Overcoming the *H‐NO x Coupling Bottleneck via Palladium‐Enabled Relay Catalysis on CuCo 2 O 4 Toward Ampere‐Level Nitrate‐to‐Ammonia

Electrocatalytic nitrate reduction reaction (NO 3 RR) represents a sustainable route for both ammonia (NH 3 ) production and nitrate‐contaminated water remediation, yet its practical application is crippled by the kinetically sluggish multi‐electron/proton transfer and insufficient targeted active hydrogen (*H) supply. Herein, a Pd‐doped CuCo 2 O 4 (Pd‐CuCo 2 O 4 ) hollow spiny microsphere catalyst is designed to tackle this challenge via a synergistic relay catalysis mechanism coupled with rapid *H replenishment. Kinetics studies and theoretical calculations collectively demonstrate a clear tandem pathway for NH 3 synthesis: NO 3 − is preferentially reduced to NO 2 − on Cu sites, and then migrates to neighboring Co sites for further conversion to NH 3 . Crucially, the incorporated Pd dopants promote NO 3 − adsorption on Cu sites and *H generation on Co sites precisely. The efficient *H supply and co‐adsorption for intermediates eliminates the intrinsic kinetic bottleneck of poor *H‐NO x coupling, ensuring the tandem catalysis proceeds smoothly without interruption. Benefiting from the *H‐spillover boosted relay mechanism, an ultra‐high current density over −2.0 A cm −2 and a remarkable NH 3 yield rate of 100.43 mg h −1 cm −2 are achieved. This study underscores the synergistic interplay among the three active sites and provides a blueprint for designing high‐rate, practical NO 3 RR electrocatalysts.