Physics and Chemistry of Electrified Interfaces

“pH effects” in electrocatalysis

Professor Karen Chan, Technical University of Denmark

Beyond surface reaction energetics, the structure and composition of the electric double layer exerts an influence on the activity and selectivity of electrochemical reactions. These phenomena often manifest themselves as so-called “pH effects”, which manifest as deviations in the dependence of activity from a potential vs. RHE scale.  In this talk, I first discuss the impact of the electrolyte on electrocatalytic activity from the perspective of the impact of the proton donor and adsorbate dipole-field interactions, as well as how cations and supported single site catalysts tune the latter. I then discuss the impact of solution phase reactions and mass transport on activity and selectivity. I draw examples from hydrogen evolution and electrochemical CO₂ reduction, and discuss the implications of fundamental mechanistic understanding on catalyst design.

Water metal interfaces by ab initio molecular dynamics

Dr Marcella Iannuzzi, University of Zurich, Switzerland

Condensed aqueous systems serve an important role in many scientific fields such as materials science, electrochemistry and nanotechnology. Many important reactions occur in aqueous phases or at aqueous solid interfaces. Understanding these processes may provide useful insights on improving the reactivity for electrodes and having better control of the electro-chemical reactions. The microscopic picture of the electrochemical interface is currently investigated by means of several spectroscopies, like IR and Raman, but also using X-ray probes. The goal is to reveal important aspects like the hydrogen bonding network, the distribution of ions, coverages and
adsorption species and sites. With the help of ab initio molecular dynamics (AIMD) simulations at the density functional level of theory, we characterize the water-metal interfaces under different conditions. In particular we investigate chemisorbed water at different metal surfaces, like Pt, Au, and Pd, showing the effects of the electronic redistribution. Other chemisorbed species and ions compete with the adsorption of water and play also a role in determining the properties of the
interface. We show that AIMD simulations provide fundamental insight and understanding on microscopic structures and processes at interfaces

A Microscopic Interpretation of Pump–Probe Vibrational Spectroscopy Using Ab Initio Molecular Dynamics

Professor Marialore Sulpizi, Johannes Gutenberg University Mainz, Germany.

Time-resolved pump–probe vibrational spectroscopy is a major tool to investigate structure and dynamics of liquids. As the most important and most investigated compound on earth, water has been subject of intense research by time-resolved vibrational experiments aiming to understand the structure and dynamics of its hydrogen bond network.

Using non-equilibrium molecular dynamics simulations, also including the full electronic structure, and novel descriptors, based on projected vibrational density of states, we are able to follow the flow of excess vibrational energy from the excited stretching and bending modes.

We find that in bulk the energy relaxation, mostly mediated by a stretching–stretching coupling in the first solvation shell, is highly heterogeneous and strongly depends on the local environment [1].

We also investigate the dynamics of water at the interfaces with vapor and with solid surfaces, where slow down or acceleration of the vibrational energy relaxation may be possible.

E.g. In the case of the water/ calcium fluoride interface [2], at low pH, localized charges can develop upon fluorite dissolution. We find that strongly oriented H‐bonded water molecules in the adsorbed layer, whose orientation is pinned by the localized charge defects, can exchange vibrational energy very rapidly due to the strong collective dipole, compensating for a partially missing solvation shell.

[1] Lesnicki D, and Sulpizi M, J. Phys. Chem. B 2018, 122, 25, 6604–6609.

[2] Lesnicki D, Zhang Z, Bonn M, Sulpizi M, Backus EHG, Angewandte Chemie International Edition 59 (31), 13116-13121.

Hydrogen at electrified solid/liquid interfaces – insights from ab initio
molecular dynamics simulations

Dr Mira Todorova, Max-Planck Institut, Germany

Solid/liquid interfaces are ubiquitous and at the heart of many processes of technological importance, such as electro-catalysis, fuel cells, corrosion and others. Understanding and quantifying the fundamental mechanisms underlying these processes will enable targeted design of desired properties, but is equally challenging to theoretical modelling and experimental characterisation.
Our recent developments of a novel potentiostat design [Surendralal et al., Phys. Rev. Lett. 120, 246801 (2018)] and a subsequent canonical thermos-potentiostat [Deißenbeck et al.Phys. Rev. Lett. 126, 136803 (2021)] approach enable us to study solid/liquid interfaces under realistic conditions of applied bias. We utilize these developments to study the interaction of H with metal electrodes using ab-initio molecular dynamics [Surendralal et al., Phys. Rev. Lett. 126, 166802 (2021)]. The study of the H/Pt/H2O system provides valuable insights into the role of the solvent on work function changes at metal/electrolyte interfaces. The applications of a bias to Mg/water interfaces allows us to elucidate the mechanism underlying the experimentally observed link between H-evolution under anodic conditions and Mg dissolution.