ab initio insights into hydrogen UPTAKE AND EVOLUTION ON electrified solid/liquid interfaces

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Development of an ab initio\textit {ab initio} computational potentiostat and its application to the study of Mg corrosion

First-Principles-Modellierung unter Verwendung der Dichtefunktionaltheorie ist ein leistungsfähiges Werkzeug zur Untersuchung atomistischer Reaktionen an elektrochemischen Fest-/Flüssig Grenzflächen, die allein auf Grund von Experimenten schwer zu verstehen sind. Unter Anwendung von Konzepten der Halbleiterphysik wird ein neues $\textit {Ab initio}$-Potentiostat-Schema für die Simulation elektrochemischer Grenzflächen, unter Einfluss einer angelegten Spannung, mittels Dichtefunktionstheorie entwickelt. Mit diesem Potentiostat-Schema werden Reaktionen an anodisch polarisierten Mg/H$_2$O-Grenzflächen untersucht. Diese Studien ermöglichen es einen bisher unbekannten Reaktionsmechanismus, für die anomale Wasserstoffentwicklungsreaktion die an korrodierenden Mg-Oberflächen beobachtet wird, zu identifizieren. Ferner, wird der Mechanismus der Metallauflösung und die Rolle der dissoziativen Adsorption von Wasser an der Grenzfläche in diesem Prozess erläutert.First-principles modelling using density functional theory is a powerful tool to study atomistic reactions at solid-liquid electrochemical interfaces which are difficult to elucidate from experiments alone. Using concepts of semiconductor physics, a novel $\textit {ab initio}$ potentiostat scheme is developed for density functional theory simulations of electrochemical interfaces under the influence of applied potential bias. This potentiostat scheme is used to study reactions that take place at Mg/H$_2$O interfaces under anodic polarization. From these studies, a previously unknown reaction mechanism for the anomalous hydrogen evolution reaction observed at corroding Mg surfaces is identified. Further, the mechanism of metal dissolution and the role of dissociative adsorption of water at the interface in this process is elucidated

Laterally Resolved Free Energy Profiles and Vibrational Spectra of Chemisorbed H Atoms on Pt(111)

A scheme to compute laterally resolved free energy surfaces and spectral signatures of specifically adsorbed ions on electrode surfaces from their ab initio molecular dynamics (AIMD) trajectories is proposed. Considering H-covered Pt(111) electrodes, both in contact with water and vacuum and for various H coverages, we systematically explore the impact of explicit water and H-coverage on site occupancy, providing direct insight into the proportion of underpotential and overpotential deposited hydrogen adsorbates. Extending this approach further, we can obtain laterally resolved vibrational spectra of the Pt–H stretch modes. We discuss how the difference between the free energy basins of the on-top and fcc-hollow adsorption sites explains the features of the experimentally observed spectral fingerprints in this system. These fingerprints do not contain only information about the stable and metastable adsorption sites but also about intermediate short-lived adsorbate configurations. Our results also show that for these properties chemisorbed H2O acts as a spectator and does not qualitatively influence the relative stabilities of the adsorption sites and their spectral fingerprints