Effects Of Electric Field And Electron On Adsorption And Dissociation Of Nitrogen Molecules For Plasma-assited Ammonia Synthesis

With the introduction of"carbon peaking"and"carbon neutrality"strategies,the realization of the"dual carbon"goal has become the top priority of current social development.The energy issue is the first challenge,especially the safe and efficient storage of new energy.Nowadays,battery energy storage and hydrogen-based chemical energy storage are research hot topics.Ammonia gas has recently aroused interest of researchers as a long-term efficient energy storage medium.The hydrogen-ammonia conversion technology for energy storage based on plasma catalysis is green and environmentally friendly,and suitable for intermittent new energy with flexible switching characteristics,so it has broad development prospects.The coupling between the low-temperature plasma and the catalyst and its influence on the ammonia synthesis reaction are still lacking in the microscopic mechanism.In this thesis,the key factors such as the electric field and excess elctrons in the plasma environment are investigated based on the density functional theory（DFT）.The simulation of the dissociation of nitrogen molecules on different kinds of catalysts for ammonia synthesis reaction is of great significance to explaining the coupling effect of plasma environment and catalysts in ammonia synthesis reaction.It is also helpful for future screening and searching for synergistic effects with plasma.Firstly,the catalyst surface model in the plasma environment has been built up using CP2K.The catalyst surfacesare divided into ferromagnetic metals（Ru and Ni）that perform better in the plasma environment,non-ferromagnetic metals（Cu）with poor performance in plasma environment while better performance in thermal catalysis,and oxides（Al₂O₃）generally used as catalyst supports.In order to understand the effects of electric field and excess electrons,the effect of a external electric field and the effect of excess electrons alone this paper are firstly investigated,and finally the combined effect of the two,so as to study the catalytic mechanism of the plasma environment and the catalyst surface.Secondly,when only an external electric field is applied to the simulation model,the distance between the N₂ molecule and the surface adatom decreases and the distance between the two N atoms increases.The adsorption configuration of the N₂ molecule and the surface atom has been optimized.The adsorption bond is strengthened while the N-N triple bond is weakened.At the same time,the adsorption energy increases,and the energy of the system after adsorption is lower and more stable,which promotes the adsorption reaction from a thermodynamic point of view.The addition of an applied electric field after dissociation also increases the dissociative adsorption energy between N atoms and the surface,which promotes the dissociation process.When only electrons are added without applying an electric field,since the surface charge accumulation hardly changes,the effect of the addition of excess electrons on the adsorption properties of N₂ molecules on the metal surface is almost negligible.For Al₂O₃,the addition of extra electrons has a negative effect on the adsorption of N₂molecules.At last,the combined effect of an externally applied electric field and ecxess electrons are investigated.The addition of surface electrons in the presence of an external electric field further promotes the adsorption and dissociation on each surface,and the combined effect has a marginal effect.The enhancement of Ni surface with weaker activation to N₂,is relatively significant,resulting in a different performance order of the catalysts under the plasma environment than under thermal catalysis.At the same time,the combined effect of the applied electric field and excess electrons changes the optimal adsorption sites on Ru catalysts,thus exhibiting different properties from conventional thermocatalysis.