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Abstract:
The severe consequences of global warming, including extreme weather events like heavy rainfall, droughts, and hurricanes, are affecting every part of the world. To mitigate climate change, humanity must reduce its reliance on fossil fuels and develop technologies that enable a carbon-neutral future based on renewable energy. One promising approach is storing excess energy in chemical bonds, where e-fuels, synthesized from hydrogen and CO2 using renewable electricity, play a key role. E-fuels have the advantage of easier handling compared to green hydrogen and can be integrated into existing infrastructure. Copper is currently the only pure metal catalyst capable of converting CO2 into valuable C2+ hydrocarbons and alcohols through electrochemical reduction. However, the precise mechanism and the nature of the active site behind Cu’s unique ability is not fully understood, hindering the rationa design of more efficient catalysts. Although Cu can produce C2+ products, it suffers from low selectivity, limiting its broader application. This research addresses these challenges by studying ultra-clean, well-defined Cu single crystal surfaces as model catalysts for CO2 reduction. Using a combination of UHV surface preparation, electrochemical methods and high-resolution microscopy, this study shows that surface defects play a crucial role. Perfect, defect-free Cu surfaces mainly produce hydrogen, while surfaces with step edges generate hydrocarbons. The study also reveals that Cu surfaces undergo restructuring during the reaction, with the introduction of step edges. As soon as a threshold amount of step density is achieved on the Cu single crystal surface, the single crystal facet determines the exact restructuring as well as the exact product selectivity. Kinked step edges, in particular, are more effective at driving hydrocarbon production than straight ones. In conclusion, this thesis provides valuable insights into the active sites on Cu for CO2 reduction, contributing to a deeper understanding of electrochemical CO2 reduction and advancing the development of efficient catalysts for e-fuel production.
