Hydrogen (H2) is an important substance for clean energy storage, but the financial feasibility of large-scale water electrolysis remains a challenge. A promising approach to improve the economics of industrial electrolyzers is the anodic production of hydrogen peroxide (H2O2) during alkaline water electrolysis. This dual production could attract H2O2 producers and increase the value of electrolyzer output. However, achieving high H2O2 selectivity is difficult due to competition with other oxidation products. Recent studies have shown that incorporating polytetrafluoroethylene (PTFE) on carbon fiber paper (CFP) electrodes can enhance H2O2 production. Xia et al. suggest that PTFE's hydrophobicity confines O2, driving the reaction toward H2O2. However, PTFE’s inert characteristic makes complete coverage of the electrode impractical. Vogel et al. further noted that the O2 bubble perimeter, which attracts more OH-, a key reactant for H2O2, could also increase H2O2 yield.

This project explores the effects of varying PTFE applications on carbon electrodes, focusing on three approaches: increasing the PTFE perimeter patterns (P1<P2<P3<P4), increasing the PTFE area patterns (A1>A2>A3>A4), and dip-coating the electrode in PTFE emulsion. The study uses a two-electrode system in a flow cell with a K2CO3 electrolyte, observing performance lifetime via chronopotentiometry and measuring H2O2 yield through permanganate titration. SEM and EDX are also used for electrode observation.

Results show that increasing the PTFE perimeter (P1 to P2) enhances H2O2 yield due to better O2 bubble formation, but further increases (P2 to P4) have little effect. Increasing the PTFE area patterns generally shortens operational lifetime and reduces H2O2 yield, with A2 and A3 showing similar results due to potentially non-optimal spacing. PTFE dip-coating leads to rapid performance degradation, confirming that PTFE’s lack of active sites makes it unsuitable for initiating reactions. Overall, optimizing PTFE surface area is improving H2O2 production in alkaline water electrolysis over than perimeter or dip-coating.

This study aims to relate the size, number density, and surface coverage of bubbles adhering to a vertical gas-evolving electrode to the current density and shear rate of alkaline electrolyte flow.
A force balance that includes the known forces on the bubbles is formulated. This force balance is made to predict the release radius of the adhered bubbles. Because the electric and Marangoni forces are still an open topic of research, they are approximated using a constant. Also, because the influence of the drag force on bubbles in alkaline water electrolysis is not exactly known, it is approximated using the Stokes drag force with a multiplicative fit factor. An equation for this force balance model that approximates the release radius of the bubbles is formulated. To know the exact value of the shear rate on the electrode, this study uses laminar, fully developed flow. Equations are formulated to relate the fully developed laminar flow to the shear rate.
The bubbles adhered to the electrode are visualized using a high-speed camera. The camera films through a PMMA rod that goes through the first electrode, allowing visualization of the bubble-covered surface of the second electrode. A long stainless steel rectangular duct develops the Laminar flow before it arrives at the electrode.
The experiment is to relate the bubble size, bubble number density, and surface coverage to the shear rate due to forced flow and the current density. Increasing the shear rate has the biggest effect on the largest bubbles adhered to the surface. The maximal radius reduces, while, for the range in shear rate used in this study, the median stays almost constant. The bigger bubbles will be replaced by smaller bubbles. This will reduce the surface coverage and increase the bubble number density. Increasing the current density, for the range in current density used in this study, means an increase in bubble interactions. This means an increase in bubble coalescence, collisions between bubbles, large bubbles being pushed off the surface by smaller ones behind them, and the increased shear rate from natural convection caused by moving bubbles. These increased bubble interactions will result in a reduction in bubble sizes, surface coverage and an increase in bubble number density.
The force balance model is related to the maximal radius of the bubbles. The constant of the electric and Marangoni forces is negative at the anode and positive at the cathode, which is expected because the forces should be attractive at the anode and repulsive at the cathode. The multiplicative fit factor of the drag force due to forced flow indicates a higher force than the Stokes drag force because the flow is not perfectly homogeneous and will flow through other bubbles, which can accelerate the local flow velocities. Also, bubbles will collide at a higher speed with increased forced flow. The multiplicative fit factor of the drag force due to natural convection indicates a higher force than the Stokes drag force because of the increased bubble interactions with increasing current density. Both the higher multiplicative fit factors are observed at the anode and cathode.

This study aims to relate the size, number density, and surface coverage of bubbles adhering to a vertical gas-evolving electrode to the current density and shear rate of alkaline electrolyte flow. A force balance that includes the known forces on the bubbles is formulated. This force balance is made to predict the release radius of the adhered bubbles. Because the electric and Marangoni forces are still an open topic of research, they are approximated using a constant. Also, because the influence of the drag force on bubbles in alkaline water electrolysis is not exactly known, it is approximated using the Stokes drag force with a multiplicative fit factor. An equation for this force balance model that approximates the release radius of the bubbles is formulated. To know the exact value of the shear rate on the electrode, this study uses laminar, fully developed flow. Equations are formulated to relate the fully developed laminar flow to the shear rate. The bubbles adhered to the electrode are visualized using a high-speed camera. The camera films through a PMMA rod that goes through the first electrode, allowing visualization of the bubble-covered surface of the second electrode. A long stainless steel rectangular duct develops the Laminar flow before it arrives at the electrode. The experiment is to relate the bubble size, bubble number density, and surface coverage to the shear rate due to forced flow and the current density. Increasing the shear rate has the biggest effect on the largest bubbles adhered to the surface. The maximal radius reduces, while, for the range in shear rate used in this study, the median stays almost constant. The bigger bubbles will be replaced by smaller bubbles. This will reduce the surface coverage and increase the bubble number density. Increasing the current density, for the range in current density used in this study, means an increase in bubble interactions. This means an increase in bubble coalescence, collisions between bubbles, large bubbles being pushed off the surface by smaller ones behind them, and the increased shear rate from natural convection caused by moving bubbles. These increased bubble interactions will result in a reduction in bubble sizes, surface coverage and an increase in bubble number density. The force balance model is related to the maximal radius of the bubbles. The constant of the electric and Marangoni forces is negative at the anode and positive at the cathode, which is expected because the forces should be attractive at the anode and repulsive at the cathode. The multiplicative fit factor of the drag force due to forced flow indicates a higher force than the Stokes drag force because the flow is not perfectly homogeneous and will flow through other bubbles, which can accelerate the local flow velocities. Also, bubbles will collide at a higher speed with increased forced flow. The multiplicative fit factor of the drag force due to natural convection indicates a higher force than the Stokes drag force because of the increased bubble interactions with increasing current density. Both the higher multiplicative fit factors are observed at the anode and cathode.

The long-distance maritime transport sector plays one of the most relevant roles in the transport sector. Therefore, this project designs a modular solid hydrogen solution, studying the assumptions made in the literature and including new simplifications that reduce the computational costs of its simulation. Moreover, this project compares the viability of this solution with the different prototypes found on the market.

A water electrolyzer is an electrochemical device that produces hydrogen and oxygen from water via electricity. A sustainable way of producing hydrogen with renewable electricity, also known as green hydrogen, could enable its use in decarbonisation of sectors that depend on fossil fuels. However, to scale up the production of green hydrogen, larger water electrolyzers are required, which presents challenges. Water electrolyzers produce hydrogen in the form of bubbles, which are transported away through outlet channels. The geometry of the outlet channel is important for performance and safety. A channel that is too wide can result in unwanted ionic current leakage, reducing efficiency and increasing the risk of explosion. To reduce the leakage current, the electrical resistance in the channel can be increased to make it difficult for ions to flow through. However, a narrow channel can increase the hydraulic resistance, leading to clogging due to bubble build-up. This study focuses on the characterization of the slug flow regimes that eventually lead to clogging of the outlet channel in a novel electrolyzer design. To characterize the flow when blockage develops, electrochemical tests with industrially relevant 6M KOH were carried out at room temperature and ambient pressure in conjunction with high-speed video recording. The examined channel was 2 mm high, 3 mm wide, and 40 mm long. The experiments showed that clogging occurs for certain flow regimes. The hydraulic configuration caused clogging at the hydrogen side, which caused the liquid flow prefer to travel via the anode rather than the cathode, which was reflected in the temperature plots. Clogging did not occur when the superficial gas velocity was greater than 0.3 cm/s, which corresponds to a current density of 140 mA/cm2. The clogging was also not visible at a superficial liquid velocity greater than 0.25 cm/s. Below these values, clogging is expected to take place for the investigated channel dimensions. The bubble diameters in the bubble layer in front of the channel were measured with a microscopic camera. The mean bubble diameter was 0.4 mm, which is 80% smaller than the height of the channel through which they flow. However, exceptional bubble sizes that were 3 to 4 times the channel height, which ultimately led to clogging of the channel, were also present. The bubble layer thickness and velocity at increasing liquid flow rates and current densities were measured using a high-speed camera. At low current densities, the velocity and thickness of the bubble layer were not affected by the liquid flow rate. At higher current densities, a higher liquid flow rate appeared to reduce the thickness of the bubble layer, but not the velocity of the bubble layer. The bubble layer thickness as well as the velocity strongly depend on the applied current density (and thus the gas flow velocity). This knowledge might be, when the flow regimes are scaled to larger electrolyzer dimensions accordingly, essential for future electrolyzer manufacturers and operators for the operation and design of larger-scale electrolyzers. It will give insight into which flow regimes should be avoided in order to avoid clogging and thus explosion risks during operation.

A magnetorheological fluid is a type of smart fluid that can change its rheological properties when a magnetic field is applied to the fluid. The fluid is a suspension of magnetizable particles in a non-magnetic carrier fluid. When a magnetic field is applied to the fluid, the particles will form structures along the magnetic field lines. These structures resist flow, thereby increasing the viscosity of the fluid. In a non-uniform magnetic field that is generated by a permanent magnet, the particles separate from the fluid and aggregate on the surface of the magnet. This phenomenon is of use in hydrodynamic bearings, where textures are used to increase the load capacity of the bearing. Replacing the fluid in the bearing by a magnetorheological fluid and placing permanent magnets at the desired texture locations, results in particles separating from the fluid, aggregating on the permanent magnets and forming textures. These textures are of a self-healing nature, because any particle that is sheared off, returns into the fluid and is replaced by another particle. Currently, not much is known about the formation of these textures and the influence of their formation on the rheological behavior of the magnetorheological fluid. Therefore, several discrete element models are constructed, that can simulate a magnetorheological fluid in non-uniform field. These models use basic physical laws to determine the dynamics of the particles. A single core model is constructed to simulate the behavior of the magnetorheological fluid in small domains using two different methods for the magnetic interaction forces between the particles. A parallel model is made to simulate the magnetorheological fluid in larger domains. Finally, a model that is used to simulate particulate flows, is modified to research whether two-way coupling is required to determine the steady state behavior of the magnetorheological fluid. The models show that the particles do not separate from the fluid due to the attractive force of the magnet by itself, but rather by a combination of the attractive force and the deformation of the structures when a flow is applied. Furthermore, the rheological behavior of the fluid can still be approximated using the standard viscoplastic models. Finally, the modified particulate flow model showed that two-way coupling is not required to determine the steady state behavior of the magnetorheological fluid.

The decarbonization of the transport sector is a major challenge for the transition towards a sustainable economy. Amongst the different measures to lower the impact of road transportation on the environment is the use of biofuels, especially for heavy duty vehicles. For biofuels to be affordable and well integrated, improvements in the production process in terms of energy performance and economic feasibility need to be made.

Consequently, this thesis aims at the techno-economic assessment of the integration of pyrolysis oil gasification with electrolysis and syngas catalytic upgrading. Oxygen, being a co-product of electrolysis, is used as an oxidizer for entrained flow gasification of biomass derived pyrolysis oil. Hydrogen from the electrolyzer is used to enhance the production of biofuel. The process was designed to have a high-temperature solid oxide electrolysis cell (SOEC) and the biofuel was chosen to be compressed natural gas (bio-CNG). The modeling of the process was performed on Aspen Plus software and calculations of parameters for the gasifier and electrolyzer were done using Fortran and Matlab respectively.
As aimed by the integration of electrolysis, the hydrogen produced is added to the syngas to obtain a feed ratio of 3, required for an optimum methane production. The increase in the feed ratio at the level of the gasifier is mainly limited by the oxygen equivalence ratio (OER), considering the extent of combustion reactions and the operating temperature. The amount of steam inputted was found to increase the molar ratio of H2 to CO without significant change in the feed ratio due to the increase in the concentration of CO2. However, steam was still necessary for adjusting the temperature of the gasifier to values that are in accordance with experimental ones in literature. The obtained final product stream of bio-CNG at 250 bar and 15℃ has a purity of 98.63 mol% and 99.15 wt%.

Moreover, by applying heat integration to the process, the resulting surplus heat was 10.71 MW, which was assumed to be used to generate steam that is inputted to the SOEC for producing hydrogen as an additional product. The process was found to have an overall efficiency of 73.8% (LHV basis) and 78.2% (HHV basis). Heat integration increased the process efficiency by 15% (LHV basis) and 23% (HHV basis), by removing to a great extent the need for external heat and by having hydrogen as an energy output added to CNG.
As a complement to the energy performance, the economic feasibility of the process was assessed. The total capital investment was found to be 889.5 Euros/kWinput, the net present value was 6.0342 million Euros and the rate of return on investment 30.02%.

The last decade has seen an increase in the world wide energy demand, it was recorded as the highest spike encountered in the energy demand over a decade. On analyzing the main sources which were able to satisfy this overwhelming demand it was found that the majority was still from non-renewable sources or fossil fuels such as coal, oil and natural gas. The aftermath of the continued use of these fossil fuels are already well known, one can argue that there has still not been a serious attempt to phase out these non-renewable sources even though the concerns regarding the harmful emissions being released with their continued use are subject of numerous discussions and studies. It is paramount that the share of renewable energy technologies in the overall energy mix needs to be increased,various options must be explored such that it is possible to substitute these renewable energy sources in place of fossil fuels particularly in energy and emission intensive industries without a comprise in meeting their energy demand. Refuse derived fuel (RDF), which is the combustible fraction that has been separated from municipal solid waste (MSW) has gained attention due to it being seen as an alternative to convectional fossil fuels as well as a method of sustainable waste management and disposal. The reason for their use as an alternative fuel is mainly attributed to their physical and chemical characteristic such as their low moisture content, high grindability and calorific value. However, the challenges faced in their application as a substitute fuel or feedstock is attributed mainly to the high variability in the properties of the RDF material that is being supplied to the relevant industries. Therefore a standardization in its properties needs to be carried out particularly with regards to their moisture content and calorific value in order to promote their application. Torrefaction, also referred to as mild pyrolysis is a thermal treatment method that usually is carried out in temperature ranges of 200-300°C and residence times of 30-60 min in the absence of oxygen. The material that is being subject to this treatment method partly decomposes to release volatiles,and the left over solid product has been reported to undergone a modification its physical and chemical characteristics when compared to the initial solid material. From a chemical point of view the final solid product is reported to have an increase in the carbon content and decrease in the hydrogen and oxygen content which leads to a higher calorific value than the original material. Several experimental studies have been conducted for the torrefaction of RDF with aim of improving and standardizing the calorific value and have yielded promising results. However there has not yet been a work that has focused on the torrefaction of RDF on large scale, that takes into account the process design and economics associated with their production. The aim of this thesis was to carry out a techno-economic evaluation into the torrefaction of refuse derived fuel. An initial composition of raw RDF was selected from literature which has a high moisture content and low calorific value. The raw material is then subject to several process such as drying, torrefaction, grinding and pellitization with the aim producing torrefied RDF pellets. These process were simulated and optimized through Aspen Plus in order to obtain a better understanding of the influence of process parameters such as moisture content, drying temperature, torrefaction temperature and residence time on the final product as well as to select the optimum route for their production. Economic evaluation was also carried out to determine if the implementation of such a project is feasible. This was done on the basis of certain economic or profitability indicators. Results from simulations show that the optimum torrefaction conditions were 250°C and residence time of 30 min, which resulted in the final torrefied RDF having an increased calorific value. The economic analysis provides positive results particularly when moving towards a higher processing capacity of initial raw RDF. Finally, the effect of substitution of the torrefied RDF in a cement plant was also evaluated and has shown that significant savings can be achieved through the reduction in fossil fuel consumption and carbon dioxide emissions.