Impact of Surface Defects like Vacancies and Dopants on The Design of Energy-Efficient Ag Nanoparticle/Ligand-Based Catalysts for Electroreduction of CO₂

Capture and subsequent conversion of CO₂ to value-added chemicals is a promising strategy to tackle the increase in CO₂ concentrations in the atmosphere. CO₂ electroreduction to CO is often the first step in such a conversion, necessitating the design of effective electrocatalysts that can not only produce CO with high selectivity but also do so energy-efficiently. The Ag-Nanoparticle/Ordered Ligand Interlayer (Ag-NOLI) catalyst produces CO at high selectivity. However, to achieve the catalytically active phase, the material needs to be biased to a large negative potential. Thus, any effort to create the catalytically active phase at lower magnitudes of negative potential can pave the way towards designing a more energy-efficient catalyst. We used density functional theory calculations to engineer the Ag surface by introducing vacancies, and Cu and Ag dopants, evaluated the relative energies of all the configurations, and computed the transition potentials needed to get to the catalytically active phase. We found that while introducing Ag vacancies and Cu dopants increase the magnitude of the transition potential, the opposite is seen with Au dopants, making Au dopants a suitable design modification. Moreover, while Cu increases the stability of all the phases compared to Ag, Au decreases it. The source of this Cu < Ag < Au energy trend was evaluated and we found that the ligand-surface interaction was the most prominent contributor compared to other interactions in the system. Finally, we found that the trend in the ligand-surface interaction energy can be attributed partially to the intrinsic chemical interaction between the surface and ligand atoms, by investigating systems where the geometry of the topmost layer was kept fixed. Overall, this Cu < Ag < Au energy trend can be ascribed partially to the electronegativity differences with O, making it an important descriptor in the design of energy-efficient Ag-NOLI-based catalysts.