## 4 Conclusions  
In summary, this paper presents a technique for synthesizing ammonia through gas-liquid plasma in the WF-DBD reactor. This method allows the synthesis of ammonia from N\({}_{2}\) and H\({}_{2}\)O without the use of a catalyst. The synthesis rate, energy consumption, and selectivity of ammonia synthesized in plasma were investigated using Lissajous figures and UV spectrophotometry. The experimental results show that a higher ammonia synthesis rate (12.69 umol\(\cdot\)min\({}^{-1}\)) as well as excellent product selectivity (80.7% NH\({}_{4}\)+) can be obtained under the condition of using hermetically sealed N\({}_{2}\) as the discharge gas. The water in the liquid cycle not only serves as a source of hydrogen for the reaction but also solubilizes the products in the gas phase and thus synthesizes ammonia in one step in the liquid phase. Another advantage of this method is that the discharge consumes only N\({}_{2}\) sealed in the reactor, which is more feedstock efficient compared to flowing N\({}_{2}\).  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app15031410/s1](https://www.mdpi.com/article/10.3390/app15031410/s1)]([https://www.mdpi.com/article/10.3390/app15031410/s1](https://www.mdpi.com/article/10.3390/app15031410/s1)). Figure S1: The standard curves for (a) NH\({}_{4}\)+, (b) NO\({}_{3}\)\({}^{-}\), and (c) NO\({}_{2}\)\({}^{-}\) measurements. Figure S2: Schematic diagram of a sectional view of the WF-DBD reactor. Figure S3: (a) Detailed structure of WF-DBD reactor and (b) digital photograph of reactor. Table S1: Main structural parameter of the WF-DBD. Table S2: Main parameters in the process of WF-DBD. Table S3: Partial study of ammonia synthesis by gas-liquid plasma in recent years.  
Methodology and investigation, Z.L. and X.Y.; data curation and writing--original draft preparation, X.Y.; writing--review and editing, Y.Z., H.L., C.T., and J.C. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Enshi State Science and Technology Plan Project (D20230089), the Graduate Education Innovation Project of Hubei Minzu University (MYK2024049), and the National Natural Science Foundation of China (62341305).  
Not applicable.  
Data Availability Statement: Data are contained within this article or Supplementary Materials.  
We wish to thank [PERSON] (Research and Development Center, Baowu Heavy Industry Company Limited) for his help in reactor design. We also extend our gratitude to Shiyanjia Lab (www.shiyanjia.com) ( accessed on 28 January 2025) for the IC rest.  
The authors declare no conflicts of interest.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline Year & Power (W) & Type of Plasma & Max Production & Selectivity of &
\begin{tabular}{c} Energy \\ Consumption (M)\(\cdot\)mol\({}^{-1}\)) \\ \end{tabular} & Ref. \\ \hline
2018 & 5 & Plasma jet + UV & 2.5 & 4.32 & - & [20] \\
2019 & \(\sim\)1 & Plasma electrolytic & 0.407 & - & 147.27 & [7] \\
2020 & 0.1 & Plasma jet & 0.063 & 95 & 95 & [4] \\
2022 & - & Gliding arc plasma & 0.63 & - & 2492.3 & [43] \\
2023 & - & Pulsed discharge & 7.1 & - & 95.3 & [22] \\
2024 & \(\sim\)150 & WF-DBD & 12.69 & 79.1 & 491.86 & This work \\ \hline \end{tabular}
\end{table}
Table 1: Comparison of synthesis rates and energy consumption for ammonia production via non-catalytic plasma technologies.