Surface DBD in moist air for nitrogen fixation: a comparative study of pulsed versus amplitude-modulated AC powered discharge

Surface DBD discharge maintained in moist air in the immediate vicinity of the water surface is an effective source of reactive species for the production of plasma-activated water. In this work, we investigated the water activation process for two different DBD energization methods; i.e. using periodic HV pulses with nanosecond risetimes and amplitude-modulated HV AC. We combined UV-vis-NIR ICCD spectroscopy with electrical characteristics to determine the basic characteristics of surface DBD microfilaments. Formation of N2O5/NO2/N2O/H2O2/NO2-/NO3- species was followed and the production yields of species generated in plasma-activated water (H2O2/NO2-/NO3-) were determined in a flow-through reactor under well-defined and stable discharge conditions. Both energization methods reached comparable energy efficiencies of nitrogen fixation in the range of 1-6 g/kWh with minimal concentrations of H2O2 (10s µM). However, the AC-powered SDBD produced mainly NO3- with minimal NO2- (1/10 of NO3-), while in the case of pulsed SDBD the better-balanced NO2-/NO3- ratio was achieved.