(521es) Reversible Oxidation of Copper via Chemical Interaction with Carbon Dioxide Investigated by Ambient Pressure X-ray Photoelectron Spectroscopy

A fundamental understanding of the chemical interactions between copper (Cu) and carbon dioxide molecules is pivotal to gain detailed insights on the initial steps of carbon dioxide conversion on Cu surfaces. Herein, ambient pressure X-ray photoelectron spectroscopy (AP-XPS) using synchrotron radiation-based tender X-rays (4 keV) was employed to study the chemical dynamics of Cu surfaces with increasing the pressure of carbon dioxide. The surface Cu of polycrystalline metal foil was oxidized to Cu(II) upon exposure to carbon dioxide, particularly beyond 10 Torr, and then reduced back when removing the carbon dioxide gas to restore high vacuum condition. A linear correlation was built up between carbon dioxide pressure and surface Cu(II) proportion. The growth and recession of the Cu(II) overlayer is attributed to the interaction of adsorbed oxygen species from the direct dissociation of adsorbed carbon dioxide with the surface metallic Cu sites and their fast transport through the Cu(II) overlayer. The observed reversible phenomenon of the Cu(II) layer evolution induced by dissociative carbon dioxide adsorption on Cu surface has been verified on other two reported carbon dioxide-reduction systems: p-GaN/Au/Cu and p-Si/TaOx/Cu. We unveil a universal and reversible oxidation of Cu towards Cu(II) at the initial step of carbon dioxide conversion, providing atomistic insights for the design and construction of highly efficient and selective Cu-based catalysts.

Key words: reversible Cu oxidation; chemical interaction with CO₂; ambient-pressure XPS