Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.731631
Title: Simulating electric double layers at transition metal-water interfaces from density functional theory based molecular dynamics
Author: Le, Jiabo
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2017
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Abstract:
This PhD project aims at understanding the electric double layers (EDLs) at transition metal-water interfaces with density functional theory based molecular dynamics (DFTMD). We plan to develop a method for computationally determining the electrode potential of an interface, which bridges experiments and theoretical computation. After that, we will investigate the microscopic structure of the EDLs, including ion distribution, water orientation, hydrogen bonding and so on. Furthermore, we are interested in the charge transfer between metal surface and water at different configurations, and some consequences this may lead to. In the first part, we have simulated Pt(111)-, Au(111)-, Pd(111)- and Ag(111)-water interfaces at a well-defined condition, potential of zero charge (PZC), by DFTMD. We find the water coverage of the metal surface is ⇠0.8ML, and there is no ordered pattern formed at room temperature. Moreover, we have characterised three configurations (watA, watB-down and watB-up) from the surface water layer, and revealed their hydrogen bonding networks. In the second part, we have developed a computationally efficient scheme for determining the electrode potential of the metal-water interfaces with respect to standard hydrogen electrode (SHE), and obtained the PZC values of Pt(111), Au(111), Pd(111) and Ag(111)-water interfaces within a good accuracy. Furthermore, we find that the interface dipole potentials are almost entirely caused by charge transfer from water and to the metal surfaces, the magnitude of which depends on the bonding strength between water and the metals, while water orientation hardly contributes at the PZC condition. In the third part, we have calculated the vibrational spectrum of the chemisorbed water on Pt(111) and Au(111), and found their peak positions of the stretch vibrational frequency are red-shifted, the magnitude of which is dependent to the strength of the metal-water interaction and the local hydrogen bonding. We have also suggested that the chemisorbed water is the source of the peaks at 2850-3000 cm-1 observed in experiments. In the last part, we have simulated a series of EDLs at Au(111)-water interfaces, their reliability is confirmed by comparing the differential capacitance with experimental values. We find the Stern layer gets compressed and the partial solvation layer of the ion is peeled off at a negatively charged surface. Moreover, we find the configuration of the interfacial water is reoriented from 'parallel water', to 'H-downwater', then further to 'perpendicular water' when the metal surface is progressively charged with electrons.
Supervisor: Not available Sponsor: University of Aberdeen
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.731631  DOI: Not available
Keywords: Interfaces (Physical sciences) ; Molecular dynamics ; Ion exchange
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