In recent years, there has been growing interest in the magnetocaloric effect (MCE) which is a magneto-thermodynamic phenomenon observed in certain magnetic materials. MCE materials undergo temperature changes when subjected to magnetic fields. Researchers are now exploring the possibilities of utilizing this material in biomedical application technologies, as they offer the potential for non-invasive control of their properties through external magnetic fields. However, there is a lack of research on suitable magnetic compositions that exhibit desired magnetic properties for medical purposes, while ensuring no adverse effects on the cells.

This master project explores the potential of a magnetocaloric (Mn,Fe)2(P,Si)-based compound as a biodegradable membrane for multi-cell separation in organ-on-chip platforms. Mn0.65Fe1.30Si0.37P0.65 compound was selected due to its sharp phase transition characteristics and tunable Curie temperature (Tc), which enable self-regulation of temperature within the therapeutic range, thus preventing potential damage to living cells. The synthesized Mn0.65Fe1.30Si0.37P0.65 compound exhibited a transition temperature of 316 K (43°C) with particle sizes ranging from 1-5 µm. A magnetocaloric wax-based composite was synthesized by integrating these particles with a wax component. Characterization under alternating magnetic fields (AMF) showed a significant temperature rise with higher magnetic concentrations and field amplitudes. At an applied AMF of 9 mT and a frequency of 244 kHz, a sample containing 15 vol.% magnetic particles stabilized at 44°C, effectively maintaining controlled temperatures within the therapeutic range (42-47°C) and efficiently melting the wax without harming living cells. Water absorption tests and SEM imaging further demonstrated the composite's low water permeability and minimal development of microcracks over time. These findings validate the potential of magnetocaloric materials with adjustable Curie temperatures for precise self-regulation of temperature in biomedical applications. The observed high heating efficiency and prevention of overheating offer promising opportunities for controlled thermal activation processes across various biomedical fields.

In this report, a model is presented to alleviate some of the computational work that goes into the effort of finding the magnetic properties of magnetocaloric materials. The model utilizes an interior point optimization routine to solve for the minimal exchange energy configuration of a system, given the exchange interactions of the material. The model is tested against four materials (Ni, MnO, Fe\textsubscript{2}P and Mn\textsubscript{2}Sb). For Ni and MnO, the exchange interactions are also computed. Three iterations of the model are compared. The base model, which only considers exchange interactions inside a chosen supercell, the base model with the inclusion of boundary conditions, and the base model with boundary conditions and the addition of an algorithm to find optimal solutions. \\ The algorithm analyzes the found results by the optimization routine, and if the result is considered not properly symmetric, runs the optimization routine another time, from a symmetrical starting point obtained from the outcome of the previous run. \\ In all versions of the model, effectiveness (percent of runs that resulted in the optimal configuration) and average run times were recorded. Three initialization methods for the model were used, and also tested for their effectiveness. For the algorithm, a parameter $\gamma$ is introduced that changes the size of some of the moments for the new starting points. Six different values for $\gamma$ were tested for their effectiveness against a test set of suboptimal solutions.
The model with the addition of boundary conditions and the algorithm performed the best out of the three iterations of the model, with an effectiveness of 99.895\%, and an average run time ranging from 0.62 s for 2$\times$2$\times$2 Ni, to 94.64 s for 3$\times$3$\times$3 Fe\textsubscript{2}P, in the case of $\gamma = 0.3$. To conclude, the model with the inclusion of the boundary conditions and the algorithm proves to be a robust method to evaluate the magnetic configuration of a material, especially for smaller systems.

Magnetocaloric heat pumps are those types of heat pumpswhich use a solidMagnetoCaloricMaterial (MCM) in place of a refrigerant to provide the work for the heat pump. MCMs are materials whose temperature changes on the application or removal of a magnetic field. This effect is known as the MagnetoCaloric Effect (MCE). Magnetocaloric heat pumps have the potential in replacing the conventional vapour compression technology for Dutch dwellings, since they have minimum environmental impact due to the absence of the coolant fluids that can harm the environment. A model of the regenerator of the magnetocaloric heat pump is developed in this project having in mind the application of this type of heat pumps to Dutch dwellings. The magnetic field that is used in the development of the model is 0.875 T, with permanent magnets being the source of the magnetic field. A sensitivity analysis is carried out in order to obtain the methods to optimize the regenerator for improving the performance of the heat pump. The performance of the heat pump is measured through its average cooling capacity, average heating capacity, temperature span and Coefficient of Performance (COP) for heating. TheMCM used for the regenerators is Gd with a totalmass of 1.18 kg. The parameter that influences the performance of the heat pump the most is the porosity of the regenerator. The heat losses through the casing have the least impact on the performance of the regenerator. The frequency of the cycle also has a profound impact on the heating capacity and cooling capacity up to temperature spans of around 18 K, but it does not have such an impact on the heating COP. After increasing the frequency, decreasing the particle diameter and decreasing the porosity, the heating capacity and the temperature span are optimized. For a temperature span of 15 K, the heating capacity is 164.2W, and for a temperature span of 20 K, the heating capacity is 99.1W.

Fischer-Tropsch synthesis (FTS) is a catalytic reaction, which involves the production of liquid hydrocarbon fuel from synthesis gas obtained from natural gas, biomass or coal via gasification and steam reforming. From an industrial perspective, both Co and Fe based catalysts have been applied. However, Co-based catalysts are preferred in FTS particularly for gas-to-liquid (GTL) processes as they have high activity, high selectivity to linear hydrocarbons and low activity for the unwanted water-gas shift reaction. However, Co-based catalysts are relatively expensive and deactivate in time. To make the FTS process economically more effective, a stable performance of the catalyst is required. Therefore, studying the catalyst deactivation is an important topic in the development of better industrial catalysts. Oxidation, sintering of active phase and deposition of oxygenated compounds are potential causes for deactivation. The possible role of oxygenates and their effect of catalyst deactivation, however, is less understood. With the aim to investigate the deposition of oxygenated compounds, particularly carboxylates, as hypothetical deactivation mechanism, operando characterisation techniques were adapted to monitor the chemical and physical properties and structure-activity relationship of the catalyst during the reaction. Operando Diffuse Reflectance Infrared Fourier Transform (DRIFT) and Mössbauer emission spectroscopy setups were employed that can be operated at industrially relevant FTS conditions.@en

With green energy well on its way to becoming a necessity rather than a commodity it is vital to not only focus on improving the source of energy, but also the efficiency of the eventual energy usage. Vapor-compression based household refrigerators are one of the most used electrical appliances in the common household and consume electricity throughout the day, so finding a more efficient alternative would be beneficial. One such alternative uses the magnetocaloric effect as cooling mechanism and could theoretically reach a much higher efficiency. However, the search for the right material with the right characteristics for the commercial realization of this technology is still ongoing and this thesis aims to assist in making progress in said search. The focus of this thesis is on the substitution of manganese with nickel in Mn-Fe-P-Si compounds and how the magnetocaloric properties of these compounds hold up against similar compounds that had manganese substituted with cobalt as this lowered the Curie temperature and decreased the thermal hysteresis, which are favourable results. Unfortunately, there are a few factors such as price and criticality that motivated replacing cobalt with a close relative such as nickel in hope of achieving similar results. Measurements done with a superconducting quantum interference device (SQUID) indicated that the synthesized Mn-Fe-Ni-P-Si compounds have very similar magnetic properties to the Mn-Fe-Co-P-Si compounds. Differential scanning calorimetry (DSC) measurements showed that both compounds reduce thermal hysteresis similarly, but the nickel compounds are capable of lowering the curie temperature much more with increased doping compared to the cobalt compounds. X-ray powder diffraction (XRD) analysis proved that nickel is substituted in the proper place and that the decreasing Curie temperature is the result of a change in the ratio of the unit cell parameters a and c. Nickel thus showed to be an excellent replacement of cobalt to be used to substitute manganese with to lower the Curie temperature of the initial Mn-Fe-P-Si compound and reduce thermal hysteresis. More research could be done on further tuning the composition by for example increasing the silicon doping as this has shown to increase the Curie temperature rather than decrease it whilst also reducing the thermal hysteresis. Combined with the results from this thesis it could lead to a composition with more favourable magnetocaloric characteristics.

The sustainable energy transition relies on energy storage technology. Crucial to meet the ever increasing energy storage demand is profound understanding of the governing processes. Yet, due to the inherent difficulty to study light ions with conventional techniques, limited methodology is available for operando monitoring of lithium ion batteries. A non-invasive and versatile alternative is Neutron Depth Profiling(NDP). This technique provides information on the spatial and temporal lithium concentration during (dis)charge. In this work NDP is used to shed light on key challenges for lithium ion batteries. The results provide detailed understanding of electrode parameters such as tortuosity and Li-ion transport. This allows to reduce the battery internal resistance or increase charging current, thereby reducing charge times. Post lithium ion battery technology relies on a reversible lithium-metal anode, this would enable batteries based on the conversion reaction of lithium with oxygen or sulfur. Furthermore, a lithium metal anode can double pack level energy density when employing current cathodes. Using NDP, we can monitor the lithium concentration profile as the material is plated. This allows to study the dependency with respect to current density, electrolyte composition and cycling history. Moreover NDP allows to follow lithium independent of oxidation state. Hence enabling to monitor battery failure originating from lithium polysulfide dissolution in the liquid electrolyte. The findings as presented rationalize electrode design towards high energy-dense, safe and low-cost Li-S batteries. The thesis concludes with a revolutionary concept based on a gas filled gridpix time projection chamber. A gridpix detector allows a 3D particle trace reconstruction. Hence a 3D spatial isotope specific, lithium-6, distribution is obtained. This technique would cater for a whole new range of topics to study.@en

Computational modeling is shaping the fundamental understanding of key thermodynamic and kinetic properties in batteries, the importance of which is undeniable for the implementation of next-generation batteries, mobile and large-scale applications (chapter 1). In the present thesis, we employ density functional theory (DFT) at the nanoscale and phase field modeling at the mesoscale (chapter 2) to study both state-of-the-art and novel battery chemistries...@en