Reversible catalysis is a hallmark of energy‐efficient chemical transformations, but can only be achieved if the changes in free energy of intermediate steps are minimized and the catalytic cycle is devoid of high transition‐state barriers. Using these criteria, we demonstrate reversible CO2/HCO2− conversion catalyzed by [Pt(depe)2]2+ (depe=1,2‐bis(diethylphosphino)ethane). Direct measurement of the free energies associated with each catalytic step correctly predicts a slight bias towards CO2 reduction. We demonstrate how the experimentally measured free energy of each step directly contributes to the <50 mV overpotential. We also find that for CO2 reduction, H2 evolution is negligible and the Faradaic efficiency for HCO2− production is nearly quantitative. A free‐energy analysis reveals H2 evolution is endergonic, providing a thermodynamic basis for highly selective CO2 reduction.

Reversible catalysis is a hallmark of energy‐efficient chemical transformations, but can only be achieved if the changes in free energy of intermediate steps are minimized and the catalytic cycle is devoid of high transition‐state barriers. Using these criteria, we demonstrate reversible CO2/HCO2− conversion catalyzed by [Pt(depe)2]2+ (depe=1,2‐bis(diethylphosphino)ethane). Direct measurement of the free energies associated with each catalytic step correctly predicts a slight bias towards CO2 reduction. We demonstrate how the experimentally measured free energy of each step directly contributes to the <50 mV overpotential. We also find that for CO2 reduction, H2 evolution is negligible and the Faradaic efficiency for HCO2− production is nearly quantitative. A free‐energy analysis reveals H2 evolution is endergonic, providing a thermodynamic basis for highly selective CO2 reduction.