Preliminary study of an open-air water-contacting discharge for direct nitrogen fixation

Efficient nitrogen fixation through a reactive plasma process attracts intense interest due to the environmental issues induced by the conventional Haber–Bosch method. In this work, we present a direct and simple fixation routine without any catalysts for nitrogen in open air using an atmospheric-pressure pin-to-solution plasma electrolytic system. Nitrate, nitrite, and ammonia as the nitrogen-derived chemicals in solution were analyzed as indicators under various discharge conditions to estimate the energy efficiency of this process. The results show that the nitrogen fixation process was much more efficient by the pin-positive discharge compared to the negative one. N chemicals preferred to be formed when the solution was of negative polarity. It was also found that, with the help of solution circulation, the energy efficiency was enhanced compared to that of static liquid. However, an inverse trend was observed with the increase of the discharge current. Further study by optical emission spectroscopy indicates the important roles of active N 2 * and water vapour and their derived species near the plasma–water interface in the fixation process.