Atomic‐Level Hydrogen Pumping Enables Near‐Unity Faradaic Efficiency in Nitrate‐to‐Ammonia Electroreduction

ABSTRACT Electrochemical nitrate reduction (NO 3 RR) offers a sustainable route for ammonia synthesis and wastewater remediation, yet its efficiency is often constrained by the spatial mismatch between hydrogen (H) generation and consumption, leading to H accumulation, parasitic H 2 evolution, and intermediate poisoning. Here we report an atomic‐level hydrogen pump that directionally regulates hydrogen flux across a well‐defined Cu 2 O@Co 3 O 4 core–shell interface. By anchoring Pd single atoms either at the interface (Pd‐in) or on the outer shell (Pd‐out), we demonstrate that only the interfacial configuration enables efficient *H relay from Co 3 O 4 hydrogen‐generation sites to Cu 2 O nitrate‐reduction centers. This design suppresses *NO 2 accumulation and minimizes hydrogen evolution, achieving a near‐unity Faradaic efficiency of 99.9% and an exceptional NH 3 yield of 63.9 mg h −1 mg cat −1 at −0.55 V versus RHE, outperforming most reported systems. Operando spectroscopy, kinetic isotope effects (KIEs), and DFT calculations reveal that interfacial Pd lowers the *H migration barrier from 1.21 to 1.01 eV, thereby kinetically favoring hydrogenation over HER. The generality of this hydrogen‐pump mechanism is further demonstrated in urea synthesis, hydrodehalogenation of 2,4,6‐tribromophenol, and Zn‐NO 3 − battery systems. These findings establish hydrogen flux regulation via single‐atom positioning as a general strategy for optimizing multi‐step electrocatalytic reactions.