Cations impact the thermodynamics of the RDS of CO2RR on Au (Eq. 1) via tuning the property of the proton donor. The fitted 𝐸 * * value becomes more negative following the sequence of Li -Na -K -Cs -TMA -TEA -TPA, suggesting that the RDS becomes increasingly thermodynamically unfavorable. A linear relation between 𝐸 * * and the hydration free energy of cations (∆𝐺 /0& ) is identified (Fig. ), implying that the equivalent standard potential is correlated with the interaction between the cation and water molecules in its first hydration shell. It could be deduced that the water molecules in the first hydration shell of cations are the proton donor of the RDS, and then Eq. 1 could be rewritten as: