Bimetallic diatomic nanoclusters with longitudinal Fe–O–Fe units and latitudinal Cu–S–Fe–S–Cu units as efficient ORR active sites

Abstract

In this work, Fe–Cu diatomic nanoclusters (Fe–Cu DA-NCs) with sizes of 0.5–2.5 nm loaded in porous carbons (denoted as Fe–Cu DA-NC/C) were successfully prepared by virtue of the strong chelation interaction between tannic acid (TA) and metal ions (Cu²⁺ and Fe³⁺) as well as the doping interaction between metal ions and imino groups from polyaniline (PANI) chains. A detailed analysis revealed that Fe–Cu DA-NCs are composed of longitudinal N₂–Fe–O–Fe–N₂ units and latitudinal N₃–Cu–S–Fe–S–Cu–N₃ units, and are proposed as a new type of active site for the oxygen reduction reaction (ORR) for the first time, to the best of our knowledge. Thanks to the appropriate cluster sizes of 0.5–2.5 nm and the bimetallic active sites, the as-prepared Fe–Cu DA-NC/C catalysts have a favourable interface micro-environment for the adsorption and desorption of intermediates, thus leading to an enhanced electrocatalytic performance. Accordingly, the as-prepared Fe–Cu DA-NC/C catalysts exhibited a higher half-wave potential (E_1/2 = 0.951 V), a larger kinetic-limiting current density (38.5 mA cm⁻² at 0.9 V) and better long-term stability in alkaline media, compared with commercial Pt/C catalysts (E_1/2 = 0.89 V). Moreover, the fabricated Zn–air batteries also exhibited a remarkable performance and exceptionally high stability.