Optimization of electrochemical systems such as electrolyzers for CO 2 conversion involves considering the elementary reactions occurring on the catalyst surface and the tuning of multi-physical transport processes . While catalyst optimization has seen significant advancements guided by binding energy descriptors and volcano plots , the intricate multi-scale nature of the catalyst-electrolyte interface known as microenvironment remains to be elucidated . Engineering the microenvironment is especially relevant in electrochemical CO 2 reduction (eCO 2 R) as the reaction cannot occur on Cu, Ag and Au if cations are not present in the electrolyte . On Ag and Au, higher concentrations of electrolyte cations favor CO formation at mildly reductive potentials, but at strongly negative potentials, they adversely impact cell performance, decreasing the CO Faradaic efficiencies and hampering device stability due to salt precipitation . The nature of the alkali cation also impacts current densities, with higher values obtained with increasing atomic number . Descriptors such as cation's hydrated size and acidity were considered to rationalize the observed behavior. Other larger organic cations also promote eCO 2 R in aqueous electrolytes by modulating the double layer thickness and strength . However, there is a lack of robust tools for designing microenvironments that optimize the operating conditions for eCO 2 R.