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

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 Cu₂O_1-δ with Ru single-atom modification and Ni buffer doping, thus achieving a record robust electrocatalyst Ru₁@(Cu,Ni)₂O_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.