Theoretical Studies On Dynamics Of Dissociative Chemisorption Of Molecules And Electrocatalytic Mechnisms On Solid Surfaces

Chemical reactions occurring at gas-solid interfaces are of great importance in many fields,such as heterogeneous catalysis,corrosion,electrocatalysis,and so on.These processes often involve elementary reaction steps like the(dissociative)adsorption of reactants on the surface,diffusion,reaction,and desorption of products from the surface,which are affected by molecule-surface interactions and energy transfer between them.Therefore,in order to gain an in-depth understanding of these complex processes,it is necessary to elucidate the microscopic reaction dynamics of surface elementary reactions.The dissociative chemisorption of methane on metal catalysts is a rate-determining step(RDS)in the industrial process of methane steam reforming.Despite a large body of investigations,as one of the energy transfer pathways during this process,the collision-induced electron-hole pair(EHP)excitation has not been studied.In this thesis,the effects of EHP excitation on the dissociation chemisorption of CH4/CH3D/CHD3 on Ni(111)was studied in theory.To this end,molecular dynamics calculations on the dissociative chemisorption of CH4/CH3D/CHD3 on Ni(111)surface were performed using the quasi-classical trajectory method on a twelve-dimensional(12D)PES.The energy dissipation induced by surface EHPs excitations is modeled as a friction force introduced in the generalized Langevin equation,in which the independent atomic friction coefficients are determined within the local-density friction approximation(LDFA).Our results clearly indicate that the electron-hole pair effects are generally small,both on absolute reactivity of each vibrational state and on the mode specificity and bond selectivity.Another energy transfer pathway in surface reactions is from the molecule to surface phonons.CO2 is an important factor causing global warming,so its conversion has attracted much attention.We studied the energy transfer dynamics in CO2 dissociative chemisorption on Ni(100)based on a nine-dimensional potential energy surface obtained from first-principles.To reduce the computational cost,dynamical calculations have been done using the generalized Langevin oscillation(GLO)model combined with LDFA,in which the former accounts for the surface motion and the latter accounts for the low-energy EHP excitation.In spite of its simplicity,it is found that the GLO model yields quite satisfactory results,including the significant energy loss and product energy disposal,trapping,and steering dynamics.However,the GLO model fails to describe the reactivity enhancement due to the lattice motion.On the other hand,the energy transferred to EHPs is found to play a minor role and barely alter the dynamics.These results motivate us to improve the GLO model and stimulate future experimental studies on this system.The other part of my thesis is about reaction mechanisms of electrocatalysis on novel nanomaterials,which involve many more elementary steps and much more complex catalyst structures and reaction conditions.To simplify the problem,in collaboration with experiments,we only consider the most important aspects in the reaction network and calculate the energetics of relevant reactions by density functional theory(DFT),using single-crystal surfaces as representatives of catalysts.In the first case,experimentally,a novel ultrathin trimetallic alloy with atomically dispersed Cu and Pt single atoms on Pd nanorings exhibits excellent activity in the hydrogen evolution reaction(HER).To explain this phenomenon,we proposed three possible structures with three or four Cu atoms binding to a Pt atom,in light of the coordination information measured by EXAFS.We found that the adsorption free energy of hydrogen(△GH.)on the single Pt atom in the vicinity of Cu atoms,is close to zero than that on Pt(111).This suggests the adsorbed hydrogen binds neither too weakly nor too strongly to this Pt site with assistance of neighboring Cu atoms and provide theoretical evidence for the HER catalytic activity of the new dual site trimetallic alloy catalyst.In another case,in the oxygen evolution reaction(OER),the experimental group synthesized layer-controllable PdO@RuO2 core-shell materials by a solution-based epitaxial growth method.Our DFT calculations show that the weak interaction between O*and the four-layer RuO2(110)stacked on the PdO(101)substrate,is favorable to promote the RDS of OER.This agrees well with the layer dependence of PdO@RuO2 catalyst observed in experiments and supports the significantly improved OER performance of PdO decorated by a few atomic layers of RuO2.