Expanding Two‐Dimensional Electrochemical Window Enables Durable Copper‐Based Electrocatalysts for Nitrate‐to‐Ammonia Conversion

Abstract The excessive presence of nitrate pollution in water poses a persistent challenge. Electrochemical nitrate reduction offers a potential approach to address this issue but lacks effective electrocatalysts. Despite being promising electrocatalysts for nitrate reduction to ammonia, copper‐based oxides undergo an evolution process that is poorly understood, while also demonstrating poor stability. Herein, we discovered a two‐dimensional electrochemical window of copper‐based oxide electrocatalysts, influenced not only by the bias potential but also by the nitrate concentration. We expand the two‐dimensional stable operation window of Cu 2 O 1−δ with Ru single‐atom modification and Ni buffer doping, thus achieving a record robust electrocatalyst Ru 1 @(Cu,Ni) 2 O 1−δ for nitrate‐to‐ammonia conversion over 11 000 h at a high current density of 1.6 A cm −2 . Utilizing this electrocatalyst, we designed a hundred‐watt‐scale membrane electrode assembly electrolyzer for the conversion of nitrate to ammonia that can be operated at an industrial‐grade current density of 400 mA cm −2 and a cell voltage of 1.5 V (with a total current of 80 A, 120 W). Furthermore, we developed a solar‐powered integrated system that facilitates the daily synthesis of liquid ammonia at the hundred‐gram scale from wastewater alongside potable water purification.