Dual Sites of Fe─N4/Co─N4 Single Atoms and the Third Site of Pillaring FeCo Nanoparticles Synergistically Enable Exceptionally Bifunctional Activity for Oxygen Electrocatalysis.

Non-precious triple-site (tri-site) electrocatalysts that combine bimetallic single atoms with nanoparticles are promising for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, we presentg a strategy of precisely constructing a tri-site catalyst, FeCoSA/NP@NGA-600, with a low concentration of metal precursors at a relatively low pyrolysis temperature of 600°C. This catalyst comprises a relatively high density of iron single-atom sites (Fe─N4), cobalt single-atom sites (Co─N4), and small-sized iron-cobalt alloy nanoparticles (FeCoNP), achieving efficient synergistic catalysis. This catalyst also forms a biomimetic hierarchical pore architecture, ensuring sufficient site exposure and fast mass transport, demonstrating outstanding catalysis activity: a 0.93 V half-wave potential for ORR, a 1.54 V overpotential for OER, and a 385 h cycle life in a liquid zinc-air battery (LZAB), better than commercial Pt/C and RuO2. With experimentally-guided construction of tri-site models, theoretical calculations reveal that the inherent synergy is associated with electronic modulation, optimized O2 adsorption, and direct O─O bond cleavage (*OOH → *O + *OH) in ORR kinetically, and a low energy barrier in the rate-determining step thermodynamically. This study contributes an effective approach to design and an insightful understanding of multi-site masterful electrocatalysts containing metals with different coordination abilities.