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Understanding the Mechanism of Catalytic Selectivity During Electrochemical CO2 Reduction Using Nonlinear Soft X-Ray Spectroscopy


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The environmental consequences of continued fossil fuel consumption, as well as the economic uncertainty of hydrocarbon sources are strong motivations for developing catalysts capable of reducing CO2 to a high-energy-density fuel or other value-added products. Selectively converting CO2 to fuels requires control of electron motion at a catalyst surface. Detailed understanding of electron dynamics at surfaces of heterogeneous catalysts can inform relevant design parameters for next generation materials with high efficiency for CO2 reduction to valuable products. Unfortunately, there is a shortage of spectroscopic probes capable of following these charge transfer processes with element specificity, ultrafast time resolution, and surface sensitivity. To enable the study of surface electron dynamics, we have recently designed and constructed an ultrafast soft X-ray and extreme ultraviolet (XUV) light source based on high harmonic generation (HHG). Using this light source, we have shown that XUV reflectionabsorption (RA) spectroscopy combines the benefits of X-ray absorption, such as element and oxidation state specificity, with surface sensitivity and ultrafast time resolution, having a probe depth of only a few nm and an instrument response less than 100 fs. Addtionally, by operating in a grazing angle reflectivity, XUV RA spectroscopy is independent of the sample thickness. This provides a major advantage over traditional transmission experiments where the sample thickness is limited to approx100 nm. Since catalytic properties of metal oxides change with thickness, it is imperative to study the electron dynamics of actual functional materials that show highest catalytic activity and selectivity toward CO2 reduction.



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