(135c) Identifying Active Electrocatalytic Catalysts By Model Studies

The inherent inhomogeneity and dynamic nature of real world heterogeneous catalysts often cause difficulty in the identification of the active sites and selective chemistry. Thus, this is a grand challenge in the fundamental understanding of the relationship between the material properties of catalyst and the catalytic reaction. To rationalize the design and facilitate the discovery for high performance catalysts, we have synthesized and studied model catalysts with well controlled surface compositions and structure. These model studies have proven to be excellent benchmarks for understanding the source of activity and unique selectivity in powder catalysis and electrocatalysis due to their uniform surface structure and electronic properties. In this study, Hf-Ir bimetallic surfaces were fabricated and characterized under ultrahigh vacuum (UHV) and the electrocatalytic performance was evaluated under alkaline aqueous conditions. It is found that the catalytic performance of the Hf-Ir surfaces is strongly dependent on the surface structure and oxidation states of surface Hf.  With precise control of composition and structure through surface modification, these model catalysts demonstrated large enhancement in activity for multiple electrochemical reactions including the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), and the direct ethanol oxidation (EO).  The combined studies utilizing surface science approaches and electrochemical measurements have provided a thorough understanding of the origin of high catalytic activity of these systems. More importantly, it can build the foundation for modifying the chemical properties required for developing high performance, inexpensive, and durable PEM fuel cells and electrolyzers.