Study of the oxygen reduction reaction by kinetic Monte Carlo simulations from first-principles

Typ
Examensarbete för masterexamen
Master's Thesis
Program
Övrigt, MSc
Physics (MPPHS), MSc
Publicerad
2024
Författare
Vanmoerkerke, Willem
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Sammanfattning
While the oxygen reduction reaction is a technologically important and widely studied reaction, the origin of the onset overpotential remains debated. This study aims to elucidate the reaction mechanism and the rate-determining step by kinetic Monte Carlo simulations based on first-principles calculations. It is found that the overpotential is determined by a potential dependent coverage of oxygen species (∗O, ∗OH, ∗H2O) that block O2 adsorption. The coverage is largely determined by adsorbate-adsorbate interactions. Therefore, the origin of these interactions are studied extensively. A model is proposed and implemented in the kinetic Monte Carlo simulations based on d-band shifts of surface atoms and hydrogen bonding interactions. Additionally, attention is given to the effect of an aqueous environment on the adsorbent by employing ab-initio molecular dynamics simulations. The effect of strain, particle size and shape is investigated and particles are optimized using Bayesian optimization. It is shown that particles with sizes between 3 and 6 nm and a large proportion of (111) facets are optimal for the reaction. Furthermore, compressive strains have a positive effect on the activity, while tensile strain reduces activity. Effects of experimentally determined site-specific strain and grain boundaries are explored, which further improve the activity of the catalyst. Subsequently, the limits of the activity is explored by generating kinetic volcano plots from the kinetic Monte Carlo simulations. Following that, the model is generalized to metal alloys, showing how strong interactions between Ag clusters and Pt clusters in AgxPt1–x binary surface alloys can improve catalyst activity. Finally, a framework is presented to simulate linear sweep voltammetries, which can be readily compared with experimental data. Overall, this thesis underscores the significance of interaction effects in accurately describing experimental conditions and introduces a first-principles method for catalyst exploration.
Beskrivning
Ämne/nyckelord
Oxygen reduction reaction , fuel cell , computational catalysis , electrochemistry , platinum nanoparticles , adsorbate-adsorbate interactions , kinetic Monte Carlo , Density-functional Theory , Bayesian optimization
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