Open AgRh Hollow Nanocubes With Interfacial Step Matching for Selective Nitrate‐to‐Ammonia Electrosynthesis

ABSTRACT Electrochemical nitrate‐to‐ammonia (NO 3 − to NH 3 ) conversion offers a promising route for NO 3 − removal and distributed NH 3 synthesis. However, its efficiency is constrained by sluggish NO 3 − activation, incomplete hydrogenation, and competing hydrogen evolution. Herein, open AgRh alloy hollow nanocubes (AgRh hNCs) are reconstructed from Ag nanocubes through a chloride‐assisted alloying and etching process. The catalyst possesses a porous, nanograin‐assembled framework with a Rh‐enriched near‐surface region, enhancing both mass transport and interfacial electronic coupling. Consequently, AgRh hNCs achieve up to 98% Faradaic efficiency for NH 3 , an NH 3 yield rate of 10.6 mg h −1 mg cat −1 , and excellent durability in the alkaline nitrate reduction reaction (NO 3 RR). Combined theoretical and experimental studies reveal a tandem‐like interfacial step‐matching mechanism, in which Ag promotes the NO 3 ‐to‐NO 2 step, while Rh‐centered sites drive deep hydrogenation of nitrogen‐containing intermediates to NH 3 . Moreover, AgRh hNCs show high hydrazine oxidation reaction (HzOR) activity, enabling a membrane‐separated NO 3 RR||HzOR electrolyzer with a 1.58 V lower cell voltage than the oxygen evolution reaction‐coupled system at 10 mA cm −2 . This work demonstrates that integrating an open hollow structure with cooperative Ag‐Rh interfacial sites is an effective strategy for selective NO 3 − ‐to‐NH 3 electrosynthesis.