The crucial role of electrolyte cations in CO₂ electroreduction has received intensive attention. One prevailing theory is that through electrostatic interactions or direct coordination, larger cations such as Cs⁺ can better stabilize the key intermediate species for CO and multicarbon (C₂₊) product generation, for example, on silver and copper, respectively. Here we show that smaller, more acidic alkali metal cations greatly enhance CO₂-to-methanol conversion kinetics (Li⁺ > Na⁺ > K⁺ > Cs⁺) on an immobilized molecular cobalt catalyst, unlike the trend observed for CO and C₂₊. Through electrokinetic analyses and kinetic isotope effect studies along with computational investigations, we show that the hydration shell of a cation serves as a proton donor in the rate-determining protonation step of adsorbed CHO where acidic cations promote the proton-coupled electron transfer. This study reveals the promotional effect of cation solvation environment on CO₂ electroreduction beyond the widely acknowledged stabilizing effect of cations.

电解质阳离子在CO ₂电还原中的关键作用受到了广泛关注。一种流行的理论是，通过静电相互作用或直接配位，较大的阳离子（例如 Cs ^+）可以更好地稳定 CO 和多碳 (C ₂₊ ) 产物生成的关键中间体物质，例如分别在银和铜上。在这里，我们表明，与 CO 观察到的趋势不同，更小、更酸性的碱金属阳离子大大增强了固定化分子钴催化剂上的 CO ₂到甲醇的转化动力学 (Li ⁺ > Na ⁺ > K ⁺ > Cs ⁺ )和C ₂₊ 。通过动电分析和动力学同位素效应研究以及计算研究，我们发现阳离子的水合壳在吸附的 CHO 的决定速率的质子化步骤中充当质子供体，其中酸性阳离子促进质子耦合电子转移。这项研究揭示了阳离子溶剂化环境对CO ₂电还原的促进作用超出了广泛认可的阳离子稳定作用。