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

Abstract

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.