Dynamic (Sub)surface-Oxygen Enables Highly Efficient Carbonyl-Coupling for Electrochemical Carbon Dioxide Reduction

Nowadays, high-valent Cu species (i.e., Cu delta+) are clarified to enhance multi-carbon production in electrochemical CO2 reduction reaction (CO2RR). Nonetheless, the inconsistent average Cu valence states are reported to significantly govern the product profile of CO2RR, which may lead to misunderstanding of the enhanced mechanism for multi-carbon production and results in ambiguous roles of high-valent Cu species. Dynamic Cu delta+ during CO2RR leads to erratic valence states and challenges of high-valent species determination. Herein, an alternative descriptor of (sub)surface oxygen, the (sub)surface-oxygenated degree (kappa), is proposed to quantify the active high-valent Cu species on the (sub)surface, which regulates the multi-carbon production of CO2RR. The kappa validates a strong correlation to the carbonyl (*CO) coupling efficiency and is the critical factor for the multi-carbon enhancement, in which an optimized Cu2O@Pd2.31 achieves the multi-carbon partial current density of approximate to 330 mA cm-2 with a faradaic efficiency of 83.5%. This work shows a promising way to unveil the role of high-valent species and further achieve carbon neutralization. High-valent Cu species significantly affect the product profile of electrochemical CO2 reduction reaction (CO2RR)CO2 but their dynamic evolutions and roles are not well evaluated. An alternative descriptor of (sub)surface oxygen, the (sub)surface-oxygenated degree (kappa) to quantify the active high-valent Cu species, is proposed in this work, which is the critical factor to regulate the multi-carbon production of CO2RR. image