Hydrogen fuel cells are expected to be pivotal in the energetic transition towards renewable energy sources such as solar and wind power. However, their industrial scalability is severely hindered... Show moreHydrogen fuel cells are expected to be pivotal in the energetic transition towards renewable energy sources such as solar and wind power. However, their industrial scalability is severely hindered by the high cost and degradation rate of platinum catalysts, one of their key components. Addressing this challenge necessitates developing better catalysts, which requires a better fundamental understanding of their reactivity and degradation mechanism. In this thesis, we investigate the (in)stability of model platinum surfaces submerged in liquid and under applied voltage, thus simulating the operational conditions of fuel cells. For this we use a home-build Electrochemical Scanning Tunneling Microscope (EC-STM), which allows us to observe, in real time, the surface structure at the atomic scale. Our findings elucidate the origin of the platinum surface roughening that takes place upon voltage cycling. Moreover, we demonstrate that closely-spaced atomic steps are prone to bunch together, resulting in steps with multi-atomic height. This structural change has a significant effect on the catalyst reactivity, as we explain in detail. Overall, this dissertation contributes to a deeper fundamental understanding of the surface processes that drive platinum surface restructuring as well as their implications for reactivity. Show less
Chronic obstructive pulmonary disease (COPD) is a chronic lung disease, characterised by inflammation and destruction of the airways. There are no curative options yet. However, COPD is a... Show moreChronic obstructive pulmonary disease (COPD) is a chronic lung disease, characterised by inflammation and destruction of the airways. There are no curative options yet. However, COPD is a treatable disease, whereby reduction of symptoms is a major treatment goal. In this thesis, we focussed on morning symptoms. The relation between morning symptoms and physical activity was studied in search of novel treatment options. We concluded in a systematic review that there was a negative association between morning symptoms and self-reported physical activity. We confirmed this association in the MOrning symptoms in-Depth observationAl Study (MODAS), an observational cross-sectional study, in which we objectively measured physical activity. We also found that patients with high morning symptom scores took fewer steps in morning and afternoon than those with low morning symptom scores, but not during evening and night. These factors can be used as targets in future interventional studies. A subsequent real life study showed that participating physicians recorded more symptoms and lifestyle advises when a designated approach was used. To pay more attention to morning symptoms and physical activity in clinical practice, we encourage the use of a systematic approach that includes these items. Show less
Today, the energy sector is highly dependent on heterogeneous catalysis because a future solution to end our dependency on natural sources lies in generating hydrogen by splitting water. Several... Show moreToday, the energy sector is highly dependent on heterogeneous catalysis because a future solution to end our dependency on natural sources lies in generating hydrogen by splitting water. Several transition metals, such as Pt, are known to be good catalyst materials for water splitting reactions. They play a key role in understanding the fundamental aspects of the elementary interactions occurring on the surfaces of catalysts. These surfaces, however, are generally very complex and contain a wide distribution of structurally and chemically different sites with different activities. One of the key issues in optimizing the activity of the catalysts is to distinguish and specify the active sites on the surface. In this thesis we use highly corrugated Pt surfaces and UHV techniques (TPD, LEED, and STM) to explore the effects of surface defects on adsorption and desorption of water and related adsorbates. We elucidate to what extent the substrate type influences the structure of interfacial water both in the monolayer and thin film regime. Our studies also show that step geometry is the determining factor in low temperature oxygen dissociation. Show less
