Insights into plasma-catalytic nitrogen fixation from catalyst microanalysis and chemical kinetics modelling

Current industrial nitrogen fixation technology is unsustainable and has adverse environmental effects due to its reliance on fossil fuels. Using electricity-driven non-thermal plasma catalysis to fix nitrogen into NO₃⁻ is a promising solution, but the underlying mechanisms remain largely unknown. This study integrates a structured catalyst into a plasma column with a water-electrode bubble reactor that can fix nitrogen at ambient pressure and temperature with a 93% selectivity to NO₃⁻ with excellent catalytic stability. Characterizations of the catalyst and in situ plasma diagnostics indicate that the enhanced production of nitrate ions is due to abundant chemisorbed oxidized nitrogens species originating from NO and NO₂ produced by the air plasma. The plasma chemistry model combined with DFT simulations demonstrates the role of structured TiO₂ supported by 5% graphene oxide (GO) to improve NO_x surface association while minimizing NO_x backwards dissociation. The modelling results suggest the critical role of NO_3(ad) in enhancing NO_x production predominantly in the form of N₂O₅ molecule in the gas phase, resulting in efficient NO₃⁻_(aq) production as a final product in water. The study offers novel findings on plasma-catalyzed nitrogen fixation, advancing its potential for clean energy and eco-friendly chemical production through plasma-based power-to-chemical processes.