We also evaluated 0.01 M BaCO 3 buffer, since Ba 2+ is the bivalent cation observed to promote the highest eCO 2 R current densities . The constrained AIMD simulations reveal that in contrast to monovalent cations (Figure ), Ba 2+ shifts its coordination by 2 water molecules (from 7 to 5) as it moves from OHP towards the electrode surface, which corresponds to a desolvation energy of 0.60 eV. DFT energetics show that the binding energy of CO 2 and COOH are stabilized by 0.28 and 0.14 eV respectively as compared to K + , in line with higher charge of Ba 2+ (Figure ). This leads to an order of magnitude higher CO current densities than K + (Figure It is worth noting that BaCO 3 is scarcely soluble in water at neutral and basic pH ,