Fresh water is a scarce source. Demand for freshwater is greater than supply, due to the increasing industrialisation of countries and the low natural supply of freshwater sources such as rivers and lakes. Contamination of these natural freshwater sources by industrial wastewater adds to the freshwater deficit. Throughout history, technologies have been developed to increase the supply of fresh water by desalinating other water sources into fresh water. Reverse osmosis is the most widely used desalination technology for seawater desalination, but the energy transition calls for electric-based technologies that can desalinate water using renewable energy sources. Capacitive deionisation is a relatively new desalination technology that uses electrical energy to desalinate brackish water. The capacitive deionisation cell is an electrochemical cell in which the feed water flows between two electrodes. When electricity is applied to these electrodes, ions in the water are attracted to move towards the porous electrodes where they are adsorbed within the electrical double layer. Unfortunately, the capacitive deionisation system has some challenges: it is a batch-system, has a low freshwater production and it has not been built for large-scale production. Avsalt AB, a Swedish company, has developed a new capacitive deionisation architecture to address these challenges, called the multichannel capacitive deionisation system (MC-CDI). This system consists of two capacitive porous electrodes and several membrane-like electrodes between them, referred to as capacitive membrane electrodes (CMEs). To maximise the performance of the multichannel deionisation system, the performance of the capacitive membrane electrodes should be enhanced. Therefore, the aim of his thesis is to optimise the physical properties of the capacitive membrane electrodes that affect the performance of the capacitive membrane electrodes and to gain a better understanding of how the microscopic properties of the CMEs should be carefully tailored to improve the performance. To address these questions we can turn to Electrochemical Impedance Spectroscopy (EIS). EIS is a non-invasive measurement technique that may be regarded as a much more sophisticated resistance measurement compared to, for example, a multimeter. In contrast to the latter device, EIS measures the impedance, which is a combination of the resistance and the reactance, at a wide range of frequencies. The frequency dependency of the measured impedance can be used to find a so-called equivalent electrical circuit model (EECM). For EIS measurements on electrochemical cells, such as batteries, fuel cells, and electrolysers, the EECM elucidates the different electrochemical processes that occur at different timescales and impedance plots are used to analyse and compare these electrochemical processes. EIS has been successfully used to analyse the electrochemical processes within CDI electrodes and ion exchange membranes, but capacitive membrane electrodes used in an MC-CDI system have never been studied with an accurate and fast measurement technique such as EIS. Because CMEs do not have a solid support structure, in contrast to most CDI electrodes, ions are free to migrate through the electrodes. Therefore, the alternating current that is needed in EIS measurements can be applied on an external set of electrodes, while the response alternating voltage can be picked up at the CMEs. This 4-point impedance measurement configuration enables precise determination of the ionic resistance and capacitance of the electrode material. Therefore, an electrochemical impedance spectroscopy setup is built to determine the performance indicators of the CMEs and to gain a better understanding of the electrochemical processes taking place at the interface of the CMEs. The resulting Nyquist and Bode plots are used to analyse the ion diffusion and capacitive behaviour of the electrodes. To enable the analysis, first, an equivalent electrical circuit is determined for these freestanding electrodes. It was found that the CME can be represented by the Transmission-line model, which in the equivalent electrical circuit takes the form of a junction of three complex impedances. From the values of the electrochemical parameters, the performance indicators of the CME, membrane conductivity and permselectivity, were evaluated. The CME meter presents itself as an accurate measurement system to quickly evaluate the performance indicators of the CME, with the aim of efficiently searching for the CME that will show the best performance within the MC-CDI system, without placing it within the MC-CDI system. Further research should be conducted to investigate the extent to which EIS could be used to estimate the permselectivity of the CME and whether the total measurement time to predict permselectivity is still short enough to propose EIS as an alternative measurement technique.

This thesis aims to find out whether electrokinetic transport of a calcium chloride solution can be controlled by adding sodium ions by performing molecular dynamics simulations. The idea that electrokinetic transport control is a possibility originates from research that found that charge inversion is reduced when monovalent ions are added to a multivalent solution. Consequently, flow reversal suppression is expected. Many mechanisms are known to contribute to charge inversion and ion competition, but it is unclear how they exactly relate to charge inversion reduction and flow reversal suppression. This work aims to replicate charge inversion reduction and flow reversal suppression in a system with an amorphous silica interface for mixed electrolytes with calcium, sodium and chloride. To allow insight into the structural behaviour of the electrical double layer and the electrokinetic properties for varying concentrations, molecular dynamics simula- tions are used. No variation in charge inversion and flow reversal reduction was found for the simulated concentrations. However, the adsorption behaviour of ions in the electrical double layer changed due to ion competition between sodium and calcium, where sodium outcompetes calcium for inner sphere surface complex adsorption. This work also shows that the electroosmotic flow behaviour for mixtures is sensitive to the dynamic adsorption behaviour of ions, emphasizing the importance of correctly tuned force field parameters between surface and ions.

Enhancing the efficiency of industrial water electrolysis for hydrogen production is vital for the energy transition. In Alkaline Water Electrolysis (AWE), hydrogen is produced at the cathode, and the bubbles are formed when the local hydrogen concentration exceeds the solubility limit. It is important to understand the exact local conditions that result in the nucleation of bubbles in this multi-phase and reactive system. With modeling, it is possible to gain insight into the relation between various local properties, but the model needs to include all relevant physics and chemistry. Thus, this work focuses on the multi-species electrochemical transport phenomena with reaction occurring on the electrode-electrolyte interface. The electrochemical transport phenomena and the bubble nucleation are meso-scale phenomena occurring at the electrode-electrolyte interface. Lattice Boltzmann Method (LBM) is well suited for modeling meso- scale behavior but it is computationally memory expensive. Consequently, a hybrid approach combining Finite Difference Method (FDM) and LBM has been developed to simulate transport phenomena in the migration-diffusion problem with heterogeneous reaction kinetics. The Debye-Hückel theory is used as a benchmark to validate the developed model. Subsequently, the model is employed to simulate the transport phenomena occurring in the hydrogen half-cell of AWE, with a specific focus on the Hydrogen Evolution Reaction (HER) governed by the Butler-Volmer kinetics equation. The model captures the dynamic evolution of physical parameters such as electric potential, concentration of species, and fluxes within the system particularly in the Electric-Double layer (EDL). The effect of electrode potential on the distribution of species involved in the reaction are studied by performing simulations for different electrode potential. The influence of secondary fluxes on the species distribution is studied by implementing a spatially varying boundary condition to the reacting site. Finally, the formulated methodology is extended to solve a multi-phase system with species transportation occurring around a catalyst particle.

During specific operations, offshore marine contractor Heerema Marine Contractors reduces the draft of their Semi-Submersible Crane Vessel (SSCV) such that the floaters are submerged in close proximity to the free surface. This draft is also known as inconvenient draft. At this draft the motions of the vessel do not fully comply anymore with the computed prediction using linear diffraction theory. A proper motion prediction is required to ensure a safe execution of the offshore operation. The key issue is the submerged part of the floater, since discrepancies occur as soon as there is only a small water column on top of the floaters. Motion RAOs are computed via the hydrodynamic coefficients and wave loads. The reason why this leads to discrepancies in the motion RAO is not yet known. In addition, qualitative hydrodynamic data should be gathered for an object submerged in close proximity of the free surface. Therefore, in this study the cause of the discrepancies in motion RAO is studied on an experimental basis for an object submerged in close proximity to the free surface. The scope is narrowed down to a two-dimensional cross-section of a SSCV-floater. Numerical simulations using linear diffraction theory are performed in WAMIT. The results are compared to experimental data obtained via model tests performed at the towing tank facilities at the faculty 3mE at Delft University of Technology. Based on experimental data is concluded that linear diffraction theory does not predict physical phenomena that satisfy the boundary conditions and that underlie principles of the theory. Despite the fact that the experimental data does satisfy the boundary conditions of the numerical simulation, discrepancies occur at the hydrodynamic coefficients and wave load. As a result, it can be concluded that linear diffraction theory malfunctions at the inconvenient draft region, and therefore is not the correct theory to determine RAOs for an object on inconvenient draft. Discrepancies in motion RAO are found to be dominated by the discrepancies the wave load, except for the frequency at which the added mass equals negative inertia of the body. Discrepancies for added mass are less significant than for the damping coefficient and wave load. At higher frequencies inertia becomes dominant over damping and damping deviations affect the RAO less. The pitch motion about the center of the cross-section does not represent a rotational motion about same the degree of freedom for an SSCV. However, it allowed to experimentally investigate the global numerical extremes. In addition, it led to the finding that it seems that the rotational data is more affected than the heave data. There is a strong suspicion that poles in the complex plane are the cause of the discrepancies in the hydrodynamic data, which result of the used Green's function by Wehausen and Laitone. This suspicion is based on characteristics of the numerical data in combination with findings in literature and the experimental data, accumulate. Currently, an approach that makes use of free surface damping is applied to predict the motion of an SSCV at inconvenient draft. Based on experimental data can be concluded that the use of free surface damping without further modifications does not result in an accurate motion prediction. Lastly, the effect of nonlinearities when increasing the oscillation or wave amplitude. The wave load is found to be more prone to nonlinear effects than the hydrodynamic coefficients.The force signal remained dominantly harmonic, but higher harmonic forces did show up. Furthermore, with the exception of most tests at the largest tested submergence, higher harmonic waves were measured and visually observed during the tests. These higher harmonic waves arose at the transition from the shallow to deep water regime and vice versa. These forces were found to have hardly any effect on the force signal.

Non-photochemical laser-induced nucleation (NPLIN) is a process where a crystalline phase is formed out of solution by exposure to a laser beam. In NPLIN, the nucleation probability is strongly dependent on the beam intensity and weakly dependent on the wavelength. NPLIN offers a feasible alternative to energy-intensive industrial crystallisation methods. Although several mechanisms have been proposed, little is known about NPLIN at the molecular level. Some theories suggest that nucleation rates are enhanced through the heating of nanoparticles by absorption of electromagnetic energy. In this work, molecular dynamics simulations are performed on the clustering of ions in the vicinity of a heated nanoparticle in an aqueous supersaturated KCl solution. The spherical symmetry of a spherical nanoparticle in solution is exploited by modelling a laterally periodic water column of an initial length of 500 Angstrom enclosed between a planar iron(III) oxide nanoparticle surface and a graphene piston. A cavitation bubble is formed after nanoparticle heating, leading to an increase of clustered ions according to a bond order criterion. The clustering should correspond to nucleation in experimental systems because the clusters satisfy Delta G < 0 for locally valid NPT ensembles. The results corroborate concentration based NPLIN mechanisms as the clustering is visibly induced by local solute evaporation. Pressure based mechanisms appear ineffective because no effects of pressure waves are observed. Thermostatting the graphene sheet does not yield observable dissipation of the thermal energy generated through the nanoparticle heating and at the ion clustering sites and, obstructing completion of the cavitation cycle at a feasible simulation duration. It is suggested to repeat the simulations using a conically shaped system and a piston of higher transverse thermal conductivity.

Due to rising concerns about climate change, a lot of research is currently underway with respect to the development of new technologies which can contribute to the decline of atmospheric CO2, and will allow further penetration of renewables into the energy mix. A promising technology which is currently actively researched is the electrochemical reduction of CO2 (ERC). This technology utilizes otherwise polluting and unwanted CO2 and converts it into value-added products under the influence of an electrical current. The process can therefore be designed as an energy storage mechanism since electrical energy is stored as chemical bonds. In this research, ERC towards formic acid has been investigated from two perspectives. First, the feasibility of the commercial production of formic acid compared to other products of ERC was investigated. The electrochemical production of the most common reduction products have been compared based on production costs, energy storage capabilities, toxicity and manageability. Due to the relatively low energy consumption for 2-electron products, namely formic acid, carbon monoxide and oxalic acid, it is found that these products have the most promising business case. Additionally, ERC to formic acid is best studied compared to other products, and high selectivities are commonly reported. Formic acid and methanol are liquid at atmospheric conditions, which is beneficial as relatively large amounts of energy per unit volume can be stored without the need of additional compression or cooling. This will also allow for easy transportation. As hydrogen carrier, formic acid has the advantage that it can be decomposed in H2 and CO2 near room temperature. In the second part of this research, the use of numerical modeling to study the reduction of CO2 in an electrochemical cell towards formic acid/formate at elevated CO2 pressures is presented. The model investigates to impact on the cathodic half-cell of a cell designed for the reduction of CO2 in aqueous electrolyte solutions at a constant temperature of 25℃, simultaneously assuming non-limiting conditions with respect to the anodic half-cell. The modeled part of the cell has been divided in three main regions, namely the bulk, cathode surface region and the electrode surface, which are discussed separately. The bulk is assumed to be the region of equilibrated concentrations which are constant in time, as they are not dynamically influenced by any mass transport phenomena. Reactants are supplied from the bulk to the electrode surface and products are removed vice versa via the cathode surface region, which is a thin region in the vicinity of the electrode. The transfer of species within this region and the chemical reactions between the species, form a system of diffusion-reaction equations. This system is solved numerically using appropriate boundary conditions. The actual reduction of CO2 occurs on the electrode surface, and the kinetics of the electrochemical reactions towards HCOO-, CO and H2 are described using Tafel-type kinetics. The electrochemical model has been verified and compared with experimental data, and despite various simplifications has proven to be predictive of the electrochemical reduction of CO2. It is found that the potentially beneficial effects of an elevated CO2 pressure on both the production rate and selectivity, as experimentally observed, can be reproduced with reasonable accuracy. The CO2 concentration at the electrode surface is identified as the main limiting factor for achieving both a high selectivity towards formate and a higher production rate on formate producing metals. The model shows that with an increased CO2 pressure the amount of CO2 dissolved into the solution is increased significantly, resulting in a higher concentration of CO2 at the electrode and less mass transfer limitations.

In the pursuit of gaining a better understanding of the mechanisms of oxide-electrolyte interfaces, this thesis presents a working model that mimics a dynamic surface charge distribution by introducing protonation and deprotonation events using MD simulation. Due to the limitations of measurement equipment that operate on an atomic scale, literature cannot provide us with exact time scales for protonation and deprotonation events. Consequently, previous research simulated the surface charge distribution of oxide surfaces as being static and assumed the effect of local protonation and deprotonation to be negligible. This work shows that varying the (de)protonation event period τ significantly influences the characteristics of the electric double layer (EDL). Continuous protonation and deprotonation changes the diffusion coefficient and subsequently alters the structure of the Stern layer, screening function, and preferential adsorption type. As a whole, dynamic surface charge distribution has a considerable impact on the characteristics of the electric double layer depending on τ and should be considered in future MD simulations.

Experimentally investigating the nanoscale behavior at oxide-electrolyte interfaces has proven to be extremely challenging. Molecular Dynamics (MD) simulations have arisen as a potential computational alternative to gain atomic level insights at these interfaces. But how accurately do these simulations represent the physics and chemistry at the interface? In many situations we do in fact not know. Validation at the interface remains challenging. The force fields used in MD simulations, that describe the inter-particle interactions, are generally optimized for purposes deviating considerably from interfaces. Yet, these same force fields are blindly used to model surface-fluid interactions, yielding wildly varying results of for example ion adsorption. This dissertation tackles the problem of simulating interfaces by critically looking at MD simulations and proposing novel solutions, both for MD simulations in general and specifically targeting their validity and limitations with regards to modeling interfaces… @en

Capacitive deionisation (CDI) is a desalination technology that removes ionic species from water through electrostatic attraction. Recently, a new CDI cell architecture has been developed with multiple channels and electrodes. Here, the ions are driven to migrate from channel to channel to desalinate the water. The inner electrodes of such a cell function as selective membranes when charged, therefore called capacitive membrane electrodes (CME). This thesis used an experimental approach to investigate the effect of the electrostatic charge and the microstructure of the CMEs on the permselectivity of these CMEs. Five different CMEs were tested in a cell to determine their permselectivities. A porometer (utilising the capillary flow technique) was used to determine the pore size distributions of the CMEs. When comparing the data from both measurements, it was found that CMEs with a higher fluid permeability also showed lower ionic resistances. A lower ionic resistance indicates a lower permselectivity. To achieve good desalination performance in multi-channel CDI, CMEs must offer low ionic resistance when ions are driven from low salinity to high salinity, while still being permselective when ions want to migrate back from high to low salinity.

Crystallization is employed in a wide range of industries but our ability to control it remains far from perfect. New methods are being continuously developed and improved to provide enhanced kinetics and control. Non-photochemical laser induced nucleation (NPLIN) is one of the avenues being looked into extensively since its accidental discovery about two decades ago. Despite providing improved nucleation kinetics and potential polymorph control, the mechanism behind NPLIN is still unknown. Four different theories have been proposed in the literature with varying amounts of agreement between different research groups. The main aim of this thesis is to try to determine the mechanism behind NPLIN. This report can be divided into two parts, each focusing on a possible mechanism. The first is the optical Kerr effect, which involves investigating the effect of polarization of light on glycine polymorph formed. This is achieved by varying the laser light polarisation and number of pulses for a range of glycine supersaturation. The second part deals with an experimental setup designed to work with microscale volumes. This will give us the capability to isolate the nuclei and observe the events leading up to their formation. For studying the optical Kerr effect, the experiment performed by Sun et al. was repeated. A significant temperature increase inside the solution was obtained because of exposure to a high number of pulses (600) of infrared light. No dependence of laser light polarization on polymorph formation was found. The polymorph formed by laser is different than that obtained by crash cooling. In the second part of the thesis, the attention is shifted towards the role of impurities present in the solution which can also absorb the laser light leading to formation of a cavitation bubble. This possibility was examined with the help of the setup mentioned above. It was noted that the crystals were nucleating at multiple points around the laser focus at a distance which is similar to the size of the cavitation bubble previously reported in literature. These observations made can be attributed towards the presence of a bubble.

Energy demand is constantly increasing and the use of fossil fuels causes an accumulation of carbon dioxide (CO2) which is an important environmental problem that needs to be solved. A promising solution to this problem would be the electrochemical reduction of CO2 to useful products, using the surplus of electricity from renewable sources. This would be a way of storing this excess of electricity in chemical bonds. However, this has not reached high efficiency and selectivity needed for establishing its use. For this process, the CO2 is usually dissolved in an aqueous electrolyte. This thesis proposes the new approach, using Deep Eutectic Solvents (DES) which would capture a higher concentration of CO2 helping to make the whole process more efficient. However, not all salt mixtures reach the eutectic point and therefore, the solvents formed are a low-transition temperature mixtures (LTTMs) of the selected salts. Experimental work was performed to find out if these solvents can be used for electrochemical carbon dioxide reduction. Non-reported LTTMs were synthetized; they were formed with mixtures of the hydrogen bond donor citric acid (CA), fructose (F) and diethanolamine (DEA) with the hydrogen bond acceptor tetrabutylammonium chloride (TBA-Cl) and different quantities of water, which was found necessary to carry out electrochemistry since the solvents formed were too viscous, and this water has an important effect in the electrocatalytic reduction of CO2 as proton source and charge carrier. These solvents were characterized electrochemically, performing studies to find out on which metallic surface they behave better (wider working potential window, low degree of decomposition and adsorption) and how different water quantities affect this process. These studies were performed using cyclic voltammetry. From this, it was seen that the solvents are more stable during electrochemical process in presence of copper. Moreover, the solvent formed by DEA:TBA-Cl:H2O in the molar proportions 1:1:1,375 was found to have interesting features that resemble CO2 reduction. As result, this solvent was further analysed using electrochemical in-situ Fourier-Transformed Infrared (FTIR) spectroscopy in surface-enhanced attenuated total reflectance configuration. With this, it was seen that the carbon dioxide was captured by the solvent and that there are visible changes when applying potential. Remarkably, the data shows the formation of a dimer OCCO on the Cu electrode surface, stabilized by the solvent. This project shows for the first time the electrochemical reduction of CO2 in LTTMs, evaluating different solvents, metals and water quantities. Determining that the carbon dioxide reduction is possible with the solvent DEA:TBA-Cl:H2O in the molar proportions 1:1:1,375 in a copper polycrystalline electrode.

In this thesis, a proof of concept was established for the use of a novel coupled QM-MD approach to modelling metallic (copper) electrode-electrolyte interfaces. SCC-DFTB calculations of the instantaneous electronic structure of a copper electrode were coupled to a classical MD simulation of an electrode-electrolyte interface. The applied QM-MD method was described rigorously, and used to investigate the compound distribution and dynamics at the interface, relative to a fully classical MD simulation. Polarisation effects were observed to bring about a significant increase in the attraction between cations and the cathode. Moreover, local polarisation of the cathode was found to immobilise adsorbed cations, and induce an increased orientational preference of the nearby water dipoles. The secondary goal of this thesis was to explore to what extent neural networks are able to replicate SCC-DFTB calculations of the electronic charge density on a metallic electrode. Using a computer vision approach, qualitative evidence was obtained indicating that neural networks can be used to replicate SCC-DFTB predictions on periodic metallic surfaces.