follow the order K + ≈ Cs + > Li + , in line with experimental evidence . When varying buffer concentrations, all cations show the same general behavior: higher concentrations promote CO 2 R at first and then demote it (see Figures and). In terms of FE (Figure (d)), Cs + shows the highest CO FE across the potential range. Li + shows low CO Faradaic efficiencies at less negative potentials due to acidic pHs (Figure ), resulting in dominance of H + reduction. In the strongly negative potential region, the low Li + current densities lead to a rapid decrease of the CO FE as compared to K + in favor of H 2 OR as the latter is not affected by transport.