(Invited) The Oxidation Mechanism of Cu with Operando X-Ray Spectroscopy Techniques

Artificial photosynthesis capable of the CO 2 reduction reaction (CO 2 RR), with solar energy as external excitation energy and water (H 2 O) as the electron and proton source, has been considered an attractive method to achieve a sustainable energy cycle, since it allows direct solar-to-chemical energy conversion. To design such systems, X-ray techniques play an important role for gaining the fundamental understanding needed to tailor its components and assemblies, by providing their chemical and structural information. For example, Cu is unique in the electrocatalytic conversion of CO 2 /CO to C 2+ products, but with poor selectivity and durability. To understand the redox behavior of Cu under operation conditions, we have utilized surface-sensitive hard X-ray techniques to investigate the interaction of metal catalytic surfaces with electrolytes under operando conditions. Modulation excitation spectroscopy has proven to be an effective approach to enhance diluted signals. We discuss current challenges of studying artificial photosynthetic systems .