(510f) Can Alloys Break Scaling? Unique Reactivity of Defect Sites on Alloy (Electro)Catalysts

Alloys offer the potential for improved activity, selectivity, and stability for many electrocatalytic reactions. The rational design and synthesis of alloy catalysts is difficult however as their behavior is more complex than that of the pure metals. In this work, we use density functional theory modeling to determine how the activity and selectivity of oxygen reduction and methane activation depend on the composition and structure of a simple surface alloy, produced via step decoration. In step decoration, a single-atom wide row of one metal is selectively deposited on or segregates to the defect sites naturally present on the surface of another metal or of an alloy, producing a bimetallic surface site with a known composition and structure. This allows the effect of interactions between the two metals on their activity, selectivity, and stability to be quantified relative to their pure state. Using this model surface alloy, we extend the idea of strain effects, ligand effects, and ensemble effects, typically examined on flat “pristine” surfaces, to the step-edge defect. We find the behavior of the step is much less sensitive to strain than a flat surface and that the adsorption of reaction intermediates onto an ad-atom at the step depends only weakly on the choice of substrate. This enables the bimetallic site at the decorated step to break the scaling relations that typically limit catalyst design. Implications for rational catalyst design and for long-term (alloy) stability will be discussed.