Theoretical Study On Electrochemical Reaction Mechanism Of Interfacial Complex System

In recent years,energy and environmental problems have become increasingly serious.Therefore,it is urgent to seek alternative clean energy,and it can be converted and stored into electricity that is widely used by people.This shows that energy storage and utilization of electrical energy are particularly important.As an energy storage device,lithium metal batteries have a very high battery capacity of 3860 mAh g^-1 and a very low anode potential of-3.04 V vs SHE（Standard Hydrogen Electrode）,which has attracted widespread attention.In addition,the utilization of electrical energy is also particularly important.Electrocatalysts can apply electrical energy to improve chemical reaction conditions and improve reaction rates and selectivity.Therefore,electrocatalysts and lithium metal batteries have extremely high research value and commercial application prospects.However,the catalytic mechanism of many catalysts is still unclear,the dendrite nucleation and growth mechanism of lithium metal batteries,and the morphology and composition of solid electrolyte interface（SEI,Solid Electrolyte Interphase）are also unclear.Works are divided into two parts,one aimed to design electrocatalysts and predict their performance through theoretical simulation methods,the other studied the formation mechanism of lithium dendrites and SEI,and further studied the factors affecting the growth of dendrites.These research results give some theoretical guidance and predictions.The main contents and conclusions of this paper are as follows:1.The single-atom catalyst MoS₂@SACs for NRR（Nitrogen Reduced Reaction,NRR）was systematically studied.First,we studied catalytic mechanism of Fe@MoS₂ catalyzing NRR,and found that the adsorption of N₂ in the reaction path,the formation energy of the first hydrogenation activation of N₂ and the desorption of ammonia would greatly affect the efficiency of the whole reaction.Second,in order to determine the structural stability of single-atom catalysts,we calculated the diffusion energy barrier of single atoms on the surface of MoS₂.The higher the diffusion energy barrier,the more stable the structure.From the results,it can be found that the single-atom structures such as Re and Cr are the most stable,and most of the single-atom catalysts have good structural stability.Taking the activity of this catalyst into consideration,we calculated the adsorption energy of N₂,the formation energy of the rate-determining step,and the desorption energy of ammonia.The results show that single-atom catalysts with better N₂ adsorption energy have higher desorption energy corresponding to ammonia,and Fe,Mn,Ir single-atom catalysts in the middle region are relatively better.For evaluating the selectivity of the catalyst,we calculated the Faradaic efficiency.From the calculated results,Ir@MoS₂ has a relatively high Faradaic efficiency of 64.11%and structural stability.In summary,we believe that Ir@MoS₂ is the one with the best catalytic efficiency among the 23 singleatom catalysts.2.Hydrogen production by electrolysis of water is a possible direction to deal with the energy crisis,but it is limited by the high OER thermodynamic potential of the corresponding electrode of 1.23 V.If hydrazine is used to produce hydrogen,there will be no such problem,and the pollutants in industrial wastewater can be well solved.Therefore,we hope to construct an efficient bifunctional catalyst for hydrazine oxidation and hydrogen evolution.The noble metals Pt,Rh,etc.naturally have good electrocatalytic properties such as structural stability,electron-rich active sites,and high crystal face selectivity.Based on the results of experimental synthesis and characterization,we constructed Rh/RhO_x,Rh（111）,and Pt（111）to study the mechanism.The calculated results show that the rate-determined step in the Rh/RhO_x and Rh（111）catalyst systems changes,and the former determines The speed step is the second dehydrogenation,and the latter is the first dehydrogenation and formation energy of the corresponding step is significantly reduced,and the speed step formation energy is also lower than that of pure Pt（111）.This suggests that the introduction of oxygen enhances the ability of hydrazine to oxidize.In addition,through the study of the hydrogen evolution reaction,it is found that Rh/RhO_x has the lowest HER energy barrier.This shows that Rh/RhO_x is also an excellent catalyst for hydrogen evolution with high selectivity.In conclusion,Rh/RhO_x is an excellent bifunctional catalyst.3.Dendrites in lithium metal batteries are an important factor inhibiting their applications and safety.At present,the ideal way is to construct,uniform and dense SEI films to suppress the growth of lithium dendrites.We simulated the Li dendrite growth process by developing a Kinetic Monte Carlo（KMC）model and applying an external electric field and considering the SEI film component.It was found that the pulsed charging method inhibited the growth of dendrites effectively,and the dense and uniform SEI film also inhibited the growth of dendrites directly.4.Znion water-based batteries are widely used in wearable devices,and the solvated structure in the solution will have a great influence on the migration rate of ions,which in turn affects the capacitance of the battery.Based on the experimental results,we constructed a 2M ZnSO₄,ZnCl₂ solution system for molecular dynamics simulation,and calculated the number of hydrogen bonds,analyzed radial distribution function,and solvated structure size of the simulated trajectory.The radial distribution function shows that the ionic coordination in ZnSO₄ solution is hexacoordinated,while the ionic coordination in ZnCl₂ solution is tetracoordinated,which indicates that the introduction of C1 atom will replace one H2O;and the amount of hydrogen bonds in ZnSO₄ solution is lower than ZnCl₂,indicating that the introduction of Cl atoms changed the solvated structure in the solution and improved the mobility of Zn2+;through volume size analysis,it was found that the size of Zn2+ solvated structure in the ZnSO₄ solution was larger than that in ZnCl₂ solution,again indicating that the introduction of Cl atoms can improve the mobility of Zn2+ in graphene pores.