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

Electrochemical nitrate (NO3-) reduction to ammonia (NH3) offers a sustainable approach for NH3 synthesis while concurrently addressing NO3- pollution. However, achieving efficient NO3--to-NH3 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 NH3 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 NO3--to-NH3 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 NO2-. This nanocatalyst is realized via a Kirkendall effect-driven strategy, with its structural features systematically optimized. The resulting catalyst demonstrates outstanding NH3 production performance in a 0.1 M KNO3 + 0.1 M KOH electrolyte, delivering a Faradaic efficiency of 97.4%, a yield of 152.6 mg h-1 mgmetal-1, and an energy efficiency of 40% at a low potential of -0.1 VRHE─positioning it as a top contender among state-of-the-art NO3--to-NH3 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 NO3--to-NH3 electroconversion and broader sustainable catalytic transformations.