CO2 electrolysis to form CO with the use of electricity from renewable sources is a promising technique in closing the carbon cycle. Via the electrochemical reduction CO2 can be converted into different hydrocarbon products. These value-added products are for example CO, HCOOH, CH3OH or C2H4. The direct electrochemical route of CO2 reduction is often tested on three metrics: the faradaic efficiency, the current density and the energy efficiency. The implementation of CO2 reduction has some technical challenges. One of which is controlling the local pH and carbonate formation inside the electrochemical cell producing hydrocarbon products. Controlling the pH inside the electrochemical cell becomes an issue because of the production of hydroxide anions that increase the pH. A high faradaic efficiency is affected by the local pH. With an increasing pH CO2 is consumed to form carbonate and Hydrogen Evolution Reaction (HER) is favored. Mass transfer limitations result in the pH increasing near the electrode. The local pH is dependent on the electrochemical reaction, buffering reactions inside the electrolyte and mass transfer within the electrolyte flow. Previous studies have used numerical modelling to obtain a 2D transport model to present concentration gradient along the cathode or inside the cathode. Other studies that show the pH experimentally do this using scanning probe techniques or measure the intensity of dye sensitive to pH.
In this project the effects on the local pH are studied with the use of Fluorescence Lifetime Imaging Microscopy (FLIM). This method is able to image the local pH with the use of a fluorescent dye that has a lifetime dependent on the local surroundings. This thesis researched the effects of three process parameters: electrolyte anion type and concentration, the catholyte flow rate and the current density. The electrolytes studied are: 0.1 M KHCO3, 1 M KHCO3 and 0.4 M K2SO4. The catholyte flow rates studied are corresponding to Reynolds number 0.8, 8 and 47. The different current densities are −1, −5, −10 and −50 mA cm-2 . The effect of these parameters was studied with performing electrochemical tests and studying the cell potential.
This study obtains a fluorescence lifetime-pH calibration curve inside an electrochemical cell. From this calibration curve could be concluded that we have a clear trend above pH 9 to the phase-shift fluorescence lifetime. We also concluded that the used salt KHCO3 is likely to have an effect on the performance of the alpha dye. An unexpected effect of using FLIM onto the spatial resolution in an electrolyser was due to the presence of bubbles. We suggest a more elaborate study into the effects of the settings used in the FLIM method.
The results show that the characteristics affected by the anion type and concentration of electrolytes can be described in the buffer capacity and conductivity of the electrolytes. With increasing buffer capacity and bicarbonate concentration the pH difference between the bulk and near the cathode decreased. The study also found that the overall cell potential was increasing with increasing conductivity of the electrolyte. We cannot distinguish a clear effect of the concentration overpotential as an effect of the buffer capacity onto the overall cell potential.
Additionally, the study found that a higher Reynolds number leads to a decrease in potential due to lower concentration overpotential and better gas removal. From a study on the current density and its effects could be concluded that even though we expect laminar flow with these Reynolds number mass transfer is occurring perpendicular to the flow of the electrolyte. This is an effect of the formation of hydrogen or carbon monoxide bubbles inside the electrolyte that improve mixing. This was also shown in the decrease of pH increase near the cathode with increasing Reynolds number. For the highest current density an overall increase of the bulk pH was linked to the improved mixing due to gas bubbles. The effect of gas bubbles onto the local pH and the cell potential should not be underestimated. Improvement of gas removal with a higher Reynolds number of the electrolyte flow rate or in other ways remains a recommended field of research. We suggest the use of Particle Image Velocimetry alongside of FLIM to obtain more insights into the flow profile inside the catholyte affected by the formation and removal of gas bubbles. Finally, we recommend to research the system with the implementation of the gas channel and different types of membranes.

The vast amounts of greenhouse gas (GHG) emissions, surging gas prices, and increasing proportion of intermittent energy sources force the energy sector to structurally modify the energy system. The reversible Solid Oxide Cell (rSOC) is considered to be part of the solution due to its high efficiency, good scalability, and ability to balance the energy grid. The rSOC is a high-temperature, electrochemical device that can convert both power-to-gas and gas-to-power during its Solid Oxide Fuel Cell (SOFC) and Solid Oxide Electrolysis Cell (SOEC) modes. The integration of the SOFC with a combined cycle gas turbine (CCGT) features exceptional synergies. Although the synergies of the SOFC and CCGT have already been widely reviewed, the combination of an rSOC and a CCGT has remained unexplored.

The research objective of this study is to assess the benefits of retrofitting an rSOC to an existing CCGT by simulating its exegetic performance, relative GHG emissions and gross profit, and comparing these results to those of an existing CCGT. During the integration of the rSOC (operating in SOFC mode) with the CCGT, the performance of the reversed SOEC mode must be taken into account because it will have to operate with the same operating conditions and the same system components. In order to decrease the system investment cost, this work examines to what extent the rSOC can be retrofitted into the currently deployed CCGTs.

This research optimizes the process plant design and scrutinizes the effect of various operating conditions on the system performance. The optimization is performed through exergy analyses of a zero-dimensional Aspen Plus model. A case study, in which the proposed system is inserted into an energy resource allocation model of the Amsterdam metropolitan area, is used to examine the gross profit of the proposed multi-energy system.

The optimization of the SOFC-CCGT system results in an exergy efficiency of 61.5%, generating 518 MWe, which enhances the performance of the existing CCGT by 3.8% and decreases the GHG emissions [CO2e t/MWh] by 21.3%. When the combined heat and power (CHP) mode of the CCGT is considered, the resulting SOFC-CCGT CHP system achieves an exergy efficiency of 61.2%, while generating 474 MWe and 103 MWth. The SOFC-CCGT CHP outperforms the exergy efficiency of the original CCGT CHP with 4.2%, while emitting 13.2% less GHG emissions. The same operating conditions of the SOFC were applied to the SOEC, which manages to operate with an exergy efficiency of 84.3%.

Implementing the rSOC-CCGT CHP system into the energy resource allocation model results in a 118% increased net present value (NPV) of the gross profit compared to the original CCGT. The proposed multi-energy system is able to adjust its operating mode to anticipate the price variations in the energy grid and thereby increases the gross profit. Adding a thermal energy storage system decouples the consumption and production of heat, which enhances the NPV of the gross profit by an additional 1.4%.

Since the European Commission concluded that green hydrogen is a key priority in the achievement of Europe’s energy transition, hydrogen is included in transition strategies of many parties. The Netherlands has the ambition to become the European leader of hydrogen deployment within their strategy. The oversea import of hydrogen is highly needed in the future, as it is expected that NW-Europe does not have sufficient renewable energy sources to locally produce the entire hydrogen demand. Due to the extensive gas network and distribution infrastructure, the strategic location of Rotterdam has the potential to become the new hydrogen energy import hub of Europe. As Vopak, world’s leading independent tank storage company, sees opportunities in the large scale import and storage of hydrogen, an evaluation of the entire green liquid hydrogen supply chain is done. In this paper, an evaluation of the green liquid hydrogen supply chain is presented. The literature review of the individual elements led to the construction of the supply chain existing of the consecutive elements: renewable energy generation, electrolyser technology, liquefaction plant, onshore storage, oversea shipping, onshore storage, distribution of hydrogen and consumption by end-users. Within this supply chain, liquid
hydrogen is taken into account due to its favorable volumetric density of 70.8kg/m3. This results in the handling and storage of hydrogen at cryogenic conditions: 20K at a pressure of 1.1 bar. The scope of the project is determined to be from the liquefaction plant to the distribution of the hydrogen into the different transportation modes on the importing terminal. A technical and economic model is created in order to analyse different throughput scenarios. These scenarios transport the hydrogen from a country X in which abundant renewable feedstocks are expected to be produced to the importing location of Rotterdam. By creating and merging a technical and economic model, an in-depth research is conducted. The model determines optimized configurations and their sensitivity for certain throughput scenarios. The technical research led to the following findings: 1. The storage tank has an expected maximal spherical capacity of 40 000m3 with an according BOR of 0.043%/day. If higher capacities are required, the shape
of the tank shifts towards cylindrical structures, due to the vacuum insulation technique. Whenever this capacity is increased, the currently used technology of vacuum MLI is expected to shift towards membrane technology. This is due to that vacuum insulation is not applicable to flat surfaces unless a very thick inner wall is constructed. The exact technology and according BOR of membrane technology is highly proprietary. 2. The liquefaction plant is a mature technology of which the capacity can be easily increased. The current largest plant capacities can be increased from 50tpd to 500tpd, due to easily transportable cold boxes. The current energy consumption of 8kWh/kg can presumably decreased to around 6kWh/kg. Although the minimum capacity of a plant is 20%, the energy consumption is heavily affected. 3. The first oversea LH2 vessel, with a capacity of 1250m3, is currently in its sea trials. Concept designs and interviews led to the perspective that a LH2 vessel of 100 000m3 can be expected in the year 2030. 4. The BOP systems do not exist on industrial scale. Although the handling systems do not exist, the transfer loss during a transfer of a parcel is estimated to be 1.5%. 5. The energy consumption throughout the supply chain shows that the liquefaction plant plays a dominant role. The second most energy intensive process is the oversea shipping. The economic simulations led to the following findings: 1. The LCOH in Rotterdam can decrease to 2.78USD/ kg when a throughput scenario of 3.5Mt/year from the location of Saudi Arabia is realised. 2. The competitiveness tipping point (3.15USD/kg) from the location of Morocco and Saudi Arabia is around 0.35Mt/year. 3. Australia does not reach an economically attractive liquid hydrogen oversea supply chain to Europe, unless the demand highly increases. 4. In small throughput scenarios the storage tank has the most dominant impact on the LCOH. This is due to that the liquefaction plant and ship are scalable to a single unit, while the storage tank has a minimum of three tanks per terminal. The combination of the technical and economic results led to an overall conclusion that a green liquid hydrogen supply chain is economically competitive at a throughput scenario of 0.31Mt/year from Morocco. Although the technical elements within this scenario are currently still in concept phase, expectations look very promising and can be deployed by 2030. Further BOP and handling systems are not yet commercially available, similar expectations are set for the year 2030. Whenever the hydrogen demand in NW-Europe increases, an acceleration of the oversea hydrogen deployment is established. Therefore further research needs to keep a close eye on the technical development of the supply chain.

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

Greenhouse gas concentrations are ever increasing in the Earth's atmosphere, causing the global temperature to have reached over a 1.0 degree Celsius increase relative to pre-industrial levels. A further increase in this temperature can have disastrous effects on our society, thus the increase in greenhouse gases must be attenuated. Electrochemical water splitting and CO2 reduction have been identified as promising routes to generate carbon neutral fuels. Efforts are made to increase the performance of the electrochemical configuration, however, a stable system that is applicable for industrial applications has not yet been achieved. The research field is ever changing and thus the choice of electrolytes and catalysts fluctuates. There is a desire for a stable configuration that can cope with these changes. A bipolar membrane (BPM) has the unique ability to pair two different electrolytes which can be optimized for their respective oxidation and reduction reactions. A BPM configuration is applicable for high performance rates, since it splits water at the interface layer, therefore accelerating the rate of ion transport compared to a conventional monopolar membrane. Despite the advantages of the BPM, there are still knowledge gaps on the exact mechanism behind the BPM and its electrochemical response. It is known that co-ion permeation through the BPM lowers the efficiency of the water dissociation reaction, thus decreasing the stability of the system in the long run. Therefore, it is relevant to further explore the effect of ion characteristics on ion cross-over. This research focuses on the degree of ion cross-over for a variety of electrolytes, with different pKa values. Multiple buffer solutions were tested at the cathode in a flow cell configuration for a current density range of 0-150 mA/cm2. The anolyte was a 0.5M NaOH solution for every tested catholyte. All experiments were performed for a constant period of time, after which the electrolytes were analysed for ion cross-over. It has been observed that the pKa value, the mobility and the valence of an ion influence the ion cross-over through the bipolar membrane. A large ion size decreases the ion cross-over to negligible amounts, for permeation through the membrane is limited. However, high BPM potentials have been detected for large molecules due to an assumed diffusion boundary layer, which increases the resistance at the cation exchange layer. For all tested catholytes low co-ion permeation (%) is measured at high current densities. Thereupon, the age of the BPM significantly affects the degree of ion cross-over. This observation is stronger for the anion exchange layer, for its permselectivity is lower. Additionally, the catholyte choice appears to influence the opposing Na+ flow from the anolyte to the catholyte.
This thesis demonstrates that for high current densities co-ion permeation reaches negligible values. In addition, the results indicate that an ideal ion size region exists, where ions cannot permeate the membrane easily, yet do not form a diffusion boundary layer (thus do not increase the BPM potential). This knowledge is relevant for optimizing the BPM configuration for industrial applications, since a clever choice of electrolytes can further stabilize the system. Future research should focus on up-scaling the set-up and testing the commercial BPM for stability and permselectivity.