The chemical state of iron species influence on the performance of Fe-N-C bifunctional electrocatalyst for Zn-air batteries.

Fe-N-C materials have emerged as promising alternatives to precious metals foroxygen reduction reaction/oxygen evolution reaction (ORR/OER). In this study, astrategy is presented to investigate the influence of different chemical states of ironspecies in Fe-N-C materials on their electrocatalytic performance. Three Fe-N-Ccatalysts, containing either zero-valent Fe or Fe3O4 nanoparticles, aresynthesized using
acid pickling, high-speed centrifugation and ultrasound-assisted hydrothermal methods,
respectively. The findings manifest that the chemical state of iron significantly affects
the electrocatalytic activity of Fe-NX active sites, namely zero-valent Fe enhancing Fe-
NXactivity while Fe3O4weakening its activity. Notably, the Fe@FeNC catalyst
containing only zero-valent iron, demonstrates the only 0.621 V potential difference
between the ORR half-wave potential and the OER potential at 10 mA cm-2.
Furthermore, the rechargeable Zn-air battery assembled with Fe@FeNC as the air
cathode exhibits a remarkable peak power density of 179.0 mW cm-2, excellent cycling
stability over 210 h (with a cycle frequency of one every 10 minutes), and the minimal
voltage gap of 0.710 V. These results reveal the significance of different chemical statesof metal-based nanoparticles in Fe-NX activity of Fe-N-C catalysts and offer insights&#xD.