Strategies To Optimize And Improve The Key Components Of Ammonia Electrosynthesis System

Electrosynthesis of ammonia（NH₃）with the merits of operating in mild conditions and being driven by renewable energy such as wind and solar energy has attracted much attention recently.However,due to the chemical inertness of the N₂ molecule and the competition of hydrogen evolution reaction（HER）,the yield rate and Faradaic efficiency of NH₃ electrosynthesis are relatively low,which seriously restricts its further development and application.In all,optimizing the NH₃ electrosynthesis system covering reactors,electrocatalysts,electrolytes,etc.to improve the performances of NH₃ electrosynthesis become challengeable.Focusing on these crucial issues,we first optimize the reactor to improve the accuracy of NH₃ detection.On the basis of this,we optimize the critical components of the NH₃ electrosynthesis system,and further combine with macroscopic driving forces to improve the performances of NH₃electrosynthesis.The main research contents are summarized as follows:An oxidized molybdenum sulfide material（Mo S_x）supported on carbon nanotubes（Mo S_x/CNTs）is fabricated by acid precipitation and thermal oxidation methods.The effects of annealing temperature and oxidation time on the chemical composition,Lewis acidity,and the N₂ activation ability of the Mo S_x/CNTs are investigated.It is revealed that with the incremental of oxidation time,the Lewis acidity of Mo S_x/CNTs gradually increases,whereas their activation abilities towards the N₂ molecules present a volcanic tendency.The Mo S_x-O₆₀/CNTs exhibits the strong activating ability for N₂ molecules,achieving a NH₃ yield rate of 40.4μg h^-1 mg_cat.^-1and a Faradaic efficiency of 21.6%.Density functional theory calculations verify that the electron transfer of N₂ molecules to the Mo sites of Mo S_x-O₆₀/CNTs can be accelerated,finally enhancing the N₂ activation process via theσ-donation effects.A mixed methanol-water electrolyte is constructed for NH₃ electrosynthesis using methanol as the solvent and water as the proton donor.Employing Fe OOH/CNTs as the catalyst,the effects of water content in the methanol-water electrolyte on the structure of the electrode-electrolyte interface and the performance of NH₃ electrosynthesis are investigated,and the reasons of suppressed HER activity in the methanol-water electrolyte are also decoupled.It is demonstrated that the methanol-water electrolyte can effectively suppress the HER,and the content of water is the critical factor to influence the performances of NH₃ electrosynthesis.In the methanol-water electrolyte with a water content of 0.16%,the Fe OOH/CNTs catalyst achieves a high NH₃ yield rate of 262.5μg h^-1 mg_cat.^-1and a Faradaic efficiency of 75.9%,superior to the performances in conventional aqueous electrolytes.Raman spectroscopy further reveals that the inhibition of HER in the methanol-water electrolyte is attributed to the limited availability of water and the hydrogen bonding interaction between water and methanol molecules.A plasma-enabled N₂ oxidation-electroreduction system is developed for NH₃ electrosynthesis.The effects of discharge distance and oxygen content in feeding gas on the composition and concentration of discharge products are investigated.It is revealed that the discharge distance of 2.0 cm and oxygen content of 50.0%are the optimal parameters for the plasma system.The concentration of NO_x reaches 2.6 m M after discharge for 10 min,and the conversion efficiency of N₂ in the plasma system is confirmed to be～42%.Using Cu nanoparticles as the catalyst,the system achieves a NH₃ yield rate of 12240μg h^-1 mg_cat.^-1and a Faradaic efficiency of nearly 90%.In situ Raman spectroscopy further reveals that the reconstructed Cu⁰ species over the surface are the active sites for NH₃ electrosynthesis.