The current global average CO2 concentration in the air is 427 ppm, rising at a rate of 2 ppm per year, faster than ever before. This underscores the urgency to capture and either utilise or sequester the carbon. The energy transition is driving a shift from fossil-based generation towards renewable energy sources, with wind and solar energy generation at the forefront. The intermittency of supply from renewable energy generation presents opportunities during peak electricity generation to reduce CO2 electrochemically.
The electrochemical utilisation of captured CO2 offers a sustainable pathway to close the carbon loop by converting waste carbon into value-added chemicals. This thesis explores the electrochemical dicarboxylation of 1,3-butadiene with CO2 to produce 3-hexene-1,6-dioic acid (3HDA), a direct precursor to adipic acid. Adipic acid is a key raw material in Nylon-66 production, and its conventional synthesis from cyclohexane emits significant quantities of N2O, a greenhouse gas with a global warming potential of 298 times that of CO2. In contrast, the pathway studied here aims to decarbonise the process using renewable electricity.
The electrochemical synthesis of 3HDA from 1,3-butadiene and CO2 is employed in an electrolyser cell. Using a sealed, undivided electrochemical cell with acetonitrile and tetraethylammonium chloride as the electrolyte solution, the study systematically investigates the influence of various electrocatalyst morphologies and materials, and process parameters on faradaic efficiency, product selectivity and yield.
Nickel wire was identified as the most effective working electrode, outperforming copper wire and other nickel-based morphologies, employed alongside aluminium coil as a sacrificial anode. Electrochemical characterisation using cyclic voltammetry and chronoamperometry revealed –2.6 V vs Ag/AgCl as the optimal reduction potential for 3HDA formation, with a faradaic efficiency achieved of 14% for 3HDA and 100% selectivity among the carboxylated products. Competing side reactions, such as 3-pentenoic acid (3PA), formate and oxalic acid production, were observed at other reduction potentials. Reduced moisture content in the electrolyte was found to poorly influence the faradaic efficiency. The dry acetonitrile has a similar 3HDA faradaic efficiency when the water content is reduced from 350 ppm to 150 ppm in the electrolyte. Temperature studies indicated that higher temperatures enhance the reaction rate but increase product solubility, reducing solid product formation. Solubility measurements confirmed this behaviour. On calculating the faradaic efficiency of the dissolved 3HDA as well, the efficiency stands at 6.58% for at 40◦C and 3.59% at 60◦C. Further, experimentation with alternative supporting electrolytes like TBABF4 and TBAPF6 was inconclusive due to practical limitations.
Overall, the thesis demonstrates a promising proof-of-concept for the sustainable electrochemical conversion of CO2 and 1,3-butadiene to value-added chemicals of 3HDA. The findings contribute to the broader goals of electrifying chemical synthesis and valorising captured CO2, inspiring future work recommended in improving the process conditions and refining electrolyte and electrode design.

Traditional carbon capture processes require large amounts of energy to regenerate the solvents used. Recent research has proposed to decrease the energy requirements of this process by integrating the system of carbon capture and electrochemical conversion, removing the need for the traditional regeneration step. The integration of these two steps involves the use of the same medium for both the carbon capture solvent and for the electrolyte for electrochemical conversion of the captured CO2. The proposed methodology takes advantage of the inherent elevated temperatures resulting from ohmic losses in the electrochemical system, especially at an industrial scale and helps optimize the efficiency of the conversion process. This study investigates the use of non-aqueous solutions of 1:4 choline chloride to ethylene glycol coupled with monoethanolamine as the medium for this process, particularly focussing on its use as the catholyte in this system. Specifically, this project targets the production of carbon monoxide using silver cathodes in small laboratory scale compact H-cells, with an anolyte of 0.5 M sulphuric acid and a Nafion-117 cation exchange membrane separating the compartments. Different operating conditions, including pulsed electrolysis, are utilised to attempt to modify the levels of carbon monoxide production and stabilise the system for long term operation.
Initial investigations into this system found that carbon monoxide could successfully be produced at constant reduction potentials vs. Ag/AgCl of -1.5 V and -1.7 V for approximately 10 minutes of operation when operating at 65 °C. Pulsed electrolysis has been proven to be able to increase the stability of carbon monoxide production for up to an hour of operation. The study found that the most promising conditions for the pulsed electrolysis are using positive anodic potentials vs. Ag/AgCl of either + 0.1 V or + 1.5 V for between 5 and 40 seconds in combination with cathodic potentials vs. Ag/AgCl of - 1.5 V. The faradaic efficiency of carbon monoxide production was able reach up to 24 % for one hour of operation with relatively stable production profiles when using pulsed electrolysis.
The results of this project show that this system can produce the desired carbon dioxide reduction reaction and with the use of pulsed electrolysis this can be achieved for at least one hour with faradaic efficiencies of carbon monoxide production greater than 20%. These findings showed a better overview for the next stage of this research. In particular, further work involving longer term operation of the cells is of interest after this research.

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.

Alkaline water electrolysis emerges as a promising technology for green hydrogen production, playing a significant role in global decarbonization. Nickel-based electrodes are widely used in alkaline water electrolysis due to their excellent catalytic properties for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, nickel electrodes often experience a decrease in activity over time. Attempts of existing literature to investigate nickel deactivation employ conditions that differ from industry standards. Therefore, a more profound understanding of these phenomena under industry-relevant conditions is crucial for averting specific degradation pathways in future electrode design. This thesis investigates the deactivation phenomena and the timescales of untreated nickel electrodes during the OER and HER at 323 K and 30 wt% KOH, employing a current density of 1 A cm-2. The electrolyte concentration and current density match industry standards, and the temperature aligns more with industrial practices than literature. The OER overpotential increases under these conditions in 2.5 hours by 0.19 V and still increases after this period. The HER overpotential increases by 0.65 V and stabilizes after 20 minutes. Electrochemical and surface analytical tests suggest that both reactions primarily deactivate due to a redox reaction.

The primary objective of this study was to address the lack of understanding of the commercial- scale implementation of novel CO2 based carbon nanomaterial (CNM) production and its comparison with status quo CNM production processes using unsustainable fossil resources. To accomplish this objective, first, a literature review was performed on the status quo commercial- scale CNM production, the lab-scale CO2 based processes and the CNM market. In regards to the status quo processes, the literature review yielded mainly chemical vapor deposition (CVD) processes of carbon nanotubes (CNTs) and graphene production. With respect to the lab scale CO2 based processes, the literature review involved categorising the identified processes into four different approaches based on their working principles - CO2 based CVD, molten salt based electrochemical CO2 reduction, liquid metal catalyst aided CO2 reduction and metal reductant enabled CO2 reduction. With regards to the CNM market, CNT materials were found to have the highest market share followed by that of graphene. Startup spinoffs working on the graphene and CNT production from CO2 were identified with origins to university-based research groups.

Following such literature review, a framework was developed to select one process each from the status quo CVD processes and the novel CO2 based processes, which produced comparable CNM. This framework was applied to the processes obtained from the literature review, which led to the selection of a methane-based CVD process and a molten salt-based electrochemical CO2 reduction process for small-diameter multi-walled (MW) CNT production. The methane-based CVD process involved the use of Ni-Mo catalyst on MgO support and high-temperature operating condition of 975°C. The molten salt-based electrochemical CO2 reduction process involved the use of Ni and steel electrodes, pure molten Li2CO3 electrolyte and high-temperature operating condition of 750°C. These selected processes were designed and simulated in Aspen Plus at a commercial-scale production level of 5000 tonnes per operating year. The mass balance, energy balance, and equipment cost data obtained from the simulations were used to assess the technical, economic, and environmental performance of the ex-ante CO2 based production process and the status quo CVD production process.

The technical performance assessment involved the estimation of resource intensity and energy efficiency indicators of the two processes, wherein the CVD process outperformed the electrochemical process in both indicators. The economic performance assessment involved the estimation of total capital investment, operational expenditure, net present value, and payback period. The CVD process performed better than the electrochemical process in all the indicators except total capital investment. Both processes indicated positive net present values and short payback periods, indicating the realisation of commercial scale plants of both processes to be profitable. The environmental performance assessment was carried out using the life cycle assessment methodology in the CMLCA software. The climate change impact indicators at scope 1 and 2 levels along with the net avoided impact from using CO2 were estimated using the CML 2001 impact assessment family. The electrochemical process was shown to perform considerably better than the CVD process in all the climate change impact indicators. Overall, the technical and economic performance of the CVD process was better than that of the electrochemical process. However, the environmental performance of the electrochemical process was shown to outperform that of the CVD process.

The limitations associated with modeling decisions taken in the two processes and with the uncertainty associated with the lack of data were highlighted. Further, the relevance of this study was discussed with respect to the industrial symbiosis potential of using waste CO2 from industries leading to GHG emission reduction and subsequent deceleration of climate change impacts. Finally, future potential studies were highlighted that could build on the research and insights generated in this study. One of these studies involved a case study on the implementation of a commercial-scale electrochemical process for MWCNT production in Port of Rotterdam region. Another study involved a techno-economic and environmental assessment of atmospheric CO2 capture and conversion to carbon nanomaterials for applications that can potentially achieve net negative emissions.

The rise of CO2 concentration in the atmosphere is a leading cause of global warming. Utilizing CO2 ob- tained from point sources, such as chemical industries, as a feedstock to produce high energy density fuels and chemicals could mitigate the emission of CO2 as well as provide various economic bene- fits. One promising technology is the electrochemical reduction of CO2, however, the presence of contaminants in the industry-supplied feedstock and the separation of products downstream would be challenging in a continuously operated large-scale plant. To address these challenges and indentify the bottlenecks involved, it is important to study which pre-treatment and post-treatment steps are required and how to integrate these in a large-scale electrochemical CO2 reduction process.

The gas and liquid feed streams to the CO2 electrolyzers are first cleaned to the desired levels. The liquid feed stream is water from the river Rhine that is purified so the specifications of the water meet the requirements for type 1 water (ultrapure water). The gas feed stream is the flue gas stream of an average steel-producing plant in Europe and is cleaned to remove sulfur and nitrogen compounds. A two-step electrolysis process is used where CO2 is first reduced to CO, followed by the reduction of CO to C2+ products. The electrolyzer for the first step is a membrane electrode assembly-based flow cell with a current density of 300 𝑚𝐴 𝑐𝑚2− and a faradaic efficiency (FE) of 96% to CO. In the second step, a gas diffusion electrode-based flow cell with a current density of 300 𝑚𝐴 𝑐𝑚2− and a faradaic efficiency of 9.35%, 15.49%, 45.57%, and 16.38% towards acetic acid, ethanol, ethylene, and propanol, respectively, is used. The anolyte and catholyte in the reactors are recycled 3,500 and 2,000 times, respectively, to reduce the size of purification of the liquid feed stream section and increase the liquid product concentration. In both steps, unreacted CO2 and CO are recycled. The gaseous and liquid products are separated and purified to meet the industry standards using established separation techniques.

The total capital investment for a process with an industrial gas feed of 381.678 tons per hour is 4,053.5 million dollars with a daily operating cost of 7.403 million dollars. The daily income from selling the products is 2.363 million dollars, but this could increase if the FE towards acetic acid is increased since this product has the highest income per electron consumed. The net present value (NPV) for the base case, assuming current technological and market conditions, is -19.4 billion dollars after 15 years. To analyze which parameters have the most influence on the NPV, a sensitivity analysis is also per- formed with a better and optimistic scenario. It was found that the economic feasibility of the currently designed process is not limited by the technological progress, but mainly by the market conditions.

The target of this process is to reduce the emission of CO2, however, the operation of the plant itself contributes to some CO2 emissions. Therefore the process should consume more CO2 than it emits. The units that consume most energy and emit the most CO2 are the CO to C2+ products electrolyzer and the first distillation column in the liquid product separation section to remove acetic acid. It was found that the process is only carbon negative when the consumed energy is generated by nuclear, wind, or solar energy. The net CO2 emission is the lowest when nuclear or wind is used as an energy source. Generating all the required energy from these sustainable sources brings another challenge since the total installed capacity of these sources are currently not sufficient to cater to the needs of such a large-scale continuously operating CO2 electrolysis plant.

Keywords: Electrochemical CO2 reduction, large-scale, pre-treatment, post-treatment, technoeconomical analysis, energy analysis

In the coming energy transition, the availability of reliable and affordable energy storage will be of vital importance. Battery storage is a large factor in the energy storage sector, and current battery storage is dominated by lithium-based batteries. However, lately, alternatives to lithium have been given renewed attention, due to the insufficient abundance of lithium in the earth’s crust and the promising theoretical aspects of these other types of batteries. Fluoride-based batteries, for example, have high theoretical capacities and are theorized to be very suitable for application in solid-state battery technology. Fluoride-based batteries have only been produced on a lab-scale relatively recently, with the first reversible solid-state fluoride-ion battery produced in 2011, and the first room temperature reversible fluoride-ion battery produced in 2018, yet interest in this technology has drastically increased over the past few years. The current main issues fluoride- ion batteries are running into are its poor cyclability, its low current densities, and its inability to meet the theoretical capacities. In this report, multiple facets of fluoride-ion batteries have been analyzed in an effort to improve on these characteristics. In particular a focus has been placed on two commonly used materials in fluoride-ion batteries: electrolyte BaSnF4 and cathode material BiF3. The ionic conductivity dependence on pressure was deduced for each material, with BaSnF4 having its highest ionic conductivity at ∼280 MPa and BiF3 having its highest ionic conductivity at ∼680 MPa. To test the effect of oxides in BiF3, which form spontaneously when BiF3 is exposed to air or humidity, various Bi-O-F compounds were synthesized and had their ionic conductivity measured. It was found that each of the compounds that contained oxygen had a drastically lower (factor 1,000-10,000) ionic conductivity than pure BiF3. An attempt was also made to improve the ionic conductivity of BiF3 by doping that material with SnF2. BiF3 doped with SnF2 concentrations of 5-20% were synthesized, and had their ionic conductivity measured. It was found that the ionic conductivity was increased by dopant concentrations of 5% and 10%, with the material with 10% SnF2 having the highest ionic conductivity, while the materials with 15% and 20% SnF2 had a similar ionic conductivity to pure BiF3. Symmetric fluoride-ion batteries were also produced, with BiF3 as an electrode material and BaSnF4 as an electrolyte material. The produced batteries reached charge and discharge capacities with values of at most only 30% of the values reported in literature. The batteries also had poor capacity retention over multiple charge-discharge cycles. Batteries were also produced using BiF3 doped with 5% and 10% SnF2 as an electrode material. These batteries had higher initial capacities but had even poorer capacity retention over subsequent cycles. It was however also found that the critical current density for the batteries had increased as a result of doping with SnF2, allowing higher current densities to be applied to the batteries.

In the last decade, many initiatives have been undertaken by governments, companies and other institutions to reduce the output and concentration of CO2 in the atmosphere. The current non-emitting energy sources with highest potential are solar and wind energy. Unfortunately, these energy sources vary in power production, while the demand fluctuates far less. Hence, a solution is needed for crossing the times when there is a mismatch in energy supply and demand. One potential solution is to store excess energy in chemical bonds by using electrochemical CO2 reduction.

The steel making industry is highly energy intensive and a great contributor of greenhouse gas (GHG) emissions. It generated between 7% and 9% of direct emissions from the global use of fossil fuels in 2017 [1]. Gas emissions in an integrated steel mill (ISM) arise mainly from three streams: coke oven gas (COG), blast furnace gas (BFG) and basic oxygen furnace gas (BOFG).

This study focuses on the short term solutions to become a carbon neutral steelmaker where blast furnaces (BF) and basic oxygen furnaces (BOF) are still a fundamental part of the steel making process. The Rectisol® process is used to capture CO2 from the works arising gases (WAGs) of an ISM and to generate syngas which can be used as a chemical building block to produce liquid fuels among others.

The Rectisol® wash is a patented process by Air Liquide and Linde which uses chilled MeOH as a solvent. Both processes were first validated against stream data provided by the patents. PC-SAFT EOS was used to simulate the purification plant because of its strong theoretical foundation and its ability to adapt the parameters to predict component behaviour. Various binary interaction parameters proposed in literature were used to simulate the purification plants. From these simulations, it was found that the standard binary interaction parameters with the adjusted parameter for H2S-CH3OH, as proposed by Sun et al. [2], showed the best results.
The configurations of Air Liquide and Linde were used as base configuration to clean the feed stream. From these simulations, it was observed that in both configurations large portions of CO2 are lost in the stripping process of both configurations. Enhanced CCS configurations were investigated to increase the CO2 recovery of both configurations. The desorption of CO2 was altered by introducing multiple intermediate flashes to increase the desorption of CO2. Without optimisation, the downstream constraint for the CO2-rich stream of 95% CO2 content was almost met in the Linde configuration and requires further upgrading in the Air Liquide configuration. The decision was made to use the Linde enhanced CCS configuration as a base configuration since this would solely require a change in operating conditions to meet the downstream CO2 requirement of 95% content in the CO2-rich stream.

HCN and H2O require a seperate wash to avoid accumulation in the main wash. To treat these components together with H2S and COS, two pre-wash configurations combined with the Linde enhanced CCS configuration were looked into. A pre-wash configuration with a separate absorber column and dividing wall column (DWC) and a pre-wash configuration with a separate absorber column and rectifier with purge were examined. Both configurations meet the downstream requirements for the purified gas stream and CO2-rich stream. The main difference between the two configurations is the difference in thermal utility consumption and make-up MeOH. The decision was made to move forward with the pre-wash integrated configuration comprising of a rectifier and purge since additional make-up MeOH would be more cost-effective. The energy recovery method proposed by Linnhoff [3] was used to identify any potential energy saving of the purification plant. A heat exchanger network was designed which reduced the cooling duty by 57% to 54,9 MWth and the reboiler duty by 50,6% to 26,8 MWth. Finally, an economic evaluation was made of the final energy integrated configuration. Equivalent annual cost and operating expenditures of the purification plant were estimated at €12.32m and €51.13m respectively per year. This gives a cost per ton captured CO2 of €37,87.

The Dutch government has set out to largely reach reductions in carbon emissions in the electricity sector with the utilization of offshore wind energy. Due to the intermittency of wind energy this poses new problems and challenges for the future electricity system in the Netherlands. The objective of this report is to identify the challenges for the electricity supply of offshore wind farms and to research how energy storage and alternative wind turbine design can aid in these challenges. The problems experienced and possible solutions are first identified by conducting a literature review and data analysis. Subsequently a Matlab model is constructed to simulate an offshore wind farm and energy storage system. This model is used to determine the most cost-efficient storage technique and the impact of this technique on the future electricity system.
Of the challenges for future offshore wind farms do the short-term profile effects have the most influence. These effects negatively affect: 1. the security of supply in the electricity system, 2. the stability of the load on the high voltage grid and 3. the market value of the produced electricity. The impact of these effects is intensified by the strong correlation in power production between the connected (future) onshore and offshore wind farms. To reduce profile effects energy storage is used, the optimal configuration of the storage system has a power capacity between 0.23 and 0.27 times the rated power of the wind farm. For the optimal energy capacity, however, no optimum is found, and the design depends on the desired impact of the system. An analysis on the impact of an optimal design has shown that an offshore wind and energy storage system does not result in an economical feasible system. Short-term profile effect reduction with energy storage, however, is shown to be essential in a future electricity system that is dominated by wind and solar power. The short-term profile effects of wind energy production are correlated too much and will have a too high impact on the system if no energy storage is included in offshore wind electricity production.

The worlds energy demand is increasing however, the majority of the energy supply is still based on fossil fuels. The consumption of fossil fuels results in the emission of carbon dioxide which is one of the main greenhouse gases responsible for the ongoing climate change. In order to reduce the carbon dioxide emissions, more and more energy is produced in a re-newable way. Mainly from solar and wind energy. This energy is however intermittent in char-acter and comes in the form of electricity. To overcome the intermittency, the excess pro-duced electricity has to be stored in an efficient reversible way, so that the energy can re-leased again when it is needed. One possible solution that tackles both problems is the elec-trochemical reduction of carbon dioxide in aqueous electrolytes into highly valuable chemicals, or so called solar fuels. In this study, a new infrared spectroelectrochemical cell with an easy exchangeable electrocatalyst is developed to study the reaction mechanism on a silver cata-lyst in 0.1 M KCl and 0.1 M KHCO3 electrolytes at applied potentials of -1.4, -1.6 and -1.8 V vs a Ag/AgCl reference electrode. The performance of the new developed cell is compared to the already proven ATR cell configuration. Investigation of the infrared signal strength showed high infrared signals at angles of incidence of the infrared beam between 30° and 45°. The measured infrared absorption spectra in the thin layer flow cell show three absorption bands which are also present in the obtained infrared absorption spectra of the ATR cell. In the ATR spectra however, three further infrared absorption bands can be observed. Due to the lower number of absorption bands present in the FTIR spectra measured in the new designed thin layer flow cell, it can be concluded that despite the high IR signal no new insights on the reac-tion mechanism of the carbon dioxide reduction reaction can be acquired.

Based on the Paris Accord, various governments have agreed to a long- term goal of keeping the increase in global average temperature to well below 2°C above pre-industrial levels; The Netherlands has committed to reduce its CO2 emissions with 80% by 2050; in this plan, the Dutch government has set an ambitious target for the industry to reduce their emissions by 70 million tonnes of CO2 annually. In The Netherlands, the steel industry contributes to nearly 7% of the total greenhouse gas emissions inventory. To meet the Dutch Government target, Tata Steel IJmuiden is exploring various options to reduce its CO2 emissions. One of the options being considered is CO2 Capture, whereby the CO2 could be captured from the Works Arising Gases (WAGs). Currently, the use of chemical absorption is the most mature technology to capture CO2 from any gas. This study has evaluated the performance, equipment sizing and cost of capturing CO2 using MEA or MDEA/Pz solvents. The performance of the chemical absorption process capturing 90% of the CO2 from a mixture of Blast Furnace Gas and Basic Oxygen Furnace Gas has been evaluated. The process was modeled in ASPEN Plus® . For cases using MEA as solvent, the conventional configuration were evaluated. It could be concluded that the optimal lean loading is around 0.19 mol/mol resulting to a specific reboiler duty of around 3.95 MJ/kg CO2 captured. Different advanced process flow configurations were also assessed. The results showed that the use of intercoolers in combination with a flash split-flow or LVC could result in a reduction of the specific reboiler duty. For cases using of MDEA and Pz as solvent, the conventional configuration operating with 1 and 10 bara absorber pressure were modeled. Resulting to a specific reboiler duty of 3.56 and 2.70 MJ/kg CO2 for 1 and 10 bara operating pressure, respectively. Furthermore, different advanced configurations were also assessed. This consisted of the incorporation of intercoolers and 1-stage or 2-stage configurations. With intercooling, the specific reboiler duty could be lowered down to 2.85 and 2.43 MJ/kg CO2 for operating pressure at 1 bara and 10 bara, On the other hand, based on the UCARSOL 1-stage configurations operating at 10 bara, the specific reboiler duty could be reduced down to 2.34 MJ/kg CO2. A reduction in specific reboiler duty for the 2-stage configuration could be significantly lowered. Preliminary economic evaluations were undertaken in this study to obtain the specific CO2 capture cost – based on CAPEX and OPEX estimates using 8% discount rate and an economic lifetime of 25 years. For the MEA cases evaluated, the costs of CO2 captured are in the range of 52.7 to 65.8 €/tonne CO2; the lowest cost is achieved with the LVC configuration in combination with intercooling. On the other hand, the results for the MDEA/Pz cases indicated that the costs of CO2 captured are in the range of 54.1 to 67.3 €/tonne CO2; the lowest cost is given in the configuration with intercooling operating at 1 bara.

An exponential growth in CO2 concentration over the past few decades has led to an accelerated impact of climate change on planet earth. In a bid to curb these emissions, people across the globe are slowly transitioning towards renewable energy sources with battery technology aiding this growth. Given that battery technology is still in its nascent stage, the “Electrochemical reduction of CO2” could be a viable solution supporting it without decelerating the momentum gained towards renewable development. Although plausible, the direct reduction of CO2 to liquid fuels entails huge energy expenditure thus requiring the implementation of catalysts. Unique in its ability, palladium reversibly reduces CO2 to formic acid making it an interesting candidate for the reduction reaction. In addition to the production of formic acid, palladium is also know to produce carbon monoxide (CO) which completely deactivates the surface preventing further reactions from occurring.

Thus the aim of the current study is focused on analysing the electrochemical reduction of CO2 on palladium thin films using surface enhanced infrared absorption spectroscopy to better understand the deactivation mechanisms of CO on the palladium thin film. The smoothness of the as- sputtered 15 nm palladium thin film with a RMS roughness of 0.511 nm and partially coalesced islands were ascertained, thus requiring surface activation to introduce the enhancement mechanism. Experimental analysis of CO2 reduction on the palladium thin film was performed to unearth significant insights through the combination of electrochemical analysis techniques with surface enhanced infrared absorption spectroscopy. Results obtained through implementation of these methodologies provided substantial information not only on the influence of the palladium-hydrogen system on the electrochemical reduction of CO2 but also on the impact of alkali metal cations on the palladium-hydrogen system and the CO2 reduction reaction over the sputtered palladium thin film. CO formation, accumulation and desorption coupled with hydrogen evolution and desorption were some of the few avenues that were enumerated upon during the experimental investigation. The identity of CO chemisorbed on the palladium thin film along with bicarbonate direct/ indirect reduction to form CO was confirmed through the utilization of N2 saturated C13 NaHCO3 solution. In addition to the analysis of the reduction reaction, emphasis on the oxidation of CO was also provided suggesting the formation of dense CO structures with the existence of strong CO dipole – dipole coupling on the palladium surface.