where 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 = 𝑝𝐾 0 (𝐶𝑂𝑂𝐻) + 𝐸 / -1.09. Unfortunately, the presence of Faradaic currents could complicate the 𝐶 ! measurement at large overpotentials . To estimate the |𝜎|, we thus assume that 𝐶 ! curve follows the Gouy-Chapman-Stern model, which predicts a constant 𝐶 ! value at a potential far from pzc . Specifically, we assume 𝐶 ! as a constant value at the potential below -0.1 V (denoted as 𝐶 !,H/.J 8 ), where both CO2RR and HER activities are very low on Au. This assumption is generally in line with the trend of measured 𝐶 ! (Fig. ). Then |𝜎| at a certain potential could be calculated by: 𝐶 ! from 1.0 V to -0.1 V were determined via PEIS and shown in Fig. . The minimum is located at ~0.7 V, which is taken as the potential of zero charge (pzc) of Au. This value is similar to the reported pzc . 𝐶 ! with various cations at different potentials is roughly in line with the trend of Cs ≈ K > Na > Li > TMA > TEA > TPA, which is consistent with the literature .