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 Mossbauer 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. The Hm/Cy@C-900 catalyst exhibits a ORR performance (E1/2 0.845 V vs. RHE), and its equipped zinc-air battery reaches a power density of 192 mW cm-2@260.7 mA cm-2, which is attributed to the promotional effect of FeSx and Fe3C clusters with FeNx sites.