A future based on renewable energy requires energy storage. Electrochemical CO2 reduction is a potential candidate for this process, since CO2 and electricity are converted into valuable chemicals, such as hydrocarbons and oxygenates. Copper is unique for catalyzing this reaction, however its complex behavior under reaction conditions limits any industrial scale up at this stage. Therefore, in this thesis I applied theoretical methods to model CO2 reduction on copper-based catalysts. In particular, I focused on studying: (i) surface reconstruction at negative potential, (ii) modifiers as strong tethering sites, and (iii) electrolyte effects. Chapters 1 and 2 were dedicated to the motivations and methods. In Chapter 3 I benchmarked well-established experimental results, such as the dependence of CO2 product distribution on copper morphology. Once validated the methodology, I investigated the reconstruction of polycrystalline copper at negative potentials in Chapter 4. This process is driven by local surface polarization, which destabilizes close-packed domains and promotes (100) facets and defects. Following theoretical guidelines, I synthesized an effective copper-based catalyst which produces ethylene at high yield and high current density. Then, in Chapter 5 I modeled a complex oxide-derived copper material to study copper oxidation state, its coordination and surface ensembles. Among the outcomes, I demonstrated that polarization drives CO2 reduction activity, whilst a newly reported intermediate, a deprotonated glyoxylate, triggers C2+ selectivity. In Chapter 6 I assessed the effects of chalcogen modifiers on copper reactivity. Sulfur atoms, acting as strong tethering centers, enable the generation of formate, a chemical employed for animal food stock conservation. Finally, in Appendix A I introduced cation effect on CO2 reduction. This phenomenon is not yet fully understood but it has a clear relevance on this reaction. Overall, this work provides new theoretical methods to study copper under reduction conditions and suggests synthetic routes for devising more selective catalysts.

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