In this thesis, we consider various (electro)chemical phenomena at surfaces and nanoparticles and their underlying atomistic processes, which we studied using first-principles methods such as... Show moreIn this thesis, we consider various (electro)chemical phenomena at surfaces and nanoparticles and their underlying atomistic processes, which we studied using first-principles methods such as density functional theory. These phenomena range from CO2 reduction to C2 and C3 species, through solvation of adsorbates on various surface features of late transition metals, to the impact of graphene on hydrogen evolution reaction, cathodic corrosion and surface oxidation of Pt. With our thermodynamic and kinetic calculations, we provide explanations for experimental observations by unraveling underlying phenomena, support novel computational methods and techniques, and propose new atomic structures that explain prior findings and provide inroads into future electrocatalytic research. Show less
Metals surfaces form a group of effective catalysts for the reaction of small molecules such as hydrogen (H2). In order to improve the predictive power of theory with respect to the catalytic... Show moreMetals surfaces form a group of effective catalysts for the reaction of small molecules such as hydrogen (H2). In order to improve the predictive power of theory with respect to the catalytic activity of small molecules reacting at metal surfaces, the way in which metal surfaces modify the potential energy of molecules needs to be understood at a fundamental level. Currently density functional theory (DFT) is the only electronic structure method that is accurate enough to achieve chemical accuracy while being cheap enough to make large comparative studies feasible. The work in this thesis is concerned with the creation of highly accurate density functionals that can give a simultaneously good description of the metal surface, the molecule, and the molecule interacting with the metal surface, as well as the description and simulation of supersonic molecular beam experiments and associative desorption experiments needed to validate the obtained results. Show less
This research was about to better understanding of heterogeneous catalyzed processes which would help to design better and more efficient catalysts but it is hard to achieve because of their high... Show moreThis research was about to better understanding of heterogeneous catalyzed processes which would help to design better and more efficient catalysts but it is hard to achieve because of their high level of complexity. In this way, we compared molecular beam experiments with molecular dynamics simulations to improve over the theoretical method used, called density functional theory (DFT), to achieve chemical accuracy (i.e., errors smaller than 1 kcal/mol) for the reaction studied. Show less
Sodium alanate (NaAlH4) is a prototype system for storage of hydrogen in chemical form. However, a key experimental finding, that early transition metals (TMs) like Ti, Zr, and Sc are good... Show moreSodium alanate (NaAlH4) is a prototype system for storage of hydrogen in chemical form. However, a key experimental finding, that early transition metals (TMs) like Ti, Zr, and Sc are good catalysts for hydrogen release and re-uptake, while traditional hydrogenation catalysts like Pd and Pt are poor catalysts for NaAlH4, has so far gone unexplained. We have performed density functional theory calculations at the PW91 generalised gradient approximation level on Ti, Zr, Sc, Pd, and Pt interacting with the (001) surface of nanocrystalline NaAlH4, employing a cluster model of the complex metal hydride. A key difference between Ti, Zr, and Sc on the one hand, and Pd and Pt on the other hand is that exchange of the early TM atoms with a surface Na ion, whereby Na is pushed on to the surface, is energetically preferred over surface absorption in an interstitial site, as found for Pd and Pt. The theoretical findings are consistent with a crucial feature of the TM catalyst being that it can be transported with the reaction boundary as it moves into the bulk, enabling the starting material to react away while the catalyst eats its way into the bulk, and effecting a phase separation between a Na-rich and a Al-rich phase. In addition, the role of different active species such as Ti2 and TiH2 has been studied using the same model. The results imply that Ti2 and TiH2 are more stable in the subsurface region of the cluster than on the surface. Calculations were performed on the decomposition of two calcium alanates, to determine zero-point energy corrected enthalpies of dehydrogenation for these compounds, and to determine whether destabilization of LiBH4 by CaH2 might improve the performance of this material. Show less
