Revisiting Factors Controlling the Electrochemical CO2 Reduction to CO and HCOOH on Transition Metals with Grand Canonical Density Functional Theory Calculations

The design of highly selective catalysts to form a single product represents one of the biggest challenges in electrochemical carbon dioxide reduction reactions (eCO2RR). However, the controversial and simplified mechanistic studies hinder the proposal of effective principles guiding rational catalyst design. Herein, by using grand canonical density functional theory (GC-DFT) calculations and the hybrid solvent model, we revisited the reaction mechanism of two-electron eCO2RR on a group of transition metals with an emphasis on illustrating why gold favors CO while Indium favors HCOOH. We identified the potential difference (Ud) between the onset potential for stable ∧-shaped *CO2– formation (U∧-CO2) and the potential of zero charge system (UPZC–CO2) as a crucial indicator for the selective HCOOH production, representing a good addition to the criteria via a binding strength comparison of *COOH and HCOO* species. Our results not only deepen the mechanistic understanding of the two-electron eCO2RR process on metals at different potentials but also provide effective guidance for rational catalyst design to produce HCOOH selectively.