Bond-Making and Breaking between Carbon, Nitrogen, and Oxygen in Electrocatalysis

Many catalytic reactions involving small molecules, which are key transformations in sustainable energy and chemistry, involve the making or breaking of a bond between carbon, nitrogen and oxygen. It has been observed that such heterogeneously (electro)­catalyzed reactions often exhibit remarkable and unusual structure sensitivity, in the sense that they take place preferentially on catalyst surfaces with a long-ranged two-dimensional (100) atomic structure. Steps and defects in this two-dimensional structure <i>lower</i> the catalytic activity. Such structure sensitivity must be due to the existence of a special active site on these two-dimensional (100) terraces. Employing detailed density functional theory calculations, we report here the identification of this special active site for a variety of catalytic reactions. The calculations also illustrate how this specific site breaks the well-known rule that under-coordinated surface atoms bind adsorbates stronger, thereby providing the atomic-level explanation for the lack of reactivity of steps and defects for the reactions under consideration. The breakdown of such rule results in significant deviations from commonly observed energetic scaling relations between chemisorbates. Thus, this work provides new design rules for the development of thermodynamically efficient catalysts for an important class of bond-making and bond-breaking reactions