Interfacial Water Regulation for Nitrate Electroreduction to Ammonia at Ultralow Overpotentials

Abstract

Nitrate electroreduction is promising for achieving effluent waste-water treatment and ammonia production with respect to the global nitrogen balance. However, due to the impeded hydrogenation process, high overpotentials need to be surmounted during nitrate electroreduction, causing intensive energy consumption. Herein, a hydroxide regulation strategy is developed to optimize the interfacial H₂O behavior for accelerating the hydrogenation conversion of nitrate to ammonia at ultralow overpotentials. The well-designed Ru─Ni(OH)₂ electrocatalyst shows a remarkable energy efficiency of 44.6% at +0.1 V versus RHE and a nearly 100% Faradaic efficiency for NH₃ synthesis at 0 V versus RHE. In situ characterizations and theoretical calculations indicate that Ni(OH)₂ can regulate the interfacial H₂O structure with a promoted H₂O dissociation process and contribute to the spontaneous hydrogen spillover process for boosting NO₃ ^- electroreduction to NH₃ at Ru sites. Furthermore, the assembled rechargeable Zn-NO₃ ^-/ethanol battery system exhibits an outstanding long-term cycling stability during the charge-discharge tests with the production of high-value-added ammonium acetate, showing great potential for simultaneously achieving nitrate removal, energy conversion, and chemical synthesis. This work can not only provide a guidance for interfacial H₂O regulation in extensive hydrogenation reactions but also inspire the design of a novel hybrid flow battery with multiple functions.