). Herein, we rationally developed a Hm/Cy@C-900 electrocatalyst comprising multiple iron active sites of FeSx and Fe3C clusters and FeNx sites, which was characterized using XRD, S/TEM, and Mössbauer analyses. Hm/Cy@C-900 exhibited a high ORR performance (E1/2 0.845 V vs. RHE) in an O2-saturated KOH electrolyte, which outperformed the Hm/TCA@C-900 counterpart and commercial Pt–C electrocatalysts. Furthermore, the equipped zinc–air battery (ZAB) of Hm/Cy@C-900 could reach a power density of 192 mW cm−2@260.7 mA cm−2, which is much more efficient than that of Hm/TCA@C-900 (131 mW cm−2@201.2 mA cm−2) and a 20 wt% Pt–C catalyst (109 mW cm−2@221.3 mA cm−2). The superior ORR performance of Hm/Cy@C-900 was attributed to the promotional effect of FeSx and Fe3C clusters with FeNx active sites. Our work provides a rational design for and in-depth synthesis of FeNSC electrocatalysts for promoting the ZAB activity.