Atmospheric pressure plasma generation at liquid interface for nitrogen fixation*

In recent years, plasma nitrogen fixation has been proposed as a sustainable nitrogen fixation method, which composes nitrogen compounds exclusively from air and water. The energy cost for the plasma nitrogen fixation, reaction processes from nitrogen dissociation to storable nitrogen compounds such as nitrate, is an unresolved issue despite of its accessibility to renewable energy sources. This study focuses on exploring the nitrogen fixing reaction pathways at the plasma - liquid water interface, where radicals can directly reach and unknown reaction pathways, potentially beneficial to overcome the energy cost, might exist. This work specifically focuses on characterizing the air and nitrogen plasma generation at the liquid water interface with approximately 10 to 50 kHz AC high voltage, allowing significant specific energy input aiming for radical generation affecting near-surface reactions. Discharge plasma volume extension with multiple electrodes configuration is found effective for tuning the power density with 50 kHz burst AC discharge. These plasma control at the interface enables reaction studies at the plasma-liquid interface. Further discussion on the plasma-liquid interface will be presented, regarding the electric charge and the reactive species generation.