In-situ diagnostics of key species of a magnetically stabilized atmospheric pressure glow discharge (MS-APGD) plasma for nitrogen fixation

Abstract Plasma electrification presents a promising solution for sustainable nitrogen fixation, yet it continues to face significant challenges, notably high energy costs. The energy efficiency of plasma-based nitrogen fixation is governed by multiple parameters, including electrical parameters, gas compositions, and reactor configurations. However, conventional plasma nitrogen fixation reactors struggle to independently control plasma parameters through experimental adjustments, limiting insights into the underlying mechanisms of the process. In this study, we used a magnetically stabilized atmospheric pressure glow discharge system that allows independent control of plasma parameters such as gas temperature and electric field. Furthermore, we employed laser-induced fluorescence for in situ measurement of the spatial density distributions of key species, including O, N, and NO, generated in the plasma. The effects of discharge current, discharge power, gas flow rate, and gas composition on the concentrations of these key species were investigated. The results show that O and N atoms are mainly distributed along the plasma channel, with the density of O atoms being approximately two orders of magnitude higher than that of N atoms. In contrast, NO molecules exhibit a ‘hollow’ distribution, characterized by the lowest concentration at the center of the channel and accumulation in the downstream region. This phenomenon is attributed to the high concentration of O atoms in the plasma channel, which rapidly oxidize NO into NO 2 ; the downstream NO is generated through the subsequent conversion of NO 2 . Furthermore, increasing the O 2 concentration effectively eliminates the hollow NO distribution, which is associated with the suppression of the reaction N + NO−> N 2 + O.