Nanoparticles have a large impact in multiple scientific fields mainly due to i) their large specific surface area and ii) the possibility of tuning the electronic structure of the material by modifying its size and shape. This has been particularly relevant in the field of catalysis with precious transition metals. To characterize the nanoparticle catalytic properties several experimental and computational techniques have been developed. Most of the computational efforts devoted to understand the catalytic activity of nanoparticles, however, employ extended surfaces to represent the material. Indeed, to the best of our knowledge, few examples of reactions catalyzed by metal oxide nanoparticles have been studied by using nanoparticles models. This limits the exploration of particular sites only present in the nanoparticle surfaces and thus, the use of more realistic models is desirable. One of the bottlenecks in the use of realistic nanoparticle models is the fact that model construction is not straightforward, particularly for multicomponent materials such as transition metal oxides._x000D_ _x000D_ _x000D_ _x000D_ This thesis has two main parts. Firstly, we develop a computational tool able to construct nanoparticle models for multicomponent compounds with controlled stoichiometry and surface termination in an automatized manner, which removes human subjectivity and bias. Secondly, we use slab and nanoparticle models to evaluate the key factors that determine the water adsorption and the catalytic performance of IrO2 for the oxygen evolution reaction (OER) by using DFT simulations. The OER performance of IrO2 has been explored through the water nucleophilic attack (WNA) and oxo-coupling (I2M) mechanisms for both surfaces and nanoparticle models._x000D_ _x000D_ _x000D_ _x000D_ We have found that the water dissociation is controlled by the intrinsic material properties like the Ir acidity, the Obr basicity, the nature of the vacant site and the cooperative effects between adsorbed water molecules. Concerning the OER mechanism, our results suggest that both the WNA and the I2M mechanisms require radical intermediates to be feasible. Moreover, the WNA mechanism seems to be the most favorable for almost all studied sites on surfaces and nanoparticles. Indeed, the I2M mechanism only seems to be the preferred one on the (011) surface, were the oxyl character of O atoms on the surface is larger and the interatomic distance between the oxyl groups is rather short. Furthermore, and quite remarkably, the tip site of the nanoparticle exhibits an OER potential that is only slightly larger than the ideal one, thereby suggesting that tetracoordinated sites should be explored to improve the catalytic performance of IrO2 for the OER.
Automatized Nanoparticle Models Generation and Application to the Oxygen Evolution Reaction Catalyzed by IrO2. Slab vs Nanoparticle Models.
GONZALEZ FORERO, D. (Author). 17 Dec 2020
Student thesis: Doctoral thesis
Student thesis: Doctoral thesis