The electrochemical reduction of CO₂ has the capacity to address climate change by utilizing CO₂ to produce valuable compounds that can be used as fuels or as chemical feedstocks. Unfortunately, current electrocatalysts exhibit limited activities, efficiencies, and stabilities. Furthermore, the complex multi-electron reduction mechanism is poorly understood. This thesis aims to design electrocatalysts and provide detailed mechanistic studies on the electrochemical reduction of CO₂ towards advanced products (2e^–), such as hydrocarbons and alcohols.

In the first project, metal-organic framework/ionic liquid hybrid catalysts are synthesized for the selective production of CH₄ from CO₂ reduction, reaching a maximum faradaic efficiency (FE) of 65.5% at −1.13 V vs. RHE. Hydrogen evolution is...[ Read more ]

The electrochemical reduction of CO₂ has the capacity to address climate change by utilizing CO₂ to produce valuable compounds that can be used as fuels or as chemical feedstocks. Unfortunately, current electrocatalysts exhibit limited activities, efficiencies, and stabilities. Furthermore, the complex multi-electron reduction mechanism is poorly understood. This thesis aims to design electrocatalysts and provide detailed mechanistic studies on the electrochemical reduction of CO₂ towards advanced products (>2e^–), such as hydrocarbons and alcohols.

In the first project, metal-organic framework/ionic liquid hybrid catalysts are synthesized for the selective production of CH₄ from CO₂ reduction, reaching a maximum faradaic efficiency (FE) of 65.5% at −1.13 V vs. RHE. Hydrogen evolution is also significantly inhibited in the presence of the embedded ionic liquid, reaching a minimum FE of 6.8%. The ionic liquid molecules are proposed to enhance local CO₂ concentrations. Furthermore, DFT calculations show that the presence of ionic liquid molecules on the metallic Cu active sites can improve the thermodynamics of the CO₂-to-CH₄ electrochemical pathway. In the second project, 4-(dimethylamino)pyridine (4-DMAP) was embedded within a dealloyed, porous Pd substrate to selectively produce methanol. The resulting electrocatalyst achieved a maximum FE of 22% at −0.7 V vs. RHE. In-situ FTIR experiments show that in the presence of 4-DMAP, the formation of strongly adsorbed bridge-bonded *CO on palladium is promoted over weakly-adsorbed linearly-bonded *CO, thereby enhancing its further reduction over CO desorption. The transient formation of a suspected intermediate for methanol formation in the in-situ IR spectra is observed, indicating that methanol formation may be governed by a transient process.

The production of C₂ compounds from CO₂ was also extensively studied via the reduction of glyoxal, a suspected CO₂RR intermediate, on a copper cathode. Three main reaction pathways were observed – (1) reduction to aldehydes (glycolaldehyde, acetaldehyde) and alcohols (ethanol, ethylene glycol), (2) disproportionation to glycolate and formate, and (3) carboncarbon coupling via aldol reactions. The local pH was shown to significantly affect the preferred reaction pathway due to the pH-dependence of carbonyl hydration, Cannizzaro disproportionation, and aldol addition. The results indicate that glyoxal is not the main intermediate for ethanol production on copper due to the low CO₂RR FE towards other glyoxal reduction products (such as ethylene glycol) commonly observed on polycrystalline copper. In-situ FTIR results show that the anodization of copper enhances the *CO coverage at intermediate potentials, promoting its further reduction. A suspected C₂ intermediate was also observed at intermediate potentials, indicating that a low-overpotential pathway towards C-C coupling exists on oxide-derived copper. To selectively produce alcohols and hydrocarbons, MOF-derived porous bimetallic CuO/Ag and CuO/ZnO electrocatalysts were synthesized by annealing HKUST-1 in air. The resulting porous CuO exhibited a maximum C₂₊ product FE of 61.1%. The presence of Ag significantly improved the alcohol over hydrocarbon selectivity, reaching a maximum FE ratio of 1.7 at −0.92 V vs. RHE. The high observed selectivity can be attributed to the initial oxidation of copper, which can promote both CO production (for further reduction) and C-C coupling, as shown in the FTIR results. Furthermore, the CO spillover from Ag sites and further entrapment of CO in the porous structures are also hypothesized to contribute to the large FEs achieved.