N-modulated Cu0-Cu+ sites for C1/C2 selectivity regulation of carbon dioxide electrocatalytic reduction

Controlling the valence states of copper is pivotal in determining the selectivity of products in CO2 electroreduction. In this study, we developed a Cu doped carbon catalyst (CuNC) derived from a metal-organic framework (MOFs) through a straightforward solution reaction and calcination method. The N-modulated Cu0-Cu+ sites exhibited adjustable C1 and C2 selectivity in electrocatalytic CO2 reduction (CER). Specifically, the CuNC-700 demonstrated an impressive C2 Faradaic efficiency (FE) of 56.0% at -1.0 V vs reversible hydrogen electrode (RHE), and a remarkable C1 FE of 56.7% with a total current density of 600 mA/cm2 at -1.6 V vs RHE. In the entire potential range, the CuNC-700 consistently maintained high FE values of > 92% for CER, while the FE values for hydrogen evolution reaction is below 8%. This study unveiled the correlation between the selectivity and the valence states of copper. At low applied potentials, the abundance of N-modulated Cu0-Cu+ sites led to the predominant production of the C2 products. The Cu0 played a primary role in activating CO2 and facilitating subsequent electron transfer, while the Cu+ enhanced the adsorption of *CO, further promoting the C-C coupling. Under high applied potentials, both Cu2+ and Cu+ were converted to Cu0, favoring the methanation process. This research paves the way for future design of Cu-based MOF-derived materials, enabling precise regulation of C1/C2 selectivity in CER.