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

Sammanfattning

While the oxygen reduction reaction is a technologically important and widely studiedreaction, the origin of the onset overpotential remains debated. This studyaims to elucidate the reaction mechanism and the rate-determining step by kineticMonte Carlo simulations based on first-principles calculations. It is found that theoverpotential is determined by a potential dependent coverage of oxygen species(∗O, ∗OH, ∗H2O) that block O2 adsorption. The coverage is largely determinedby adsorbate-adsorbate interactions. Therefore, the origin of these interactions arestudied extensively. A model is proposed and implemented in the kinetic MonteCarlo simulations based on d-band shifts of surface atoms and hydrogen bondinginteractions. Additionally, attention is given to the effect of an aqueous environmenton the adsorbent by employing ab-initio molecular dynamics simulations. Theeffect of strain, particle size and shape is investigated and particles are optimizedusing Bayesian optimization. It is shown that particles with sizes between 3 and6 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 strainreduces activity. Effects of experimentally determined site-specific strain and grainboundaries are explored, which further improve the activity of the catalyst. Subsequently,the limits of the activity is explored by generating kinetic volcano plotsfrom the kinetic Monte Carlo simulations. Following that, the model is generalizedto metal alloys, showing how strong interactions between Ag clusters and Ptclusters in AgxPt1–x binary surface alloys can improve catalyst activity. Finally, aframework is presented to simulate linear sweep voltammetries, which can be readilycompared with experimental data. Overall, this thesis underscores the significanceof interaction effects in accurately describing experimental conditions and introducesa first-principles method for catalyst exploration.