Dynamics of Electrified Interfaces and Hydrogen Evolution from Density Functional Theory

Julkaisun otsikon käännös: Dynamics of Electrified Interfaces and Hydrogen Evolution from Density Functional Theory

Rasmus Kronberg

Tutkimustuotos: Doctoral ThesisCollection of Articles

Abstrakti

Rational catalyst design is pivotal for a sustainable deployment of electrochemical energy conversion technologies. To this end, density functional theory (DFT)-based simulations are frequently applied to access atomistic information on composition and activity beyond experimental resolution. A rigorous atomic-scale modeling of electrocatalysts is, however, complicated by the intricate structure of electrified solid–liquid interfaces, which is decisively affected by factors including the electrode potential, the distribution of (non-)specifically adsorbed ions and solvent dynamics. Consequently, most computational efforts employ static water models or ignore the solvent altogether in favor of numerical efficiency. While such simplifications can be useful for inferring activity trends between consistently modeled systems, a holistic approach to simulating electrochemical environments was taken in this thesis to further a comprehensive understanding of electrocatalysis. Focusing on the influence of molecular dynamics (MD) on the hydrogen evolution reaction (HER), DFT-MD simulations were performed to establish the effects of a variable hydrogen coverage on the structure and dynamics of a Pt(111)–water interface. An increasing hydrogen coverage was ob-served to displace co-adsorbed water molecules, thus accelerating solvent dynamics. The preferential site distribution of the hydrogen adlayer was discovered to concomitantly evolve from a mobile mixture of top and hollow occupations to a stationary top-exclusive monolayer. On the other hand, separate simulations of the dynamics of H+ and OH– within rigid interfacial water suggested that facile solvent reorganization might not be crucial for efficient HER. Although repulsion of OH– from the immediate vicinity of the surface was observed due to hindered hypercoordination, both ions displayed an overall surface propensity and low interfacial proton transfer barriers despite sluggish water dynamics, an effect enabled by the anomalous Grotthuss diffusion of water self-ions. Constrained DFT-MD simulation of the HER was conducted as a careful benchmark for methods relying on static solvent models and saddle point search algorithms. A numerically light carbon nanotube test system was initially employed to efficiently gauge the performance of trial reaction coordinates. Distance difference-based constraints were deemed suitable for steering the HER in a controlled, yet sufficiently indirect manner to preserve fast degrees of freedom of the system. Subsequent thermodynamic integration of the HER on Pt(111) revealed a marked decrease of the rate-limiting Tafel free energy barrier with increasing coverage. This was argued to follow from a decreased entropic barrier for desorption caused by quenched adlayer dynamics. The blue moon ensemble method with capacitive constant potential corrections was found to be advantageous for avoiding biased results due to ambiguous solvent structure choices, while improving the slow con-vergence of the electrode potential and modeling of grand canonical conditions were identified as important avenues for future research.
Julkaisun otsikon käännösDynamics of Electrified Interfaces and Hydrogen Evolution from Density Functional Theory
AlkuperäiskieliEnglanti
PätevyysTohtorintutkinto
Myöntävä instituutio
  • Aalto-yliopisto
Valvoja/neuvonantaja
  • Laasonen, Kari, Vastuuprofessori
  • Laasonen, Kari, Ohjaaja
Kustantaja
Painoksen ISBN978-952-64-1010-4
Sähköinen ISBN978-952-64-1011-1
TilaJulkaistu - 2022
OKM-julkaisutyyppiG5 Artikkeliväitöskirja

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