First-Principles Modeling of Solid-Liquid Interfaces and Electrocatalysis

Hörmann Group

 

Our group investigates electrochemical energy conversion at electrified solid–liquid interfaces using first-principles electronic-structure methods. We aim to understand how applied potentials, interfacial water, electrolyte composition, and surface chemistry influence thermodynamics, kinetics, and macroscopic observable behavior. To achieve this, we combine density functional theory with thermodynamics, statistical mechanics, molecular simulations, and increasingly machine learning. Our goal is to build predictive, physically consistent descriptions of interface structure, energetics, and reactivity under realistic electrochemical conditions.

Constant-Potential Electrochemical Thermodynamics and Kinetics

A central focus of our work is the rigorous description of electrochemical systems under applied potentials, leveraging DFT simulations interfaced with electrochemical environments using implicit solvent models. Such models allow the explicit application of a potential in mixed atomistic–continuum simulations and the study of interfacial energetics within an electronically grand canonical, constant potential ensemble.

Building on this theoretical basis, we developed perturbative, Taylor-expanded approaches that efficiently predict potential-dependent adsorption energies and reaction barriers without performing explicit simulations for every charge or potential of interest. This methodology explains pH and electrolyte concentration effects, for example for underpotential deposited hydrogen or experimental cyclic voltammograms and enables rational analysis of electrochemical driving forces in constant potential or in constant charge simulations.

Metal–Water Interfaces Beyond Implicit Solvation

While implicit solvation models provide efficient access to electrochemical systems, many interfacial phenomena require explicit solvent descriptions. A major focus of our work is therefore the microscopic characterization of interfacial water and its impact.

We showed that interfacial water competes directly with molecular adsorbates for surface sites and that the metal–water interaction strength—largely absent from continuum models—can determine adsorption stability and reactivity trends. Beyond these static effects, our explicit simulations revealed how the structure and response of the interfacial water layer govern key electrochemical observables such as capacitances. In particular, we identified interfacial water-layer reorientation, electronic polarization and electron spillover as central contributions to the capacitance of the Pt(111)/water interface, providing a microscopic basis for features long inaccessible to mean-field models.

Current work combines explicit–implicit simulations with machine learning to develop response-augmented machine learned interatomic potentials (RAZOR), that promise to enable nanosecond-scale molecular dynamics simulations of electrified interfaces under applied bias with first-principles accuracy.

Selected Publications

Selected recent publications are listed below (a full list can be found under Publications):

Machine Learning the Energetics of Electrified Solid-Liquid Interfaces, N. Bergmann, N. Bonnet, N. Marzari, K. Reuter, and N.G. Hörmann, Phys. Rev. Lett. (2025)

Grand canonical view on electrochemical energetics at applied potential in a nutshell, N. G. Hörmann, Curr. Opin. Electrochem. (2025) 

Electron Spillover into Water Layers: A Quantum Leap in Understanding Capacitance Behavior, L. Li, T. Eggert, K. Reuter, and N.G. Hörmann, J. Am. Chem. Soc. (2025)

Converging Divergent Paths: Constant Charge vs Constant Potential Energetics in Computational Electrochemistry, N.G. Hörmann, S.D. Beinlich, and K. Reuter,  J. Phys. Chem. C (2024)

Controlled Electrochemical Barrier Calculations without Potential Control, S.D. Beinlich, G. Kastlunger, K. Reuter, and N. G. Hörmann, J. Chem. Theory Comput. (2023) 

Thermodynamic Cyclic Voltammograms Based on Ab Initio Calculations: Ag(111) in Halide-Containing Solutions, N.G. Hörmann, and K. Reuter, JCTC (2021)

Electrosorption at metal surfaces from first principles, N.G. Hörmann, N. Marzari, and K. Reuter, npj Comput. Mater. (2020)

Grand canonical simulations of electrochemical interfaces in implicit solvation models, N.G. Hörmann, O. Andreussi, and N. Marzari, J. Chem. Phys.  (2019)

Phase field parameters for battery compounds from first-principles calculations, N.G. Hörmann, and A. Groß, Phys. Rev. Mater. (2019)