Cu/Zn ratio-programmed tandem electrocatalysis enables highly selective nitrate-to-ammonia conversion

The electrochemical nitrate reduction reaction (NO 3 RR) represents an attractive and sustainable strategy for simultaneously addressing nitrate contamination and producing value-added ammonia under ambient conditions. Compared with the energy- and carbon-intensive Haber-Bosch process, NO 3 RR offers a decentralized pathway for green ammonia synthesis powered by renewable electricity. However, achieving high ammonia selectivity remains challenging because nitrate-to-ammonia conversion involves a multistep proton-coupled electron transfer cascade, in which the initial two-electron reduction of nitrate to nitrite and the subsequent hydrogenation of nitrite-derived intermediates must proceed in a kinetically coordinated manner. In practice, this cascade is often hindered by reactivity mismatch between the upstream and downstream steps, resulting in nitrite accumulation, incomplete hydrogenation of NO x intermediates, and intensified competition from the hydrogen evolution reaction. Despite the conceptual promise of tandem catalysis, a practical framework for quantifying and optimizing such kinetic matching remains insufficiently developed. Here, we report a layered double hydroxide-derived Cu-Zn dual-site electrocatalyst in which the Cu/Zn ratio is used as a compositional lever to regulate cascade coordination during NO 3 RR in neutral electrolyte. Among the investigated compositions, Cu 1.5 Zn 1.5 Al-R exhibits the optimal balance between nitrate activation and subsequent hydrogenation, delivering a peak Faradaic efficiency of 95% for ammonia at −0.7 V vs. RHE, together with a high ammonia yield of 1526.0 mmol·g −1 ·h −1 . Time-dependent product analysis further shows that this optimal catalyst displays suppressed nitrite accumulation together with rapid ammonia formation, indicating an effective kinetic coupling between the consecutive reduction steps. Mechanistic studies based on online differential electrochemical mass spectrometry and in situ infrared spectroscopy reveal that the reaction mainly proceeds through a *NOH-mediated pathway. The results suggest that Cu-rich motifs are responsible for promoting nitrate adsorption and the initial two-electron reduction step, while Zn-associated motifs regulate the local hydrogenation microenvironment and facilitate the further hydrogenation of nitrite-derived intermediates near adjacent Cu sites. As a result, the Cu/Zn ratio serves as a key compositional parameter to balance the tandem reaction kinetics and improve ammonia selectivity. This work demonstrates that ratio-programmed Cu-Zn tandem catalysis is an effective strategy to enhance nitrate-to-ammonia conversion by kinetically matching the sequential elementary steps. The present study not only provides a viable catalyst design principle for selective NO 3 RR, but also offers useful insight into the regulation of multistep electrocatalytic reactions through compositional engineering.