Catalyst-free synthesis of ammonia using dc-driven atmospheric-pressure plasma in contact with water

Abstract Atmospheric-pressure plasma, generated using a dc power supply, in contact with water was investigated as a green, catalyst-free method for the ammonia synthesis. Stable nitrogen plasmas were generated inside bubbles which were obtained by inserting a dielectric tube with the gas flow into water. A higher production rate was obtained at a higher discharge current, a higher flow rate of nitrogen, and a lower conductivity of water. In addition, the production rate when the water worked as the cathode of the discharge was higher than that with the inverted polarity of the dc power supply. The maximum production rate of ∼0.98 µ mol min −1 was realized at the optimized discharge condition, which is higher than the literature value obtained using a dc discharge in contact with water (Hawtof et al 2019 Sci. Adv. 5 eaat5778). We also discussed the possible reaction fields for the ammonia synthesis in the experimental condition.