Multielectron reactions at the plasma-air/water interface

There are three major multi-electron reactions in nature: nitrogen fixation by bacteria, water oxidation in photosynthesis, and oxygen reduction during respiration. Industrial fixation of molecular nitrogen in the Haber-Bosch process is very expensive and requires extremely high temperatures and pressures. Here we found that cold atmospheric pressure He-plasma jet (CAPPJ) can oxidize N₂ to HNO₃ and HNO₂ at low temperature and atmospheric pressure at the plasma/water interface. Analysis of the images showed that redox reactions occur at the plasma-air/water interface and the products of electrochemical reactions slowly diffuse into the bulk of the aqueous solution. Acidification of an aqueous solution during the CAPPJ treatment correlates with an increase in HNO_x concentration in the aqueous phase. HNO₂ is unstable and can be oxidized to HNO₃ by plasma-generated H₂O₂ or ozone. The mechanisms of the interfacial multielectron reactions at the plasma-air/water interface are discussed and evaluated. Plasma-induced production of HNO_x at the plasma/water interface at room temperature and atmospheric pressure can be used in the industry for nitrogen fixation and production of nitrogen compounds, replacing the expensive old technology processes. Plasma-activated water can be used in medicine and agriculture for disinfection, sterilization, and decontamination.