Studying the cation dependence of CO reduction intermediates at Cu by VSFG spectroscopy.

The nature of the electrolyte cation is known to have a significant impact on electrochemical reduction of CO at catalyst|electrolyte interfaces. An understanding of the underlying mechanism responsible for catalytic enhancement as the alkali metal cation group is descended is key to guide catalyst development. Here, we use vibrational sum frequency generation (VSFG) spectroscopy to monitor changes in the binding modes of the CO intermediate at the electrochemical interface of a polycrystalline Cu electrode during CO reduction as the electrolyte cation is varied. A CO mode is observed only when using Cs, a cation that is known to facilitate CO reduction on Cu, supporting the proposed involvement of CO sites in CO coupling mechanisms during CO reduction. measurements show that the cation dependent CO modes correlate with morphological changes of the Cu surface.