UC Irvine

Carbon dioxide (CO2) is a greenhouse gas that contributes significantly to the warming of the Earth's atmosphere. The greenhouse effect is the process by which the Earth's atmosphere traps solar radiation, keeping the planet warm enough to support life. However, human activities such as the burning of fossil fuels and deforestation have increased the concentration of atmospheric CO2, intensified the greenhouse effect, and led to global warming. This has resulted in rising sea levels, more frequent and severe weather events, and widespread ecological disruption. Therefore, reducing CO2 emissions and remaining CO2 content in the environment is crucial for mitigating the greenhouse effect and ensuring a sustainable and habitable planet for future generations.

CO2 electroreduction is a promising technology that converts CO2 gas into value-added products such as fuels and chemicals using renewable electricity. This technology offers a potential solution to mitigate greenhouse gas emissions while providing an alternative pathway to produce sustainable fuels and chemicals. The electroreduction of CO2 requires the development of efficient and selective electrocatalysts and optimized electrochemical systems. Herein, this dissertation focused on probing the advanced electrocatalysts, optimized electrochemical system, and fundamental mechanism of CO2 electroreduction to value-added products. The following researches have been investigated:

i) Catalytic hybrid electrocatalytic/biocatalytic cascades for carbon dioxide reduction and valorization.A feasible cascade reaction system of hybrid electrocatalysis and biocatalysis has been reviewed and proposed. The electrocatalysts and related cascade reaction pathways are summarized in a descriptive “connectivity map”, identifying the most important reaction pathways.

ii) Robust palladium hydride catalyst for electrocatalytic formate formation with high CO tolerance.A hydrogen-rich Palladium hydride catalyst (PdH0.5/C) derived from a one-step organic solvent synthesis method has been developed. This electrocatalyst showed a 93.1% faradaic efficiency towards formate at -0.4 V (vs. RHE). The working lifetime reached a record of 4 hours, which was ~15 times longer than a commercial Pd catalyst and outperformed all previous Pd-based electrocatalysts for CO2-HCOO- conversion. The high CO tolerance was attributed to the selectivity improvement induced by lattice hydrogen and the weak CO adsorption strength on diverse active sites (i.e., kink, step, and terrace). Isotopic analysis revealed the direct participation of the lattice hydrogen in the protonation of CO2 molecules in formate formation.

iii) Promoting electrolysis of carbon monoxide toward acetate and 1-propanol in flow electrolyzer.Practical approaches for improving acetate and 1-propanol selectivity and yield from CO electrolysis using a commercial copper catalyst have been studied. Acetate showed a strong pH dependence with an optimum performance at 90% Faradaic efficiency and 128 mA cm−2 current density. In addition, 1-propanol showed a strong catalyst-loading dependence, achieving 20% Faradaic efficiency under high-catalyst-loading conditions. In situ Raman and Multiphysics modeling further demonstrated the mechanism of the improvements.