Quantum Effects In The Dissociation,adsorption And Diffusion Of Hydrogen On The Cu (001) Surface

As a promising clean energy source,hydrogen mainly exists in the form of molecules in nature.Materials involving metal elements are commonly utilized as catalysts for hydrogen production and storage to harvesting hydrogen based energy.The elementary dynamics(e.g.,adsorption and diffusion)of hydrogen on transition metal surfaces are closely related to some important physical and chemical processes such as crystal growth,hydrogen embrittlement in metals,surface corrosion,and technological applications like radiation protection in fusion reactor reactions,electrode reactions in fuel cells,and surface catalysis.In this thesis,the complete process from dissociation to adsorption and diffusion of hydrogen molecules on Cu(001)surface is studied theoretically.The activation barrier height for the dissociation of H2 on Cu(001)was obtained by first-principles calculations to be～0.59 eV.Electron transfer from the substrate Cu to H2 plays a key role in the activation,breaking of the H-H bond and the formation of the Cu-H bonds.At around the critical height of bond breaking,two stationary states are identified,which correspond respectively to the molecular and dissociative state.Using the transfer matrix method(TMM),we are able to study the role of quantum tunneling in the dissociation process along the minimum energy pathway(MEP),which is found to be significant at room temperature and below.At given temperatures,the tunneling contributions from the translational and vibrational motions of H2 are quantified for the dissociation process.Within a wide range of temperatures,our work reveals the effects of quantum tunneling on the effective barriers of dissociation and the rate constants.The deduced energetic parameters associated with thermal equilibrium and non-equilibrium(molecular beam)conditions are comparable with experimental data.In the low-temperature region,the transition region from classical-dominated to quantum-dominated is identified.Based on first-principles calculations,we have further investigated the adsorption and diffusion of individual hydrogen atoms on Cu(001).After considering the zero-point energy(ZPE)correction,the originally identical barriers are shown to be different for H and D,which are respectively calculated to be～158 meV and～139 meV in height.Based on the transfer matrix method(TMM),we are able to calculate the accurate probability of transmission across the barriers.The crucial role of quantum tunneling is clearly demonstrated at low-temperature region.By introducing a temperature-dependent attempting frequency prefactor,the rate constants and diffusion coefficients are calculated.The results are in agreement with the experimental measurements at temperatures from～50 K to 80 K.