Thermodynamics is important for the design of amine scrubbing CO₂ capture processes. CO₂ solubility and amine volatility in aqueous amines were measured at high temperature and pressure. A rigorous thermodynamic model was developed for MEA-CO₂-H₂O in Aspen Plus®. CO₂ solubility at 80-190°C was obtained from total pressure measurements. Empirical models as a function of temperature and loading were developed for CO₂ solubility from 40 to 160°C in aqueous monoethanolamine (MEA), piperazine (PZ), 1-methylpiperazine (1MPZ), 2-methylpiperazine (2MPZ), PZ/2MPZ, diglycolamine® (DGA®), PZ/1MPZ/1,4-dimethylpiperazine (1,4-DMPZ), and PZ/methyldiethanolamine (MDEA). The high temperature CO₂ solubility data for MEA is comparable to literature and compatible with previous low temperature data. For MEA and PZ, amine concentration does not have obvious effects on the CO₂ solubility. The heat of CO₂ absorption derived from these models varies from 66 kJ/mol for 4 m (molal) PZ/4 m 2MPZ and to 72, 72, and 73 kJ/mol for MEA, 7 m MDEA/2 m PZ, and DGA. The heat of absorption estimated from the total pressure data does not vary significantly with temperature. At 0-0.5 loading ([alpha]), 313-413 K, 3.5-11 m MEA (mol fraction x is 0.059-0.165), the empirical model of MEA volatility is ln(PMEA/xMEA) = 30.0-8153/T-2594[alpha]²/T. In 7 m MEA with 0.2 and 0.5 loading, PMEA is 920 and 230 Pa at 120°C. At 0.3-0.5 loading, the enthalpy of MEA vaporization, -[Delta]Hvap,MEA, is about 70-73 kJ/mol MEA. At 0.25-0.4 loading, 313-423 K, 4.7-11.3 m PZ (x is 0.078-0.169), the empirical model of PZ volatility is ln(PPZ/xPZ) = -123+21.6lnT+20.2[alpha]-18174[alpha]²/T. In 8 m PZ with 0.3 and 0.4 loading, PPZ is 400 and 120 Pa at 120°C, and 2620 and 980 Pa at 150°C. At 0.25-0.4 loading, -[Delta]Hvap,PZ is about 85-100 kJ/mol PZ at 150°C and 66-80 kJ/mol PZ at 40°C. [Delta]Hvap,PZ has a larger dependence on CO₂ loading than [Delta]Hvap,MEA in rich solution because of the more complex speciation/reactions in PZ at rich loading. Specific heat capacity of 8 m PZ is 3.43-3.81 J/(g•K) at 70-150°C. Two new thermodynamic models of MEA-CO₂-H₂O were developed in Aspen Plus® starting with the Hilliard (2008) MEA model. One (Model B) includes a new species MEACOOH and it gets a better prediction than the other (Model A) for CO₂ solubility, MEA volatility, heat of absorption, and other thermodynamic results. The Model B prediction matches the experimental pKa of MEACOOH, and the measured concentration of MEACOO-/MEACOOH by NMR. In the prediction the concentration of MEACOOH is 0.1-3% in 7 m MEA at high temperature or high loading, where the heat of formation of MEACOOH has effects on PCO₂ and CO₂ heat of absorption. Model B solved the problems of Model A by adding MEACOOH and matched the experimental data of pKa and speciation, therefore MEACOOH may be considered an important species at high temperature or high loading. Although mostly developed from 7 m MEA data, Model B also gives a good profile for 11 m (40 wt%) MEA. / text

The threat of the ongoing climate crisis requires the complete reduction of carbon emissions in the next two to three decades. Carbon dioxide electrochemical reduction (CO₂ER) poses a promising pathway to be able to maintain our current energy infrastructures in a carbon neutral fashion, by allowing the production of fuels and chemicals, such as CO, methanol and ethylene, with the use of carbon capture technologies and green energy. Thus far, Cu is the only metal that has demonstrated the ability to form hydrocarbon products. However, Cu is hindered by low selectivity. Improvements have been observed by coupling Cu with noble metals, such as Ag and Au. However, despite significant advancements, the technology has yet to achieve sufficient performance in activity, stability and selectivity for commercial viability. As such, this work pursued to further advance the activity of CO₂ER through the use of plasmonic Cu-based catalysts and the study of novel dinitrile-based electrolytes. It has recently been identified that CO₂ER can benefit from direct plasmonic effects induced by light illumination. In essence, certain light wavelengths can induce collective oscillations of the free electrons in the metallic particles, leading to an enhancement of their electrocatalytic performance. As such, the first project of this work involved the development and testing of plasmonic Cu-Ag bimetallic catalysts for the application of CO₂ER. Cu, Ag, as well as Cu-Ag bimetallic particles with variable morphologies were able to be synthesized through a facile one-pot sodium borohydride chemical reduction method. The synthesized catalyst performance was also compared to commercial catalysts. The synthesized particles were found to be active catalysts for CO₂ER, with improved electro-catalytic activities exhibited by Cu₈₅Ag₁₅, Cu₆₀Ag₄₀ and Cu syntheses in respective order. All nanoparticles demonstrated increases in the catalytic activity ranging between 15-26% under white light illumination, attributed to plasmonic promotion. The best plasmonic promotion of 26% was observed in the CuAg commercial alloy. Meanwhile, the best promotion of the synthesized bimetallic particles was of 18% found in the Cu₆₀Ag₄₀ catalyst. Additionally, improved electrochemical and plasmonic stability was observed with the use of the Cu-Ag bimetallic synthesized structures compared to monometallic Cu. In addition, most studies pertaining CO₂ER involve aqueous electrolytes due to their low cost and low toxicity. However, these systems are hindered by mass transfer limitations due to the low solubility of CO₂ in water. Organic-based electrolytes have been subjects of research as they possess higher CO₂ solubilities to water. As dinitriles pose a novelty in the role of CO₂ER, dinitrile-based electrolytes were studied and tested for the application. It was hypothesized that due to the decreased polarity in dinitrile solvents, CO₂ concentrations in the electrolyte would increase leading to improved catalytic activity. The testing was conducted by evaluating and comparing acetonitrile (ACN), adiponitrile (ADN) and sebaconitrile (SBN) solvent-based electrolytes. Increased CO₂ solubility was observed in the dinitriles with 582 mM and 503 mM of dissolved CO₂ in ADN and SBN respectively, compared to 270 mM in ACN. Results were corroborated through DFT modelling, indicating preference of CO₂ absorbance to nitrile groups on the molecules. However, despite increases in CO₂ concentration, the electrochemical activity decreased from ACN > ADN > SBN. The trend in activity was observed to be inversely proportional to the viscosity of the dinitrile solvents, which affected the ionic conductivity. Based on these developments, the present thesis opens a new perspective for the use of Cu-based nanoparticles for direct plasmonic enhancement with the use of a broad-range wavelength white light. Furthermore, the work also sheds light on the properties and resulting electrocatalytic activities of the use of dinitrile organic electrolytes for CO₂ER. The presented findings provide significant groundwork for further developments in the realm of CO₂ER.