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In dieser Dissertation wurden strukturelle Informationen (Größe und Form) und der chemische Zustand der hergestellten Katalysatoren mittels verschiedener oberflächenwissenschaftlicher Mikroskopie- und Spektroskopietechniken einschließlich AFM, SEM, TEM und XPS untersucht. Die \(\it In-situ\)- und \(\textit Operando\)-Charakterisierung zeigte Einblicke in den dynamischen katalytischen Mechanismus und in Parameter, die die Reaktivität und Lebensdauer der Katalysatoren beeinflussen. Meine Arbeit diskutiert die Rolle von niedrig-koordinierten Plätzen, Oberflächenrauhigkeit und dem Vorhandensein von kationischen Metallspezies in der elektrokatalytischen Leistung. Mit diesen grundlegenden Einsichten liefert diese Dissertation wertvolle Informationen darüber, wie stabile und effiziente Elektrokatalysatoren entworfen werden können., In this dissertation, I synthesized electrocatalysts for 2-propanol oxidation and CO\(_2\) electro-reduction in order to tune activity and selectivity via inverse micelle encapsulation leading to well-dispersed Au nanoparticles and pre-plasma treatments of Ag surface, respectively. Structural information (size and shape) and chemical state of the prepared catalysts were investigated via a variety of surface science microscopy and spectroscopy techniques including AFM, SEM, TEM and XPS. The \(\textit {in situ}\) and \(\it operando\) characterization showed insights on dynamic catalytic mechanism and the parameters influencing reactivity and lifetime of the catalysts. My work discusses the role of low-coordinated site, surface roughness and the presence of metal cationic species in electrocatalytic performance. With these fundamental insights, this dissertation provides valuable information on how to design stable and efficient electrocatalysts.

Journal of the American Chemical Society 141(13), 5261 - 5266 (2019). doi:10.1021/jacs.8b12766, CO$_2$ electroreduction into useful chemicals and fuels is a promising technology that might be used to minimize the impact that the increasing industrial CO2 emissions are having on the environment. Although plasma-oxidized silver surfaces were found to display a considerably decreased overpotential for the production of CO, the hydrogen evolution reaction (HER), a competing reaction against CO$_2$ reduction, was found to increase over time. More stable and C1-product-selective SnO$_x$/AgO$_x$ catalysts were obtained by electrodepositing Sn on O$_2$-plasma-pretreated Ag surfaces. In particular, a strong suppression of HER (below 5% Faradaic efficiency (FE) at −0.8 V vs the reversible hydrogen electrode, RHE) during 20 h was observed. Ex situ scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDS), quasi in situ X-ray photoelectron spectroscopy (XPS), and operando X-ray absorption near-edge structure spectroscopy (XANES) measurements showed that our synthesis led to a highly roughened surface containing stable Sn$^{δ+}$/Sn species that were found to be key in the enhanced activity and stable CO/formate (HCOO$^–$) selectivity. Our study highlights the importance of roughness, composition, and chemical state effects in CO$_2$ electrocatalysis., Published by American Chemical Society, Washington, DC

Two-dimensional molybdenum-disulfide (MoS₂) catalysts can achieve high catalytic activity for the hydrogen evolution reaction upon appropriate modification of their surface. The intrinsic inertness of the compound's basal planes can be overcome by either increasing the number of catalytically active edge sites or by enhancing the activity of the basal planes via a controlled creation of sulfur vacancies. Here, we report a novel method of activating the MoS₂ surface using swift heavy ion irradiation. The creation of nanometer-scale structures by an ion beam, in combination with the partial sulfur depletion of the basal planes, leads to a large increase of the number of low-coordinated Mo atoms, which can form bonds with adsorbing species. This results in a decreased onset potential for hydrogen evolution, as well as in a significant enhancement of the electrochemical current density by over 160% as compared to an identical but non-irradiated MoS₂ surface.