Electric vehicles have become the focal point to reduce GHG in the quest for cleaner and more efficient means of transportation. At the core of this transition lies the key component of energy storage, the battery pack. The battery pack has electrodes manufactured with the binder PVDF. Using fluorine-rich compounds makes processing and recycling a more difficult process and it is also harmful for the environment. Therefore, alternative binders should be explored to adhere to the principles of sustainability. In this thesis, a comparative study is presented between electrodes fabricated with fluorine free polymeric binders and PVDF. Moreover, a battery cell solely constituted of fluorine free components is fabricated and tested. By using the analysis techniques electrochemical performance testing, electrochemical impedance spectroscopy and scanning electron microscopy the effect of the binders and electrolytes on the electrode performance is explored. The findings reveal that during rate performance cycling, graphite half cells based on the binder PAA demonstrated the highest discharge capacities at C-rates up to 4C with a capacity retention of 39%. NMC811 half cells based on a composite binder CMC/SBR achieved the highest capacity retention after 100 cycles, being 24%. All the fabricated full cells suffered from a 30-40% initial capacity depletion after the first charge, presumably originating from oxidative degradation of the electrolyte. Consequently, the highest capacity retention after 150 cycles was 14% for a PVDF based full cell. Fluorine free cells using a PAA anode and CMC/SBR cathode exhibited expected capacities with a higher overpotential.

Ammonia is essential for global food production as a component of fertiliser, and a potential energy carrier in the energy transition. Electrochemical ammonia synthesis faces numerous challenges as an alternative to the carbon intensive Haber-Bosch process, including competition from hydrogen evolution, and mass transport limitations. An unconventional cell design with a hydrogen permeable electrode could help to address these problems. The reaction mechanism and performance of ammonia synthesis using hydrogen permeable electrodes was investigated at elevated temperatures and pressures of up to 120 °C and 8 bar. Furthermore, a facile method for enhancing the electrochemical surface area of the electrode was developed and tested. Operation at elevated pressure resulted in a moderate increase in cell performance. However, replenishment of the nitrogen vacancies in the nickel nitride catalyst through dinitrogen adsorption is identified as the elementary step that limits activity and stability. The amount of pre-deposited N is found to significantly influence the ammonia production rate and its stability. Dynamics of ammonia desorption could also play a role in nitride regeneration. In future studies, the presence of a decomposition reaction of the nitride should be investigated. Usage of more stable nitride species or a combination of host nitride and dopants is recommended to improve stability and simultaneously promote dinitrogen activation and hydrogenation to ammonia. These findings expand the understanding of the mechanisms underlying the nitrogen reduction reaction, paving the way for the development of a more efficient green ammonia synthesis process.

The Paris Agreement aims to limit global warming to 2 degrees Celsius by reducing carbon dioxide emissions. Data centers are essential to the digital world and contribute approximately 1% to global electricity consumption. Major tech companies like Amazon, Microsoft, Google, and Meta are large contributors to this consumption. In countries like the Netherlands, this contribution is higher due to the Netherlands being a digital hub, accounting for 3% of the total national electricity consumption. Considering their significant energy usage, it is interesting to research how data centers can transition to using only renewable energy sources on an hourly basis so they can decrease their footprint. This thesis aims to identify a feasible and cost-effective configuration for a 100 MW data center that operates 100% on renewable energy on an hourly basis. The research will assess the environmental impacts, focusing on CO2 emissions (CO2e) and land usage, with the main goal of achieving the lowest Levelized Cost of Electricity (LCOE). First, an overview of potential energy storage technologies is provided to find suitable solutions. Based on different criteria, Lithium-ion (Li-ion), lead-acid, vanadium redox flow batteries (VRFB), zinc-bromide flow batteries (ZBFB), alkaline and PEM (proton exchange membrane) electrolyzers, storage tanks, and PEM fuel cells are chosen. With these technologies, eight different configurations are composed, combining various battery types and electrolyzer types with the storage tank and PEM fuel cell: Li-ion with alkaline (1), lead-acid with alkaline (2), Li-ion with PEM (3), lead-acid with PEM (4), VRFB with alkaline (5), ZBFB with alkaline (6), VRFB with PEM (7), and ZBFB with PEM (8). An energy model is developed to identify the most feasible and cost-effective solution, using solar, wind, and load profiles as input. The assets are modeled based on their technical parameters and limitations. A 10-year simulation of the hourly energy flows is executed. In this simulation, the constraints, degradation, and replacement of the assets are taken into account. The costs are determined based on Capital Expenditures (CAPEX), Operating Expenses (OPEX), replacement costs, and residual costs of the asset after 10-year. The connection costs are also considered. The configuration dimensions are optimized based on the LCOE using the particle swarm optimization method. The two configurations with the lowest LCOE are evaluated for environmental impacts, including CO2e and land usage. The study shows that combining a Li-ion battery or VRFB with an alkaline electrolyzer is the most cost-effective and feasible configuration for a data center. The LCOE is 0.243 and 0.241 €/kWh, respectively. Additionally, this reduces kg CO2e/kWh by 7-8 times compared to the current grid emissions in the Netherlands, which are approximately 0.037 and 0.032 kg CO2e/kWh. However, the required land usage is approximately 20 km², and the LCOE of the configuration is about 2.5 times higher than the current power purchase agreement (PPA) price for a data center, which is 0.10 €/kWh. Therefore, it is recommended to initially start with an 80% renewable scenario using only a Li-ion battery and renewable energy sources. This approach reduces the LCOE to 0.12 €/kWh, which is approximately the same as the current PPA price if an additional 0.01 €/kWh for the connection to the grid is included. Furthermore, kg CO2e/kWh is three times lower compared to the current situation, which is 0.08 kg CO2e/kWh. This strategy also mitigates the potential risks associated with the infancy of VRFB and the combination of intermittent renewable sources and an electrolyzer, as these are excluded in this scenario.

Ammonia is a precursor in fertilizer production and a potential carbon-free energy carrier, which is essential for the energy transition to more renewable energy sources. To that end, the current fossil fuel based method of industrial ammonia production through the Haber-Bosch process should be replaced by electrochemical ammonia synthesis. However, research into this topic faces several challenges, including a strong dinitrogen bond, competition from the hydrogen evolution reaction and low solubility of nitrogen in aqueous electrolytes, limiting the availability of nitrogen at the reaction sites on the electrode surface. In this study, in order to better understand these limitations to electrochemical nitrogen reduction to ammonia, a porous iron electrode is used in a cell design allowing both aqueous electrolyte and nitrogen gas access to the surface, which is successfully reduced electrochemically to serve as a nitrogen dissociation catalyst. Careful control of the applied potential limits the competition from the hydrogen evolution reaction. Nuclear magnetic resonance spectroscopy and ion chromatography measurements of the electrolyte were performed to check for possible contamination by nitrogen containing species. Small amounts of ammonia were measured using gas chromatography-mass spectroscopy on the gas output, but only with a high residence time of the nitrogen gas inside the cell. Since reduced iron surfaces are known to be good nitrogen dissociation catalysts, even at ambient temperature and pressure, the cause of the low ammonia production rate reported here is the abundant presence of water, which blocks nitrogen from the surface adsorption sites even when the catalytic surface is not submerged in the electrolyte. These results show that creating a surface with sufficient catalytic activity to break the dinitrogen bond is very well possible, but the main challenge is keeping the surface clean to prevent blocking of the reaction sites. This gives additional insight for future efforts in developing electrochemical ammonia synthesis methods.

Carbon sequestration involves the conversion of carbon dioxide gas into carbonates through reactions with magnesium or calcium bearing minerals, presenting a potential method to mitigate CO2 emissions and reduce their release into the atmosphere. This process can be classified into two categories: in-situ (subsurface) and ex-situ (surface). CO2 mineralization has demonstrated the ability to permanently store substantial quantities of CO2 without the need for extensive post-monitoring efforts, while also offering potential business model benefits for the generated end products. However, the field of mineralization still faces substantial technical and economic challenges, including high cost projections and slow carbonation kinetics, impeding further technological advancements in the field. Additionally, logistical challenges related to plant design and associated emissions contribute to the complexity of finding solutions to these problems.

In this particular study, the investigation focused on ex-situ carbon dioxide sequestration primarily through direct aqueous mineral carbonation, incorporating a direct air capture element. This approach was chosen due to the flexibility provided by direct air capture in terms of CO2 supply and the desirable characteristics of direct aqueous carbonation. Various models were developed using Aspen Plus software and compared, leading to the selection of the direct aqueous carbonation system as the optimal choice for CO2 carbonation. Further enhancements were implemented in the system, including recycled streams and heat integration, to reduce overall energy consumption. Optimization steps were also undertaken to determine the appropriate sizing of key equipment that make up the majority of the system's overall costs and to improve system efficiency.

An economic analysis was then performed, revealing that plant scales of 50 ktons/year yielded a positive Net Present Value (NPV), indicating profitability. Conversely, smaller-scale plants of 0.5 ktons/year and 5 ktons/year did not generate positive revenue, even with a high carbon credit price. This was followed by a sensitivity analysis that showcased the relevant parameters that holds significant effects on the economic performance of the system.

Moreover, business model cases were also explored, and it was concluded that utilizing the end products in building materials and road construction could potentially generate additional revenue for the mineralization system beyond storage options.

Overall, this investigation highlights the potential of ex-situ carbon sequestration through direct aqueous mineral carbonation, considering direct air capture, and emphasizes the importance of economic viability and revenue diversification in the successful implementation of mineralization systems to mitigate the effects of global warming.

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

As the variable renewable energy share keep on increasing throughout the energy transition, power systems require more and different flexibility measures. Battery energy storage can provide these essential services that enable the energy system to carbonise and transform on short time scales. Energy arbitrage, the trading of electricity on the electricity markets, can create economic value for batteries. This research assesses the energy arbitrage opportunities for utility-scale battery energy storage in the Netherlands. It compares five different battery technologies and defines the optimal size and power capacity with a linear mixed-integer Matlab optimization model. Furthermore, the operation of for the most optimal technology is simulated for one year with a Model Predictive Control algorithm to be able to compare the effects of forecasting accuracy of the electricity prices on the estimated profits. The results show that according to optimized planning and dispatch in the operation of a battery system can lead to financial opportunities in the Netherlands regarding energy arbitrage for flow batteries. If not today, then in the future. It has been shown that towards 2030 the business case for battery energy storage will significantly increase due to decreasing capital costs and increasing price volatility with the rise of the VRES and phase-out of fossil energy sources. With this research, a contribution is delivered towards the realisation of commercially operating an independent utility-scale battery energy storage facility. Insights are provided on what battery configuration is best suited for energy arbitrage purposes and the effectiveness of simulating the optimized operation of a battery facility with a model predictive control method has been shown. This has lead to clearer insights into the profitability of operating a BESF in the Netherlands.

Zero Emission Fuels B.V. (ZEF) is developing an integrated micro-plant to produce methanol from captured CO2 and green Hydrogen produced via alkaline water electrolysis. The electrolysis unit represents one of the largest financial and energetic costs in the system and is required to operate at 166 mA/cm2 under 2 V. In order to decrease the costs, ZEF is looking to synthesize highly efficient nickel-based electrodes to avoid using expensive noble-metal ones.
The objective of this work was the synthesis of efficient and stable nickel-based electrodes. Two electrodes were synthesized through electrodeposition (Raney nickel and NiFe) and one was synthesized through hydrothermal treatment (NiFe-LDH) and were compared to a RuO2-containing (Permascand) electrode and to a smooth nickel electrode. On/off cycles for 2.5 hours were carried out to measure the stability of the electrodes. Additionally, performance tests in a pressure range of 1-5 bar were carried out to measure the effect of increasing pressure. The experiments were carried out in an in-house designed and built zero-gap alkaline electrolysis cell.
Raney nickel, with a measured roughness factor of 150 was the best performing of the synthesized electrodes. After the stability tests, it was able to produce 166 mA/cm2 at 1.9 V (1.73 and 2.12 V for Permascand and smooth nickel, respectively). Raney nickel as anode material presented significant degradation. Raney nickel is the most promising material for HER, none of the synthesized materials presented significant stability for OER.
From the nickel-iron electrodes, NiFe with a roughness factor of 19.5 presented the best performance of the synthesized materials with 2.04 V for the mentioned current density. NiFe presented significant degradation, especially as anode material. NiFe presented a relative high performance considering its low electrochemical active surface area attributed to the presence of highly efficient active sites. NiFe-LDH was quickly degraded during the tests as cathode and anode material.
The pressure tests showed an inverse relationship between voltage and pressure. This hints that a decrease in bubble size with pressure is the cause behind the decrease in voltage. A simple model, based on experimental data and thermodynamic considerations, estimated that operating the cell at 50 bar reduces the voltage by 0.25 V compared to operation at 1 bar. The estimated reduction in voltage at a pressure of 50 bar would allow to operate the electrolysis cell under 2 V even with smooth nickel mesh as electrode.

In a bid to battle global warming the Dutch government has set ambitious targets to cut CO2 emissions in the Dutch Climate Agreement [1]. Aside from this state-driven initiative in line with the Paris agreement, several Dutch cities have presented their own climate initiatives. The city of Amsterdam has pledged to reduce its CO2 emissions by 55% in 2030 compared to 1990 levels which surpasses the national goal by 5% [2]. The capital has laid out a detailed plan to achieve these goals and it is clear that the electrification of mobility and heating, along with the roll-out of solar energy across the city, will play an important role in the future. Amsterdam is planning to install 1 million solar panels by 2022, aims to ban non-electric cars from the city by 2030 [3] and wants all buildings to be heated gas-free by 2040. While all of these steps are very helpful regarding the reduction of greenhouse gasses, they pose a big challenge to local grid operator Liander to ensure sufficient grid capacity [4]. The spokesperson of Alliander (parent of Liander) estimates that in 2050, peak power demand in Amsterdam could be 2.5 to 6 times higher than now. From the 25 substations in the city, which transform high-voltage electricity to middle-voltage, a minimum of 11 will not have sufficient capacity by 2030. The problem lies with an increase in both electricity supply and demand. On the supply side, as more and more Renewable Energy Sources (RES) have entered the Dutch energy mix in the past decade the strain on the electricity grid has increased. While wind turbines have largely been built offshore and feed into the high voltage grid, on-land turbines and especially large scale solar generation are mainly connected to the middle-voltage (MV) grid which is primarily designed to distribute electricity, not to accept it. On a sub-level, solar panels installed on private roofs deliver their electricity to the low-voltage (LV) grid. The capacities of cables and transformers in residential areas are sized to deliver electricity from generator to consumer, and not the other way around. Liander has indicated that capacity is sufficient to deal with privately owned solar for now, but that the significant increase envisioned by the city of Amsterdam will pose a problem in the future.

Up until now, ammonia has primarily served the fertilizer and chemical industry with limited regards to carbon emissions. The hydrogen within the ammonia molecule is commonly produced using fossil fuels; this process accounts for 1,2 % of the global CO2 emissions. Rather than using fossils fuels, electrolysis with renewable energy could be used to produce “green” carbon-free hydrogen and ammonia. The transition could decarbonize the ammonia industry and reduce carbon emissions drastically. Considering future emission restrictions and emerging new technologies, the techno-economic cost of green ammonia is expected to decrease. Accordingly, the the research question to be answered was: What are the effects of techno-economic induced cost reductions on the potential for green ammonia in the current and future global ammonia market? This report investigates the production and import costs over several global-oriented supply chains using a supply chain model. Rather than predicting the future, the aim is to gain an insight into the future of the global ammonia market. The scope of this thesis considers world scale ammonia production facilities with a capacity of 2200 ton NH3 per day. Due to their potential to become a producer or consumer of green and grey ammonia, the following countries are examined in more detail: Australia, Brazil, Chile, China, India, Japan, Morocco, Mexico, the Netherlands, Norway, Oman, South Korea, Trinidad & Tobago, United Kingdom, United States. The supply chain model distinguishes between the “grey” (with hydrogen from natural gas through SMR) and “green” (with hydrogen from electrolysis on renewable energy) production process. The supply chain model that is used to gain insight into the future global ammonia market models a green ammonia production process. The following components are included in the model: a 1,5 GW electrolyser (78 % efficient, 2020), 100 MW Haber-Bosch reactor, 57 MW air separation unit, and a 94 MW fuel cell (60 % efficient) for a location that has 5000 FLH. The modelled production plant is sized according to the full load hours in a given country and implemented electrolyser efficiency according following a learning curve (75 % in 2020 to more than 82 % from 2030. In future research, it would be more exact to optimize the production plant’s exact sizing using the available resources at one specific location. Results show that up until 2030 importing grey ammonia is cheaper than domestically producing green ammonia. In addition, due to the sensitivity of the ammonia industry to carbon leakage, a strong CO2 policy is essential to the transition. The main cost drivers for green ammonia are the hydrogen buffer and firm up power of the Haber-Bosch reactor and air separation unit; both are directly related to the cost of the renewable energy, which in turn is strongly dependent on the weather conditions. Currently, Morocco, Chile and China are considering the domestic production of green energy as it is expected to become cost-competitive with domestic grey production of ammonia by 2020. The analyses show that in addition to these countries, Australia, the United States of America and Oman show optimal conditions for domestic production of green ammonia as well.

This report aims to evaluate the feasibility of a small pilot plant placed near Broome, Australia to produce 3 tons of hydrogen per day using photovoltaic (PV) energy. Using PVsyst, a PV modelling software, the maximum power operating points were determined for a test layout. This was then transformed to other layouts which allowed the optimum layout to be found for a system connected to electrolyzers using maximum power point tracking technology. A second scenario using a battery was also modelled and optimized. Finally, the third scenario used direct coupling, meaning that the PV panels were not operated at their maximum power point but rather at where the electrolyzer and PV current and voltage lines crossed. This resulted in a lower power yield but also lower costs. To find the current and voltage curve for the PV field, the data from PVsyst analyzed to find the short circuit current and the open circuit voltage. This allowed the full current and voltage curve to be determined, which allowed the intersection point with the (experimental) electrolyzer current and voltage curve to be determined.

In all simulations piping storage was used to remove the intermittency of the hydrogen production by having a capacity of 3 tons of gaseous H2. This ensures a constant stream of hydrogen to the liquefaction system.

Using preliminary results an electrolyzer degradation simulation was carried out, to find how the electrolyzer would behave after 20 years of use. Although the influence of intermittency could not be found in literature, it was shown that the electrolyzer produces, on average during its 20 year lifetime, approximately 5.7% less hydrogen than it would without any degradation. This has been included in all financial analyses carried out in this report, along with a 7% weighted average cost of capital.

The financial framework has been based off of a number of different sources and forecasts. Due to the limitations of publicly available data some forecasts were replaced with constant prices which do not evolve throughout the years.

Using the hydrogen production models and financial frameworks it is possible to compare the different scenarios. From this a price of 4.16$/kg was found for a MPP coupled system, 4.39$/kg for a MPP coupled system including a battery, and 4.02$/kg for a direct coupled system. The third scenario was furthermore looked at in terms of physical layout; it was found that the decentralized layout consisting of smaller subplots was slightly more expensive than the standard centralized layout (4.09$/kg). For this pilot plant it is advised to use a decentralized topology, combined with a decentralized layout consisting of multiple smaller plots. Although the centralized layout is slightly cheaper, it contains more system critical components which could cause a large portion of the system to be inactive if they are broken.

The battolyser concept is based on an old fashioned nickel iron battery, consisting of a positive nickel(oxy) hydroxide electrode and negative iron (hydroxide) electrode. Research has been performed on the structural changes of the nickel and iron electrode upon charge and discharge. A lot of research can be found for the nickel electrode, but crystal structure studies are few. Much less research is performed on the iron electrode. Therefore the structural changes of the nickel(oxy) hydroxide and iron (hydroxide) electrodes during operation are further researched. Ni(OH)2 exists in the form of an α- or β-modification and NiOOH in a β- or γ-modification. The structure of the nickel(oxy)hydroxide phases has layers of edge-sharing NiO2 octahedra, where in between guest atoms can situate. Conventional nickel electrodes operate mainly between β-Ni(OH)2 and β-NiOOH, so most research focussed on this area. Upon overcharge the γ-NiOOH is formed and when discharging a direct reduction of β-NiOOH and γ-NiOOH into β-Ni(OH)2 occurs. The research on the nickel electrode published in this thesis is compared with a previous discharge study performed by Morishita et al. In their Rietveld refinement of the β-phases an ideal and fault phase model are assumed and the weight fraction of all phases present in the samples at 0, 50, 100 and 150% of state of charge (SOC) are determined. For the iron electrode four phases can be distinguished. The pure Fe in the electrode upon discharge becomes Fe(OH)2, under deep discharge this transforms even further towards FeOOH. For the deactivation process the reaction moves towards magnetite (Fe3O4). First the battery electrodes from the shelf are analysed by SEM-edx , X-ray diffraction and neutron diffraction. Then neutron powder and X-ray diffraction analysis have been performed to study the structural changes of the electrodes during charge and discharge. The nickel electrodes are measured at various states of charge from 0 to 100% and iron electrodes 0 to 90%. Preliminary experiments for the in-situ neutron diffraction test setup are performed. Different thicknesses of quartz glass, several sizes of nickel foam current collectors are tested for the amount of their background noise. In the nickel electrode are next to the carbon, 3 phases present. In the comparison with Morishita et al. significant differences are found. The transition towards β-NiOOH and subsequently γ-NiOOH occurs faster. Already at 50% of SOC the weight fraction of β-NiOOH is 58 wt% and at 100% of SOC the γ-NiOOH is 57 wt%. The c-parameter of γ-NiOOH is in agreement with Morishita et al. with a lattice distance of 20.8 Å. Morishita et al. did not specify how they determined the state of charge, so maybe they calculated the SOC in a different way. In the iron electrode three phases are identified, namely iron (Fe), goethite (FeOOH) and magnetite (Fe3O4). This is a strange result, because where Fe(OH)2 is expected, FeOOH is found. Probably discharged too far, moving the reaction into the second discharge plateau. The weight fraction of Fe increases and FeOOH decreases with increasing state of charge. The hydrogen content is decreasing with increasing SOC proportional to the background function for both the nickel and iron electrode.

Lithium ion batteries are currently the most attractive choice for mobile energy storage and power sources [4] in terms of energy density. However, it is unlikely that current battery chemistries will reach the energy density desired for future applications [8]. Li-metal, which has the highest reduction potential of all metals and the highest achievable capacity per weight unit, could significantly increase the energy density when used as an Anode. Unfortunately, the dendritic growth of Li-metal is a safety hazard, and the low electrochemical potential of Li-metal
is outside the stability window of many electrolytes leading to capacity degradation.
It has been suggested that safe Li-metal Anodes may be possible in combination with solid electrolytes, as the higher shear modulo of solid over liquid electrolytes may be able to suppress dendrite formation [21].
To study the stability of the interface between Li-metal and the solid electrolyte Li6PS5Cl, electrochemical measurements of the cells, ex-situ x-ray diffraction, and solid state Nuclear Magnetic Resonance measurements were made. It was not possible to confirm the decomposition products that were proposed in literature by density functional theory calculations and in-situ XPS. The XRD-pattern of the cycled electrolyte did not show additional phases. The NMR spectra developed broader peaks and one additional phosphorous environment upon cycling. As a tool to study dendritic growth through Li-ion concentration profiles, a cell for in-situ neutron depth profiling (NDP) was developed. The electrochemical performance is comparable to regular cells, except for a voltage drop due to contact problems during the break after Li-metal stripping. A thin layer of Li-metal between the window and the electrolyte pellet, as well as a collimator plate to put some pressure on the window, could be the solution
to go towards operando measurements.
The current standard data analysis method was implemented and its sensitivity towards gaussian broadening, due to energy straggling (from small angle scattering in the material and the stochastic nature of energy loss), was
investigated. It is shown that the standard deviation of energy straggling is larger than that of energy broadening due to the detector resolution, and that the error on the depth scale is in the order of micrometers.

This thesis provided an overview of the achievable ammonium concentrations, and the energy used to achieve these concentrations, by ion exchange, electrodialysis and reverse osmosis. The need for this overview arose during research for the N2kWh project, where one step in the process focused on increasing the ammonium concentration of (anaerobic digestion) reject water. The research presented some knowledge gaps. As available reports focused on the ammonium removal from the solution, the concentration in the residual stream was barely mentioned. Even when concentrations were reported, the conditions between the discussed technologies made it hard to make a comparison between the three technologies. Even less was reported on the energy that was needed to achieve the various concentrations.

To compare the three technologies, a 1.5 g NH4+/L solution was used as feed water for all three technologies. The technologies used different techniques to increase the ammonium concentration (using zeolites, electrical current over a membrane or high pressure through a membrane). This made comparing the technologies, very difficult. By using the same feed water for all experiments, the achieved concentrations and the energy that was used in the process could be used to compare the three technologies.

The highest ammonium concentration that was achieved during the experiments (7.1 g NH4+/L) was produced by Electrodialysis. Ion exchange achieved a concentration of 6.0 g NH4+/L, while a laboratory scale Reverse Osmosis achieved 4.5 g NH4+/L. The amount of energy used by the three technologies to produce 6 g NH4+/L was: ion exchange = 0.24 kWh, electrodialysis = 6 kWh, reverse osmosis = 4 kWh (per m3 of produced concentrated NH4+ solution). ROSA software was used to estimate energy use for Reverse Osmosis to achieve 6 g NH4+/L (as the laboratory scale Reverse Osmosis was unable to provide sufficient pressure to achieve this concentration). So ion exchange was the most energy efficient, but the maximum achievable ammonium concentration was the lowest of the three technologies. Electrodialysis was able to achieve the highest ammonium concentration but was less energy efficient and used more energy in the process.

As the public demand for electric vehicles and consumer electronics grows at an exponential rate, traditional energy storage systems like lithium-ion batteries are proving to be insufficient. A potential candidate to replace these conventional systems is the lithium metal battery. However, replacing the anode of lithium-ion batteries with lithium (Li) metal comes with its own challenges. Safety concerns and capacity loss during cycling (discharge-charge) are caused by internal dendrite formation and infinite volume change of the Li metal. In this work, two different strategies have been explored to counter these issues:

1. 3-dimensional metallic host for Li metal
2. Surface layer deposition

As the 3D metal host, a 3D porous nickel (3DPNi) substrate was used. It was fabricated in-house through a facile template-free electrodeposition process. Detailed electrochemical Li cycling tests were performed using a symmetric cell to investigate the performance of the substrate. Different aspects of the Li cycling like substrate structure and morphology, electrolyte modification (with LiNO3), kinetics of Li+ diffusion and the electrochemical impedance performance of the substrate were investigated. The 3DPNi substrate was also tested for its compatibility with sodium metal. To investigate the effect of surface layer deposits, atomic layer depositions (ALD) of Al2O3 and TiO2 were done on planar nickel substrates. Each of these were subjected to electrochemical Li cycling tests.

Our results show that the 3DPNi substrate can be effectively cycled with Li for up to 300 cycles at a capacity of 0.5 mAh⋅cm-2 and a current rate of 1 mA⋅cm-2. Increasing the capacity to 3 mAh⋅cm-2 (6 times) at the same current rate resulted in up to 60 cycles. It was also found out that this substrate could be used for sodium metal cycling. ALD on planar substrates have enabled the Li metal to be cycled for more than 300 cycles without failure, albeit at a capacity of 0.25 mAh⋅cm-2 and a current rate of 0.125 mA⋅cm-2. Hence, our study confirms that both the methods significantly improve the performance of the lithium (and sodium) metal anodes.

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 the study described in this thesis, it is demonstrated that combined short-term and long-term energy storage in one device, the battolyzer, is possible. The battolyzer is a device that works as a rechargeable battery, and that is capable of performing highly efficient electrolysis with any excess electricity. The battolyzer was based on the Nickel-Iron-Battery, which was developed by Thomas Edison and Waldemar Jungner, and on alkaline electrolysis. Both are well-established technologies that were developed more than a century ago.
The main research question in this thesis is: "Is an energy storage system based on Nickel and Iron suitable to operate as an integrated battery and electrolyzer, and what would be the overall energy efficiency of such a device?".
Firstly, a test-series that was designed to simulate various real-life situations, including partial and full charging and discharging, rapid switching, continuous overcharging, and the around-the-clock cycling. Neither the battery, nor the electrolysis have noticeably deteriorated after the many cycles. The remarkable finding is that the reversible discharge capacity of the battery is not adversely affected by such harsh test conditions.
Secondly, the gas quality was analyzed, qualitatively and quantitatively. The outcome of these tests was that overcharging leads to gas production with a Coulombic (or Faradaic) conversion efficiency of equal to 100%, within the experimental accuracy.
In a final step, optimal operating conditions for the battolyzer have been identified. Tests show that the overall energy efficiency of the battolyzer could surpass 90%. However, the most remarkable finding of the whole project is the stability of the energetic efficiency at 80-90% over many different types of cycles, including all cycles to simulate real-life situations.
We anticipate these results to be a starting point for a robust grid-scale energy storage solution in a low-cost, abundant-element based, intrinsically flexible device that has close to full-time operability: as electrical power storage, switchable electricity supply, and as a hydrogen producer.