This thesis investigates how operational strategies influence the performance of offshore PEM electrolyser systems powered by intermittent offshore wind power. The central research question is:

“How does the operational strategy for managing intermittent offshore wind power supply in an
offshore PEM electrolyser system affect hydrogen production, stack degradation and the LCOH?”

The study follows three phases. A literature review establishes PEM electrolysis as the most suitable technology for offshore hydrogen production, identifies degradation mechanisms under intermittent power operation, and derives a degradation relation. A dynamic Simulink model is then developed to simulate stack performance under variable power inputs. Finally, a techno-economic model in Python integrates the Simulink results with degradation data to evaluate operational strategies.

The analysis compares three strategies: equal-, serial-, and optimal efficiency power distribution over the stacks. Results show that operational strategy is a decisive factor. Equal distribution achieves the lowest LCOH of 12.17 $/kg with 68 stack replacements over a 15 year horizon, while serial distribution results in a 30% higher LCOH of 15.83 $/kg and requires 90 replacements. Hydrogen output differences between strategies are minimal. Strategy performance is best when operation under high current density is avoided, as this is a driving factor for degradation. The LCOH values remain significantly higher than those of fossil fuel based hydrogen.

The findings of this thesis also expose a critical knowledge gap: PEM electrolyser degradation under intermittent operation is poorly understood. Testing protocols are inconsistent, datasets fragmented, and long-term field data scarce. This complicates the viability assessment of future offshore hydrogen projects.

This research contributes by (1) highlighting the urgent need for standardized degradation testing and long-term datasets, (2) introducing a simulation framework that combines time-resolved dynamic modelling with techno-economic analysis, and (3) establishing operational strategy as a critical design factor for offshore hydrogen systems.

Future research should focus on (i) long-term degradation testing under realistic renewable power profiles, (ii) advanced time-resolved modelling with higher time resolution and incorporation of transient effects, (iii) development of optimization-based operational strategies, and (iv) integrated techno-economic analysis that includes dynamic electricity prices, offshore infrastructure, and possible integration of batteries.

To answer the research question: the operational strategy for managing intermittent offshore wind power supply has a significant impact on the performance of offshore PEM electrolyser systems, as strategies that avoid high current density operation substantially reduce degradation and lower the LCOH by up to 30%, while having only a limited effect on hydrogen production.

As part of the global energy transition, large amounts of hydrogen will be needed to provide fuel for heavy-duty transport, heat for industrial processes, and as a feedstock in chemical processes. To be environmentally sustainable, this hydrogen has to be generated using electricity via water electrolysis. With an increase in hydrogen production, however, the additional demand for freshwater in water electrolysis will start to compete with other freshwater consumers, especially humans. One approach to lessen the freshwater impact of water electrolysis is to use seawater as the process feed and perform in-situ water purification. Among others, this purification can be done by using forward osmosis membranes. However, previous research on this topic has only been performed at low current densities, while simultaneously demonstrating high cell overpotentials. Therefore, the overall aim of this thesis is to quantify the attainable current density of the forward osmosis-based purification method, and to optimise the cell performance through use of a zero-gap design. In addition, an evaluation of performance and material degradation is pursued. To this end, tests were conducted to quantify the water flux over the forward osmosis membrane within the given system. Next, a variety of long-term electrochemical tests were performed, both with and without water purification, and at different current densities. Furthermore, the cell voltages before and after testing were broken down into anode, cathode, and membrane contributions to gauge performance degradation and locate its origins. Finally, a variety of testing methods such as SEM, EDX, and XPS were used to evaluate the observed material and performance degradation and its causes. The maximum current density attainable within the designed system is found to to amount to 62.39 mA/cm2 . Furthermore, an initial performance improvement is found for the zero-gap cell design. This performance improvement is attributed to lower concentration and bubble overpotentials. However, the cell design exhibits strong material and performance degradation under all investigated testing parameters. The performance degradation is caused by increasing anode and membrane overpotentials. The anode overpotential increase is hypothesised to be due to the dissolution of a catalytically-active iron and nickel-rich anode top layer. The membrane overpotential is hypothesised to be due to membrane blockage by material deposits, and sodium-proton substitution in the membrane. In contrast, stable, or even improving, cathode overpotentials are found. This observation is attributed to the formation of catalytically superior metal phosphates and nickel hydroxide on the cathode surface. Lastly, the root cause of all degradative processes is found to be the use of a selective membrane, which enables a gradual acidification of the anolyte and thus creates a highly corrosive environment at the stainless steel anode. The results of this thesis allow for a better understanding of the inherent limitations connected to the use of FO membranes in electrolysis cells. It also offers a wide range of opportunities for improving the system and cell design in future research. Specifically, it enables a more careful membrane selection for future cell designs. By highlighting the limited achievable water influx with the given system, it also emphasises the need for larger FO membranes, and thus a different system architecture, or alternatively the need for a switch to a different draw solution or electrolyte.

This research aimed to enhance and quantify the wettability and water affinity of Expancel microparticles which generally demonstrates a lack of affinity with water. To enhance their water affinity, hydrophilic coatings like SiO2 and TiO2 were deposited onto the microparticles using atomic layer deposition (ALD). Various experimental techniques were employed to analyse the affinity, wettability, surface morphology, surface charge, and elemental compositions of the coated particles. TGA was conducted to examine the water affinity by subjecting the particles to direct heat in the temperature range of 25 ̊C to 130 ̊C under inert conditions. Weight loss% w.r.t temperature were measured, with a focus from the initial stage 25 ̊C to 80 ̊C, representing moisture loss from the surface. An increase in weight loss% was observed for SiO2 samples as the number of coating layers increased, indicating enhanced affinity with water. SEM images were captured at different temperatures of 80 ̊C, 100 ̊C, and 130 ̊C to clarify and explain the trend observed in TGA graphs. It was discovered that there is no expansion until 80 ̊C, full expansion at 100 ̊C, and particle ruptures at 130 ̊C due to the fact that the encapsulated gas escapes the particles completely. Experiments to measure WCA were conducted to quantify the wettability of coated particles and compare them to uncoated particles. The data indicated improved wettability for SiO2 and TiO2-coated particles, as evidenced by reduced contact angles. As Expancel microparticles tend to agglomerate in the presence of water, focused beam reflectance measurement (FBRM) analysis was employed to measure real-time agglomerate size. The FBRM measurements demonstrated reduced agglomerate sizes for coated particles compared to uncoated particles. XPS analysis was used to examine the elemental compositions on the particle surface after coating with varying no. of coating layers; higher silicon (Si) concentrations were found as compared to titanium (Ti). ICP-EOS was used to quantify the amount of Si and Ti weight% after varying no. of deposition layer. The data indicated that the amount of Si was measured to be a lot more than the theoretical value, which implied CVD behaviour in our reactor. LEIS analysis revealed that one layer of coating achieved full surface coverage with SiO2, and subsequent coating cycles did not significantly alter the surface composition.

Ammonia is an important chemical used in the production of fertilizers and has the potential to become a green energy carrier. It is synthesized through the Haber-Bosch (HB) process, which involves nitrogen and hydrogen reacting at high temperature and pressure and consumes approximately 2% of the global energy supply. An alternative to this energy intensive process is the electrocatalytic nitrogen reduction reaction (NRR). The main challenge of this approach is the competing hydrogen evolution reaction (HER) that consumes most of the applied electricity, making the ammonia production inefficient. Based on the Sabatier principle, an ideal catalyst for the NRR would bind nitrogen and ammonia optimally, while hydrogen would be bound too strongly or too weakly, suppressing the HER. So far, no such catalyst has been found. A strategy that could lead to the discovery of a suitable catalyst is alloying, since materials with new adsorption properties can be created this way. The main goal of this project is to design an electrochemical cell that can be used for the screening of large numbers of bimetallic catalysts, increasing the chance of finding a suitable NRR catalyst. For this so-called high-throughput approach an electrochemical cell was designed that allows the screening of up to 16 catalysts in parallel. Furthermore, methods for sample preparation, characterisation and detection were developed that are compatible with a high-throughput technique

UV/chlorine, as an emerging advanced oxidation process, is able to degrade organic micropollutants in water via the generation of reactive oxidant species and direct reaction with HOCl/OCl- as well. In this study, light-emitting diodes (LEDs) were applied as the UV sources to investigate the efficacy of UV/chlorine process for the degradation of trimethoprim (TMP, a frequently detected antibiotic in waters), at slightly alkaline pH.

While colloidal suspensions of non-spherical particles have been studied relatively extensively, granular suspensions of non-spherical particles are rarely studied. The rheological behaviour of elongated granular particles is therefore not well known. This thesis deals with suspensions of rod-like particles of aspect ratio 4 subjected to shear flow in a low-density, highly viscous Newtonian fluid. CFD-DEM simulations for a periodic shear box have been performed for a pre-estimated range of shear rates and volume fractions. Dependence of rheological properties like shear stresses, relative viscosity, granular temperature, pressure and normal stress differences on the shear rate and volume fraction have been studied. These granular rods show shear thickening behaviour. The spherocylindrical particle suspensions experience less collisional stresses than spherical particles due to preferred particle alignment in the shear direction. Herschel and Bulkley [1] model is used to fit the collisional stress data. Two different regimes have been identified for granular suspension based on the flow index. Interestingly, a relatively large range of shear rates and associated stress can be expressed in the form of a simple equation based on Broughton and Squires [2] model. This stress closure will further be used in more coarse grid models like MP-PIC which can simulate an industrial fluidized bed reactors of non-spherical particles.