Pushing the Bifunctional Activity Limit of Oxygen Electrocatalysis in FeCa–N–C Dual-Atom Catalysts

Rechargeable zinc-air batteries offer high energy density and intrinsic safety but remain fundamentally limited by sluggish oxygen reduction and evolution kinetics, which impose a narrow activity ceiling on bifunctional electrocatalysts. Here, grand-canonical density functional theory integrated with microkinetic modeling establishes a predictive framework that pushes the bifunctional activity limit through coordination-topology engineering of FeCa–N–C dual-atom catalysts. The optimal FeCa–N–C configuration achieves an ORR half-wave potential of 1.06 V and an ultralow OER overpotential of 42 mV at 10 mA cm–2, yielding an exceptionally small bifunctional potential gap of 0.22 V, effectively pushing the bifunctional activity toward its intrinsic limit and setting a new benchmark for nonprecious catalysts. Thermodynamic descriptor analysis reveals that tuning the OH adsorption free energy drives the FeCa–N–C catalysts toward near-ideal intermediate binding and bifunctional oxygen electrocatalytic performance, while spin-polarized electronic-structure investigations reveal that selective metal–adsorbate orbital hybridization stabilizes key intermediates and accounts for near-ideal catalytic performance. Collectively, these results suggest that significant room remains to further narrow the bifunctional potential gap, potentially approaching ∼0.2 V, and position FeCa–N–C as a viable candidate for subsequent experimental verification.