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 CO to higher-order products beyond CO. Here, combining the grand-canonical density functional theory with the constrained 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 MN units) can actually function as an active site along with the metal center. The shared nitrogen is found to facilitate the dissociation of HO 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 HO 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.