Double-Layer Design Enables Independent Kinetic Modulation in CO ₂ Electrolysis

Selective electrochemical reduction of CO2 (CO2RR) to CO represents an opportunity to convert a waste product into a useful reactant with a near-term technoeconomic viability. The electrolytes applied in the CO2 electrolyzers strongly affect their performance through cationic activation of interfacial CO2 and H2O in the electric double layer (EDL). In this work, we demonstrate an electrolyte design strategy that leverages Al3+ complexation with tartrate2– to form stable solutions in a HCO3– buffer, improving the selectivity of the CO production and activity on Au. We also find that tartrate2– significantly reduces the onset of hydrogen evolution, even in the absence of Al3+. Ab-initio molecular dynamics (AIMD) simulations reveal that interfacial tartrate2– polarize H2O away from the negatively polarized Au electrode and that Al3+ induces greater activation of *CO2 than K+. Hence, the rate limiting steps for the hydrogen evolution reaction (HER) and the CO2RR are slowed by tartrate2– and accelerated by Al3+. This work demonstrates electrolyte design beyond standard alkali metal solutions to further improve the CO2RR selectivity.