Stepwise Upgrading of Waste Nitrate by Fast Joule‐Heating and Electrochemical Reduction at Wide Potentials

ABSTRACT Nitrate contamination in groundwater is threatening ecological environment and human health. The conventional physical treatment of nitrate‐rich wastewater suffers from high treatment cost and severe secondary pollution. Here we propose a stepwise upgrading route for treating nitrate‐rich wastewater, which synchronizes catalyst synthesis and conversion of waste nitrate into valuable ammonia. The metal‐nitrate‐derived bimetallic catalyst synthesized by fast Joule‐heating shows a superior nitrate electroreduction performance with ∼100% Faradaic efficiency for NH 3 production at the wide potential range, outperforming state‐of‐the‐art electrocatalysts. By utilizing the membrane electrode assembly (MEA) electrolyzer, a long‐term stability over 300 h can be achieved at an industrial current density of 200 mA cm −2 . A series of in situ characterizations confirm the stable phase of catalyst under electrochemical conditions and identify the reaction pathway of nitrate electroreduction by capturing the intermediate signals. Theoretical calculations reveal the bimetallic electronic interaction mechanism and its influence on the nitrate electroreduction performance. Furthermore, techno‐economic analysis shows the potential commercialization value of coupling nitrate reduction with hydrazine oxidation by extending the applications of stepwise upgrading route. This work provides a promising route for achieving sustainable treatment of waste nitrate, with the potential to promote the industrial applications of electrochemical nitrate upgrading.