Characterization of Electrode Activity through Photoelectron Spectroscopy: A Coordinated Synchrotron and Laboratory XPS Approach to Electrocatalysis

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This project, funded by the Analytical and Surface Chemistry Program, addresses the correlation between core level electron binding energy shifts and electrocatalytic reactivity at binary and ternary electrode catalysts for small molecule oxidation/reduction reactions. The catalysts are formed by spontaneous deposition of transition metals on single crystal substrates of Pt, Ru, Pd and Au. There is strong evidence that the admetals are arranged in two- and three-dimensional nanoislands, as monitored by in situ STM. This work is carried out in the laboratory of Andrzej Wieckowski at the University of Illinois and at the Synchrotron Radiation Center (SRC) at the University of Wisconsin-Madison; the intense synchrotron x-ray light is needed to measure the binding energy shifts at the low and very low admetal coverage levels. Moreover, the high resolution of the synchrotron radiation makes possible accurate measurements of the binding energy shifts. A strong and direct link between experiment (Wieckowski UIUC, PI) and theory (Bagus UNT, co-PI) is a key element of this project that basically determines the chemical and physical significance of the measured core level binding energies. The synchrotron work brings high x-ray intensity, high resolution, and low detection level for the admetal coverage. Overall: electrochemical characterization determines reactivity, synchrotron XPS and laboratory XPS yield the binding energy shifts, and theory provides quantitative link between the reactivity and electronic structure of the studied surfaces. These electronic-level results produce understanding of how transition and noble metal bimetallic catalysts work for electrocatalytic reactions of clear basic-science and applied significance. The materials studied show promise as effective oxidation and reduction catalysts in small molecule fuel cell applications. Therefore, information obtained from these fundamental investigations may aid in the design of improved fuel cell catalytic systems.