| Despite its apparent simplicity, the interface between high purity water and a metal electrode is considerably complex. The following work presents the development and application of a model that captures much of this using a first-principles approach that models the electrode as a semi-infinite metallic surface, and the solution phase as a condensed phase ensemble of structures derived from ab initio molecular dynamics. By modeling one such ensemble of water over two model electrode surfaces, Cu and Ni(111), the electrochemical activation of water was described, leading to the elucidation of the structure and thermodynamics of not only interfacial water, but also hydroxyl, oxygen and hydrogen. Formation of an oxygen-covered surface was demonstrated to be synchronous with early stages of metal dissolution. Surface Pourbaix diagrams were then derived for temperatures 300 and 600 K.; Using molecular dynamics, a number of water ensembles over the Cu(111) surface were generated to describe the time and ensemble averaged potential of zero charge for Cu(111)/H2O. Both randomization of the zero Kelvin arrangement of water and the dissociation of a water molecule into surface hydroxgen and oxygen species were observed, raising the potential of zero charge from -3.0 V NHE in the symmetric ice-Ih type configuration to +0.5 V NHE in randomized water. Further time steps would be required to fully equilibrate the liquid.; The approximate methodology used to calculate electrode potentials at interfaces is tested against higher fidelity methods, and the ability to model interfacial water using a small number of static ensembles via a consideration of mono- and bi-layer models for water over Cu(111) and Ni(111) is examined. The model used to generate electrode potentials is sufficient, as dependent on model choices, such as water ensemble states and simulation dimensions. Certain orientations for water are favorable over the (111) surfaces studied and can be modeled as ice-like 'bilayers'.; It is also demonstrated that significant challenges remain for the inclusion of ions and the determination of electrochemical kinetics, using the current first principles paradigm. Positive results for the modeling of non-ideal surface features and adsorbates such as under-potential deposition products are obtained. |
