Size and Morphology Dependent Activity of Cu Clusters for CO Activation and Reduction: A First Principles Investigation.

Various Cu-based materials in diverse forms have been investigated as efficient catalysts for electrochemical reduction of CO; however, they suffer from issues such as higher over potential and poor selectivity. The activity and selectivity of CO electro reduction have been shown to change significantly when the surface morphology (steps, kinks, and edges) of these catalysts is altered. In light of this, size and morphology dependent activity of selected copper clusters, Cu (n=2-20) have been evaluated for the activation and reduction of CO molecule. The phase-space of these copper clusters is rich in conformations of distinct morphologies starting from planar, 2D geometries to prolate-shaped geometries and also high-symmetry structures. The binding efficiency and the activation of CO are highest for medium sized clusters (n=9-17) with prolate-morphologies as compared to small or larger sized CuCO clusters that are existing mainly as planar (triangular, tetragonal etc.) or highly-symmetric geometries (icosahedron, capped-icosahedron etc.), respectively. The best performing (prolate-shaped) CuCO conformations are quite fluxional and also they are thermally stable, as demonstrated by the molecular dynamics simulations. Furthermore, on these CuCO conformations, the step-by-step hydrogenation pathways of CO to produce value-added products like methanol, formic acid, and methane are exceptionally favorable and energy-efficient.