Molecular‐Level Insights Into Alkali‐Metal‐Cation–CO 2 Interactions at Electrified Cu(100) Interfaces by Molecular Dynamics Simulations

The activity of the electrochemical CO 2 reduction reaction depends on the electric double layer, where partially dehydrated alkali metal (AM + ) ions can stabilize CO 2 molecules and intermediates. However, whether such interaction‐enabled configurations form under electrochemical conditions and how potential controls their probability remain unclear. Herein, we used classical molecular dynamics simulations to evaluate how the hydration environment of AM + ions and their spatial relationship with CO 2 molecules evolve as functions of the applied potential and alkali‐metal‐cation identity. The simulations revealed that at potentials more negative than −0.92 V versus point of zero charge, larger AM + ions such as Cs + and K + partially dehydrate near the Cu(100) surface. For K + at q = −14.3 μC cm −2 , the hydration number decreased from 7.5 in the bulk region to 5.6 in the first interfacial layer, while the coordination number of K + around CO 2 was 0.49 near the surface and 0.20 in the bulk region. The likelihood of partially dehydrated AM + ions residing within the first coordination shell of CO 2 molecules increased with AM + ion size. At q = −9.52 μC cm −2 , the coordination number of AM + ions around CO 2 increased from 0.08 for Li + to 0.23 for Cs + .