Molecular-Level Insights Into Alkali-Metal-Cation-CO₂ Interactions at Electrified Cu(100) Interfaces by Molecular...

The activity of the electrochemical CO₂ reduction reaction depends on the electric double layer, where partially dehydrated alkali metal (AM⁺) ions can stabilize CO₂ 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 CO₂ 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 CO₂ 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 CO₂ molecules increased with AM⁺ ion size. At q = -9.52 μC cm^-2, the coordination number of AM⁺ ions around CO₂ increased from 0.08 for Li⁺ to 0.23 for Cs⁺.