Nitrogen Fixation in a Plasma/Liquid Interfacial Reaction and Its Switching between Reduction and Oxidation

Abstract

There are multiple active species at the interface between the discharged gas phase and the water phase. Activated nitrogen species are generated in the nitrogen plasma gas by dielectric barrier discharge (DBD). The reaction at the interface between the gas phase containing the activated nitrogen species and water phase (P/L reaction) can produce nitrogen-derived compounds (N-compounds) in water. We have already clarified the mechanism of the P/L reaction focusing on highly active atomic nitrogen in a previous study. In this study, we report the mechanism of the P/L reaction by excited but metastable nitrogen molecules. Involving excited nitrogen molecules [N2(A3Σu+)] with a long lifetime, the reaction selectivity of N-compounds was clarified by quantitative analysis. Moreover, the active species in the water phase (H·, HO·, H2O2) of the P/L reaction were measured, and the involvement of the reaction in the generation of N-compounds was confirmed. The findings clarify that each activated nitrogen species reacts differently with H2O. These results suggest that the occurrence of either an oxidation reaction or a reduction reaction can be regulated by controlling the activated nitrogen species.