Electrochemical synthesis of nitric acid from air and ammonia through waste utilization

Abstract

Commercial nitric acid (HNO₃) and ammonia (NH₃) are mostly produced through the Ostwald process and the Haber-Bosch process, respectively. However, high energy demand and enormous greenhouse gas accompy these processes. The development of economical and green ways to synthesize HNO₃ and NH₃ is highly desirable for solving the global energy and environmental crisis. Here, we present two energy-efficient and environmentally friendly strategies to synthesize HNO₃ and NH₃ at distributed sources, including the electrocatalytic oxidation of N₂ in air to HNO₃ and the electrocatalytic reduction of residual |${\rm NO_{3}^{-}}$| contamination in water to NH₃. The isotope-labeling studies combined with theoretical calculation reveal the reaction path of the two proposed strategies, confirming the origin of the electrochemical products. Importantly, the electrooxidation-generated |${\rm NO_{3}^{-}}$| ions may also serve as reactants for the electroreduction synthesis of NH₃ in the future. Our work may open avenues for energy-efficient and green production of HNO₃ and NH₃ at distributed sources.