Langmuir-Hinshelwood pathway enables 1000-h stable nitrate-to-ammonia electroreduction at 1 A cm−2

Achieving stable and selective electrocatalytic nitrate reduction (NO3RR) at high current densities demands a fundamental understanding of the hydrogenation mechanism. We demonstrate that alloying cobalt with ruthenium (RuCo) switches the dominant hydrogenation pathway from the Eley-Rideal (E-R) mechanism, involving solvated protons, to the Langmuir-Hinshelwood (L-H) mechanism, utilizing adsorbed protons. Microkinetic modeling, in situ spectroscopy and density functional theory (DFT) calculations reveal that the competitive E-R pathway on pure Co causes sluggish hydrogenation kinetics and low Faradaic efficiency. In contrast, the L-H pathway on RuCo sustains high hydrogen coverage (θH ≈ 0.45), enabling efficient hydrogen-atom transfer for high-rate and deep hydrogenation. Leveraging this mechanistic insight, we achieve a satisfactory ammonia yield rate of 135.53 ± 1.18 mg h−1 cm−2 with 100% Faradaic efficiency and robust 1000-h stability at 1 A cm⁻². This work provides critical understanding of electrochemical hydrogenation pathways for designing efficient catalysts operating under industrially relevant conditions. Unclear hydrogenation mechanisms in nitrate-to-ammonia electrosynthesis hampers its performance at industrial current densities. Here, the authors report RuCo alloys to steer the reaction along the Langmuir-Hinshelwood pathway, maintaining 1000 h stability at 1 A cm−2 with ~100% Faradaic efficiency.