Shared Nitrogen in M-N-C Single-Atom Electrocatalysts Unlocks Langmuir–Hinshelwood Mechanism for CO-to-Formaldehyde Conversion

Nitrogen atoms coordinated with metals in metal-nitrogen-carbon single-atom catalysts (M-N-C SACs) are generally considered inert, rendering the isolated metal centers ineffective in converting CO₂ to higher-order products beyond CO. Here, combining the grand-canonical density functional theory with the constrained ab initio molecular dynamics simulations, we show that in contrast to the conventional wisdom, the shared nitrogen in M-N-C SACs (i.e., the nitrogen atom connecting two MN₄ units) can actually function as an active site along with the metal center. The shared nitrogen is found to facilitate the dissociation of H₂O to hydrogen (*H), and when joined by chemisorbed CO at the adjacent metal center, activates the Langmuir–Hinshelwood mechanism for two-electron conversion of CO to formaldehyde. We uncover that being electron-deficient, *H on the shared nitrogen does not interact strongly with solvent H₂O molecule, thus suppressing the competing hydrogen evolution reaction. Our findings provide an alternative strategy to address the challenges associated with CO electroreduction and highlight the inherent advantages of M-N-C SACs for energy-related applications.