Engineering Cu/Ru Heterointerface-Shelled Nanocavities by the Kirkendall Effect for Highly Efficient Nitrate Electroreduction to Ammonia

Electrochemical nitrate (NO 3 – ) reduction to ammonia (NH 3 ) offers a sustainable approach for NH 3 synthesis while concurrently addressing NO 3 – pollution. However, achieving efficient NO 3 – -to-NH 3 conversion remains challenging due to sluggish multistep proton-coupled electron transfer processes and poor intermediate converison. Here, we present a nanocatalyst featuring a hollow nanocavity encased within a shell rich in Cu/Ru heterointerfaces, which synergistically leverages both interfacial and structural advantages to effectively lower energy barriers and accelerate intermediate conversion kinetics, thereby enhancing the overall catalytic performance for NH 3 production. Density functional theory (DFT) computations, supported by operando and control experiments, reveal that CuRu heterointerfaces with their optimized electronic structure act as the primary active sites, establishing a favorable NO 3 – -to-NH 3 reaction pathway. Simultaneously, the catalytic synergy between Cu and CuRu sites enables tandem catalysis, which is further amplified by nanocavity-induced spatial confinement of the key intermediate NO 2 – . This nanocatalyst is realized via a Kirkendall effect–driven strategy, with its structural features systematically optimized. The resulting catalyst demonstrates outstanding NH 3 production performance in a 0.1 M KNO 3 + 0.1 M KOH electrolyte, delivering a Faradaic efficiency of 97.4%, a yield of 152.6 mg h –1 mg metal –1, and an energy efficiency of 40% at a low potential of −0.1 V RHE ─positioning it as a top contender among state-of-the-art NO 3 – -to-NH 3 electrocatalysts. By elucidating mechanistic insights into interfacial effects, tandem catalysis, and nanoconfinement, this work highlights the synergistic impact of compositional and structural engineering and offers a generalizable design strategy for advancing NO 3 – -to-NH 3 electroconversion and broader sustainable catalytic transformations.