CO₂ elektrokimyasal indirgeme sürecinde elektrokatalizör üzerindeki arayüzey dinamiklerine yönelik içgörüler

The electrochemical reduction of carbon dioxide (CO2RR) into valuable hydrocarbons is a promising approach to address the environmental challenges posed by high atmospheric CO2 levels. CO2RR, as an inevitable pathway to achieve carbon neutrality, offers the conversion of CO2 into high-demand chemical feedstocks, such as carbon monoxide (CO), methane (CH4), and ethylene (C2H4). Despite numerous experimental and computational studies on this topic aimed at increasing the efficiency and selectivity of desired CO2RR products, a comprehensive understanding of the mechanisms and the role of multiple influencing parameters remains unclear. The product selectivity of CO2RR is highly dependent on the properties of the electrocatalysts, electrolyte conditions, and the electrocatalyst/electrolyte interfacial dynamics. Particularly on copper-based electrocatalysts, which are capable of forming multi-carbon products through multistep pathways, understanding the role of each factor controlling selectivity is essential to optimize performance and make CO2RR commercially viable. In this thesis, we seek to gain deeper insights into the mechanisms that favor the formation of specific products, such as hydrocarbons that contain two or more carbon atoms in their molecular structure (C2+) by investigating the structural and chemical changes that occur on the surface of the electrocatalysts during the reaction. The major part of this study focuses on the role of morphology and chemical state of copper-based electrocatalysts in promoting certain reaction pathways over others, such as hydrogen evolution reaction (HER). This has been attainable using the in-situ spectroscopy technique. We investigated CO2RR on two Cu oxide electrodes with distinct structures, finding that the compact structure achieved double faradaic efficiency for C2+ products (40%). Operando Raman spectroscopy revealed that the formation of a metastable malachite phase shifted local pH, potentially by consuming bicarbonate species, and hindered further reduction by preventing CO dimerization, thus limiting C2+ product formation. Additionally, we explore the impact of the reaction environment, particularly the influence of electrolyte composition. This study explores the impact of Cs+, K+, and Li+ cations on CO₂ reduction to CO over a ZnO nanorod electrode using the fast and facile technique of rotating ring disk electrode (RRDE). Our results show that Cs+ boost CO₂RR activity by regulating OH⁻ concentration and maintaining local pH, highlighting the role of cations in influencing CO2RR dynamics on oxide-derived Zn electrodes. Moreover, we investigate the structural changes and chemical states of synthesized Cu oxide nanocubes as the electrocatalyst, affected by the presence of Cs+, K+, and Li+ cations during CO2RR. Operando Raman spectroscopy and ex-situ XAS and XPS demonstrate that these cations induce structural rearrangements and alter the surface chemistry of the electrocatalysts, which eventually influence the product selectivity. Li+ promotes Cu dissolution, led to significant restructuring of the surface and a mainly metallic Cu phase, favoring CH4 production, while K+ and Cs+ stabilize oxide/hydroxide species on the surface, enhancing C2H4 formation. This research also addresses the stability of copper-based electrocatalysts, a critical factor for applying pulsed CO2RR technologies. We explore the mechanism of Cu dissolution during pulsed CO2RR using a rotating ring-disk electrode (RRDE) and an electrochemical scanning tunneling microscopy (STM) setups. Key factors such as anodic potential, surface roughness, CO concentration, electrolyte composition, and pH were analyzed. Our findings highlight the strong and direct role of higher anodic potential in further Cu ion oxidation and its dissolution, as well as the impact of CO2RR intermediates (CO and OH⁻) in forming a new surface structure that prevents further Cu species dissolution into the electrolyte. Insights from this research will help optimize pulsed CO2RR techniques for better Cu catalyst preservation. Throughout this thesis, we combine characterization techniques and electrochemical analysis to provide a better understanding of the main factors influencing CO2RR outcomes. The insights gained contribute to developing more efficient and durable electrocatalysts, paving the way for the practical performance of CO2RR technologies in sustainable chemical manufacturing.