Achieving Near 100% Faradaic Efficiency of Electrocatalytic Nitrate Reduction to Ammonia on Symmetry-Broken Medium-Entropy-Alloy Metallene

Electrochemical nitrate reduction (NO3RR) offers an ecofriendly way for ammonia production. However, improving the sluggish kinetics of such a multistep reaction still remains challenging. Herein, an asymmetry strategy is proposed to adjust the charge distribution of the active centers on metallene by presenting novel symmetry-broken medium-entropy-alloy (MEA) metallene via heteroatom alloying. Benefiting from the maximized exposure of the well-regulated active sites, proof-of-concept PdCuCo MEA metallene delivers near 100% NH3 Faradaic efficiency in both neutral and alkaline electrolytes, along with a record-high NH3 yield rate over 532.5 mg h–1 mgcat–1. Moreover, it enables 99.7% conversion of nitrate from an industrial wastewater level of 6200 ppm to a drinkable water level. Detailed studies further revealed that charge redistribution is induced by the elemental electronegativity difference on symmetry-broken MEA metallene, which will weaken the N–O bond of *NO, thus reducing the energy barrier of the rate-determining step. Meanwhile, the competitive HER and the formation of NO2– are also hindered. We believe that our strategy proposed in this work will shed light on the design of efficient NO3RR catalysts to a more practical level.