(705f) Understanding Bifunctional Bimetallic Catalysts By Selective Step-Decoration

Bimetallic catalysts have been gaining attention in recent years because of their enhanced catalytic activity and selectivity over monometallic catalysts. While the behavior of pure-metal catalysts is well understood and can be predicted from the metal properties such as d-band energy and surface coordination number, there is no established descriptor that can explain the change in behavior (changes in electronic, ensemble and bifunctional effect) of bimetallic alloys relative to their pure metal components. This lack of fundamental understanding of alloy behavior limits our ability to tune the stability, activity, and selectivity of these bimetallic alloy catalysts for sustainable catalytic reactions. Also, the synthesis techniques to tune the alloy composition and structure at the catalyst surface, where the reaction occurs, are not well-developed. In this research, our goal is to address and mitigate this knowledge gap on bimetallic catalysts. By using selective step decoration, an electrochemical underpotential deposition (UPD) technique where ad-atoms of one metal are selectively decorated onto the step-sites of another metal substrate, onto single-crystal electrodes, we have synthesized model bimetallic catalysts with a well-defined surface composition and structure. Using this technique, we have experimentally measured how the electrochemical stability and electrocatalytic activity of a given ad-atom depends on the choice of substrate metal by measuring i) the oxidative stripping potential of-, and ii) binding strength of reactive intermediates on- a given ad-atom across different substrates and electrolyte conditions (i.e. pH), as well as iii) the rate of a “bifunctional” electrocatalytic reaction (where the binding of two or more intermediates must be independently optimized) across various ad-atom/substrate pairs. By correlating changes in ad-atom behavior with properties of the substrate, such as work function and reactive intermediate adsorption strength (H-binding on substrate metal for nitrite reduction reaction), we can identify predictive descriptors to enable rational bimetallic catalytic design.