## 3 Results and Discussion
### Effect of Ar and He Addition on NH\({}_{3}\) Formation  
In NTP-assisted ammonia synthesis applications, the gas flow rate can affect the ammonia synthesis. The effect of the total gas flow rate on ammonia synthesis was explored using 13 kV, 1200 Hz pulse parameters without noble gas addition, always keeping the gas  
Figure 2: Effect of Ar and He addition on voltage–current profile. ratio H\({}_{2}\):N\({}_{2}\) = 3. Figure S1 illustrates that elevating the low flow rate enhances both the ammonia synthesis rate and the energy yield. This enhancement plateaus once the flow rate hits 120 mL/min and starts to decline when exceeding 280 mL/min. Increasing the gas flow rate will provide a larger supply of raw reactant gas, thereby increasing the collision probability between reactive particles. This will be beneficial for ammonia production [26]. At the same time, with the shortening of the residence time, the possibility of effective collisions of electrons with the reacting material, both on the surface of the packing and in the gas phase, decreases, thus reducing the rate of NH\({}_{3}\) synthesis [33]. Similarly, [PERSON] et al. combined experiments and calculations to conclude that a reasonable increase in the flow rate would improve the synthesis rate of NH\({}_{3}\). However, too high a flow rate leads to a decrease in the specific energy input (SEI), which is the main reason for the decrease in NH\({}_{3}\) yield [34]. Based on the experimental results, we conclude that increasing the initial number of reactants significantly increases the efficiency of ammonia synthesis at low flow rates. Once the \"synthesis capacity\" of the system is reached, the reduction in the SEI and the shortened reaction time result in a decrease in the rate of ammonia synthesis. In the experiments investigating the effect of noble gas addition on ammonia synthesis, the total gas flow rate was always maintained at 120-280 mL/min. Although the ammonia synthesis rate and energy yield decreased slightly in this flow rate range, the ammonia synthesis rate did not decrease by more than 5.76% and the energy yield did not decrease by more than 8.06%. Therefore, it was considered to be a stable \"flow rate window\". The flow rates of the added gases under various conditions are shown in Table S1. Under the same pulse parameters (13 kV, 1200 Hz), the effect of the feed gas ratio and adding noble gases to different feed gas ratios on the effect of ammonia synthesis was investigated. Figure 3 shows the energy yield of ammonia synthesis with different raw gas ratios and with the addition of Ar and He to different raw gas ratios. As shown in the figure, the energy yield of ammonia synthesis without the addition of Ar and He increases with the nitrogen content and has a maximum value of 0.417 g-NH\({}_{3}\)/kWh at H\({}_{2}\):N\({}_{2}\) = 3. Beyond this ratio, the energy yield starts to decrease with increasing nitrogen content. This is consistent with the gas ratios in the theoretical reaction (N\({}_{2}+3\)H\({}_{2}\leftrightarrow\) 2 NH\({}_{3}\)) [35]. The dissociation of N\(\equiv\)N is the rate-limiting step of the entire reaction, owing to the significantly higher dissociation energy of N\({}_{2}\) (9.75 eV) compared to that of H\({}_{2}\) (4.52 eV) [36]. When the value of H\({}_{2}\):N\({}_{2}\) changes from 3 to 5, the energy yield decreases, which suggests that increasing the H\({}_{2}\) content also decreases the energy utilization because excess active hydrogen contributes to ammonia decomposition. Energy yield also begins to decrease when the H\({}_{2}\):N\({}_{2}\) ratio exceeds 3. Increasing the N\({}_{2}\) concentration beyond the optimum ratio will use less H\({}_{2}\) for ammonia production. With the addition of noble gases, the optimal ratio of gases changed; the optimal ratio with the addition of Ar was H\({}_{2}\):N\({}_{2}\) = 1, while the optimal ratio with the addition of He was H\({}_{2}\):N\({}_{2}\) = 2.