Janus-like WC-Co Heterostructures Enable Orbital-Level Modulation for Durable Seawater Zinc-Air Batteries

Seawater-based zinc-air batteries (SWZABs) offer a compelling pathway for energy supply in marine environments due to their high theoretical energy density and abundant electrolyte resources. Their practical deployment, however, is fundamentally limited by chloride-induced corrosion, catalyst poisoning, and sluggish oxygen reduction/evolution reaction (ORR/OER) kinetics at air cathodes. Here, we report a heterostructured catalyst consisting of WC-Co nanoparticles interfaced with atomically dispersed Co sites on N-doped carbon (Co_NP/WC@CoNC), which delivers bifunctional oxygen electrocatalysis under seawater conditions. In situ electrochemical characterization and computational calculations reveal that WC with spatially extended W 5d orbitals acts as an interfacial electronic modulator that downshifts the Co d-band center through W 5d-Co 3d hybridization, accelerating *OH desorption and *OOH conversion steps in ORR and OER, respectively. Simultaneously, this W 5d-Co 3d coupling effect suppresses chloride-triggered corrosion and thus ensures robust stability. Accordingly, Co_NP/WC@CoNC exhibits a small ORR/OER potential gap of 0.68 V, and the derived SWZAB achieves a high peak power density (233.4 mW cm^-2) and superior lifespan (>2500 h). This work provides insights into using 5d transition-metal carbides as an interfacial electronic modulator for designing durable and highly active bifunctional catalysts for seawater-compatible energy devices.