Competition between ammonia and nitrogen oxides during nitrogen fixation using N2 and H2O plasma without catalysis

Abstract

The global energy crisis highlights the need for sustainable energy solutions. Nitrogen fixation, converting N₂ into valuable products, is gaining attention. In this study, we investigate the effect of water vapor in gas-phase nitrogen fixation via gas–liquid mixed-phase pulsed discharge. Results show that increasing water vapor enhances nitrogen fixation efficiency but introduces a competitive mechanism between NH₄⁺ and NO_x. This study examines the effect of water vapor on nitrogen fixation via pulsed discharge at 20 kV and 10 Hz. When water vapor content reached 100%, NH₄⁺ concentration decreased by 49.2%, while NO₃⁻ concentration increased by 19%. Additionally, raising the liquid temperature from 6 °C to 80 °C reduced NH₄⁺ by 57.6% and increased NO₃⁻ by 54.1%. Spectral diagnostics and radical scavenging experiments confirmed the key role of H and OH radicals in the fixation process. Reaction kinetics analysis further validated the competition between NH₄⁺ and NO_x synthesis. While water as a raw material is critical for green nitrogen fixation, its impact on product distribution must be considered in optimizing future applications.