The reaction of carbon dioxide with hydroxide to form carbonate in near-neutral or alkaline medium severely limits the energy and carbon efficiency of CO₂ electroreduction. Here we show that by suppression of the otherwise predominant hydrogen evolution using alkali cations, efficient CO₂ electroreduction can be conducted in acidic medium, overcoming the carbonate problem. The cation effects are general for three typical catalysts including carbon-supported tin oxide, gold and copper, leading to Faradaic efficiency as high as 90% for formic acid and CO formation. Our analysis suggests that hydrated alkali cations physisorbed on the cathode modify the distribution of electric field in the double layer, which impedes hydrogen evolution by suppression of migration of hydronium ions while at the same time promoting CO₂ reduction by stabilization of key intermediates.

二氧化碳与氢氧化物在近中性或碱性介质中反应形成碳酸盐严重限制了CO ₂电还原的能量和碳效率。在这里，我们表明，通过使用碱金属阳离子抑制其他主要的氢析出，有效的 CO ₂电还原可以在酸性介质中进行，克服了碳酸盐的问题。阳离子效应对于三种典型的催化剂（包括碳负载的氧化锡、金和铜）是普遍的，导致甲酸和 CO 形成的法拉第效率高达 90%。我们的分析表明，物理吸附在阴极上的水合碱金属阳离子改变了双层中的电场分布，通过抑制水合氢离子的迁移来阻止氢的析出，同时通过稳定关键中间体来促进 CO ₂的还原。