Electronic Modulation of Cu Sites via Iron Incorporation in Cu₅FeS₄ Bimetallic Sulfide for High-Efficiency Oxygen Reduction Reaction

The sluggish kinetics of the oxygen reduction reaction (ORR) necessitate developing oxygen electrodes with enhanced electrocatalytic activity for practical zinc–air battery applications. In this study, an iron-doped copper sulfide electrocatalyst (CuFeNS-PNC) anchored on metal–organic framework-derived carbon substrates was designed, featuring a bimetallic Cu₅FeS₄ architecture where iron electronically modulates copper sites. The performance enhancement of this copper–iron sulfide bimetallic system relative to a monometallic copper sulfide arises from synergistic Fe-Cu interactions, as confirmed by X-ray photoelectron spectroscopy (XPS), revealing electron transfer from iron to copper. Density functional theory (DFT) calculations demonstrate that iron incorporation downshifts the copper d-band center, weakening OH* adsorption energy to a more optimal level, thereby boosting ORR kinetics. Consequently, the CuFeNS-PNC catalyst achieves superior electrocatalytic performance with an ORR onset potential (E_onset) of 0.988 V and a half-wave potential (E_1/2) of 0.874 V, significantly surpassing commercial Pt/C and conventional metallic sulfide catalysts. When integrated into a zinc–air battery, it delivers a high open-circuit voltage (1.450 V), specific capacity (789 mAh g⁻¹), and peak power density (117.9 mW cm⁻²). This work provides valuable guidelines for the rational design and synthesis of electronically modulated metallic sulfides to enhance ORR activity for energy storage and conversion applications.