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

Selective electrochemical reduction of CO 2 (CO 2 RR) 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 CO 2 electrolyzers strongly affect their performance through cationic activation of interfacial CO 2 and H 2 O in the electric double layer (EDL). In this work, we demonstrate an electrolyte design strategy that leverages Al 3+ complexation with tartrate 2– to form stable solutions in a HCO 3 – buffer, improving the selectivity of the CO production and activity on Au. We also find that tartrate 2– significantly reduces the onset of hydrogen evolution, even in the absence of Al 3+ . Ab-initio molecular dynamics (AIMD) simulations reveal that interfacial tartrate 2– polarize H 2 O away from the negatively polarized Au electrode and that Al 3+ induces greater activation of *CO 2 than K + . Hence, the rate limiting steps for the hydrogen evolution reaction (HER) and the CO 2 RR are slowed by tartrate 2– and accelerated by Al 3+ . This work demonstrates electrolyte design beyond standard alkali metal solutions to further improve the CO 2 RR selectivity.