Overcoming the *H‐NO _x Coupling Bottleneck via Palladium‐Enabled Relay Catalysis on CuCo ₂ O

ABSTRACT

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.