Manipulating copper stability and reactivity in the electrochemical CO2 reduction reaction via colloidal atomic layer deposition

The electrochemical CO2 reduction reaction (CO2RR) is a promising route to store intermittent renewable electricity in the form of chemical feedstock. Among all metals, copper is the only one that catalyzes the formation of high-value C2+ products (e.g., ethylene, ethanol) from CO2 with reasonable production rates. Major advances in catalyst design and device engineering have led to near unity selectivity at industrially relevant current densities. Yet, operational instability remains the main bottleneck toward industrial implementation. Copper catalysts suffer from extensive structural reconstruction under reaction conditions, which alters their surface chemistry, degrades performance over time, and complicates the derivation of reliable structureâ activity relationships. This thesis addresses the challenge of copper instability during CO2RR by utilizing a material chemistry approach to advance the current understanding of the key factors behind it and to propose concrete solutions against copper instability. Chapter 3 proposes the deposition of hybrid organic-inorganic oxide coatings on copper as a means to render it structurally stable during CO2RR. The developed methodology to grow these coatings is colloidal atomic layer deposition (c-ALD). This chapter establishes the fundamental chemistry for growing porous hybrid AlOx coatings on a variety of metallic nanocatalysts (Cu, Ag, Ni, Sn), with surface hydroxyl groups identified as key to initiating oxide growth. The resulting Cu nanocatalyst coated with the c-ALD-grown AlOx exhibits significantly enhanced structural stability under COâ RR conditions. Mechanistic insights from operando X-ray absorption spectroscopy reveal that the coating suppresses surface redox cycling responsible for morphological degradation. Following the developed oxide growth methodology, Chapter 4 investigates how the porosity of the AlOx shell modulates copperâ s reactivity during CO2RR as a result of microenvironment effects. Interestingly, the data show that tuning porosity alters product selectivity, shifting from ethylene to methane and hydrogen as porosity decreases. This behavior is attributed to changes in the local active sites distribution. The developed platform correlates catalyst coating porosity, electrolyte cation identity, and surface charge density, which has not been proposed before. Finally, Chapter 5 explores the role of surface composition on copper stability, with the aim of contributing to elucidate discrepancies in Cu-based catalyst stability reported across the literature. Using in situ electrochemical liquid-phase transmission electron microscopy and X-ray photoelectron spectroscopy, the study shows that oxide-derived surfaces degrade and deactivate more rapidly compared to metallic surfaces. Furthermore, the data introduce the importance of copper carbonate formation in the copper deactivation process, which provides additional insights into previous suggestions in the literature on the rol