Nitrogen fixation efficiency enhancement using plasma jet: Impact of grounded electrode

Energy cost reduction for nitrogen fixation (NF) using non-thermal plasma remains a global challenge. Researchers are exploring to reach the theoretical energy cost limit of 0.2 MJ.mol-1 for NF. A fixed grounded electrode (FGE) plasma jet has designed, studied NOx production efficiency and energy cost, and compared the results with the traditional floating water ground electrode (FWGE) configuration. The plasma was characterized by the optical emission spectroscopic (OES) technique. The experimental setup was optimized for gas composition and flow rate. The efficient gas composition ratio was identified as air:O2::5:3 with the flow rate of 3 L.min-1, and the temporal evolution of NOx production and efficiency were analyzed for both electrode configurations. For FGE, the NOx synthesis rate was 3.83 mmol.h-1 and the energy cost was 25.74 MJ.mol-1 for a 10 min treatment, and the synthesis rate was decreased, whereas the energy cost was increased with water treatment time. While for FWGE, the synthesis rate and energy cost were 1.71 mmol.h-1 and 71.5, MJ.mol-1, respectively, for the same treatment time. The synthesis rate was decreased with treatment time, whereas the energy cost was increased initially but decreased as the treatment time progresses. The promising result of this experiment is that the FGE configuration achieved a significantly lower energy cost and higher synthesis rate compared to FWGE. The proposed FGE plasma jet system might provide a way in plasma-assisted NF at low energy cost through the synergistic optimization of ground electrode, jet configuration, plasma-catalyst incorporation, gas flow dynamics, and treatment duration.