Construction of highly active FeN4@Fex(OH)y cluster composite sites for the oxygen reduction reaction and the oxygen evolution reaction

Abstract

Seeking cost-effective and earth-abundant electrocatalysts with excellent activity for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in zinc–air batteries (ZABs) is critically important. In this work, the ORR and OER performance of the Fe_x cluster supported on FeN₄ composite sites (FeN₄@Fe_x) is investigated based on density functional theory. Based on the charge density difference between the Fe_x cluster and the FeN₄ substrate, the conclusion that the decreased charge density of the chemical bond between the metal and the adsorbate can weaken the adsorption of the adsorbate can be drawn. The results of the d-band center also confirm this. Furthermore, the ORR and OER free energy change profiles show that FeN₄@Fe₈ exhibits the best ORR and OER activity. This is because the electronic environment regulated by the Fe_x cluster can improve the adsorption of intermediates, which is conducive to enhancing catalytic activity. Further considering the solution environment, the activity of FeN₄@Fe_x with preadsorbed OH (FeN₄@Fe_x(OH)_y) was studied. It is found that FeN₄@Fe₈(OH)₆ is still the best catalyst. This work introduces new highly active composite sites for catalyzing the ORR in an acid medium.