Spatially Separated Ag@Cu 3 N Tandem Electrocatalyst with High Nitrate‐to‐Ammonia Selectivity via Decoupled Deoxygenation‐Hydrogenation Pathway

Abstract Electrochemical nitrate reduction reaction (NO 3 RR) offers a promising approach for sustainable ammonia synthesis and environmental remediation, yet simultaneously achieving high activity and selectivity remains challenging due to complex multi‐electron transfer processes and competing reaction pathways. Herein, a rationally designed tandem electrocatalyst comprising Ag nanoparticles anchored on nitrogen vacancies‐rich Cu 3 N nanowires (Ag@Cu 3 N/CF) for highly efficient NO 3 RR is presented. By the synergetic effect between heterostructures, Ag@Cu 3 N/CF demonstrates an exceptional ammonia yield of 1.91 mmol h −1 cm −2 and remarkable Faradaic efficiency of 95.9% at −0.3 V versus RHE, significantly outperforming individual components and recently reported high‐end electrocatalysts. Comprehensive mechanistic investigations reveal a spatially separated tandem catalytic pathway, where Ag sites facilitate the initial deoxygenation process (NO 3 − →NO 2 − ) while vacancies‐rich Cu 3 N sites promote subsequent hydrogenation reaction (NO 2 − →NH 3 ). This hierarchical and closely integrated dual‐functional electrocatalyst design effectively decouples the conflicting requirements of multi‐step nitrate reduction to ammonia, thus enabling efficient interfacial intermediate adsorption/transfer and minimizing side reactions. Furthermore, an aqueous Zn‐nitrate battery constructed with this catalyst achieves an open circuit voltage of 1.081 V, maximum power density of 12.08 mW cm −2 , and exceptional cycling stability over 30 h. This work provides fundamental insights into tandem electrocatalyst design and establishes new strategies for sustainable ammonia production and environmental applications.