The electrochemical carbon dioxide reduction reaction (CO2RR) has emerged as an attractive approach to convert CO2 into high-value chemicals. Among catalysts, copper (Cu) is notable for efficiently generating multicarbon (C2+) products. Considerable efforts have focused on improving the current density, selectivity, and stability through catalyst development and device engineering. However, the dynamic evolution of the catalyst, interfacial microenvironment, and device configuration complicates mechanistic understanding and limits industrial implementation. A multiscale investigation encompassing catalyst, electrode, and device level is therefore essential.

Chapter 2 elucidates the influence of the interfacial microenvironment on CO2RR performance by incorporating a covalently grown layer of functionalized aryl groups on Cu under industry-relevant current densities. A significant increase in ethylene and C2+ production is observed, with the highest performance achieved for the bromoaryl-modified Cu catalyst. Operando infrared spectroscopy, isotope effect measurements, and electrochemical impedance spectroscopy suggest that surface grafting promotes alkali cation dehydration at the electrode-electrolyte interface. This weakens the interfacial hydrogen-bond network, enhancing water dissociation and proton supply to CO2RR intermediates. Plus, the reduced hydration shell increases cation density at the outer Helmholtz plane, generating a stronger local electric field to stabilize C2+ intermediates. This in-depth investigation highlights the crucial role of interfacial cations in C2+ production.

Chapter 3 employs ionomers to modulate Cu-catalyzed CO2RR selectivity. The electrochemical behavior of Cu catalysts combined with three ionomers -Nafion, Sustainion XA-9, and poly(terphenyl piperidinium) (PTP)- was evaluated. Nafion shows minimal influence, whereas XA-9 promotes CO formation, and PTP hydrogen and formate production. In situ Raman spectroscopy reveals that PTP accelerates formyl group desorption, while XA-9 weakens CO adsorption, inhibiting CO dimerization. X-ray photoelectron spectroscopy and contact angle measurements identify charge and hydrophobicity/hydrophilicity as key parameters governing ionomer effects, demonstrating the structure-sensitive nature of ionomer-catalyst interactions.

Chapter 4 enhances operation durability by optimizing the microporous layer (MPL) within the gas diffusion layer (GDL). Electrochemical tests show that MPL thickness and the type of carbon black significantly affect stability and failure mechanisms. Thinner, more microporous MPLs improve durability by promoting electrolyte removal, thus reducing flooding and salt precipitation. Scanning electron microscopy, porosimetry, and contact angle measurements identify MPL hydrophobicity and microporosity as governing parameters. This underscores the crucial role of MPL and GDL design in extending CO2RR lifetime, thereby bringing operation closer to industrially relevant conditions.

Overall, this thesis integrates catalyst design, interfacial modification, and electrode architecture to advance efficient and durable Cu-catalyzed CO2 electrolysis. By bridging the gap between molecular-scale insights and device-level performance, it provides design principles for next-generation CO2 electrolyzers that operate efficiently, selectively, and stably under practical conditions.