To predict the system's selectivity towards carbon products, we evaluated CO 2 reduction to HCOOH in the presence of Li + and K + . The energetics for formic acid pathway were unfavorable with respect to the CO pathway by 0.58 eV and 0.47 eV for K + and Li + respectively (Figure )). The multiscale simulations predict that the HCOOH current densities are 6 to 10 orders of magnitude lower than the CO current densities, in agreement with single facet studies in the literature showing that formate is detected as a product in trace amounts only (Figure ). Li + promotes relatively higher HCOOH current densities with respect to K + . In both cases, higher cation concentrations promote relatively higher HCOOH current densities at less cathodic voltages, and relatively lower current densities at strongly cathodic voltages. DFT simulations on Ag (211) in presence of K + show that OCO* binding is favorable by 0.32 eV compared to Ag(111) for HCOOH pathway, indicating the formic acid production may occur on step surfaces (Figure ).