UCLA

Electrochemical conversion of greenhouse gases to value-added products has emerged as a promising strategy to mitigate climate change and expand the penetration of renewable energy sources into the various sectors of our economy. As the accumulation of greenhouse gases in the atmosphere continues to increase, researchers have been exploring ways to utilize electrochemistry to capture and convert these gases into useful chemicals and fuels. This approach not only reduces the accumulation of greenhouse gases in the atmosphere but also provides a sustainable solution to the production of high-value chemicals and fuels. CH4, CO2 and other greenhouse gases can be converted into a range of valuable products, such as methanol, ethanol, formic acid, and hydrocarbons. The use of renewable electricity sources, such as solar and wind energy, to drive the electrochemical conversion process further enhances its sustainability. The development of efficient and selective electrochemical conversion strategies for greenhouse gas utilization holds great potential for meeting the energy demands of the future while addressing the challenges of climate change starting today.In this doctoral dissertation work, a series of systematic studies are carried out to elucidate the mechanisms of electrochemical CH4 partial oxidation to methanol (Chapter 2), and the reactive capture of CO2 to CO in amine and carbonate capture solutions (Chapter 3). Among the catalysts for partial oxidation of methane studied in Chapter 2, electrochemically deposited transition metal (oxy)hydroxides are found to be active even without the application of a bias potential. Taking CoOx as a prototypical methane partial oxidation electrocatalyst and combining systematic experiments in a rotating cylinder electrode (RCE) cell with DFT calculations, optimal conditions of low catalyst film thickness, intermediate overpotentials, intermediate temperatures, and fast methanol transport are identified to favor methanol selectivity. CO2 reactive capture and conversion (RCC) is also investigated with the RCE cell in Chapter 3. In the RCE cell, the transport properties are well-defined in the gas, liquid, and solid phases, which allows the elucidation of the origin of carbon sources during the electrochemical reduction of bicarbonate and amine-based CO2 capture solutions on a silver catalyst electrode. In this study, dissolved CO2 is revealed to be the primary carbon species being consumed while the CO2-absorber complex appears to serve as a secondary carbon source only at highly negative potentials. Through the development of experimental methods for the differentiation of carbon species in solution during electrochemical carbon upgrading, the work presented here allows the comparison of experimental results to density function theory (DFT) calculations and contributes to the acceleration of catalyst discovery and reactor design for RCC technologies. This thesis work stablishes new methodological approaches to catalyst and reactor design in the Morales-Guio group, and contributes broadly to the development of electrocatalytic technologies for the capture and conversion of greenhouse gases.