Atomic-Level Insights into the Cation-Mediated Electrocatalytic C-N Coupling Mechanism over Cu Model Catalyst

Electrocatalytic C-N coupling of organic carbon and nitrogen sources has emerged as a promising route to high-value chemicals in heterogeneous catalysis over the past decade. Most research has focused on optimizing catalyst active sites to accelerate C-N coupling at the catalyst/electrolyte interface, but the electrolyte's role remains poorly understood. Here, we introduce Li⁺, Na⁺, and K⁺ into the electrolyte and use slow-growth molecular dynamics with explicit solvation models to examine their impact on C-N coupling at the Cu/electrolyte interface. We show that K⁺ enables a one-step mechanism in which C-N bond formation and hydrogenation occur simultaneously, yielding the *OC-NOH intermediate with a barrier of 0.68 eV. Differential electrochemical mass spectrometry (DEMS) demonstrates that the m/z = 59, assigned to the *OC-NOH intermediate, is detected over the Cu catalyst in 0.1 M KHCO₃. Without K⁺, the reaction follows a two-step pathway with a higher overall barrier of 1.0 eV (0.71 eV for C-N formation, 0.29 eV for hydrogenation), and the *OC-NOH intermediate is not detected by DEMS. Interfacial analysis reveals that K⁺ enriches hydrogen near the interface and enhances charge transfer to activate *NO, enabling concurrent coupling and hydrogenation. This results in a Faradaic efficiency of 67.25 ± 3.27% and a urea production rate of 21.02 ± 0.83 mmol g^-1 h^-1 on pure Cu in 0.1 M KHCO₃ at -0.5 V vs RHE─surpassing all previous Cu-based systems. Our work identifies a more efficient one-step C-N coupling mechanism through simple electrolyte modulation.