Specifically adsorbed alkali metal cations on metal electrodes have been hypothesized to influence the reduction of CO₂. However, experimental detection of these cations during CO₂ reduction remains elusive. Herein, employing the asymmetric CH₃ deformation band of tetramethylammonium as a vibrational probe of the aqueous electrolyte–polycrystalline Au interface, we monitored the displacement of specifically adsorbed tetramethylammonium by alkali metal cations. We found that the coverage of specifically adsorbed alkali metal cations during CO₂-to-CO reduction follows the order Li⁺ < Na⁺ < K⁺ < Cs⁺ for the same bulk concentration. The alkali metal cations’ experimentally observed surface coverages correlate with their free energies of hydration. Furthermore, the rate of CO₂-to-CO conversion increases with the coverage of specifically adsorbed alkali metal cations. Our observations suggest that the degree to which alkali metal cations undergo partial dehydration at the electrode–electrolyte interface plays a key role in their ability to promote CO₂-to-CO reduction.

已经假设金属电极上特别吸附的碱金属阳离子会影响CO ₂的还原。然而，在CO ₂还原过程中对这些阳离子的实验检测仍然难以捉摸。在此，我们利用四甲基铵的不对称 CH ₃变形带作为水系电解质-多晶 Au 界面的振动探针，监测了碱金属阳离子对特定吸附的四甲基铵的位移。我们发现，在 CO ₂还原为 CO 的过程中，特定吸附的碱金属阳离子的覆盖范围遵循 Li ⁺  < Na ⁺  < K ⁺  < Cs ^+的顺序对于相同的体积浓度。碱金属阳离子的实验观察到的表面覆盖率与它们的水合自由能相关。此外，CO ₂到 CO 的转化率随着特定吸附的碱金属阳离子的覆盖而增加。_{我们的观察表明，碱金属阳离子在电极-电解质界面发生部分脱水的程度在它们促进 CO 2}还原为CO 的能力中起着关键作用。