The Development and Stability of Palladium-based Thin Films for Hydrogen-related Energy Applications

Hydrogen has been contemplated as a desirable energy source of the future with enormous possibilities to create a carbon-neutral society. Since palladium (Pd) readily absorbs hydrogen even at low pressure and room temperature, Pd and its alloys are suitable for hydrogen production, purification, storage, gas sensors, and fuel cell catalyst. However, primary requirements for industrial applications are not always satisfied, such as usability under operation conditions, minimum capital cost, and sustained hydrogen embrittlement. Therefore, developing stable Pd-based thin films to investigate correlations between microstructural features and mechanical properties of a material is of great importance for many hydrogen-related technologies.In this thesis particular interest has been focused on the stability of a series of magnetron sputtered Pd thin films of different nanostructures i.e., non-voided compact and nano-voided open columnar morphology. The X-ray diffraction (XRD) analysis methods are advanced, utilizing the tailored microstructures of the Pd films suitable to investigate the interplay between microstructure and hydrogenation properties of Pd-based thin films. Interpretation of the stress state and microstructural changes during hydrogen cycling are studied utilizing XRD line-profile analysis and the deformation mechanisms are systematically discussed. The change in dislocation density by the generation and annihilation of dislocations at interfaces reflects the difference in film-substrate interaction. The insertion of an intermediate layer between the Pd film and a rigid substrate can prevent buckle-delamination that is caused by the large volume expansion due to hydrogen absorption but it also changes the hydrogen absorption performance. The different effects on the absorption properties in the case of compliant (polyimide) and rigid (titanium) intermediate layers are illustrated. The results of this work showed that the strong clamping usually suppresses or reduces hydrogen absorption, whereas, the flexible layer enhances the lifetime of Pd thin films when exposed to prolonged hydrogen during cycling. The research in this thesis deepens the understanding about an appropriate combination of film microstructure and choice of the intermediate layer to strengthen Pd-based thin films.Team Amarante Bottge

Does the sun shine for all? Revealing socio-spatial inequalities in the transition to solar energy in The Hague, The Netherlands

With technological advances and decreasing prices, solar energy is a key technology in the urban energy transition. However, the focus on increasing the overall installed capacity has overshadowed energy justice considerations, leading to inequalities in solar energy adoption. This paper adopts an equity perspective to analyse the transition to solar (photovoltaic) energy in the city of The Hague, The Netherlands. Access to solar energy is at the core of the research, encapsulating factors that influence the ability of a household to adopt solar energy. Through a socio-spatial analysis at the postcode level, we identify four distinct groups with varying levels of access to solar energy. Our results show that these groups are not only strongly segregated across the city but also overlap with existing socio-spatial inequalities. The four levels of access to solar energy are then compared to current solar adoption rates and technical rooftop energy potential in the city. Results show that decreasing levels of access to solar energy align with decreasing adoption rates, revealing that current policies fail to provide equitable access to solar energy leading to inequalities in adoption rates. Furthermore, we show that most of the technical potential available in The Hague is in areas where access to solar energy is limited, representing opportunities to exploit a significant amount of untapped technical potential while addressing existing socio-spatial inequalities. Here, we also identify two groups of interest and related leverage points for future policy interventions to address equity in the transition to solar energy in The Hague.Policy AnalysisEthics & Philosophy of TechnologySpatial Planning and Strateg

The role of the substrate on the mechanical and thermal stability of Pd thin films during hydrogen (de)sorption

In this work, we studied the mechanical and thermal stability of ~100 nm Pd thin films magnetron sputter deposited on a bare oxidized Si(100) wafer, a sputtered Titanium (Ti) intermediate layer, and a spin-coated Polyimide (PI) intermediate layer. The dependence of the film stability on the film morphology and the film-substrate interaction was investigated. It was shown that a columnar morphology with elongated voids at part of the grain boundaries is resistant to embrittlement induced by the hydride formation (α↔β phase transitions). For compact film morphology, depending on the rigidity of the intermediate layer and the adherence to the substrate, complete transformation (Pd-PI-SiO2/Si) or partly suppression (Pd-Ti-SiO2/Si) of the α to β-phase was observed. In the case of Pd without intermediate layer (Pd-SiO2/Si), buckling delamination occurred. The damage and deformation mechanisms could be understood by the analysis of the stresses and dislocation (defects) behavior near grain boundaries and the film-substrate interface. From diffraction line-broadening combined with microscopy analysis, we showed that in Pd thin films, stresses relax at critical stress values via different relaxation pathways depending on film-microstructure and film-substrate interaction. On the basis of the in-situ hydriding experiments, it was concluded that a Pd film on a flexible PI intermediate layer exhibits free-standing film-like behavior besides being strongly clamped on a stiff SiO2/Si substrate.Team Amarante BottgerQN/Afdelingsburea

Effectiveness of trip planner data in predicting short-term bus ridership

Predictions on Public Transport (PT) ridership are beneficial as they allow for sufficient and cost-efficient deployment of vehicles. On an operational level, this relates to short-term predictions with lead times of less than an hour. Where conventional data sources on ridership, such as Automatic Fare Collection (AFC) data, may have longer lag times and contain no travel intentions, in contrast, trip planner data are often available in (near) real-time and are used before traveling. In this paper, we investigate how such data from a trip planner app can be utilized for short-term bus ridership predictions. This is combined with AFC data (in this case smart card data) to construct a ground truth on actual ridership. Using informative variables from the trip planner dataset through correlation analysis, we develop 3 supervised Machine Learning (ML) models, including k-nearest neighbors, random forest, and gradient boosting. The best-performing model relies on random forest regression with trip planner requests. Compared with the baseline model that depends on the weekly trend, it reduces the mean absolute error by approximately half. Moreover, using the same model with and without trip planner data, we prove the usefulness of trip planner data by an improved mean absolute error of 8.9% and 21.7% and an increased coefficient of determination from a 5-fold cross-validation of 7.8% and 18.5% for two case study lines, respectively. Lastly, we show that this model performance is maintained even for the trip planner requests with prediction lead times up to 30 min ahead, and for different periods of the day. We expect our methodology to be useful for PT operators to elevate their daily operations and level of service as well as for trip planner companies to facilitate passenger replanning, in particular during peak hours.Transport and PlanningPolicy Analysi

Dislocations, texture and stress development in hydrogen-cycled Pd thin films: An in-situ X-ray diffraction study

For Pd thin films, microstructural changes involved during hydrogen cycling provide the information needed to predict and optimize the film's mechanical strength. In this paper, a systematic study of the morphology, microstructure, texture, and stress has been performed on Pd thin films during hydrogen loading and deloading cycles at room temperature. Pd thin films of similar morphology were prepared by magnetron sputtering on substrates of different compliances, i.e., Si-oxide, Titanium (Ti) and Polyimide (PI). The evolution of the morphology, grain-orientation distribution (texture), state of stress, and dislocation densities are analyzed for each of the film substrate types for 20 hydrogen loading/deloading cycles. The lattice expansion and contraction caused by the transition from Pd to Pd-hydride and back result in a strong stress increase. This stress increase stabilizes after a few cycles by grain boundary motion that leads to a gradual enhancement of the (111) texture and changes in the dislocation density for Pd films that are strongly clamped on to an oxidized Si(100) wafer substrate with an intermediate layer (Ti or PI). For Pd on PI, the stress is also partly released by a crack-based (crack widening/growth/propagation) pathway. Pd films on Ti and PI do not buckle or blister after 20 hydrogen cycles. By providing a sufficiently compliant substrate the traditional problems of buckle-delamination of a film on a stiff substrate are mitigated.Team Amarante Bottge

Heterogeneous impact of a lockdown on inter-municipality mobility

Without a vaccine, the fight against the spreading of the coronavirus has focused on maintaining physical distance. To study the impact of such measures on inter-municipality traffic, we analyze a mobile dataset with the daily flow of people in Portugal in March and April 2020. We find that the reduction in inter-municipality traffic depends strongly on its initial outflow. In municipalities where the mobility is low, the outflow reduced by 10-20% and this decrease was independent of the population size. Whereas, for municipalities of high mobility, the reduction was a monotonic increasing function of the population size and it even exceeded 60% for the largest municipalities. As a consequence of such heterogeneities, there were significant structural changes on the most probable paths for the spreading of the virus, which must be considered when modeling the impact of control measures.Policy Analysi