Tuning the Selectivity Switch for CO ₂ Reduction: The Role of Coordination-Induced Conformational Locking on Sn Single-Atom Catalysts

Sn single-atom catalysts exhibit exceptional tunability for CO2 electroreduction, yet atomic-scale mechanisms governing product selectivity (HCOOH vs CO) remain unresolved. Through slow-growth molecular dynamics simulations, we reveal that intermediate conformational dynamics, governed by Sn coordination environments, critically steer selectivity. For HCOOH-selective Sn-N4 sites, facile conformational flipping of *COOH to *OCHO during hydrogenation enabled formate production. For CO-selective Sn-ON3, electronegative O-ligands enhance Sn electrophilicity, immobilizing CO2– and suppressing conformational flipping. This steric-electronic constraint directs the addition of H+ to carbon, favoring *COOH formation and CO production. Coordination-dependent conformational locking emerges as the decisive selectivity factor, establishing a universal paradigm for catalyst design via coordination engineering.