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Dual single-atom sites coupled with graphene-encapsulated core–shell Fe–Cu nanoalloy for boosting the oxygen reduction reaction

Katam Srinivas,Zhuo Chen,Anran Chen,He Huang,Chengtao Yang,Fei Wang,Ming-qiang Zhu,Yuanfu Chen

Replacing platinum-based electrocatalysts with iron single-atom catalysts (Fe–N4–C) for the oxygen reduction reaction (ORR) remains challenging due to the symmetric electronic structure of atomically dispersed Fe–N4 sites and sluggish kinetics. To address this issue, we introduce Cu–Nx sites and graphene-encapsulated core–shell Fe–Cu nanoalloy (FeCu@G) particles into the Fe–Nx site surroundings through the self-assembly and pyrolysis of a metal–organic framework (MOF). This strategy leverages synergistic interactions with the associated species to modify the uniform electronic structure of Fe single-atom sites, thereby enhancing oxygen-adsorption/desorption kinetics. Density functional theory (DFT) calculations reveal that the incorporation of Cu–Nx sites and FeCu@G nanoalloy particles significantly alters the electronic structure of Fe–Nx sites, leading to improved ORR activity. Consequently, the optimized FeCu-DSAs@CNT, comprising dual single-atom sites (DSAs: Fe–Nx and Cu–Nx) and FeCu@G nanoalloy within MOF-derived nitrogen-doped carbon nanotubes (CNTs), exhibits a significantly improved half-wave potential (E1/2 = 0.91 V) and feasible ORR kinetics (Tafel slope = 48.15 mV dec−1), surpassing the Pt/C benchmark (E1/2 = 0.847 V and Tafel slope = 56.76 mV dec−1). Notably, FeCu-DSAs@CNT shows a 58 mV more positive E1/2 compared to monometallic Fe–SAs@CNT, attributed to synergistic interactions with Cu species. Moreover, it demonstrates excellent power density, specific capacity, and cycling stability in a lab-made zinc–air battery, outpacing the Pt/C-battery. This study addresses gaps in understanding Fe–Nx site interactions with associated species, providing valuable insights for the advancement of Fe–Nx–C electrocatalysts.