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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 …