Precise engineering of bimetallic sites via molecular coordination strategy for enhanced bifunctional oxygen electrocatalysis.

Dual-atom catalysts show great promise for catalyzing both the oxygen reduction and evolution reactions (ORR and OER). However, the controllable synthesis and precise engineering of their atomic configurations remain challenging. Here, we develop Ni-Fe bimetallic sites with tunable local atomic structure, ranging from isolated FeN4/NiN4 dual-atom sites, to a Fe4 nanocluster-decorated FeN4/NiN4 heterostructure (FeN4-Fe4-NiN4), and finally to NiFe alloy nanoparticles, via a dicyandiamide-mediated coordination strategy. The coordination behavior between organic molecules and metal precursors precisely modulates the dispersion of iron and nickel species and their local structure on the porous carbon fiber network. The unique FeN4-Fe4-NiN4 catalyst exhibits remarkable ORR and OER performance, significantly surpassing those of FeN4/NiN4, NiFe alloy, and benchmarks Pt/C and RuO2. Spectroscopic characterizations combined with density functional theory calculations suggest that Fe4 nanoclusters modulate the local coordination/electronic environment of neighboring FeN4/NiN4 sites, optimize *O/*OH adsorption at the rate-determining steps, and thereby accelerate both ORR and OER kinetics. Moreover, a zinc-air battery equipped with FeN4-Fe4-NiN4 as the cathode catalyst demonstrates exceptional cycling stability for over 3300 h. This work offers a general molecular coordination strategy for the precise engineering of local atomic structure in multi-metal catalysts.