The large concentrations of anthropogenic CO2 emissions present in our atmosphere are causing a severe thread on the world as we know it. It is therefore highly necessary to move away from fossil fuels to sustainable alternatives. In order to do so, lots of research has focused already on finding new ways to create renewable energy, through for example solar and wind energy. These renewable energy sources will be able to replace the energy that we need to warm our houses and drive our cars. However, these technologies are not able to replace the chemicals that we use in our daily lives that are made through fossil-based processes. For example, plastic bottles and packing, synthetic fabrics such as polyester and nylon, cosmetics, and detergent are all made from fossil-based chemicals. An sustainable alternative process to make these chemicals is through electrochemical CO2 reduction, where CO2 is converted into chemicals by applying electricity. This involves capturing CO2 from the atmosphere and transforming it into a value-added chemical. In this way, CO2 becomes a resource instead of a waste gas that is vented off into the atmosphere and a so called circular carbon economy can be established.

Typical CO2 capture systems use a thermal step to remove the captured CO2 from the capture solvent and regenerate the solution such that it can be recycled back to the capture step. This thermal process is highly energy intensive and therefore a costly step in the CO2 capture process. However, regeneration of the capture solvent can potentially also be achieved by an electrochemical process. The CO2 rich solvent is sent directly to the electrolyser in which the CO2 is converted into carbon products and simultaneously creates a CO2 lean solvent at the outlet that is suitable for a new CO2 capture cycle. This dissertation studies the feasibility of integrating CO2 capture with electrochemical conversion. This is done by looking at two different pathways using two different solvents. The first pathway investigates the use of an organic solvent and the second pathway uses a (bi)carbonate solvent. This dissertation addresses different challenges related to the effective electrochemical CO2 conversion for these two different solvents and provides a perspective on the feasibility of integrating CO2 with electrochemical conversion.

Electrochemical CO₂ reduction in non-aqueous solvents is promising due to the increased CO₂ solubility of organic-based electrolytes compared to aqueous electrolytes. Here the effect of nine different salts in propylene carbonate (PC) on the CO₂ reduction product distribution of polycrystalline Cu is investigated. Three different cations (tetraethylammonium (TEA), tetrabutylammonium (TBA), and tetrahexylammonium (THA)) and three different anions (chloride (Cl), tetrafluoroborate (BF₄), and hexafluorophosphate (PF₆)) were used. Chronoamperometry and in-situ FTIR measurements show that the size of the cation has a crucial role in the selectivity. A more hydrophobic surface is obtained when employing a larger cation with a weaker hydration shell. This stabilizes the CO₂⁻ radical and promotes the formation of ethylene. CO₂ reduction in 0.7 M THACl/PC shows the highest hydrocarbon formation. Lastly, we hypothesize that the hydrocarbon formation pathway is not through C−C coupling, as the CO solubility in PC is very high, but through the dimerization of the COH intermediate.

Electrolytic bicarbonate conversion holds the promise to integrate carbon capture directly with electrochemical conversion. Most research has focused on improving the faradaic efficiencies of the system, however, the stability of the system has not been thoroughly addressed. Here, we find that the bulk electrolyte pH has a large effect on the selectivity, where a higher pH results in a lower selectivity. However, the bulk electrolyte pH has no effect on the stability of the system. A decrease in CO selectivity of 30 % was observed within the first three hours of operation in an optimized system with 3 M KHCO₃ and gap between the membrane and electrode. Single-pass electrolyte experiments at various constant pH values (8.5, 9.0, 9.5, and 10.0), show that only at a pH of 10 the CO selectivity was stable during three hours, reaching a faradaic efficiency toward CO of only 18 % as compared to an initial 55 % at pH 8.5. Trace metal impurities present in the electrolyte were found to be the cause of the decrease in stability as these deposit on the electrode surface. By complexing the trace metal ions with ethylenediaminetetraacetic acid (EDTA), the metal deposition was avoided and a stable CO selectivity was obtained.

Aqueous electrolytes are most commonly used for the CO₂ reduction reaction (CO₂RR), but suffer from a low CO₂ solubility that limits the reaction. Electrochemical CO₂ reduction in nonaqueous electrolytes can provide a solution, due to the higher CO₂ solubility of organic solvent-based electrolytes. Herein, the product distribution of the electrochemical CO₂ reduction on polycrystalline Cu in 0.7 m tetraethylammonium chloride in propylene carbonate with different water additions (0, 10, and 90 v%), and for different operating conditions (10, 25, 40, and 60 °C), is investigated. It is found that CO₂ reduction on Cu in a propylene carbonate solution results in H₂, CO, and formic acid formation only, even though Cu is known to produce C₂₊ products such as ethylene and ethanol in aqueous electrolytes. Increasing the operating temperature increases the CO₂RR kinetics and shows an improvement in CO formation and decrease in H₂ formation. However, increasing the operating temperature also increases water transport through the membrane, resulting in an increase of H₂ formation over time when operating at 60 °C.