Site‐Specific Functioning of CuN 3 –PdS 3 Janus Dual‐Atom Sites Enable Near‐Unity Faradaic Efficiency for Nitrate Electroreduction to Ammonia

Electrochemical nitrate reduction reaction (NO 3 RR) using renewable electricity offers a carbon‐free and energy‐saving route to remediating nitrate‐polluted wastewater while producing ammonia (NH 3 ). However, conventional catalysts for NO 3 RR suffer from strong adsorption of NO x intermediates that hinders further hydrogenation, resulting in diminished selectivity and catalyst deactivation. Here we construct a Janus‐type CuN 3 −PdS 3 dual‐atom catalyst featuring N/S dual bridging, namely CuPd‐SNC, to enable decoupled NO x species adsorption and hydrogen supply for hydrogenation on Cu and Pd sites, respectively. Excitingly, CuPd‐SNC delivers a near‐unity Faradaic efficiency of 99.58% for NH 3 synthesis and a production rate of 1.34 mmol h −1 cm −2 . When integrated into a Zn–nitrate battery, CuPd‐SNC achieves a maximum power density of 13.0 mW cm −2 and demonstrates stable operation for >160 h. In situ spectroscopic and theoretical analyses reveal the site‐specific functionalities of the CuN 3 −PdS 3 Janus configuration, wherein Cu sites markedly enhance the adsorption/activation of NO x − intermediates, Pd sites enable continuous proton supply and reduce the energy barriers for multi‐step *NO x hydrogenation, while N/S dual bridges serve as a proton reservoir. These findings highlight the site‐specific but complementary functioning of dual‐atom catalysts in synergistically pushing the limit of conventional electrocatalysts, offering fundamental insights into the rational catalyst design for NH 3 synthesis.