The linear scaling relationship of the binding energies of different intermediates limits the catalyst performance in CO 2 electroreduction. Here we demonstrate a cation concentration gradient strategy to promote the activity and tune the selectivity of CO 2 electroreduction, thereby breaking the scaling relationship. In optimal concentrations of the potassium acetate (KAc) electrolyte, Cu, Ag and In catalysts deliver current densities that are 7.1, 3.2, 2.7 times higher than those obtained in 0.5 M KAc for C 2 H 4 , CO, and formate production, respectively. Increasing the concentration of KAc also changes the selectivity from CO to formate on Ag, and from CO to C 2 products on Cu. In situ surface-enhanced Raman spectroscopy and computational simulations reveal that the binding energies of intermediates are changed at different electrolyte concentrations, which is due to a local electrostatic interaction modulated by potassium cations at the electrode surface.