Tailoring nanocatalysts and reaction interfaces for water- and CO2-electrolysis

Renewable energy sources offer a promising solution for mitigating sustainability and CO2 emissions-related issues due to their vast energy generation capacity. They enable hydrogen production via water electrolysis, as well as carbon capture and utilization techniques, leading to negative carbon emissions. However, these solutions rely on electrochemical reactions such as water- and CO2-electrolysis, with the anodic oxygen evolution reaction (OER) and the cathodic CO2 reduction reaction (CO2RR), which suffer from high overpotentials and limited efficiencies. Thus, the development of catalysts to enhance the activity and stability of these reactions is imperative for their practical application.

The primary challenge of OER research is the development of cost-effective catalysts to replace expensive benchmark materials. Additionally, the challenge of enabling CO2 reduction in aqueous environments is mainly the low CO2 efficiency and uncontrolled product selectivity. Copper-based materials have become the focus of extensive research due to their unique ability to convert CO2 into multi-carbon (C2+) compounds, requiring further investigations for a better understanding of their catalytic properties.

This thesis describes a comprehensive study aimed at developing catalysts with improved activities and stabilities, as well as promoting their selectivity for specific targeted products. Furthermore, we conducted an in-depth study of the structure of the catalyst and attempted to determine the underlying mechanisms responsible for these improvements.

First, we explored the role of surface oxygen functionalization on the dispersion and activity of Co-based catalysts in the context of OER. We found that carbon supports rich in acidic oxygen-containing functional groups enhanced the adsorption of metal cations and the dispersion of the catalysts.

Second, we studied how the incorporation of Fe impacts the OER activity of Co-based catalysts. Through in situ synthesis, we found that Fe is incorporated as a solid solution, primarily through the substitution of Fe3+ at Co3+ sites. Our CoFe catalyst exhibited excellent OER performance, as evidenced by a low Tafel slope and overpotential, making it one of the top-performing CoFe-based materials.

Next, we focused on improving the electrocatalytic reduction of CO2 to C2+ products by tuning the hydrophilicity of polymer binders. Fluorinated ethylene propylene (FEP), a hydrophobic, CO2-philic polymer, significantly increased the CO2RR selectivity toward C2+ products. We proved that the hydrophobicity of FEP resulted in the retention of CO2 and intermediate CO on the surface of the catalyst, promoting the formation of C2+ products.

Finally, we identified the primary degradation mechanisms of CO2 electrolysis in acidic environments to be the flooding of gas diffusion electrodes (GDEs). By separating the inlet catholyte from the outlet liquid products, we successfully kept the pH near the catalyst below a critic