1e:T40e,Unveiling the active phase of catalytic materials under reaction conditions is important for the construction of efficient electrocatalysts for selective nitrate reduction to ammonia. The origin of the prominent activity enhancement for CuO (Faradaic efficiency: 95.8 %, Selectivity: 81.2 %) toward selective nitrate electroreduction to ammonia was probed. ¹⁵ N isotope labeling experiments showed that ammonia originated from nitrate reduction. ¹ H NMR spectroscopy and colorimetric methods were performed to quantify ammonia. In situ Raman and ex situ experiments revealed that CuO was electrochemically converted into Cu/Cu₂ O, which serves as an active phase. The combined results of online differential electrochemical mass spectrometry (DEMS) and DFT calculations demonstrated that the electron transfer from Cu₂ O to Cu at the interface could facilitate the formation of *NOH intermediate and suppress the hydrogen evolution reaction, leading to high selectivity and Faradaic efficiency.1f:T532,Electrochemical conversion of nitrate (NO₃^-) into ammonia (NH₃) recycles nitrogen and offers a route to the production of NH₃, which is more valuable than dinitrogen gas. However, today's development of NO₃^- electroreduction remains hindered by the lack of a mechanistic picture of how catalyst structure may be tuned to enhance catalytic activity. Here we demonstrate enhanced NO₃^- reduction reaction (NO₃^-RR) performance on Cu₅₀Ni₅₀ alloy catalysts, including a 0.12 V upshift in the half-wave potential and a 6-fold increase in activity compared to those obtained with pure Cu at 0 V vs reversible hydrogen electrode (RHE). Ni alloying enables tuning of the Cu d-band center and modulates the adsorption energies of intermediates such as *NO₃^-, *NO₂, and *NH₂. Using density functional theory calculations, we identify a NO₃^-RR-to-NH₃ pathway and offer an adsorption energy-activity relationship for the CuNi alloy system. This correlation between catalyst electronic structure and NO₃^-RR activity offers a design platform for further development of NO₃^-RR catalysts.20:T523,The limitations of the Haber-Bosch reaction, particularly high-temperature operation, have ignited new interests in low-temperature ammonia-synthesis scenarios. Ambient N₂ electroreduction is a compelling alternative but is impeded by a low ammonia production rate (mostly <10 mmol g_cat^-1 h^-1), a small partial current density (<1 mA cm^-2), and a high-selectivity hydrogen-evolving side reaction. Herein, we report that room-temperature nitrate electroreduction catalyzed by strained ruthenium nanoclusters generates ammonia at a higher rate (5.56 mol g_cat^-1 h^-1) than the Haber-Bosch process. The primary contributor to such performance is hydrogen radicals, which are generated by suppressing hydrogen-hydrogen dimerization during water splitting enabled by the tensile lattice strains. The radicals expedite nitrate-to-ammonia conversion by hydrogenating intermediates of the rate-limiting steps at lower kinetic barriers. The strained nanostructures can maintain nearly 100% ammonia-evolving selectivity at >120 mA cm^-2 current densities for 100 h due to the robust subsurface Ru-O coordination. These findings highlight the potential of nitrate electroreduction in real-world, low-temperature ammonia synthesis.

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